U.S. patent application number 11/200816 was filed with the patent office on 2006-08-10 for process for producing steel components with highest stability and plasticity.
Invention is credited to Arndt Gerick, Tilmann Haug, Wolfgang Kleinekathoefer.
Application Number | 20060174983 11/200816 |
Document ID | / |
Family ID | 35508252 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060174983 |
Kind Code |
A1 |
Gerick; Arndt ; et
al. |
August 10, 2006 |
Process for producing steel components with highest stability and
plasticity
Abstract
Processes for manufacture of metal components with high hardness
and plasticity by deforming with high degree of deformation of
metals, in particular steels, of which the deformation leads to a
hardening by TWIP (Twinning Induced Plasticity) or SIP (Shearband
Induced Plasticity) Effect, wherein the metal after the final step
of annealing or crystallization annealing is deformed in at least
one step into a semi finished product or the finished metal
component, wherein the total elongation is in the range of 10 to
70%, as well as semi finished products, in particular continuous
sheets, of steel with TWIP (Twinning Induced Plasticity) or SIP
(Shearband Induced Plasticity) Effect, wherein the semi finished
product exhibits a tensile strength of greater than 800 MPa and an
elongation of greater than 35%.
Inventors: |
Gerick; Arndt; (Ulm, DE)
; Haug; Tilmann; (Weissenhorn, DE) ;
Kleinekathoefer; Wolfgang; (Waldstetten, DE) |
Correspondence
Address: |
AKERMAN SENTERFITT
P.O. BOX 3188
WEST PALM BEACH
FL
33402-3188
US
|
Family ID: |
35508252 |
Appl. No.: |
11/200816 |
Filed: |
August 10, 2005 |
Current U.S.
Class: |
148/620 |
Current CPC
Class: |
C21D 8/00 20130101; C21D
7/02 20130101 |
Class at
Publication: |
148/620 |
International
Class: |
C21D 8/00 20060101
C21D008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2004 |
DE |
10 2004 038 855.5 |
Nov 10, 2004 |
DE |
10 2004 054 444.1 |
Claims
1. A process for manufacture of metal components or semi-finished
products with high hardness and plasticity by the cold deforming of
steel, wherein the degree of deformation lies at a total elongation
in the range of 10 to 70%, comprising: selecting a metal of which
the deformation leads to a hardening by TWIP (Twinning Induced
Plasticity) or SIP (Shearband Induced Plasticity) Effect, and cold
deforming following the last stage of annealing or crystallization
annealing to the extent that a hardness increase of at least 30% of
the start value is imparted and the residual tensile elongation of
the metal is reduced by less than 20%.
2. The process according to claim 1, wherein the cold deforming is
carried out in a first step with an elongation of 10 to 60% and
with a final deformation in a subsequent step with an elongation of
less than 10%.
3. The process according to claim 1, wherein the deforming is
carried out as cold deforming with an elongation in at least one
spatial direction of 10 to 35%.
4. The process according to claim 1, wherein the deforming is
carried out to the extent until a hardness increase of at least 300
MPa is imparted.
5. The process according to claim 1, wherein the sum of the
elongation of the deformation steps does not exceed 50%.
6. The process according to claim 1, wherein the metal is selected
from steels with the following composition (amounts in wt. %): 1 to
6 Si, 1 to 8 Al, and 10 to 30 Mn, or 2 to 3.5 Si, 2 to 3.5 Al, and
12 to 30 Mn, or 0.1 to 6 Si, 8 to 12 Al, wherein Al+Si>12, 18 to
35 Mn, 0.5 to 2 C, and at least one of the elements Mg, Ga, Be
being up to 3, or 3 to 6 Si, 8 to 12 Al, wherein Al+Si>12, 18 to
35 Mn, 0.5 to 2 C, at most 0.05 B, at most 3 Ti and at least one of
the elements Mg, Ga, Be with a content of respectively 0.3 to 3, or
0.1 to 0.25 Si, 0 to 0.01 Al, 18 to 25 Mn, 0.4 to 0.9 C, 0 to 0.01
N, or 0.05 to 1 Si, 0 to 0.008 Al, 15 to 30 Mn, 0.4 to 0.7 C, 0.001
to 0.01 N, besides iron and conventional minor components of
steel.
