Patent Application
20230212425
The present invention relates generally to steel sheets provided with aluminized, i.e. aluminum-based, coating compositions for protecting the steel sheet from unwanted oxidation and oxide formation that occurs during the metallurgical process of heat-stamping. The compositions of the invention relate to the scientific, engineering, and technical fields and subjects of inorganic chemistry, organic chemistry, metallurgy, ceramics, steel, coil steel fabrication, and coil steel coating.
The steel industry continually searches for novel methods and technologies to lower the costs of producing steel. This includes all factors that are a part of the cost of steelmaking, including materials, energy, labor, and environmental cleanup. For example, the automobile industry, which is an indispensable means of transport in daily life and activities, is constantly requiring its sources of steel automobile components to deliver components that reduce automobile body weight, but also that increase the structural integrity and strength of such components, particularly to enable automobile designers and engineers to develop auto body structural members that improve automobile crashworthiness and passenger safety. The structure of an automobile is formed largely of steel, particularly steel sheet, and reducing the weight of the steel sheet is essential for vehicle body weight reduction. As just pointed out, however, mere reduction of steel sheet weight is not a sufficient design criterion because the mechanical strength of the steel sheet must also be ensured. Such requirements for steel sheet are not limited to the automaking industry but also apply similarly to various other manufacturing sectors, for example appliances. Research and development has therefore been conducted with regard to steel sheet that, by enhancing the mechanical strength of the steel sheet, is capable of maintaining or increasing such mechanical strength even when the sheet steel is made thinner than the steel sheet used previously.
A steel material having high mechanical strength generally tends to decline in shape flexibility performance and formability performance during bending and other forming movements due to metal fatigue, so that the metalworking itself becomes more and more challenging when the desired final shape becomes more complex. An important case in point is when the steel sheet piece is to take on some variation of an accordian-like corrugated article.
One means available for overcoming this formability problem is the so called “hot stamping” method (variously also referred to as heat-stamping, hot-pressing, hot press forming, high-temperature stamping, or die-quenching, etc.). This product is commonly known in the industry as Press Hardened Steel (PHS). A typical tensile strength for PHS is about 1,500 Mega Pascals (MPas). In the hot stamping method, the steel material to be formed is initially heated to a high temperature, and then the steel sheet that has been softened by the heating is stamped and then cooled. Since the hot stamping method softens the steel material by initially heating it to a high temperature, the material can be readily stamped and thus strength hardened, and additionally the mechanical strength of the material can be increased by the quenching effect of rapid cooling subsequent to the stamp-forming. The hot stamping method therefore makes it possible to obtain a formed article that simultaneously achieves good shape-ability and high mechanical strength. As disclosed in U.K. Patent 1,490,535, the disclosure of which is incorporated herein by reference, according to the technology of hot press forming, it is possible to form a steel sheet into a complicated shape with good dimensional accuracy since the steel sheet is softer and more ductile at high temperature.
PHS parts commonly used in the automobile industry include front and rear bumper beams, door reinforcements, windscreen pillar reinforcements, B-pillar reinforcements, floor and roof reinforcements, roof and dash panel cross members, and racking for the batteries of electric and hybrid vehicles.
Another advantage of hot press forming is that of strengthening of the steel sheet, due to the phenomenon of martensite crystal structure transformation (so-called work hardening in the field of metallurgy) which can be simultaneously achieved, in parallel, by heating the steel sheet to the austenite crystal structure region (region where austenite exists on a y-axis temperature versus x-axis time cartesian chart) and then performing rapid quenching at the same time as press forming in the die. However, since hot press forming is a method in which a heated steel sheet is subjected to working or work hardening, the surface of the steel sheet to be worked is unavoidably oxidized. Even if the steel sheet is heated in a non-oxidizing atmosphere in a heating furnace, the sheet retains the possibility of contacting the atmosphere, for example, when it is removed from the furnace before press forming, resulting in the oxidation formation of iron oxides on the surface of the steel sheet. These iron oxides have the cost disadvantage that they may fall off during press forming and adhere to stamping or forming dies, thereby decreasing productivity and increasing cost and expense due to the need for extra cleaning and the cost of reduced lifetime of the die. Furthermore, an oxide film (i.e. scale on the surface of the steel) made up of such iron oxides remains on a product produced by press forming and worsens its appearance, thereby necessitating it removal by sanding, grinding, shot blasting, and the like, all of which are time and labor intensive and raise the cost of production.
Furthermore, if these oxide films remain on a press-formed product, in a situation where the product is subsequently to be coated with a paint, the resulting painted surface film has poor adhesion to the steel sheet and the product fails of its essential purpose of constituting a paint-finished steel piece. Furthermore, if the iron oxide layer is removed, then the uncoated steel sheet by itself will have very poor rust prevention properties. Even if the alternative of using a low alloy steel or a stainless steel is utilized so as to prevent the formation of such oxide films during heating prior to hot press forming and to thereby guarantee corrosion resistance, it is impossible to entirely prevent the formation of an oxide film, and the total costs have then become significantly higher than they would be for plain steel.
Another strategy to prevent such surface oxidation of sheet steel at the time of hot press forming, is to use a non-oxidizing atmosphere for both the atmosphere present at the time of heating and the atmosphere present during the entire pressing process, but this alternative strategy also results in a large increase in equipment and energy costs.
These multiple additional costs mean that even at the present time, hot press-forming is not sufficiently utilized industry-wide. This leads to an examination of alternative approaches to the problem of reducing oxide formation in hot press-forming steel. A review of current technologies which has been disclosed in patent applications is now presented
As noted, one advantage of hot press forming is that heat treatment may be performed simultaneously with press forming. It is therefore proposed in JP 07-116900A (1995), the disclosure of which is incorporated herein by reference, to simultaneously perform surface treatment at press forming time. However, there is no disclosure therein with respect to a means of solving the above-described problems due to surface oxidation. A steel sheet for hot working is proposed in JP 2000 38640A, the disclosure of which is incorporated herein by reference, that has been coated with aluminum in order to provide the steel sheet with resistance to oxidation at the time of hot working. However, this processed steel sheet has been found to be too expensive when compared to plain steel. As proposed in JP 06-240414A (1994), the disclosure of which is incorporated herein by reference, from just the standpoint of improving rust preventing properties or corrosion resistance, the addition of alloying elements such as Cr and Mo to the steel composition of a steel material is employed in some cases. (The entire disclosures of the above cited Japanese publications is incorporated herein by reference). However again, such countermeasures excessively raise the costs of the steel. Furthermore, when the option is pursued of adding Cr and Mo, there is a resultant problem of a deterioration in press formability due to added presence of these alloying elements. Any of various materials, including organic materials and inorganic materials, have been generally used for antioxidant coatings on steel sheet. Among them, steel sheet having a zinc-based coating that provides the steel sheet with a sacrificial corrosion protection effect is widely used for automotive steel sheet and the like. However, the heating temperature in hot stamping (700 to 1000° C.) is higher than, for example, the decomposition temperatures of organic materials and the boiling points of Zn-based and other metallic materials, so that the effect of heating to such temperatures during hot stamping may sometimes evaporate an applied surface-coating layer and then cause marked degradation of the sheet steel surface properties.
Therefore, it has been found that for steel sheet that is to be subjected to hot stamping involving high-temperature heating, it is preferable to use a steel sheet having an Al-based metal coating, which has a higher boiling point than an organic material coating or a Zn-based metal coating, referred to in the industry as aluminum plated steel sheet. Providing an Al-based metal coating prevents scale from adhering to the steel sheet surface and improves productivity by making descaling or other such scale removal processes unnecessary. Moreover, corrosion resistance after painting the sheet improves because the Al-based metal coating has a corrosion-proofing effect. The prior art describes a method which performs hot stamping using an aluminum-plated steel sheet obtained by coating a steel having a predetermined steel composition with an Al-based metal coating. However, when an Al-based metal coating is applied, and depending on the preheating conditions prior to stamping in the hot stamping process, it may happen that the Al coating first melts and is then changed to an Al—Fe alloy layer by the process of Fe diffusion from the steel sheet, whereby such newly formed Al—Fe alloy comes to extend itself to the steel sheet surface through the growth of the Al—Fe alloy. This compound layer is called the alloy layer. Since this alloy layer has the property of being extremely hard, processing scratches are formed by contact with the die during stamping. The surface of the Al—Fe alloy layer by its nature is relatively resistant to slipping and is poor in lubricity, a desirable property in stamping and rolling operations. In addition, the Al—Fe alloy layer is not only hard but is relatively friable and is thus susceptible to cracking, so that formability is liable to decrease owing to cracking, flaking, and powdering of the plating layer. Moreover, the quality of the stamped product is degraded by adhesion to the die of exfoliated Al—Fe alloy layer particles and of the strongly scored surface of the Al—Fe alloy. This makes it necessary to remove the Al—Fe alloy powder that has adhered to the die during repair, which again lowers productivity and increases cost. In addition, the Al—Fe alloy allow is relatively low in reactivity in situ with conventional phosphate metal treatment, which hinders the formation of the sought-after phosphate film that is ordinarily produced by a chemical conversion reaction that is part of electrocoating pretreatment. There is also a tradeoff between increasing the weight of the Al plating layer in order to improve paint adhesion, but where the increase in weight tends to aggravate the die adherence problem. The prior art most prevalent sheet steel coating product is known as Usibor®, made and/or distributed by the ArcelorMittal company, also called Ultralume® PHS.
