U.S. patent application number 15/417921 was filed with the patent office on 2018-08-02 for two-step hot forming of steels.
The applicant listed for this patent is GM Global Technology Operations LLC. Invention is credited to Qi Lu, Anil K. Sachdev, Jianfeng Wang.
Application Number | 20180216205 15/417921 |
Document ID | / |
Family ID | 62843372 |
Filed Date | 2018-08-02 |
United States Patent
Application |
20180216205 |
Kind Code |
A1 |
Wang; Jianfeng ; et
al. |
August 2, 2018 |
TWO-STEP HOT FORMING OF STEELS
Abstract
Methods for press hardening steel alloys comprised of medium-Mn
are provided. The press-hardened steel alloy may have an ultimate
tensile strength (UTS) of at least 1,700 MPa and a tensile
elongation of at least 8%. The press-hardened steel alloy may be
formed in two forming steps above the martensitic finish
temperature. The press-hardened steel may have a microstructure
comprising martensite at greater than or equal to about 80% to less
than or equal to about 98% and retained austenite at less than or
equal to about 20% to greater than or equal to about 2%.
Inventors: |
Wang; Jianfeng; (Nanjing,
CN) ; Lu; Qi; (Pudong New District, CN) ;
Sachdev; Anil K.; (Rochester Hills, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM Global Technology Operations LLC |
Detroit |
MI |
US |
|
|
Family ID: |
62843372 |
Appl. No.: |
15/417921 |
Filed: |
January 27, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 2211/001 20130101;
C21D 6/005 20130101; C21D 2211/008 20130101; C23C 2/26 20130101;
B21D 22/022 20130101; C23C 2/40 20130101; C23C 2/28 20130101; C21D
1/18 20130101; C23C 2/06 20130101; C22C 38/04 20130101; B21D 35/005
20130101; B32B 15/013 20130101; C21D 8/005 20130101; C21D 9/0068
20130101 |
International
Class: |
C21D 9/00 20060101
C21D009/00; C23C 2/06 20060101 C23C002/06; C23C 2/40 20060101
C23C002/40; C23C 2/28 20060101 C23C002/28; C22C 38/04 20060101
C22C038/04; C21D 8/00 20060101 C21D008/00; C21D 1/18 20060101
C21D001/18; B21D 22/02 20060101 B21D022/02 |
Claims
1. A method of press-hardening a medium-Mn steel alloy, the method
comprising: heating a blank of medium-Mn steel alloy to a
temperature of less than or equal to about 850.degree. C. to
austenitize the medium-Mn steel alloy; press hardening the blank of
the medium-Mn steel alloy to form a press-hardened component at a
temperature greater than or equal to about a martensitic start
temperature; and further forming the press-hardened component at a
temperature greater than or equal to about a martensitic finish
temperature to less than or equal to about the martensitic start
temperature, wherein the press-hardened component has an ultimate
tensile strength of greater than or equal to about 1,700 MPa.
2. The method of claim 1, wherein the heating of the blank is to a
temperature of less than or equal to about 800.degree. C. to
austenitize the medium-Mn steel alloy.
3. The method of claim 1, wherein the medium-Mn steel alloy
comprises carbon at greater than or equal to about 0.1 wt. % to
less than or equal to about 0.4 wt. % and manganese at greater than
or equal to about 5 wt. % to less than or equal to about 12 wt.
%.
4. The method of claim 1, wherein the medium-Mn steel alloy blank
is galvanized before heating.
5. The method to claim 1, wherein the press-hardened component has
a tensile elongation of greater than or equal to about 8%.
6. The method of claim 1, wherein the press-hardened component is
air cooled to the martensitic finish temperature after further
forming the press-hardened component.
7. The method of claim 1, wherein the press-hardened component has
a microstructure comprising martensite at greater than or equal to
about 80% to less than or equal to about 98% and retained austenite
at less than or equal to about 20% to greater than or equal to
about 2%.
8. A method of press-hardening a medium-Mn steel alloy, the method
comprising: heating a blank of medium-Mn steel alloy to a
temperature of less than or equal to about 850.degree. C. to
austenitize the medium-Mn steel alloy; press hardening the blank of
the medium-Mn steel alloy to form a press-hardened component at a
temperature greater than or equal to about a martensitic start
temperature; and further forming the press-hardened component at a
temperature of greater than or equal to about the martensitic start
temperature to form a press-hardened component having an ultimate
tensile strength of greater than or equal to about 1,700 MPa.
9. The method of claim 8, wherein the heating of the blank is to a
temperature of less than or equal to about 800.degree. C. to
austenitize the medium-Mn steel alloy.
10. The method of claim 8, wherein the medium-Mn steel alloy
comprises carbon at greater than or equal to about 0.1 wt. % to
less than or equal to about 0.4 wt. % and manganese at greater than
or equal to about 5 wt. % to less than or equal to about 12 wt.
%.
11. The method of claim 8, wherein the medium-Mn steel alloy blank
is galvanized before heating.
12. The method to claim 8, wherein the press-hardened component has
a tensile elongation of greater than or equal to about 8%.
13. The method of claim 8, wherein the press-hardened component is
air cooled to the martensitic finish temperature after further
forming the press-hardened component.
