Patent Application
20220356540
This application claims the benefit and priority of Chinese Application No. 202110487225.4, filed May 5, 2021. The entire disclosure of the above application is incorporated herein by reference.
This section provides background information related to the present disclosure which is not necessarily prior art.
Press-hardened steel (PHS), also referred to as “hot-stamped steel” or “hot-formed steel,” is one of the strongest steels used for automotive body structural applications, having tensile strength properties of about 1500 MPa. Such steel has desirable properties, including forming steel components with significant increases in strength-to-weight ratios. PHS components have become ever more prevalent in various industries and applications, including general manufacturing, construction equipment, automotive or other transportation industries, home or industrial structures, and the like. For example, when manufacturing vehicles, especially automobiles, continual improvement in fuel efficiency and performance is desirable; therefore, PHS components have been increasingly used. PHS components are often used for forming load-bearing components, like door beams, which usually require high strength materials. Thus, the finished state of these steels are designed to have high strength and enough ductility to resist external forces, such as, for example, resisting intrusion into the passenger compartment without fracturing so as to provide protection to the occupants. Moreover, galvanized PHS components may provide cathodic protection.
Many PHS processes involve austenitization of a sheet steel blank in a furnace, immediately followed by pressing and quenching of the sheet in dies. Austenitization is typically conducted at temperatures of greater than 850° C. PHS processes may be direct or indirect. In the direct method, the PHS component is formed and pressed simultaneously between dies, which quenches the steel. In the indirect method, the PHS component is cold formed to an intermediate partial shape before austenitization and the subsequent pressing and quenching steps. The quenching of the PHS component hardens the component by transforming the microstructure from austenite to martensite. A discontinuous oxide layer often forms on the surface of the component during furnace heating and transferring from the furnace to dies when the component is fabricated from uncoated steel. Therefore, after quenching, the oxide must be removed from the PHS component and the dies. The oxide is typically removed, i.e., descaled, by shot blasting.
The PHS component may be made from bare or coated alloys. Coating the PHS component with, e.g., zinc (Zn) or aluminum-silicon (Al—Si), provides a protective layer to the underlying steel component. Zn coatings, for example, offer cathodic protection; the coating acts as a sacrificial layer and corrodes instead of the steel component, even where the steel is exposed. Oxide generated on surface of Zn-coated PHS components must be removed by shot blasting or other descaling processes. It would be beneficial to manufacture components from a coating-free stainless PHS with excellent mechanical performance and long-term corrosion resistance. The following disclosure is directed to such a PHS.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The present disclosure relates to press hardening steel with a combination of superior corrosion resistance and ultra-high strength.
In various aspects, the current technology provides a steel composition including carbon (C) at a concentration of greater than or equal to about 0.02 wt. % to less than or equal to about 0.45 wt. %, manganese (Mn) at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. %, nickel (Ni) at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. %, chromium (Cr) at a concentration of greater than or equal to about 11 wt. % to less than or equal to about 17 wt. %, silicon (Si) at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, and a balance of iron (Fe), wherein the combined concentration of the Mn and the Ni is greater than or equal to about 2 wt. % to less than or equal to about 8 wt. %.
In one aspect, the steel composition further includes molybdenum (Mo) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, tungsten (W) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, aluminum (Al) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, copper (Cu) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, or combinations thereof, wherein, when the Cu and the Mo are both present in the steel composition, the combined concentration of the Cu and the Mo is less than or equal to about 5 wt. %.
In one aspect, the steel composition includes the Cu, wherein the surface oxide layer further includes oxides of the Cu after being subjected to press hardening.
In one aspect, the steel composition further includes vanadium (V) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, niobium (Nb) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, titanium (Ti) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, or combinations thereof, wherein, when at least two of the V, the Nb, or the Ti are present in the steel composition, the combined concentration of the at least two of the V, the Nb, or the Ti is less than or equal to about 0.5 wt. %.
In one aspect, the steel composition is in the form a coiled sheet.
