Patent Application
20230140215
This application claims the benefit and priority of Chinese Application No. 202111271386.6, filed Oct. 29, 2021. The entire disclosure of the above application is incorporated herein by reference.
This section provides background information related to the present disclosure which is not necessarily prior art.
In various manufacturing processes, such as manufacturing in the automobile industry, sheet metal panels or blanks may be stamped, where the sheet metal panel is pressed between a pair of dies, to create a complex three-dimensional shaped component. A sheet metal blank is usually first cut from a coil of metal material. The sheet metal material is chosen for its desirable characteristics, such as strength, ductility, and other properties related to the metal alloy.
Press-hardening steel (PHS), also referred to as “hot-stamped steel” or “hot-formed steel,” is one of the strongest steels used for automotive body structural applications. In certain applications, PHS may have tensile strength properties of about 1,500 megapascal (MPa). Such steel has desirable properties, including forming steel components with significant increases in strength-to-weight ratios. PHS components have become ever more prevalent in various industries and applications, including general manufacturing, construction equipment, automotive or other transportation industries, home or industrial structures, and the like. For example, when manufacturing vehicles, especially automobiles, continual improvement in fuel efficiency and performance is desirable; therefore, PHS components have been increasingly used. PHS components are often used for forming load-bearing components, like door beams, which usually require high strength materials. Thus, the finished state of these steels is designed to have high strength and enough ductility to resist external forces, such as, resisting intrusion into the passenger compartment without fracturing so as to provide protection to the occupants.
Many PHS processes involve austenitization of a sheet steel blank in a furnace, immediately followed by pressing and quenching of the sheet in dies. Austenitization is typically conducted in the range of about 880° C. to 950° C. PHS processes may be indirect or direct. In the direct method, the PHS component is formed and pressed simultaneously between dies, which quenches the steel. In the indirect method, the PHS component is cold-formed to an intermediate partial shape before austenitization and the subsequent pressing and quenching steps. The quenching of the PHS component hardens the component by transforming the microstructure from austenite to martensite.
The PHS may be quenches using differential cooling, in which local adjustments of the strength and elongation properties in the PHS component may be accomplished by using different cooling conditions. Cooling rates above 27 K/s in a boron-manganese steel (e.g., 22MnB5) lead to the formation of a martensitic structure, while lower cooling rates force the formation of a more ductile microstructure with lower strength, such asbainite and ferrite-pearlite. Accordingly, methods of producing tailored quenching and alloy compositions to improve strength and/or ductility are desired.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
In certain aspects, the present disclosure relates to method of selectively quenching at least one region of a shaped steel object. The method may include pressing and quenching a heated blank in a die to form the shaped steel object. The pressing and quenching includes selectively cooling a first portion of a heated blank at a first cooling rate and selectively cooling a second portion of the heated blank at a second cooling rate, the first cooling rate being less than the second cooling rate. The shaped steel object has an alloy composition including: chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 6 wt. %; carbon (C) at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.5 wt. %; manganese (Mn) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 3 wt. %; silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %; nitrogen (N) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.01 wt. %; nickel (Ni) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; copper (Cu) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; molybdenum (Mo) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; vanadium (V) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 1 wt. %; niobium (Nb) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.1 wt. %; and a balance of the alloy composition being iron.
In one aspect, after the selectively cooling the first portion and selectively cooling the second portion, the first portion has a greater ductility than the second portion.
In one aspect, after the selectively cooling the first portion, the first portion has a bending angle greater than or equal to 90°.
In one aspect, the alloy composition further includes at least one of nickel, molybdenum, copper, niobium, vanadium, or titanium.
In one aspect, the die includes a first shell having a first surface region corresponding to the first region of the heated blank and a second surface region corresponding to the second region of the heated blank. The first surface region of the first shell includes a first material with a lower thermal conductivity than a second material of the second surface region.
In one aspect, the die includes a first shell having a first region configured to interface with the first portion of the heated blank and a second region configured to interface with the second portion of the heated blank. The first region of the first shell includes a first plurality of cooling channels and the second region includes a second plurality of cooling channels. The first plurality of cooling channels is distinct from the second plurality of cooling channels.
