US20160145731A1

US20160145731A1 - Controlling Liquid Metal Embrittlement In Galvanized Press-Hardened Components

Info

Publication number: US20160145731A1
Application number: US14/627,579
Authority: US
Inventors: Anil K. Sachdev; Tyson W. BROWN
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2014-11-26
Filing date: 2015-02-20
Publication date: 2016-05-26
Also published as: CN105734413A

Abstract

Methods for press hardening galvanized, pre-treated, optionally non-annealed steel alloys are provided. The press-hardened steel alloy may have an ultimate tensile strength (UTS) of at least about 1,000 MPa and is substantially free of liquid metal embrittlement (LME). The press-hardened steel alloy may be further quenched to below room temperature. The press-hardened steel may have a multi-phase microstructure of ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/085,081, filed on Nov. 26, 2014. The entire disclosure of the above application is incorporated herein by reference.

FIELD

The present disclosure relates to methods of press-hardening galvanized, pre-treated, optionally non-annealed, steel alloys to form high-strength press-hardened components that are substantially free of liquid metal embrittlement.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.
Press-hardened steel (PHS), also referred to as “hot-stamped steel,” is one of the strongest steels used for automotive body structural applications, having tensile strength properties on the order of about 1,500 mega-Pascal (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, thus PHS components have been increasingly used. PHS components are often used for forming load-bearing components, like door beams, which usually require high strength materials. Thus, the finished state of these steels are designed to have high strength and enough ductility to resist external forces, for example, to resist intrusion into the passenger compartment without fracturing so as to provide protection to the occupants. Moreover, galvanized PHS components may provide cathodic protection.
Typical PHS processes involve austenitization in a furnace of a sheet steel blank immediately followed by pressing and quenching of the sheet in dies. There are two main types of PHS processes: indirect and direct. Austenitization is typically conducted in the range of about 900° C. Under the direct method, the PHS component is formed and pressed simultaneously between dies, which quenches the steel. Under 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. To the extent the PHS component is uncoated, an oxide layer forms during the transfer from the furnace to the dies. After quenching, therefore, the oxide must be removed from the PHS component and the dies. The oxide is typically removed by shot blasting.
The PHS component may be coated prior to applicable pre-cold forming (if the indirect process is used) or austenitization. Coating the PHS component provides a protective layer (e.g., galvanic protection) 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.
Liquid metal embrittlement (LME) may occur when a metallic system is exposed to a liquid metal, such as zinc, during forming, 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 of zinc-coated PHS components, the indirect method (i.e., cold forming before austenitization) is typically employed. Such a method includes annealing a steel prior to hot dipping in a zinc bath for galvanization. Further, a pre-forming step is used prior to heating for austenitizing to reduce the effects of Zn embrittlement. As additional steps are required, the indirect method of press hardening, however, is not as efficient as the direct method. Thus, there is an ongoing need for PHS processes further streamlining the ability to provide via the direct press-hardening method a galvanized PHS component substantially free of LME.

