DE102020134324A1 - PRESS-HARDENING STEEL WITH HIGH OXIDATION RESISTANCE - Google Patents

Abstract

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% by weight silicon (Si), more than 0-2% by weight copper (Cu) and the remainder of iron (Fe). The combined concentration of the Mn, Cr and Cu is greater than about 2 weight percent. The steel composition is configured to form a surface oxide layer comprising oxides of Cr, Si, and Cu after being press hardened. Press hardened steel made from the steel composition and a method of making a press hardened steel component from the steel composition are also provided.

Description

INTRODUCTION

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

A press-hardened steel (PHS), also known as "hot stamped steel" or "hot formed steel", is one of the strongest steels used for body structure applications with tensile strength properties of around 1,500 megapascals (MPa) in automobiles . Such steel exhibits desirable properties including the formation of steel components with significant increases in strength to weight ratios. PHS components have become increasingly common in various industries and applications, including the general manufacturing, construction equipment, automotive or other transportation industries, home or industrial structures, and the like. For example, in the manufacture of vehicles, particularly automobiles, continuous improvement in fuel efficiency and performance is desirable; therefore, PHS components have been increasingly used. PHS components are often used to form load bearing components, such as door beams, which usually require high strength materials. Thus, the finished state of these steels is designed to have high strength and enough ductility to withstand external forces such as withstanding intrusion into the passenger compartment without breaking to provide protection for the occupants. Electroplated PHS components can also provide cathodic protection.

Many PHS processes involve austenitizing a sheet steel blank in a furnace, followed immediately by pressing and quenching the sheet in dies. Austenitizing is typically carried out in the range from about 880 ° C to 950 ° C. PHS processes can be indirect or direct. In the direct process, the PHS component is formed between dies and pressed at the same time, which quenches the steel. In the indirect process, the PHS component is cold-formed into an intermediate part shape before austenitizing and the subsequent pressing and quenching steps. Quenching the PHS component hardens the component by converting the microstructure from austenite to martensite. An oxide layer often forms during the transfer from the furnace to the dies. Therefore, after quenching, the oxide must be removed from the PHS component and the matrices. The oxide is typically removed, i.e., descaled, by shot peening.

The PHS component can be made from bare or coated alloys. A coating of the PHS component with, for example, zinc or Al-Si provides the steel component underneath with a protective layer. For example, zinc coatings offer cathodic protection; the coating acts as a sacrificial layer and corrodes instead of the steel component even where the steel is exposed. However, such a zinc-coated PHS generates oxides on the surfaces of the PHS components, which must be removed by shot peening. Accordingly, alloy compositions that do not require coatings or other treatments are desired.

SUMMARY

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its entire scope or all of its features.

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

In various aspects, current technology provides 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% by weight to less than or equal to about 5% by weight; 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 balance of iron (Fe), wherein the combined concentration of the 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, the oxides of Cr, Si and Comprises Cu after being press hardened.

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%, with the combined concentration of the Mn, Cr, Cu and Ni being greater than or equal to is 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 press hardened.

In one aspect, the steel composition is free of coatings.

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 coiled sheet.

In various other aspects, current technology provides press hardened steel comprising an 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% by weight to less than or equal to about 5% by weight; 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 residue of iron (Fe); and an oxide layer formed on a surface of the alloy matrix during hot working of the press-hardened steel, the oxide layer comprising oxides of Cr, Si, and Cu, the oxide layer protecting the alloy matrix from oxidation.

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

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 oxides of the Ni.

The oxide layer is uniform and continuous.

The oxide layer has a thickness of greater than or equal to approximately 1 nm to less than or equal to approximately 10 μm.

The matrix has a microstructure that comprises greater than or equal to about 90 vol% martensite and a balance comprising residual austenite and optionally ferrite, with the ferrite having a concentration greater than 0 vol. -% to less than or equal to about 5% by volume.

