U.S. patent application number 16/618293 was filed with the patent office on 2021-05-27 for sheet-metal formed component and method for the production of the sheet-metal formed component.
The applicant listed for this patent is BENTELER AUTOMOBILTECHNIK GMBH, THYSSENKRUPP HOHENLIMBURG GMBH, THYSSENKRUPP STEEL EUROPE AG. Invention is credited to Karsten BAKE, Georg FROST, Anastasia Viviana HOEHNE, Markus KETTLER, Karin SCHRADER, Andreas TOMITZ.
Application Number | 20210156000 16/618293 |
Document ID | / |
Family ID | 1000005389313 |
Filed Date | 2021-05-27 |
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United States Patent
Application |
20210156000 |
Kind Code |
A1 |
TOMITZ; Andreas ; et
al. |
May 27, 2021 |
SHEET-METAL FORMED COMPONENT AND METHOD FOR THE PRODUCTION OF THE
SHEET-METAL FORMED COMPONENT
Abstract
The invention relates to a sheet-metal formed component and a
method or producing the sheet-metal formed component, produced by
hot-working and press-quenching from a quenchable, unitary and
materially uniform steel alloy, wherein the sheet-metal formed
component has multiple superposed martensite layers, wherein a
respectively outer martensite layer of the sheet-metal formed
component has higher ductility than an underlying martensite
layer.
Inventors: |
TOMITZ; Andreas; (Hagen,
DE) ; HOEHNE; Anastasia Viviana; (Dortmund, DE)
; SCHRADER; Karin; (Iserlohn, DE) ; KETTLER;
Markus; (Schlangen, DE) ; BAKE; Karsten;
(Delbrueck, DE) ; FROST; Georg; (Steinheim,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BENTELER AUTOMOBILTECHNIK GMBH
THYSSENKRUPP STEEL EUROPE AG
THYSSENKRUPP HOHENLIMBURG GMBH |
Paderborn
Duisburg
Hagen |
|
DE
DE
DE |
|
|
Family ID: |
1000005389313 |
Appl. No.: |
16/618293 |
Filed: |
June 1, 2018 |
PCT Filed: |
June 1, 2018 |
PCT NO: |
PCT/DE2018/100530 |
371 Date: |
November 29, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 1/673 20130101;
C21D 2211/009 20130101; C21D 2211/008 20130101; C21D 2211/005
20130101; C21D 8/0405 20130101; C21D 8/0426 20130101; B21D 28/26
20130101; C21D 9/48 20130101 |
International
Class: |
C21D 9/48 20060101
C21D009/48; C21D 8/04 20060101 C21D008/04; C21D 1/673 20060101
C21D001/673; B21D 28/26 20060101 B21D028/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2017 |
DE |
10 2017 112 164.1 |
Claims
1-10. (canceled)
11. A sheet-metal formed component, produced by hot-working and
press-quenching from a quenchable, unitary and materially uniform
steel alloy, the sheet-metal formed component comprising: a
plurality of superposed martensite layers, wherein one of the
plurality of superposed martensite layers is an outer martensite
layer and another one of the plurality of superposed martensite
layers is an underlying martensite layer underlying the outer
martensite layer, the outer martensite layer having higher
ductility than the underlying martensite layer, the sheet-metal
formed component has a tensile strength of greater than 1200 MPa,
and the sheet-metal formed component has a bending angle of greater
than 60.degree. for a wall thickness of 0.5 to 1.5 mm or a bending
angle of greater than 45.degree. for a wall thickness of 1.5 to 2.5
mm.
12. The sheet-metal formed component according to claim 11, wherein
the plurality of superposed martensite layers comprises at least
three martensite layers between two opposite surfaces of the
sheet-metal formed component over the wall thickness, and the outer
martensite layer has a thickness of 4 .mu.m to 140 .mu.m.
13. The sheet-metal formed component according to claim 11, wherein
the plurality of superposed martensite layers is superposed between
two opposite surfaces of the sheet-metal formed component, and both
of the surfaces are surface-decarburized layers comprising an
ferritic material structure.
14. The sheet-metal formed component according to claim 11, wherein
the plurality of superposed martensite layers is produced from a
semi-finished product having an outer ferrite layer with an
underlying pearlite layer.