SUMMARY

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.
In certain aspects, the present disclosure contemplates a method of press-hardening a steel alloy. The method comprises creating a blank from a galvanized, pre-treated steel alloy. The blank is heated to a temperature of less than or equal to about 782° C. to partially austenitize the galvanized steel alloy. The blank is then press hardened to form a press-hardened component. The press-hardened component has a strength (e.g., ultimate tensile strength, UTS) of greater than or equal to about 1,000 MPa and is substantially free of liquid metal embrittlement. In certain aspects, the press-hardened component may have a strength (UTS) of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa. In certain variations, the press-hardened component is quenched to below room temperature after the press hardening. In certain other variations, the pre-treated, galvanized steel alloy is a cold-rolled steel alloy that is not annealed prior to creating the blank. In certain aspects, the galvanized steel may be galvanized by hot-dipping. Thus, the methods may further include hot-dip galvanizing a pre-treated steel alloy in a zinc galvanization bath. In other aspects, the methods may further include galvannealing the hot-dipped galvanized pretreated steel alloy. In still other aspects, the methods may further include electrogalvanizing the pretreated steel alloy. The steel alloy may comprise carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %. The steel alloy may comprise manganese at greater than 0 weight % to less than or equal to about 6 weight %, and, in certain variations, manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %. The steel alloy may further comprise silicon at greater than 0 weight % to less than or equal to about 1 weight %. In certain variations, the steel alloy may comprise carbon at about 0.3 weight % and manganese at about 1.5 weight %. The press-hardened component may have a strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa. The heating may occur at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C. The press-hardened component may comprise a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%.
In other aspects, a method of press-hardening a galvanized steel alloy is provided that comprises creating a blank from a cold-rolled, non-annealed, galvanized steel alloy. The blank is heated to a temperature of less than or equal to about 782° C. to partially austenitize the galvanized steel alloy. The blank is then press hardened to form a press-hardened steel component, where the press-hardened component has a strength (e.g., ultimate tensile strength, UTS) of greater than or equal to about 1,000 MPa and is substantially free of liquid metal embrittlement. In certain aspects, the steel alloy comprises carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight %, or in certain variations, the steel alloy may optionally include manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight % and/or carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %. The steel alloy may further comprise silicon at greater than 0 weight % to less than or equal to about 1 weight %. In other variations, the steel alloy may comprise carbon at about 0.3 weight % and manganese at about 1.5 weight %. The press-hardened component is substantially free of liquid metal embrittlement. The press-hardened component may also be quenched to below room temperature after the press hardening. In certain variations, the cold-rolled, non-annealed, galvanized steel may be galvanized by hot-dipping. In other aspects, the methods may further include galvannealing the cold-rolled steel alloy. In yet other aspects, the methods may involve electrogalvanizing the pre-treated steel. The press-hardened component may have a strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa. The heating may occur at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C. The press-hardened component may comprise a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%.
In yet other aspects, a method of press-hardening a galvanized steel alloy is provided that comprises creating a blank from a cold-rolled, non-annealed, galvanized steel alloy. The blank is heated to a temperature of less than or equal to about 782° C. to partially austenitize the galvanized steel alloy. The blank is then press hardened to form a press-hardened component comprising a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. The press-hardened component is substantially free of liquid metal embrittlement. In certain variations, the press-hardened component is also quenched to below room temperature after the press hardening. In certain variations, the cold-rolled, non-annealed, galvanized steel may be galvanized by hot-dipping. In other aspects, the methods may further include galvannealing the cold-rolled steel alloy. In yet other aspects, the methods may involve electrogalvanizing the pre-treated steel. The steel alloy may comprise carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight %, or in certain variations, the steel alloy may optionally include manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight % and/or carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %. The steel alloy may further comprise silicon at greater than 0 weight % to less than or equal to about 1 weight %. In other variations, the steel alloy may comprise carbon at about 0.3 weight % and manganese at about 1.5 weight %. The press-hardened component may have a strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa. The heating may occur at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.
In certain variations, the method further consists essentially of uncoiling a cold-rolled non-annealed coil comprising the steel alloy and hot-dip galvanizing the cold-rolled non-annealed steel alloy to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy, then uncoiling and creating a blank from the cold-rolled, non-annealed hot-dipped galvanized steel alloy before the heating.
In another aspect, the method may consist essentially of uncoiling a cold-rolled non-annealed coil comprising the steel alloy and hot-dip galvanizing the cold-rolled non-annealed steel alloy in a zinc galvanization bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy, then uncoiling and creating a blank from the cold-rolled, non-annealed hot-dipped galvanized steel alloy followed by the heating step.
In yet other variations, the method further consists essentially of uncoiling a cold-rolled non-annealed coil comprising a steel alloy and hot-dip galvanizing the cold-rolled non-annealed steel alloy in a zinc galvanization bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy, then uncoiling and creating a blank from the cold-rolled, non-annealed hot-dipped galvanized steel alloy before the heating step. The method further includes quenching the press-hardened component after the press hardening step.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

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

FIG. 1 shows a representative automotive A-pillar manufactured according to an aspect of the present invention;

FIG. 2 shows a representative automotive B-pillar manufactured according to an aspect of the present invention;

FIG. 3 shows a conventional process for forming a hot-dipped galvanized press hardened steel (PHS) component;

FIG. 4 shows an exemplary process for providing a hot-dipped galvanized, cold-rolled, non-annealed steel alloy in accordance with certain aspects of the present disclosure;

FIG. 5 shows an exemplary process for providing a hot-dipped galvanized, austenitized, steel alloy in accordance with certain other aspects of the present disclosure; and

FIG. 6 is a schematic chart depicting ultimate tensile strengths that may be achieved depending on the austenitization temperature according to known steel alloys.

