U.S. patent application number 13/156260 was filed with the patent office on 2011-10-06 for method for producing a component having improved elongation at break properties.
This patent application is currently assigned to THYSSENKRUPP STEEL EUROPE AG. Invention is credited to Janko Banik, Franz-Josef Lenze, Sascha Sikora.
Application Number | 20110240179 13/156260 |
Document ID | / |
Family ID | 42026716 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110240179 |
Kind Code |
A1 |
Lenze; Franz-Josef ; et
al. |
October 6, 2011 |
Method for Producing a Component Having Improved Elongation at
Break Properties
Abstract
The invention relates to a process for producing a component
having improved elongation at break properties, in which a
component (6) is firstly produced, preferably in a hot forming or
press curing process (4), and the component (6) is heat treated
after hot forming and/or press curing (4), where the heat treatment
temperature T and the heat treatment time t essentially satisfy the
numerical relationship T.gtoreq.900T.sup.-0.087, where the heat
treatment temperature T is in .degree. C. and the heat treatment
time t is in seconds. The invention also relates to a component, in
particular an automobile body component or the chassis of a motor
vehicle, which has been produced by such a process. The invention
further relates to the use of such a component as part of an
automobile body or a chassis of a motor vehicle.
Inventors: |
Lenze; Franz-Josef;
(Lennestadt, DE) ; Sikora; Sascha; (Lunen, DE)
; Banik; Janko; (Altena, DE) |
Assignee: |
THYSSENKRUPP STEEL EUROPE
AG
Duisburg
DE
|
Family ID: |
42026716 |
Appl. No.: |
13/156260 |
Filed: |
June 8, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2009/066984 |
Dec 11, 2009 |
|
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13156260 |
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Current U.S.
Class: |
148/518 ;
148/400; 148/527; 148/559; 148/620 |
Current CPC
Class: |
C21D 6/008 20130101;
C21D 8/005 20130101; C25D 7/00 20130101; C23C 22/78 20130101; C25D
3/44 20130101; C25D 5/36 20130101; C21D 7/13 20130101; C22C 38/04
20130101; C23C 22/05 20130101; C23C 22/02 20130101; C21D 9/48
20130101; C21D 9/52 20130101; C21D 1/25 20130101; C23C 2/02
20130101; C22C 38/002 20130101; C22C 38/02 20130101; C21D 1/673
20130101; C23C 2/12 20130101 |
Class at
Publication: |
148/518 ;
148/559; 148/620; 148/527; 148/400 |
International
Class: |
C25D 5/50 20060101
C25D005/50; C21D 9/00 20060101 C21D009/00; C21D 8/00 20060101
C21D008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2008 |
DE |
10 2008 055 514.2 |
Claims
1. Method for manufacturing a component with improved elongation at
break properties, comprising: producing a component (6) that is
firstly produced, by one of a hot forming and press curing process
(4), and in which the component (6) is tempered after one of hot
forming and press curing (4) characterised in that the tempering
temperature T and the tempering time t substantially satisfy the
numerical relationship T.gtoreq.900t.sup.-0.087, wherein the
tempering temperature T is to be expressed in .degree. C. and the
tempering time t in seconds.
2. Method according to claim 1, characterised in that the tempering
temperature T is lower than the AC.sub.1 temperature, in particular
lower than 700.degree. C.
3. Method according to claim 1, characterised in that the tempering
time at a tempering temperature of approximately 500.degree. C. is
at least 20 minutes, at a tempering temperature of approximately
550.degree. C. at least 5 minutes, and at a tempering temperature
of approximately 600.degree. C. at least 3 minutes.
4. Method according to claim 1, characterised in that the tempering
temperature is at least 500.degree., preferably 550.degree. C., in
particular 600.degree. C. and the tempering time is selected to be
high enough that the elongation at break value A80 of the component
(10) is increased by approximately 15%, in particular by
approximately 20%, preferably by approximately 25%.
5. Method according to claim 1, characterised in that the component
(6, 10) substantially consists of a manganese-boron steel, in
particular a manganese-boron tempering steel, preferably a 22MnB5
tempering steel.
6. Method according to claim 1, characterised in that the component
(6, 10) is coated or uncoated.
7. Method according to claim 1, characterised in that prior to
tempering, the component (6) is coated with an inorganic, an
organic and/or an inorganic-organic coating.