14. The method of claim 8, wherein the press-hardened component has
a microstructure comprising martensite at greater than or equal to
about 80% to less than or equal to about 98% and retained austenite
at less than or equal to about 20% to greater than or equal to
about 2%.
15. A method of press-hardening a medium-Mn steel alloy, the method
comprising: heating a blank of medium-Mn steel alloy to a
temperature of less than or equal to about 850.degree. C. to
austenitize the medium-Mn steel alloy; press hardening the blank of
the medium-Mn steel alloy to form a press-hardened component;
further forming the press-hardened component at a temperature
greater than or equal to a martensitic finish temperature, wherein
the further forming includes at least one of trimming, punching, or
re-striking the press-hardened component; and controlling the rate
at which the press-hardened component cools between a martensitic
start temperature and the martensitic finish temperature, wherein
the press-hardened component has a microstructure comprising
martensite at greater than or equal to about 80% to less than or
equal to about 98% and retained austenite at less than or equal to
about 20% to greater than or equal to about 2%.
16. The method of claim 15, wherein the heating the blank is to a
temperature of less than or equal to about 800.degree. C. to
austenitize the medium-Mn steel alloy.
17. The method of claim 15, wherein the medium-Mn steel alloy
comprises carbon at greater than or equal to about 0.1 wt. % to
less than or equal to about 0.4 wt. % and manganese at greater than
or equal to about 5 wt. % to less than or equal to about 12 wt.
%.
18. The method to claim 15, wherein the press-hardened component
has an ultimate tensile strength of greater than or equal to about
1,700 MPa.
19. The method of claim 15, wherein the press-hardened component is
air cooled to the martensitic finish temperature after further
forming the press-hardened component.
20. The method of claim 15, wherein medium-Mn steel alloy blank is
galvanized before heating.
Description
INTRODUCTION
[0001] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0002] The present disclosure relates to two-step forming methods
of press-hardening steel alloys to form high-strength
press-hardened components.
[0003] 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) and total elongation on the
order of about 5% to 6%. Such steel has many desirable properties
and uses, including forming steel components with significant
increases in strength-to-weight ratios. Further, PHS components
have become increasingly 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, in automotive
manufacturing applications, continual improvement in fuel
efficiency and performance is desirable; PHS components have
therefore 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.
[0004] Typical PHS processes involve austenitization in a furnace
of a sheet steel blank immediately followed by pressing and
quenching of the sheet in dies. Steels used to manufacture PHS
components typically contain boron; one well-known steel used to
manufacture PHS components is commercially known as 22MnB5 (which
comprises 0.22% C, 1.2% Mn, 0.2% Si, 0.001-0.005% B, trace elements
including P, N, S and O as impurities by weight, and a balance of
Fe). There are two main types of PHS processes: indirect and
direct. Austenitization is typically conducted in the range of
about 900.degree. 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. The PHS component must be quenched at
a rate of at least 27.degree. C./s to ensure the austenite
transfers to martensite and not to an undesirable microstructure,
such as ferrite and bainite. 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. After shot blasting, further forming of the PHS
component is typically accomplished with laser cutting, as die
cutting is typically not effective given the high strength of the
PHS component. There is a continuing need to increase the strength
and elongation of PHS components and reduce the processing time and
concomitant cost associated with manufacturing them.
SUMMARY
[0005] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0006] In certain aspects, the present disclosure contemplates a
method of press-hardening a steel alloy. A blank of a medium-Mn
steel alloy is heated to a temperature of less than or equal to
about 850.degree. C. to austenitize the steel alloy. The blank is
then press hardened to form a press-hardened component at a
temperature greater than or equal to about the martensitic start
temperature. The press-hardened component is further formed at a
temperature of less than or equal to about the martensitic start
temperature to greater than or equal to about the martensitic
finish temperature, and the press-hardened component has an
ultimate tensile strength of greater than or equal to about 1,700
MPa. In other embodiments, the blank is heated to a temperature of
less than or equal to about 800.degree. C. to austenitize the
medium-Mn steel alloy. In yet other embodiments, the medium-Mn
steel alloy comprises carbon at greater than or equal to about 0.1
wt. % to less than or equal to about 0.4 wt. % and manganese at
greater than or equal to about 5 wt. % to less than or equal to
about 12 wt. %. In further embodiments, the medium-Mn steel alloy
blank is galvanized before heating. In yet further embodiments, the
press-hardened component has a tensile elongation of greater than
or equal to about 8%. In even further embodiments, the
press-hardened component is air cooled to less than or equal to
about room temperature after further forming the press-hardened
component. In additional embodiments, the press-hardened component
has a microstructure comprising martensite at greater than or equal
to about 80% to less than or equal to about 98% and retained
austenite at less than or equal to about 20% to greater than or
equal to about 2%.
[0007] In other aspects, a method of press-hardening a steel alloy
is provided that comprises heating a blank of a medium-Mn steel
alloy to a temperature of less than or equal to about 850.degree.