15. The sheet-metal formed component according to claim 11, wherein
the quenchable steel alloy comprises a manganese boron steel having
a proportion by weight of 0.5 to 1.7% (inclusive) of manganese and
0.0008 to 0.005% (inclusive) of boron.
16. The sheet-metal formed component according to claim 11, wherein
certain area regions of the sheet-metal formed component have at
least one of different strengths, or different wall
thicknesses.
17. A method of producing a sheet-metal formed component, the
method comprising: hot-rolling a quenchable steel alloy to obtain a
hot-rolled product, generating, on a surface of the hot-rolled
product, a ferrite-pearlite lamination with a ferrite layer over an
entire strip breadth of the product, individualizing the product to
obtain blanks, rapid heating of the blanks at a heating rate of
greater than 30 K/s from ambient temperature to above an
austenizing temperature, and hot-working and press-quenching each
of the rapid heated blanks into a sheet-metal formed component,
wherein the sheet-metal formed component comprises a plurality of
superposed martensite layers, one of the plurality of superposed
martensite layers is an outer martensite layer and another one of
the plurality of superposed martensite layers is an underlying
martensite layer underlying the outer martensite layer, the outer
martensite layer having higher ductility than the underlying
martensite layer, the sheet-metal formed component has a tensile
strength of greater than 1200 MPa, and the sheet-metal formed
component has a bending angle of greater than 60.degree. for a wall
thickness of 0.5 to 1.5 mm or a bending angle of greater than
45.degree. for a wall thickness of 1.5 to 2.5 mm.
18. A method of producing a metal semi-finished product from a
quenchable steel alloy for further processing into a sheet-metal
formed component, the method comprising: hot-rolling the quenchable
steel alloy to obtain a hot-rolled product, generating an outer
ferrite layer and an underlying pearlite layer on both of opposite
surfaces of the hot-rolled product, over an entire strip breadth of
the product, and individualizing the product to obtain blanks each
of which is a metal semi-finished product to be further processed
into a sheet-metal formed component, wherein the sheet-metal formed
component comprises a plurality of superposed martensite layers,
one of the plurality of superposed martensite layers is an outer
martensite layer and another one of the plurality of superposed
martensite layers is an underlying martensite layer underlying the
outer martensite layer, the outer martensite layer having higher
ductility than the underlying martensite layer, the sheet-metal
formed component has a tensile strength of greater than 1200 MPa,
and the sheet-metal formed component has a bending angle of greater
than 60.degree. for a wall thickness of 0.5 to 1.5 mm or a bending
angle of greater than 45.degree. for a wall thickness of 1.5 to 2.5
mm.
19. The method according to claim 17, wherein the hot-rolling
comprises: heating a slab of the quenchable steel alloy to a core
temperature of above 1200.degree. C. for a time of greater than 60
s, rolling the heated slab first to a preliminary strip thickness
of between 45 and 55 mm, and then to a strip thickness of 13 to 25
mm to obtain a rolled steel strip, wherein a rolling end
temperature of the rolled steel strip is 860 to 920.degree. C., and
a rolling end velocity is 3-12 m/s, and after the rolling, cooling
the rolled steel strip over a path of 65 to 80 m at a cooling rate
of 15 to 30 K/s until reaching a reel temperature of 650 to
800.degree. C. to obtain the hot-rolled product.
20. The method according to claim 17, wherein the rapid heating is
carried out by contact heating at a heating rate of greater than 50
K/s.
21. The sheet-metal formed component of claim 11, wherein the
sheet-metal formed component has a tensile strength of greater than
1350 MPa.
22. The sheet-metal formed component according to claim 11, wherein
the plurality of superposed martensite layers comprises at least
five martensite layers between two opposite surfaces of the
sheet-metal formed component over the wall thickness, and the outer
martensite layer has a thickness of 4 .mu.m to 140 .mu.m.
23. The sheet-metal formed component according to claim 11, wherein
the plurality of superposed martensite layers comprises at least
seven martensite layers between two opposite surfaces of the
sheet-metal formed component over the wall thickness, and the outer
martensite layer has a thickness of 4 .mu.m to 140 .mu.m.
