U.S. patent application number 13/357138 was filed with the patent office on 2012-06-21 for method and device for energy-efficient hot forming.
This patent application is currently assigned to GMF Urnformtechnik GmbH. Invention is credited to Janko Banik, Siegfried Losch, Sascha Sikora.
Application Number | 20120152410 13/357138 |
Document ID | / |
Family ID | 42731946 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120152410 |
Kind Code |
A1 |
Sikora; Sascha ; et
al. |
June 21, 2012 |
Method And Device for Energy-Efficient Hot Forming
Abstract
The invention relates to a method for hot forming of steel
parts, in particular blanks or semi-finished products of steel, in
which the steel parts are heated in a furnace for at least partial
austenitisation to a temperature above the Ac1 temperature and hot
formed in a forming tool. The object of providing a method for hot
forming of steel parts which allows an energy-efficient performance
of the hot forming while at the same time reducing the cycle times
for producing a hot formed component, is achieved in that the waste
heat from the furnace is used for further heat treatment steps of
the steel part before and/or after the at least partial
austenitisation of the steel part.
Inventors: |
Sikora; Sascha; (Lunen,
DE) ; Banik; Janko; (Altena, DE) ; Losch;
Siegfried; (Berlin, DE) |
Assignee: |
GMF Urnformtechnik GmbH
Ludwigsfelde
DE
ThyssenKrupp Steel Europe AG
Duisburg
DE
|
Family ID: |
42731946 |
Appl. No.: |
13/357138 |
Filed: |
January 24, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2010/060052 |
Jul 13, 2010 |
|
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13357138 |
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Current U.S.
Class: |
148/530 ;
148/648; 266/160 |
Current CPC
Class: |
C21D 9/0006 20130101;
C21D 2221/00 20130101; B21D 22/22 20130101; B21D 24/005 20130101;
C21D 1/673 20130101; C21D 9/0062 20130101; B21D 22/208 20130101;
B21D 37/16 20130101; C21D 9/48 20130101; C21D 1/25 20130101 |
Class at
Publication: |
148/530 ;
148/648; 266/160 |
International
Class: |
C21D 8/02 20060101
C21D008/02; C21D 6/00 20060101 C21D006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 2009 |
DE |
102009026251.2 |
Claims
1. Method for hot forming of steel parts, in particular blanks or
semi-finished products of steel, in which the steel parts are
heated in a furnace for at least partial austenitisation to a
temperature above the AC1 temperature and hot formed in a forming
tool, comprising using waste heat from the furnace in a heat
treatment step for the steel parts occurring at least one of before
and/or after the at least partial austenitisation of the steel
parts.
2. Method according to claim 1, wherein a continuous furnace is
used for the at least partial austenitisation of the steel
parts.
3. Method according to claim 1, wherein the furnace for at least
partial austenitisation of the steel parts is at least partially
heated by gas and the waste heat from the combustion exhaust gases
from the furnace is used for the heat treatment step.
4. Method according to claim 1, wherein using the waste heat from
the furnace in a heat treatment step is achieved in a preheating
furnace to pre-alloy the steel parts.
5. Method according to claim 1, wherein the forming tool for hot
forming is at least partially heated with the waste heat from the
furnace for at least partial austenitisation of the steel part.
6. Method according to claim 1, wherein using the waste heat from
the furnace in a heat treatment step includes tempering of the
formed steel parts.
7. Method according to claim 1, wherein the heat treatment step on
the steel parts are performed by forced convection.
8. Method according to claim 1, wherein the steel parts are heated
in the preheating furnace to a temperature of 200.degree. C. to Ac1
temperature.
9. Device for performing a method according to claim 1, comprising:
a furnace for heating steel parts to above the Ac1 temperature in
order to form an at least partially austenitic structure; a forming
tool for hot forming of the steel parts; means for transporting the
steel parts from the furnace to the forming tool; means for using
the waste heat from the furnace in a heat treatment step in at
least one of before and/or after the at least partial
austenitisation of the steel parts.
10. Device according to claim 9 wherein the means using the waste
heat are provided for heating at least one of a preheating furnace,
the forming tool, and/or a tempering furnace.
11. Device according to claim 9, wherein the furnace is a
continuous furnace.
12. Device according to claim 10, wherein as means for heating the
preheating furnace, the forming tool, and the tempering furnace, at
least one of medium supply lines and fans are provided for guiding
the combustion exhaust gases from the furnace for the at least
partial austenitisation.
13. Method according to claim 2, wherein the continuous furnace is
a roller hearth furnace and is used for the at least partial
austenitisation of the steel parts.
14. Method according to claim 1, wherein the steel parts are
AlSi-coated steel parts.
15. Method according to claim 1, wherein the steel parts are heated
in the preheating furnace to a temperature of about 250.degree. C.
to about 700.degree. C.
