CN113215481A

CN113215481A - Press hardening steel with high oxidation resistance

Info

Publication number: CN113215481A
Application number: CN202010070823.7A
Authority: CN
Inventors: 卢琦; 王建锋; S.M.安德森; C.D.霍尔瓦思; J.J.科里尔
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2020-01-21
Filing date: 2020-01-21
Publication date: 2021-08-06
Anticipated expiration: 2040-01-21
Also published as: US20210222265A1; CN113215481B; DE102020134324A1

Abstract

The present invention relates to a press hardened steel having high oxidation resistance. A steel composition is provided. The steel composition comprises 0.1-0.45 wt.% carbon (C), more than 0-4.5 wt.% manganese (Mn), 0.5-5 wt.% chromium (Cr), 0.5-2.5 wt.% silicon (Si), more than 0-2 wt.% copper (Cu), and the remainder iron (Fe). The combined concentration of Mn, Cr and Cu is greater than about 2 wt%. The steel composition is configured to form a surface oxide layer comprising oxides of Cr, Si and Cu after being subjected to press hardening. Also provided are press hardened steels made from the steel compositions and methods of making press hardened steel parts from the steel compositions.

Description

Press hardening steel with high oxidation resistance

Technical Field

The present application relates to press hardened steel having high oxidation resistance.

Background

This section provides background information related to the present disclosure that 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 automotive body structure applications, having tensile strength properties of about 1500 megapascals (MPa). Such steels have desirable properties, including forming steel components with significantly increased strength to weight ratios. PHS components have become increasingly prevalent in various industries and applications including general manufacturing, construction equipment, automotive or other transportation industries, household or industrial structures, and the like. For example, when manufacturing vehicles, particularly automobiles, continued improvements in fuel efficiency and performance are desired; accordingly, PHS components have been increasingly used. PHS components are commonly used to form load bearing components, such as door beams, which generally require high strength materials. As a result, these steels are designed in their finished state to have high strength and sufficient ductility to resist external forces, such as intrusion into the passenger compartment, without cracking, thereby providing protection for the occupants. In addition, the galvanized PHS component may provide cathodic protection.

Many PHS processes involve austenitizing a sheet steel blank in a furnace and then immediately pressing and quenching the sheet in a die. Austenitization is typically carried out in the range of about 880 ℃ to 950 ℃. The PHS process may be indirect or direct. In the direct method, the PHS component is simultaneously formed and pressed between dies, which quenches the steel. In the indirect method, the PHS component is cold formed into an intermediate partial shape prior to austenitizing and subsequent pressing and quenching steps. Quenching of PHS components hardens the component by transforming the microstructure from austenite to martensite. When a part is made from uncoated steel, a discontinuous oxide layer is typically formed on the surface of the part during furnace heating and transfer from the furnace to the mold. Therefore, after quenching, the oxides must be removed from the PHS component and the mold. The oxides are usually removed by shot blasting, i.e. descaling (scaled).

The PHS component may be made of bare or coated alloy. Coating the PHS component with, for example, zinc or Al-Si provides a protective layer for the underlying steel component. Zinc coatings, for example, provide cathodic protection; the coating acts as a sacrificial layer and corrodes in place of the steel component, even where steel exposure occurs. However, zinc coated PHS produces oxides on the PHS component surface that must be removed by shot blasting. Accordingly, it is desirable to have alloy compositions that do not require coatings or other treatments.

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.

The present disclosure relates to press hardened steel having high oxidation resistance.

In various aspects, the present techniques provide a steel composition comprising carbon (C) in a concentration of greater than or equal to about 0.1 wt.% to less than or equal to about 0.45 wt.%; manganese (Mn) at a concentration of greater than 0 wt% to less than or equal to about 4.5 wt%; chromium (Cr) at a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 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%; copper (Cu) at a concentration of greater than 0 wt% to less than or equal to about 2 wt%; and a remainder of iron (Fe), wherein the combined concentration of Mn, Cr, and Cu is greater than or equal to about 2 wt%, and wherein the steel composition is configured to form a surface oxide layer comprising oxides of Cr, Si, and Cu after being subjected to press hardening.