24. The sheet-metal formed component according to claim 11, wherein
the plurality of superposed martensite layers comprises two
outermost martensite layers at two opposite surfaces of the
sheet-metal formed component, respectively, and the two outermost
martensite layers are surface-decarburized layers having an
essentially ferritic material structure.
25. The sheet-metal formed component according to claim 14, wherein
the semi-finished product has further underlying alternating
ferrite layers and pearlite layers.
26. The method according to claim 17, wherein the rapid heating is
carried out by contact heating at a heating rate of greater than 80
K/s.
27. The method according to claim 17, wherein the rapid heating of
the blanks is carried out at a heating rate of greater than 50 K/s,
from ambient temperature to above the austenizing temperature.
Description
RELATED APPLICATIONS
[0001] The present application is a National Phase of International
Application Number PCT/DE2018/100530 filed Jun. 1, 2018, which
claims priority to German Application Number 10 2017 112 164.1
filed Jun. 1, 2017.
FIELD
[0002] The present disclosure relates to a sheet-metal formed
component, produced by hot-working and press-quenching.
[0003] The present disclosure further relates to a method for the
production of the sheet-metal formed component, and to a method for
the production of a metal semi-finished product.
BACKGROUND
[0004] The production of sheet-metal formed components is known
from the prior art. To that end, sheet-metal blanks are shaped
using conventional shaping methods, for example deep drawing, to
give a three-dimensionally shaped component. Sheet-metal formed
components of this kind are used to a great extent in the motor
vehicle industry and in that context are used as motor vehicle
components. Consequently, and in the context of this disclosure,
sheet-metal formed components are to be understood essentially as
motor vehicle components.
[0005] In the context of motor vehicles, a distinction is drawn
between, among other things, motor vehicle structural components
which are used to produce a self-supporting motor vehicle body.
Known examples of these are motor vehicle pillars, an A-pillar or a
B-pillar, longitudinal beams, transverse beams, roof spars, door
sills, transmission tunnels or similar components. Body outer skin
components of the motor vehicle can also be produced, for example
an engine hood, a roof outer skin or a door outer skin. It is also
possible to produce add-on parts or crash components, for example a
crash box, a bumper crossmember or the like.
[0006] However, the motor vehicle industry requires consistent
implementation of lightweight construction methods as well as
improved stiffness or, as the case may be, crash properties of the
components. Hot-working and press-quenching technology was
developed for this purpose. This makes it possible to heat a blank
or a preformed semi-finished product made of a quenchable steel
alloy to a temperature above the austenizing temperature (AC3). The
blank is shaped in this hot state. This has the advantage, on one
hand, that the heating to above the austenizing temperature
increases the degree of shaping of the blank that it is possible to
generate. Already during and/or after shaping, the still-hot
sheet-metal formed component is cooled at such a high rate that the
structure changes from austenite to martensite, making it possible
to set high strengths.
[0007] The components in this manner by hot-working and
press-quenched have high strength. However, the high strength can
also be accompanied by brittleness or reduced ductility of the
sheet-metal formed component produced in this manner.
[0008] However, this is generally not desired since it can lead to
brittle fractures and, in the event of a crash, to the sheet-metal
formed component tearing off at coupling points.
[0009] Use is generally made of conventional furnace heating
systems which have for example a 30 to 40 m-long heating path.
Accordingly, an associated heating time to above the austenizing
temperature is required.
[0010] The sheet-metal formed components produced by hot-working
and press-quenching, for example made of a steel of the 22MnB5
type, have good properties with regard to strength and at the same
time ductility.
[0011] However, in recent years contact heating has become known,
specifically in the field of hot-working and the heating to above
the austenizing temperature required for that purpose. In this
context it is possible, with a small footprint in a production hall
with at the same time high heating rates of greater than 30 K/s, or
greater than 50 K/s, to heat the blanks much more rapidly for
hot-working and subsequent press-quenching. However, it has been
observed that, when using known quenchable steel alloys, although
high strengths are achieved in the finished product, the short
heating time leads to reduced ductility and consequently reduced
bending angle. This makes the production of crash-relevant
components impossible or unreliable with rapid heating.