There is therefore a general need for steel coating compositions that have the ability to: cure following application to steel within the period of time that a coil steel processing line allows before initiating the next step in the coil steel's processing procedure, (generally 15 to 90 seconds); maintain coating integrity under conditions of complex steel shape stamping; withstand the high temperatures and physical forces prevalent during steel hot-press forming; display properties of improved inhibition of iron oxide formation, oxidation and corrosion prevention and resistance; reduce iron oxide die adhesion and clean-up; show no spring-back; work well as a paint primer and otherwise show improved paint adhesion; reduce rust formation; reduce reliance on the use of low alloy steel or stainless steel; reduce reliance on the need for non-oxidizing atmospheres in a steel mill in general and eliminate such specific coating-protective atmospheres otherwise required in the step of austenizing in furnaces; reduce reliance on Cr and Mo alloy elements; exhibit higher melting temperatures and decomposition temperatures; resist high temperature steel surface evaporation; resist the formation of Al—Fe alloys in situ; reduce adhesion of deposits onto die tooling surfaces; reduce surface scratches on die tooling; display acceptable lubricity; be resistant to flaking, scaling, cracking and powdering; eliminate need for shot-blasting after formation; avoid interference with phosphate film electrocoating; form a film that is electrically conductive; form a film-coated steel product that is weldable; have lowered surface coating weight; have reduced manufacturing costs; show greater chemical stability; yield reliably repeatable batch manufacture; possess the ability to obtain complex geometry of final directly stamped or indirectly stamped products; show uniformity of mechanical properties obtained in stamped final parts; show improved fatigue strength of stamped final parts; show improved impact resistance of stamped final parts, thereby enabling significant weight reduction to be achieved; eliminate need for oiling after stamping; display improved resistance to corrosion of the stamped part; have the potential for scalability as the size of batch outputs increases; have better affordability; have greater ease of use; lend themselves readily to storage, transportation and distribution; and display aesthetically pleasing appearance of an intermediate or a final product. The compositions of the invention meet these needs, enable a method of their manufacture, and enable a method of their use, resulting in steel coated products that are made by these methods and that will themselves have novel and advantageous properties over coatings of prior art compositions or manufacturing processes.
This background information is provided to present and disclose information believed by the applicants to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
In summary of a most preferred embodiment of the invention, it is a type of aluminum ceramic, and more specifically, an oxidation-protective coating composition for steel sheets comprising an aromatic organic solvent, at least one source of aluminum, a silazane and, an organic synthesis catalyst. The aromatic organic solvent may advantageously be selected from one or more compounds of the group consisting of 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, polyethylbenzene, bicyclo[4.4.0]deca-1,3,5,7,9-pentaene, 2-methylindole, and 2-phenylpropane. A source of aluminum is present in the form of an aluminum pigment, which may be present in the form of a coordination complex of aluminum, and is preferably strongly anhydrous, by which is meant that there is substantially little to no water nor any organic alcohol in the aluminum preparation, nor any other source of hydroxyl or hydroxy functional groups, nor other organic functional groups that can form water in situ, directly or through an intermediate(s) e.g. carboxyls, ethers, thiols, amines, aldehydes, nor carbonyls or other acyls. A preferred silazane is a polysilazane polymer resin comprising silicon and nitrogen, and an alternative preferred embodiment uses a polysilazane that is an organic polysilazane. However, equally advantageous alternative embodiments may comprise an inorganic polysilazane, or admixtures of organic and inorganic polysilazines. The organic synthesis catalyst may be an organohetercyclic compound, preferably an azepane, and more preferably 1,8-diazabicyclo[5.4.0]undec-7-ene. Additionally, the composition may additionally comprise an organophosphorus compound, preferably a phosphazene, and more preferably for example 2-tert-Butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diaza phosphorine.
In terms of concentration ranges, the aromatic organic solvent is preferably present in a w/w concentration of from about 30% to 60%; the aluminum is preferably present in a w/w concentration of from about 5% to 25%; the silazane is preferably present in a w/w concentration of from about 20% to 60%; and the organic synthesis catalyst is preferably present in a concentration of from about 0.5% to 5%. The aromatic organic solvent is more preferably present in a w/w concentration of from about 40% to 50%; the aluminum is more preferably present in a w/w concentration of from about 10% to 20%; the silazane is more preferably present in a w/w concentration of from about 30% to 50%; and the organic synthesis catalyst is more preferably present in a concentration of from about 1% to 4%. The aromatic organic solvent is most preferably present in a w/w concentration of about 44 to 45%; the aluminum is most preferably present in a w/w concentration of from about 12% to 14%; the silazane is most preferably present in a w/w concentration of from about 38% to 42%; and the organic synthesis catalyst is most preferably present in a w/w concentration of approximately about 2%.
A preferred method of protecting surfaces of carbon steel during high temperature stamping comprises roller-coating the surfaces of the steel to be stamped with a coating comprised of any of the above described compositions.
The invention further comprises a method of making or furthermore applying the steel oxidative-protective coating compositions of those as described above, comprising the steps of admixing the aromatic organic solvent, the aluminum, the silazane, and the catalyst to a homogeneous consistency admixture; calculating an amount of time needed to achieve an optimized drying time or cure rate of this admixture; adding the selected organophosphorous compound to the admixture product in an amount sufficient to obtain the optimized drying or cure rate; and applying the optimized admixture to a steel article in need of protection from oxidation, by applying the dry-time or cure rate-optimized admixture to the steel article prior to heat-stamping that steel article.
The invention further comprises a coated steel sheet that has been prepared for heat-stamping, in accordance with the method as described above.
Additionally, the invention preferably comprises an aluminum-plated steel sheet for hot-stamping, comprising said steel sheet having at least one surface coated by a composition comprising an aromatic organic solvent, a source of aluminum, a silazane; and an organic synthesis catalyst, where each component may be present in any of the preferred alternative concentrations described above, and in any of the ranges of concentrations described above.
In another summary, another preferred embodiment of the invention comprises an oxidation-protective coating composition for steel sheets comprising the chemical components of: an aromatic organic solvent; at least one source of aluminum; a silazane; an organic synthesis catalyst; or alternatively comprising additionally an organophosphorus compound.
Most preferably, these coating compositions of the invention have an aromatic organic solvent present during the admixture process of making the compositions, where the aromatic organic solvent is preferably selected from one or more solvents such as 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, polyethylbenzene, bicyclo[4.4.0]deca-1,3,5,7,9-pentaene, 2-methylindole, or 2-phenylpropane. The coating compositions of the invention utilize at least one source of aluminum, most preferably sourced as an aluminum pigment, while another source or an additional source of aluminum may be a coordination complex of aluminum. A preferred coordination complex of aluminum is aluminum acetylacetonate.
The coating compositions of the present invention utilize a silazane. Preferably, the silazane component is a polysilazane, which may be a polymer resin comprised of silicon and nitrogen, and the polysilazane furthermore may be an organic silazane or an inorganic polysilazane. The coating compositions of the invention preferably use an organic synthesis catalyst, more preferably an organohetercyclic compound, and most preferably an azepane. A particularly advantageous organic synthesis catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene.
