CN113025877A

CN113025877A - High performance press hardened steel

Info

Publication number: CN113025877A
Application number: CN201911347138.8A
Authority: CN
Inventors: 卢琦; 王建锋
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2019-12-24
Filing date: 2019-12-24
Publication date: 2021-06-25
Also published as: DE102020131993A1; US20210189531A1

Abstract

The present invention relates to high performance press hardened steel. In particular, the present invention relates to a press hardened steel component after hot forming comprising an alloy composition comprising carbon in a concentration of greater than or about 0.01 wt.% to less than or about 0.2 wt.%, chromium in a concentration of greater than or about 0.5 wt.% to less than or about 6 wt.%, manganese in a concentration of greater than or about 0.5 wt.% to less than or about 4.5 wt.%, silicon in a concentration of greater than or about 0.5 wt.% to less than or about 0.5 wt.%, and the balance of the alloy composition being iron, wherein the press hardened steel component comprises greater than or about 90 vol.% martensite and bainite with an ultimate tensile strength of greater than or about 800mpa to less than or about 1200mpa and a VDA 238-100 bend angle of greater than or about 60 ° to less than or about 80 °.

Description

High performance press hardened steel

Technical Field

The present invention relates to high performance press hardened steel.

Background

This section provides background information related to the present disclosure, but is not necessarily prior art.

Press-hardened steel (PHS), also known as "hot stamped steel" or "hot formed steel", is one of the strongest steels for vehicle body structural applications. In some applications, PHS may have a tensile strength characteristic of about 1500 megapascals (MPa). Such steels have desirable properties, including forming steel components with significantly increased strength to weight ratios. PHS assemblies have become increasingly popular in various industries and applications including conventional manufacturing, construction equipment, automotive or other transportation industries, home or industrial structures, and the like. For example, when manufacturing vehicles, particularly automobiles, continued improvements in fuel efficiency and performance are desired; accordingly, PHS assemblies have been increasingly used. PHS assemblies are commonly used to form load bearing assemblies, such as door beams, which typically require high strength materials. Thus, the final state of these steels is designed to have high strength and sufficient ductility to resist external forces, such as intrusion into the passenger compartment without rupture, thereby providing protection for the occupants. In addition, the galvanized PHS assembly may provide cathodic protection.

Many PHS processes involve austenitizing a steel sheet blank in a furnace and then immediately pressing and quenching the sheet in a die. Austenitization is generally carried out in the range of about 880 ℃ to 950 ℃. The PHS processing may be indirect or direct. In the direct method, the PHS assembly is formed and pressed simultaneously between dies, which quenches the steel. In the indirect method, the PHS assembly is cold formed into an intermediate partial shape prior to austenitizing and 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 is often formed during the transfer from the oven to the mold. Therefore, after quenching, the oxides must be removed from the PHS assembly and the mold. The oxides are usually removed by shot blasting, i.e. descaling.

The PHS component may be made from bare or aluminum silicon (Al-Si) coated alloy using a direct method or may be made from zinc coated PHS using a direct or indirect method. Coating the PHS component to provide a protective layer for the underlying steel component (e.g.，Plating protection). The zinc coating provides cathodic protection; even where the steel is exposed, the coating acts as a sacrificial layer and is subject to corrosion in place of the steel component. Such coatings also produce oxides on the surface of the PHS assembly that are removed by shot blasting. Thus, alloy compositions that do not require coatings or other treatments are desired.

Disclosure of Invention

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 techniques provide a hot formed press hardened steel component comprising an alloy composition, the alloy composition includes 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 the balance of the alloy composition is iron (Fe), wherein the press hardened steel component comprises greater than or equal to 90 volume percent martensite and bainite and has an ultimate tensile strength of greater than or equal to about 800MPa to less than or equal to about 1200MPa and a VDA 238-100 bend 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 at 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 concentration of niobium (Nb) is 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 in a concentration of greater than or equal to about 1 wt% to less than or equal to about 3 wt%, and Si in 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 comprises a first surface layer comprising an oxide and having a thickness greater than or equal to about 0.01 μ ι η to less than or equal to about 10 μ ι η, the first surface layer being continuous.

In one aspect, the oxide of the first surface layer is rich in 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 quenching treatment.

