Patent Publication Number: US-2021189531-A1

Title: High performance press-hardened steel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit and priority of Chinese Patent Application No. 201911347138.8 filed Dec. 24, 2019. The entire disclosure of the above application is incorporated herein by reference. 
     INTRODUCTION 
     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. In certain applications, PHS may have tensile strength properties of about 1,500 megapascal (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 in the range of about 880° C. to 950° C. PHS processes may be indirect or direct. 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. An oxide layer often forms during the transfer from the furnace to the dies. 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 aluminum-silicon (Al—Si) coated alloy using the direct method or from zinc-coated PHS using the direct method or indirect method. Coating the PHS component provides a protective layer (e.g., galvanic protection) to the underlying steel component. Zinc coatings offer cathodic protection; the coating acts as a sacrificial layer and corrodes instead of the steel component, even where the steel is exposed. Such coatings also generate oxides on the PHS components&#39; surfaces, which are removed by shot blasting. Accordingly, alloy compositions that do not require coatings or other treatments are desired. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In various aspects, the present technology provides a press-hardened steel component after hot forming including an alloy composition including carbon (C) at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.2 wt. %, chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 6 wt. %, manganese (Mn) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 4.5 wt. %, silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. %, and a balance of the alloy composition being iron (Fe), wherein the press-hardened steel component includes greater than or equal to 90 volume % martensite and bainite, and has an ultimate tensile strength of greater than or equal to about 800 megapascals to less than or equal to about 1,200 megapascals and a VDA 238-100 bending angle of greater than or equal to about 60° to less than or equal to about 80°. 
     In one aspect, the alloy composition further includes molybdenum (Mo) at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.8 wt. %, niobium (Nb) at a concentration of less than or equal to about 0.8 wt. %, vanadium (V) at a concentration of less than or equal to about 0.8 wt. %, or a combination thereof less than or equal to about 0.8 wt. %, boron (B) at a concentration of less than or equal to about 0.005 wt. %, nitrogen (N) at a concentration of less than or equal to about 0.008 wt. %, and nickel (Ni) at a concentration of less than or equal to about 5 wt. %. 
     In one aspect, the niobium (Nb) is at a concentration of greater than or equal to about 0.02 wt. % to less than or equal to about 0.04 wt. % 
     In one aspect, the alloy composition includes Cr at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, and Si at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 2 wt. %. 
     In one aspect, the alloy composition includes C at a concentration of greater than or equal to about 0.08 wt. % to less than or equal to about 0.12 wt. %, Mn at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 4.5 wt. %, Cr at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, and Si at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 2 wt. %. 
     In one aspect, the press-hardened steel component further includes a first surface layer including oxides and having a thickness of greater than or equal to about 0.01 μm to less than or equal to about 10 μm, the first surface layer being continuous. 
     In one aspect, the oxide of the first surface layer is enriched with Cr, and Si. 
     In one aspect, the press-hardened steel component is free of any applied surface coating. 
     In one aspect, the alloy composition has been subjected to a quench process. 
