WO2011009769A9 - Method and device for energy-efficient hot forming - Google Patents

Abstract

The invention relates to a method for hot forming steel parts, particularly blanks or semi-finished products made of steel, wherein the steel parts are heated in a furnace to a temperature above the Acl temperature to at least partially austenitize and are hot-formed in a forming tool. The aim of providing a method for hot forming steel parts, which makes it possible to carry out the hot forming operation in an energy-efficient manner and at the same time reduces the cycle times for producing a hot-formed component, is achieved by using the waste heat of the furnace for other heat treatment steps of the steel part and/or after the at least partial austenitizing of the steel part.

Description

 Method and device for energy-efficient

 Orgasm

The invention relates to a method for hot working steel parts, in particular blanks or semi-finished steel, in which the steel parts are heated in an oven for at least partial austenitization to a temperature above the Acl temperature and hot-formed in a forming tool. In addition, the invention relates to an apparatus for carrying out the method with a furnace for heating the steel parts above the ACl temperature to form an at least partially austenitic structure, a forming tool for hot working of the steel parts and means for transporting the steel parts from the furnace to

Forming tool.

Steel parts in the context of the present invention are

For example, boards or semi-finished products, which for a

Hot forming are provided. The semi-finished products can

for example, as a blank or as pre-formed boards. To carry out the hot forming, the steel parts intended for hot forming must first be placed on a

Temperature are heated above the ACl temperature point, so that at least a partial austenitization of the structure of the steel part takes place. Preferably, the

Steel parts but completely austenitized. These are usually heated to a temperature above the AC3 temperature point at which the formation of the austenitic structure is completed and thus the

Steel part is completely in austenitic structure. Subsequently, the steel part is in a Ümformwerkzeug

and hot-worked at a temperature above the ACl temperature point. With the help of

Forming then takes place a so-called "press hardening", in which due to the rapid cooling the

austenitic structure of the formed steel part in

martensitic structure is converted. This results in the enormous strength corresponding to hot-formed

Steel parts. To during the temperature treatment of

Steel parts to prevent scaling and at the same time to provide corrosion protection, hot-forming steel parts are preferably coated with an AlSi coating. Finally, the press hardening can be followed by another step, in which the formed steel parts of another

Heat treatment, for example, be subjected to tempering to certain areas or in total the

To change the properties of the steel part again,

for example, to increase its ductility.

On the one hand, hot forming is a very energy intensive process, because the steel parts are left on for several minutes

Temperature must be heated above the ACl temperature point or must be heated above the AC3 temperature point and at this temperature for several minutes

remain. Further energy in the form of heat is needed in the forming tool and a further heat treatment step subsequent to the forming. This also applies to a preheating, possibly before heating the steel part to a temperature above the ACl temperature point. It has been shown that energy costs, especially in mass production of corresponding Steel parts adversely affect the economy of the

Affect the procedure. In addition, it was found that the cycle times for the production of the hot-formed

Steel part are in need of improvement. From the German

Patent DE 10 2005 033 042 B3 is known, the

To use preheating of a semifinished product provided for press-hardening with a metallic coating using the waste heat of the cooling process of the semifinished product heated to at least above the ACl temperature. However, it has been shown that the originating from the cooling process of the semifinished product

Residual heat amounts for a significant reduction of

Energy costs are insufficient.

Object of the present invention is thus, a

To provide a method of hot working steel parts that allows for energy efficient performance of hot working while reducing cycle times for producing a hot formed part. In addition, a device for carrying out the method according to the invention is to be proposed.

For a generic method, the above-indicated object is achieved according to a first teaching of the present invention in that the waste heat of the furnace for more

Heat treatment steps of the steel part before and / or after the at least partial austenitization of the steel part

is used.

It has been shown that the ovens used for

Performing the at least partial austenitization of the steel part produce enormous amounts of waste heat, which have not yet been used. According to the invention, the waste heat of the furnace now for further heat treatment steps on the steel part before and / or after the at least partial

Austenitization of the steel part can be used, so that significant energy can be saved.