The matrix further comprises an additional element selected from the group consisting of molybdenum (Mo) at a concentration of greater than 0% by weight to less than or equal to about 1% by weight; 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 making a press hardened steel component, the method comprises: heating a blank to a temperature greater than or equal to about 880 ° C to less than or equal to about 950 ° C to form a heated blank, the blank comprising a steel composition; the carbon (C) at a concentration of greater than or equal to about 0.1% by weight to less than or equal to about 0.45% by weight; 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% by weight to less than or equal to about 5% by weight; 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 comprises a residue of iron (Fe); pressing the heated blank into a die to form a structure having a predetermined shape from the heated blank; and quenching the structure to a temperature less than or equal to about a martensite finish temperature (Mf) of the steel composition and more than or equal to about room temperature to form the press hardened steel component, the press hardened steel component comprising: 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 Cr, Si and Cu and configured to resist oxidation, and a 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 is free of any coating.

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

In one aspect, the press hardened steel component 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.

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

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 from secondary heat treatment after quenching.

In one aspect, the press hardened steel component is an automobile part selected from the group consisting of a wheel, a pillar, a bracket, a bumper, a roof rail, a swing rail, a rocker, a control arm, a beam, a tunnel, a step, a subframe element , a pan, a plate and a reinforcement plate.

Further areas of applicability are evident from the description provided here. 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.

Figure list

• 1 ist ein Ablaufdiagramm, das ein Verfahren zur Herstellung einer pressgehärteten Stahlkomponente gemäß verschiedener Aspekte der aktuellen Technologie veranschaulicht.
• 2 ist eine graphische Darstellung, die Temperatur versus Zeit für ein Warmpressverfahren zeigt, das verwendet wird, um eine Stahlzusammensetzung zu verarbeiten, gemäß verschiedener Aspekte der aktuellen Technologie.
• 3 ist eine Veranschaulichung eines pressgehärteten Stahls gemäß verschiedener Aspekte der aktuellen Technologie.

The drawings described herein are selected embodiments for illustrative purposes only and are not intended to limit the scope of the present disclosure.

• 1 Figure 13 is a flow diagram illustrating a method of making a press hardened steel component in accordance with various aspects of current technology.
• 2 Figure 13 is a graph showing temperature versus time for a hot pressing process used to process a steel composition according to various aspects of current technology.
• 3 Figure 3 is an illustration of a press hardened steel according to various aspects of current technology.

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

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will be thorough and fully conveyable to those of ordinary skill in the art. Numerous specific details are set forth, such as examples of specific compositions, components, devices, and methods in order to provide a thorough understanding of embodiments of the present disclosure. It will be understood by those skilled in the art that specific details must be omitted, that example embodiments can be embodied in many different forms, and that none should limit the scope of the disclosure. In some example embodiments, known processes, known device structures, and known technologies are not described in detail.

The terminology used herein is used to describe certain exemplary embodiments and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “der, die, das” may include the plural forms as well, unless the context dictates otherwise. The terms “comprises”, “comprising”, “including” and “having (with)” are inclusive and therefore specify the presence of, but do not exclude, specified features, elements, compositions, steps, integers, operations and / or components Presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. Although the open term “comprising” is to be understood as a non-limiting term used to describe and claim various embodiments set forth herein, the term may alternatively be understood in certain aspects as a more restrictive and restrictive term, such as, for example "Consisting of" or "consisting essentially of". Thus, for any embodiment that recites compositions, materials, components, elements, features, features, integers, operations and / or process steps, the present disclosure also expressly includes embodiments derived from such recited compositions, materials, components, Elements, features, integers, operations and / or process steps consist or essentially consist of these. In the case of “consisting of” the alternative embodiment excludes all additional compositions, materials, components, elements, features, integers, operations and / or process steps, while in the case of “consisting essentially of” all additional compositions, materials, components , Elements, features, integers, operations and / or process steps that significantly affect the basic and new properties are excluded from such an embodiment, but with all compositions, materials, components, elements, features, integers, operations and / or process steps that do not significantly affect the basic and novel properties can be included in the embodiment.