     In various aspects, the present technology provides a press press-hardened steel automotive component after hot forming including an alloy matrix having an alloy composition including carbon (C) at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.2 wt. %, chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 6 wt. %, manganese (Mn) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 4.5 wt. %, silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. %, and a balance of the alloy composition being iron (Fe), wherein the alloy matrix includes greater than or equal to 90 volume % martensite and bainite, a continuous surface layer disposed directly on the alloy matrix, the continuous surface layer having a thickness of greater than or equal to about 0.01 μm to less than or equal to about 10 μm, and including an oxide enriched with chromium (Cr) and silicon (Si), wherein the press-hardened steel component has an ultimate tensile strength of greater than or equal to about 800 megapascals to less than or equal to about 1,200 megapascals, a VDA 238-100 bending angle of greater than or equal to about 60° to less than or equal to about 80°. 
     In one aspect, the alloy composition further includes molybdenum (Mo) at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.8 wt. %, niobium (Nb) at a concentration of less than or equal to about 0.8 wt. %, vanadium (V) at a concentration of less than or equal to about 0.8 wt. %, or a combination thereof less than or equal to about 0.8 wt. %, boron (B) at a concentration of less than or equal to about 0.005 wt. %, nitrogen (N) at a concentration of less than or equal to about 0.008 wt. %, and nickel (Ni) at a concentration of less than or equal to about 5 wt. %. 
     In one aspect, the niobium (Nb) is at a concentration of greater than or equal to about 0.02 wt. % to less than or equal to about 0.04 wt. % 
     In one aspect, the alloy matrix includes martensite and bainite at a concentration greater than or equal to about 90 vol. %, ferrite at a concentration of less than or equal to 5 vol. %, and austenite at a concentration of less than or equal to 10 vol. %. 
     In one aspect, the alloy composition further includes the C at a concentration of greater than or equal to about 0.08 wt. % to less than or equal to about 0.12 wt. %, the Mn at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 4.5 wt. %, the Cr at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, and the Si at a concentration of greater than or equal to about 1 wt. % to less than or equal to about 2 wt. %. 
     In one aspect, the press-hardened steel automotive component is free of any applied surface coating. 
     In one aspect, the press-hardened steel has an ultimate tensile strength (UTS) of greater than or equal to about 1,000 megapascals. 
     In various aspects, the present technology also provides a method of forming a press-hardened steel component; the method including heating a blank of a steel alloy to a temperature above an upper critical temperature (Ac 3 ) of the alloy composition to form a heated blank comprising austenite, the upper critical temperature being greater than or equal to about 880° C. to less than or equal to about 950° C., wherein the steel alloy is uncoated and includes chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 6 wt. %, carbon (C) at a concentration of greater than or equal to about 0.1 wt. % to less than or equal to about 0.2 wt. %, manganese (Mn) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 4.5 wt. %, silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. %, and a balance of the alloy composition being iron; stamping the heated blank into a predetermined shape to form a stamped component; and quenching the stamped component at a constant rate to a temperature less than or equal to about a martensite finish (Mf) temperature of the steel alloy and greater than or equal to about room temperature to form the press-hardened steel component having a tensile strength of greater than or equal to about 800 megapascals to less than or equal to about 1,200 megapascals and a bend angle of greater than or equal to about 60° to less than or equal to about 80°, wherein the method is free of a descaling step, and the press-hardened steel component is free of any applied coating. 
     In one aspect, the quenching includes decreasing the temperature of the stamped object at a rate of greater than or equal to about 20° C/s until the stamped object reaches a temperature below a martensite finish (Mf) temperature of the steel alloy for greater than or equal to about 120 seconds to less than or equal to about 1,000 seconds. 
     In one aspect, the press-hardened steel component is free of any coating including zinc (Zn), aluminum (Al), silicon (Si), and combinations thereof. 
     In one aspect, the method is free from pre-oxidizing the steel alloy, coating the shaped steel object, and shot blasting. 
     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. 
    