Will the steel part before the at least partial

Heating austenitization using the waste heat of the furnace, the cycle time for the entire hot working can be reduced because the components in the furnace for at least partial austenitization due to the higher

 Inlet temperature much faster the desired

Achieve temperature without significantly more energy used for the process. The amounts of waste heat from the furnace for the at least partial austenitisation of the steel part are so great that they are needed even after the heat treatment

 Amounts of heat can be provided by the waste heat of the furnace. The energy efficiency of the method according to the invention can thereby be further increased. According to a first embodiment of the invention

Process becomes a continuous furnace, preferably one

Roller hearth furnace used for at least partial austenitization of the steel part. A continuous furnace or a

Roller hearth furnace offers an easy way of at least partially austenitizing the steel part in one

to carry out a continuous process and in one

to embed the corresponding process line.

The amounts of waste heat, which upstream or downstream

Heat treatments can be used are increased by the fact that the oven for at least partial

Austenitizing the steel part at least partially with gas is heated and the waste heat of the combustion gases from the furnace is used. These so-called jet furnaces can heat the component in a very short time to the desired temperature above the ACl temperature point or even above the AC3 temperature point, so that the cycle times for the at least partially austenitizing the steel part are relatively short. In addition, the waste heat of the combustion gases can be used in a simple manner, in which, for example via heat exchangers, the amount of energy is withdrawn from the gas or the exhaust gas directly for more

 Heat treatments is used. It is conceivable, the furnace heated with gas additionally with means for inductive

Heat transfer and / or means to transfer the heat by radiation equip.

Are used in a preheating furnace using the waste heat of the furnace for at least partial austenitization of the

Steel part, the steel parts, in particular metallically ^¬ coated, preferably ÄlSi-coated steel parts heated or pre-alloyed, the cycle times, which for the passage in the oven to at least partially

Austenitization of the steel part needed to be reduced while saving energy. This is on the one hand because the already heated steel part requires less energy to be heated to the desired temperature. On the other hand will

For example, by pre-alloying a metal-coated, preferably an AlSi-coated steel part achieved a relatively high iron content in the AlSi coating, which leads to a roughening of the surface layer, so that the radiant heat in the furnace to at least partially Austenitisierung the steel part clearly can be used more efficiently. The reflection properties of the pre-alloyed metal-coated, preferably AlSi-coated steel part are significantly improved. A further increase in the energy efficiency of the

The method according to the invention can be achieved by at least partially transforming the hot forming forming tool at least partially with the waste heat of the furnace

Austenitization of the steel part is heated. To the

In accordance with heated points, for example, a different microstructure in the steel part can be partially adjusted, so that different component properties can be provided in the formed steel part. Optionally, after the forming of the steel part, another heat treatment takes place, which according to another

Embodiment of the inventive method advantageously using the waste heat of the furnace for at least

partial austenitization of the steel part is performed.

For example, a typical post-forming heat treatment is tempering, such as partial tempering of the formed, tempered steel part, around the

To change component properties locally, for example.

In order to further increase the efficiency in the utilization of the waste heat, the heat treatment steps of the steel part are carried out before and / or after the at least partial austenitization of the steel part by forced convection. In a forced convection, the heat transfer is significantly increased because the steel parts to be heated or, for example, parts of the tool flow with a hot gas jet so that is an intense contact between hot

Gas particles and the part to be heated takes place.

Preferably, the steel parts are heated in the preheating oven to a temperature of 200 ° C to ACl temperature, preferably at 250 ° C to 700 ° C. Uncoated steel parts

then require only small amounts of energy to heat to above the ACl temperature in the oven for at least partial austenitization. In addition, coated components can be pre-alloyed, for example, with an AlSi coating in this temperature range with a short residence time, in particular to achieve a shortened heating time in the oven for at least partial austenitization of the steel part.

According to a second teaching of the present invention, the above-described object for a device is achieved by providing means for using the waste heat of the furnace before and / or after at least partially austenitizing the steel part.