In various aspects, the current technology also provides a PHS including an alloy core having carbon (C) at a concentration of greater than or equal to about 0.02 wt. % to less than or equal to about 0.45 wt. %, manganese (Mn) at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. %, nickel (Ni) at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. %, chromium (Cr) at a concentration of greater than or equal to about 11 wt. % to less than or equal to about 17 wt. %, silicon (Si) at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, molybdenum (Mo) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, tungsten (W) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, aluminum (Al) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, copper (Cu) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, and a balance of iron (Fe), wherein the combined concentration of the Mn and the Ni is greater than or equal to about 2 wt. % to less than or equal to about 8 wt. % and wherein the combined concentration of the Cu and the Mo is greater than 0 wt. % to less than or equal to about 5 wt. %, and an oxide layer formed on a surface of the alloy core during hot forming of the PHS, the oxide layer including oxides of at least one of the Cr, the Si, or the Cu.
In one aspect, the combined concentration of the Cr and the Si is greater than or equal to about 15 wt. % to less than or equal to about 20 wt. %.
In one aspect, the PHS further includes an element selected from the group consisting of vanadium (V) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, niobium (Nb) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, titanium (Ti) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, and combinations thereof, wherein, when at least two of the V, the Nb, or the Ti are present in the steel composition, the combined concentration of the at least two of the V, the Nb, or the Ti is less than or equal to about 0.5 wt. %.
In one aspect, the oxide layer is uniform and continuous.
In one aspect, the oxide layer has a thickness of greater than or equal to about 5 nm to less than or equal to about 10 μm.
In one aspect, the PHS has a strength of greater than or equal to about 500 MPa to less than or equal to about 2000 MPa.
In one aspect, the alloy core includes a prior austenite grain size of less than or equal to about 20 μm.
In various aspects, the current technology further includes an automobile part including the PHS.
In various aspects, the current technology yet further includes a method of fabricating a PHS component, the method including heating a blank to a temperature of greater than or equal to about 850° C. to less than or equal to about 950° C. to form a heated blank, the blank including a steel composition including carbon (C) at a concentration of greater than or equal to about 0.02 wt. % to less than or equal to about 0.45 wt. %, manganese (Mn) at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. %, nickel (Ni) at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. %, chromium (Cr) at a concentration of greater than or equal to about 11 wt. % to less than or equal to about 17 wt. %, silicon (Si) at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, molybdenum (Mo) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, tungsten (W) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, aluminum (Al) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, copper (Cu) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, and a balance of iron (Fe), wherein the combined concentration of the Mn and the Ni is greater than or equal to about 2 wt. % to less than or equal to about 8 wt. % and wherein the combined concentration of the Cu and the Mo is greater than 0 wt. % to less than or equal to about 5 wt. %; transferring the heated blank through air to a die, wherein the heated blank cools by greater than or equal to about 150° C. to less than or equal to about 250° C. during the transferring; pressing the heated blank into the die to form a structure having a predetermined shape; and quenching the structure to a temperature of less than or equal to about a martensite finish (Mf) temperature of the steel composition and greater than or equal to about room temperature to form the PHS component, wherein the PHS component has an alloy core including the C, the Mn, the Ni, the Cr, the Si, the Cu, the Mo, and the Fe and an oxide layer formed on a surface of the alloy core, the oxide layer being continuous and uniform and including oxides of at least one of the Cr, the Si, or the Cu, and wherein the PHS component is formed without descaling and is free of a coating.
In one aspect, the steel composition and the alloy core further include an element selected from the group consisting of vanadium (V) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, niobium (Nb) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, titanium (Ti) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %, and combinations thereof, wherein, when at least two of the V, the Nb, or the Ti are present in the steel composition, the combined concentration of the at least two of the V, the Nb, or the Ti is less than or equal to about 0.5 wt. %.
In one aspect, the method is free of a secondary heat treatment after the quenching.
In one aspect, the method further includes heat treating the PHS component, the heat treating including heating the PHS component to a temperature of greater than or equal to about 100° C. to less than or equal to about 300° C. for greater than or equal to about 1 minute to less than or equal to about 100 minutes.