The coating compositions may optionally alternatively or additionally comprise an organophosphorus compound, preferably a phosphazene. A particularly preferred phosphazene is 2-tert-Butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diaza phosphorine.
The aforesaid components of the compositions of the invention are typically present as the aromatic organic solvent in a w/w concentration of from about 30% to 60%; the aluminum sources present in a w/w concentration of from about 5% to 25%; the silazane present in a w/w concentration of from about 20% to 60%; the organophosphorus, when it is additionally used, being present in a w/w concentration of from about about 5% to 25%; and the organic synthesis catalyst present in a w/w concentration of from about 0.5% to 5%. More preferable ranges of components of the compositions of the invention are: aromatic organic solvent present in a w/w concentration of from about 40% to 50%; aluminum sources present in a w/w concentration of from about 10% to 20%; silazane present in a w/w concentration of from about 30% to 50%; organophosphorus, when it is additionally used, present in a w/w concentration of from about 10% to 20%; and organic synthesis catalyst present in a concentration of from about 1% to 4%. In a highly preferred embodiment of the coating compositions of the invention, the aromatic organic solvent is present in a w/w concentration of about 44% to 45%; the aluminum sources are present in a w/w concentration of from about 12% to 14%; the silazane is present in a w/w concentration of from about 38% to 42%; the organophosphorus, when it is additionally used, is present in a w/w concentration of approximately about 20%; and the organic synthesis catalyst is present in a w/w concentration of approximately about 2%.
Alternative metals that can form alternative embodiments of the invention are Boron, Gallium, Indium, Thallium, Tungstun, Molybdenum, Chromium, Cobalt, Ruthenium, Iridium, Nickel, Platinum, Palladium, Silver, Gold, Copper, and the nitrides, sulfides, or nanocatalysts thereof any of these metals.
The present invention also covers a method of protecting surfaces of steel, preferably carbon steel during high temperature stamping, comprising coating the surfaces of the steel to be stamped with a coating composition made up of an aromatic organic solvent; at least one source of aluminum; a silazane; an organic synthesis catalyst; and optionally additionally an organophosphorus compound, each chemical component present in the w/w ranges described above.
The protective coating compositions of the invention are made by a method comprising the steps of admixing the aromatic organic solvent, at least one aluminum source, the silazane, and the catalyst, in an amount calculated to achieve desired drying time or cure time, to a homogeneous consistency; achieving an optimally desired coating admixture drying time or cure time by selectively adding sufficient amounts of aluminum and optionally an organophosphorus compound to the admixture product; and applying the optimized dry-time or cure-time admixture product to a steel article in need of protection from oxidation, by applying the admixture to such a steel article prior to heat-stamping it.
By following this composition preparation method there will be produced a coated steel sheet, having a chemical surface layer composition that is novel and unique, and that is now prepared for heat-stamping, which will be protected against oxidation that tends to otherwise take place during a heat-stamping process.
The compositions of the invention are intended to be used in the preparation of sheet steel generally, and carbon steel in particular, to produce a sheet of steel that can withstand the oxidative effects of oxygen present in the steel production factory or mill, whose oxidative effects are otherwise made more corrosive by the high temperatures and high stamping forces typically utilized in steel heat-stamping manufacturing.
The present invention in its varying embodiments will now be described more fully. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those of ordinary skill in the art.
Although the detailed description of this Specification contains many specifics for the purposes of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss or diminution of generality to, and without imposing limitations upon, the claimed invention.
As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art on how to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure of the invention, which is defined solely by the claims.
Furthermore, in this detailed description, a person skilled in the art should note that quantitative qualifying terms such as “generally,” “substantially,” “mostly,” and other terms are used, in general, to mean that the referred-to object, characteristic, or quality constitutes a majority of the subject of the reference. The meaning of any of these terms is dependent upon the context within which it is used, and the meaning may be expressly modified.
Abbreviations, nomenclature, and technical & non-technical term definitions as used in these examples are as follows.
The phrase “a” or “an” in the context of an entity or moiety as used herein refers to one or more of that entity or moiety, as in for example. “a” compound refers to one or more compounds or at least one compound. As such, the terms “a” (or “an”). “one or more,” “at least one,” and “can or “and”, may be used interchangeably. The term “about” has its plain and ordinary meaning of “approximately.” Numerical ranges are to be interpreted as including standard rounding error. Regarding metal ion ratios and closing amounts, the qualifier “about” reflects the standard experimental error commonly used by those of ordinary skill in the chemistry, materials, and metallurgy arts. The terms “optional” or “optionally” as used herein means that a subsequently described event or circumstance may, but need not, occur and that the description includes instances where the event or circumstance occurs and instances in which it does not.
The term “mixing” or “efficient mixing” as used herein is not limited to the same compounding process; it involves all mixing methods in a manufacturing process.
The compositions of the present invention can be prepared readily according to the following examples or modifications thereof using readily available starting materials, reagents and conventional synthesis procedures. In these reactions, it is also possible to make use of variants which are themselves known to those of ordinary skill in this art, but these are not mentioned in greater detail.
The most preferred compositions and their constituent compounds of the invention are any or all of those specifically set forth in these examples. These compositions are not, however, to be construed as forming the only genus that is considered as the invention, and any combination of the compositions and constituent compounds or their moieties may itself form a genus. The following examples further illustrate details for the preparation and the quantitative and qualitative analysis of the compounds of the present invention. Those skilled in the art will readily understand that known variations of the conditions and processes of the following preparative procedures can be used to prepare these compounds. All temperatures are degrees Celsius unless noted otherwise.
Silazanes. Silicon-nitrogen compounds with alternating silicon- (“sila”) and nitrogen atoms (“aza”) are designated as silazanes. Simple examples of silazanes are disilazane H3Si—NH—SiH3 and hexamethyldisazane (H3C)3Si—NH—Si(CH3)3. If only one silicon atom is bound to the nitrogen atom, the materials are known as silylamines or aminosilanes (for example triethylsilylamine (H5C2)3Si—NH2). If three silicon atoms are bound to each nitrogen atom, the materials are called silsesquiazanes. Small ring-shaped molecules with a basic network of Si—N are named cyclosilazanes (for example cyclotrisilazane [H2Si—NH]3).
Polysilazanes. Polysilazanes are silazane polymers consisting of both large chains and rings showing a range of molecular masses. Polysilazanes are a class of polymers in which silicon and nitrogen atoms alternate to form the basic backbone. Polysilazanes are a preferred category of silazanes utilized in the present invention. A polymer with the general formula (CH3)3Si—NH—[(CH3)2Si—NH]n—Si(CH3)3 is designated as poly(dimethylsilazane). According to the IUPAC rules for the designation of linear organic polymers, the compound would actually be named poly[aza(dimethylsilylene)], and according to the preliminary rules for inorganic macromolecules catena-poly[(dimethylsilicon)-m-aza]. By “polysilazane” is meant any oligomeric or polymeric composition comprising a plurality of Si—N repeat units. By “oligomer” is meant any molecule or chemical compound which comprises several repeat units, generally from about 2 to 10 repeat units. “Polymer”, as used herein, means a molecule or compound which comprises a large number of repeat units, generally greater than about 10 repeat units. Since each silicon atom is bound to two separate nitrogen atoms and each nitrogen atom to two silicon atoms, both chains and rings of the formula [R1R2Si—NR3] may occur, where R1-R2 can be hydrogen atoms or organic substituents. If all substituents R are H atoms, then the polymer is designated as perhydropolysilazane, polyperhydridosilazane, or inorganic polysilazane ([H2Si—NH]n). If hydrocarbon substituents are bound to the silicon atoms, the polymers are designated as organopolysilazanes. The synthesis of polyorganosilazanes was first described in 1964 by Kruger and Rochow. C. R. Krüger, E. G. Rochow, J. Polym. Sci. Vol. A2, 1964, 3179-3189, the disclosure of which is incorporated herein by reference. By reacting ammonia with chlorosilanes (ammonolysis), trimeric or tetrameric cyclosilazanes were formed initially and further reacted at high temperatures with a catalyst to yield higher molecular weight polymers. Ammonolysis of chlorosilanes still represents an important synthetic pathway to polysilazanes, but it is not a preferred method of preparation of the polysilazines of the present invention. In the 1960s, the first attempts to transform organosilicon polymers into quasi-ceramic materials were described.[2] At this time, suitable (“pre-ceramic”) polymers heated to 1000° C. or higher were shown to split off organic groups and hydrogen and, in the process, the molecular network is rearranged to form amorphous inorganic materials. Using polymer derived ceramics (PDCs), alternative embodiments of the invention are disclosed here, especially in the area of high-performance, i.e. high temperature and/or work-hardened steel materials. The most important pre-ceramic polymers in the production of PDCs are polysilanes [R1R2Si—R1R2Si]n, polycarbosilanes [R1R2Si—CH2], polysiloxanes [R1R2Si—O]n and polysilazanes [R1R2Si—NR3]n.). In polysiloxanes, each silicon atom is bound to two oxygen atoms and each oxygen atom to at least two silicon atoms. In polysilazanes, however, each silicon atom is bound to two nitrogen atoms and each nitrogen atom to at least two silicon atoms (three bonds to silicon atoms are also possible. If all remaining bonds are with hydrogen atoms, the result is perhydropolysilazane [H2Si—NH]n. In organopolysilazanes, at least one organic substituent is bound to the silicon atom. The amount and type of organic substituents have a predominant influence on the macro-molecular structure of polysilazanes.