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

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying 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, integers, steps, operations, elements, 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. The 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.
It should be understood for any recitation of a method, composition, device, or system that “comprises” certain steps, ingredients, or features, that in certain alternative variations, it is also contemplated that such a method, composition, device, or system may also “consist essentially of” the enumerated steps, ingredients, or features, so that any other steps, ingredients, or features that would materially alter the basic and novel characteristics of the invention are excluded therefrom.
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. If, for some reason, the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein may indicate a possible variation of up to 5% of the indicated value or 5% variance from usual methods of measurement.
As used herein, the term “composition” refers broadly to a substance containing at least the preferred metal elements or compounds, but which optionally comprises additional substances or compounds, including additives and impurities. The term “material” also broadly refers to matter containing the preferred compounds or composition.
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.
The present disclosure provides methods of press-hardening a galvanized, pre-treated steel alloy to form a press-hardened component having high strength and lacking liquid metal embrittlement. Referring first to FIGS. 1 and 2, automotive structural components, such as the A-pillar 10 and the B-pillar 20 are shown that can be produced from a press-hardened steel component comprising a galvanic coating comprising zinc that is formed from a galvanized, pre-treated steel alloy blank. In certain variations, such a press-hardened steel component comprises a galvanic coating comprising zinc that is formed from a hot-dipped galvanized, cold-rolled, non-annealed steel alloy blank (e.g., that is not annealed or subjected to any annealing process prior to creating the blank). In certain variations, the cold-rolled, non-annealed, galvanized steel may be galvanized by hot-dipping. In other aspects, the methods may further include galvannealing the cold-rolled steel alloy. In yet other aspects, the methods may involve electrogalvanizing the pre-treated steel. It will be appreciated by those skilled in the art that numerous other components may be fabricated by the methods of the present invention, and that such additional components are deemed to be within the scope of the present invention. Thus, while exemplary components are illustrated and described throughout the specification, it is understood that the inventive concepts in the present disclosure may also be applied to any structural component capable of being formed of galvanized, pre-treated steel alloy, including those used in vehicles, like automotive applications including, but not limited to, pillars, such as hinge pillars, panels, including structural panels, door panels, and door components, interior floors, floor pans, roofs, exterior surfaces, underbody shields, wheels, storage areas, including glove boxes, console boxes, trunks, trunk floors, truck beds, lamp pockets and other components, shock tower cap, control arms and other suspension, undercarriage or drive train components, and the like. Specifically, the present disclosure is particularly suitable for any piece of hardware subject to loads or impact (e.g., load bearing) or requiring cathodic protection.
As mentioned above, the use of such galvanic coatings on press-hardened steel has a number of advantages over uncoated steel. Such a galvanic coating (e.g., comprising zinc) provides cathodic protection to the underlying steel. In addition to providing an additional measure of corrosion-resistant benefits as a barrier coating, subsequent cleaning operations following press hardening to remove scale from the die surfaces and parts are not necessary.
In various aspects, a particularly suitable, non-limiting steel is commercially available as American Steel and Iron Institute (AISI) 1530, which when modified according to certain aspects of the present disclosure may be used in an efficient streamlined press-hardening process to form a high strength PHS component. AISI 1530 comprises 0.3 weight % weight carbon and 1.5 weight % manganese. Optionally, the AISI 1530 alloy may further comprise less than or equal to about 0.05 weight % silicon, less than or equal to about to 0.03 weight % aluminum, less than or equal to about 0.04 weight % phosphorus, and less than or equal to about 0.05 weight % sulfur. In certain aspects, the present disclosure contemplates modifying such conventional steel alloy compositions so that they may have zinc galvanic coatings, yet be processed via press hardening (PHS) to form components with high strength and negligible liquid metal (e.g., zinc) embrittlement (LME).
Zinc coatings may cause LME at temperatures of greater than 782° C. However, PHS components formed from conventional steel alloys processed with a heating step in an oven heated to less than 782° C. have only about two-thirds of the ultimate tensile strength that such PHS components would have in ovens heated to at greater than or equal to about 900° C. to less than or equal to about 950° C. Thus, in minimizing temperatures to below 782° C. to avoid LME, the press hardened steels lack adequate strength. While other steps have been used to mitigate the impact of LME and to improve strength, as will be discussed further below, such steps introduce additional processing time and costs.
In accordance with certain aspects of the present disclosure, methods of forming press-hardened steels having a galvanic coating are heated to temperatures of less than or equal to about 782° C., while exhibiting both good strength and minimal LME.
In accordance with various aspects of the present disclosure, press hardened steel (PHS) components are substantially free of liquid metal embrittlement (LME). The term “substantially free” as referred to herein means that the LME microstructures and defects are absent to the extent that undesirable physical properties and limitations attendant with their presence are avoided (e.g., cracking, loss of ductility, and/or loss of strength). In certain embodiments, a PHS component that is “substantially free” of LME defects comprises less than about 5% by weight of the LME species or defects, more preferably less than about 4% by weight, optionally less than about 3% by weight, optionally less than about 2% by weight, optionally less than about 1% by weight, optionally less than about 0.5% and in certain embodiments comprises 0% by weight of the LME species or defects.
Suitable steel compositions may comprise carbon at greater than or equal to 0.1 weight %, or optionally greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % carbon, or optionally greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %. In certain aspects, steel may have manganese at greater than 0 weight % to less than or equal to about 6 weight %, optionally at greater than or equal to about 1 weight % to less than or equal to about 2 weight %, and in certain aspects, manganese is optionally present at greater than or equal to about 1 weight % to less than or equal to about 1.5 weight %. Silicon is optionally present at less than or equal to about 0.5 weight %. Aluminum is optionally present at less than or equal to about 0.01 weight %. One or more impurities in the steel alloy are cumulatively present at less than or equal to about 0.5 weight %. A balance of such a steel composition is iron.