In one aspect, the blank is substantially free of a coating.
In one aspect, the PHS component is an automobile part selected from the group consisting of a battery tray component, a bed liner, a wheel, a pillar, a bracket, a bumper, a roof rail, a rocker rail, a rocker, a control arm, a beam, a tunnel, a step, a subframe member, a pan, a panel, and a reinforcement panel.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.
Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.
When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.
Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.
Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.
In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.
Example embodiments will now be described more fully with reference to the accompanying drawings.
As discussed above, there are certain disadvantages associated with descaling uncoated PHS and coating PHS. Moreover, some uncoated PHS are subject to corrosion. Accordingly, the current technology provides a steel composition that is configured to be hot stamped into a press-hardened component having a predetermined shape without coatings and a need to perform descaling and exhibiting long-term corrosion resistance.
The steel composition is in the form of a coil or sheet and comprises carbon (C), manganese (Mn) and/or nickel (Ni), chromium (Cr), silicon (Si), and iron (Fe). In some aspects, the steel composition further comprises at least one of niobium (Nb), vanadium (V), or titanium (Ti). In other aspects, the steel composition yet further comprises an additional element selected from the group consisting of molybdenum (Mo), tungsten (W), aluminum (Al), copper (Cu), and combinations thereof. The steel composition is free or substantially free of a coating, where “substantially free” means that the steel composition is not intentionally coated, but may contain at least one discontinuous portion that includes unavoidable surface layers as an impurity. During a hot stamping process, portions of the Cr, Si, Ni (when present), and Cu (when present) migrate to a surface of the resulting PHS and combine with atmospheric oxygen to form a continuous oxide layer comprising an oxide or oxides enriched with the portions of at least one of the Cr, Si, Ni (when present), or Cu (when present). The oxide layer resists, i.e., prevents, inhibits, or minimizes, further oxidation and corrosion. Put another way, the oxide layer protects the PHS from corrosive oxidation. Therefore, descaling steps, such as shot blasting or sand blasting, are not required.
The C is present in the steel composition at a concentration of greater than or equal to about 0.02 wt. % to less than or equal to about 0.45 wt. %, greater than or equal to about 0.1 wt. % to less than or equal to about 0.45 wt. %, or greater than or equal to about 0.1 wt. % to less than or equal to about 0.3 wt. % and subranges thereof. In various aspects, the steel composition comprises C at a concentration of about 0.02 wt. %, about 0.05 wt. %, about 0.075 wt. %, about 0.1 wt. %, about 0.12 wt. %, about 0.14 wt. %, about 0.16 wt. %, about 0.18 wt. %, about 0.2 wt. %, about 0.22 wt. %, about 0.24 wt. %, about 0.26 wt. %, about 0.28 wt. %, about 0.3 wt. %, 0.32 wt. %, about 0.34 wt. %, about 0.36 wt. %, about 0.38 wt. %, about 0.4 wt. %, about 0.42 wt. %, about 0.44 wt. %, or about 0.45 wt. %. The C provides the steel composition with strength and hardenability.