16. Device according to claim 11, wherein the continuous furnace is
a roller hearth furnace.
Description
[0001] CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0002] This patent application is a continuation of
PCT/EP2010/060052, filed Jul. 13, 2010, which claims priority to
German Application No. 102009026251.2, filed Jul. 24, 2009, the
entire teachings and disclosure of which are incorporated herein by
reference thereto.
FIELD OF THE INVENTION
[0003] The invention relates to a method for hot forming of steel
parts, in particular blanks or semi-finished products of steel, in
which the steel parts are heated in a furnace for at least partial
austenitisation to a temperature above the Ac1 temperature and hot
formed in a forming tool. In addition the invention relates to a
device for performing the method with a furnace for heating the
steel parts to above the Ac1 temperature in order to form an at
least partially austenitic structure, a forming tool for hot
forming of the steel parts and means for transporting the steel
parts from the furnace to the forming tool.
BACKGROUND OF THE INVENTION
[0004] Steel parts within the meaning of the present invention are
for example blanks or semi-finished products provided for hot
forming. The semi-finished products may for example be in the form
of cut-outs or pre-formed blanks. In order to perform the hot
forming the steel parts provided for hot forming must initially be
heated to a temperature above the Ac1 temperature point, so that at
least a partial austenitisation of the structure of the steel part
takes place. Preferably, however, the steel parts are fully
austenitised. To this end they are usually heated to a temperature
above the Ac3 temperature point, at which the formation of the
austenitic structure is complete and thus the steel part exists
with a fully austenitic structure.
[0005] The steel part is then placed in a forming tool and hot
formed at a temperature above the Ac1 temperature point. By means
of the forming tool a so-called "press hardening" takes place
during which because of the rapid cooling the austenitic structure
of the formed steel part is converted into a martensitic structure.
This is what gives hot formed steel parts their enormous strength.
In order to prevent scaling during heat treatment of the steel
parts and at the same time provide corrosion protection, the steel
parts provided for hot forming are preferably coated with an AlSi
coating. Finally, the press hardening can be followed by a further
work step in which the formed steel parts undergo a further heat
treatment, for example tempering, in order to again change the
characteristics of the steel part in certain areas or as a whole,
for example to increase its ductility.
[0006] Hot forming is on the one hand a very energy-intensive
process, since the steel parts have to be heated for a plurality of
minutes to a temperature above the Ac1 temperature point or must be
heated to above the Ac3 temperature point and remain at this
temperature for a plurality of minutes. Further energy in the form
of heat is then required by the forming tool and in any further
heat treatment step. This is also the case with any preheating that
takes place prior to heating of the steel part to a temperature
above the Ac1 temperature point. It has transpired that the energy
costs, in particular for the mass production of such steel parts,
have a negative effect on the economic efficiency of the method. It
has also been found that the cycle times for producing the hot
formed steel part are in need of improvement. From German patent
specification DE 10 2005 033 042 B3 it is known to preheat a
semi-finished product having a metallic coating provided for press
hardening by using the waste heat from the cooling process of the
semi-finished product heated to at least above the Ac1 temperature.
It has, however, transpired that the residual quantities of heat
emanating from the semi-finished product cooling process are
insufficient for a significant reduction in energy costs.
[0007] The object of the present invention, therefore, is to
provide a method for hot forming of steel parts, which allows an
energy-efficient performance of hot forming and at the same time
reduces the cycle times for producing a hot formed component. In
addition a device should be proposed for performing the method
according to the invention.
SUMMARY OF THE INVENTION
[0008] For a generic method the above object is achieved by a first
teaching of the present invention in that the waste heat from the
furnace is used for further heat treatment steps of the steel part
before and/or after the at least partial austenitisation of the
steel part.
[0009] It has transpired that the furnaces used for performing the
at least partial austenitisation produce enormous amounts of waste
heat which to date has remained unused. According to the invention
the waste heat from the furnace is now used for further heat
treatment steps on the steel part before and/or after the at least
partial austenitisation of the steel part, allowing significant
energy savings to be made.
[0010] If the steel part is preheated prior to the at least partial
austenitisation using the waste heat from the furnace, the cycle
time for the hot forming as a whole can be reduced, since the
components in the furnace for at least partial austenitisation
because of their higher entry temperature reach the desired
temperature more quickly without significantly more energy being
used for the process. The quantities of waste heat from the furnace
for at least partial austenitisation of the steel part are so great
that quantities of heat that are also necessary after heat
treatment can be provided by the waste heat from the furnace. This
allows the energy efficiency of the method according to the
invention to be increased further.