In yet other aspects, the present disclosure contemplates steel alloy compositions suitable for providing good strength and exhibiting minimal LME when heated at temperatures below 782° C. optionally have a composition comprising carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % of the alloy. Manganese is optionally present at greater than or equal to about 1 weight % to less than or equal to about 6 weight % of the alloy. Silicon is optionally present at less than or equal to about 1 weight %. Aluminum is optionally present at greater than or equal to about 0.02 weight % to less than or equal to about 0.2 weight %. Niobium is optionally present at less than or equal to about 0.2 weight %. One or more impurities in the steel alloy are cumulatively present at less than or equal to about 0.5 weight % of the alloy, while a balance is iron.
Referring to FIG. 3, a flowchart showing the steps of a conventional press-hardening process 100 is shown. A cold rolled coil 110 of a steel alloy is annealed in an annealing chamber 120 at a temperature of about 680° C. The annealed steel alloy is then hot-dipped galvanized in a zinc galvanizing bath 130, followed by a subsequent coiling of the cold rolled, annealed, hot-dipped galvanized steel alloy to provide a cold rolled, annealed, hot-dipped galvanized steel alloy coil 140. The steel alloy coil 140 is then uncoiled and sheared to form blank 150. The blank 150 is preformed by cold forming 160 prior to austenitizing. The preformed blank is then heated in an oven 170 having a temperature of about 950° C. for a predetermined period (e.g., about 300 seconds). The preformed blank is then press hardened between dies 180 and 190 to form and simultaneously quench the PHS component 195. The PHS component 195 is then cleaned, for example, with shot blasting 200, to remove scale as necessary.
In accordance with certain aspects of the present disclosure, the methods of press-hardening a steel component contemplated use hot-dipped galvanized steel alloy but provide the ability to eliminate one or more of the following: the annealing step, the preforming step, and/or the surface cleaning step of the PHS component. Furthermore, the PHS component has high strength. Thus, the overall process according to the present disclosure desirably reduces processing time, energy requirements, and cost. Moreover, the use of the hot-dipped galvanized steel alloy according to the present disclosure eliminates much, if not all, of the likelihood of LME occurring.
As used herein, the term “pre-treated” means either or both of cold-rolling or cooling austenite from a high temperature to obtain a predetermined microstructure comprising martensite, bainite, pearlite, austenite, ferrite, and the like, including combinations thereof. Generally, when pre-treating involves cold-rolling, the cold rolling may be accomplished by methods typically known in the art to increase the steel alloy's strength by strain hardening. Generally, when pre-treating involves austenitizing, the pre-treatment involves heating the steel alloy to a temperature greater than or equal to about 900° C. to less than or equal to about 950° C. to promote austenite formation. Alternatively, the process may make use of austenite that is present from other methods known in the art involving high temperature (e.g. hot-rolling). The steel alloy comprised of austenite may then be quenched, rapidly cooled, or slowly cooled such that the steel alloy undergoes a microstructure transformation to at least one of martensite, bainite, pearlite, austenite, ferrite, and the like, including combinations thereof. In certain preferred aspects, the austenitized steel alloy is quenched to allow for martensitic transformation. Such a pre-treated alloy may then be formed into a blank for processing in accordance with certain aspects of the present disclosure.
Referring to FIG. 4, the process 210 according to one aspect of the present disclosure is shown. The steel alloy is first cold-rolled into a coil 220. Cold rolling the steel alloy increases the steel alloy's strength by strain hardening. The coil 220 of the steel alloy is then unwound and undergoes hot-dip galvanizing in a zinc galvanizing bath 230. In certain variations, while not shown, a galvannealing furnace (e.g., induction furnace) may be used after the zinc galvanizing bath 230 for galvannealing the galvanic coating. Notably, annealing (e.g., as shown in the annealing furnace 120 in FIG. 3) prior to hot-dip galvanizing in the zinc galvanizing bath 230 is not required in this process. Thus, a non-annealed cold-rolled steel alloy may be directly introduced into the zinc galvanizing bath 230.
Continuous hot-dip galvanizing is used to coat the steel alloy. The coating is applied by passing the uncoiled steel alloy through the zinc galvanizing bath 230 held above about 420° C., and, more preferably, at a temperature of greater than or equal to about 420° C. up to about 480° C., followed by cooling to solidify the zinc into a surface coating. Continuous hot-dip galvanizing provides a relatively pure zinc coating with high cathodic corrosion resistance. Alternatively, aluminum may be added to the zinc galvanizing bath 230, promoting formation of a layer that prevents extensive diffusion between the zinc and iron. In some aspects, the steel alloy may be galvannealed following the hot-dipped galvanizing by heating the hot-dipped galvanized steel alloy to greater than or equal to about 500° C. to less than or equal to about 565° C. and holding for a few seconds. The steel alloy may then be coiled again into coil 240 for easier transportability. Notably, steps 220 and 240 are optional.
The steel alloy is then uncoiled, if coiled, and a blank 250 is formed by shearing sections of the steel alloy. The blank 250 may be sheared with trim dies, alligator shears, bench shears, guillotines, power shears, throatless shears, or the like. A pre-forming step (e.g., as shown at step 160 in FIG. 3) is not required using the steel alloy according to the present disclosure.
The blank 250 is placed in an oven 260 (e.g., austenitizing furnace). The blank 250 is heated to less than or equal to about 782° C., so that as recognized by those in the art, the temperature in the oven 260 may potentially exceed 782° C. Notably, the blank 250 introduced to oven 260 need not be preformed to achieve the desired strength and to be substantially free of LME. By way of example, the blank 250 is placed in a furnace for at least 5 minutes, so the blank reaches a temperature of about 780° C. The heated blank 265 is then immediately transferred to dies 270 and 280 and is press hardened into PHS component 290. Because the temperature of the blank 250 is at a temperature of less than about 782° C., LME is limited, if it occurs at all.
Optionally, PHS component 290 is quenched via a rapid cooling process. PHS component 290 may be quenched in the dies 270 and 280, for example, quenched at a rate of more than 27° C./s to transform the austenite into martensite.