In one aspect, the die includes a first shell having a first surface region configured to interface with the first portion of the heated blank and a second surface region configured to interface with the second region of the heated blank. The first surface region has a first surface roughness that is lower than a second surface roughness of the second surface region.
In one aspect, the die includes a first shell having a first region configured to interface with the first portion of the heated blank and a second region configured to interface with the second portion of the heated blank. The first region of the first shell is configured to have a first contact pressure with the first portion of the heated blank that is greater than a second contact pressure of the second region with the second portion of the heated blank.
In one aspect, the die includes a first shell having a first region configured to interface with the first portion of the heated blank and a second region configured to interface with the second portion of the heated blank. The first region of the first shell has a first die gap and the second region has a second die gap that is distinct from the first die gap.
In one aspect, after selectively cooling the first portion of the heated blank, the first portion has a microstructure including greater than or equal to 0.1% by volume to less than or equal to 12% by volume retained austenite in a matrix of martensite. Further, the second portion of the cooled heated blank has a microstructure including greater than or equal to 0.1% by volume to less than or equal to 5% by volume retained austenite in a matrix of martensite.
In one aspect, the first cooling rate is greater than or equal to 20K/s to less than or equal to 60K/s.
In certain other aspects, the present disclosure relates to a method of selectively quenching at least one region of a shaped steel object. The method includes pressing and quenching a heated blank disposed in a die to form the shaped steel object. The pressing and quenching includes selectively cooling the heated blank at a first cooling rate less than 60 K/s. The shaped steel object has an alloy composition including: chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 6 wt. %; carbon (C) at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.5 wt. %; manganese (Mn) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 3 wt. %; silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %; nitrogen (N) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.01 wt. %; nickel (Ni) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; copper (Cu) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; molybdenum (Mo) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; vanadium (V) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 1 wt. %; niobium (Nb) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.1 wt. %; and a balance of the alloy composition being iron.
In one aspect, after the selectively cooling the heated blank, the press hardened blank has a microstructure including greater than or equal to 0.1% by volume to less than or equal to 12% by volume retained austenite in a matrix of martensite.
In one aspect, the alloy composition further includes at least one of nickel, molybdenum, copper, niobium, vanadium, or titanium.
In one aspect, the pressing and quenching occurs for greater than or equal to 6 seconds to less than or equal to 10 seconds.
In one aspect, a die contact pressure for the heated blank is greater than or equal to 0.5 MPa to less than or equal to 4 MPa.
In yet other aspects, the present disclosure relates to a method of selectively quenching at least one region of a shaped steel object. The method includes pressing and quenching a heated blank in a die for greater than or equal to 6 seconds to less than or equal to 10 seconds having a die contact pressure of greater than or equal to 0.5 MPa to less than or equal to 4 MPa to form the shaped steel object. The pressing and quenching includes selectively cooling a first portion of a heated blank at a first cooling rate of greater than or equal to about 20K/s to less than or equal to about 60K/s. The method also includes selectively cooling a second portion of the heated blank at a second cooling rate, the first cooling rate being less than the second cooling rate. The shaped steel object includes an alloy composition including: chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 6 wt. %; carbon (C) at a concentration of greater than or equal to about 0.01 wt. % to less than or equal to about 0.5 wt. %; manganese (Mn) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 3 wt. %; silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %; nitrogen (N) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.01 wt. %; nickel (Ni) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; copper (Cu) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; molybdenum (Mo) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %; vanadium (V) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 1 wt. %; niobium (Nb) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.1 wt. %; and a balance of the alloy composition being iron.
In one aspect, after the selectively cooling the first portion and selectively cooling the second portion, the first portion has a greater ductility than the second portion.
In one aspect, after the selectively cooling the first portion, the first portion has a bending angle greater than or equal to 90°.