In various aspects, the present technology provides a press hardened steel automotive component after hot forming, comprising an alloy matrix having an alloy composition comprising carbon (C) in a concentration of greater than or equal to about 0.01 wt% to less than or equal to about 0.2 wt%, chromium (Cr) in a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 6 wt%, manganese (Mn) in a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 4.5 wt%, silicon (Si) in a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 2.5 wt%, and the balance of the alloy composition being iron (Fe), wherein the alloy matrix comprises greater than or equal to 90 vol% bainite and martensite, 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 comprises chromium (Cr) and silicon (Si) rich oxides, wherein the press hardened steel component has an ultimate tensile strength of greater than or equal to about 800MPa to less than or equal to about 1200MPa and a VDA 238-100 bend 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 at 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 alloy matrix includes martensite and bainite in a concentration of greater than or equal to about 90 volume%, ferrite in a concentration of less than or equal to 5 volume%, and austenite in a concentration of less than or equal to 10 volume%.

In one aspect, the alloy composition further includes C in a concentration of greater than or equal to about 0.08 wt% to less than or equal to about 0.12 wt%, Mn in a concentration of greater than or equal to about 1 wt% to less than or equal to about 4.5 wt%, Cr in a concentration of greater than or equal to about 1 wt% to less than or equal to about 3 wt%, and Si in 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 1000 megapascals.

In various aspects, the present techniques also provide a method of forming a press hardened steel component; the method includes heating a blank of a steel alloy to a temperature above an upper critical temperature (Ac 3) of the alloy composition to form a austenite-containing heated blank, the upper critical temperature being greater than or equal to about 880 ℃ to less than or equal to about 950 ℃, wherein the steel alloy is not coated and comprises 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 is iron; stamping the heated blank into a predetermined shape to form a stamped assembly; and quenching the stamped assembly at a constant rate to a temperature of less than or equal to about the martensitic finish (Mf) temperature of the steel alloy and greater than or equal to about room temperature to form a press hardened steel assembly having a tensile strength of greater than or equal to about 800 megapascals to less than or equal to about 1200 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 assembly is free of any applied coatings.

In one aspect, quenching includes reducing the temperature of the stamped object at a rate of greater than or equal to about 20 ℃/s until the stamped object reaches a temperature below the martensitic transformation complete (Mf) temperature of the steel alloy for a time of greater than or equal to about 120 seconds to less than or equal to about 1000 seconds.

In one aspect, the press hardened steel component is free of any coating comprising zinc (Zn), aluminum (Al), silicon (Si), and combinations thereof.

In one aspect, the method does not require pre-oxidation of the steel alloy, coating and shot blasting of the formed steel object.

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 of a method of manufacturing a press hardened steel structure in accordance with aspects of the present technique.

FIG. 2 is a graph illustrating temperature versus time for a hot pressing method for processing a steel alloy in accordance with aspects of the present technique.

FIG. 3 is an illustration of a cross-section of a press hardened steel in accordance with aspects of the present technique.

Fig. 4 is an image of a steel made from an alloy composition according to 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 skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components/assemblies, 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, none of which 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, components, steps, integers, operations, and/or components/groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. While the open-ended term "comprising" should be understood as a non-limiting term used to describe and claim certain exemplary embodiments described herein, in certain aspects the term may instead be understood as a more limiting and limiting term such as "consisting of … …" or "consisting essentially of … …". Thus, for any given exemplary embodiment that recites a composition, material, component/assembly, element, feature, integer, operation, and/or processing step, the disclosure also specifically includes exemplary embodiments that consist of, or consist essentially of, such described composition, material, component/assembly, element, feature, integer, operation, and/or processing step. In the case of "consisting of … …, alternative embodiments exclude any additional compositions, materials, components/assemblies, elements, features, integers, operations, and/or processing steps, and in the case of" consisting essentially of … …, exclude from such embodiments any additional compositions, materials, components/assemblies, elements, features, integers, operations, and/or processing steps that substantially affect the basic and novel characteristics, but not substantially any compositions, materials, components/assemblies, elements, features, integers, operations, and/or processing steps that substantially affect the basic and novel characteristics may be included in the embodiments.

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 a certain order of performance. It is also to be understood that additional or alternative steps may be used, unless otherwise stated.

When a component, element, or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it can be directly on, engaged, connected, or coupled to the other element, or layer, or intervening elements or layers may be present. Conversely, when an element is referred to as being "directly on," "directly engaged with," "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 similar manner (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/assemblies, regions, layers and/or sections, these steps, elements, components/assemblies, regions, layers and/or sections should not be limited by these terms unless otherwise specified. 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.