Any procedural steps, processes and operations described herein are not to be construed as necessarily requiring their execution in the order explained or illustrated, unless they are expressly identified as the order of execution. It should also be understood that additional or alternative steps can be used unless otherwise specified.

When a component, element, or layer is referred to as being "on," "engaged with," "connected to," or "coupled to" another element or layer, it can be directly attached to the other component, the attached or coupled to another element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as "directly on", "directly engaged with", "directly connected to", or "directly coupled to" another element, there must be no intervening elements or layers. Other words used to describe the relationship between the elements should be interpreted in a similar way (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. can 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 followed through these terms are restricted unless otherwise stated. These terms may only be 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 mean any sequence or order unless the context clearly indicates them. Thus, a first step, element, component, region, layer, or section discussed below could be referred to as a second step, element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

Spatially or temporally relative terms such as "before", "after", "inner", "outer", "below", "below", "lower", "above", "upper" and the like can be used here for a simple description the relationship of one element or feature to another element (s) or feature (s) can be used as shown in the figures. Spatially or temporally relative terms can be intended to encompass different orientations of the device or the system in use or operation or in addition to the orientation shown in the figures.

Throughout this disclosure, the numerical values represent approximate measures or limits for ranges in order to cover slight deviations from the stated values and embodiments with approximately the mentioned value as well as with exactly the mentioned value. Apart from the working examples provided at the end of the detailed description, all numerical values of parameters (e.g. quantities or conditions) in this specification, including the appended claims, are to be understood to be amended in all cases to include the term "about", whether "about" actually appears in front of the numeric value or not. “About” indicates that the specified numerical value allows for a slight inaccuracy (with an approximation of the accuracy of the value; approximately or fairly close to the value; almost). Unless the inaccuracy provided by “about” is understood differently in the art with this common meaning, then “about” as used herein indicates at least variations that may result from common methods of measuring and using such parameters. For example, “about” can be 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 as or equal to 0.5% and, in certain aspects, optionally include less than or equal to 0.1%.

In addition, the disclosure of realms includes the disclosure of all values and others divided areas within the entire area including endpoints and sub-areas indicated for the areas.

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

As discussed above, there are certain disadvantages associated with descaling press hardened steels and coating press hardened steels. Accordingly, current technology provides a steel composition configured to be hot stamped into a press hardened component having a predefined shape with no coatings and no need to perform descaling.

The steel composition is in the form of a coil or sheet and includes carbon (C), manganese (Mn), chromium (Cr), silicon (Si), copper (Cu) and iron (Fe). In some aspects, the steel composition also includes nickel (Ni). During a hot stamping process, portions of the Cr, Si, Cu and Ni (if any) migrate to a surface of the steel composition and combine with atmospheric oxygen to form a continuous oxide layer that is an oxide or one with the portions of Cr, Si, Cu and Includes Ni (if any) enriched oxide. The oxide layer resists further oxidation, i.e. prevents, inhibits or minimizes further oxidation. In other words, the oxide layer protects the press-hardened steel from oxidation. Therefore, descaling steps such as shot peening or sandblasting are not required.

The C is in the steel composition at a concentration of greater than or equal to about 0.1% by weight to less than or equal to about 0.45% by weight or more than or equal to about 0.1% by weight to less present as or equal to about 0.3 weight percent and subranges thereof. In various aspects, the steel composition comprises C at a concentration of about 0.1% by weight, about 0.12% by weight, about 0.14% by weight, about 0.16% by weight, about 0, 18% by weight, about 0.2% by weight, about 0.22% by weight, about 0.24% by weight, about 0.26% by weight, about 0.28% by weight , about 0.3% by weight, 0.32% by weight, about 0.34% by weight, about 0.36% by weight, about 0.38% by weight, about 0.4% by weight %, about 0.42% by weight, about 0.44% by weight, or about 0.45% by weight.