In one aspect, after the selectively cooling the first portion of the heated blank, the first portion has a microstructure including greater than or equal to 0.1% by volume to less than or equal to 12% by volume retained austenite in a matrix of martensite, and the second portion of the cooled heated blank has a microstructure including greater than or equal to 0.1% by volume to less than or equal to 5% by volume retained austenite in a matrix of martensite.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.
Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.
When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.
Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.
Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.
As used herein, all amounts are weight % (or mass %), unless otherwise indicated.
In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.
As referred to herein, the word “substantially,” when applied to a characteristic of a composition or method of this disclosure, indicates that there may be variation in the characteristic without having a substantial effect on the chemical or physical attributes of the composition or method.
Example embodiments will now be described more fully with reference to the accompanying drawings.
The present disclosure pertains to methods of forming high-strength components from a novel press hardening steels. A press hardening steel is one that has an ultimate tensile strength of greater than or equal to exactly or about 1,000 megapascals (MPa), for example, greater than or equal to exactly or about 1,400 MPa to less than or equal to exactly or about 2,200 MPa.
In various embodiments, the press hardening steel may be the alloy composition as in Table 1, although the disclosure of the inventive concepts is not limited thereto. In various embodiments, the alloy composition of Table 1 may be used to form a press hardened steel component with an ultimate tensile strength of greater than or equal to exactly or about 1,300 MPa to less than or equal to exactly or about 2,000 MPa.
The alloy composition of the press hardening steel may comprise silicon (Si) at a concentration of greater than or equal to exactly or about 0.5 wt. % to less than or equal to exactly or about 2 wt. %, greater than or equal to exactly or about 0.6 wt. % to less than or equal to exactly or about 1.8 wt. %, or greater than or equal to exactly or about 0.8 wt. % to less than or equal to exactly or about 1.5 wt. %. For example, in various embodiments the alloy composition of the press hardening steel may comprise Si at a concentration of exactly or about 0.5 wt. %, exactly or about 0.6 wt. %, exactly or about 0.7 wt. %, exactly or about 0.8 wt. %, exactly or about 0.9 wt. %, exactly or about 1 wt. %, exactly or about 1.1 wt. %, exactly or about 1.2 wt. %, exactly or about 1.3 wt. %, exactly or about 1.4 wt. %, exactly or about 1.5 wt. %, exactly or about 1.6 wt. %, exactly or about 1.7 wt. %, exactly or about 1.8 wt. %, exactly or about 1.9 wt. %, or exactly or about 2 wt. %. This high amount of Si in the alloy composition improves oxidation resistance, permits a lower amount of chromium to be added while still not requiring coating or shot blasting after forming, and prevents, inhibits, or decreases cementite formation during a quench and partitioning process.
The alloy composition of the press hardening steel may also comprise chromium (Cr). The alloy composition of the press hardening steel may comprise Cr at a concentration of greater than or equal to exactly or about 0.5 wt. % to less than or equal to exactly or about 6 wt. %, greater than or equal to exactly or about 1.5 wt. % to less than or equal to exactly or about 5 wt. %, greater than or equal to exactly or about 1.75 wt. % to less than or equal to exactly or about 4 wt. %, greater than or equal to exactly or about 2 wt. % to less than or equal to exactly or about 3 wt. %, or greater than or equal to exactly or about 2 wt. % to less than or equal to exactly or about 2.5 wt. %. For example, in various embodiments the alloy composition of the press hardening steel may comprise Cr at a concentration of exactly or about 0.5 wt. %, exactly or about 1 wt. %, exactly or about 1.5 wt. %, exactly or about 2 wt. %, exactly or about 2.5 wt. %, exactly or about 3 wt. %, exactly or about 3.5 wt. %, exactly or about 4 wt. %, exactly or about 4.5 wt. %, exactly or about 5 wt. %, exactly or about 5.5 wt. %, or exactly or about 6 wt. %.