8. Method according to claim 1, characterised in that the component
(6, 10) is coated with a corrosion protection coating.
9. Method according to claim 1, characterised in that prior to
tempering, the component (6) is coated electrolytically and/or by
hot-dip processing.
10. Method according to claim 1, characterised in that the
component (6, 10) is a body part or a chassis of a motor
vehicle.
11. A component, produced by one of a hot forming and press curing
process (4), and in which the component (6) is tempered after one
of hot forming and press curing (4), the tempering temperature T
and the tempering time t substantially satisfy the numerical
relationship T.gtoreq.900t.sup.-0.087, wherein the tempering
temperature T is to be expressed in .degree. C. and the tempering
time t in seconds, comprising a component that has a tensile
strength Rm of 700-1100 MPa, a yield point Rp0.2 of 750-1000 and an
elongation at break value A80 of more than 6%.
12. Component according to claim 11, characterised in that in the
event of a crash, the component (10) is subjected to a tensile
loading.
13. Component according to claim 11, characterised in that the
component (10) is a side rail (32, 34) of a vehicle frame (30).
14. The component of claim 11, wherein the component is
incorporated into a body or chassis of a motor vehicle.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application is a continuation of co-pending PCT
Application No. PCT/EP2009/066984, filed Dec. 11, 2009, which
claims the benefit of German Application No. 10 2008 055 514.2,
filed Dec. 12, 2008, the entire teachings and disclosure of which
are incorporated herein by reference thereto.
FIELD OF THE INVENTION
[0002] The invention relates to a method for producing a component
having improved elongation at break properties, in which a
component is firstly produced, preferably in a hot forming and/or
press curing process, and the component is tempered after hot
forming and/or press curing. The invention also relates to a
component produced with this method, preferably a component of the
body or the chassis of a motor vehicle. The invention further
relates to the use of such a component as part of the body or
chassis of a motor vehicle.
BACKGROUND OF THE INVENTION
[0003] In the construction of motor vehicles the safety of the
motor vehicle and economy of production and operation both have
important roles to play. On the one hand the body or the chassis of
the motor vehicle should provide a high level of safety in a crash,
and on the other the weight of these components should be kept as
low as possible in order to lower material costs and operating
costs. For this reason in the state of the art hardened components,
preferably hot formed or press cured components are used. To this
end sheet steel or a pre-formed component is heated to an
austenetisation temperature of higher than AC.sub.3 and then
rapidly cooled in a tool, so that within the component a
martensitic and/or a bainitic structure develops. In this way
strengths R.sub.m of 1200-1600 MPa, yield strengths R.sub.p0.2 of
more than 900 MPa and A.sub.80 elongation at break values of up to
6% can be achieved. Such components have high dimensional stability
and are highly resistant to deformation in a crash. But these
components do lack residual strain capability. In order to avoid
cracking of the components due to their high level of hardness, it
is necessary that the components also have a certain ductility. In
order to achieve this, such components are tempered following a
press curing or hot forming process. Up until now during such
tempering processes the components have been tempered for a dwell
time of, for example, approximately 10 minutes at an average
temperature of 400.degree. C. The components tempered in this way
demonstrate a clear improvement in their ductility or their folding
behaviour. In order to reduce the risk of material failure during
an axial crash loading, i.e. in particular during a head-on crash
or rear shunt, it is necessary, however, to increase the elongation
at break values A.sub.80 of the components.
[0004] Elongation at break means the residual relative change in
length compared with the starting length after the break of the
test piece in a tensile test. Here the elongation at break value
A.sub.5 relates to a round test piece, the starting length of which
is five times its diameter. The elongation at break value A.sub.80
on the other hand refers to a test piece with a starting length of
80 mm. For the same A.sub.5 material the elongation at break value
will take higher values than the elongation at break values
A.sub.80. Unless otherwise stated, in this application the
elongation at break value A.sub.80 is intended.
[0005] From DE 10 2005 054 847 B3 a highly rigid steel component is
known for which the elongation at break value A.sub.5 was increased
by a tempering process in the temperature range between 320 and
400.degree. C. to between 6% and 12%. It has been shown, however,
that the known method does not lead to high elongation at break
values with sufficient reliability.