In one aspect, the steel composition further comprises nickel (Ni) at a concentration of greater than 0 wt.% to less than or equal to about 5 wt.%, wherein the combined concentration of Mn, Cr, Cu, and Ni is greater than or equal to about 2 wt.%, and wherein the steel composition is configured to form a surface oxide layer comprising oxides of Cr, Si, Cu, and Ni after being subjected to press hardening.

In one aspect, wherein the steel composition is free of a coating.

In one aspect, the steel composition further comprises an additional element selected from the group consisting of: molybdenum (Mo) at a concentration of greater than 0 wt.% to less than or equal to about 1 wt.%; vanadium (V) at a concentration of greater than 0 wt% to less than or equal to about 1 wt%; niobium (Nb) at a concentration of greater than 0 wt.% to less than or equal to about 0.5 wt.%; boron (B) at a concentration of greater than 0 wt.% to less than or equal to about 0.01 wt.%; titanium (Ti) at a concentration of greater than 0 wt% to less than or equal to about 0.1 wt%; aluminum (Al) at a concentration of greater than 0 wt% to less than or equal to about 0.5 wt%; and combinations thereof.

In one aspect, the steel composition is in the form of a wound sheet.

In various other aspects, the present techniques provide a press hardened steel including an alloy matrix (matrix) including carbon (C) at a concentration of greater than or equal to about 0.1 wt.% to less than or equal to about 0.45 wt.%; manganese (Mn) at a concentration of greater than 0 wt% to less than or equal to about 4.5 wt%; chromium (Cr) at a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 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%; copper (Cu) at a concentration of greater than 0 wt% to less than or equal to about 2 wt%; and the remainder iron (Fe); and an oxide layer formed on a surface of the alloy matrix during hot forming of the press hardened steel, the oxide layer comprising oxides of the Cr, Si, and Cu, wherein the oxide layer protects the alloy matrix from oxidation.

In one aspect, the combined concentration of Mn, Cr, and Cu is greater than or equal to about 2 wt%.

In one aspect, the matrix further comprises nickel (Ni) at a concentration of greater than 0 wt% to less than or equal to about 5 wt%, and wherein the oxide layer further comprises an oxide of the Ni.

In one aspect, the oxide layer is uniform and continuous.

In one aspect, the oxide layer has a thickness of greater than or equal to about 1 nm to less than or equal to about 10 μm.

In one aspect, the matrix has a microstructure comprising greater than or equal to about 90% by volume martensite and a remainder comprising retained austenite and optionally ferrite, wherein when the remainder comprises ferrite, the ferrite has a concentration of greater than 0% by volume to less than or equal to about 5% by volume.

In one aspect, the matrix further comprises an additional element selected from the group consisting of: molybdenum (Mo) at a concentration of greater than 0 wt.% to less than or equal to about 1 wt.%; vanadium (V) at a concentration of greater than 0 wt% to less than or equal to about 1 wt%; niobium (Nb) at a concentration of greater than 0 wt.% to less than or equal to about 0.5 wt.%; boron (B) at a concentration of greater than 0 wt.% to less than or equal to about 0.01 wt.%; titanium (Ti) at a concentration of greater than 0 wt% to less than or equal to about 0.1 wt%; aluminum (Al) at a concentration of greater than 0 wt% to less than or equal to about 0.5 wt%; and combinations thereof.

In one aspect, the press hardened steel is an automotive part.

In yet various other aspects, the present techniques provide a method of manufacturing a press hardened steel partThe method of (a), the method comprising heating a blank (blank) to a temperature of greater than or equal to about 880 ℃ to less than or equal to about 950 ℃ to form a heated blank, the blank comprising a steel composition comprising carbon (C) at a concentration of greater than or equal to about 0.1 wt% to less than or equal to about 0.45 wt%; manganese (Mn) at a concentration of greater than 0 wt% to less than or equal to about 4.5 wt%; chromium (Cr) at a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 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%; copper (Cu) at a concentration of greater than 0 wt% to less than or equal to about 2 wt%; and the remainder iron (Fe); pressing the heated blank in a mold to form a structure having a predetermined shape from the heated blank; and quenching the structure to less than or equal to about the martensitic transformation end (M) of the steel composition_f) A temperature of greater than or equal to about room temperature to form the press hardened steel component, wherein the press hardened steel component comprises an alloy matrix comprising the C, Mn, Cr, Si, Cu, and Fe, an oxide layer formed on a surface of the alloy matrix, the oxide layer being continuous and uniform, comprising oxides of the Cr, Si, and Cu, and configured to be oxidation resistant, and a microstructure comprising greater than or equal to about 90 vol% martensite, and wherein the press hardened steel component is formed without descaling and without a coating.