7. The process according to claim 1 or 2, wherein the metal is
steel with a duplex microstructure with austensitic and ferritic
crystallites, or with a triplex microstructure with austensitic,
ferritic and perovskite crystallites.
8. A semi-finished product, or motor vehicle component produced by
a process comprising: selecting a metal of which deformation leads
to a hardening by TWIP (Twinning Induced Plasticity) or SIP
(Shearband Induced Plasticity) Effect, and cold deforming following
the last stage of annealing or crystallization annealing to the
extent that a hardness increase of at least 30% of the start value
is imparted and the residual tensile elongation of the metal is
reduced by less than 20%, wherein the semi-finished product
exhibits a tensile strength of greater than 800 MPa and an
elongation of greater than 35%.
9. The semi-finished product or motor vehicle component according
to claim 8, wherein it exhibits a tensile strength of greater than
1000 MPa and a elongation in the range of 35 to 55%.
10. The semi-finished product or motor vehicle component according
to claim 8, wherein the steel is pre-stretched by deforming in at
least one spatial direction by 10 to 40%.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention concerns a process for production of metal
components, in particular steel components, with highest strength
and plasticity, by a multiple deformation of metals of which the
deformation leads to an increase in hardening (work hardening), in
particular of steels with TWIP-(Twinning Induced Plasticity) or
SIP-(Shearband Induced Plasticity) Effect, as well as semi finished
products such as continuous sheets of steel with TWIP-(Twinning
Induced Plasticity) or SIP-(Shearband Induced Plasticity)
Effect.
[0003] 2. Related Art of the Invention
[0004] High hardness steels are developed for the motor vehicle
industry, for the construction industry, as well as air and space
travel applications with various characteristics, and are already
employed in manufacturing processes. Herein there is, in particular
for employment in the motor vehicle industry, increasingly the
desire in the foreground, to undertake a weight reduction of the
vehicle by the use of new materials. The goal therein is the
manufacture of specific lighter steel alloys, of which the
otherwise hitherto desirable characteristics remain retained or as
the case may be are further improved, or of high hardness steels,
in which a weight reduction is achievable by reduction of the
component cross section. Of substantial importance herein is the
achievement of component hardness while maintaining of good
deformability or, as the case may be, plasticity of the steel semi
finished products as well as the finished components.
[0005] The conventional deforming processes in the motor vehicle
industry include the deformation of semi-finished products, in
particular continuous sheets (coils), for example by stamping,
stretching or deep drawing. These deformation processes require a
semi-finished product with comparatively high plasticity. In the
case of insufficient plasticity there is, among other things, the
danger of a tearing of the steel component and a high tool friction
wear.
[0006] The increase of the component hardness can be achieved by
the employment of high hardness multi-phase, complex phase or
martensitic steels, as well as air hardened steels, such as for
example BAS 100 or press hardened steels, such as for example
Uisbor 1500 or BTR 165. If components made of these materials are
incorporated into vehicles, then these still exhibit in general
only plasticity reserves below approximately 10%. This is likewise
critical for components relevant to operational hardness, since
crack propagation can occur, as well as for crash relevant vehicle
components, since the low flexibility values can lead to brittle
material failures and low deformation energy absorption.