For ease of description, spatially and temporally relative terms, such as "before", "after", "inside", "outside", "below", "lower", "upper", "lower", and the like, may be used herein to describe one element or feature's relationship to another element or feature or elements as illustrated in the figures. Spatially and 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, numerical values represent approximate measurements or range limits to include embodiments that deviate slightly from the given value and that generally have the listed values, as well as embodiments that have exactly the listed values. Other than in the operating examples provided at the end of the detailed description, all numbers in this specification (including the claims) including parameters such as amounts or conditions are to be understood as modified in all instances by the term "about", whether or not "about" actually appears before the number. By "about" is meant that the numerical value allows for some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). As used herein, "about" refers to at least variations that may result from ordinary methods of measuring and using such parameters, provided that the imprecision provided by "about" is not otherwise understood in the art with such ordinary meaning. For example, "about" may include 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, the disclosure of a range includes all values within the full range and further sub-ranges, including the endpoints and sub-ranges given for these ranges.

Example embodiments will now be described more fully with reference to the accompanying drawings.

As discussed above, there are certain disadvantages to descaling press hardened steel and coating press hardened steel. Thus, the current art provides steel alloys configured to be hot stamped to form a press hardened component having a predetermined shape without a coating and without the need for descaling. In various aspects, the steel alloy is subjected to a hot forming process, such as a press hardening process, to form a press hardened component. These press hardened components may have moderate strength levels, for example, an ultimate tensile strength of greater than or equal to about 800MPa to less than or equal to about 1200MPa, while also exhibiting high toughness levels. As will be described in more detail below, high toughness may be expressed by the bend angle of the component.

Press hardened steel components formed according to certain aspects of the present disclosure are particularly suitable for use in components of automobiles 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, as non-limiting examples, aerospace components, consumer goods, equipment, buildings (e.g., houses, offices, sheds, warehouses), office equipment and furniture, and industrial equipment machinery, agricultural or agricultural equipment or heavy machinery. Non-limiting examples of automotive components include hoods, pillars (e.g., a-pillars, hinge pillars, B-pillars, C-pillars, etc.), panels including structural panels, door panels, and door assemblies, interior floors, chassis, roofs, exterior surfaces, underbody shields, wheels, control arms and other suspensions, crash cans, bumpers, structural rails and frames, body rails, underframe or driveline components, and the like.

In certain aspects, the steel alloy may be in the form of a coil or sheet and comprise carbon (C), chromium (Cr), silicon (Si), and iron (Fe) prior to the press hardening process. The steel alloy may be free of any applied coating such that the steel alloy does not comprise any layers or coatings not derived from the alloy composition. In the hot stamping process, a portion of the steel alloy combines with atmospheric oxygen to form an oxide-containing surface layer. For example, Cr and Si may combine with atmospheric oxygen to form a surface layer comprising oxides rich in Cr and Si moieties. The thickness of the surface layer comprising an oxide can be, for example, greater than or equal to about 0.01 μm to less than or equal to about 10 μm, such as 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 5.6 μm, about 6 μm, about 8 μm, a thickness of about 9.5 μm, or about 10 μm.

Thus, the current technology relates to press hardened steel components formed from alloy compositions having high chromium content, which are suitable for hot stamping applications, which do not require coatings prior to hot stamping processing and do not require descaling, shot blasting or other oxidative removal and cleaning processes after hot stamping, and which are oxidation resistant, i.e., do not require pre-oxidation prior to press hardening. The alloy composition has a high chromium content to eliminate coating requirements and contains a high silicon (Si) content to improve oxidation resistance. The high silicon content also allows the chromium concentration to be reduced. In addition, the alloy composition has a tailored carbon concentration to provide the desired level of strength and toughness.

In various aspects of the current technology, the alloy composition is in the form of a blank for a hot stamping process. Here, the blank is formed into a press hardened steel after the hot stamping process. Components within the alloy composition (e.g., boron and chromium) may reduce the critical cooling rate in the hot stamping process relative to the critical cooling rate employed when such components are not used.

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, C is present from greater than or equal to about 0.01 wt% to less than or equal to about 0.15 wt%, optionally from greater than or equal to about 0.02 wt% to less than or equal to about 0.13 wt%, optionally from greater than or equal to about 0.05 wt% to less than or equal to about 0.12 wt%, and in certain variations, optionally from greater than or equal to about 0.07 wt% to less than or equal to about 0.10 wt%. In certain exemplary embodiments, the steel alloy includes 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.%. The weight percent (wt%) or mass percent is a value obtained by dividing the weight of the component by the weight of the entire alloy composition multiplied by 100. For example, 3 lbs. C in a 100 lbs. steel alloy sample is 3 weight percent.