The zinc coating protects PHS component 290 from oxidation that would otherwise occur between the austenitizing and press-hardening steps. There is, therefore, little to no need for surface cleaning of PHS component 290 after the press hardening.
Referring to FIG. 5, the process 310 according to another aspect of the present disclosure is shown. The steel alloy is first austenitized at a temperature from greater than or equal to about 900° C. to less than or equal to about 950° C. in an austenitizing furnace 220. The austenitized steel alloy is then quenched, rapidly cooled, or slowly cooled to obtain a microstructure comprising martensite, bainite, pearlite, austenite, ferrite, and the like, including combinations thereof. Preferably, the austenitized steel alloy is quenched to allow for martensitic transformation. The austenitized steel alloy then undergoes hot-dip galvanizing in a zinc galvanizing bath 330 that optionally includes a galvannealing furnace.
Continuous hot-dip galvanizing is used to coat the steel alloy. The coating is applied by passing the steel alloy through the zinc galvanizing bath 330 held above about 420° C., and, more preferably, at a temperature of greater than or equal to about 420° C. up to about 480° C., followed by cooling to solidify the zinc into a surface coating. Continuous hot-dip galvanizing provides a relatively pure zinc coating with high cathodic corrosion resistance. Alternatively, aluminum may be added to the zinc galvanizing bath 330, promoting formation of a layer that prevents extensive diffusion between the zinc and iron. In some aspects, the steel alloy may be galvannealed following the galvanizing by heating the hot-dipped galvanized steel alloy to greater than or equal to about 500° C. to less than or equal to about 565° C. and holding for a few seconds. The steel alloy may then be coiled into coil 340 for easier transportability. Notably, step 340 is optional.
The steel alloy is then uncoiled, if coiled, and a blank 350 is formed by shearing sections of the steel alloy. The blank 350 may be sheared with trim dies, alligator shears, bench shears, guillotines, power shears, throatless shears, or the like. A pre-forming step (e.g., as shown at step 160 in FIG. 3) is not required using the steel alloy according to the present disclosure.
The blank 350 is placed in an oven 360 (e.g., austenitizing furnace). The blank 350 is heated to less than or equal to about 782° C., so that as recognized by those in the art, the temperature in the oven 360 may potentially exceed 782° C. Notably, the blank 350 introduced to oven 360 need not be preformed to achieve the desired strength and to be substantially free of LME. By way of example, the blank 350 is placed in a furnace for at least 5 minutes, so the blank reaches a temperature of about 780° C. The heated blank 365 is then immediately transferred to dies 370 and 380 and is press hardened into PHS component 390. Because the temperature of the blank 350 is at a temperature of less than about 782° C., LME is limited, if it occurs at all.
Optionally, PHS component 390 is quenched via a rapid cooling process. PHS component 390 may be quenched in the dies 370 and 380, for example, quenched at a rate of more than 27° C./s to transform the austenite into martensite.
The zinc coating protects PHS component 390 from oxidation that would otherwise occur between the austenitizing and press-hardening steps. There is, therefore, little to no need for surface cleaning of PHS component 390 after the press hardening.
The galvanized, pre-treated press hardened steel alloy according to the present disclosure provides excellent strength. When the pre-treatment involves cold rolling, the press hardened steel is optionally non-annealed. More specifically, the galvanized, pre-treated press hardened steel alloy according to the present disclosure has an ultimate tensile strength (UTS) of greater than or equal to about 1,000 MPa to about less than or equal to about 2,000 MPa. FIG. 6 shows ultimate tensile strengths (designated “610” in MPa units) that certain existing conventional steel alloys (e.g., 22MnB5, which comprises 0.22% C, 0.44% Mn, 0.19% Si, 0.001% B remainder Fe, by weight) attain upon heating to varying austenitizing temperatures (designated “620” in ° C.). More specifically, conventional steel alloys that undergo austenitization at a temperature of less than or equal to about 782° C. according to the present disclosure may only yield an ultimate tensile strength of only about 900 MPa. Such a conventional composition does not sufficiently lower the austenitizing temperature to at or below 782° C., so that an amount of martensite formed during the PHS process is maximized. Thus, such a steel alloy may require modifications to the alloy chemistry, such as introduction of additional manganese and/or carbon, to ultimately enhance martensite formation and strength to acceptable levels in a hardened state (e.g., in the PHS components). If a tougher PHS component is desired, carbon may be reduced, while manganese is increased, all while selecting an alloy that has an austenitizing temperature at or below 782° C.
The galvanized, pre-treated steel alloy according to the present disclosure provides a PHS component having a multi-phase microstructure, including martensite. Upon cooling, the PHS component undergoes a diffusionless martensitic transformation at a temperature of around 400° C. if the cooling rate exceeds 27° C./s. The martensitic transformation ends at about 280° C. In certain aspects, the martensitic transformation provides high strength to the PHS component. The amount of carbon present and the austenitizing temperature in the galvanized, pre-treated steel alloy determines the amount of ferrite that is transformed to austenite and then martensite. In certain aspects, a PHS component may have a multi-phase microstructure comprising ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and greater than or equal to about 40% to less than or equal to about 99% of a combined volume percentage of martensite, retained austenite, and other transformation products.
In one exemplary method, the process comprises creating a blank from a galvanized, pre-treated steel alloy. The blank is then heated in an oven, so that the blank reaches a temperature of less than or equal to about 782° C. to partially austenitize the galvanized steel alloy. The heated blank is then immediately transferred to the dies and is press hardened into the PHS component. The PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa and is substantially free of liquid metal embrittlement. In certain other variations, the pre-treated, hot-dipped galvanized steel alloy is not annealed prior to creating the blank. The process may further include quenching the PHS component to below room temperature after the press hardening. The process may further include hot-dip galvanizing a cold-rolled, non-annealed steel alloy in a zinc galvanizing bath. In other aspects, the process may further include galvannealing the pre-treated steel alloy. In yet other aspects, the process may involve electrogalvanizing the pre-treated steel. In certain aspects, the steel alloy comprises carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight %, or in certain variations, the steel alloy may optionally include manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight % and/or carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %. The steel alloy may further comprise silicon at greater than 0 weight % to less than or equal to about 1 weight %. In other variations, the steel alloy may comprise carbon at about 0.3 weight % and manganese at about 1.5 weight %. The PHS component may have an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa. The heating of the blank may occur at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C. The PHS component may comprise a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%.