    
     
       DRAWINGS 
       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. 
         FIG. 1  is a flow diagram illustrating a method of making a press-hardened steel structure according to various aspects of the current technology. 
         FIG. 2  is a graph showing temperature versus time for a hot pressing method used to process a steel alloy according to various aspects of the current technology. 
         FIG. 3  an illustration of a cross-section of a press-hardened steel according to various aspects of the current technology. 
         FIG. 4  is an image of a steel made from an alloy composition according to various aspects of the current technology. 
     
    
    
     DETAILED DESCRIPTION 
     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 certain example 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 example embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes example 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&#39;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 press-hardened steels and coating press-hardened steels. Accordingly, the current technology provides a steel alloy that is configured to be hot stamped into a press-hardened component having a predetermined shape without coatings and without a need to perform descaling. In various aspects, the steel alloys are subjected to a hot forming process, for example, a press hardening process to form a press-hardened component. These press-hardened components may have intermediate strength levels, for example, an ultimate tensile strength of greater than or equal to about 800 MPa to less than or equal to about 1,200 MPa, while also exhibiting high toughness levels. As will be described in greater detail below, high toughness can be expressed by bending angle of the component. 
     The press-hardened steel components formed in accordance with certain aspects of the present disclosure are particularly suitable for use in components of an automobile or other vehicles (e.g., motorcycles, boats, tractors, buses, motorcycles, mobile homes, campers, and tanks), but they may also be used in a variety of other industries and applications, including aerospace components, consumer goods, devices, buildings (e.g., houses, offices, sheds, warehouses), office equipment and furniture, and industrial equipment machinery, agricultural or farm equipment, or heavy machinery, by way of non-limiting example. Non-limiting examples of automotive components include hoods, pillars (e.g., A-pillars, hinge pillars, B-pillars, C-pillars, and the like), panels, including structural panels, door panels, and door components, interior floors, floor pans, roofs, exterior surfaces, underbody shields, wheels, control arms and other suspension, crush cans, bumpers, structural rails and frames, cross car beams, undercarriage or drive train components, and the like. 
     In certain aspects, prior to the press-hardening process, the steel alloy may be in the form of a coil or sheet and comprises carbon (C), chromium (Cr), silicon (Si), and iron (Fe). The steel alloy may be free of any applied coating such that the steel alloy does not comprise any layer or coating that is not derived from the alloy composition. During a hot stamping process, portions of the steel alloy combine with atmospheric oxygen to form a surface layer comprising an oxide. For example, the Cr and Si may combine with atmospheric oxygen to form a surface layer comprising an oxide enriched with the portions of the Cr and Si. The surface layer comprising an oxide may have a thickness, for example, greater than or equal to about 0.01 μm to less than or equal to about 10 μm, such as a thickness of about 0.01 μm, about 0.05 μm, about 0.1 μm, about 0.15 μm, about 0.25 μm, about 0.3 μm, about 0.35 μm, about 0.4 μm, about 0.45 μm, about 0.5 μm, about 0.55 μm, about 0.6 μm, about 0.65 μm, about 0.7 m, about 0.75 μm, about 0.8 μm, about 0.85 μm, about 0.9 μm, about 0.95 μm, 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. 
     Accordingly, the current technology relates to a press-hardened steel component formed of an alloy composition having a high chromium content that is suitable for hot stamping applications, that does not require coating prior to hot stamping processing or descaling, shot blasting or other oxidation removal and cleaning processes after hot stamping, and that is resistant to oxidation, i.e., does not require pre-oxidation prior to being press hardened. The alloy composition has a high chromium content to preclude a coating requirement, and includes a high silicon (Si) content for improving oxidation resistance. The high silicon content also permits the chromium concentration to be decreased. Furthermore, the alloy composition has tailored concentration of carbon to provide desired strength and toughness levels. 