The composition comprises at least one of the Mn or Ni at a total combined concentration of greater than or equal to about 2 wt. % to less than or equal to about 8 wt. %, such as at a total combined concentration of about 2 wt. %, about 2.5 wt. %, about 3 wt. %, about 3.5 wt. %, about 4 wt. %, about 4.5 wt. %, about 5 wt. %, about 5.5 wt. %, about 6 wt. %, about 6.5 wt. %, about 7 wt. %, about 7.5 wt. %, or about 8 wt. %. Therefore, the Mn is present in the steel composition at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. % or greater than or equal to about 2 wt. % to less than or equal to about 8 wt. % and subranges thereof. In various aspects, the steel composition comprises Mn at a concentration of 0 wt. %, about 0.5 wt. %, about 1 wt. %, about 1.5 wt. %, about 2 wt. %, about 2.5 wt. %, about 3 wt. %, about 3.5 wt. %, about 4 wt. %, about 4.5 wt. %, about 5 wt. %, about 5.5 wt. %, about 6 wt. %, about 6.5 wt. %, about 7 wt. %, about 7.5 wt. %, or about 8 wt. %. Also, the Ni is present in the steel composition at a concentration of greater than or equal to 0 wt. % to less than or equal to about 8 wt. % or greater than or equal to about 2 wt. % to less than or equal to about 8 wt. % and subranges thereof. In various aspects, the steel composition comprises Ni at a concentration of 0 wt. %, about 0.5 wt. %, about 1 wt. %, about 1.5 wt. %, about 2 wt. %, about 2.5 wt. %, about 3 wt. %, about 3.5 wt. %, about 4 wt. %, about 4.5 wt. %, about 5 wt. %, about 5.5 wt. %, about 6 wt. %, about 6.5 wt. %, about 7 wt. %, about 7.5 wt. %, or about 8 wt. %. Accordingly, the steel composition comprises greater than or equal to about 0 wt. % to less than or equal to about 8 wt. % Mn and greater than or equal to about 0 wt. % to less than or equal to about 8 wt. % Ni, with the proviso that that the total combined concentration of the Mn and Ni is greater than or equal to about 2 wt. % to less than or equal to about 8 wt. %. The Mn and Ni provide an austenitization temperature (Ac3) that is lower than that of conventional stainless martensitic steels and hardenability. The Mn can additionally effectively reduce martensite start (Ms) temperature so as to promote the formation of beneficial retained austenite after hot forming.
The Cr is present in the steel composition at a concentration of greater than or equal to about 11 wt. % to less than or equal to about 17 wt. % and subranges thereof. In various aspects, the steel composition comprises Cr at a concentration of about 11 wt. %, about 11.5 wt. %, about 12 wt. %, about 12.5 wt. %, about 13 wt. %, about 13.5 wt. %, about 14 wt. %, about 14.5 wt. %, about 15 wt. %, about 15.5 wt. %, about 16 wt. %, about 16.5 wt. %, or about 17 wt. %. The Cr provides oxidation and corrosion resistance and hardenability.
The Si is present in the steel composition at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 3 wt. % and subranges thereof. In various aspects, the steel composition comprises Si at a concentration of about 1 wt. %, about 1.5 wt. %, about 2 wt. %, about 2.5 wt. %, or about 3 wt. %. The Si provides oxidation and corrosion resistance and hardenability.
In some aspects, the steel composition comprises the Cr and Si at a total combined concentration of greater than or equal to about 12 wt. % to less than or equal to about 20 wt. %, such as at a total combined concentration of about 12 wt. %, about 12.5 wt. %, about 13 wt. %, about 13.5 wt. %, about 14 wt. %, about 14.5 wt. %, about 15 wt. %, about 15.5 wt. %, about 16 wt. %, about 16.5 wt. %, about 17 wt. %, about 17.5 wt. %, about 18 wt. %, about 18.5 wt. %, about 19 wt. %, about 19.5 wt. %, or about 20 wt. %. The combined addition of the Cr and Si can significantly improve the oxidation and corrosion resistances both at high temperatures and room temperature.
The Fe makes up the balance of the steel composition.
In some aspects, the steel composition includes at least one of the Nb, V, or Ti at individual and independent concentrations of greater than or equal to 0 wt. % to less than or equal to about 0.5 wt. %, greater than or equal to about 0.01 wt. % to less than or equal to about 0.5 wt. %, or greater than or equal to about 0.1 wt. % to less than or equal to about 0.5 wt. % and subranges thereof. In various aspects, the steel composition comprises at least one of the Nb, V, or Ti at individual and independent concentrations of 0 wt. %, about 0.01 wt. %, about 0.02 wt. %, about 0.04 wt. %, about 0.06 wt. %, about 0.08 wt. %, about 0.1 wt. %, about 0.15 wt. %, about 0.2 wt. %, about 0.25 wt. %, about 0.3 wt. %, about 0.35 wt. %, about 0.4 wt. %, about 0.45 wt. %, or about 0.5 wt. %. In other aspects, the steel composition includes at least one of the Nb, V, or Ti at a total combined concentration of greater than or equal to 0 wt. % to less than or equal to about 0.5 wt. %, greater than or equal to about 0.01 wt. % to less than or equal to about 0.5 wt. %, or greater than or equal to about 0.1 wt. % to less than or equal to about 0.5 wt. % and subranges thereof. In various aspects, the steel composition comprises at least one of the Nb, V, or Ti at a total combined concentration of 0 wt. %, about 0.01 wt. %, about 0.02 wt. %, about 0.04 wt. %, about 0.06 wt. %, about 0.08 wt. %, about 0.1 wt. %, about 0.15 wt. %, about 0.2 wt. %, about 0.25 wt. %, about 0.3 wt. %, about 0.35 wt. %, about 0.4 wt. %, about 0.45 wt. %, or about 0.5 wt. %.