In one aspect, the blank and the matrix further comprise nickel (Ni) at a concentration of greater than 0 wt% to less than or equal to about 5 wt%, and wherein the oxide layer further comprises an oxide of the Ni.

In one aspect, the press hardened steel component includes about 0.2 wt.% C, about 1.5 wt.% Mn, about 1.5 wt.% Cr, about 1.5 wt.% Si, about 0.8 wt.% Ni, about 0.3 wt.% Cu, and about 0.03 wt.% Nb.

In one aspect, the combined concentration of Mn, Cr, Cu, and Ni in the blank and in the matrix is greater than or equal to about 2 wt%.

In one aspect, the microstructure of the press hardened steel component further comprises greater than about 0 vol% to less than or equal to about 10 vol% retained austenite and greater than or equal to about 0 vol% to less than or equal to about 5 vol% ferrite.

In one aspect, the method is free of a secondary heat treatment after the quenching.

In one aspect, the press hardened steel part is an automotive part selected from the group consisting of a wheel, a pillar (pilar), a cradle (braker), a bumper, a roof rail, a rocker, a control arm, a beam, a tunnel, a step, a sub-frame member, a pan, a panel (panel), and a reinforced panel.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

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 chart illustrating a method of manufacturing a press hardened steel component in accordance with aspects of the present technique.

FIG. 2 is a graph showing temperature versus time for a hot pressing process for processing steel compositions in accordance with various aspects of the present technique.

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

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Detailed Description

The exemplary 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, 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 exemplary embodiments, well-known methods, well-known device structures, and well-known techniques have not been 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, 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 the various embodiments described herein, in certain aspects the term is instead understood to be a more limiting and limiting term such as "consisting of … …" or "consisting essentially of … …". Thus, for any given embodiment that recites a composition, material, component, element, feature, integer, operation, and/or process step, the disclosure also specifically includes embodiments that consist of, or consist essentially of, such recited composition, material, component, element, feature, integer, operation, and/or process step. In the case of "consisting of … …, alternative embodiments exclude any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, and in the case of" consisting essentially of … …, "exclude from such embodiments any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that substantially affect the basic and novel characteristics, but may include in such embodiments any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not substantially affect the basic and novel characteristics.

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 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 may be directly on, engaged, connected, or coupled to the other element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being directly on another element or layer, "directly engaged", "directly connected", or "directly coupled" to the other 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" vs "directly between", "adjacent" vs "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 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 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 examples provided at the end of the detailed description, all numerical values of parameters (such as amounts 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. By "about" is meant that the 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 at least refers to variations that may result from ordinary methods of measuring and using such parameters. For example, "about" may encompass variations 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.

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

As noted above, there are certain disadvantages associated with descaling uncoated press hardened steel and coating press hardened steel. Accordingly, the present technology provides a steel composition that is configured to be uncoated and hot stamped into a press hardened part having a predetermined shape without descaling.

The steel composition is in the form of a coil or sheet and comprises carbon (C), manganese (Mn), chromium (Cr), silicon (Si), copper (Cu) and iron (Fe). In some aspects, the steel composition further comprises nickel (Ni). During hot stamping, portions of the Cr, Si, Cu, and Ni (when present) migrate to the surface of the steel composition and combine with atmospheric oxygen to form a continuous oxide layer comprising one or more oxides enriched in the portions of Cr, Si, Cu, and Ni (when present). The oxide layer resists, i.e., prevents, inhibits or minimizes, further oxidation. In other words, the oxide layer protects the press hardened steel from oxidation. Thus, no descaling step, such as shot blasting or sand blasting, is required.