The alloy composition of the press hardening steel may also comprise carbon (C) at a concentration of greater than or equal to exactly or about 0.01 wt. % to less than or equal to exactly or about 0.4 wt. %, greater than or equal to exactly or about 0.01 wt. % to less than or equal to exactly or about 0.35 wt. %, greater than or equal to exactly or about 0.10 wt. % to less than or equal to exactly or about 0.4 wt. %, greater than or equal to exactly or about 0.15 wt. % to less than or equal to exactly or about 0.3 wt. %, greater than or equal to exactly or about 0.15 wt. % to less than or equal to exactly or about 0.25 wt. %, or greater than or equal to exactly or about 0.15 wt. % to less than or equal to exactly or about 0.2 wt. %. For example, in various embodiments the alloy composition of the press hardening steel may comprise C at a concentration of exactly or about 0.01 wt. %, exactly or about 0.05 wt. %, exactly or about 0.1 wt. %, exactly or about 0.2 wt. %, exactly or about 0.3 wt. %, exactly or about 0.35 wt. %, or exactly or about 0.4 wt. %.
The alloy composition of the press hardening steel may include manganese (Mn) at a concentration of greater than or equal to exactly or about 0 wt. % to less than or equal to exactly or about 3 wt. %, greater than or equal to exactly or about 0.25 wt. % to less than or equal to exactly or about 2.5 wt. %, greater than or equal to exactly or about 0.5 wt. % to less than or equal to exactly or about 2 wt. %, greater than or equal to exactly or about 0.75 wt. % to less than or equal to exactly or about 1.5 wt. %, or greater than or equal to exactly or about 1 wt. % to less than or equal to exactly or about 1.5 wt. %. In some example embodiments, the alloy composition of the press hardening steel is substantially free of Mn. As used herein, “substantially free” refers to trace component levels, such as levels of less than or equal to exactly or about 1.5%, less than or equal to exactly or about 1%, less than or equal to exactly or about 0.5%, or levels that are not detectable. In various embodiments, the alloy composition of the press hardening steel is substantially free of Mn or comprises Mn at a concentration of less than or equal to exactly or about 0.5 wt. %, less than or equal to exactly or about 1 wt. %, less than or equal to exactly or about 1.5 wt. %, less than or equal to exactly or about 2 wt. %, less than or equal to exactly or about 2.5 wt. %, or less than or equal to exactly or about 3 wt. %. A balance of the alloy composition of the press hardening steel is iron. However, the inventive concepts are not limited to the above compositions, for example, other metals may be included, for example, nitrogen, nickel, copper, molybdenum, vanadium, niobium and the like. For example, the alloy composition of the press hardening steel may further include at least one of nitrogen (N) at a concentration of greater than or equal to exactly or about 0 wt. % to less than or equal to exactly or about 0.01 wt. %, nickel (Ni) at a concentration of greater than or equal to exactly or about 0 wt. % to less than or equal to exactly or about 5 wt. %, copper (Cu) at a concentration of greater than or equal to exactly or about 0 wt. % to less than or equal to exactly or about 5 wt. %, molybdenum (Mo) at a concentration of greater than or equal to exactly or about 0 wt. % to less than or equal to exactly or about 5 wt. %, vanadium (V) at a concentration of greater than or equal to exactly or about 0 wt. % to less than or equal to exactly or about 1 wt. %, niobium (Nb) at a concentration of greater than or equal to exactly or about 0 wt. % to less than or equal to exactly or about 0.1 wt. %, or a combination thereof.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mn, Fe, and any impurities cumulatively present at less than or equal to or about 0.5 weight %. In certain variations, it will be understood that cumulative impurity levels may instead be less than or equal to or about 0.4 wt. %, optionally less than or equal to or about 0.3 wt. %, optionally less than or equal to or about 0.2 wt. %, and optionally less than or equal to or about 0.1 wt. %. In another embodiment, the alloy composition consists of Si, Cr, C, Mn, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mn, Al, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Mn, Al, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mn, Al, Mo, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Mn, Al, Mo, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mn, Al, Mo, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Mn, Al, Mo, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mn, Al, Mo, Ni, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Mn, Al, Mo, Ni, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mn, N, Ni, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Mn, N, Ni, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mn, Al, N, Mo, Ni, B, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Mn, Al, N, Mo, Ni, B, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
In one embodiment, the alloy composition consists essentially of Si, Cr, C, Mo, B, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %. In another embodiment, the alloy composition consists of Si, Cr, C, Mo, B, Nb, V, Fe, and any impurities cumulatively present at less than or equal to about 0.5 weight %.