Polysilazanes are colorless to pale yellow liquids or solid materials. Conditional of manufacturing, the liquids often contain dissolved ammonia that can be detected by smell, though this is not a preferred embodiment of the present invention and ammonia-free or lowered ammonia preparations are preferred. The average molecular weight can range from a few thousand to approximately 100.000 g/mol while the density normally lies around 1 g/cm3. The state of aggregation and the viscosity are both dependent on the molecular mass and the molecular macrostructure. Solid polysilazanes are produced by chemical conversion of the liquid materials (crosslinking of smaller molecules). The solid materials can be fusible or unmeltable and can be soluble or insoluble in organic solvents. Sometimes, polysilazane solids behave as thermosetting polymers, but in some cases, thermoplastic processing is possible. After the synthesis, an aging process frequently takes place in which dissolved ammonia plays an important role. The R3Si—NH2 groups resulting from the ammonolysis reaction form silazane units by splitting off ammonia. If ammonia cannot escape, the silazane units can be split again into R3Si—NH2 groups. Therefore, frequent venting of ammonia can lead to an increase in preferred molecular mass. The most preferred forms of polysilzanes used in the invention are of reduced ammonia content or ammonia free. Also, functional groups that are not bound directly into the polymer backbone can react under suitable conditions (for example Si—H with N—H groups) and increase crosslinking of the rings and chains. An increase in molecular weight can also be observed during storage at higher temperatures or in sunlight.
With contact to water or moisture, polysilazanes decompose more or less quickly. Water molecules attack the silicon atom and the Si—N bond is cleaved. The R3Si—NH—SiR3 forms R3Si—NH2 and HO—SiR3 which can further react (condensation) to form R3Si—O—SiR3 (siloxanes). The rate of the reaction with water (or other OH containing materials like alcohols) depends on the molecular structure of the polysilazanes and the substituents. Perhydropolysilazane [H2Si—NH]n will decompose very quickly and exothermically with contact to water while polysilazanes with large substituents react very slowly. Polysilazanes are not vaporizable because of strong intermolecular forces. Heating polysilazanes results in crosslinking to form higher molecular weight polymers. At temperatures of about 100-300° C., further crosslinking of the molecules takes place with evolution of hydrogen and ammonia. If the polysilazane contains further functional groups such as vinyl units, additional reactions can take place. In general, liquid materials will be converted to solids as the temperature increases. At about 400-700° C., the organic groups decompose with the evolution of small hydrocarbon molecules, ammonia and hydrogen which are preferably vented off. Between about 700 and 1200° C., a highly preferred three-dimensional amorphous network develops containing Si, C and N (“SiCN ceramics”) with a density of ca. 2 g/cm3. A further temperature increase can result in crystallization of the amorphous material and the formation of silicon nitride, silicon carbide and carbon. This so-called pyrolysis of the polysilazanes produces preferred ceramic materials from low-viscosity liquids with very high yield (up to 90%). Due to the organic groups that are often used to give good polymer processability, preferred ceramic yield is normally in the range of 60-80%. For a long time polysilazanes have been synthesized and characterized, and their great potential for many applications was acknowledged. However, up to now, very few products have been developed into a marketable commodity.
The most preferred polysilazane used in a most preferred embodiment of the invention is a commercially available product called Durazane® 1800, available from Merck KGaA of Darmstadt, Germany. This polysilazane is a liquid phase, low-viscosity, solvent-free organic polysilazane resin having the industrial properties of being a coating binder and a polymeric ceramic precursor. Durazane® 1800 exhibits good adhesion, good hardness, hydrophobicity, and good barrier properties. When used as a polymeric ceramic precursor, it yields a preferred pyrolyzed ceramic material that shows excellent high temperature stability, being able to endure peak temperatures of up to 1000° C., which is well within the range of temperatures encountered in the hot-stamping process. It has a high ceramic yield of about 80 to 90%, depending on the atmosphere used. Its applications are in the field of high temperature coatings for the protection of metals against corrosion in industrial applications, in the formulation of non-stick high temperature coatings for rollers or molds, and for the infiltration of porous preforms and resin transfer moldings. Durazane 1800 exhibits the following properties in approximately or about the quantities and ranges expressed here:
Dry film thickness: 8-10 μm.
Non-cured temperature stability: up to 350-400° C.
Pencil Hardness: up to 5H (DIN EN ISO 15184).
Indentation Hardness (DIN EN ISO 14577-1).
Radical Initiator DCP cured for 2 h @ 150° C.: 60-65 MPa.
Radical Initiator LP cured for 2 h @ 130° C.: 185-200 MPa.
Contact angle water: 90-96°.
Contact angle oil: 42-44°.
Surface energy: 24-26 mN/m.
Polar part: 2-3 mN/m.
Dispersive part: 22-23 mN/m.
Adhesion by cross cut: 0 (DIN EN ISO 2409:2013, where 0=excellent,
5=no adhesion).
Cured temperature stability: up to 1000° C.
Appearance: clear to trace hazy liquid.
Color: Colorless to trace yellow.
Density @25° C.: 0.950-1.050 g/cm3 (ISO 2811-1).
Viscosity @20° C.: 10-40 cP.
Conditions of use:
Pretreatment:
Grease and dust/particle free surface of substrates are required.
Sandblasting of metal substrates is preferred.
Curing conditions:
Optimally cured with radical initiators, which allows a reduction of the curing temperature or time (for example 2h/150° C. with addition of 0.5-2 wt.-% dicumylperoxide [DCP] or 2 h/130° C. with addition of 0.5-2 wt.-% Luperox531M80 [LP]).
Non catalytic curing: 250° C. for 0.5 h; 180° C. for 3-4 h.
Pyrolysis:
Pyrolysis takes place at temperatures >500° C.
Dilution/Formulation:
Dilution: Dilution is possible with organic solvents such as alkanes (e.g. heptane, isoalkanes), esters (e.g. ethyl acetate, butyl acetate, propylene glycol, methyl ether acetate), ethers (e.g. THF, di-n butyl ether), aromates (e.g. toluene, xylene) or ketones (e.g. methyl ethyl ketone). The resin reacts in the presence of water, water vapor or alcohols therefore it is important to use above mentioned solvents with lowest possible water content.
Formulation: Durazane® 1800 may be blended with multiple alternative embodiment coating components, including organic pigments, pigment preparations, metal powders (zinc, aluminum), ceramic powders to increase the ceramic properties of the final admixture (e.g. silicon nitride, boron carbide, aluminum oxide, boron nitride, or silicon nitride) and many alternative co-binders and additives.
Aluminum. Aluminum Pigment as a Source. The preferred metal constituent of the invention is the metal aluminum. In a most preferred embodiment, aluminum is sourced from the use of a suitable aluminum pigment.
The most preferred aluminum source used, in a most highly preferred embodiment of the invention, is a commercially available as a non-waterborne aluminum paste product called STAPA Metallic R 507 R Aluminium Paste, article number 057307G70, SDS number 102000030579, available from the United States Eckart America Corporation, at 830 East Erie Street, Painesville, Ohio, 44077, which is a division of Eckart GmbH & Co. KG, Kaiserstrasse 30, D-90763 Furth, a division of Altana Corporation, of Hartenstein, Germany. This aluminum paste, which is a silver pasty in appearance and more specifically a non-leafing aluminum pigment paste, and more specifically a pigment paste of flaky (comflake) aluminum powder produced of pure aluminum. CAS number 7429-90-5, with an inorganic coating.