C is present in the steel composition at a concentration of greater than or equal to about 0.1 wt.% to less than or equal to about 0.45 wt.% or greater than or equal to about 0.1 wt.% to less than or equal to about 0.3 wt.%, and subranges thereof. In various aspects, the steel composition comprises C at a concentration of about 0.1 wt.%, about 0.12 wt.%, about 0.14 wt.%, about 0.16 wt.%, about 0.18 wt.%, about 0.2 wt.%, about 0.22 wt.%, about 0.24 wt.%, about 0.26 wt.%, about 0.28 wt.%, about 0.3 wt.%, 0.32 wt.%, about 0.34 wt.%, about 0.36 wt.%, about 0.38 wt.%, about 0.4 wt.%, about 0.42 wt.%, about 0.44 wt.%, or about 0.45 wt.%.

Mn is present in the steel composition at a concentration of greater than 0 wt.% to less than or equal to about 4.5 wt.% or greater than or equal to about 1 wt.% to less than or equal to about 2 wt.% and subranges thereof. In various aspects, the steel composition includes Mn at a concentration of about 0.02 wt.%, about 0.04 wt.%, 0.06 wt.%, 0.08 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.%, or about 4.5 wt.%.

Cr is present in the steel composition at a concentration of greater than or equal to about 0.5 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.%, and subranges thereof. In various aspects, the steel composition comprises Cr at a concentration of about 0.05 wt.%, 0.06 wt.%, 0.08 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.%, or about 5 wt.%.

Si is present in the steel composition at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.5 wt.% and subranges thereof. In various aspects, the steel composition 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.%, about 2 wt.%, about 2.1 wt.%, about 2.2 wt.%, about 2.3 wt.%, about 2.4 wt.%, or about 2.5 wt.%.

Cu is present in the steel composition at a concentration of greater than 0 wt.% to less than or equal to about 2 wt.% or greater than or equal to about 0.1 wt.% to less than or equal to about 0.5 wt.%, and subranges thereof. In various aspects, the steel composition comprises Cu at a concentration of about 0.1 wt.%, about 0.2 wt.%, about 0.3 wt.%, about 0.4 wt.%, 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.%.

When Ni is included, Ni is present in the steel composition at a concentration of greater than 0 wt.% to less than or equal to about 5 wt.% or greater than or equal to about 0.5 wt.% to less than or equal to about 1.5 wt.%, and subranges thereof. In various aspects, the steel composition comprises a concentration of about 0.02 wt.%, about 0.04 wt.%, 0.06 wt.%, 0.08 wt.%, about 0.1 wt.%, about 0.12 wt.%, about 0.14 wt.%, about 0.16 wt.%, about 0.18 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 4.6 wt.%, about 4.8 wt.%, about 5 wt.%, or about 5 wt.% Ni.

Fe constitutes the remainder of the steel composition.

In some aspects, the combined concentration of Mn, Cr, and Cu in the steel composition is greater than or equal to about 2 wt.%. When the steel composition includes the Ni, the combined concentration of the Mn, Cr, Cu, and Ni in the steel composition is greater than or equal to about 2 wt.%. In other aspects, the combined concentration of Cr, Si, and Cu in the steel composition is greater than or equal to about 2 wt.%. When the steel composition includes the Ni, the combined concentration of the Cr, Si, Cu, and Ni in the steel composition is greater than or equal to about 2 wt%.

In various aspects, the steel composition also includes molybdenum (Mo) at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 1 wt.% and subranges thereof. In various aspects, the steel composition comprises Mo at a concentration of about 0.05 wt.%, about 0.1 wt.%, 0.15 wt.%, 0.2 wt.%, about 0.25 wt.%, about 0.3 wt.%, about 0.35 wt.%, about 0.4 wt.%, about 0.45 wt.%, or about 0.5 wt.%, about 0.55 wt.%, about 0.6 wt.%, about 0.65 wt.%, about 0.7 wt.%, about 0.75 wt.%, about 0.8 wt.%, about 0.85 wt.%, about 0.9 wt.%, about 0.95 wt.%, or about 1 wt.%. In some aspects, the steel composition is substantially free of Mo. As used herein, "substantially free" refers to trace component levels, such as levels less than or equal to about 0.1 wt% or undetectable levels.