By way of non-limiting example, the methods of the present disclosure pertain to certain press hardening steels. In certain aspects, such press hardening steels have a microstructure with retained austenite embedded in a primary matrix of martensite after a hot stamping and/or press-hardening process including tailored cooling process. For example, as shown in
By way of background, hot forming of the selected press hardening steels, may be conducted as follows. A sheet or blank of press hardening steel may be formed into a three-dimensional component via hot forming. Such a high-strength three-dimensional component may be incorporated into a device, such as a vehicle. While the high-strength structures are particularly suitable for use in components of an automobile or other vehicles (e.g., motorcycles, boats, tractors, buses, motorcycles, mobile homes, campers, and tanks), they may also be used in a variety of other industries and applications, including aerospace components, consumer goods, office equipment and furniture, industrial equipment and machinery, farm equipment, or heavy machinery, by way of non-limiting example. Non-limiting examples of components and vehicles that can be manufactured by the current technology include automobiles, tractors, buses, motorcycles, boats, mobile homes, campers, and tanks. Other exemplary structures that have frames that can be manufactured by the current technology include construction and buildings, such as houses, offices, bridges, sheds, warehouses, and devices. The high-strength structural automotive component may be selected from the group consisting of: rocker rails, structural pillars, A-pillars, B-pillars, C-pillars, D-pillars, bumper, hinge pillars, cross-members, body panels, vehicle doors, roofs, hoods, trunk lids, engine rails, and combinations thereof in certain variations.
Press hardening steels that are press-hardened into press hardening steel components may require cathodic protection. The press hardening steel component may be coated prior to applicable pre-cold forming or before austenitization. Coating the press hardening steel component provides a protective layer to the underlying steel component. Such coatings typically include an aluminum-silicon alloy and/or zinc. 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, liquid metal embrittlement (LME) may occur when a metallic system is exposed to a liquid metal, such as zinc, during forming at high temperature, resulting in potential cracking and a reduction of total elongation or diminished ductility of a material. LME may also result in decreased ultimate tensile strength. To avoid LME in conventional press hardening steel processes for conventional press hardening steels, numerous additional processing steps are conducted, adding processing time and expense.
In some example embodiments, the press hardening steel component is coating free. For example, the alloy composition of Table 1 may have sufficient corrosion resistance so as to not require cathodic protection.
During hot forming, the press hardening steel, in the form of, for example, a sheet blank, may be introduced into a furnace or other heat source. The amount of heat applied to the sheet blank heats and soaks the sheet blank to a temperature of at least the austenitization temperature of the selected press hardening steel. In certain aspects, the press hardening steel has an austenitization temperature (T1) of greater than or equal to exactly or about 880° C. to less than or equal to exactly or about 950° C. The sheet blank is soaked for a period long enough to austenitize the press hardening steel to a desired level.
After exiting the furnace, the sheet blank can be transferred into a stamping press. The stamping press may include a die having a cooling system or mechanism. For example, the die(s) may have a water-cooling system, which are well known in the art. The die is designed to form a desired final three-dimensional shape of the component from the austenitized sheet blank. The die may include a first forming die and a second forming die that are brought together to form the desired final shape of the three-dimensional component therebetween.
The cooled dies thus may quench the formed sheet blank in a controlled manner across surfaces of the formed component to cause a phase transformation from austenite to martensite. Therefore, the first and second die may cooperate to function as a heat sink to draw heat from, and otherwise quench, the formed component. In certain variations, the press hardening steel has a critical cooling rate that is the slowest rate of cooling to produce desired material properties in the component. Different regions of the component may have different desired material properties, and thus different critical cooling rates.