C. to austenitize the steel alloy. The blank is then press hardened
to form a press-hardened component at a temperature greater than or
equal to about the martensitic start temperature. The
press-hardened component is further formed at a temperature of
greater than or equal to about the martensitic start temperature,
and the press-hardened component has an ultimate tensile strength
of greater than or equal to about 1,700 MPa. In other embodiments,
the blank is heated to a temperature of less than or equal to about
800.degree. C. to austenitize the medium-Mn steel alloy. In yet
other embodiments, the medium-Mn steel alloy comprises carbon at
greater than or equal to about 0.1 wt. % to less than or equal to
about 0.4 wt. % and manganese at greater than or equal to about 5
wt. % to less than or equal to about 12 wt. %. In further
embodiments, the medium-Mn steel alloy blank is galvanized before
heating. In yet further embodiments, the press-hardened component
has a tensile elongation of greater than or equal to about 8%. In
even further embodiments, the press-hardened component is air
cooled to less than or equal to about room temperature after
further forming the press-hardened component. In additional
embodiments, the press-hardened component has a microstructure
comprising martensite at greater than or equal to about 80% to less
than or equal to about 98% and retained austenite at less than or
equal to about 20% to greater than or equal to about 2%.
[0008] In yet other aspects, a method of press-hardening a
medium-Mn steel alloy is provided that comprises heating a blank of
a medium-Mn steel alloy to a temperature of less than or equal to
about 850.degree. C. to austenitize the steel alloy. The blank is
then press hardened to form a press-hardened component. The
press-hardened component is formed a second time at a temperature
of greater than or equal to about the martensitic finish
temperature. The further forming includes at least one of trimming,
punching, or re-striking the press-hardened component. The
press-hardened component is cooled at a controlled rate between the
martensitic start temperature and the martensitic finish
temperature such that the press-hardened component has a
microstructure comprising martensite at greater than or equal to
about 80% to less than or equal to about 98% and retained austenite
at less than or equal to about 20% to greater than or equal to
about 2%. In other embodiments, the blank is heated to a
temperature of less than or equal to about 800.degree. C. to
austenitize the medium-Mn steel alloy. In yet other embodiments,
the medium-Mn steel alloy comprises carbon at greater than or equal
to about 0.1 wt. % to less than or equal to about 0.4 wt. % and
manganese at greater than or equal to about 5 wt. % to less than or
equal to about 12 wt. %. In further embodiments, the press-hardened
component has an ultimate tensile strength of greater than or equal
to about 1,700 MPa. In even further embodiments, the press-hardened
component is air cooled to less than or equal to about room
temperature after further forming the press-hardened component. In
additional embodiments, the medium-Mn steel alloy blank is
galvanized before heating.
[0009] In certain variations, the method further consists
essentially of pre-treating the medium-Mn steel alloy.
[0010] 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
[0011] 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.
[0012] FIG. 1 shows a representative automotive A-pillar
manufactured according to an aspect of the present invention;
[0013] FIG. 2 shows a representative automotive B-pillar
manufactured according to an aspect of the present invention;
[0014] FIG. 3 shows a conventional process for forming a press
hardened steel component;
[0015] FIG. 4 shows an exemplary process for providing a press
hardened steel component in accordance with certain aspects of the
present disclosure; and
[0016] FIG. 5 shows an exemplary process for providing a press
hardened steel component in accordance with certain other aspects
of the present disclosure.
[0017] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0018] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] The present disclosure provides methods of press-hardening a
medium-Mn steel alloy to form a press-hardened component having
high strength. Referring first to FIGS. 1 and 2, automotive
structural components, such as A-pillar 10 and B-pillar 20 are
shown that can be produced from a press-hardened steel component
comprising by two-step forming a medium-Mn steel alloy blank. The
press-hardened component is formed by shaping the medium-Mn steel
alloy at a high temperature (e.g., at less than or equal to about
850.degree. C.; however, in certain embodiments, the temperature
may be greater than or equal to about 850.degree. C.) followed by
forming (e.g., trimming, punching, or re-striking) the
press-hardened component a second time at a lower temperature that
is less than or equal to the martensitic start temperature for the
medium-Mn steel alloy blank. In other aspects, the further forming
at a lower temperature occurs at a temperature greater than or
equal to the martensitic finish temperature to a temperature less
than or equal to the martensitic start temperature for the
medium-Mn steel alloy blank. In other aspects, the medium-Mn steel
alloy blank comprises a galvanic coating comprising zinc. 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 medium-Mn 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).
[0029] As mentioned above, in certain embodiments, the use of
galvanic coatings on press-hardened steel is contemplated. Such
components have 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.
[0030] In various aspects, a particularly suitable, non-limiting
steel is medium-Mn steel alloy, which comprises manganese at
greater than or equal to about 5 weight % to less than or equal to
about 12 weight % and greater than or equal to about 0.1 wt. % to
less than or equal to about 0.4 wt. % carbon. Optionally, the
medium-Mn steel alloy may further comprise less than or equal to
about 1.6 wt. % aluminum, less than or equal to about less than 1.8
wt. % silicon, less than or equal to about 0.25 wt. % molybdenum,
less than or equal to about 0.05 wt. % niobium, less than or equal
to about 0.01 wt. % phosphorus, less than or equal to about 0.005
wt. % sulfur, and less than or equal to about less than or equal to
about 0.006 wt. % nitrogen. In yet other embodiments, the medium-Mn
steel alloy may be pre-treated. More specifically, the medium-Mn
steel alloy may be pre-treated by hot-rolling. In yet other
aspects, the medium-Mn steel alloy may be pre-treated by
hot-rolling, followed by cold rolling. In even other aspects, the
medium-Mn steel alloy may be pre-treated by hot-rolling, followed
by cold-rolling, followed by annealing.