In various aspects, the steel composition further comprises vanadium (V) at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 1 wt.% and subranges thereof. In various aspects, the steel composition comprises V at a concentration of about 0.05 wt.%, about 0.1 wt.%, 0.15 wt.%, 0.2 wt.%, about 0.25 wt.%, about 0.3 wt.%, about 0.35 wt.%, about 0.4 wt.%, about 0.45 wt.%, or about 0.5 wt.%, about 0.55 wt.%, about 0.6 wt.%, about 0.65 wt.%, about 0.7 wt.%, about 0.75 wt.%, about 0.8 wt.%, about 0.85 wt.%, about 0.9 wt.%, about 0.95 wt.%, or about 1 wt.%. In some aspects, the steel composition is substantially free of V.

In various aspects, the steel composition further includes niobium (Nb) at a concentration of greater than or equal to about 0 wt% to less than or equal to about 0.5 wt% or greater than or equal to about 0.02 wt% to less than or equal to about 0.05 wt%, and subranges thereof. In various aspects, the steel composition comprises Nb 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 0.1 wt.%, about 0.15 wt.%, about 0.2 wt.%, about 0.25 wt.%, about 0.3 wt.%, about 0.35 wt.%, about 0.4 wt.%, about 0.45 wt.%, or about 0.5 wt.%. In some aspects, the steel composition is substantially free of Nb.

In various aspects, the steel composition also includes aluminum (Al) at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 0.5 wt.% and sub-ranges thereof. In various aspects, the steel composition comprises Al 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 0.1 wt.%, about 0.15 wt.%, about 0.2 wt.%, about 0.25 wt.%, about 0.3 wt.%, about 0.35 wt.%, about 0.4 wt.%, about 0.45 wt.%, or about 0.5 wt.%. In some aspects, the steel composition is substantially free of Al.

The steel composition may also contain unavoidable impurities. As used herein, an "impurity" is an element not intentionally added to a steel composition at a concentration of less than or equal to about 0.1 weight percent. Thus, the Mo, V, Nb, and Al are impurities when not intentionally included in the steel composition and when having a concentration of less than or equal to about 0.1 wt.%. Non-limiting examples of other impurities include boron (B) and titanium (Ti). For example, the steel composition includes B at a concentration of greater than or equal to about 0 wt% to less than or equal to about 0.01 wt% and Ti at a concentration of greater than or equal to about 0 wt% to less than or equal to about 0.1 wt%. When the B and Ti are not intentionally included in the steel composition by themselves, they are impurities.

The steel compositions may comprise various combinations of C, Mn, Cr, Si, Cu, Ni, Mo, V, Nb, Al, B, Ti and Fe (where C, Mn, Cr, Si, Cu and Fe are essential components) in their respective concentrations described above. In some aspects, the steel composition consists essentially of C, Mn, Cr, Si, Cu, and Fe or consists essentially of C, Mn, Cr, Si, Cu, Ni, and Fe. As noted above, the term "consisting essentially of … …" means that the steel composition excludes additional compositions, materials, components, elements, and/or features that substantially affect the basic and novel properties of the steel composition, e.g., the steel composition does not require a coating or descaling when formed into a press hardened steel part, but in this aspect may include any compositions, materials, components, elements, and/or features that do not substantially affect the basic and novel properties of the steel composition, e.g., the impurities defined above. Thus, when the steel composition consists essentially of C, Mn, Cr, Si, Cu, and Fe, or consists essentially of C, Mn, Cr, Si, Cu, Ni, and Fe, the steel composition may further comprise any combination of Mo, V, Nb, Al, B, and Ti provided above that does not substantially affect the basic and novel properties of the steel composition. In other aspects, the steel composition consists of C, Mn, Cr, Si, Cu and Fe or C, Mn, Cr, Si, Cu, Ni and Fe in their respective concentrations described above and optionally at least one of Mo, V, Nb, Al, B and Ti in their respective concentrations described above. Other elements not described herein may also be included as impurities, provided they do not substantially affect the basic and novel characteristics of the steel composition.