The Mn is present in the steel composition at a concentration of greater than 0% by weight to less than or equal to about 4.5% by weight or more than or equal to about 1% by weight to less than or equal to about 2% by weight. -% and subranges thereof available. In various aspects, the steel composition comprises Mn at a concentration of about 0.02% by weight, about 0.04% by weight, 0.06% by weight, 0.08% by weight, about 1% by weight. %, about 1.2% by weight, about 1.4% by weight, about 1.5% by weight, about 1.6% by weight, about 1.8% by weight, about 2% by weight %, about 2.2% by weight, about 2.4% by weight, about 2.5% by weight, about 2.6% by weight, about 2.8% by weight, about 3% by weight, about 3.2% by weight, about 3.4% by weight, about 3.5% by weight, about 3.6% by weight, about 3.8% by weight , about 4% by weight, about 4.2% by weight, about 4.4% by weight, or about 4.5% by weight.

The Cr is 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 present. In various aspects, the steel composition comprises Cr at a concentration of about 0.05% by weight, 0.06% by weight, 0.08% by weight, about 1% by weight, about 1.2% by weight. %, about 1.4% by weight, about 1.5% by weight, about 1.6% by weight, about 1.8% by weight, about 2% by weight, about 2.2% by weight %, about 2.4% by weight, about 2.5% by weight, about 2.6% by weight, about 2.8% by weight, about 3% by weight, about 3, 2% by weight, about 3.4% by weight, about 3.5% by weight, about 3.6% by weight, about 3.8% by weight, about 4% by weight, about 4.2% by weight, about 4.4% by weight, about 4.5% by weight, about 4.6% by weight, about 4.8% by weight or about 5% by weight .

The 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% by weight, about 1% by weight, about 1.1% by weight, about 1.2% by weight, about 1.3% by weight, about 1.4% by weight, about 1.5% by weight, about 1.6% by weight, about 1.7% by weight, about 1.8% by weight, about 1.9% by weight, about 2% by weight % about 2.1% by weight, about 2.2% by weight, about 2.3% by weight, about 2.4% by weight, or about 2.5% by weight.

The Cu is in the steel composition with a concentration of more than 0 % By weight to less than or equal to about 2% by weight, or more than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight and subranges thereof. In various aspects, the steel composition comprises Si at a concentration of about 0.1% by weight, about 0.2% by weight, about 0-3% by weight, about 0.4% by weight, about 0 , 5% by weight, about 0.6% by weight, about 0.7% by weight, about 0.8% by weight, about 0.9% by weight, about 1% by weight, about 1.1% by weight, about 1.2% by weight, about 1.3% by weight, about 1.4% by weight, about 1.5% by weight, about 1.6% by weight %, about 1.7% by weight, about 1.8% by weight, about 1.9% by weight or about 2% by weight.

When included, the Ni is 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 weight percent and sub-ranges thereof present. In various aspects, the steel composition comprises Ni at a concentration of about 0.02% by weight, about 0.04% by weight, 0.06% by weight, 0.08% by weight, about 0.1% by weight %, about 0.12% by weight, about 0.14% by weight, about 0.16% by weight, about 0.18% by weight, about 1% by weight, about 1, 2% by weight, about 1.4% by weight, about 1.5% by weight, about 1.6% by weight, about 1.8% by weight, about 2% by weight, about 2.2% by weight, about 2.4% by weight, about 2.5% by weight, about 2.6% by weight, about 2.8% by weight, about 3% by weight , about 3.2% by weight, about 3.4% by weight, about 3.5% by weight, about 3.6% by weight, about 3.8% by weight, about 4% by weight -%, about 4.2% by weight, about 4.4% by weight, about 4.6% by weight, about 4.8% by weight or about 5% by weight.