SUMMARY OF THE INVENTION
[0006] The object forming the basis of the invention is thus to
provide a component and a method for the production thereof, in
which the elongation at break properties are further improved and
achieved in a process that offers greater reliability. In this
patent application a component can also be understood to be a
semi-finished product.
[0007] This object is achieved according to the invention in that
the tempering temperature T and the tempering time t substantially
satisfy the numerical relationship T.gtoreq.900t.sup.0.087, wherein
the tempering temperature T is to be expressed in .degree. C. and
the tempering time t in seconds. It has been shown that in a
tempering process that observes the abovementioned numerical
relationship the elongation at break value A.sub.80 is increased
sufficiently and in a process that offers reliability.
[0008] An excessive reduction in the hardness of the component can
be avoided in a preferred embodiment in that the tempering
temperature T is lower than the AC.sub.1 temperature, in particular
lower than 700.degree. C. It has been shown that in this way the
structure of the martensite changes, but a conversion of the
martensite into other structural components and thus an excessive
reduction in the strength or the yield point can be prevented.
[0009] In a further preferred embodiment the tempering time at a
tempering temperature of approximately 500.degree. C. is at least
20 minutes, at a tempering temperature of approximately 550.degree.
C. at least 5 minutes, and at a tempering temperature of
approximately 600.degree. C. at least 3 minutes. It has been shown
that these parameters, for performing the tempering process,
guarantee a sufficient increase in the elongation at break value
A.sub.80 and at the same time prevent too great a loss in
hardness.
[0010] The production of a component with particularly good crash
properties under axial loading is achieved in a further embodiment
of the method in that the tempering temperature is at least
500.degree., preferably 550.degree. C., in particular 600.degree.
C. and the tempering time is selected to be great enough that the
elongation at break value A.sub.80 of the component is increased by
approximately 15%, in particular by approximately 20%, preferably
by approximately 25%.
[0011] In a further embodiment of the method the component
substantially consists of a manganese-boron steel, in particular a
manganese-boron tempering steel, preferably a 22MnB5 tempering
steel. The advantage of using such steels is that the components
produced with the method have a particularly high hardness and as a
result a reduction in the material thickness and thus a lower
weight is possible.
[0012] In a further embodiment of the method the component is
coated or uncoated. The advantage of using coated components is
that the material properties of the component can be matched to
specific requirements by means of the coatings. So, for example,
scale-free hot forming can be guaranteed. The use of uncoated
components is, on the other hand, more economical than using coated
components.
[0013] In a further embodiment of the method prior to tempering the
component is coated with an inorganic, an organic and/or or an
inorganic-organic coating. Such coatings can serve as corrosion
protection, provide an improvement in the paint adhesion compared
with uncoated components, such as for example in epoxy resin
systems, or perform other functions.
[0014] The production of a component that guarantees in particular
long-term crash safety is achieved in a further embodiment in that
the component is coated with a corrosion protection coating. The
corrosion protection coating prevents the component being attacked
by corrosion with a deterioration over time in its crash safety
properties.
[0015] A particularly even application of the coating and thus the
production of components with homogeneous surface properties are
achieved in a further embodiment of the method in that prior to
tempering, the component is coated electrolytically and/or by
hot-dip processing. Thus prior to tempering the component can for
example be coated with an aluminium-silicon (AS), a zinc (Z) and/or
an electrolytically applied zinc (ZE) or aluminium coating.
[0016] In a further preferred embodiment of the method the
component is a component of the body or chassis of a motor vehicle.
The method is particularly well-suited to the production of such
components since for these components in order to achieve a high
level of crash safety a higher elongation at break A.sub.80 value
is required.
[0017] The problem for the invention is further solved by a
component which has in particular been produced by a method
according to the invention, wherein the component has a tensile
strength R.sub.m of 700-1,100 MPa, a yield point R.sub.p0.2 of
750-1,000 and an elongation at break value A.sub.80 of more than
6%.
[0018] It has been shown that such components have a particularly
favourable combination of good elongation at break properties and
high strength.
[0019] In a particularly preferred embodiment of the component, in
the event of a crash the component is subjected to a tensile
loading. This is particularly advantageous since the good
elongation at break properties of the component are also able to
withstand a strong tensile loading without this resulting in
failure of the material.