[0007] From DE 197 27 759 A1 the use of a cold deformable, in
particular good deep draw capable, austensitic/ferritic light steel
(duplex-steel) is known, which exhibits TRIP and/or TWIP
characteristics. A preferred supposition includes 1 to 6% Si, 1 to
8% Al, wherein (Al+Si)<12%, 10 to 30% Mn and as remainder
essentially iron, inclusive of conventional steel component
elements. One area of application the material is used for
stiffening or reinforcing body sheet metal or panels. On the basis
of their TWIP characteristics, it is possible to achieve with these
steels tensile strengths of up to 1100 MPa and maximal elongation
of 90%. This type of duplex light steel exhibits, besides reduced
weight, also high hardness and very good deep or stretch draw
characteristics.
[0008] From DE 102 311 25 A1 high hardness .alpha./.gamma.-duplex
or .alpha./.gamma./.epsilon.-triplex light steels are known, which
have a specific weight of less than 7 g/cm.sup.3. They exhibit TWIP
characteristics. The preferred composition (content in weight %) is
18 to 35% Mn, 8 to 12% Al, Si, wherein Al+Si>12%, at least 0.5%
C, at most 0.05% B, with the rest being essentially iron, inclusive
of conventional steel component elements. Further alloy elements
include 0.03 to 2% Ti, as well as less than 0.3% N, less than 0.5%
Nb and less than 0.5% V.
[0009] The highest hardness of this type of TWIP-steel is only
achieved by a deformation process, in which by the stretching of
the steel material a mechanical twinning or duplex formation is
induced in the austenitic phase. This twinning formation in
particular leads to a strong increase in hardness. In particular in
the case of steels with triplex microstructure the stress induced
hardening is introduced by the formation of homogenous shearbands,
the so called SIP-Effect (Shearband Induced Plasticity).
[0010] DE 100 60 948 A1 discloses a process for production of a hot
rolled strip of a steel with high Mn-content. This steel is cast
very thin and thereupon is continuously further process to a hot
rolled strip, in that in a single hot rolling pass it is rolled to
the final thickness of the hot rolled strip. The thereby obtainable
continuous sheet has TWIP and TRIP-characteristics. This type of
TWIP steel however still does not exhibit after manufacture the
extremely high hardness. Rather, these steels are characterized by
extreme high plasticity. Thereby on the one hand a very good
deformability (deep draw ability) may be produced, however the
required hardness cannot be achieved.
SUMMARY OF THE INVENTION
[0011] It is thus the task of the invention to provide a process
for providing steel components, which makes it possible to utilize
conventional steel deformation techniques and which leads to a high
component hardness.
[0012] The task is inventively solved by a process for production
of metal components, in particular steel components, with high
hardness and plasticity by deforming metals of which the deforming
leads to a hardness, in particular of steels with TWIP (Twinning
Induced Plasticity) or SIP (Shearband Induced Plasticity) Effect,
with the characterizing features of claim 1, as well as by a semi
finished product, in particular a continuous sheet, of steel with
TWIP (Twinning Induced Plasticity) or SIP (Shearband Induced
Plasticity) Effect, with the characterizing features of claim 10,
as well as motor vehicle components obtainable therefrom.
[0013] In a first aspect of the invention a process is envisioned,
which inclueds a one-time or repeated deformation of metals which
are stress or deformation induced hardness type metals, in
particular steels. Therein in particular the use of TWIP (Twinning
Induced Plasticity) or SIP (Shearband Induced Plasticity) Effect is
of significance. In accordance with the invention it is therewith
provided, that the stress or, as the case may be, deformation
induced hardened metals, in particular steels, are deformed by a
deformation with elongation in the range of 10 to 60% in the semi
finished product or metal component. The semi finished component is
deformed or, as the case may be, finish formed with less stretching
in a subsequent deformation process into metal components, in
particular steel components.
[0014] The inventive process has the advantage, that by the
deformation process with high elongation very high hardness values
can be established. Nevertheless there remains, despite the high
hardness, a plasticity reserve which makes possible in a
conventional subsequent final deformation the manufacture of
components by means of conventional deformation techniques. With
the inventive process there is achieved the highest possible
hardness values with high deep-drawing ability. In the final
component there remains, beyond this, the highest hardness and yet
substantial plasticity reserves, which substantially exceed the
plasticity of known highly hardened steels.