The Fe makes up the rest of the steel composition.

In some aspects, the combined concentration of the Mn, Cr, and Cu in the steel composition is greater than or equal to about 2 weight percent. 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% by weight. In other aspects, the combined concentration of the Cr, Si, and Cu in the steel composition is greater than or equal to about 2 weight percent. 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 further comprises molybdenum (Mo) at a concentration of greater than or equal to about 0% by weight to less than or equal to about 1% by weight and subranges thereof. In various aspects, the steel composition comprises Mo at a concentration of about 0.05% by weight, about 0.1% by weight, 0.15% by weight, 0.2% by weight, about 0.25% by weight %, about 0.3% by weight, about 0.35% by weight, about 0.4% by weight, about 0.45% by weight or about 0.5% by weight, about 0.55% by weight, about 0.6% by weight, about 0.65% by weight, about 0.7% by weight, about 0.75% by weight, about 0.8% by weight. -%, about 0.85% by weight, about 0.9% by weight, about 0.95% by weight or about 1% by weight. In some aspects, the steel composition is substantially free of Mo. As used herein, “substantially free” refers to levels of trace components, such as levels less than or equal to about 0.1 wt% or levels that are undetectable are.

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

In various aspects, the steel composition further comprises 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% by weight and sub-ranges thereof. In various aspects, the steel composition comprises Nb at a concentration of about 0.01% by weight, about 0.02% by weight, about 0.04% by weight, about 0.06% by weight, about 0, 08% by weight, about 0.1% by weight, about 0.15% by weight, about 0.2% by weight, about 0.25% by weight, about 0.3% by weight , about 0.35% by weight, about 0.4% by weight, about 0.45% by weight or about 0.5% by weight. In some aspects the steel composition is essentially free of Nb.

In various aspects, the steel composition further comprises aluminum (Al) at a concentration of greater than or equal to about 0% by weight to less than or equal to about 0.5% by weight and subranges thereof. In various aspects, the steel composition comprises Al at a concentration of about 0.01% by weight, about 0.02% by weight, about 0.04% by weight, about 0.06% by weight, about 0, 08% by weight, about 0.1% by weight, about 0.15% by weight, about 0.2% by weight, about 0.25% by weight, about 0.3% by weight , about 0.35% by weight, about 0.4% by weight, about 0.45% by weight or about 0.5% by weight. In some aspects, the steel composition is essentially free of Al.

The steel composition may also include unavoidable impurities. As used herein, "impurities" are elements with a concentration less than or equal to about 0.1 weight percent that are not intentionally added to the steel composition. Therefore, if not intentionally included in the steel composition, and if a concentration of less than or equal to about 0.1 wt%, the Mo, V, Nb and Al are impurities. Non-limiting examples of other impurities include boron (B) and titanium (Ti). For example, steel composition includes B at a concentration greater than or equal to about 0 wt% to less than or equal to about 0.01 wt% and Ti at a concentration greater than or equal to about 0 wt% to less as or equal to about 0.1 wt. %. If the B and Ti are not intentionally contained individually in the steel composition, they are impurities.

The steel composition can be various combinations of C, Mn, Cr, Si, Cu, Ni, Mo, V, Nb, Al, B, Ti and Fe (where the C, Mn, Cr, Si, Cu and Fe are required components) in their respective concentrations described above. In some aspects, the steel composition consists essentially of C, Mn, Cr, Si, Cu and Fe or C, Mn, Cr, Si, Cu, Ni and Fe. As described above, the term "consists essentially of" means that the steel composition excludes additional compositions, materials, components, elements and / or features that significantly affect the basic and novel properties of the steel composition, such as the steel composition that does not have coatings or does not require descaling when formed in a press hardened steel component, however any compositions, materials, components, elements and / or features that do not significantly affect the basic and novel properties of the steel composition may be included in the aspect, such as impurities, as defined above. Therefore, when the steel composition consists essentially of C, Mn, Cr, Si, Cu and Fe or C, Mn, Cr, Si, Cu, Ni and Fe, the steel composition can also be any combination of Mo, V, Nb, Al , B and Ti include, as provided above, which do not significantly 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 here may also be included as impurities, provided that they do not significantly affect the basic and novel properties 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, consists essentially of, or consists of about 0.2 wt% C, about 1.5 wt% Mn, about 1.5 wt% Cr, about 1.5 wt. -% Si, about 0.8% by weight Ni, about 0.3% by weight Cu and about 0.03% by weight Nb.