[0031] In certain aspects, the present disclosure further
contemplates modifying such steel alloy compositions so that they
have zinc galvanic coatings, yet be processed via press hardening
process to form components with high strength and negligible liquid
metal (e.g., zinc) embrittlement (LME). In such aspects, the
medium-Mn steel alloy is press-formed at a temperature of less than
or equal to about 782.degree. C. In accordance with such aspects,
the PHS components are substantially free of 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.
[0032] Referring to FIG. 3, a flowchart showing the steps of a
conventional direct press-hardening process 100 is shown. A rolled
coil 110 of a conventional steel alloy is uncoiled and sheared to
form blank 120. Blank 120 is heated in an oven 130 having a
temperature of about 930.degree. C. for a predetermined period
(e.g., about 360 seconds) to austenitize blank 120. Blank 120 is
then press hardened between dies 140 and 150 to form and
simultaneously quench PHS component 160. Notably, forming and
pressing a galvanized blank 120 between dies 140 and 150 to form
and simultaneously quench PHS component 160 would result in LME and
therefore an unsatisfactory PHS component. For conventional steel
alloys, quenching at a rate of at least 27.degree. C./s to a
temperature below the 280.degree. C. martensitic finish temperature
is required to prevent the formation of bainitic or pearlitic
microstructures. To arrive at a galvanized PHS component, indirect
press-hardening processes, which introduces an extra step of cold
forming blank 120 to an intermediate partial shape before
austenitization, must be used to prevent LME. PHS component 160 is
then cleaned, for example, with shot blasting 170, to remove scale
as necessary. PHS component 160 is further trimmed and/or punched
as necessary by laser cutter 180 to achieve formed PHS component
190.
[0033] In accordance with certain aspects of the present
disclosure, the methods of press-hardening a steel component
comprised of the steel alloys contemplated herein provide the
ability to eliminate laser cutting and traditional quenching while
still achieving a formed PHS component. Furthermore, the PHS
component has higher strength and better ductility than
conventional steels made according to conventional PHS processes.
Thus, the overall process according to the present disclosure
desirably reduces processing time, energy requirements, and
cost.
[0034] As used herein, the term "pre-treated" means any of (1)
hot-rolling, (2) hot-rolling, followed by cold rolling, or (3) hot
rolling, followed by cold-rolling, followed by annealing. In any
aspect, the pre-treated alloy may then be galvanized. 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.degree. C. to less than or equal to about 950.degree. 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.
[0035] Referring to FIG. 4, the process 200 according to one aspect
of the present disclosure is shown. Optionally, a rolled coil 210
of a steel alloy is pre-treated. After any optional pre-treat,
blank 220 is formed by shearing a section of rolled coil 210 of a
steel alloy. Blank 220 may be sheared with trim dies, alligator
shears, bench shears, guillotines, power shears, throatless shears,
or the like after any necessary uncoiling having previously
occurred. Optionally, before or after shearing, continuous hot-dip
galvanizing is used to coat the steel alloy. The coating is applied
by passing the steel alloy through a zinc galvanizing bath (not
shown) held above about 420.degree. C., and, more preferably, at a
temperature of greater than or equal to about 420.degree. C. up to
about 480.degree. 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, 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.degree. C. to less than or equal
to about 565.degree. C. and holding for a few seconds. If shearing
has not yet occurred, the steel alloy may then optionally be coiled
into a coil for easier transportability.
[0036] After any optional galvanizing and/or coiling and resultant
uncoiling, sheared blank 220 is placed in an oven 230 (e.g.,
austenitizing furnace). Blank 220 is heated to less than or equal
to about 850.degree. C., so that as recognized by those in the art,
the temperature in the oven 230 may potentially exceed 850.degree.
C. By way of example, blank 220 is placed in a furnace for at last
5 minutes, so blank 220 reaches a temperature of about 850.degree.
C. The heated blank is immediately transferred to dies 240 and 250
and is press hardened into PHS component 260. No rapid quenching
process is required; dies 240 and 250 may remain closed or be
opened on PHS component 260, and the temperature of PHS component
may decrease (e.g., on the order of about 10.degree. C./s) as a
result of heat transferring to the ambient surroundings or air
cooling.
[0037] Before PHS component 260 reaches the martensitic start
temperature, trimmers, punchers, or additional dies (collectively
shown as 270 and 280) may further form (e.g., trim, punch, and/or
re-strike) PHS component 260 to further process PHS component
260.
[0038] Notably, the steel alloys disclosed herein do not require
cooling PHS component 260 at the critical cooling rate of
27.degree. C./s, as is required in typical conventional steel alloy
PHS processes to ensure full martensitic transformation. Rather,
the steel alloys disclosed herein do not transform to bainite or
pearlite as quickly as conventional steel alloys. Therefore, it is
possible to undertake further forming of PHS component 260 while
PHS component 260 is yet above the martensitic start temperature
but falling below the austenitization temperature without risking
inadvertent bainitic or pearlitic transformation. Further, it is
possible to control the amount of retained austenite formed by
controlling the ending temperature of the resulting PHS component
260 undergoing process 200.