[0020] Particularly high stability of the body of a motor vehicle
in a crash is achieved in a further embodiment in that the
component is a side rail of a vehicle frame. In particular in the
event of a head-on crash or rear shunt, the side rails of a vehicle
frame are subject to high axial loadings so that the good
elongation at break properties of the component play an important
role at such a point.
[0021] The object forming the basis of the invention is finally
achieved in that a component according to the invention is used as
part of the body or chassis of a motor vehicle. The component is
particularly well-suited to such an application, since because of
its high level of hardness and its very good elongation at break
properties the safety of the occupants of the vehicle is increased.
The high level of hardness of the component also allows a low
material thickness to be used and thus a reduction in the weight of
the vehicle body work. This can lead to lower material costs and
lower consumption by the vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Further features and advantages of the present invention
will be explained in more detail in the description of an exemplary
embodiment wherein reference is made to the attached drawings. The
drawing shows as follows:
[0023] FIG. 1 is an exemplary embodiment of the method according to
the invention for producing a component with improved elongation at
break properties;
[0024] FIG. 2 is a diagram with the parameters for the tempering
process;
[0025] FIG. 3a is a diagram showing the influence of the tempering
time on the material properties of a component at a tempering
temperature of 450.degree. C.;
[0026] FIG. 3b is a diagram similar to FIG. 3a for a tempering
temperature of 500.degree. C.;
[0027] FIG. 3c is a diagram similar to FIG. 3a for a tempering
temperature of 550.degree. C.;
[0028] FIG. 3d is a diagram similar to FIG. 3a for a tempering
temperature of 600.degree. C.;
[0029] FIG. 4 is four cross-sectional views of coated components
following various tempering treatments and
[0030] FIG. 5 is a vehicle frame of a motor vehicle with exemplary
embodiments of components according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] FIG. 1 shows an exemplary embodiment of a method for
producing a component with improved elongation at break properties.
From a bar 2, which is for example made from manganese-boron steel,
initially in a hot forming and press curing process 4, a component
6 is produced. The component 6 is for example a side rail of a
motor vehicle's body work. As a result of the hot forming and press
curing process the material of the component 6 has a substantially
martensitic structure and thus a high level of hardness. The
component 6 is then tempered in a tempering step 8. The tempering
can for example take place in an oven provided for the purpose, in
which the component 6 is maintained by way of example for
approximately 10 minutes at approximately 550.degree. C. Compared
with the component 6 the tempered component 10 has an elongation at
break value A.sub.80 that is 60% higher. The hardness of the
tempered component 10 is not excessively reduced compared with the
component 6.
[0032] FIG. 2 shows a diagram with the parameters for the tempering
process. The tempering time t in seconds is plotted against the
abscissa and the tempering temperature T in .degree. C. against the
ordinate. The solid line curve corresponds to the numerical
relationship T=900t.sup.-0.087, wherein the tempering temperature T
is expressed in .degree. C. and the tempering time t in
seconds.
[0033] For the selection of the tempering temperature T and the
tempering time t all pairs of values that are located in the
diagram above the plotted curve and below the AC.sub.1-temperature
are suitable. Out of practical considerations here a tempering time
t of between 180 and 1200 s is taken into account in particular.
Thus at lower tempering times the necessary tempering temperatures
are too high and at high tempering times on the other hand the
production time is too long.
[0034] In FIGS. 3a to 3d the influence of the tempering temperature
and of the tempering time on the material properties of components
is shown. The components are strips of 22MnB5 steel of 1.47 mm in
thickness with an aluminium-silicon coating (AS). In a first step
the samples were heated for 6 minutes at 920.degree. C. and
austenetised and then press cured for 15 seconds at a pressure of 6
bar in a cooling tool. In a second step the components obtained in
this way were tempered at differing tempering temperatures in the
forced-air oven for various tempering times.