With reference to 1 the current technology also provides a process 10 ready to manufacture a press-hardened steel component. In particular, the method includes hot pressing the steel composition described above to form the press hardened steel component. The steel composition is processed in a bare form, ie without any coatings such as Al-Si or Zn (galvanized) coatings. In addition, the method does not lead to the formation of scale on the press-hardened steel component and is free from a descaling step, ie free from shot peening, sandblasting or any other method for preparing a smooth and homogeneous surface. The press hardened steel component can be any component that is generally made by hot stamping, such as a vehicle part. Non-limiting examples of vehicles having parts capable of being produced by the current process include bicycles, automobiles, motorcycles, boats, tractors, buses, caravans, RVs, gliders, airplanes, and tanks. In various aspects, the press-hardened steel component is an automobile part selected from the group consisting of a wheel, a pillar, a bumper, a roof rail, a swing rail, a rocker, a control arm, a beam, a tunnel, a subframe element, a pan, a plate and a reinforcement plate.

The procedure 10 includes obtaining a coil 12th a steel composition according to the existing technology and cutting a blank 14th out of the coil 12th . Although not shown, the blank can 14th alternatively cut from a sheet of steel composition. The steel composition is bare, ie uncoated. The procedure 10 also includes hot pressing the blank 14th . In this regard, the procedure includes 10 austenitizing the blank 14th by heating the blank 14th in an oven 16 to a temperature above its upper critical temperature (Ac3) temperature in order to completely austenitize the steel composition. The heated blank 14th becomes a die or a Press 18th , optionally by a robotic arm (not shown). Here the procedure includes 10 an embossing of the blank 14th in the die or press 18th to form a structure having a predefined shape and quenching the structure at a constant rate to a temperature less than or equal to about a martensite finish temperature (Mf) of the steel composition and greater than or equal to about room temperature to the press hardened steel component form. The quenching includes lowering the temperature of the structure at a constant rate of greater than or equal to about 20 ° C./sec.

The procedure 10 is free from a step of descaling. Hence the procedure includes 10 for example, no steps of shot peening or sandblasting. In so far as the steel composition is bare, the press-hardened steel component does not include a layer of zinc (Zn) or an aluminum-silicon (Al-Si) coating, for example. The procedure 10 is also free from secondary heat treatment after quenching. As used herein, a “discontinuous oxide layer” is a non-uniform layer or a plurality of clusters of oxide layers that should be removed from the surface of press-hardened steel components, for example by descaling or shot peening. The procedure 10 is also free from secondary heat treatment after quenching. As discussed in more detail below, the press hardened steel component comprises press hardened steel which comprises an alloy matrix (with the components of the steel composition) and a uniform and continuous oxide layer comprising oxides of Cr, Si, Cu and, if present, Ni on the oxide layer is trained. By "continuous" it is meant that the oxide layer covers all or substantially all (ie, greater than or equal to about 90%) of the exposed surfaces of the press hardened steel component. By “uniformly” it is meant that the thickness of the oxide layer varies less than or equal to about 20%.