In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Cu, and Fe.

In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Cu, Fe and at least one of Ni, Mo, V, Nb, Al, B, or Ti.

In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Cu, Ni, and Fe.

In one aspect, the steel composition comprises, consists essentially of, or consists of C, Mn, Cr, Si, Cu, Ni, Fe and at least one of Mo, V, Nb, Al, B, or Ti.

In one aspect, the steel composition comprises about 0.2 wt.% C, about 1.5 wt.% Mn, about 1.5 wt.% Cr, about 1.5 wt.% Si, about 0.8 wt.% Ni, about 0.3 wt.% Cu, and about 0.03 wt.% Nb, consisting essentially of about 0.2 wt.% C, about 1.5 wt.% Mn, about 1.5 wt.% Cr, about 1.5 wt.% Si, about 0.8 wt.% Ni, about 0.3 wt.% Cu, and about 0.03 wt.% Nb, or consisting of about 0.2 wt.% C, about 1.5 wt.% Mn, about 1.5 wt.% Cr, about 1.5 wt.% Si, about 0.8 wt.% Ni, about 0.3 wt.% Cu, and about 0.03 wt.% Nb.

Referring to fig. 1, the present technique also provides a method 10 of manufacturing a press hardened steel component. More specifically, the method comprises hot pressing the above-described steel composition to form the press hardened steel part. The steel composition is processed in bare form, i.e. without any coating, such as Al-Si or Zn (zinc) coating. Furthermore, the method does not lead to scale formation (scale) on the press hardened steel part and does not have a descaling step, i.e. shot blasting, sand blasting or any other method for producing a smooth and uniform surface. The press hardened steel part may be any part, such as a vehicle part, which is typically manufactured by hot stamping. Non-limiting examples of vehicles having parts suitable for production by the present method include bicycles, cars, motorcycles, boats, tractors, buses, trailer homes (mobile homes), campers, gliders, airplanes, and tanks. In various aspects, the press hardened steel part is an automotive part selected from the group consisting of a wheel, a pillar, a bracket, a bumper, a roof side rail, a rocker beam, a rocker, a control arm, a cross member, a tunnel, a pedal, a sub-frame member, a tray, a panel, and a reinforced panel.

The method 10 includes obtaining a coil 12 of a steel composition according to the present technique and cutting a blank 14 from the coil 12. Although not shown, the blank 14 may alternatively be combined from the steelAnd (4) cutting the sheet of the object. The steel composition 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 (Ac3) temperature to fully austenitize the steel composition. The heated blank 14 is transferred to a mold or press 18, optionally 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 rate to less than or equal to about the martensite transformation end (M) of the steel composition_f) A temperature greater than or equal to about room or ambient temperature to form the press hardened steel part. The critical cooling rate, i.e., the minimum cooling rate that provides the desired microstructure described below, is about 15 ℃/s. Thus, the quenching includes reducing the temperature of the structure at a rate of greater than or equal to about 15 ℃/s.

The method 10 is free of a descaling step. Thus, the method 10 does not include a step such as shot blasting or sand blasting. Since the steel composition is bare, the press hardened steel part is free of and does not include, for example, a discontinuous oxide layer, a zinc (Zn) layer, or an aluminum-silicon (Al-Si) coating. As used herein, a "discontinuous oxide layer" is a non-uniform layer or clusters of multiple oxide layers that should be removed from the surface of a press hardened steel part by, for example, descaling or shot blasting. The method 10 also lacks a secondary heat treatment after the quenching. As discussed in more detail below, the press hardened steel component comprises a press hardened steel comprising an alloy matrix (having the components of the steel composition) and a uniform and continuous oxide layer comprising oxides of Cr, Si, Cu and, when present, Ni formed on the oxide layer. By "continuous," it is meant that the oxide layer covers all or substantially all (i.e., greater than or equal to about 90%) of the exposed surface of the press hardened steel component. By "uniform," it is meant that the thickness of the oxide layer varies by less than or equal to about 20%.