[0011] According to a first embodiment of the method according to
the invention a continuous furnace, preferably a roller hearth
furnace is used for at least partial austenitisation of the steel
part. A continuous furnace or a roller hearth furnace offers a
simple option for performing the at least partial austenitisation
of the steel part in a continuous process and incorporating this in
a corresponding process line.
[0012] The quantities of waste heat which can be used in upstream
and downstream heat treatments, are increased in that the furnace
for at least partial austenitisation of the steel part is at least
partially heated by gas and the waste heat from the combustion
exhaust gases from the furnace is used. These so-called radiant
furnaces can in a very short space of time heat the component to
the desired temperature above the Ac1 temperature point or also to
above the Ac3 temperature point, so that the cycle times for the at
least partial austenitisation of the steel part are relatively
short. Furthermore the waste heat from the combustion gases can be
simply used in that for example by means of a heat exchanger the
quantity of energy is removed from the gas or the waste gas is used
directly for further heat treatments. It is conceivable to further
equip the furnace heated with gas with means for inductive heat
transfer and/or means of radiated transmission of the heat.
[0013] If in a preheating furnace using the waste heat from the
furnace for at least partial austenitisation of the steel part the
steel parts, in particular metal-coated, preferably AlSi-coated
steel parts are heated or pre-alloyed, the cycle times that are
necessary for passing through the furnace for at least partial
austenitisation of the steel part can be reduced and at the same
time energy saved. This is because on the one hand the already
heated steel part requires less quantities of energy in order to be
heated to the desired temperature. On the other hand, for example
through pre-alloying of a metal-coated, preferably an AlSi-coated,
steel part, a relatively higher iron proportion in the AlSi coating
is achieved, which leads to a roughening of the surface layer, so
that radiant heat in the furnace can be used considerably more
efficiently for at least partial austenitisation of the steel part.
The reflection characteristics of the pre-alloyed metal-coated,
preferably AlSi-coated, steel part, are considerably improved.
[0014] A further increase in the energy efficiency of the method
according to the invention can be achieved in that the forming tool
for hot forming is at least partially heated with the waste heat
from the furnace for at least partial austenitisation of the steel
part. At the correspondingly heated points, for example, another
structure in the steel part can be partially set, so that varying
component characteristics in the formed steel part can be
provided.
[0015] Optionally following forming of the steel part a further
heat treatment takes place, which according to a further
configuration of the method according to the invention is
advantageously carried out using the waste heat from the furnace
for at least partial austenitisation of the steel part.
[0016] A typical heat treatment following forming is for example
tempering, for example partial tempering of the formed, annealed
steel part, in order to for example change the component
characteristics on a localised basis.
[0017] In order to further increase the efficiency of use of the
waste heat, the heat treatment steps on the steel part are
performed before and/or after the at least partial austenitisation
of the steel part by forced convection. In a forced convection the
heat transfer is considerably increased, since the steel parts to
be heated or for example parts of the tool have a hot gas jet
passed over them so that an intensive contact between hot gas
particles and the part to be heated takes place.
[0018] Preferably the steel parts are heated in the preheating
furnace to a temperature of 200.degree. C. to Ac1 temperature,
preferably to 250.degree. C. to 700.degree. C. Uncoated steel parts
then require even less quantities of energy for heating above the
Ac1 temperature in the furnace for at least partial
austenitisation. Furthermore, coated components can for example be
pre-alloyed with an AlSi coating in this temperature range with a
short dwell time, in order to achieve in particular a shorter
heating time in the furnace for at least partial austenitisation of
the steel part.
[0019] According to a second teaching of the present invention the
object illustrated above for a device is achieved in that means are
provided for using the waste heat from the furnace before and/or
after at least partial austenitisation of the steel part.
[0020] The means for using the waste heat from the furnace for at
least partial austenitisation of the steel parts are manifold and
can take different forms. As a rule they comprise pipelines and fan
devices, which can be used for the use and transport of such hot
gases. In addition heat exchangers can be provided which transfer
the heat from the combustion exhaust gases from the furnace to a
further heat conduction medium. As a result of the use of these
means the energy efficiency of the method according to the
invention for hot forming of steel parts is considerably improved
and in addition the cycle times for producing hot formed steel
parts is reduced.
[0021] Preferably therefore means are provided, which are used for
heating a preheating furnace, the forming tool and/or a tempering
furnace. In this way the utilisation of the waste heat from the
furnace for at least partial austenitisation of the steel part is
used, in order to operate the essential processes from preheating
to tempering of the steel part in an energy efficient manner. The
heating of the preheating furnace in particular, however, leads to
a considerable increase in energy efficiency since here large
quantities of energy are required.
[0022] According to a next configuration of the device according to
the invention a continuous furnace, preferably a roller hearth
furnace is provided for at least partial austenitisation of the
steel parts. As already explained, by using a continuous furnace,
preferably a roller hearth furnace a simple integration of the
heating of the steel part to above the Ac1 temperature in a process
chain for producing hot formed steel parts is possible.