     In various aspects of the current technology, the alloy composition is in a form of a blank for hot stamping processes. Here, the blank forms a press hardening steel after hot stamping processes. Components within the alloy composition, such as, for example, boron and chromium, may lower a critical cooling rate in hot stamping processes relative to critical cooling rates employed without such components. 
     The C is present in the steel alloy at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.2 wt. % and subranges thereof. In certain aspects, the C is present at greater than or equal to about 0.01 wt. % to less than or equal to about 0.15 wt. %, optionally greater than or equal to about 0.02 wt. % to less than or equal to about 0.13 wt. %, optionally greater than or equal to about 0.05 wt. % to less than or equal to about 0.12 wt. %, and in certain variations, optionally greater than or equal to about 0.07 wt. % to less than or equal to about 0.10 wt. %. In certain example embodiments, the steel alloy comprises C at a concentration of about 0.01 wt. %, about 0.02 wt. %, about 0.04 wt. %, about 0.06 wt. %, about 0.08 wt. %, about 0.09 wt. %, about 0.1 wt. %, about 0.11 wt. %, about 0.12 wt. %, about 0.14 wt. %, about 0.16 wt. %, about 0.18 wt. %, about 0.2 wt. Weight percent (wt. %) or mass percent, is the weight of a component divided by the weight of the overall alloy composition multiplied by 100. For example, 3 pounds of C in a 100-pound sample of steel alloy would have a weight percent of 3. 
     The Cr is present in the steel alloy at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 6 wt. %, greater than or equal to about 0.5 wt. % to less than or equal to about 5 wt. %, greater than or equal to about 0.5 wt. % to less than or equal to about 4 wt. %, or greater than or equal to about 0.5 wt. % to less than or equal to about 3 wt. %, or greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, or greater than or equal to about 1 wt. % to less than or equal to about 4 wt. %. In certain example embodiments, the steel alloy comprises Cr at a concentration of about 0.5 wt. %, about 0.6 wt. %, about 0.7 wt. %, about 0.8 wt. %, about 0.9 wt. %, about 1 wt. %, about 1.2 wt. %, about 1.4 wt. %, about 1.5 wt. %, about 1.6 wt. %, about 1.8 wt. %, about 2 wt. %, about 2.2 wt. %, about 2.4 wt. %, about 2.5 wt. %, about 2.6 wt. %, about 2.8 wt. %, about 3 wt. %, about 3.2 wt. %, about 3.4 wt. %, about 3.5 wt. %, about 3.6 wt. %, about 3.8 wt. %, about 4 wt. %, about 4.2 wt. %, about 4.4 wt. %, about 4.5 wt. %, about 4.6 wt. %, about 4.8 wt. %, about 5 wt. %, about 5.2 wt. %, about 5.4 wt. %, about 5.5 wt. %, about 5.6 wt. %, about 5.8 wt. %, about 6 wt. %. 
     The Si is present in the steel alloy at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. % or greater than or equal to about 1 wt. % to less than or equal to about 2 wt. %. In certain example embodiments, the steel alloy comprises Si at a concentration of about 0.5 wt. %, about 0.6 wt. %, about 0.7 wt. %, about 0.8 wt. %, about 0.9 wt. %, about 1 wt. %, about 1.1 wt. %, about 1.2 wt. %, about 1.3 wt. %, about 1.4 wt. %, about 1.5 wt. %, about 1.6 wt. %, about 1.7 wt. %, about 1.8 wt. %, about 1.9 wt. %, or about 2 wt. %, about 2.1 wt. %, about 2.2 wt. %, about 2.3 wt. %, about 2.4 wt. %, about 2.5 wt. %. 
     In certain example embodiments, the steel alloy further comprises manganese (Mn) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 4.5 wt. %, greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, greater than or equal to about 1.5 wt. % to less than or equal to about 2.5 wt. %. In certain example embodiments, the steel alloy comprises Mn at a concentration of less than or equal to about 4.5 wt. %, less than or equal to about 4 wt. %, less than or equal to about 3.5 wt. %, less than or equal to about 3 wt. %, less than or equal to about 2.5 wt. %, or less than or equal to about 2 wt. %, less than or equal to about 1.5 wt. %, less than or equal to about 1 wt. %, less than or equal to about 0.5 wt. %, such as at a concentration of about 4.5 wt. %, about 4.4 wt. %, about 4.2 wt. %, about 4 wt. %, about 3.8 wt. %, about 3.6 wt. %, about 3.4 wt. %, about 3.2 wt. %, about 3 wt. %, about 2.8 wt. %, about 2.6 wt. %, about 2.4 wt. %, about 2.2 wt. %, about 2 wt. %, about 1.8 wt. %, about 1.6 wt. %, about 1.4 wt. %, about 1.2 wt. %, about 1 wt. %, about 0.8 wt. %, about 0.6 wt. %, or about 0.5 wt. %. 
     As described further below, other alloying components may be present in the steel alloy composition. Further, the alloy may comprise a cumulative amount of impurities and contaminants at less than or equal to about 0.1 wt. % of the total alloy composition, optionally less than or equal to about 0.05 wt. %, and in certain variations, less than or equal to about 0.01 wt. %. 
     The Fe makes up the balance of the steel alloy. 