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 4 wt.%. In certain exemplary embodiments, the steel alloy comprises 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 5.2 wt%, about 5.5 wt%, cr in a concentration of about 6 wt%.

Si is present in the steel alloy in 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 includes 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 includes 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 exemplary embodiments, the steel alloy comprises Mn in 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 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.%, a concentration of 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 can include impurities and contaminants in a cumulative amount of less than or equal to about 0.1 wt%, optionally less than or equal to about 0.05 wt%, and in certain variations, less than or equal to about 0.01 wt%, based on the total weight of the alloy composition.

Fe makes up the balance of the steel alloy.

In certain example embodiments, the steel alloy further includes 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 includes N in 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.%, e.g., 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 less. In some example embodiments, the steel alloy is substantially free of N. As used herein, "substantially free" refers to trace component levels, for example, levels less than or equal to about 0.0001 wt% or undetectable levels.

In certain example embodiments, the steel alloy further includes 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 includes Mo in 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 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 less. For example, in certain example embodiments, the steel alloy is substantially free of Mo, such as at a level of less than or equal to about 0.0001 wt.% Mo or at an undetectable level.

In certain example embodiments, the steel alloy further includes 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 includes B in 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 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 less. For example, in certain example embodiments, the steel alloy is substantially free of B, such as at a level of less than or equal to about 0.0001 wt.% B or an undetectable level.

In certain example embodiments, the steel alloy further includes 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 includes a concentration of Nb 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 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 less. For example, in certain example embodiments, the steel alloy is substantially free of Nb, such as at a level of less than or equal to about 0.0001 wt.% Nb or at an undetectable level.

In certain example embodiments, the steel alloy further includes 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 a concentration of V that is 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 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 less. For example, in certain example embodiments, the steel alloy is substantially free of V, such as at a level of less than or equal to about 0.0001 wt% V or at an undetectable level.

In certain example embodiments, the steel alloy further includes 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 exemplary embodiments, the steel alloy comprises Ni in 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%, for example, 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 2.8 wt%, about 2.6 wt%, about 2.4 wt%, about 2.2 wt%, a concentration of 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, such as at a level of less than or equal to about 0.0001 wt.% Ni or an undetectable level.

The steel alloy may contain certain combinations of C, Cr, Si, Mn, N, Ni, Mo, B, Nb, V, and Fe in the 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 "consisting essentially of … …" means that the steel alloy does not include other compositions, materials, components, elements, and/or features that substantially affect the basic and novel characteristics of the steel alloy, such as steel alloys that do not require coating or descaling when formed into a press hardened steel component, but may include any compositions, materials, components, elements, and/or features that do not substantially affect the basic and novel characteristics of the steel alloy in the example embodiments. Thus, when the steel alloy consists essentially of C, Cr, Si, Mn, and Fe, as provided above, the steel alloy may further comprise any combination of N, Ni, Mo, B, Nb, and V, so long as it does not substantially affect the basic and novel characteristics of the steel alloy. In other exemplary embodiments, the steel alloy consists of C, Cr, Si, Mn, and Fe in the respective concentrations described above and at least one of N, Ni, Mo, B, Nb, and V in the respective concentrations described above. Other elements not described herein may also be included in trace amounts, i.e., amounts 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 undetectable amounts, so long as they do not substantially affect the basic and novel properties 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 exemplary embodiments, the steel alloy consists essentially of C, Cr, Si, Mo, B, Nb, V, and Fe. In some exemplary 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 exemplary embodiments, the steel alloy consists of C, Cr, Si, Mo, B, Nb, V, Ni, and Fe.

Table 1 shows the compositions of exemplary embodiments of steel alloys

Table 1: composition of steel alloy according to example embodiments

The alloy composition may be in the form of a metal coil prior to processing. As described above, the alloy composition may be free of any applied coating. The applied coating may comprise a galvanic coating, such as a zinc-based coating, or an aluminum silicon oxidation resistant coating. In this form, the roll may be unrolled and cut into a predetermined shape or blank. The blank may be hot stamped using a conventional quenching process or by a quenching and separating process (partial method).