[0023] According to a simple configuration of the device according
to the invention as means for heating the preheating furnace, the
forming tool and/or the tempering furnace gas pipes and/or fans for
guiding the combustion exhaust gases from the furnace for the at
least partial austenitisation of the steel parts to the individual
devices are provided. As already explained, heat exchangers can
also be used if the combustion gases are not used directly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] There are now a plurality of possibilities for configuring
and developing the device according to the invention. To this end
reference is made on the one hand to the dependent claims of claims
1 and 9 and to the description of an exemplary embodiment in
conjunction with the drawing.
[0025] FIG. 1 shows in a schematic view an exemplary embodiment of
a device for performing the method according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The exemplary embodiment shown in FIG. 1 of a method
according to the invention comprises a furnace 1 for at least
partial austenitisation of a steel part 2. The steel part 2, in
this case a flat blank of a temperable steel, is in the exemplary
embodiment according to FIG. 1 heated to a temperature of at least
850.degree. C. and maintained for approximately 2 to 15 minutes at
this temperature in the furnace 1, which takes the form of a roller
hearth furnace. Through the temperature of 850.degree. C. and
higher a complete austenitisation of the blank 2 is achieved.
Preferably the blank consists of a type 22MnB5 steel.
[0027] The furnace for at least partial austenitisation of the
blank 2 is heated by gas. Corresponding means 3 for heating the
furnace are shown schematically in FIG. 1. In addition the
transport rollers 4 typical of a roller hearth furnace are likewise
shown in FIG. 1. The combustion exhaust gases from the roller
hearth furnace 1 are extracted via the medium supply lines 5, 6, 7
for further heat treatments from the roller hearth furnace 1. For
introducing the hot gases into the preheating furnace 8, the
forming tool 9 or the tempering furnace 10 are also provided with
additional fans 5a, 6a and 7a.
[0028] The medium supply line 5 carries the hot combustion exhaust
gases to a preheating furnace 8, in which the blank 2 is heated to
a temperature of more than 200.degree. C. to Ac1 temperature,
preferably to a temperature of between 250.degree. C. and
700.degree. C. The dwell time in the preheating furnace is
approximately 3 to 20 minutes, preferably however 5 to 10 minutes.
For transporting the blanks into the preheating furnace rollers 4
are likewise shown. In the preheating furnace the blank 2 as
already described is heated to a relatively high temperature. If
the blank 2 is made with an AlSi coating, then at corresponding
temperatures, which for example may be between 500 and 700.degree.
C., these can be pre-alloyed in the preheating furnace and in this
respect obtain a roughened surface structure, making the heating of
the blank 2 for example in the roller hearth furnace 1 easier. Via
the heating medium supply line 5 the temperature of the preheating
furnace can be adjusted by means of control means that are not
shown.
[0029] By using the waste heat from the roller hearth furnace 1
for, by way of example, preheating the blank 2 in the preheating
furnace 8, a considerable energy saving is made, since the high
temperatures which are necessary for pre-alloying of the coated
blanks, can be provided in a simple manner. Following
austenitisation in the roller hearth furnace 1 the blank 2 by means
of a handling system, not shown, is placed at an as high as
possible temperature in a forming tool 9 where it is hot formed,
preferably press hardened. Blanks 2 with an AlSi-coating can on the
one hand be heated without scaling to austenitisation temperature
and likewise hot formed or press hardened in the forming tool
9.
[0030] The medium supply line 7 is used for tempering the forming
tool at specific positions using the waste heat from the roller
hearth furnace 1. At the heated or tempered areas of the forming
tool another structure, for example a more ductile structure, of
the formed steel part 11 can be specifically created, whereas in
the other areas of the formed steel part 11 a martensitic structure
is created by a rapid cooling. The formed steel part 12 can
optionally undergo heat treatment again in a tempering furnace 10.
The tempering furnace 10 can also use the energy of the waste gases
from the roller hearth furnace 1, in order to perform the tempering
process, for example in partial sections of the annealed steel part
12.
[0031] The energy saving which is achieved by using the waste heat
from the roller hearth furnace 1 is considerable. The transport
between the individual stations, in particular the preheating
furnace 8, the roller hearth furnace 1, the forming tool 9 and the
tempering furnace 10 can be ensured by handling systems that are
not shown. A rollerway 4, as illustrated in the present exemplary
embodiment, can alternatively be replaced by handling systems. The
result of this is that with the method according to the invention
or with the device according to the invention, as shown in FIG. 1,
a considerable reduction in cycle times for producing a hot formed
steel part 11, 12 with a simultaneous reduction in energy
consumption can be ensured.
* * * * *