Means for using the waste heat of the furnace for at least partially austenitizing the steel parts are varied and can be designed differently. Typically, they include piping and blower devices that are useful for the use and transportation of such hot gases. In addition, heat exchangers can be provided, which pass on the heat of the combustion exhaust gases of the furnace to another heat conducting medium. As a result, by the use of these means, the energy efficiency of the inventive method for hot working steel parts significantly improved and also reduces the cycle times for the completion of hot-formed steel parts.

Preferably, therefore, means are provided, which for

Heating a preheating furnace, the ümformwerkzeugs and / or a tempering furnace are used. This will be the

Use of the waste heat of the furnace for at least partial

Austenitization of the steel part used to operate the essential processes energy-efficient from preheating to tempering the steel part. In particular, however, the heating of the preheating furnace leads to a significant increase in energy efficiency, since large amounts of energy are needed here. According to a next embodiment of the device according to the invention is a continuous furnace, preferably a

Roller hearth furnace intended for at least partial austenitization of the steel parts. As already explained above, by using a continuous furnace, preferably a roller hearth furnace, a simple integration of the heating of the steel part to above the ACl temperature in one

Integrate process chain for the production of hot-formed steel parts. According to a simple embodiment of the device according to the invention are as means for heating the preheating furnace, the Ümformwerkzeugs and / or the tempering furnace gas lines and / or blower for supplying the combustion gases of the furnace for at least partial austenitization of

Steel parts provided to the individual devices. As already stated, heat exchangers can also be used when the combustion gases are not used immediately.

There are a lot of possibilities now

inventive method and the invention

 Design and develop device. Reference is made on the one hand to the claims 1 and 9 subordinate claims and to the description of an embodiment in conjunction with the drawings. In the drawing shows the only figure in one

schematic view of an embodiment of a

Apparatus for carrying out the inventive

Procedure. The illustrated in Fig. 1 embodiment of a

The method according to the invention comprises a furnace 1 for at least partially austenitizing a steel part 2. The steel part 2, in this case a planar board made of one

hardenable steel is heated in the embodiment of FIG. 1 to a temperature of at least 850 ° C and held for about 2 to 15 minutes at this temperature in the furnace 1, which is designed as a roller hearth furnace. Due to the temperature of 850 ° C and higher, a full

Austenitization of the board 2 achieved. Preferably, the board is made of 22MnB5 steel.

The furnace for the at least partial austenitisation of the

Board 2 is heated with gas. Corresponding means 3 for heating the furnace are shown schematically in FIG. In addition, the typical for a roller hearth furnace transport rollers 4 in Fig. 1 are also shown. The

Combustion gases of the roller hearth furnace 1 are about Media feeds 5, 6, 7 removed for further heat treatments from the roller hearth furnace 1. For the introduction of the hot gases in the preheating furnace 8, the forming tool 9 or the tempering furnace 10 are also fans 5a, 6a and 7a

intended.

The media supply 5 directs the hot combustion exhaust gases to a preheating furnace 8, in which the board 2 to a temperature of more than 200 ° C to ACl temperature,

is preferably heated to a temperature between 250 ° C and 700 ° C. The residence time in the preheating oven is about 3 to 20 minutes, but preferably 5 to 10 minutes. To transport the board 2 in the preheating furnace rollers 4 are also shown. In the preheating furnace, the board 2 is heated to a relatively high temperature, as already stated. If the board 2 is designed with an AlSi coating, it can be pre-alloyed at corresponding temperatures, which can be, for example, between 500 and 700 ° C. in the preheating furnace and thus receives a roughened surface structure, which is the heating of the board 2, for example in the roller hearth furnace 1 facilitated. About the heating medium supply 5, the temperature of the

Preheating oven via control means, not shown

be set.

By using the waste heat of the roller hearth furnace 1 for example, the preheating of the board 2 in the preheating 8 occurs a significant energy savings, since the high temperatures, which are also required for pre-alloying the coated board, can be provided in a simple manner. Following the austenitization in the

Roller hearth furnace 1, the board 2 using a Not shown handling system with the highest possible

Temperature inserted in a forming tool 9 and there

hot formed, preferably press hardened. On the one hand, boards 2 provided with an AlSi coating can

be heated to austenitizing temperature without scale and also hot-formed or press-hardened scale-free in the forming tool 9.