SUMMARY
[0012] The present disclosure therefore has the object, proceeding
from the prior art, of specifying a component and a method for the
production of the component that overcome the above-mentioned
drawbacks.
[0013] The above-mentioned object is achieved, according to the
disclosure, with a sheet-metal formed component, produced by
hot-working and press-quenching.
[0014] The method-relevant part of the object is further achieved
by a method for the production of the sheet-metal formed
component.
[0015] A further method-relevant part of the object is achieved by
a method for the production of a metal semi-finished product.
[0016] The sheet-metal formed component according to the disclosure
is produced by hot-working and press-quenching. The sheet-metal
formed component is in that context produced from a quenchable,
unitary and materially uniform steel alloy. This means that it is
not a plated material but rather a material that is unitary and
materially uniform in section. In that context, the sheet-metal
formed component has a tensile strength Rm of greater than 1200
MPa, or greater than 1350 MPa. Moreover, the sheet-metal formed
component has a bending angle of greater than 60.degree. for a wall
thickness of 0.5 to 1.5 mm. For a greater wall thickness of 1.5 to
2.5 mm, the sheet-metal formed component has a bending angle of
greater than 45.degree.. The tensile strength should not exceed
2500 MPa.
[0017] The bending angle is determined in the plate bending test
according to VDA 238-100:2010, at a proof stress Rp 0.2 of greater
than 900 MPa.
[0018] According to the disclosure, the sheet-metal formed
component is henceforth characterized in that, proceeding from both
surfaces, in each case laminated martensite plies or martensite
layers are formed. Consequently, from an upper side and an
underside of the three-dimensionally shaped sheet-metal formed
component, adjacent martensite layers with different properties are
formed over the sheet thickness, or wall thickness. These are, in
alternation, more ductile and harder martensite layers. The more
ductile martensite layer is always on the surface, or outer
side.
[0019] According to the disclosure, the above-mentioned sheet-metal
formed component is produced from a hot-rolled product, hereinafter
also termed semi-finished product. The hot-rolled product is
produced so as to be unitary and materially uniform. However, at
the end of the rolling process it does have different layers in the
material structure. The layers can also be termed plies or lines.
The layers are areal and extend over the entire surface area of the
resulting semi-finished product, but at least over the entire strip
breadth. The semi-finished product is provided in the form of a
blank.
[0020] According to the disclosure, the respective outer layer of
the semi-finished product is designed as a ferrite layer. This in
turn has a thickness of 4 to 140 .mu.m. Consequently, an outer
ferrite layer is created on the upper side and the underside of the
semi-finished product. Beneath this ferrite layer, a pearlite layer
is created with a thickness of 4 to 25 .mu.m. Adjoining this are,
respectively in alternation, further ferrite and pearlite layers
over the strip thickness or wall thickness. The layers always
extend over the entire strip breadth.
[0021] From the semi-finished product that is laminated in this
manner, following the rapid heating, hot-working and subsequent
cooling during press-quenching, an outer carbon-poor martensite
layer and an underlying carbon-rich martensite layer can be
created, since the rapid heating causes no diffusion equalization
between the ferritic and pearlitic layers. Thus, the outer ferrite
layer is converted to a martensite layer which has lower strength
while at the same time having high ductility. The underlying
pearlite layer is converted to a martensite layer which has, by
contrast, higher strength but reduced ductility.
[0022] Over the wall thickness, there are at least three, five or
seven layers of martensite formed.
[0023] A delta or difference in the strength between a martensite
layer having higher strength but reduced ductility and the
martensite layer having lower strength but higher ductility is at
least between 100 and 300 MPa. This means that the higher-strength
martensite layer is at least 100 to 300 MPa stronger than the
martensite layer having greater ductility but lower strength.
However, the delta between the individual martensite layers of
different strength should not exceed approximately 1000 MPa.
[0024] It can further be provided, by additional targeted surface
decarburization of the semi-finished product, to create the
outermost layer as a surf ace-decarburized layer which has a very
low carbon content.