In another example, the process may consist essentially of the following steps. A coil comprising a cold-rolled non-annealed steel alloy may be uncoiled, followed by hot-dip galvanizing of the cold-rolled non-annealed steel alloy in zinc galvanizing bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy. Next, the cold-rolled non-annealed hot-dipped galvanized steel alloy may be coiled and sheared into a blank from the coil, followed by heating in an oven to reach a temperature of less than or equal to about 782° C. Then, the heated blank may be immediately transferred to the dies and press hardened into a PHS component such that the PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa and is substantially free of liquid metal embrittlement. In certain other variations, such a process may be further limited as follows: (1) the process may further consist essentially of quenching the PHS component to below room temperature after the press hardening; (2) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than 0 weight % to less than or equal to about 6 weight %; (3) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %; (4) having a steel alloy comprised of silicon at greater than 0 weight % to less than or equal to about 1 weight %; (5) having a steel alloy comprised of carbon at about 0.3 weight % and manganese at about 1.5 weight %; (6) a PHS component having an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa; (7) galvannealing the cold-rolled, hot-dipped galvanized steel alloy; (8) the process may further consist essentially of heating in an oven at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.; and (9) where the process forms the PHS component having a multi-phase microstructure with ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. Notably, such a process enables formation of high strength PHS components while avoiding liquid metal embrittlement, while excluding one or more of the following: annealing, pre-forming, or cleaning steps required in conventional PHS processes, which can result in time, energy, and cost savings benefits. Moreover, the austenitizing temperature is lower than under known PHS processes.
In yet another exemplary method, the process may consist essentially of the following steps. A cold-rolled, non-annealed coil comprising a steel alloy may be uncoiled then hot-dip galvanized in a zinc galvanizing bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy. The cold-rolled, non-annealed hot-dipped galvanized steel alloy may be coiled, sheared into a blank from the coil, and then heated in an oven to reach a temperature of less than or equal to about 782° C. The heated blank may then be immediately transferred to the dies, press hardened and quenched to form the PHS component, where the PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa and is substantially free of liquid metal embrittlement. In certain other variations, such a process may be further limited as follows: (1) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than 0 weight % to less than or equal to about 6 weight %; (2) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %; (3) having a steel alloy comprised of silicon at greater than 0 weight % to less than or equal to about 1 weight %; (4) having a steel alloy comprised of carbon at about 0.3 weight % and manganese at about 1.5 weight %; (5) wherein the PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa; (6) galvannealing the cold-rolled, hot-dipped galvanized steel alloy; (7) wherein the process further consists essentially of heating in an oven at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.; and (8) where the PHS component has a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. Notably, such a process excludes the conventional annealing, pre-forming and cleaning steps previously required in conventional PHS processes, which results in cost saving benefits as less energy need be expended to form the PHS component. Moreover, the austenitizing temperature is lower than under known PHS processes.
In another exemplary method, the process comprises creating a blank from a galvanized, cold-rolled non-annealed steel alloy. The blank is then heated in an oven to a temperature of less than or equal to about 782° C., so as to partially austenitize the galvanized steel alloy. The heated blank is then immediately transferred to the dies and is press hardened into the PHS component. The PHS component has a strength (e.g., ultimate tensile strength, UTS) of greater than or equal to about 1,000 MPa and is substantially free of liquid metal embrittlement. In certain aspects, the steel alloy comprises carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight %, or in certain variations, the steel alloy may optionally include manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight % and/or carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %. The steel alloy may further comprise silicon at greater than 0 weight % to less than or equal to about 1 weight %. In other variations, the steel alloy may comprise carbon at about 0.3 weight % and manganese at about 1.5 weight %. The PHS component may have an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa. The heating may occur at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C. The PHS component may comprise a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. The process may further include hot-dip galvanizing a cold-rolled, non-annealed steel alloy in a zinc galvanizing bath. The process may further include galvannealing after hot-dip galvanizing. In yet other aspects, the process may involve electrogalvanizing the pre-treated steel. The process may further include quenching the PHS component to below room temperature after press hardening.
In another example, a process may consist essentially of uncoiling a cold-rolled non-annealed coil comprising a steel alloy, followed by hot-dip galvanizing the cold-rolled non-annealed steel alloy in a zinc galvanizing bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy into a coil, and shearing a blank from the coil. The blank may be heated in an oven so that it reaches a temperature of less than or equal to about 782° C. The heated blank is immediately transferred to the dies and press hardened into a PHS component. The steel alloy comprises carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight %. In certain other variations, the process may be further limited as follows: (1) further consisting essentially of quenching the PHS component to below room temperature after the press hardening; (2) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %; (3) having a steel alloy comprised of silicon at greater than 0 weight % to less than or equal to about 1 weight %; (4) having a steel alloy comprised of carbon at about 0.3 weight % and manganese at about 1.5 weight %; (5) wherein the PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa; (6) galvannealing the cold-rolled, hot-dipped galvanized steel alloy; (7) further consisting essentially of heating in an oven at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.; and (8) where the PHS component has a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. Notably, the process excludes the annealing, pre-forming and cleaning steps, which results in cost savings benefits as less energy need be expended to form the PHS component. Moreover, the austenitizing temperature is lower than that of known PHS processes.