Fig. 2 shows a diagram 50 providing additional details regarding hot pressing. The figure shows50 have a y-axis 52 representing temperature and an x-axis 54 representing time. Line 56 on fig. 50 represents heating conditions in the hot pressing process. Here, the blank is heated to a final temperature 58 above an upper critical temperature (Ac3) 60 of the steel composition to fully austenitize the steel composition and form a heated blank. The final temperature 58 is greater than or equal to about 880 ℃ to less than or equal to about 950 ℃. The heated blank is then transferred to a press or die. The temperature of the heated blank may be reduced by greater than or equal to about 100 ℃ to less than or equal to about 200 ℃ during the transfer. Thus, the temperature of the heated blank is reduced to about the Ac3 temperature of 60 or less and the heated blank is stamped or thermoformed into a structure having a predetermined shape and then set at greater than or equal to about 15 ℃ s^-1Greater 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 15 ℃ s^-1About 18 ℃ s^-1About 20 ℃ s^-1About 22 ℃ s^-1About 24 ℃ s^-1About 26 ℃ s^-1About 28 ℃ s^-1About 30 ℃ s^-1Or more rapidly until the temperature drops below the end of the martensitic transformation (M)_f) A temperature 66 such that the press hardened steel component is formed. The press hardened steel part comprises a substrate comprising the steel composition components and the above-mentioned oxide layer formed on the substrate. The press hardened steel component, i.e., the substrate, has a microstructure comprising greater than or equal to about 90 vol% martensite, greater than or equal to about 0 vol% to less than or equal to about 10 vol% retained austenite, and greater than or equal to about 0 vol% to less than or equal to about 5 vol% ferrite. For example, the microstructure can include greater than or equal to about 90% to less than 100% martensite by volume, and the remainder includes (or consists of) a combination of retained austenite and ferrite, but the ferrite is not present at a concentration greater than about 5% by volume. Thus, in certain aspects, the microstructure comprises or consists of martensite, comprises or consists of martensite and retained austenite, or comprises or consists of the group of martensite, retained austenite and ferriteAnd (4) obtaining.

In some aspects, the hot pressing, i.e., the heating, stamping, and quenching, is performed in an aerobic atmosphere. In other aspects, the hot pressing may be performed in an oxygen-free atmosphere, such as by supplying an inert gas into at least one of the oven or the mold. The inert gas may be any inert gas known in the art, such as nitrogen or argon, as non-limiting examples.

Referring to fig. 3, the present technique also provides a press hardened steel 80. The press hardened steel 80 is obtained by hot pressing the steel composition by the above method. Thus, the press hardened steel structure manufactured by the above method consists of said press hardened steel 80.

The press hardened steel 80 includes a substrate 82 comprising the steel component and an oxide layer 84 formed on the substrate, wherein the oxide layer 84 is continuous and uniform. It should be understood that fig. 3 shows a cross-sectional view of only a portion of the press hardened steel 80, and that the oxide layer 84 surrounds or coats all or substantially all of the alloy matrix 82. The press hardened steel 80 has an Ultimate Tensile Strength (UTS) of greater than or equal to about 500 MPa, greater than or equal to about 750 MPa, greater than or equal to about 1,000 MPa, greater than or equal to about 1,250 MPa, greater than or equal to about 1,600 MPa, greater than or equal to about 1,700 MPa, or greater than or equal to about 1,800 MPa. In some aspects, the press hardened steel 80 has a UTS greater than or equal to about 1,600 MPa and less than or equal to about 2000 MPa.

The alloy matrix 82 contains the components of the steel composition described above and their respective concentrations, but has the microstructure described above.

In the hot pressing process, oxide layer 84 is formed as a continuous and uniform layer on substrate 82 and disposed directly on substrate 82, and comprises oxides rich in Cr, Si, Cu, and Ni (when Ni is present in the steel composition), including Cr oxides, Si oxides, Cu oxides, and Ni oxides (when Ni is present in the steel composition).