Referring to fig. 1, the present technology also provides a method 10 of manufacturing a press hardened steel component that may be used in an automobile. More particularly, the method comprises hot pressing the above-described steel alloy to form a press hardened steel component. The steel alloy being in bare form (e.g. in the form of，Without any coating, such as Al-Si or Zn (zinc) coating). Furthermore, the process does not have a descaling step, i.e. shot peening, sand blasting or any other method for producing a smooth and homogeneous surface. The press hardened steel component may be any component, such as a vehicle component, that is typically formed by hot stamping. Non-limiting examples of vehicles having components suitable for manufacture 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 automotive part selected from the group consisting of: a pillar, a bumper, a roof rail, a rocker, a control arm, a beam, a channel, a beam, a step, a subframe element, and a stiffener.

The method 10 includes obtaining a coil 12 of steel alloy according to the present technique, and cutting a blank 14 from the coil 12. Although not shown, the blank 14 may alternatively be cut from a sheet of steel alloy. The steel alloy is bare, i.e. uncoated. The method 10 also includes hot pressing the blank 14. In this regard, the method 10 includes austenitizing the blank 14 by heating the blank 14 in a furnace 16 to a temperature above its upper critical temperature (Ac 3) to fully austenitize the steel alloy. The heated blank 14 is optionally transferred to a mold or press 18 by a robotic arm (not shown). Here, the method 10 includes stamping the blank 14 in a 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 the martensitic finish (Mf) temperature of the steel alloy and greater than or equal to about room temperature to form a press hardened steel component. Quenching includes reducing the temperature of the structure at a constant rate of greater than or equal to about 20 ℃/s.

Method 10 has no descaling step. Thus, the method 10 does not include a step such as shot blasting or sand blasting. Since the steel alloy is bare, the press hardened steel component does not comprise, for example, a zinc (Zn) layer or an aluminum silicon (Al-Si) coating. Method 10 also does not have a secondary heat treatment after quenching. As discussed in more detail below, the press hardened steel component comprises a press hardened steel having an alloy matrix (with components of the steel alloy) and may further comprise a layer rich in oxides of Cr and Si derived from the alloy composition described above.

Fig. 2 shows a graph 50 that provides additional detail regarding hot pressing. Graph 50 has a y-axis 52 representing temperature and an x-axis 54 representing time. Line 56 on graph 50 represents the heating conditions during hot pressing. Here, the blank is heated to a final temperature 58, which is above the 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 ℃ to less than or equal to about 950 ℃, and in certain aspects, greater than or equal to about 900 ℃. The austenitized blank is then stamped or hot formed into a structure having a predetermined shape at a stamping temperature 62 between a final temperature 58 and Ac 360, and then at greater than or equal to about 20 ℃ s^-1Greater than or equal to about 25 ℃ s^-1Or greater than or equal to about 30 ℃ s^-1Cooling at a rate of, for example, about 20 ℃ s^-1About 22 ℃ s^-1About 24 ℃ s^-1About 26 ℃ s^-1About 28 ℃ s^-1About 30 ℃ s^-1Or faster until the temperature is reduced to 64 deg.f below the martensite finish (Mf) temperature, such that the resulting press hardened steel of the press hardened structure is consolidatedThe gold matrix has a microstructure in which martensite and bainite account for greater than or equal to about 90% by volume, and thus those containing oxides rich in Cr and Si can be formed.

In some example embodiments, the quenching is performed by cooling the formed object at the above-described rate until the stamped object reaches a temperature below the martensitic transformation complete (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 can comprise less than or equal to 10 wt% austenite, less than or equal to 5 wt% ferrite, or a combination thereof, as long as the microstructure comprises greater than or equal to about 90 wt% martensite and bainite, e.g., 95 wt% martensite and bainite.

FIG. 4 shows an alloy composition containing 3% Cr and 1.5% Si. In some example embodiments, this is an alloy composition in accordance with the present techniques that has not been pre-oxidized and heated to 900 ℃ for 4-10 minutes and then cooled. The alloy has good surface quality.

Without being bound by theory, the addition of high levels of Cr to the alloy composition, for example about 3% Cr by weight of the composition, lowers the austenitizing temperature. This can be seen in the equation below, which relates the composition according to an exemplary embodiment of the steel alloy and the Ac3 temperature of the alloy.

[ equation 1 ].

Ac3 (ºC)=910-203*%C^1/2-30%Mn+31.5*Mo-11*%Cr+44.7*%Si< 900℃。

The hardened steel made from the alloy composition has an Ultimate Tensile Strength (UTS) of greater than or equal to about 800MPa to less than or equal to about 1200MPa, greater than or equal to about 1000MPa to less than or equal to about 1200MPa, greater than or equal to about 900 MPa to less than or equal to about 1100 MPa, or about 1000 MPa.