Properties that characterize the aluminum pigments in the HYDROLAN® line of aluminum pigments are that these silica-encapsulated pigments are very shear-stable, and that they are off-gassing resistant. The specific gravity is about about 1.5 kg/l and its density may preferably be in a range of approximately 1.3 g/cm3 to approximately 2 g/cm3. The highly preferred solvents used are mineral spirits and hydrotreated heavy petroleum naptha, CAS number 64742-48-9, and light aromatic petroleum solvent naptha, where the ratio of the mineral spirits presence to the combined naptha presence is in a ratio of 1/1 by weight, giving the product a non-volatile content of approximately 63 to 67% and a volatile content of approximately 33 to 37%. It passes wet sieving standard DIN 53196 at 40 μm, over 99%. The particle size distribution is: D 10, approximately 7 μm, D 50 approximately 21 μm, and D90, approximately 44 μm.
Mineral spirits (Stoddard solvent, white spirit) for example [CAS 8052-41-3] are a genus of a type of chemical substances that are 100% petroleum distillate liquid hydrocarbon solvent mixtures of aliphatic and alicyclic petroleum-based compounds, and have no additives. As a genus, they are for example typically a mixture of aliphatic, open chain, and alicyclic C7 to C12 aromatic hydrocarbons. A typical composition for mineral spirits is >65% C10 or higher hydrocarbons that are aliphatic, aliphatic solvent hexane, and a maximum benzene content of 0.1% by volume, a kauri-butanol value of 29, an initial boiling point of 145° C. (293° F.) to 174° C. (345° F.), and a density of 0.79 g/ml.
Mineral spirits are typically formed by the molecular interaction via distillation of paraffin (aliphatic) and cyclo-propane (alicyclic) with aromatic compounds. Mineral spirits having an odor-quality suitable for use as a solvent particularly in the paint, varnish and resin trades, are produced by a process comprising (1) treating a feed naphtha boiling between about 325 and 425 F that has been derived from hydrocarbons containing from 3 to 8 carbon atoms, which feed is characterized by being essentially free of olefins and aromatic hydrocarbons and elemental sulfur, with an effective amount of sulfuric acid having a concentration of between about 90 and 100 weight percent, (2) separating acid sludge from treated naphtha, (3) rain-washing said treated naphtha with liquid water to remove substantially all of the occluded-acids ludge particles therefrom, (4) separating rain-wash water from rain-washed naphtha. (5) intimately contacting said naphtha from step (4) with liquid water. (6) separating all water from washed naphtha, (7) contacting said washed naphtha with an aqueous alkaline solution to essentially neutralize said washed naphtha, (8) separating aqueous alkaline solution from an essentially neutral naphtha, (9) water washing said neutralized naphtha and (10) removing occluded aqueous alkaline solution from said neutralized naphtha, wherein to the rain-washed naphtha of step 4—there is added an effective amount of an oil soluble, aqueous-caustic insoluble oxidation inhibitor selected from the class of phenylene diamines and polyalkylphenols prior to the water washing of step 5. The feed to the process of this invention is composed essentially of a mixture of paraffinic and isoparatinic hydrocarbons, i. e., is essentially free of olefins and aromatic hydrocarbons. Very small amounts of organic sulfur compounds may be present, but are very undesirable. The feed must be essentially free of hydrogen sulfide and elemental sulfur. A typical composition for mineral spirits is: aliphatic solvent hexane having a maximum aromatic hydrocarbon content of 0.1% by volume, a kauri-butanol value of 29, an initial boiling point of 149° F. (65° C.), a dry point of approximately 156° F. (69° C.), and a specific mass of 0.7 g/cc.
Silica encapsulation materials are, for example, alkaline colloidal silicas, aqueous dispersions of silica with average particle size of approximately 12 nm to approximately 22 nm, or acidic deionized colloidal silica of particle approximately 12 nm to approximately 22 nm. Suitable silica materials are available commercially from, for example, LUDOX® Colliodal Silica Products through the Chempoint Company. Descriptions of such encapsulated aluminated pigments are found in the article “Encapsulated Aluminum Pigments”, Progress in Organic Coatings, Volume 37, Issues 3-4, December 1999, pages 179-183, the entire disclosure of which is incorporated herein by reference.
An alternative preferred source of aluminum are the waterborne systems of STAPA Hydrolan 501, also available from the Eckart division of Altana corporation, of Hartenstein, Germany. STAPA Hydrolan 501 is a most preferred embodiment of the STAPA® Hydrolan line of non-leafing, aluminum pigments. It is used in general industrial, automotive and accessories coatings. STAPA IL HYYDROLAN 501, material number 005332, is an aluminum paste, more specifically a pigment paste of flaky aluminum powder produced of pure aluminum with an inorganic coating. Properties that characterize all aluminum pigments for waterborne, aqueous coating systems in the HYDROLAN® line of aluminum pigments are that these silica encapsulated pigments are very shear-stable, and that they are off-gassing resistant. The specific gravity is 1.4 kg/l. The solvent used is isopropanol (IL) and the preparation includes miscellaneous lubricants and additives. The pigment composition is aluminum app. 53%.
Preferred Aluminum Powder characteristics:
Aluminum acetylacetonate. Aluminum acetylacetonate (aluminum 2,4-pentanedionate), also referred to as Al(acac)3, is a preferred aluminum coordination complex with formula Al(C5H7O2)3, molecular weight 324.31 g/mol, CAS number 13963-57-0. This aluminum coordination complex with three acetylacetone ligands is used as a precursor in the preparation of aluminum oxide films. The molecule has D3 symmetry, being isomorphous with other octahedral tris(acetylacetonate)s. Aluminum acetylacetonate may additionally be used to prepare transparent superhydrophobic boehmite and silica films by sublimation, to deposit aluminum oxide films by chemical vapor deposition, to deposit aluminum oxide films by chemical vapor deposition, and as a catalyst. Acetylacetonates are coordination complexes derived from acetylacetone and metal salts, most often salts of transition metals, and most preferably aluminum. These compounds allow many metal ions to be soluble in organic solvent, in contrast to most metal salts. This allows them to be used as catalyst precursors and reagents in reactions which occur in organic phase in chemical synthesis. Acetylacetonates are also frequently used as shift reagents in nuclear magnetic resonance (NMR) spectroscopy, a research and analysis technique that exploits magnetic properties of atomic nuclei to provide detailed information about a chemical substance. Aluminum acetylacetonate is commercially available from Sigman-Aldrich of St. Louis, Mo.
Alternative embodiments of the metal component of the coating invention comprise metal nitrides or carbides, with the metal nitride or carbide preferably comprising or consisting of nitrides and/or nitride anhydrates or carbides of silicon, titanium, zirconium, iron, aluminum, cerium, chromium and/or mixtures thereof.
The metallic substrates upon which the metal nitride coatings are applied may alternatively be selected from the group consisting of aluminum, copper, zinc, tin, brass (gold bronze), iron, titanium, chromium, nickel, silver, gold, steel, and also their alloys and/or mixtures. Preferred in this context is steel.
Solvents. Preferred solvents used in admixing the compositions of the invention are organic aromatic solvents. The most preferred organic aromatic solvent is commercially available as Hi Sol 15, which is itself a mixture of the organic aromatic solvents diethylbenzene,1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, 1,2,3-trimethylbenzene,1,2,4-Trimethylbenzene or 1,3,5-trimethylbenzene, polyethylbenzene, aka solvent naphtha, naphthalene, 2-methylindole, and cumene.
Catalysts. The addition of a suitable catalyst confers the advantage of achieving a customized or preferred drying time or curing time of the coating on the selected steel article. Target drying time or curing time may be achieved, reduced, or increased through selection of the catalyst and adjustment of the amount of the selected catalyst in the admixture. Typically, in the industrial setting the goal will be to reduce drying time and thereby accelerate the entire coating operation. The most preferred catalyst for use in the invention admixture is diazabicycloundecene, 1,8-Diazabicyclo[5.4.0]undec-7-ene, CAS 6674-22-2. This catalyst is commonly used in organic synthesis as a catalyst, a complexing ligand, a non-nucleophilic base, and as a protecting agent if needed during organic synthesis. The most preferred amount of this catalyst is in the range of 0.5 to 5.0% by weight, with the operator having the freedom to adjust the concentration of catalyst upward or downward to optimize the drying time or the cure time of the coating composition.