[0039] If necessary, surface cleaning of PHS component 260 and dies
240 and 250 occurs to remove superficial oxides formed during the
process.
[0040] Referring to FIG. 5, the process 300 according to another
aspect of the present disclosure is shown. Optionally, a rolled
coil 310 of a steel alloy is pre-treated. After any optional
pre-treat, blank 320 is formed by shearing a section of rolled coil
310 of a steel alloy. Blank 320 may be sheared with trim dies,
alligator shears, bench shears, guillotines, power shears,
throatless shears, or the like. Optionally, before or after
shearing, continuous hot-dip galvanizing is used to coat the steel
alloy. The coating is applied by passing the steel alloy through a
zinc galvanizing bath (not shown) held above about 420.degree. C.,
and, more preferably, at a temperature of greater than or equal to
about 420.degree. C. up to about 480.degree. 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, 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.degree. C. to less than
or equal to about 565.degree. C. and holding for a few seconds. The
steel alloy may then optionally be coiled into a coil for easier
transportability.
[0041] After any optional galvanizing and/or coiling and resultant
uncoiling, sheared blank 320 is placed in an oven 330 (e.g.,
austenitizing furnace). Blank 320 is heated to less than or equal
to about 850.degree. C., so that as recognized by those in the art,
the temperature in the oven 330 may potentially exceed 850.degree.
C. By way of example, blank 320 is placed in a furnace for at last
5 minutes, so blank 320 reaches a temperature of about 850.degree.
C. The heated blank is immediately transferred to dies 340 and 350
and is press hardened into PHS component 360. No rapid quenching
process is required; dies 340 and 350 may remain closed or be
opened on PHS component 360, and the temperature of PHS component
may decrease (e.g., on the order of about 10.degree. C./s) as a
result of heat transferring to the ambient surroundings or air
cooling.
[0042] PHS component 360 is held within the die for a time period
to reach the martensitic start temperature but before reaching the
martensitic finish temperature, trimmers, punchers, or additional
dies (collectively shown as 370 and 380) may further form (e.g.,
trim, punch, and/or re-strike) PHS component 360 to further process
PHS component 360.
[0043] Notably, the steel alloys disclosed herein do not require
cooling PHS component 360 at the critical cooling rate of
27.degree. C./s, as is required in typical conventional steel alloy
PHS processes to ensure full martensitic transformation. Rather,
the steel alloys disclosed herein do not transform to bainite or
pearlite as quickly as conventional steel alloys. Therefore, it is
possible to undertake further forming of PHS component 360 while
PHS component 360 is yet between the martensitic start temperature
and martensitic finish temperature without undue cracking or
resulting in a finished PHS component yielding inadequate strength.
Further, it is possible to control the amount of retained austenite
formed by controlling the ending temperature of the resulting PHS
component 360 undergoing process 300.
[0044] If necessary, surface cleaning of PHS component 360 and dies
340 and 350 occurs to remove superficial oxides formed during the
process.
[0045] Re-striking the press hardened steel alloys produced
according to the present disclosure allows for more aggressive
designs. By way of non-limiting example, while a first forming may
result in a suitable PHS component, the re-striking may allow for
more intricate featuring and/or designs tailored to better resist
external forces, such as a collision.
[0046] The press hardened steel alloys produced according to the
present disclosure provide a PHS component having a multi-phase
microstructure, including martensite and retained austenite. Upon
cooling, the PHS component undergoes a diffusionless martensitic
transformation at a temperature of around 250.degree. C. The
martensitic transformation continues as the PHS component is cooled
to less than or equal to about room temperature. Notably, the press
hardened steel alloys do not require a cooling rate exceeding
27.degree. C./s to ensure adequate martensitic transformation,
distinguishing them from conventional steel alloys. Rather, air
cooling, thereby providing cooling at a rate of about 10.degree.
C./s, is sufficient to prevent bainitic transformation of the press
hardened steel alloys according to the present disclosure. That
said, other cooling methods, such as quenching, may be used to
control the rate of cooling the PHS components contemplated under
the present disclosure. In certain aspects, the martensitic
transformation provides high strength to the PHS component, and the
retained austenite provides better ductility and impact toughness
than conventional steel alloys. The amount of carbon present and
the austenitizing temperature in the press hardened steel alloys
determines the amount of ferrite that is transformed to austenite
and subsequently to martensite. In certain aspects, a PHS component
may have a multi-phase microstructure comprising martensite at
greater than or equal to about 80% to less than or equal to about
98% martensite by volume and less than or equal to about 20% to
greater than or equal to about 2% retained austenite.
[0047] The press hardened steel alloys produced according to the
present disclosure provide excellent strength and tensile
elongation compared to conventional steel alloys. In one example, a
sample of a 22MnB5 alloy was subject to heating to 930.degree. C.
and holding that temperature for about 360 s, followed by quenching
to below the martensitic finish temperature. The UTS of the sample
comprised of 22MnB5 was about 1,500 MPa. A sample comprised of
medium-Mn, was subject to heating to 850.degree. C. and holding
that temperature for 240 s, followed by air cooling the sample to
about 620.degree. C., where the sample was held at that temperature
for 180 s, followed by additional air cooling to room temperature.