In one aspect, a first critical cooling rate for a first region of the press hardening steel may be greater than or equal to exactly or about 40 Kelvin/second (K/s) to less than or equal to exactly or about 150 K/s. A second critical cooling rate for a second region of the press hardening steel may be greater than or equal to exactly or about 20 Kelvin/second (K/s) to less than or equal to exactly or about 60 K/s. The selected press hardening steels of the present disclosure allow for different regions to having different (e.g., tailored) cooling rates to produce different materials properties while maintaining integrity of the component. For example, the second critical cooling rate may improve the toughness and crack formation resistance of a region of the component and make the component more resistant to failure during high stress/strain events. However, the die may still be cooled as quickly as possible to maintain processing through-put and desired materials properties.
During hot forming, the sheet blank may be introduced into a furnace or other heat source. The amount of heat applied to the sheet blank heats and soaks the sheet blank to a temperature of at least the austenitization temperature of the selected press hardening steel. In certain aspects, the press hardening steel has an austenitization temperature (T1) of greater than or equal to exactly or about 880° C. to less than or equal to exactly or about 950° C. The sheet blank is soaked for a period long enough to austenitize the press hardening steel to a desired level.
After exiting the furnace, the sheet blank can be transferred into a stamping press. The stamping press may include a die having a cooling system or mechanism. For example, the die(s) may have a water-cooling system, surfaces with at least one thermal conductivity, and the like. The die is designed to form a desired final three-dimensional shape of the component from the austenitized sheet blank. The die may include a first forming die and a second forming die that are brought together to form the desired final shape of the three-dimensional component therebetween.
The cooled dies thus may quench the formed sheet blank in a controlled manner across surfaces of the formed component to cause a phase transformation from austenite to martensite. Therefore, the first and second die may cooperate to function as a heat sink to draw heat from, and otherwise quench, the formed component. In certain variations, the dies may have different cooling rates at different regions of the formed sheet blank. In certain variations, the press hardening steel has a critical cooling rate that is the slowest rate of cooling to produce a hardened martensitic condition of less than or equal to exactly or about 100 volume % in the component (e.g., substantially fully martensite). By “substantially fully” it is meant that greater than or equal to exactly or about 80%, greater than or equal to exactly or about 85%, greater than or equal to exactly or about 90%, or greater than or equal to exactly or about 95% of the microstructure is martensite. The selected press hardening steels of the present disclosure allow for different regions to having different (e.g., tailored) cooling rates to produce different materials properties while maintaining integrity of the component. However, it should be appreciated that press hardening steel may have lower critical cooling rates, such as exactly or about 10 K/s.
A method of press-hardening a press hardening steel is thus provided that comprises creating a blank having a press hardening steel. The blank is heated to a temperature of greater than or equal to exactly or about 880° C. to less than or equal to exactly or about 950° C. to at least partially austenitize the press hardening steel. The blank is then press hardened and tailor quenched in a die to form a press-hardened component having a tailored multi-phase microstructure, such as the example embodiment multi-regional microstructures 28 and 32 illustrated in
As shown in
A second quenched region 32 of the press hardening steel 20A has undergone a different cooling rate than the first quenched region 28, and as such may have less than or equal to exactly or about 12% by volume of retained austenite 24, optionally greater than or equal to exactly or about 1% by volume to less than or equal to exactly or about 12% by volume, and in certain aspects, exactly or about 7% by volume of retained austenite in the matrix of martensite 22. As can be seen, austenite is at least partially transformed into martensite in the first quenched region 28. A transition region 34 between the first quenched region 28 and the second quenched lower region 32 may be formed, depending on the nature and extent of the tailored quenching process.
In this manner, the quenched regions can exhibit desired hardness levels, while also selectively exhibits greater ductility and/or energy absorption properties. Retained austenite improves ductility as it transforms to martensite during deformation, and hence delaying fracture. Therefore, retained austenite also improves energy absorption.