[0015] The inventive solution can also been seen as pre-stretching
of metals, in particular steels. While typical TWIP or SIP steels
exhibit, without pre-stretching, a hardness in the range of
approximately 350 to maximally 500 MPa, with the inventive
stretching of the steels a hardness level of above 800 MPa, in
extreme cases up to 1500 MPa, can be achieved. Therein it is
nevertheless of substantial significance that the draw stretching
of the pre-hardened steels does not drop to an undesirably low
level. Rather, a high residual plasticity is retained. This is of
significance in particular in comparison to known high hardened
steels on the basis of martensitic or heat deformed steels with
draw elongation substantially below 10%.
[0016] Thereby it is in particular also possible, to provide the
inventive pre-hardened steels for use in the, in principle already
known, steel structures and methods of construction, without
adapting the deformation technology to reduced deformation paths or
material plasticities. Likewise they can be employed with advantage
as crash relevant components of motor vehicles. The crash relevant
components include in principle the total body shell work.
[0017] The inventive pre-hardening of the steel is concerned with
the steel in its manufactured condition, that is, essentially steel
following casting, hardening and in certain cases rolling out. In
the following this will be referred to as the condition subsequent
to the last stage of annealing or crystallization annealing.
[0018] It is thus immaterial for the inventive step whether the
deformation with an elongation of up to 60% occurs in one single
process or is divided into multiple sequential processes with
cumulative elongation. In general it is useful to separate the
deformation into at least two steps, in which first a pre-elongated
semi-finished product is produced and in a subsequent final shaping
process the finished component is produced with substantially less
stretching.
[0019] For introduction of the pre-stretching or pre-elongation, in
principle all deformation techniques are suitable which leave the
main deformation mechanism to the mechanical twinning formation or
shearband formation and do not reverse or undo the twinning
formation or shearband formation. The preferred processes for
introduction of the pre-elongation include cold milling, stretch
forming or deep drawing. In steels, deformation temperatures of
approximately 850.degree. C. are still referred to as cold
processes, since up to the region of these temperature small
noticeable crystallographic or microstructure changes occur. Warm
deformation processes are in general not suited or, as the case may
be, not necessary, since they allow the re-crystallization of the
adjusted microstructure.
[0020] Also, warm deformation processes are suited, however, are in
general not necessary. This represents a substantial process
simplification in the deformation process.
[0021] The degree or magnitude of the pre-stretching can be
variously selected for the various metals, in particular TWIP or
SIP steels, in certain cases depending upon the type of
application. Of substantial importance herein is that a sufficient
plasticity reserve remains in the finished component. Preferably
the pre-stretching is carried out by cold deforming maximally to
the extent that in the resulting steel or steel semi-finished
product a draw elongation of greater than 20% remains.
[0022] The pre-stretching is thus preferably so adjusted, that at
least in one spatial direction a stretching in the range of 10 to
60%, particularly preferably 15 to 35%, results.
[0023] In a further variant of the inventive process the magnitude
of the first cold deformation, as the case may be pre-stretching,
is determined by the hardness of the thereby achievable
semi-finished product. Preferably the pre-stretching is carried out
up to a value, which results in a hardness increase of the steel
semi-finished product of at least 20% of the starting value. It is
particularly preferred to increase the hardness by means of
pre-stretching by at least 300 MPa.
[0024] The semi-finished products provided with the pre-stretching
provide as a rule the not-yet-finished components. Rather, in
accordance with the invention it is envisioned that these
semi-finished products are subjected to a final shaping. Therein in
principle the known deformation techniques can be employed. Also,
during the final shaping a component hardening by TWIP or SIP
Effect can occur. Both stretching as well as hardening are therein
as a rule however essentially less than the fist step of the
pre-hardening. Preferably the total of pre-stretching and
stretching during final shaping is never greater than 60%,
particularly preferably in the range of 15 to 45%. It is therein of
advantage to keep the stretching of the final shaping to less than
10%.