As discussed above, in some aspects, the steel composition can also include an additional element selected from the group consisting of Mo, W, Al, Cu, and combinations thereof. The additional element is present at individual and independent concentrations of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %, i.e., at less than or equal to about 5 wt. %, including at concentrations of 0 wt. %, about 0.5 wt. %, about 1 wt. %, about 1.5 wt. %, about 2 wt. %, about 2.5 wt. %, about 3 wt. %, about 3.5 wt. %, about 4 wt. %, about 4.5 wt. %, or about 5 wt. %. In other aspects, the steel composition includes the additional element at a total combined concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %, i.e., at less than or equal to about 5 wt. %, including at concentrations of 0 wt. %, about 0.5 wt. %, about 1 wt. %, about 1.5 wt. %, about 2 wt. %, about 2.5 wt. %, about 3 wt. %, about 3.5 wt. %, about 4 wt. %, about 4.5 wt. %, or about 5 wt. %.
The steel composition can also include unavoidable impurities. As used herein, “impurities” are elements having a concentration of less than or equal to about 0.1 wt. % that are not intentionally added to the steel composition.
The steel composition can include various combinations of C, Mn, Ni, Cr, Si, Nb, V, Ti, Mo, W, Al, Cu, and Fe (where the C, Mn and/or Ni, Cr, Si, and Fe are required components) at their respective concentrations described above. In some aspects, the steel composition consists essentially of C, Mn, Ni, Cr, Si, and Fe (and optionally at least one of Nb, V, or Ti and optionally an additional element) or C, Mn, Cr, Si, and Fe (and optionally at least one of Nb, V, or Ti and optionally an additional element), or C, Ni, Cr, Si, and Fe (and optionally at least one of Nb, V, or Ti and optionally an additional element). As described above, the term “consists essentially of” means the steel composition excludes additional compositions, materials, components, elements, and/or features that materially affect the basic and novel characteristics of the steel composition, such as the steel composition not requiring coatings or descaling when formed into a PHS component and exhibiting long-term corrosion resistance, but any compositions, materials, components, elements, and/or features that do not materially affect the basic and novel characteristics of the steel composition can be included, such as impurities as defined above. Therefore, as a non-limiting example, when the steel composition consists essentially of C, Mn, Ni, Cr, Si, Nb, V, Ti, Cu, and Fe, the steel composition can also include any other element, including those that are not discussed herein, at a concentration of less than or equal to about 0.1 wt. %, provided that they do not materially affect the basic and novel characteristics of the steel composition.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, V, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, V, Ti, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, V, Ti, Mo, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, V, Ti, Mo, W, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, V, Ti, Mo, W, Al, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Ni, Cr, Si, Nb, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, V, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, V, Ti, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, V, Ti, Mo, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, V, Ti, Mo, W, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, V, Ti, Mo, W, Al, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Nb, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, V, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, Ti, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, V, Mo, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, V, Ti, W, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, V, Ti, Mo, Al, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, V, Ti, Mo, W, Cu, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, V, Ti, Mo, W, Al, and Fe.
In one aspect, the steel composition comprises, consists essentially of, or consists of C, Ni, Cr, Si, Nb, V, Ti, Mo, W, Al, Cu, and Fe.
