Patent Application
20200318214
The present invention relates to hot-rolled steel foam and a method for manufacturing hot-rolled steel foam.
Metal is considered a foam if pores or voids are distributed within the metal to take up a certain minimum percentage of the total volume of the metal. The introduction of pores or voids into a metal component typically decreases the density and weight of the metal component compared to a solid metal component. Metal foam components also frequently display a higher plate bending stiffness and other desirable mechanical properties than solid metal components. Currently, commercial metal foam components are generally limited to aluminum, despite the fact that steel foam components would exhibit many superior properties if they could be produced in volume at reasonable cost.
Hot rolling is a metal forming process in which a metal is passed through one or more pairs of rolls to reduce the thickness of the metal and make the thickness throughout the metal uniform. The temperature of the metal being rolled is typically above the recrystallization temperature of the metal.
Embodiments of the present invention provide the ability to produce hot-rolled steel foam plates having consistent densities. In addition, embodiments of the present invention provide the ability to produce steel foam plates having predictable and enhanced mechanical properties.
Aspects of the present invention provide engineers working with hot-rolled steel a new degree of freedom: density. The design space potentially covered by steel applications can grow significantly with density as a variable. Among other things, the present invention opens new opportunities for designers to find suitable military and naval applications for not only energy absorption, but also blast resistant and ballistic applications to resist the impact of objects due to the high strength and hardness of products produced in accordance with structures and methods presented herein.
In some embodiments, the present invention provides a method of producing a hot-rolled steel sheet, wherein the method comprises preparing a steel slab by casting molten steel, the steel slab including a plurality of interconnected pores that form a substantially uniform pattern within the steel slab, cooling the steel slab, reheating the steel slab, hot rolling the steel slab at a starting temperature of between 1050 degrees Celsius and 1230 degrees Celsius to form the steel slab into the hot-rolled steel sheet, wherein the plurality of interconnected pores is flattened during hot rolling, and wherein the method further comprises cooling the hot-rolled steel sheet, and heat treating the hot-rolled steel sheet.
In some embodiments, the present invention provides a hot-rolled steel sheet comprising a steel body having a chemical composition including, by mass %: C: 0.10% to 0.35%, Si: 0.2% to 0.8%, Mn: 0.5% to 1.5%, P: 0.00% to 0.025%, S: 0.00% to 0.025%, Al: 0.01% to 0.08%, Ni: 0.00% to 2.00%, Cr: 0.00 to 1.5%, Mo: 0.00% to 0.50%, and a balance including Fe and incidental impurities. The steel body includes a plurality of interconnected pores forming a substantially uniform pattern within the body, wherein the plurality of interconnected pores are flattened during a hot rolling process.
Before embodiments of the present invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
Some embodiments of steel slabs according to the present invention are described in U.S. Pat. No. 9,623,480 filed Dec. 19, 2014 and U.S. Pat. No. 10,493,522 filed Jun. 2, 2017, both of which are entitled “STEEL FOAM AND METHOD FOR MANUFACTURING STEEL FOAM,” the entire contents of both of which are hereby incorporated by reference. Embodiment of steel slabs according to the present invention have any combination of the chemical component elements set forth below. The component elements presented below can include limitations for the reasons described below, where the unit “%” relating to the chemical component elements in the steel refers to “mass %” unless specified otherwise.
C: 0.1% to 0.35%
Carbon (C) is an element used in steels to achieve surface hardness and strength, which is determined by the percentage of carbon and subsequent heat treatment. Generally, low carbon content steels provide improved toughness. Higher carbon contents provide higher strength, hardness, and hardenability. Carbon in excess of 0.35% contributes to increased brittleness and reduced weldability. Therefore, it is preferably that the carbon content is in the range of 0.10% to 0.35%.
Si: 0.2% to 0.8%
Silicon (Si) has high work hardenability to ensure that ductility is not substantially decreased as the strength is increased, thereby contributing to providing an improved balance between strength and ductility after heat treatment. In addition, silicon is an element typically required to improve material homogeneity by promoting ferrite transformation in the hot rolling stage, and securing a desired grain size and a desired volume fraction. Silicon content of greater than 0.2% produces such an effect. If silicon content exceeds 0.8%, hot-dip galvanizing properties after annealing deteriorate significantly.
Mn: 0.5% to 1.5%
Manganese (Mn) is an element that can contribute to the hardenability of steels, meaning increasing the depth of hardness. In some embodiments, the Mn content is less than 1.5% due to the tendency of Mn to segregate, and the adverse effect of Mn on quench cracking. In quantities greater than 0.5%, Mn can reduce the potential for harmful Type II MnS inclusions in steel. The desired ratio of Mn to Sulfur is 10 to 1. Therefore, the desirable range of Mn is 0.5% to 1.5%
P: less than 0.025%
Phosphorous (P) is an element that can contribute to an increase in the ductile-to-brittle transition temperature, and reduced toughness and ductility in steels. Phosphorous is generally an undesirable element in steels, which preferably is limited to a phosphorous content of less than 0.025%.