[0025] In this surf ace-decarburized layer, the very carbon-poor
ferritic material structure that is present does not convert to
martensite during press-quenching, or does so only to a limited
degree, and as a result this structure has a markedly lower
strength. The surf ace-decarburized layer has an essentially
ferritic material structure. In comparison to the higher-strength
and reduced-ductility martensite layer, the difference in strength
can be up to 1000 MPa.
[0026] These layers having different strengths and different
ductilities then alternate over the strip thickness. However, the
overall hot-worked and press-quenched sheet-metal formed component
has high strength and at the same time high ductility so that the
above-mentioned bending angle can be achieved even in spite of the
rapid heating of the semi-finished product.
[0027] Surface decarburization can be carried out simultaneously or
additionally. Thus, in the produced sheet-metal formed component,
the ductility in the surface region is further increased while the
strength remains constant. Surface decarburization is carried out
after hot-rolling of the sheet-metal strip.
[0028] The respectively outer layer of the sheet-metal formed
component, that is to say the outer martensite layer, has a layer
thickness of 4 to 140 .mu.m, 10 to 140 .mu.m, or 14 to 140
.mu.m.
[0029] If the sheet-metal formed component has an optional surface
decarburization, this surface decarburization is external,
extending in each case from the surface into the sheet-metal formed
component, and is thus included in the above-mentioned layer
thickness of the outer layer, or the surf ace-decarburized layer
can also form the outer layer. For example, a surface
decarburization can extend in a layer from 10 to 140 .mu.m, or 20
to 100 .mu.m from the surface into the sheet-metal formed
component, or into the outer martensite layer.
[0030] For the production of the sheet-metal formed component
according to the disclosure, use can be made of quenchable steel
alloys such as 22MnB5, but also MBW 1900 or MBW 1500. These are
manganese boron steels have the following modification: it has been
found to be advantageous, for the production of the semi-finished
product, to use a quenchable manganese boron steel having a
proportion by weight of 0.5 to 1.7% (inclusive) of manganese (Mn)
and a proportion of 0.0008 to 0.005% (inclusive) of boron (B). The
manganese content slows the incubation time for the formation of
bainite and ferrite. The boron content slows the formation of
ferrite and pearlite. This combination of the alloying elements
makes it possible to generate an isolated ferritic-pearlitic
conversion region starting at the surface so that, through the
cooling conditions imposed after rolling, it is possible to create
a lattice structure/lattice layers in a targeted manner in the
semi-finished product. The targeted cooling in a cooling path after
the final rolling stand makes it possible, in that context, to
establish a laminated structure of ferrite and pearlite over the
strip thickness, proceeding from the surface. The subsequent rapid
heating, hot-working and press-quenching makes this convert into
corresponding martensite layers with mutually different strength
properties. A fine martensite structure with locally different
carbon contents is created in the ferrite layer and the pearlite
layer.
[0031] The produced sheet-metal formed components are motor vehicle
components, such as body components, or body structural components
which meet crash-relevant requirements.
[0032] The rapid heating in less than 1 minute, 30 s, or 20 s, with
a heating rate of greater than 30 K/s, or greater than 50 K/s, from
room temperature to above the AC3 temperature, is carried out in
the context of the disclosure by contact heating. To that end,
contact plates are applied to one side or to both sides of the
semi-finished product, that is to say the blank. The contact plates
are at a higher temperature so that through thermal conduction the
higher temperature of the contact plates is transferred to the
semi-finished product that is to be heated. Inductive heating, and
heating by means of a burner flame or infrared, are also
possible.
[0033] The use of contact heating technology makes it possible, in
a quasi-targeted manner, to temper only partial regions. This makes
it possible to heat only partial area regions of the semi-finished
product to above the austenizing temperature, which then leads, in
the subsequent hot-working and press-quenching, to only partial
hardening in these area regions. In the partial area regions, the
tempering and hardening takes place over the entire wall thickness.
In the case of the hardening, the various martensite layers are
created.
[0034] It is also possible to produce a semi-finished product that
has different wall thicknesses in certain area regions.