The oxide layer 84 has a thickness T greater than or equal to about 1 nm to less than or equal to about 10 μm_OLFor example, about 0.001 μm, about 0.01 μm,A thickness of 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 9.9 μm, about 10 μm.

In certain variations, the oxide layer 84 is continuous, uniform, and homogenous. Thus, the oxide layer 84 provides an exposed surface that is free or substantially free (i.e., includes less than or equal to about 10% of the exposed surface) of a discontinuous oxide layer, and which does not require descaling by, for example, shot blasting or grit blasting. In addition, oxide layer 84 resists (i.e., prevents, inhibits, or minimizes) further surface oxidation.

As noted above, the press hardened steel 80 does not include or have any layers that are not derived from the steel composition or the matrix 82.

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 can 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 comprising:

an alloy matrix, the alloy matrix comprising:

carbon (C) at a concentration of greater than or equal to about 0.1 wt% to less than or equal to about 0.45 wt%;

manganese (Mn) at a concentration of greater than 0 wt% to less than or equal to about 4.5 wt%;

chromium (Cr) at a concentration of greater than or equal to about 0.5 wt% to less than or equal to about 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%;

copper (Cu) at a concentration of greater than 0 wt% to less than or equal to about 2 wt%; and

the remainder being iron (Fe); and

an oxide layer formed on a surface of the alloy matrix during hot forming of the press hardened steel, the oxide layer comprising oxides of the Cr, Si and Cu,

wherein the combined concentration of Mn, Cr, and Cu is greater than or equal to about 2 wt%, and

wherein the oxide layer protects the alloy substrate from oxidation.

2. The press hardened steel of claim 1, wherein the matrix further comprises:

nickel (Ni) at a concentration of greater than 0 wt.% to less than or equal to about 5 wt.%, and

wherein the oxide layer further comprises an oxide of the Ni.

3. The press hardened steel of claim 1, wherein the oxide layer is uniform and continuous and has a thickness of greater than or equal to about 1 nm to less than or equal to about 10 μ ι η.

4. The press hardened steel according to claim 1, wherein said matrix has a microstructure comprising greater than or equal to about 90% by volume martensite and a remainder comprising retained austenite and optionally ferrite, wherein when said remainder comprises ferrite, said ferrite has a concentration of greater than 0% to less than or equal to about 5% by volume.

5. An automotive part comprising the press hardened steel according to claim 1.

6. A method of manufacturing a press hardened steel part, the method comprising:

heating the blank to a temperature of greater than or equal to about 880 ℃ to less than or equal to about 950 ℃ to form a heated blank, the blank comprising a steel composition comprising:

the remaining part of the iron (Fe),

wherein the combined concentration of Mn, Cr, and Cu is greater than or equal to about 2 wt%;

pressing the heated blank in a mold to form a structure having a predetermined shape from the heated blank; and

quenching the structure to less than or equal to about the end of martensitic transformation (M) of the steel composition_f) A temperature of greater than or equal to about room temperature to form the press hardened steel part,

wherein the press hardened steel component comprises:

an alloy matrix containing the C, Mn, Cr, Si, Cu and Fe,

an oxide layer formed on a surface of the alloy substrate, the oxide layer being continuous and uniform, comprising oxides of the Cr, Si, and Cu, and configured to resist oxidation, an

A microstructure comprising greater than or equal to about 90 volume percent martensite, and

wherein the press hardened steel component is formed without descaling and without a coating.

7. The method of claim 6, wherein the blank and the base further comprise:

wherein the oxide layer further comprises an oxide of the Ni.

8. The method of claim 7, wherein the combined concentration of Mn, Cr, Cu, and Ni in the blank and in the matrix is greater than or equal to about 2 wt.%.

9. The method of claim 6, wherein the microstructure of the press hardened steel component further comprises greater than about 0 vol% to less than or equal to about 10 vol% retained austenite, and greater than or equal to about 0 vol% to less than or equal to about 5 vol% ferrite.

10. The method of claim 6, wherein the press hardened steel part is an automotive part selected from the group consisting of wheels, pillars, braces, bumpers, roof rails, rocker beams, door sills, control arms, cross members, channels, pedals, sub-frame members, panels, and reinforced panels.