S: less than 0.025%
Sulfur (S) in high quantities may form low-melting iron sulfide, a grain boundary phase that causes severe hot shortness during hot rolling if manganese content is not sufficient to counter this effect. Sulfur can also decrease toughness and ductility in steels. Sulfur is generally an undesirable element in steels, which preferably is limited to a sulfur content of less than 0.025%.
Al: 0.01% to 0.08%
Aluminum (Al) is an element often required for deoxidation, which also prevents the formation of gas porosity. Al is also useful in preventing grain growth during heat treatment. In some embodiments, the content of Al is greater than 0.01% to produce such an effect. However, since Al content exceeding 0.08% can lead to the formation of aluminum nitride phase at the grain boundaries and can reduce the toughness and ductility of steel, Al content of 0.08% or less is preferred.
Ni: less than 2.00%
Nickel (Ni) is an element contributing to high strengthening of steel by reducing the ductile-to-brittle transition temperature in steel, and also contributing to high strengthening by increasing quench hardenability during heat treatment. Nickel content of greater than 2.00% can contribute to steels that are prone to the formation of undesirably retained austenite during heat treatment, since nickel is an austenite stabilizer. Therefore, it is preferred that the content of Nickel is less than 2.00%.
Cr: less than 1.5%
Chromium (Cr) is an element contributing to high strengthening of steel by improving hardenability during heat treatment. If Cr content exceeds 1.5%, quench cracking in low alloy steels typically increases. Cr is ordinarily used with other alloying elements, such as Molybdenum. Thus, Cr content of less than 1.5% is preferred.
Mo: less than 0.5%
Molybdenum (Mo) is an element contributing to high strengthening of steel by increasing quench hardenability, and is typically present in high strength low alloy steels. Mo typically reduces the temper embrittlement in steels, and improves the toughness of low alloy steels. If Mo content exceeds 0.5%, no improvement in the effect is recognized in some embodiments. Thus, Mo content of less than 0.5% is preferred.
In the chemical compositions as explained above, the balance of the steel disclosed herein is iron (Fe), and can also include incidental impurities.
The incidental impurities can include, for instance, Sb, Sn, Zn, and Co, and their permissible ranges can be Sb: 0.01% or less; Sn: 0.1% or less; Zn: 0.01% or less; and Co: 0.1% or less. In addition, Ti and Zr may be contained within ranges of ordinary steel compositions, to the extent that the desired effects are not lost. In further embodiments, steel slabs according to the present invention may include chemical compositions that differ from the chemical compositions detailed above. For example, the chemical composition may be that of high alloy steels such as stainless steels, or the like.
With continued reference to the illustrated embodiment of
Although in some embodiments (such as in the illustrated embodiment of
The pores 120 in the illustrated embodiment are arranged in a series of pore rows 124 and pore columns 128, with the pore rows 124 being parallel to a horizontal axis H, and the pore columns 128 being parallel to a vertical axis V. As used herein, terms of orientation such as “horizontal” and “vertical” are for ease of description only, and are not intended to be limiting absent specific reference to the same in the appended claims. As also shown in the embodiment of
In the illustrated embodiment, the plurality of pores 120 forms at least 20% of a total volume of the steel body 104. In some embodiments, the pores 120 may form 20% of the total volume. In other embodiments, the pores 120 may form at least 50% of a total volume of the steel body 104. In other embodiments, the pores 120 may form between 20% and 50% of the total volume. In further embodiments, the pores 120 may form less than 50% of the total volume. In still other embodiments, the pores 120 may form 25%, 30%, 35%, 40%, or 45% of the total volume of the steel body 104. In some embodiments, the calculation of volume (in which the plurality of pores 120 occupies) is made by identifying the bounds of the volume in the body 104 in which the pores 120 exist, and then calculating the space occupied within that volume. Such a calculation can be made, for example, in products in which only a portion of the body 104 has pores 120.
As just described, in some embodiments the plurality of interconnected pores 120 does not extend through an entirety of the steel body 104, such that at least a portion of the steel body 104 is solid. For example, one or more sections of the steel body 104 may include pores to decrease the density of that section(s), while one or more other sections of the steel body 104 may not include pores 120, and may be entirely or relatively solid. By way of example only, the one or more sections with pores 120 may be located in a center of the steel body 104, near one or more edges of the steel body 104, or both. In these and other embodiments, the pores 120 may create a gradient density within the steel body 104 such that the density of pores 120 is different in different locations in the body 104.