Bases. The most highly preferred base to use in the admixture of the invention is BEMP-phosphazene (2-tert-Butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diaza phosphorine), CAS 98015-45-3. This base is a member of the family of phosphazene bases. Phosphazenes refer to classes of organophosphorus compounds featuring phosphorus (V) with a double bond between P and N, for example phosphazenes having the formula RN═P(NR2)3. Phosphazene bases are strong, uncharged bases that are non-metallic, non-ionic and low nucleophilic bases. They are stronger bases than regular amine or amidine bases. Protonation takes place at the doubly bonded nitrogen atom. Properties of phosphazene bases include the ability to generate in situ highly reactive “naked” anions. e.g. for alkylation reactions or for spectroscopic investigations; that they are applicable in reactions where ionic bases cause solubility problems; that they are useful in reactions where ionic bases are sensitive towards oxidation or acylation; and that they are useful in reactions where ionic bases result in Lewis-acid catalyzed side reactions, for example in aldol reactions, epoxide-opening, hydride shifts, elimination of alkoxide, and polyanion-formation. The addition of a suitable phosphorous base compound confers the additional advantage of achieving a further customized or preferred drying time or curing time of the coating on the selected steel article. Target drying time or curing time may be achieved, reduced, or increased through selection of the phosphorous base and adjustment of the amount of the selected phosphorous base in the admixture.
Methods of Application. In the production of sheet steel in general, and in hot rolled sheet steel in particular, the process begins with heating slabs of steel to approximately 2,300 degrees Fahrenheit. The amount of heat directly affects the properties of the steel. Meaning, if the temperature is not high enough it can cause defects in the material. This is likely due to carbides (compound of carbon) and nitrates (polyatomic ion—an even more complex term) not fully dissolving. When the hot material is being transferred from the furnace, it reacts with the oxygen in the atmosphere. This reaction forms a mill scale or a flaky surface of iron oxides. Since the mill scale can affect the surface quality of the hot rolled steel if left alone, such iron oxides are removed by then sending the material through a mill scale cleanse by being cleansed by spraying with extremely high pressure water. The cleansed material is then sent through a rolling mill and is rolled from a thickness of roughly nine inches to an inch. The process consists of a series of four to five stands (set of rollers) that decrease the thickness and increase the length by horizontal rolls. The material is also squeezed vertically to control the width.
At this stage the material's ends are sheared to create a transfer bar. The transfer bar is sent through another series of stands to further reduce the thickness to the desired sheet gauge. The flat-rolled steel is delivered across a runout table that consists of cooling sprays. The cooling rate may be modified for each strip to create the desired properties of the coiled end product. After the material is so cooled it enters coilers. Once coiled, the product is ready to be delivered to service centers for further processing. It may also be delivered straight to fabricators.
The application of the curable protective coating compositions of the present invention may take place at a suitable part of the rolled sheet steel production process by using the application methods known in the prior art such as bar coating, air-knife coating, roll coating, spray coating and dip coating. In those cases in which flat substrates are to be coated, the application preferably takes place in the roller application method. If a substrate is a coil shape, for example a steel coil is to be coated, a pretreatment for Si-based passivation on the steel coil may be applied prior to the application of the coating composition on the substrate. The curable protective coating composition can be applied by roller application onto the steel surface after the steel is manufactured in a steel manufacturing mill, or can be applied by spraying or other suitable dispersive process onto the steel surface at a hot-stamping site. The post-application cured coating polymeric, pre-ceramic, or ceramic product of the invention can also provide corrosion protection to the steel during storage and transfer between two industrial sites. The coating composition can be cured by flashing off at room temperature or by accelerated curing at an elevated temperature, in which case temperatures of preferably up to 300° C. may be employed for the drying and curing of the coating. Preferably, the curable protective coating composition is cured under a temperature 100° C. to 300° C. for a polymeric coating or of 300 to 1000° C. for a ceramic coating. Accelerated curing by means for example of IR radiation, forced-air drying, UV irradiation or electron beam curing may also be useful. The coating can be applied not only to flat substrates but also to coils which are passing through a cold and/or hot forming step, or else the coating can be applied to substrates which have already undergone cold forming.
The coating composition according to the present invention may be applied in so called “direct” or “indirect” hot forming/stamping processes. In an indirect process of hot stamping, a flat substrate coated with the protective coating composition is sequentially pre-stamped, heated and then hot stamped. In a direct process, the coated flat substrate is first heated and then hot stamped.
The present coating composition is suitable particularly for the surface coating of a substrate whose surface is composed at least partly of steel. The coating composition is intended in particular for the surface coating of substrates made of carbon steel, and is suitable preferentially for the surface coating of a high-strength steel substrate which, following the surface coating, is subjected to a hot forming operation or hot stamping process, in particular to hot forming at temperatures between 800° C. and about 1000° C., preferably at between about 880° C. and about 970° C. These types of steels are, for example, duplex steels alloyed with chromium, nickel, and manganese, and boron-manganese steels.
In addition, it is possible where appropriate to add commercially customary wetting/dispersion agents, thickeners, setting agents, rheological agents, leveling agents, defoamers, hardness improving agents, lubricants and coating film modifiers or the like, all according to product performance parameters chosen through the skills of the ordinary practitioner in the art of chemistry, chemical engineering, materials science, or metallurgy, to achieve specified properties of the coating or of the coated product. Suitable examples of coating film modifiers are cellulosic materials, such as cellulose esters and cellulose ethers; homopolymers or copolymers from styrene, vinylidene chloride, vinyl chloride, alkyl acrylate, alkyl methacrylate, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, vinyl ether, and vinyl acetate monomers; polyesters or copolyesters; polyurethanes or polyurethane acrylates; epoxy resins; polyvinylpyrrolidone; polytetrafluoromethylene, polyphenyl, polyphenylene, polyimide and polytetrafluoroethylene. The compounds of the present invention can be prepared readily according to the following Examples or modifications thereof using readily available starting materials, reagents and conventional synthesis procedures. In these reactions, it is also possible to make use of variants which are themselves known to those of ordinary skill in this art, but these are not mentioned in greater detail.
The most preferred compounds of the invention are any or all of those specifically set forth in these Examples. These compounds are not, however, to be construed as forming the only genus that is considered as the invention, and any combination of the compounds or their moieties may itself form a genus. The following examples further illustrate details for the preparation, application, quantitative analysis and qualitative analysis of the compounds of the coatings of the present invention. Those skilled in the art will readily understand that known variations of the conditions and processes of the following preparative procedures can be used to prepare these compounds. All temperatures are degrees Celsius unless noted otherwise.
Into a suitably sized mixing vessel were added 445 pounds of Hi Sol 15 Aromatic 150 organic solvent, 145 pounds of Hydrolan Aluminium 501 aluminum pigment, 389.45 pounds of Durazane 1800 Polysilizane, and 20.55 pounds of 1,8-diazabicycloundecene catalyst, which were then mixed under medium speed agitation until a lump free, smooth, and homogeneous mixture was achieved; estimated curing time of the admixture was adjusted by titrating the admixture with the addition of aluminum acetylacetonate and adding 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine base. The resulting mixture was analyzed and found to not exceed 6.5 hegman cure to 350 f pmt for 30 seconds to a hardness of 2 h min at 0.4 mils dry film thickness.
Into a suitably sized mixing vessel were added 444 pounds of Hi Sol 15 Aromatic 150 organic solvent, 120 pounds of Hydrolan Aluminium 501 aluminum pigment, 415 pounds of Durazane 1800 Polysilizane, and 20.55 pounds of 1,8-diazabicycloundecene catalyst, which were then mixed under medium speed agitation until a lump free, smooth, and homogeneous mixture was achieved; estimated curing time of the admixture was adjusted by titrating the admixture with the addition of aluminum acetylacetonate and adding and 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine base. The resulting mixture was analyzed and found to not exceed 6.5 hegman cure to 350 f pmt for 30 seconds to a hardness of 2 h min at 0.4 mils dry film thickness.