With reference to
The method 10 comprises obtaining a coil 12 of a steel composition according to the present technology and cutting a blank 14 from the coil 12. The blank 14 can alternatively be cut from a sheet of the steel composition that was not in the form of a coil. The steel composition is bare, i.e., uncoated. The method 10 also comprises hot pressing the blank 14. In this regard, the method 10 comprises austenitizing the blank 14 by heating the blank 14 in a furnace 16 to a temperature above its lower critical temperature (Ac1) or upper critical temperature (Ac3) to at least partially (i.e., partially or fully) austenitize the steel composition. At temperatures between Ac1 and Ac3, the steel composition is partially austenitized, comprising ferrite, austenite, and carbides. The steel composition may be fully or partially austenitized, e.g., comprising austenite and Cr-enriched carbides, at the temperature above Ac3. The blank 14 is heated to a temperature greater than or equal to about 850° C. to less than or equal to about 950° C., such as to about 850° C., about 860° C., about 870° C., about 880° C., about 890° C., about 900° C., about 910° C., about 920° C., about 930° C., about 940° C., or about 950° C. The heated blank 14 is transferred to a die or press 18, optionally by a robotic arm (not shown). The transferring is performed in air, whereby the temperature of the heated blank 14 decreases by greater than or equal to about 150° C. to less than or equal to about 250° C., such as by a temperature of about 150° C., about 175° C., about 200° C., about 225° C., or about 250° C. The method 10 then comprises stamping the blank 14 in the die or press 18 to form a structure having a predetermined shape and quenching the structure in air, in water, or in the die or press 18 to a temperature less than or equal to about a martensite finish (Mf) temperature of the steel composition and greater than or equal to about room temperature or ambient temperature to form the PHS component 20. The critical cooling rate, i.e., the minimum cooling rate, is about 2° C./s. Therefore, the quenching comprises decreasing the temperature of the structure at a rate of greater than or equal to about 2° C./s in air, in water, or in the die or press 18.
The method 10 is free of a descaling step. As such, the method 10 does not include, for example, steps of shot blasting or sand blasting. Inasmuch as the steel composition is bare, the PHS component 20 is free of and does not include, for example, a discontinuous oxide layer, a layer of Zn, or an Al—Si coating. As used herein, a “discontinuous oxide layer” is a non-uniform layer or plurality of oxide layer clusters or islands that should be removed from the surface of PHS components by, e.g., descaling or shot blasting.
In some aspects, the method 10 is also free of a heat treatment after the quenching. However, in other aspects, the method 10 comprises heat treating (i.e., a heat treatment) the PHS component 20. The heat treating comprises heating the PHS component to a temperature of greater than or equal to about 100° C. to less than or equal to about 300° C., such as to a temperature of about 100° C., about 125° C., about 150° C., about 175° C., about 200° C., about 225° C., about 250° C., about 275° C., or about 300° C. The heating is performed for a time period of greater than or equal to about 1 minute to less than or equal to about 100 minutes, such as for about 1 minute, about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 60 minutes, about 70 minutes, about 80 minutes, about 90 minutes, or about 100 minutes.
As discussed in more detail below, the PHS component 20 comprises PHS comprising an alloy matrix (having the components of the steel composition) and a uniform and continuous oxide layer comprising oxides of at least one of Cr, Si, or, when present, Cu, formed on the alloy matrix. By “continuous,” it is meant that the oxide layer covers all, or substantially all (i.e., greater than or equal to about 90%), of the exposed surfaces of the PHS component. By “uniform,” it is meant that the thickness of the oxide layer varies by less than or equal to about 20%.
In some aspects, the hot pressing, i.e., the heating, stamping, and quenching, is performed in an aerobic atmosphere. In other aspects, the hot pressing can be performed in an anaerobic atmosphere, such as by supplying an inert gas into at least one of the furnace 16 or the die or press 18. The inert gas can be any inert gas known in the art, such as nitrogen (N) or argon (Ar), as non-limiting examples. Moreover, the PHS component 20 can optionally be subjected to a heat treatment to further improve toughness and ductility, as discussed above.