With continued reference to the illustrated embodiment of
The first panel 217 and second panel 218 of the illustrated embodiment are flat panels. The panels 217, 218 may also be referred to as skins. Each panel 217, 218 is generally rectangular and planar. In the illustrated embodiment, the first panel 217 and the second panel 218 have similar thicknesses. In other embodiments, the panels 217, 218 may have unequal thicknesses. Additionally or alternatively, the first and second panels 217, 218 may have other (e.g., non-planar and/or non-rectangular) shapes, such as circular, oblong, and the like, or any of the other shapes described above in connection with the body 104 illustrated in
Together, the first panel 217, the second panel 218, and the strut structure 230 of the illustrated embodiment form a composite panel. The composite panel may also be referred to as a sandwich panel. In some embodiments, the first panel 217, the second panel 218, and the strut structure 230 may be integrally formed as a single unit. For example, the steel slab 200 may be formed using any of the methods described in U.S. Pat. Nos. 9,623,480 and 10,493,522. In other embodiments, the first panel 217, the second panel 218, and the strut structure 230 may be formed as separate pieces that are secured together in any suitable manner, such as by welding. In such embodiments, at least the strut structure 230 may still be formed using any of the methods described in U.S. Pat. No. 9,623,480. In some embodiments, the strut structure 230 may be integrally formed with only one of the panels 217, 218, and the other panel 217, 218 may be secured (e.g., welded) to the strut structure 230.
The steel body 104b also includes a plurality of interconnected pores 120b forming a substantially uniform pattern within the body 104b. In some embodiments, the pores 120b have generally the same shape and configuration as the pores 120 described above in connection with
The steel slabs of
As described above, the pores 120, 220, 320 can become flattened (i.e., having a flattened profile) from the hot rolling process also described herein. As a result, the pores 120, 200, 320 can each take on a shape in which each pore has length and/or width dimensions (in the plane of the steel sheet 100b, 200b, 300b) that are larger than the thickness dimensions (in a direction that is perpendicular to the steel sheet 100b, 200b, 300b). In some embodiments, at least a majority of the pores in the steel sheet 100b, 200b, 300b have this shape and orientation. Also in some embodiments, at least 80% of the pores in the steel sheet 100b, 200b, 300b have this shape and orientation.
Also as a result of the hot rolling process, the pores 120, 200, 320 can each take on a shape in which each pore has length (i.e., largest dimension) oriented generally in a common direction. In some embodiments, the common direction is the direction in which the steel slab 100, 200, 300 was rolled, or in the length (i.e., largest dimension) direction of the steel slab and steel sheets 100b, 200b, 300b. In some embodiments, at least a majority of the pores in the steel sheet 100b, 200b, 300b have this orientation. Also in some embodiments, at least 80% of the pores in the steel sheet 100b, 200b, 300b have this shape and orientation.
The pores in the resulting steel sheets 100b, 200b, 300b can still have the same general shape and/or relative arrangement as that in the steel slabs 100, 200, 300 from which the steel sheets 100b, 200b, 300b were formed, albeit with a generally flattened profile as described above. Accordingly, pores 120 having different shapes interconnected as described above can still have different shapes and interconnections. Similarly, pores 120, 220, 320 having two or more different pore sizes within the steel slabs 100, 200, 300 can still have two more different flattened pore sizes within the steel sheets 100b, 200b, 300b.
At Step 400, the steel slab 100, 200, 300 is prepared by, for example, sand casting molten steel. Possible methods of preparing the steel slab 100 are disclosed in U.S. Pat. Nos. 9,623,480 and 10,493,522, the entire contents of which are incorporated by reference herein. As described above, the steel slab 100 includes the plurality of interconnected pores 120 that can form a substantially uniform pattern within the steel slab 100. In some embodiment, the interconnected pores 120 are formed through the method of casting the molten steel into the steel slab 100. In some embodiments, the interconnected pores 120 are formed as a plurality of spheres and cylinders. To prepare the steel slab of
After the steel slab 100, 200, 300 has been prepared, the steel slab 100, 200, 300 is cooled (Step 404). In some embodiments, the steel slab 100, 200, 300 may be cooled to 600 degrees Celsius. The steel slab 100, 200, 300 is cooled within, for example, six hours of completing preparation of the steel slab 100, 200, 300. In other embodiments, the steel slab 100, 200, 300 may be cooled to other suitable temperatures, or within other time periods.
After the steel slab 100, 200, 300 has been cooled in the illustrated embodiment, an antiscale coating is applied to the steel slab 100, 200, 300 (Step 408). The antiscale coating may be applied to interior and exterior surfaces of the steel slab 100, 200, 300 to reduce or minimize scaling of the interconnected pores 120 (Step 408). In some embodiments, this step may be omitted.