Into a suitably sized mixing vessel were added 404.9 pounds of Hi Sol 15 Aromatic 150 organic solvent, 255.4 pounds of Hydrolan Aluminium 501 aluminum pigment, 349.7 pounds of AW Hawthore Polysilizane, and Indopol as needed to achieve a desired admixture flow, which were then mixed under medium speed agitation until a lump free, smooth, and homogeneous mixture was achieved The resulting mixture was analyzed was found to not exceed 6.5 hegman cure to 350 f pmt for 30 seconds to a hardness of 2 h min at 0.4 mils dry film thickness.
Into a suitably sized mixing vessel are added 444 pounds of Hi Sol 15 Aromatic 150 organic solvent, 175 pounds of Hydrolan Aluminium 501 aluminum pigment, 300 pounds of Durazane 1800 Polysilizane, and 15 pounds of 1,8-diazabicycloundecene catalyst, which is then mixed under medium speed agitation until a lump free, smooth, and homogeneous mixture was achieved; estimated curing time of the admixture is adjusted by titrating the admixture with the addition of aluminum acetylacetonate and adding and 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine base. The resulting mixture should show analysis of not to exceed 6.5 hegman cure to 350 f pmt for 30 seconds to a hardness of 2 h min at 0.4 mils dry film thickness.
Into a suitably sized mixing vessel are added 444 pounds of Hi Sol 15 Aromatic 150 organic solvent, 175 pounds of Hydrolan Aluminium 501 aluminum pigment, 500 pounds of Durazane 1800 Polysilizane, and 15 pounds of 1,8-diazabicycloundecene catalyst, which is then mixed under medium speed agitation until a lump free, smooth, and homogeneous mixture is achieved; estimated curing time of the admixture is adjusted by titrating the admixture with the addition of aluminum acetylacetonate and adding and 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine base. The resulting mixture should show analysis of not to exceed 6.5 hegman cure to 350 f pmt for 30 seconds to a hardness of 2 h min at 0.4 mils dry film thickness.
The process of hot stamping for press hardening steels involves heating the steel blanks to elevated temperatures for austenitization in a furnace, followed by transferring the blanks to a stamping press for simultaneous die forming and quenching operations. Typically, the press hardening boron steels utilized for hot stamping of structural parts are hot dip coated with AlSi10Fe3 alloy (aluminized), aimed at avoiding the formation of scale during heating in the furnace. Studies known in the art have shown that during heating in the furnace, the AlSi10Fe3 coating melts at a temperature of approximately 575° C. This phenomenon facilitates the outward diffusion of Fe and Mn from the steel substrate into the molten AlSi10Fe3 layer, leading to the formation of intermetallic phases with higher melting temperatures. Research in the art has demonstrated, through the use of an interrupted heating technique at various temperatures and soaking times, that the inward diffusion of Al and Si into the steel substrate is triggered above the austenite starting temperature.n. The coating development progresses above the austenite finish temperature, where the outward diffusion of Fe and Mn from the steel substrate into the AlSi10Fe3 coating results in the formation of Al—Fe—Si intermetallic phases at the coating surface, and the inward diffusion of Al and Si from the coating into the steel substrate causes the growth of the interdiffusion layer at the steel-coating interface. Longer soaking times above these temperatures result in reduced performance during welding and painting operations of the hot formed parts, leading to an increase in the thickness of the interdiffusion layer and the total coating thickness. Industry standards, therefore, restrict the coating development during the residence time in the furnace to a maximum interdiffusion layer thickness of 12 to 16 microns and a maximum total coating thickness of 30 to 50 microns. These coating development attributes are directly related to the performance in welding and painting operations and the corrosion resistance of hot stamped parts.
In this Example, a new coating for press hardening steel (PHS) is described as an alternative to the traditional aluminized AlSi10Fe3 coating used in the hot stamping process. The new coating is a heat-resistant paint that consists of polysilazane as a pre-ceramic polymer and aluminum powder as an active filler. The heat-resistant paint coating was applied to a 22MnB5 steel substrate with a thickness of 0.9 mm in coil form using an industrial roller coating pre-paint line. A 22MnB5 PHS with a thickness of 0.9 mm and coated with a typical hot dip aluminized coating was used as a baseline for comparison purposes. The behavior and development of the new coating during heating in the furnace were analyzed using differential scanning calorimetry (DSC) and Continuum Depth Profile with Glow Digital Spectrometry (CDP-GDS). The surface phase composition of the new coating before and after heating for the hot stamping process was characterized using scanning electron microscopy, and energy-dispersive X-Ray spectroscopy (SEM-EDX). Results from the welding, E-coating, and corrosion resistance studies performed on the hot stamped parts are disclosed below, demonstrating the feasibility of a window process for the residence time in the furnace for the new PHS coating. For this study, the behavior of the polysilazane and aluminum powder coated press hardening steel (PHS) during heating in the furnace was analyzed using Differential Scanning Calorimetry (DSC). DSC is a widely utilized analytical technique that measures the heat flow and temperature changes associated with physical and chemical transitions in materials. The measurement provides both qualitative and quantitative information regarding the exothermic or endothermic processes that occur in the sample. In a DSC analysis, an endothermic process in the sample leads to a peak in the DSC signal due to the reduction in the sample temperature relative to the reference air temperature. Conversely, an exothermic process releases heat, leading to an inverse peak in the DSC signal due to the increase in the sample temperature compared to the reference air temperature. In this study, DSC investigations were conducted on heat resistant paint coated and aluminized 22MnB5 steel samples at a constant heating rate of 0.08° C./s.
The DSC signal of the aluminized coated sample exhibited a peak starting at around 580° C. and ending at approximately 640° C., which corresponds to the melting point and solidification of the AlSi10Fe3 as a eutectic coating. A second DSC signal peak was observed, starting at around 720° C. and ending at approximately 840° C., which corresponded to the phase transformation of ferrite to austenite in the 22MnB5 steel substrate. The DSC signal of the paint coated 22MnB5 sample exhibited a smooth inverted peak between 485° C. and 530° C., corresponding to a low energy exothermic reaction in the paint coating. A second peak, starting at around 720° C. and ending at approximately 840° C., was the same as the aluminized coated sample and corresponded to the phase transformation of ferrite to austenite in the 22MnB5 steel substrate. The absence of the melting point of the paint coating during heating was reflected in differences between DSC signals for the paint and for the aluminized coated samples. The normalized mass increase of the paint and aluminized coated 22MnB5 steel samples as a function of temperature showed that the mass increase during heating was due to the adsorption of oxygen from the furnace atmosphere and the formation of surface oxides. The results showed that at temperatures above 550° C., the oxygen adsorption of the paint coated sample was higher than that of the aluminized coated sample. This indicated that the paint coated 22MnB5 steel will experience higher surface oxidation and oxidation throughout the coating thickness during heating in the furnace for the hot stamping process than the aluminized coated steel. Blanks for a current production part were cut using a laser cutting process from both the roller paint coated coil and the production hot-dip aluminized coated coil. These blanks were then subjected to an industrial hot stamping trial that was carried out using an AP&T hot stamping production cell, which included a linear transfer system for loading and unloading the blanks, a multi-layered furnace, and a hydraulic press. The aluminized coated blanks underwent an optimized thermal cycle with a production intent, consisting of a 3-minute furnace residence time at 930° C. The paint coated blanks were loaded into the furnace at a soaking temperature of 930° C. and subjected to furnace residence times of 2 minutes and 5 minutes for this study. After the furnace residence time, the blanks were unloaded and transferred to the press within 10 seconds, followed by die forming and quenching with a 3-second die dwell time.
K-type thermocouples were welded onto the paint and aluminized coated blanks and were monitored using a data acquisition system to determine the temperature profiles of the 22MnB5 steel substrate during the furnace residence time. The experimental results were plotted to show the temperature profiles of the paint and aluminized coated blanks. From this it was observed that the paint coated blank reached the furnace soaking temperature of 930 C in approximately 25 seconds, with an average heating rate of 36 C/s. On the other hand, the hot-dip aluminized coated blank required approximately 130 seconds to reach the furnace soaking temperature, resulting in an average heating rate of 7 C/s. These results were attributed to differences in the radiative properties of the two coatings, such as surface emissivity, as well as absorptivity, as well as the melting and solidification of the aluminized coating during heating in the furnace. These conclusions were consistent with discrepancies observed between DSC signals for the painted and the aluminized coated samples, confirming that the paint coating did not melt during the furnace residence time. Examination of the stamped parts of the paint coated 22MnB5 blank and the hot-dip aluminized coated blank after 3 minutes of furnace residence time indicated that the paint coating demonstrated good thermal stability at high temperatures and good coating adhesion during hot plastic deformation, as no visual surface defects such as paint exfoliation, blister, or bar spots were observed on the surface of the hot stamped parts.