     In certain example embodiments, the steel alloy further comprises nitrogen (N) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.008 wt. % or greater than or equal to about 0.0001 wt. % to less than or equal to about 0.008 wt. %. For example, in certain example embodiments, the steel alloy is comprises N at a concentration of less than or equal to about 0.008 wt. %, less than or equal to 0.007 wt. %, less than or equal to 0.006 wt. %, less than or equal to 0.005 wt. %, less than or equal to 0.004 wt. %, less than or equal to 0.003 wt. %, less than or equal to 0.002 wt. %, or less than or equal to 0.001 wt. %, such as at a concentration of about 0.01 wt. %, about 0.009 wt. %, about 0.008 wt. %, about 0.007 wt. %, about 0.006 wt. %, about 0.005 wt. %, about 0.004 wt. %, about 0.003 wt. %, about 0.002 wt. %, about 0.001 wt. %, or lower. In some example embodiments, the steel alloy is substantially free of N. As used herein, “substantially free” refers to trace component levels, such as levels of less than or equal to about 0.0001 wt. % or levels that are not detectable. 
     In certain example embodiments, the steel alloy further comprises molybdenum (Mo) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.8 wt. %, greater than or equal to about 0.01 wt. % to less than or equal to about 0.8 wt. %, or less than or equal to about 0.8 wt. %. For example, in certain example embodiments, the steel alloy comprises Mo at a concentration of less than or equal to about 0.8 wt. %, less than or equal to about 0.7 wt. %, less than or equal to about 0.6 wt. %, less than or equal to about 0.5 wt. %, less than or equal to about 0.4 wt. %, less than or equal to about 0.3 wt. %, less than or equal to about 0.2 wt. %, or less than or equal to about 0.1 wt. %, such as at a concentration of about 0.8 wt. %, about 0.7 wt. %, about 0.6 wt. %, about 0.5 wt. %, about 0.4 wt. %, about 0.3 wt. %, about 0.2 wt. %, about 0.1 wt. %, or lower. For example, in certain example embodiments, the steel alloy is substantially free of Mo, for example, levels of less than or equal to about 0.0001 wt. % Mo or levels that are not detectable. 
     In certain example embodiments, the steel alloy further comprises boron (B) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.005 wt. %, greater than or equal to about 0.0001 wt. % to less than or equal to about 0.005 wt. %, or less than or equal to about 0.005 wt. %. For example, in certain example embodiments, the steel alloy comprises B at a concentration of less than or equal to about 0.005 wt. %, less than or equal to about 0.004 wt. %, less than or equal to about 0.003 wt. %, less than or equal to about 0.002 wt. %, or less than or equal to about 0.001 wt. %, such as at a concentration of about 0.005 wt. %, about 0.004 wt. %, about 0.003 wt. %, about 0.002 wt. %, about 0.001 wt. %, about 0.0005 wt. %, about 0.0001 wt. %, or lower. For example, in certain example embodiments, the steel alloy is substantially free of B, for example, levels of less than or equal to about 0.0001 wt. % B or levels that are not detectable. 
     In certain example embodiments, the steel alloy further comprises niobium (Nb) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.8 wt. %, greater than or equal to about 0.01 wt. % to less than or equal to about 0.8 wt. %, or less than or equal to about 0.8 wt. %. For example, in certain example embodiments, the steel alloy is substantially free of Nb or comprises Nb, at a concentration of less than or equal to about 0.8 wt. %, less than or equal to about 0.7 wt. %, less than or equal to about 0.6 wt. %, less than or equal to about 0.5 wt. %, less than or equal to about 0.4 wt. %, less than or equal to about 0.3 wt. %, less than or equal to about 0.2 wt. %, or less than or equal to about 0.1 wt. %, such as at a concentration of about 0.8 wt. %, about 0.7 wt. %, about 0.6 wt. %, about 0.5 wt. %, about 0.4 wt. %, about 0.3 wt. %, about 0.2 wt. %, about 0.1 wt. %, or lower. For example, in certain example embodiments, the steel alloy is substantially free of Nb, for example, levels of less than or equal to about 0.0001 wt. % Nb or levels that are not detectable. 
     In certain example embodiments, the steel alloy further comprises vanadium (V) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.8 wt. %, greater than or equal to about 0.01 wt. % to less than or equal to about 0.8 wt. %, or less than or equal to about 0.8 wt. %. For example, in certain example embodiments, the steel alloy is substantially free of V or comprises V at a concentration of less than or equal to about 0.8 wt. %, less than or equal to about 0.7 wt. %, less than or equal to about 0.6 wt. %, less than or equal to about 0.5 wt. %, less than or equal to about 0.4 wt. %, less than or equal to about 0.3 wt. %, less than or equal to about 0.2 wt. %, or less than or equal to about 0.1 wt. %, such as at a concentration of about 0.8 wt. %, about 0.7 wt. %, about 0.6 wt. %, about 0.5 wt. %, about 0.4 wt. %, about 0.3 wt. %, about 0.2 wt. %, about 0.1 wt. %, or lower. For example, in certain example embodiments, the steel alloy is substantially free of V, for example, levels of less than or equal to about 0.0001 wt. % V or levels that are not detectable. 