In certain embodiments, the after heating, the press hardening steel 20A may be placed in a die 40. The die 40 may have a top die shell 41 and a bottom die shell 42. The press hardening steel 20A may be pressed into the shape of a component by the contact pressure of the die 40. The top die shell 41 may have a first region 411 which may cool the press hardening steel 20A at a first cooling rate, and a second region 412 which may cool the press hardening steel 20A at a second cooling rate. The bottom die shell 42 may have a first region 421 which may cool the press hardening steel 20A at a first cooling rate, and a second region 422 which may cool the press hardening steel 20A at a second cooling rate. In some example embodiments, only the top die shell 41 may have the first and second regions 411, 412, and in some other example embodiments, only the bottom die shell 42 may have the first and second regions 421, 422.
The first regions 411 and 421 may have a lower cooling rate than the second regions 412 and 422. The first cooling rate may be the first critical cooling rate from above, and the second cooling rate may be the second critical cooling rate from above.
The first regions 411 and 421 may be in a region of the die 40 which bends the press hardening steel greater than or exactly or about 90 degrees, or greater than or exactly or about 45 degrees, may have a first cooling rate leading to greater ductility and/or energy adsorption properties.
In certain variations, at least one of the tailor quenched region(s) may have a greater ultimate tensile strength than another one of the tailor quenched region(s). By way of non-limiting example only, a representative strength in the a first tailor quenched region with a lower cooling rate may be greater than or equal to exactly or about 1,000 MPa to less than or equal to exactly or about 1,700 MPa (or, greater than or equal to exactly or about 1,200 MPa to less than or equal to exactly or about 1,500 MPa, or exactly or about 1,700 MPa) while another one of the tailor quenched region(s) with a higher cooling rate may have a strength of less than or equal to exactly or about 1,500 MPa to less than or equal to exactly or about 2,000 MPa (or, greater than or equal to exactly or about 1,700 MPa to less than or equal to exactly or about 1,900 MPa, or exactly or about 2,000 MPa). The mechanical performance of the hot stamped component may be significantly improved, such as fatigue strength and static/dynamic load bearing capability after the selective cooling process.
The selectively quenched and hardened regions may be formed on select areas of a three-dimensional press-hardened part. In various aspects, the selective cooling process is targeted at select regions of the component so as to provide at least two distinct regions having distinct microstructures. Thus, the at least one selectively quenched region has a first microstructure and is adjacent to one or more unquenched regions in the component having a second microstructure. A transition between the first and second microstructures may occur, depending on the selective cooling process employed to form the selectively quenched and hardened regions.
In certain aspects, the selective cooling is achieved by contacting one or more predetermined, or alternatively, desired, regions of a hot-component comprising a high-strength transformation induced plasticity steel with a surface of a die. In certain aspects, the contacting may be achieved b, for example, pressing a first die shell into a second die shell. In such a process, the pressed die shells may cool the hot-formed component by contacting the surface of the hot-formed component, and the first and/or second die shells having at least one thermal conductivity, at least one configuration of cooling medium tunnels (e.g., by the die including different numbers, or different numbers of cooling medium tunnels being activated), at least one surface roughness for the die shells, and combinations thereof. Certain regions of the component may undergo different cooling rates by at least one of the first and/or second die shells having different properties as discussed above. In certain embodiments, a first region may have a first cooling rate, and a second region may have a second cooling rate. For example, the first die shell may use tool steel with a first thermal conductivity in a first region, and a second thermal conductivity in a second region. In certain embodiments, the first die shell may have a first configuration of cooling medium tunnels in a first region, and a second configuration of cooling medium tunnels in a second region. In certain embodiments, the first die shell may have a first surface roughness in a first region, and a second surface roughness of cooling medium tunnels in a second region. The above example embodiments are not limiting but exemplary, for example, the second die shell may have the first and second regions, or both the first and second die shells may have first and second regions.
In certain aspects, the first cooling rate may be greater than or equal to exactly or about 20K/s to less than or equal to exactly or about 60K/s, optionally greater than or equal to exactly or about 20K/s to less than or equal to exactly or about 40K/s, optionally greater than or equal to exactly or about 40K/s to less than or equal to exactly or about 60K/s, optionally exactly or about 40K/s.