2 shows a graph 50 which provides additional details about hot pressing. The graphic representation 50 has a y-axis 52 that represents temperature and an x-axis 54 that represents time. A line 56 on the graph 50 represents the heating conditions during hot pressing. Here the blank is brought to a final temperature 58 heated above an upper critical temperature (Ac3) 60 of the steel alloy is to completely austenitize the steel alloy and form a heated blank. The final temperature 58 is greater than or equal to about 880 ° C to less than or equal to about 950 ° C. The heated blank is then transferred to a press or die. During transfer, the heated blank may decrease in temperature by greater than or equal to about 100 ° C to less than or equal to about 200 ° C. Therefore, the temperature of the heated parison decreases to about the Ac3 temperature 60 or lower and the heated parison is coined or thermoformed into the structure having the predetermined shape and then larger at a rate greater than or equal to about 15 ° Cs-1 as or equal to about 20 ° Cs-1, greater than or equal to about 25 ° Cs-1, or greater than or equal to about 30 ° Cs-1, such as at a rate of about 15 ° Cs-1, about 18 ° Cs-1 , about 20 ° Cs-1, about 22 ° Cs-1, about 24 ° Cs-1, about 26 ° Cs-1, about 28 ° Cs-1, about 30 ° Cs-1 or faster until the temperature is up below a martensite end temperature (Mf) 66 decreases so that the press hardened steel component is formed. The press hardened steel component includes a matrix comprising the steel composition components and the above-described oxide layer formed on the matrix. The press-hardened steel component, ie the matrix, has a microstructure that is greater than or equal to about 90% by volume martensite, more than or equal to about 0% by volume to less than or equal to about 10% by volume of retained austenite and more as or equal to about 0% by volume to less than or equal to about 5% by volume ferrite. For example, the microstructure can comprise more than or equal to about 90% by volume to less than 100% by volume martensite and the remainder comprise (or consist of) a combination of residual austenite and ferrite, but the ferrite not having a concentration greater than that is present as about 5% by volume. Accordingly, in certain aspects, the microstructure comprises or consists of martensite and retained austenite or comprises or consists of martensite, retained austenite and ferrite.

In some aspects, the hot pressing, i.e. heating, embossing and quenching, is carried out in an aerobic atmosphere. In other aspects, the hot pressing can be performed in an anaerobic atmosphere, such as by supplying a noble gas to at least one of the furnace and the die. The noble gas can be any noble gas known in the art such as, by way of non-limiting examples, nitrogen or argon.

With reference to 3 the current technology provides yet another press-hardened steel 80. The press-hardened steel 80 is a result of hot pressing the steel composition described above by the method described above. Therefore, the press hardened steel structure made by the above method is made of the press hardened steel 80 composed.

The press-hardened steel 80 includes a matrix 82 showing the steel component and one on the oxide layer 84 comprises formed matrix, wherein the oxide layer 84 is continuous and even. It should be understood that 3 just a cross-sectional illustration of a portion of the press hardened steel 80 shows and that the oxide layer 84 all or substantially all of the alloy matrix 82 surrounds or coated. The press-hardened steel 80 has an ultimate tensile strength (UTS) 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 has 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 comprises the components and their respective concentrations of the steel composition described above, but has the microstructure described above.

The oxide layer 84 is formed on and located directly on the matrix 82 as a continuous and uniform layer during the hot pressing process and includes an oxide enriched in Cr, Si, Cu, and when Ni is present in the steel composition, N includes Cr oxides, Si oxides, Cu oxides, and when Ni is in the steel composition is present Ni oxides.

The oxide layer 84 has a thickness TOL of greater than or equal to approximately 1 nm to less than or equal to approximately 10 μm, such as a thickness of approximately 0.001 μm, approximately 0.01 μm, approximately 0.05 μm, approximately 0.1 μm, approximately 0.15 µm, about 0.25 µm, about 0.3 µm, about 0.35 µm, about 0.4 µm, about 0.45 µm, about 0.5 µm, about 0.55 µm, about 0, 6 µm, about 0.65 µm, about 0.7 µm, about 0.75 µm, about 0.8 µm, about 0.85 µm, about 0.9 µm, about 0.95 µm, about 1 µm, about 1.5 µm, about 2 µm, about 2.5 µm, about 3 µm, about 3.5 µm, about 4 µm, about 4.5 µm, about 5 µm, about 5.5 µm, about 6 µm, about 6.5 µm, about 7 µm, about 7.5 µm, about 8 µm, about 8.5 µm, about 9 µm, about 9.5 µm or about 10 µm.