The media supply 7 serves to temper the

To perform forming tool at specific positions using the waste heat of the roller hearth furnace 1. At the heated or tempered areas of the forming tool, a different structure, for example more ductile structure of the formed steel part 11, can be produced in a targeted manner,

whereas in the other areas of the reshaped

 Steel part 11 martensitic structure is produced by a rapid cooling. The formed steel part 12 may optionally be subjected to another heat treatment in a tempering furnace 10. Even with the tempering furnace 10, the

Energy of the exhaust gases of the roller hearth furnace 1 are used to perform the starting process, for example in partial sections of the coated steel part 12.

The energy saving, which by the use of the

Waste heat of the roller hearth furnace 1 is achieved is significant.

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 by not shown

Handling systems are ensured. A roller conveyor 4, as shown in the present embodiment, may alternatively be replaced by handling systems. As a result, with the inventive method or with the device according to the invention, as shown in FIG. 1

shown a significant reduction in cycle times for producing a hot-formed steel part 11, 12 while reducing energy consumption

be guaranteed.

Claims

claims Process for the hot forming of steel parts, in particular blanks or semi-finished products of steel, in which the steel parts in an oven for at least partially Curd to a temperature above the Acl temperature and hot worked in a forming tool, d a d u r c h e c e n c e s, the waste heat from the oven can be used for more  Heat treatment steps of the steel part before and / or after the at least partial crusting of the steel part is used. Method according to claim 1, A continuous furnace, preferably a roller hearth furnace, is used for at least partial coarsening of the steel part. Method according to claim 1 or 2, The furnace for at least partial coarsening of the steel part is at least partially heated with gas and the waste heat from the combustion exhaust gases of the furnace is used for the further heat treatments. Method according to one of claims 1 to 3, characterized in that using the waste heat of the furnace for at least partially crusting steel parts, in particular metal-coated, preferably AlSi-coated steel parts are heated or pre-alloyed in a preheating furnace. 5. The method according to any one of claims 1 to 4,  For example, the hot forming forming tool is at least partially coextensive with the waste heat of the furnace for at least partial heating  Austenitization of the steel part is heated. 6. The method according to any one of claims 1 to 5,  d a d u r c h e c i n e c e s, using the waste heat of the oven one  Heat treatment, in particular a tempering of the  formed steel part is performed. 7. The method according to any one of claims 1 to 6,  The heat treatment steps of the steel part before and / or after the at least partial austenitization of the steel part are carried out by forced convection, respectively, can be performed. 8. The method according to any one of claims 1 to 7,  The steel parts in the preheating furnace are heated to a temperature of 200 ° C to ACl temperature, preferably to 250 ° C to 700 ° C, in the preheating furnace. 9. Apparatus for carrying out a method according to one of claims 1 to 8, with a furnace (1) for heating steel parts (2) above the ACl temperature to Forming an at least partially austenitic structure, a forming tool (9) for hot working of the steel parts (2) and with means (4) for transporting the steel parts (2) from the furnace (1) to the forming tool (9), d a d u r c h e s e n c i n e s, d a s s Means (5, 6, 7) for using the waste heat of the furnace (1) before and / or after the at least partial use Austenitization of the steel part (2) are provided. Device according to claim 9, There are provided means (5a, 6a, 7a) for heating a preheating furnace (8), the forming tool (9) and / or a tempering furnace (10). Device according to claim 9 or 10, There is provided a continuous furnace, preferably a roller hearth furnace (1) for at least partially austenitizing the steel parts (2). A method according to any one of claims 9 to 11, characterized in that as a means for heating the preheating furnace, the Umformwerkzeugs, the tempering furnace media lines (5, 6, 7) and / or blower (5a, 6a, 7a) for supplying the Combustion gases of the furnace (1) are provided for at least partial austenitization.