[0035] The present disclosure further relates to a method for the
production of a sheet-metal formed component having the following
method steps: [0036] hot-rolling a quenchable steel alloy, [0037]
generating a ferrite-pearlite lamination with, on the surface of
the hot-rolled product, a ferrite layer over the entire strip
breadth, [0038] individualizing to give blanks, [0039] rapid
heating of a blank, in a time of less than 60 s and at a heating
rate of greater than 30 K/s, 50 K/s, 60 K/s, or 80 K/s, from
ambient temperature to above the austenizing temperature, [0040]
hot-working and press-quenching of the sheet-metal formed
component.
[0041] In the above-mentioned method, the metal semi-finished
product used is a hot-rolled product which is produced by means of
the method described below: [0042] hot-rolling a quenchable steel
alloy, [0043] generating an outer ferrite-pearlite lamination with,
on the surface of the hot-rolled product, a ferrite layer over the
entire strip breadth, [0044] individualizing to give blanks.
[0045] The hot-rolling can be carried out with the following method
parameters: [0046] providing a slab and heating to a core
temperature of above 1200.degree. C. for a time of greater than 60
s, [0047] rolling to a preliminary strip thickness of between 45
and 55 mm, [0048] intermediate-rolling to a strip thickness of 13
to 25 mm, [0049] rolling end temperature of the rolled steel sheet
strip 860 to 920.degree. C., [0050] rolling end velocity 3-12 m/s,
[0051] cooling over a path of 65 to 80 m after the final rolling
stand at 15 to 30 K/s, [0052] reaching a reel temperature of 650 to
800.degree. C., [0053] coiling the steel strip produced in this
manner.
[0054] The steel sheet strip hot-rolled and cooled in this manner
has in outer layers the ferrite and pearlite structure according to
the disclosure, which, in a subsequent hot-working and
press-quenching method, serves for improved ductility of the
produced sheet-metal formed components in comparison to a
conventionally hot-worked and press-quenched steel with preceding
rapid heating.
[0055] It is also possible for the steel sheet strip to be coated,
for example with an AlSi or zinc coating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] Further advantages, features, properties and aspects of the
present disclosure form the subject matter of the following
description. Configuration embodiments are described in schematic
figures. Said figures serve for simpler understanding of the
disclosure. In the figures:
[0057] FIG. 1 shows a manufacturing sequence for the production,
first, of a semi-finished product according to the disclosure and
for the further processing to give a sheet-metal formed component
produced according to the disclosure,
[0058] FIG. 2 shows a partial section view through a semi-finished
product according to the disclosure, and
[0059] FIGS. 3a to 3c show in each case a partial section view
through a sheet-metal formed component produced according to the
disclosure,
[0060] FIG. 4 shows a sheet-metal formed component produced
according to the disclosure, having in certain regions areas of
mutually different strengths, and
[0061] FIG. 5 shows a partial section view through a sheet-metal
formed component, according to the disclosure, with different wall
thicknesses.
[0062] In the figures, the same reference signs are used for
identical or similar components, even if a repeated description is
omitted for reasons of simplicity.
DETAILED DESCRIPTION
[0063] FIG. 1 shows a production method according to the
disclosure. First, a slab 2 made of a quenchable steel alloy is
provided, is heated in a furnace 14 and is then fed through a
rolling path 3. The furnace 14 is at a temperature T.sub.1 above
1200.degree. C. After passing through the final rolling stand 4,
the steel sheet strip 5 rolled in this fashion has a rolling end
temperature. It is then fed through a cooling path 6. At the end of
the cooling path 6, the cooled steel sheet strip 7 is at a reel
temperature in order to be then coiled on a coiler 8. Thus, a
hot-rolled product is provided in the form of a coil. The strip
breadth B extends into the plane of the image.
[0064] The hot-rolled product can however also, according to the
next method step, be an appropriately individualized blank 9. In an
uncoiling process (not shown in greater detail), the steel sheet
strip 7 is supplied to an individualizer 10. The individual blanks
9 then undergo, according to the disclosure, rapid heating in a
tempering station 11 and are heated to above the austenizing
temperature. To that end, contact plates 12, which come into
contact with the blank 9 that is to be heated, are arranged in the
tempering station 11.
[0065] The heated blank 9 is transferred to a hot-working and
press-quenching tool 13, where it is hot-worked and press-quenched.
The sheet-metal formed component 1 produced according to the
disclosure is obtained at the end of the press-quenching
procedure.