The UTS of the sample comprised of medium-Mn yielded a superior UTS
of about 1,719 MPa. Further, a second sample of a medium-Mn alloy
that differed only in that it was heated to a temperature of about
800.degree. C., rather than 850.degree. C., resulted in an even
better UTS of about 1,807 MPa. The tensile elongation of each of
the samples was also assessed. The tensile elongation of the sample
comprised of 22MnB5 was about 6%. The sample comprised of
medium-Mn, however, yielded a superior tensile elongation of about
8%. The second medium-Mn sample, which differed only in that it was
heated to a temperature of about 800.degree. C., rather than
850.degree. C., resulted in a slightly better tensile elongation of
8.2%. The better tensile elongation is believed to arise from the
higher amount of retained austenite present in PHS components made
according to the present disclosure. Further, it is believed that
additional forming of the medium-Mn alloys according to the present
disclosure would result in even better tensile elongation as
additional forming would ultimately yield more retained austenite.
The retained austenite is soft and tough compared to the formed
martensite, and therefore bestows greater tensile elongation to a
PHS component.
[0048] The samples were further analyzed to determine their notched
tensile toughness. A 1.4 mm sample comprised of 22MnB5 and prepared
according to the method in the preceding paragraph was found to
exhibit a nominal engineering stress of about 1,700 MPa and a
nominal engineering strain at break of about 1.2% and roughly 30-50
J/cm.sup.2 toughness, as measured by a Charpy V-notch impact test
at room temperature. A 1.4 mm sample comprised of medium-Mn and
prepared according to the method in the preceding paragraph (where
the medium-Mn alloy was heated to 800.degree. C.) was found to
exhibit a nominal engineering stress of about 2,000 MPa and a
nominal engineering strain at break of about 2.1% and 70 J/cm.sup.2
toughness, as measured by a Charpy V-notch impact test at room
temperature.
[0049] In one exemplary method, the process comprises heating a
blank of a medium-Mn steel alloy to a temperature of less than or
equal to about 850.degree. C. to austenitize the steel alloy. The
blank is then press hardened to form a press-hardened component at
a temperature greater than or equal to about the martensitic start
temperature. The press-hardened component is further formed at a
temperature of less than or equal to about the martensitic start
temperature to greater than or equal to about the martensitic
finish temperature, and the press-hardened component has an
ultimate tensile strength of greater than or equal to about 1,700
MPa. In other variations, the blank is heated to a temperature of
less than or equal to about 800.degree. C. to austenitize the
medium-Mn steel alloy. The medium-Mn steel alloy may comprise
carbon at greater than or equal to about 0.1 wt. % to less than or
equal to about 0.4 wt. % and manganese at greater than or equal to
about 5 wt. % to less than or equal to about 12 wt. %. In yet other
variations, the medium-Mn steel alloy blank is galvanized before
heating. In other aspects, the press-hardened component has a
tensile elongation of greater than or equal to about 8%. In yet
other aspects, the press-hardened steel component may be air cooled
to the martensitic finish temperature after further forming the
press-hardened component. The press-hardened component may have a
microstructure comprising martensite at greater than or equal to
about 80% to less than or equal to about 98% and retained austenite
at less than or equal to about 20% to greater than or equal to
about 2%.
[0050] In another example, the process may consist essentially of
the following steps. A blank of a medium-Mn steel alloy is heated
to a temperature of less than or equal to about 850.degree. C. to
austenitize the steel alloy. The blank is then press hardened to
form a press-hardened component at a temperature greater than or
equal to about the martensitic start temperature. The
press-hardened component is further formed at a temperature of less
than or equal to about the martensitic start temperature to greater
than or equal to about the martensitic finish temperature, and the
press-hardened component has an ultimate tensile strength of
greater than or equal to about 1,700 MPa. In certain other
variations, such a process may be further limited as further
consisting essentially of, any combination of, or all of the
following: (1) heating the blank to a temperature of less than or
equal to about 800.degree. C. to austenitize the medium-Mn steel
alloy; (2) having a steel alloy comprised of carbon at greater than
or equal to about 0.1 wt. % to less than or equal to about 0.4 wt.
% and manganese at greater than or equal to about 5 wt. % to less
than or equal to about 12 wt. %; (3) galvanizing the medium-Mn
steel alloy balnk before heating; (4) a PHS component having a
tensile elongation of greater than or equal to about 8%; (5) air
cooling the press-hardened component to the martensitic finish
temperature after further forming the press-hardened component; and
(6) a PHS component having a microstructure comprising martensite
at greater than or equal to about 80% to less than or equal to
about 98% and retained austenite at less than or equal to about 20%
to greater than or equal to about 2%. Notably, such a process
excludes any laser cutting that are often required in conventional
processes and quenching the press-hardened component, which can
result in time, energy, and cost savings benefits.