     In certain example embodiments, the steel alloy further comprises nickel (Ni) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %, greater than or equal to about 1 wt. % to less than or equal to about 3 wt. %, greater than or equal to about 1.5 wt. % to less than or equal to about 2.5 wt. %. In certain example embodiments, the steel alloy comprises Ni at a concentration of less than or equal to about 5 wt. %, less than or equal to about 4.5 wt. %, less than or equal to about 4 wt. %, less than or equal to about 3.5 wt. %, less than or equal to about 3 wt. %, less than or equal to about 2.5 wt. %, or less than or equal to about 2 wt. %, less than or equal to about 1.5 wt. %, less than or equal to about 1 wt. %, less than or equal to about 0.5 wt. %, such as at a concentration of about 5 wt. %, about 4.8 wt. %, about 4.6 wt. %, about 4.4 wt. %, about 4.2 wt. %, about 4 wt. %, about 3.8 wt. %, about 3.6 wt. %, about 3.4 wt. %, about 3.2 wt. %, about 3 wt. %, about 2.8 wt. %, about 2.6 wt. %, about 2.4 wt. %, about 2.2 wt. %, about 2 wt. %, about 1.8 wt. %, about 1.6 wt. %, about 1.4 wt. %, about 1.2 wt. %, about 1 wt. %, about 0.8 wt. %, about 0.6 wt. %, or about 0.5 wt. %. For example, in certain example embodiments, the steel alloy is substantially free of Ni, for example, levels of less than or equal to about 0.0001 wt. % Ni or levels that are not detectable. 
     The steel alloy can include certain combinations of C, Cr, Si, Mn, N, Ni, Mo, B, Nb, V, and Fe at their respective concentrations described above. In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, and Fe. As described above, the term “consists essentially of” means the steel alloy excludes additional compositions, materials, components, elements, and/or features that materially affect the basic and novel characteristics of the steel alloy, such as the steel alloy not requiring coatings or descaling when formed into a press-hardened steel component, but any compositions, materials, components, elements, and/or features that do not materially affect the basic and novel characteristics of the steel alloy can be included in the example embodiment. Therefore, when the steel alloy consists essentially of C, Cr, Si, Mn, and Fe, the steel alloy can also include any combination of N, Ni, Mo, B, Nb, and V, as provided above, that does not materially affect the basic and novel characteristics of the steel alloy. In other example embodiments, the steel alloy consists of C, Cr, Si, Mn, and Fe at their respective concentrations described above and at least one of N, Ni, Mo, B, Nb, and V at their respective concentrations described above. Other elements that are not described herein can also be included in trace amounts, i.e., amounts of less than or equal to about 1.5 wt. %, less than or equal to about 1 wt. %, less than or equal to about 0.5 wt. %, or amounts that are not detectable, provided that they do not materially affect the basic and novel characteristics of the steel alloy. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Ni, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Mo, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Mo, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Mo, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Mo, Ni, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Mo, Nb, V, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Mo, Nb, V, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Nb, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Nb, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Mo, Nb, V, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Mo, Nb, V, Ni, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Mo, Nb, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Mo, Nb, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, Mo, Nb, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, Mo, Nb, Ni, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, N, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, N, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, N, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, N, Ni, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, N, Mo, B, Nb, V, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, N, Mo, B, Nb, V, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mn, N, Mo, B, Nb, V, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mn, N, Mo, B, Nb, V, Ni, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Ni, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mo, B, Nb, V, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mo, B, Nb, V, and Fe. 
     In some example embodiments, the steel alloy consists essentially of C, Cr, Si, Mo, B, Nb, V, Ni, and Fe. In some example embodiments, the steel alloy consists of C, Cr, Si, Mo, B, Nb, V, Ni, and Fe. 
     Table 1 shows a composition of an example embodiment of the steel alloy. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Composition of steel alloy according to example embodiments. 
               