The PHS component 20 comprises a PHS 80, as shown with reference to
The PHS 80 comprises a matrix 82, also referred to as an “alloy matrix,” comprising the steel components and an oxide layer 84 formed on at least one surface of the matrix, wherein the oxide layer 84 is continuous and uniform. It is understood that
The matrix 82 comprises the components at their corresponding concentrations of the steel composition described above and has a microstructure comprising a prior austenite grain size of less than or equal to about 20 μm.
The oxide layer 84 is formed on and disposed directly onto the matrix 82 as a continuous and uniform layer during the hot pressing process and comprises an oxide enriched with at least one of Cr, Si, or, when present, Cu, including Cr oxides, Si oxides, and/or Cu oxides.
The oxide layer 84 has a thickness TOL of greater than or equal to about 5 nm to less than or equal to about 10 μm, such as a thickness of about 5 nm, about 10 nm, about 50 nm, about 100 nm, about 150 nm, about 250 nm, about 300 nm, about 350 nm, about 400 nm, about 450 nm, about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1 μm, about 1.5 μm, about 2 μm, about 2.5 μm, about 3 μm, about 3.5 μm, about 4 μm, about 4.5 μm, about 5 μm, about 5.5 μm, about 6 μm, about 6.5 μm, about 7 μm, about 7.5 μm, about 8 μm, about 8.5 μm, about 9 μm, about 9.5 μm, or about 10 μm.
In certain variations, the oxide layer 84 is continuous, uniform, and homogenous. Therefore, the oxide layer 84 provides an exposed surface that is free of or substantially free of (i.e., comprising less than or equal to about 10% of the exposed surface) discontinuous oxide layers, and there is no need for it to be descaled by, for example, shot blasting or sand blasting. The PHS 80 does not include, or is free of, any layer that is not derived from the steel composition or the matrix 82, as discussed above. Moreover, the PHS 80 resists (i.e., prevent, inhibits, or minimizes) further surface oxidation and long-term corrosion and exhibits higher corrosion resistance at 930° C. than at 850° C. The matrix 82 exhibits a corrosion resistance that is improved relative to a comparative 22MnB5 steel subjected to 930° C. for 6 minutes and which improves as the matrix 82 is heated. For instance, at 850° C., the matrix 82 exhibits a corrosion current density of about 10−4 A/cm2, which is similar to bare 22MnB5 steel. However, at about 930° C., the matrix 82 exhibits a lower corrosion current density of about 10−5 A/cm2, which is an order of magnitude lower than at 850° C. and the bare 22MnB5 steel. Further, the matrix 82 exhibits a higher corrosion potential at 930° C. relative to the matrix 82 at 850° C. or the bare 22MnB5 steel, which exhibits the lowest corrosion potential.
The PHS component 20 comprising the PHS 80 can be any component that is generally made by hot stamping, such as a vehicle part. Non-limiting examples of vehicles having parts suitable to be produced by the current method include bicycles, automobiles, motorcycles, boats, tractors, buses, mobile homes, campers, gliders, airplanes, and tanks. In various aspects, the PHS component is an automobile part selected from the group consisting of a battery tray component, a bed liner, a wheel, a pillar, a bracket, a bumper, a roof rail, a rocker rail, a rocker, a control arm, a beam, a tunnel, a step, a subframe member, a pan, a panel, and a reinforcement panel.
Embodiments of the present technology are further illustrated through the following non-limiting example.
An exemplary steel composition including 0.18 wt. % C, 6.3 wt. % Mn, 15.9 wt. % Cr, 1.9 wt. % Si, 0.23 wt. % V, and 0.006 wt. % N is subjected to hot pressing as discussed herein to form PHS. A first sample of the PHS is heated to about 930° C. for about 6 minutes and a second sample of the PHS is heated to about 850° C. for about 10 minutes. As a comparative sample, 22MnB5 bare steel is heated to about 930° C. for about 6 minutes. The first and second samples are then subjected to a load in triplicate, during which stress and strain are measured.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110487225.4 | May 2021 | CN | national |