[0051] In yet another example, the process may consist of the
following steps. A blank of a medium-Mn steel alloy is heated to a
temperature of less than or equal to about 850.degree. C. to
austenitize the steel alloy. The blank is then press hardened to
form a press-hardened component at a temperature greater than or
equal to about the martensitic start temperature. The
press-hardened component is further formed at a temperature of less
than or equal to about the martensitic start temperature to greater
than or equal to about the martensitic finish temperature, and the
press-hardened component has an ultimate tensile strength of
greater than or equal to about 1,700 MPa. In certain other
variations, such a process may be further limited as further
consisting of, any combination of, or all of the following: (1)
heating the blank to a temperature of less than or equal to about
800.degree. C. to austenitize the medium-Mn steel alloy; (2) having
a steel alloy comprised of carbon at greater than or equal to about
0.1 wt. % to less than or equal to about 0.4 wt. % and manganese at
greater than or equal to about 5 wt. % to less than or equal to
about 12 wt. %; (3) galvanizing the medium-Mn steel alloy blank
before heating; (4) a PHS component having a tensile elongation of
greater than or equal to about 8%; (5) air cooling the
press-hardened component to the martensitic finish temperature
after further forming the press-hardened component; and (6) a PHS
component having a microstructure comprising martensite at greater
than or equal to about 80% to less than or equal to about 98% and
retained austenite at less than or equal to about 20% to greater
than or equal to about 2%. Notably, such a process excludes any
laser cutting that are often required in conventional processes and
quenching the press-hardened component, which can result in time,
energy, and cost savings benefits.
[0052] In another exemplary method, the process comprises heating a
blank comprising a medium-Mn steel alloy to a temperature of less
than or equal to about 850.degree. C. to austenitize the steel
alloy. The blank is then press hardened to form a press-hardened
component at a temperature greater than or equal to about the
martensitic start temperature. After press hardening, the
press-hardened component is further formed at a temperature of
greater than or equal to about the martensitic start temperature,
and the press-hardened component has an ultimate tensile strength
of greater than or equal to about 1,700 MPa. In other variations,
the blank is heated to a temperature of less than or equal to about
800.degree. C. to austenitize the medium-Mn steel alloy. The
medium-Mn steel alloy may comprise carbon at greater than or equal
to about 0.1 wt. % to less than or equal to about 0.4 wt. % and
manganese at greater than or equal to about 5 wt. % to less than or
equal to about 12 wt. %. In yet other variations, the medium-Mn
steel alloy blank is galvanized before heating. In other aspects,
the press-hardened component has a tensile elongation of greater
than or equal to about 8%. In yet other aspects, the press-hardened
steel component is air cooled to the martensitic finish temperature
after further forming the press-hardened component. The
press-hardened component may have a microstructure comprising
martensite at greater than or equal to about 80% to less than or
equal to about 98% and retained austenite at less than or equal to
about 20% to greater than or equal to about 2%.
[0053] In another example, the process may consist essentially of
the following steps. A blank comprising a medium-Mn steel alloy is
heated to a temperature of less than or equal to about 850.degree.
C. to austenitize the steel alloy. The blank is then press hardened
to form a press-hardened component at a temperature greater than or
equal to about the martensitic start temperature. After press
hardening, the press-hardened component is further formed at a
temperature of greater than or equal to about the martensitic start
temperature, and the press-hardened component has an ultimate
tensile strength of greater than or equal to about 1,700 MPa. In
certain other variations, such a process may be further limited as
further consisting essentially of, any combination of, or all of
the following: (1) heating the blank to a temperature of less than
or equal to about 800.degree. C. to austenitize the medium-Mn steel
alloy; (2) having a steel alloy comprised of carbon at greater than
or equal to about 0.1 wt. % to less than or equal to about 0.4 wt.
% and manganese at greater than or equal to about 5 wt. % to less
than or equal to about 12 wt. %; (3) galvanizing the medium-Mn
steel alloy blank before heating; (4) a PHS component having a
tensile elongation of greater than or equal to about 8%; (5) air
cooling the press-hardened component to the martensitic finish
temperature after further forming the press-hardened component; and
(6) a PHS component having a microstructure comprising martensite
at greater than or equal to about 80% to less than or equal to
about 98% and retained austenite at less than or equal to about 20%
to greater than or equal to about 2%. Notably, such a process
excludes any laser cutting that are often required in conventional
processes and quenching the press-hardened component, which can
result in time, energy, and cost savings benefits.
[0054] In yet another example, the process may consist of the
following steps. A blank comprising a medium-Mn steel alloy is
heated to a temperature of less than or equal to about 850.degree.
C. to austenitize the steel alloy. The blank is then press hardened
to form a press-hardened component at a temperature greater than or
equal to about the martensitic start temperature. After press
hardening, the press-hardened component is further formed at a
temperature of greater than or equal to about the martensitic start
temperature, and the press-hardened component has an ultimate
tensile strength of greater than or equal to about 1,700 MPa. In
certain other variations, such a process may be further limited as
further consisting of, any combination of, or all of the following:
(1) heating the blank to a temperature of less than or equal to
about 800.degree. C. to austenitize the medium-Mn steel alloy; (2)
having a steel alloy comprised of carbon at greater than or equal
to about 0.1 wt. % to less than or equal to about 0.4 wt. % and
manganese at greater than or equal to about 5 wt. % to less than or
equal to about 12 wt. %; (3) galvanizing the medium-Mn steel alloy
blank before heating; (4) a PHS component having a tensile
elongation of greater than or equal to about 8%; (5) air cooling
the press-hardened component to the martensitic finish temperature
after further forming the press-hardened component; and (6) a PHS
component having a microstructure comprising martensite at greater
than or equal to about 80% to less than or equal to about 98% and
retained austenite at less than or equal to about 20% to greater
than or equal to about 2%. Notably, such a process excludes any
laser cutting that are often required in conventional processes and
quenching the press-hardened component, which can result in time,
energy, and cost savings benefits.