With continued reference to the illustrated embodiment of
At Step 416, the reheated steel slab 100, 200, 300 begins a hot rolling cycle. The starting temperature of the steel slab 100, 200, 300 as it begins the hot rolling cycle may be between 1050 degrees Celsius and 1230 degrees Celsius. In some embodiments, the hot rolling cycle begins by passing the steel slab 100, 200, 300 between a first roller and a second roller of a mill. The first roller and the second roller can rotate in opposing directions, thereby moving the steel slab 100, 200, 300 through the rollers. The steel slab 100, 200, 300 can be passed through the first roller and the second roller in a range of two to six passes, or may be passed through multiple sets of rollers, forming the steel sheet 100b. The number of passes the steel slab 100, 200, 300 undergoes can correspond to a reduction of thickness of the steel slab 100, 200, 300 of between 25% and 75%. In some embodiments, the steel slab 100, 200, 300 starts the hot rolling cycle at a thickness in a range of 1 inch to 2 inches, and the steel sheet 100b finishes hot rolling at a thickness in a range of 0.25 of an inch to 0.75 of an inch. In other embodiments, the steel slab 100, 200, 300 may have other starting thicknesses, and/or the steel sheet 100b, 200b, 300c may have other finishing thicknesses.
Through the process of hot rolling, in some embodiments the interconnected pores 120 are flattened. In the illustrated embodiment of
At Step 420, the hot rolling process ends. In some embodiments, a final temperature of the steel sheet 100b, 200b, 300c as the steel sheet completes hot rolling is greater than or equal to 850 degrees Celsius. In the event that the steel sheet 100b, 200b, 300b reaches the final temperature prior to a desired thickness being reached, the steel sheet 100b, 200b, 300c can again be soaked in a soaking oven to increase the temperature of the steel sheet 100b, 200b, 300b. Once the temperature of the steel sheet 100b, 200b, 300b has increased, the hot rolling cycle may continue.
At Step 424, the steel sheet 100b, 200b, 300b is cooled. In some embodiments, cooling of the steel sheet 100b, 200b, 300b may begin within five seconds of completion of hot rolling. The cooling of the steel sheet 100b, 200b, 300b may be an uncontrolled cooling process, meaning the steel sheet 100b, 200b, 300b does not undergo further treatment to facilitate cooling. In other embodiments, the cooling process may be controlled. In one example, the steel sheet 100b, 200b, 300b is initially cooled at a cooling rate in the range of 2 degrees Celsius per minute to 10 degrees Celsius per minute until the steel sheet 100b, 200b, 300b reaches an ambient temperature of approximately 30 degrees Celsius.
At step 428 of the illustrated embodiment, the steel sheet 100b, 200b, 300b is heat treated. In some embodiments, the steel sheet 100b, 200b, 300b may be heat treated through a quenching and tempering process. In other embodiments, the steel sheet 100b, 200b, 300b may be heat treated through a normalizing and tempering process. The steel sheet 100b, 200b, 300b can be heat treated to achieve a hardness in a range of, for example, 150 Brinell hardness number (BHN) to 400 BHN. In some embodiments, the steel sheet 100b, 200b, 300b may be heat treated to have a hardness of 150 BHN, 200 BHN, 250 BHN, 300 BHN, 350 BHN, or 400 BHN. In other embodiments, the steel sheet 100b may be heat treated to have a hardness less than 150 BHN or greater than 400 BHN. In further embodiments, this step may be omitted.
As noted above,
The insert 500 can be used in a sand casting process, such as the process disclosed in U.S. Pat. Nos. 9,623,480 and 10,493,522. As such, the insert 500 may formed using similar materials and processes disclosed in the '480 and '522 patents, such as 3-D printing.
The above techniques allow for the creation of steel sheets or composite panels, with ballistic-resistant application for, for example, military structures (e.g., ballistic plates), civilian structures (e.g., building and bridges), naval applications, and the like. In some scenarios, the steel sheets may be used in ships or aircrafts. The steel sheets or composite panels also have applications in energy absorption, blast resistance, and sound absorption. The steel foam slabs used to cast the steel sheets allow for large steel sheets to be produced cost-effectively, as larger thickness sections of the steel slabs may be used. Structural advantages of steel foam sheets compared to solid steel sheets include minimization of weight, maximization of flexural strength, increased energy dissipation, and increased damping.
Although the steel slabs 100, 200, 300 are all described above as going through a hot-rolling process, in some scenarios, the steel slabs 100, 200, 300 may be used as-is without hot-rolling. For example, some applications may require a combination of panels that are both hot-rolled and not hot-rolled. Alternatively, some applications may only require panels that are not hot-rolled.
Various features and advantages of the invention are set forth in the following claims.
This application claims priority to U.S. Provisional Patent Application No. 62/829,236, filed on Apr. 4, 2019, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62829236 | Apr 2019 | US |