In yet another example, the process consists essentially of uncoiling a cold-rolled non-annealed coil comprising a steel alloy, hot-dip galvanizing the cold-rolled non-annealed steel alloy in a zinc galvanizing bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy, and shearing a blank from the coil. The blank can be heated in an oven so that it reaches a temperature of less than or equal to about 782° C., followed by immediately transferring the heated blank to the dies and press hardening and quenching the hot blank to form a PHS component. The PHS component has a strength (e.g., ultimate tensile strength, UTS) of greater than or equal to about 1,000 MPa and is substantially free of liquid metal embrittlement. The steel alloy comprises carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight In certain other variations, the process may be further limited as follows: (1) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %; (2) having a steel alloy comprised of silicon at greater than 0 weight % to less than or equal to about 1 weight %; (3) having a steel alloy comprised of carbon at about 0.3 weight % and manganese at about 1.5 weight %; (4) wherein the PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa; (5) galvannealing the cold-rolled, hot-dipped galvanized steel alloy; (6) further consisting essentially of heating in an oven at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.; and (7) wherein the PHS component has a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99% by volume. Notably, such a process excludes the conventional annealing, pre-forming and cleaning steps previously required in conventional PHS processes, which results in cost savings benefits as less energy need be expended to form the PHS component. Moreover, the austenitizing temperature is lower than under known PHS processes.
In another exemplary method, a process comprises creating a blank from a galvanized, cold-rolled, non-annealed steel alloy. The blank is then heated in an oven to a temperature of less than or equal to about 782° C. to partially austenitize the galvanized steel alloy. The heated blank is then immediately transferred to the dies and is press hardened into a PHS component. The PHS component has a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. The process may further include quenching the PHS component to below room temperature after the press hardening. The process may further include hot-dip galvanizing a cold-rolled, non-annealed steel alloy in a zinc galvanizing bath. The process may further include galvannealing the hot-dipped galvanized, pre-treated, non-annealed steel alloy. In yet other aspects, the process may involve electrogalvanizing the pre-treated steel. The steel alloy may comprise carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, manganese at greater than 0 weight % to less than or equal to about 6 weight %, and, in certain other variations, manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %. The steel alloy may further comprise silicon at greater than 0 weight % to less than or equal to about 1 weight %. In other variations, the steel alloy may comprise carbon at about 0.3 weight % and manganese at about 1.5 weight %. The PHS component may have an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa. The heating may occur at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.
In another method, a process may consist essentially of uncoiling cold-rolled non-annealed coil comprising a steel alloy, hot-dip galvanizing the cold-rolled non-annealed steel alloy in zinc galvanizing bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy, shearing a blank from the coil, heating in an oven to a temperature of less than or equal to about 782° C., immediately transferring the heated blank to the dies and press hardening the hot blank into a PHS component, such that the PHS component has a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. In certain other variations, the process may be further limited as follows: (1) further consisting essentially of quenching the PHS component to below room temperature after press hardening; (2) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than 0 weight % to less than or equal to about 6 weight %; (3) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %; (4) having a steel alloy comprised of silicon at greater than 0 weight % to less than or equal to about 1 weight %; (5) having a steel alloy comprised of carbon at about 0.3 weight % and manganese at about 1.5 weight %; (6) wherein the PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa; (7) galvannealing the cold-rolled, hot-dipped galvanized steel alloy; and (8) further consisting essentially of heating in oven at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C. Notably, such a process excludes the conventional annealing, pre-forming and cleaning steps previously required in conventional PHS processes, which results in cost savings benefits as less energy need be expended to form PHS component. Moreover, the austenitizing temperature is lower than under known PHS processes.
In yet another exemplary process, a method may consist essentially of uncoiling a cold-rolled non-annealed coil comprising a steel alloy, hot-dip galvanizing the cold-rolled non-annealed steel alloy in a zinc galvanizing bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy and shearing a blank from the coil. The blank may be heated in an oven to a temperature of less than or equal to about 782° C., immediately transferring the heated blank to the dies and press hardening and quenching the hot blank into a PHS component, such that the PHS component has a multi-phase microstructure having ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%. In certain other variations, the process may be further limited as follows: (1) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than 0 weight % to less than or equal to about 6 weight %; (2) having a steel alloy comprised of carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight %, and manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %; (3) having a steel alloy comprised of silicon at greater than 0 weight % to less than or equal to about 1 weight %; (4) having a steel alloy comprised of carbon at about 0.3 weight % and manganese at about 1.5 weight %; (5) wherein the PHS component has an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa; (6) galvannealing the cold-rolled, hot-dipped galvanized steel alloy; and (7) the process further consisting essentially of heating in an oven at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C. Notably, such a process excludes the conventional annealing, pre-forming and cleaning steps previously required in conventional PHS processes, which results in cost savings benefits as less energy need be expended to form PHS component. Moreover, the austenitizing temperature is lower than under known PHS processes.
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.