            
           
           
               
               
            
               
                   
                 Chemical Composition (wt. %) 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Composition 
                 C 
                 Mn 
                 Cr 
                 Si 
                 Others 
                 Fe 
               
               
                   
               
               
                 Range 
                 0.01-0.2 
                 0.5-4.5 
                 0.5-6 
                 0.5-2.5 
                 N &lt; 0.008,  
                 Balance 
               
               
                   
                   
                   
                   
                   
                 Ni &lt; 5,  
                   
               
               
                   
                   
                   
                   
                   
                 Mo &lt; 0.8, 
                   
               
               
                   
                   
                   
                   
                   
                 B &lt; 0.005, 
                   
               
               
                   
                   
                   
                   
                   
                 Nb/V &lt; 0.8 
               
               
                   
               
            
           
         
       
     
     Prior to processing, the alloy composition may be in the form of a coil of the metal. As noted above, the alloy composition may be free of any applied coating. The applied coatings may include galvanic coatings, such as zinc-based coatings, or aluminum-silicon anti-oxidation coatings. In this form, the coil can be uncoiled and cut into predetermined shapes or blanks. The blanks can be hot stamped using a traditional quenching method or by a quench and partitioning method. 
     With reference to  FIG. 1 , the current technology also provides a method  10  of fabricating a press-hardened steel component, which may be used in an automobile. More particularly, the method includes hot pressing the steel alloy described above to form the press-hardened steel component. The steel alloy is processed in a bare form, i.e., without any coatings, such as Al—Si or Zn (galvanized) coatings. Moreover, the method is free from a descaling step, i.e., free from shot blasting, sand blasting, or any other method for preparing a smooth and homogenous surface. The press-hardened steel component can be any component that is generally made by hot stamping, such as, a vehicle part, for example. Non-limiting examples of vehicles that have parts suitable to be produced by the current method include bicycles, automobiles, motorcycles, boats, tractors, buses, mobile homes, campers, gliders, airplanes, and tanks. In certain example embodiments, the press-hardened steel component is an automobile part selected from the group consisting of a pillar, a bumper, a roof rail, a rocker rail, a rocker, a control arm, a beam, a tunnel, a beam, a step, a subframe member, and a reinforcement panel. 
     The method  10  comprises obtaining a coil  12  of a steel alloy according to the present technology and cutting a blank  14  from the coil  12 . Although not shown, the blank  14  can alternatively be cut from a sheet of the steel alloy. The steel alloy 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 upper critical temperature (Ac 3 ) temperature to fully austenitize the steel alloy. The heated blank  14  is transferred to a die or press  18 , optionally by a robotic arm (not shown). Here, the method  10  comprises stamping the blank  14  in the die or press  18  to form a structure having a predetermined shape and quenching the structure at a constant rate to a temperature less than or equal to about a martensite finish (Mf) temperature of the steel alloy and greater than or equal to about room temperature to form the press-hardened steel component. The quenching comprises decreasing the temperature of the structure at a constant rate of greater than or equal to about 20° C/s. 
     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 alloy is bare, the press-hardened steel component does not include, for example, a layer of zinc (Zn) or an aluminum-silicon (Al—Si) coating. The method  10  is also free of a secondary heat treatment after the quenching. As discussed in more detail below, the press-hardened steel component comprises press-hardened steel comprising an alloy matrix (having the components of the steel alloy), and may further comprise a layer comprising an oxide enriched with Cr and Si derived from the alloy composition as described above. 
       FIG. 2  shows a graph  50  that provides additional details about the hot pressing. The graph  50  has a y-axis  52  representing temperature and an x-axis  54  representing time. A line  56  on the graph  50  represents heating conditions during the hot pressing. Here, the blank is heated to a final temperature  58  that is above an upper critical temperature (Ac 3 )  60  of the steel alloy to fully austenitize the steel alloy. The final temperature  58  is greater than or equal to about 880° C. to less than or equal to about 950° C., in certain aspects, greater than or equal to about 900° C. The austenitized blank is then stamped or hot-formed into the structure having the predetermined shape at a stamping temperature  62  between the final temperature  58  and Ac 3   60  and then cooled at a rate of greater than or equal to about 20° Cs −1 , greater than or equal to about 25° Cs −1 , or greater than or equal to about 30° Cs −1 , such as at a rate of about 20° Cs −1 , about 22° Cs −1 , about 24° Cs −1 , about 26° Cs −1 , about 28° Cs −1 , about 30° C −1 , or faster, until the temperature decreases below a martensite finish (Mf) temperature  64 , such that the press-hardened steel alloy matrix of the resulting press-hardened structure has a microstructure that is greater than or equal to about 90% martensite and bainite by volume (vol. %) and such that the comprising an oxide enriched with Cr and Si may be formed. 
     In some example embodiments, the quenching is performed by cooling the shaped object at a rate described above until the stamped object reaches a temperature below a martensite finished (Mf) temperature of the alloy composition. The resulting microstructure of the press-hardened steel alloy matrix may be greater than or equal to about 90 wt. % martensite and bainite. The remaining microstructure may be comprised of austenite, ferrite, or a combination thereof. The microstructure may comprise less than or equal to 10 wt. % of austenite, less than or equal to 5 wt. % ferrite, or a combination thereof, provided the microstructure comprises greater than or equal to about 90 wt. % martensite and bainite, for example 95% wt. % martensite and bainite. 
       FIG. 4  shows an alloy composition comprising 3% Cr and 1.5% Si. In some example embodiments, this is an alloy composition according to the present technology that is not pre-oxidized and heated to 900° C. for 4-10 minutes and then cooled. The surface quality is good for the alloy. 
     Without being bound by theory, adding high levels of Cr to the alloy composition, such as, for example, about 3% Cr by weight of the composition decreases the austenitization temperature. This may be seen in the following equation relating the composition according to example embodiments of a steel alloy and the Ac 3  temperature of the alloy. 
       [Equation 1] 
         Ac 3 (° C.)=910−203*% C 1/2 −30% Mn+31.5*Mo−11% Cr+44.7*% Si&lt;900° C.
 