In certain aspects, the second cooling rate may be greater than or equal to exactly or about 40K/s to less than or equal to exactly or about 150K/s, optionally greater than or equal to exactly or about 50K/s to less than or equal to exactly or about 150K/s, optionally greater than or equal to exactly or about 50K/s to less than or equal to exactly or about 10K/s, optionally exactly or about 95K/s.
In certain aspects, the cooling rate may vary with time. For example, the die tool, including a first die shell and a second die shell, may have a first cooling rate and a second cooling rate. In certain embodiments, the first cooling rate may be due to the die putting the heated blank between the first die shell and the second die shell under a first contact pressure, and the second cooling rate may be due to the die putting the heated blank under a second contact pressure, the second contact pressure being lower than the first contact pressure. Based on the second contact pressure being lower than the first contact pressure, the second cooling rate may be lower than the first cooling rate. In certain embodiments, the die may have a holding time with a first cooling rate, and subsequently release the first and second die shells to reduce the contact pressure on the heated blank for a second cooling rate, and the second cooling rate may be lower than the first cooling rate. In certain embodiments, the die has a first die gap between the first die shell and the second die shell with a first cooling rate, and a second die gap between the first die shell and the second die shell with a second cooling rate, and the second cooling rate may be lower than the first cooling rate.
In certain embodiments, the die contact pressure may be greater than or equal to exactly or about 0.5 MPa to less than or equal to exactly or about 4 MPa. In certain embodiments, the die contact pressure may be greater than or equal to exactly or about 2 MPa to less than or equal to exactly or about 3 MPa. In certain embodiments, the die contact pressure may be less than or equal to exactly or about 4 MPa.
In certain embodiments, the die may hold the first die shell and the second die shell together for greater than or equal to exactly or about 6 seconds to less than or equal to exactly or about 10 seconds. In certain embodiments, the die may hold the first die shell and the second die shell together for greater than or equal to exactly or about 7 seconds to less than or equal to exactly or about 10 seconds. In certain embodiments, the die may hold the first die shell and the second die shell together for less than or equal to exactly or about 10 seconds.
In this manner, the present disclosure provides various ways of quenching selected areas on a hot-formed steel component that is made from a high-strength press hardening steel that transforms austenite to martensite. This results in tailored properties across the hot stamped steel component, with some areas (e.g., those after being cooled at a slower rate after hot forming) being more ductile than others. This permits formation of tailor blanks having tailored properties, while reducing expense by avoiding use of other more complicated/expensive solutions to achieve tailored properties, like tailor rolled blanks and tailor blank assemblies that are welded. In certain aspects, a press hardening steel component has tailored properties that reduces mass (compared to a press hardening steel part with monolithic properties) at reduced cost (compared to other solutions for tailored properties, such as tailor-rolled/tailor-welded blanks).
With reference to
The method 80 comprises obtaining a coil 82 of a metal material having an alloy composition according to the present technology and cutting a blank 84 from the coil 82. The method also comprises austenitizing the blank by heating the blank in a furnace 86 to a temperature above its Ac3 temperature (e.g., the temperature at which ferrite is substantially completely transformed to austenite) to form a heated blank comprising austenite. Optionally by a robotic arm 88, the heated blank is transferred to a press 90. Here, the method 80 comprises stamping the heated blank into a predetermined (e.g., desired) shape to form a stamped object, and quenching the stamped object to form a shaped steel object 92, wherein the shaped steel object 92 comprises martensite and austenite. The method 80 is free of a pre-oxidation step, of a coating step, and of a descaling step (e.g., shot blasting).
In one example embodiment, the quenching is performed by cooling a first portion of the shaped object at a first cooling rate described above and a second portion of the shaped object at a second cooling rate described above until the stamped object reaches a temperature below a temperature at which martensite formation finishes during cooling (Mf) temperature of the alloy composition. Here, the shaped steel object has a tailored microstructure including a portion that contains retained austenite at a first volume percentage in a martensite matrix, and a portion that contains retained austenite at a second volume percentage in a martensite matrix, the second volume percentage being lower than the first, as discussed above.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202111271386.6 | Oct 2021 | CN | national |