[0025] With regard to the selection of suitable metals,
light-metal-poor or light-metal-free steels on the basis of Fe/Mn/C
with TWIP or SIP Effect are preferred. By appropriate cold
deforming, for example by cold milling, the starting yield stress
these steels of approximately 350 to 550 MPa can be increased to a
component hardness greater than 1000 MPa, while the remaining
plasticity is reduced only insignificantly. Therewith the inventive
treated steel components exhibit a multiple of the plasticities
achievable with known high hardened steels with comparable
hardness.
[0026] Further preferred representatives of the TWIP or SIP steels
comprise, besides Fe and conventional minor or secondary
ingredients of steel, the following alloy components in wt. %:
1 to 6 Si,
1 to 8 Al, and
10 to 30 Mn,
or
2 to 3.5 Si,
2 to 3.5 Al, and
12 to 30 Mn,
or
0.1 to 6 Si,
8 to 12 Al, wherein Al+Si>12,
18 to 35 Mn,
0.5 to 2 C, and
at least one of the elements Mg, Ga, Be being up to 3,
or
3 to 6 Si,
8 to 12 Al, wherein Al+Si>12,
18 to 35 Mn,
0.5 to 2 C,
at most 0.05 B,
at most 3 Ti and at least one of the elements Mg, Ga, Be with a
content of respectively 0.3 to 3,
or
0.1 to 0.25 Si,
0 to 0.01 Al,
18 to 25 Mn,
0.4 to 0.9 C,
0 to 0.01 N,
or
0.05 to 1 Si,
0 to 0.008 Al,
15 to 30 Mn,
0.4 to 0.7 C,
0.001 to 0.01 N.
[0027] Further suitable steels exhibit a duplex microstructure,
with austensitic and ferritic crystal components, preferably in an
amount of respectively 40 to 60%. The particularly suited steels
further include triplex steels with a microstructure of
austensitic, ferritic and perovskite crystallites.
[0028] Likewise, there are preferred also special austensitic
nickel poor stainless steels with, to a certain extent, TWIP
characteristics.
[0029] A further aspect of the invention concerns semi-finished
products of steel with TWIP (Twinning Induced Plasticity) or SIP
(Shearband Induced Plasticity) Effect, which in accordance with the
invention are adjusted to a tensile strength above 800 MPa and
elongations of longer than 25%. These types of semi-finished
products are particularly suited for manufacture of body
components, in particular for crash relevant areas. In contrast to
the semi-finished products of the conventional high hardened
steels, the inventive semi-finished products exhibit both for the
subsequent final shaping to the component, in particular body
components, as well as for the use as components, a sufficient
plasticity or as the case may be plasticity reserve. It is
particularly preferred when the tensile elongation of the
semi-finished product is adjusted to values in the range of 25 to
55%.
[0030] The inventive semi finished products are particularly
preferably formed by TWIP or SIP steels with a pre-stretching
corresponding to a cold deformation of 10 to 40% in at least one
spatial direction.
[0031] The particularly suited deformation techniques of the
semi-finished products for manufacture of components for motor
vehicle construction include rolling and deep drawing.
[0032] By the variant of the roller profiling there can
supplementally be achieved a local stiffening of the material in
that varying material stretching is realized in the component. This
can lead for example to the manufacture of shaped parts which have
in certain areas higher and in other areas a lower plasticity
reserve however higher hardness. Thereby it is possible to produce
in advantageous manner also possible integral components with local
varying adapted crash behavior.
[0033] In a further embodiment of the invention the sheets or coils
(continuous bands) are first pre-stretched in a body press and
thereupon deformed in the same press to a final component.
* * * * *