Furthermore, the hardened steel made of the alloy composition has a pass through or bend angle α in the hardened condition_t(°) performanceThe flexibility is such that the bend angle is 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 °. The bend angle can be measured by a VDA bend angle procedure using the three-point bend device procedure described in the VDA 238-100, the relevant portions of the VDA 238-100 being incorporated herein by reference. The standard specifies test conditions, tools, geometry and experimental settings and bendability limit evaluations. The VDA 238-one 100 also provides for calculating the bend angle α_tThe method of (1).

Referring to fig. 3, the current art also provides a press hardened steel 80. The steel alloy is hot-pressed by the above method to obtain a press-hardened steel 80. Thus, the press hardened steel structure made by the above method is comprised of press hardened steel 80.

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 will be appreciated that fig. 3 shows a cross-sectional illustration of only 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 as or similar to the hardened steel described above.

The first layer 84 is disposed directly on the alloy substrate 82 in a hot pressing process and comprises oxides rich in Cr and Si (including Cr oxides and Si oxides). Cr and Si are part of the Cr and Si of the steel alloy. In this regard, the Cr and Si of the first layer 84 originate from the steel alloy or alloy matrix 82. That is, the first layer 84 is formed from a portion of the Cr and Si contained in the steel alloy or alloy matrix 82.

Thickness T of first layer 84_L1From greater than or equal to about 0.01 μm to less than or equal to about 10 μm, such as 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, largeA thickness of 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 homogeneous. Thus, in some exemplary embodiments, the first layer 84 provides an exposed surface and does not require descaling by, for example, shot blasting or sand blasting.

Also as discussed above, the press hardened steel 80 does not contain any layers that are not derived from the steel alloy or alloy matrix 82. However, it does not require descaling.

The foregoing description of the embodiments has been presented 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 explicitly shown or described. It 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.

Claims

1. A press hardened steel component after hot forming comprising:

an alloy composition, comprising:

carbon (C) in 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) in a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 2.5 wt%, and

the balance of the alloy composition is iron (Fe), wherein the press hardened steel component comprises greater than or equal to 90 volume percent martensite and bainite and has an ultimate tensile strength of greater than or equal to about 800MPa to less than or equal to about 1200MPa and a VDA 238 and 100 bend angle of greater than or equal to about 60 ° to less than or equal to about 80 °.

2. The press hardened steel component of claim 1, wherein the alloy composition further comprises:

molybdenum (Mo) in 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 at 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%.

3. The press hardened steel component of claim 2, wherein the concentration of niobium (Nb) is greater than or equal to about 0.02 wt% to less than or equal to about 0.04 wt%.

4. The press hardened steel component of claim 1, wherein the alloy composition comprises:

cr in a concentration of greater than or equal to about 1 wt% to less than or equal to about 3 wt%, and

si in a concentration of greater than or equal to about 1 wt% to less than or equal to about 2 wt%.

5. The press hardened steel component of claim 1, wherein the alloy composition comprises:

c in a concentration of greater than or equal to about 0.08 wt% to less than or equal to about 0.12 wt%,

mn in a concentration of greater than or equal to about 1 wt% to less than or equal to about 4.5 wt%,

6. The press hardened steel component of claim 1, further comprising a first surface layer comprising an oxide and having a thickness greater than or equal to about 0.01 μ ι η to less than or equal to about 10 μ ι η, the first surface layer being continuous.

7. A press hardened steel component according to claim 6, wherein the oxide of the first surface layer is enriched in Cr and Si.

8. The press hardened steel component of claim 1, wherein said press hardened steel component is free of any applied surface coating.

9. A press hardened steel component according to claim 8, wherein the alloy composition has been subjected to a quenching treatment.

10. A method of forming a press hardened steel component; the method comprises the following steps:

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 ℃ to less than or equal to about 950 ℃, wherein the steel alloy is not coated and comprises:

carbon (C) in a concentration of greater than or equal to about 0.1 wt% to less than or equal to about 0.2 wt%,

the balance of the alloy composition is iron;

stamping the heated blank into a predetermined shape to form a stamped assembly; and

quenching the stamped component at a constant rate to a temperature of less than or equal to about the martensitic finish (Mf) temperature of the steel alloy and greater than or equal to about room temperature to form a press hardened steel component having a tensile strength of greater than or equal to about 800 megapascals to less than or equal to about 1200 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.