In certain variations the oxide layer is 84 continuous, uniform and homogeneous. Hence the oxide layer represents 84 provides an exposed surface that is free of, or substantially free of (ie, comprising less than or equal to about 10% of the exposed surface) discontinuous oxide layers and there is no need for it to be descaled by, for example, shot peening or sandblasting. The oxide layer is also resistant 84 (ie, prevents, inhibits, or minimizes) further surface oxidation.

The press-hardened steel 80 does not include or is free of any layer other than the steel composition or matrix 82 is derived as explained above.

The foregoing description of the embodiments has been presented for purposes of illustration and description. It is not meant to be complete or to limit the revelation. Individual elements or features of a specific embodiment are generally not limited to this specific embodiment, but are optionally interchangeable and can be used in a selected embodiment, even if it is not expressly shown or described. It can also be changed 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 (10)

Press hardened steel comprising: an 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% by weight to less than or equal to about 5% by weight; 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 residue of iron (Fe); and an oxide layer formed on a surface of the alloy matrix during hot working of the press-hardened steel, the oxide layer comprising oxides of Cr, Si and Cu, wherein the combined concentration of the Mn, Cr and Cu is greater than or equal to about 2 weight percent, and wherein the oxide layer protects the alloy matrix from oxidation. Press-hardened steel according to Claim 1 wherein the matrix further comprises: nickel (Ni) at a concentration of greater than 0% by weight to less than or equal to about 5% by weight, and wherein the oxide layer further comprises oxides of Ni. Press-hardened steel according to 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 µm. Press-hardened steel according to Claim 1 wherein the matrix has a microstructure comprising greater than or equal to about 90 vol.% martensite and a balance comprising residual austenite and optionally ferrite, wherein, if the balance comprises ferrite, the ferrite has a concentration greater than 0 vol. -% to less than or equal to about 5% by volume. An automobile part comprising the press hardened steel according to Claim 1 . A method of making a press hardened steel component, the method comprising: Heating a blank to a temperature greater than or equal to about 880 ° C to less than or equal to about 950 ° C 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% by weight to less than or equal to about 5% by weight; 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 remnant of iron (Fe), wherein the combined concentration of the Mn, Cr, and Cu is greater than or equal to about 2 weight percent; Pressing the heated blank into a die to form a structure having a predetermined shape from the heated blank; and Quenching the structure to a temperature less than or equal to about a martensite finish temperature (Mf) of the steel composition and 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 Cr, Si, and Cu and configured to resist oxidation, and 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 is free of any coating. Procedure according to Claim 6 wherein the blank and the matrix further comprise: nickel (Ni) at a concentration of greater than 0% by weight to less than or equal to about 5% by weight, and wherein the oxide layer further comprises oxides of the Ni. Procedure according to Claim 7 wherein the combined concentration of the Mn, Cr, Cu and Ni in the blank and in the matrix is greater than or equal to about 2 wt%. Procedure according to Claim 6 wherein the microstructure of the press hardened steel component further comprises greater than about 0% by volume to less than or equal to about 10% by volume of retained austenite and more than or equal to about 0% by volume to less than or equal to about 5% by volume Includes ferrite. Procedure according to Claim 6 wherein the press hardened steel component is an automobile part selected from the group consisting of a wheel, a pillar, a bracket, a bumper, a roof rail, a swing rail, a rocker, a control arm, a beam, a tunnel, a step, a subframe member, a pan, a plate and a reinforcement plate.

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