[0055] In an additional exemplary method, a process comprises
heating a blank comprised of a medium-Mn steel alloy to a
temperature of less than or equal to about 850.degree. C. to
austenitize the steel alloy. The blank is then press hardened to
form a press-hardened component. The press-hardened component is
formed a second time at a temperature of greater than or equal to
about the martensitic finish temperature. The further forming
includes at least one of trimming, punching, or re-striking the
press-hardened component. The press-hardened component is cooled at
a controlled rate between the martensitic start temperature and the
martensitic finish temperature such that the press-hardened
component has a microstructure comprising martensite at greater
than or equal to about 80% to less than or equal to about 98% and
retained austenite at less than or equal to about 20% to greater
than or equal to about 2%. In other variations, the blank is heated
to a temperature of less than or equal to about 800.degree. C. to
austenitize the medium-Mn steel alloy. The medium-Mn steel alloy
may comprise carbon at greater than or equal to about 0.1 wt. % to
less than or equal to about 0.4 wt. % and manganese at greater than
or equal to about 5 wt. % to less than or equal to about 12 wt. %.
In yet other variations, the press-hardened component has an
ultimate tensile strength of greater than or equal to about 1,700
MPa. In yet other aspects, the press-hardened steel component is
air cooled to the martensitic finish temperature after further
forming the press-hardened component. In further variations, the
medium-Mn steel alloy blank is galvanized before heating.
[0056] In another example, the process may consist essentially of
the following steps. A blank comprised of a medium-Mn steel alloy
is heated to a temperature of less than or equal to about
850.degree. C. to austenitize the steel alloy. The blank is ten
press hardened to form a press-hardened component. The
press-hardened component is formed a second time at a temperature
of greater than or equal to about the martensitic finish
temperature. The further forming includes at least one of trimming,
punching, or re-striking the press-hardened component. The
press-hardened component is cooled at a controlled rate between the
martensitic start temperature and the martensitic finish
temperature such that the press-hardened component has a
microstructure comprising martensite at greater than or equal to
about 80% to less than or equal to about 98% and retained austenite
at less than or equal to about 20% to greater than or equal to
about 2%. In certain other variations, such a process may be
further limited as further consisting essentially of, any
combination of, or all of the following: (1) heating the blank to a
temperature of less than or equal to about 800.degree. C. to
austenitize the medium-Mn steel alloy; (2) having a steel alloy
comprised of carbon at greater than or equal to about 0.1 wt. % to
less than or equal to about 0.4 wt. % and manganese at greater than
or equal to about 5 wt. % to less than or equal to about 12 wt. %;
(3) a PHS component having an ultimate tensile strength of greater
than or equal to about 1,700 MPa; (5) air cooling the
press-hardened component to the martensitic finish temperature
after further forming the press-hardened component; and (6)
galvanizing the medium-Mn steel alloy blank before heating.
Notably, such a process excludes any laser cutting that are often
required in conventional processes and quenching the press-hardened
component, which can result in time, energy, and cost savings
benefits.
[0057] In yet another example, the process may consist of the
following steps. A blank comprised of a medium-Mn steel alloy is
heated to a temperature of less than or equal to about 850.degree.
C. to austenitize the steel alloy. The blank is ten press hardened
to form a press-hardened component. The press-hardened component is
formed a second time at a temperature of greater than or equal to
about the martensitic finish temperature. The further forming
includes at least one of trimming, punching, or re-striking the
press-hardened component. The press-hardened component is cooled at
a controlled rate between the martensitic start temperature and the
martensitic finish temperature such that the press-hardened
component has a microstructure comprising martensite at greater
than or equal to about 80% to less than or equal to about 98% and
retained austenite at less than or equal to about 20% to greater
than or equal to about 2%. In certain other variations, such a
process may be further limited as further consisting of, any
combination of, or all of the following: (1) heating the blank to a
temperature of less than or equal to about 800.degree. C. to
austenitize the medium-Mn steel alloy; (2) having a steel alloy
comprised of carbon at greater than or equal to about 0.1 wt. % to
less than or equal to about 0.4 wt. % and manganese at greater than
or equal to about 5 wt. % to less than or equal to about 12 wt. %;
(3) a PHS component having an ultimate tensile strength of greater
than or equal to about 1,700 MPa; (5) air cooling the
press-hardened component to the martensitic finish temperature
after further forming the press-hardened component; and (6)
galvanizing the medium-Mn steel alloy blank before heating.
Notably, such a process excludes any laser cutting that are often
required in conventional processes and quenching the press-hardened
component, which can result in time, energy, and cost savings
benefits.
[0058] 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.
* * * * *