     Hardened steel made from the alloy composition has an ultimate tensile strength (UTS) of greater than or equal to about 800 MPa to less than or equal to about 1,200 MPa, greater than or equal to about 1,000 MPa to less than or equal to about 1,200 MPa, greater than or equal to about, 900 MPa to less than or equal to about 1,100 MPa, or about 1,000 MPa. 
     Also, the hardened steel made from the alloy composition has a toughness reflected by a bending angle, or bend angle, α t)  (°)) of greater than or equal to about 60° to less than or equal to 80°, such as about 60°, about 62°, about 64°, about 66°, about 68°, about 70°, about 72°, about 74°, about 76°, about 78°, or about 80°, in the hardened condition. The bending angle may be measured by a VDA bending angle procedure using the three point bending device procedure described in the VDA 238-100, the relevant portions of which are incorporated herein by reference. The standard specifies the test conditions, tooling, geometry and experimental settings as well as bendability limit assessment. The VDA 238-100 also specifies a method for calculating the bending angle α t . 
     With reference to  FIG. 3 , the current technology yet further provides a press-hardened steel  80 . The press-hardened steel  80  results from hot pressing the steel alloy described above by the method described above. As such, the press-hardened steel structure made by the above method is composed of the press-hardened steel  80 . 
     The press-hardened steel  80  comprises an alloy matrix  82  and at least one surface layer. In certain aspects, the at least one surface layer may comprise a first layer  84 . It is understood that  FIG. 3  only shows a cross section illustration of a portion of the press-hardened steel  80  and that the first layer  84  may surround the alloy matrix  82 . The alloy matrix  82  may be the same or similar to the hardened steel described above. 
     The first layer  84  is disposed directly on the alloy matrix  82  during the hot pressing process and comprises an oxide enriched with Cr and Si, including Cr oxides and Si oxides. The Cr and Si are portions of the Cr and Si of the steel alloy. In this regard, the Cr and Si of the first layer  84  are derived from the steel alloy or the alloy matrix  82 . Put another way, the first layer  84  is formed from portions of the Cr and the Si included in the steel alloy or the alloy matrix  82 . 
     The first layer  84  has a thickness T L1  of greater than or equal to about 0.01 μm to less than or equal to about 10 μ, such as a thickness of about 0.01 μm, about 0.05 μm, about 0.1 μm, about 0.15 μm, about 0.25 μm, about 0.3 μm, about 0.35 μm, about 0.4 μm, about 0.45 μm, about 0.5 μm, about 0.55 μm, about 0.6 μm, about 0.65 μm, about 0.7 μm, about 0.75 μm, about 0.8 μm, about 0.85 μm, about 0.9 μm, about 0.95 μm, 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. 
     The first layer  84  is continuous and homogenous. Therefore, in some example embodiments, the first layer  84  provides an exposed surface, and there is no need for it to be descaled by, for example, shot blasting or sand blasting. 
     Also as discussed above, the press-hardened steel  80  does not include any layer that is not derived from the steel alloy or the alloy matrix  82 . Nonetheless, it does not require descaling. 
     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.