Claims

What is claimed is:

1. A method of press-hardening a galvanized steel alloy comprising:

creating a blank from a pre-treated, galvanized steel alloy;

heating the blank to a temperature of less than or equal to about 782° C. to partially austenitize the galvanized steel alloy; and

press hardening the blank of the galvanized steel alloy to form a press-hardened component having an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa that is substantially free of liquid metal embrittlement.

2. The method of claim 1, wherein the steel alloy comprises carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight %.

3. The method of claim 1, wherein the steel alloy comprises:

manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %;

carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %; or

manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight % and carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %.

4. The method of claim 1, wherein the steel alloy comprises silicon at greater than 0 weight % to less than or equal to about 1 weight %.

5. The method of claim 1, wherein the heating occurs at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.

6. The method of claim 1, further comprising quenching the press-hardened component to below room temperature after the press hardening.

7. The method of claim 1, wherein the press-hardened component has a multi-phase microstructure comprising ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%.

8. A method of press-hardening a galvanized steel alloy comprising:

creating a blank from a pre-treated, galvanized steel alloy;

press hardening the blank of the galvanized steel alloy to form a press-hardened component having a microstructure that comprises ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%.

9. The method of claim 8, wherein the steel alloy comprises carbon at greater than or equal to about 0.1 weight % to less than or equal to about 0.6 weight % and manganese at greater than 0 weight % to less than or equal to about 6 weight %.

10. The method of claim 8, wherein the steel alloy comprises:

11. The method of claim 8, wherein the steel alloy comprises silicon at greater than 0 weight % to less than or equal to about 1 weight %.

12. The method of claim 8, wherein the press-hardened component has an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa.

13. The method of claim 8, wherein the heating occurs at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.

14. The method of claim 8, further comprising quenching the press-hardened component to below room temperature after the press hardening.

15. A method of press-hardening a galvanized steel alloy comprising:

creating a blank from a cold-rolled, non-annealed, hot-dipped galvanized steel alloy;

press-hardening the blank of the galvanized steel alloy to form a press-hardened component having a microstructure that comprises ferrite at greater than or equal to about 1% to less than or equal to about 60% by volume and a combined volume percentage of martensite, retained austenite, and other transformation products at greater than or equal to about 40% to less than or equal to about 99%.

16. The method of claim 15, wherein the steel alloy comprises:

carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %;

silicon at greater than 0 weight % to less than or equal to about 1 weight %; or

manganese at greater than or equal to about 1 weight % to less than or equal to about 2 weight %, carbon at greater than or equal to about 0.3 weight % to less than or equal to about 0.5 weight %, and silicon at greater than 0 weight % to less than or equal to about 1 weight %.

17. The method of claim 15, wherein the press-hardened component has an ultimate tensile strength of greater than or equal to about 1,000 MPa to less than or equal to about 2,000 MPa.

18. The method of claim 15, wherein the heating occurs at a temperature of greater than or equal to about 725° C. to less than or equal to about 782° C.

19. The method of claim 15, further comprising quenching the press-hardened component to below room temperature after the press hardening.

20. The method of claim 15, consisting essentially of uncoiling a cold-rolled non-annealed coil comprising a steel alloy and hot-dip galvanizing the cold-rolled non-annealed steel alloy to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy, and uncoiling and creating a blank from the cold-rolled, non-annealed hot-dipped galvanized steel alloy before the heating.

21. The method of claim 15, consisting essentially of uncoiling a cold-rolled non-annealed coil comprising a steel alloy and hot-dip galvanizing the cold-rolled non-annealed steel alloy in a zinc galvanization bath to form a cold-rolled, non-annealed hot-dipped galvanized steel alloy, coiling the cold-rolled, non-annealed hot-dipped galvanized steel alloy, uncoiling and creating a blank from the cold-rolled, non-annealed hot-dipped galvanized steel alloy before the heating, and quenching the press-hardened component after the press hardening step.