[0035] FIG. 3a shows for this, measurements of the yield strength
R.sub.p0.2 12, the tensile strength R.sub.m 14 and measurements of
the elongation at break A.sub.80 16 for comparative components V
and for components E produced with exemplary embodiments of the
method according to the invention. All measurements were carried
out according to DIN. The strength Rm in Mpa is plotted against the
ordinate on the left-hand side and the elongation at break A.sub.80
against the ordinate on the right-hand side in percent. The
comparative component V.sub.0 was not tempered following complete
austenitisation and press curing, V.sub.11 was tempered for 5
minutes following press curing, V.sub.12 for 10 minutes, V.sub.13
for 20 minutes and V.sub.14 for 30 minutes at 450.degree. C. Using
an exemplary embodiment of the method according to the invention
component E.sub.15 was tempered for 60 minutes at 450.degree. C. It
is clear from the diagram that the elongation at break value
initially drops during tempering and then as the tempering time
increases rises even to above the elongation at break value
directly after press curing. Thus the elongation at break value of
the component E.sub.15 exceeds that of the un-tempered component
V.sub.0 by approximately 13%. The yield point shows a slight
retraction as the tempering time increases while this is greater
for the tensile strength.
[0036] FIG. 3b shows a diagram similar to that of FIG. 3a for a
tempering temperature of 500.degree. C. The comparative component
V.sub.21 was tempered at 500.degree. C. following press curing for
5 minutes and V.sub.22 for 10 minutes. The components E.sub.23,
E.sub.24 and E.sub.25 produced using exemplary embodiments of the
method according to the invention were tempered for 20, 30 and 60
minutes respectively at 500.degree. C. The diagram shows that the
elongation at break value at this temperature for the component
E.sub.23 tempered for 20 minutes already exceeds the elongation at
break value of the component V.sub.0 by almost 30%.
[0037] FIG. 3c shows a diagram similar to that of FIG. 3a for a
tempering temperature of 550.degree. C. The components E.sub.32,
E.sub.33, E.sub.34 and E.sub.35 produced using exemplary
embodiments of the method according to the invention were tempered
for 10, 20, 30 and 60 minutes respectively at 550.degree. C.
[0038] FIG. 3d shows a diagram similar to that of FIG. 3a for a
tempering temperature of 600.degree. C. The components E.sub.41,
E.sub.42, E.sub.43 E.sub.44 and E.sub.45 produced using exemplary
embodiments of the method according to the invention were tempered
for 5, 10, 20, 30 and 60 minutes respectively at 600.degree. C. At
this tempering temperature the elongation at break value of the
component E.sub.41 already exceeds the elongation at break value of
component V.sub.o by approximately 66%.
[0039] From diagrams 3a to 3d it can be seen that with long
tempering times the elongation at break value of the components
increases more sharply or that the tensile strength and the yield
strength of the components fall more quickly the higher the
tempering temperature. It is therefore advantageous to select the
tempering temperature so that in the time available for the
tempering process the necessary increase in the elongation at break
value is achieved. In selecting the parameters for the tempering
process it is also crucial that a sensible compromise is found
between the increase in elongation at break and the reduction in
hardness of the material. It was noted among other things that the
elongation at break, when the tempering time is increased,
initially rises very quickly before transitioning to a slow
increase or even saturation. Through the selection according to the
invention of the tempering time at a specified tempering
temperature the elongation at break value can be sufficiently
increased and the yield strength and stability values reduced. The
result is that components can be provided with optimised mechanical
characteristic values in terms of yield strength, tensile strength
and elongation values.
[0040] FIG. 4 shows cross-sections of the components V.sub.12,
V.sub.22, E.sub.32 and E.sub.42 described above. The tempering time
for all components is 5 minutes. In the cross-sections the core
material 20 of the respective component and the AS coatings 21
applied to this can be seen. With all AS coatings there are clear
phase limits within the AS coating 21, which can be applied with up
to five alloy coatings 22, 24, 26, 28, 30. In step a) the core
material 20 of the component V.sub.12 exhibits the structure of
tempered martensite. For the components E.sub.32 and E.sub.42
tempered using an exemplary embodiment of the method according to
the invention the granularity of this structure has clearly
increased. A conversion of the martensitic structure has thus been
achieved without the martensite being converted into other types of
structure. In this way an excessive reduction in the stability of
the components is prevented.
[0041] FIG. 5 shows a vehicle frame 30, which has side rails in the
roof area 32 and side rails in the floor area 34. For these side
rails 32, 34 components produced by a method according to the
invention are used. Since these components have a high elongation
at break A.sub.80 value and thus in the event a crash, in
particular in a head-on crash or rear shunt and the tensile
loadings resulting from these, demonstrate high stability, the
stability of the vehicle frame 30 is thereby guaranteed.
* * * * *