[0066] FIG. 2 shows a cross section of a detail of the
semi-finished product, or of the individualized blank 9, prior to
heating, that is to say prior to austenizing. The blank 9 has an
overall wall thickness, hereinafter termed wall thickness W, which
is between 0.5 and 2.5 mm. From a respective outer surface 15, 16,
multiple layers of ferrite and pearlite are arranged one atop the
other in alternation over the wall thickness W. The ferrite and
pearlite layers are then arranged immediately next to one another.
Over the wall thickness W, the blank 9, or the semi-finished
product, is unitary and materially uniform.
[0067] The respective outer ferrite layer 17 has a thickness D17 of
4 .mu.m to 140 .mu.m. The outer ferrite layer 17 then respectively
also forms the surface 15, 16 of the blank 9. Proceeding from the
surface 15, or 16, a pearlite layer 18 is in each case arranged
beneath the ferrite layer 17. The pearlite layer 18 has a thickness
D18 of 4 .mu.m to 25 .mu.m. There then follow, in alternation,
further ferrite layers 19, in turn followed by a respective
pearlite layer 20. These can also respectively have a thickness of
4 .mu.m to 25 .mu.m.
[0068] In the depiction here, thirteen layers are formed over the
wall thickness W. According to the disclosure, at least three
layers, five layers, or more than seven layers of ferrite and
pearlite are formed over the wall thickness W. The individual
layers are not shown to scale with one another with regard to their
respective wall thickness ratio.
[0069] FIG. 3a shows the detail of FIG. 2 from the already-produced
sheet-metal formed component 1. This means that heating,
hot-working and press-quenching have taken place. Furthermore, the
individual layers are formed over the wall thickness W. However,
the structure has transformed into martensite. What were the
ferrite layers have transformed into martensite layers 21 of lower
strength and high ductility in comparison to the martensite layer
22 described below. The pearlite layers 18 which lie beneath, as
seen from the surface 15, 16, and also the deeper pearlite layers
20, have transformed into martensite layers 22 of higher strength
and lower ductility. Deeper still, lower-strength and
higher-ductility martensite layers 21 alternate with
higher-strength and lower-ductility martensite layers 22.
[0070] FIG. 3b shows a detail similar to FIG. 3a, wherein here each
outer surface has a layer 26 formed by surface decarburization.
This has an essentially ferritic material structure, or the layers
26 can also consist entirely of ferrite. The surface-decarburized
layer 26 then transitions into the outer martensite layer 21 that
has low strength but higher ductility. Optionally, the
surface-decarburized layer 26 can also form the entire outer layer.
The higher-strength martensite layer 22 then follows directly. This
is shown in FIG. 3c.
[0071] FIG. 4 shows a sheet-metal formed component 1, produced
according to the disclosure, as a motor vehicle component and in
this case specifically as a motor vehicle pillar. This sheet-metal
formed component 1 has, for example, a lower foot region 23, an
upper roof-attachment region 24, and between these two a middle
portion 25. The middle portion 25 can have a reduced wall thickness
W25 compared to, for example, the foot region 23.
[0072] A partial longitudinal section view along section line A-A
is shown in FIG. 5. That figure shows that the wall thickness W23
in the foot region 23 is less than the wall thickness W25 in the
middle portion 25. The individual martensite layers are also formed
in the region of lesser wall thickness. The individual layers are
for example produced by flexible cold-rolling of the blank 9 or of
the cooled steel sheet strip 7. This swages the ferrite and
pearlite layers so that they are thinner but still present in the
same number over the wall thickness W. Once austenizing,
hot-working and press-quenching are complete, the individual
martensite layers are formed also in the lesser wall thickness, in
the same number but thinner.
[0073] The foregoing description of some embodiments of the
disclosure has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
disclosure to the precise form disclosed, and modifications and
variations are possible in light of the above teachings. The
specifically described embodiments explain the principles and
practical applications to enable one ordinarily skilled in the art
to utilize various embodiments and with various modifications as
are suited to the particular use contemplated. It should be
understood that various changes, substitutions and alterations can
be made hereto without departing from the spirit and scope of the
disclosure.
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