The observed elemental profiles of both oxygen and iron suggested that during the furnace residence time, the oxygen from the furnace atmosphere diffused into the coating, while iron from the steel substrate migrated outward into the coating. The iron concentration, measured at the proximity of the coating surface, demonstrated an outward diffusion trend, increasing from an initial value of 2% Fe for 0 minutes furnace residence time to 6% Fe and 20% Fe for 2 minutes and 5 minutes of furnace residence time, respectively. A general increase in iron diffusion into the coating was observed as the furnace residence time increased, with the iron elemental profile exhibiting a constant level of approximately 55% Fe at a depth of approximately 0.5 microns from the coating surface. Meanwhile, the oxygen concentration measured near the surface displayed an increase from 7%0 for 0 minutes furnace residence time to 60%0 and 68%0 for 5 minutes and 2 minutes of furnace residence time, respectively.
The carbon elemental profile of the paint coating underwent significant changes upon heating at 930° C. The near-surface carbon percentage, which was measured to be approximately 22% for the 0—minute condition, decreased to 3% and 1% for the 2-minute and 5-minute furnace residence time conditions, respectively. Further, the carbon elemental profiles for the 2-minute and 5-minute conditions overlapped after a depth of 1.5 microns into the coating. These findings suggested that upon heating at 930° C., the pre-ceramic polymer underwent a polymer-to-ceramic conversion reaction.
CDP-GDS methods were utilized to determine the thickness of the paint coating on the steel substrate. The nominal thickness of the paint coating was determined by the intersection of the silicon and manganese elemental profiles, referred to as the Si—Mn intersect. Based on this method, the paint coating thickness of the 0-minute sample was measured to be 7.7 microns, while the thickness of the 2-minute and 5-minute sample conditions were measured to be 5.9 microns and 6.1 microns, respectively. The difference in the coating thickness measurements between the 0-minute condition and the 2-minute and 5—minute furnace residence time conditions can be attributed to the shrinkage of the polymer during the cross-linking and pyrolysis processes. This explanation is supported by the carbon elemental profiles and the DSC findings, which revealed an inverted peak between 485° C. and 530° C., corresponding to a low-energy exothermic reaction that occurred in the paint coating during heating. These differences in coating thickness measurements may also have been related to the change in microstructural phases of the paint, from amorphous to crystalline phases. It was observed that the paint coated blank reached the furnace soaking temperature of 930 C in approximately 25 seconds, with an average heating rate of 36 C/s. On the other hand, the hot-dip aluminized coated blank required approximately 130 seconds to reach the furnace soaking temperature, resulting in an average heating rate of 7 C/s. These results can be attributed to differences in the radiative properties of the two coatings, such as surface emissivity The results of the phase mapping analysis showed that after a 2-minute furnace residence time at 930° C., the cured surface of the paint coating was composed of a continuous network of iron-silicon oxides (approximately 19% FeSiO) surrounding a matrix of silicon-aluminum oxides (approximately 60% SiAlO) and globular particles of aluminum-silicon-iron oxides (approximately 4% AlSiFeO) evenly distributed throughout the network. With an increased furnace residence time of 5 minutes, the cured paint coating surface further evolved to consist of a matrix of silicon-aluminum oxides (approximately 34% SiAlO) with a network of iron oxide (approximately 17% FeO) and globular iron-silicon oxide (approximately 18% FeSiO), and islands of aluminum-silicon-iron oxides (approximately 9% AlSiFeO) evenly distributed throughout the network. The mechanism of the paint coating development on sheet steel is believed to be that the polysilazine polymer undergoes an exothermic reaction, resulting in a reduction in the total coating thickness due to shrinkage during cross-linking and pyrolysis and the transition from an amorphous to crystalline phase. During the residence time in the furnace, the coating is subjected to inward diffusion of oxygen from the furnace atmosphere and outward diffusion of iron from the steel substrate, leading to altered phase compositions and morphologies.
A two-minute residence time at 930° C. results in an enrichment of Si oxide islands with Fe, leading to the formation of a network of Fe—Si oxides and islands of Al—Si—Fe oxides in a Si—Al oxide matrix. Further increasing the residence time to five minutes results in additional diffusion of Fe from the steel substrate, leading to a modification of the Fe—Si oxide phase morphology from a network to a globular structure, and the formation of a new Fe oxide network. This also leads to an increase in the volume fraction of Al—Si—Fe oxide islands at the expense of the Si—Al oxide matrix. From these observations, the conclusions were reached that the new steel coating of the present invention shows considerable benefits in reducing manufacturing complexity and cost. I enables an optimized hot stamping process with lower furnace temperatures and residence time, eliminates the issue of coating buildup on furnace rollers during heating and on the die cavities during part forming, and results in lower maintenance costs for the hot stamping process. Additionally, new steel substrate alloys may be developed as a result of the lowering of austenization temperatures and higher material strength, and elimination of the concern of hydrogen embrittlement.
The mechanism of the paint coating development on sheet steel is believed to be that the polysilazine polymer undergoes an exothermic reaction, resulting in a reduction in the total coating thickness due to shrinkage during cross-linking and pyrolysis and the transition from an amorphous to crystalline phase. During the residence time in the furnace, the coating is subjected to inward diffusion of oxygen from the furnace atmosphere and outward diffusion of iron from the steel substrate, leading to altered phase compositions and morphologies.
A two-minute residence time at 930° C. results in an enrichment of Si oxide islands with Fe, leading to the formation of a network of Fe—Si oxides and islands of Al—Si—Fe oxides in a Si—Al oxide matrix. Further increasing the residence time to five minutes results in additional diffusion of Fe from the steel substrate, leading to a modification of the Fe—Si oxide phase morphology from a network to a globular structure, and the formation of a new Fe oxide network. This also leads to an increase in the volume fraction of Al—Si—Fe oxide islands at the expense of the Si—Al oxide matrix.
From these observations, the conclusions were reached that the new steel coating of the present invention shows considerable benefits in reducing manufacturing complexity and cost. I enables an optimized hot stamping process with lower furnace temperatures and residence time, eliminates the issue of coating buildup on furnace rollers during heating and on the die cavities during part forming, and results in lower maintenance costs for the hot stamping process. Additionally, new steel substrate alloys may be developed as a result of the lowering of austenization temperatures and higher material strength, and elimination of the concern of hydrogen embrittlement.
Ordinarily skilled inorganic and organic chemists and chemical engineers may modify the compositional embodiments within the specifications' teachings according to methods well known to those of ordinary skill in the arts, to provide numerous preferred alternative embodiments for a particular physico/chemical/material/structural set of desired performance parameters of coated sheet steel articles, without rendering such embodiments unstable or compromising their advantageous manufacturing characteristics.
While the above description contains a great deal of specificity, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of the presented embodiments thereof. Many other alternative embodiments and variations are possible within the teachings of the various embodiments. While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention will not be limited to the particular embodiments expressly disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, unless the text specifically reads otherwise, the use of the terms first, second, and so forth do not denote any order or hierarchy of importance, but rather the terms first, second, and so forth are used to distinguish one disclosed element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.
While the invention has been described, exemplified, and illustrated in reference to certain preferred embodiments thereof, those skilled in the art will appreciate that various changes, modifications, and substitutions can be made therein without departing from the spirit and scope of the invention.
It is intended, therefore that the invention be limited only by the scope of the claims which follow, and that such claims be interpreted as broadly as is reasonable.
The present application is a Continuation-In-Part application of U.S. application Ser. No. 18/084,533 filed Dec. 19, 2022, which is a Continuation-In-Part application of U.S. application Ser. No. 17/677,9309 filed Feb. 22, 2022, which claims the benefit of U.S. Provisional Application No. 63/152,533 filed Feb. 23, 2021, all of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63152533 | Feb 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 18084533 | Dec 2022 | US |
| Child | 18113607 | US | |
| Parent | 17677939 | Feb 2022 | US |
| Child | 18084533 | US |
