CA2999634C - Method for producing a zinc-coated steel component for a vehicle - Google Patents
Method for producing a zinc-coated steel component for a vehicle Download PDFInfo
- Publication number
- CA2999634C CA2999634C CA2999634A CA2999634A CA2999634C CA 2999634 C CA2999634 C CA 2999634C CA 2999634 A CA2999634 A CA 2999634A CA 2999634 A CA2999634 A CA 2999634A CA 2999634 C CA2999634 C CA 2999634C
- Authority
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- Canada
- Prior art keywords
- workpiece
- component
- press
- zinc
- hot
- Prior art date
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- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 title claims abstract description 46
- 239000011701 zinc Substances 0.000 title claims abstract description 46
- 229910052725 zinc Inorganic materials 0.000 title claims abstract description 46
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 36
- 239000010959 steel Substances 0.000 title claims abstract description 36
- 238000004519 manufacturing process Methods 0.000 title abstract description 10
- 238000000576 coating method Methods 0.000 claims abstract description 86
- 239000011248 coating agent Substances 0.000 claims abstract description 76
- 239000000463 material Substances 0.000 claims abstract description 54
- 238000010438 heat treatment Methods 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims description 32
- 230000015572 biosynthetic process Effects 0.000 claims description 12
- 238000001816 cooling Methods 0.000 claims description 7
- 238000003618 dip coating Methods 0.000 claims description 3
- 238000005260 corrosion Methods 0.000 abstract description 8
- 230000007797 corrosion Effects 0.000 abstract description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 17
- 239000007788 liquid Substances 0.000 description 10
- 229910052742 iron Inorganic materials 0.000 description 8
- 230000008569 process Effects 0.000 description 7
- 230000009467 reduction Effects 0.000 description 7
- 238000003780 insertion Methods 0.000 description 6
- 230000037431 insertion Effects 0.000 description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 229910052782 aluminium Inorganic materials 0.000 description 5
- 229910000734 martensite Inorganic materials 0.000 description 5
- PALQHNLJJQMCIQ-UHFFFAOYSA-N boron;manganese Chemical compound [Mn]#B PALQHNLJJQMCIQ-UHFFFAOYSA-N 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 238000005496 tempering Methods 0.000 description 4
- 229910000712 Boron steel Inorganic materials 0.000 description 3
- 238000001000 micrograph Methods 0.000 description 3
- 238000000137 annealing Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000005304 joining Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 229910000789 Aluminium-silicon alloy Inorganic materials 0.000 description 1
- 229910000760 Hardened steel Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- QYHKLBKLFBZGAI-UHFFFAOYSA-N boron magnesium Chemical compound [B].[Mg] QYHKLBKLFBZGAI-UHFFFAOYSA-N 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005244 galvannealing Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000037361 pathway Effects 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000011265 semifinished product Substances 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 238000001931 thermography Methods 0.000 description 1
- 238000009966 trimming Methods 0.000 description 1
- 230000035899 viability Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
- C23C2/29—Cooling or quenching
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/48—After-treatment of electroplated surfaces
- C25D5/50—After-treatment of electroplated surfaces by heat-treatment
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
- C25D7/06—Wires; Strips; Foils
- C25D7/0614—Strips or foils
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
- B62D25/04—Door pillars ; windshield pillars
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
- B62D25/20—Floors or bottom sub-units
- B62D25/2009—Floors or bottom sub-units in connection with other superstructure subunits
- B62D25/2036—Floors or bottom sub-units in connection with other superstructure subunits the subunits being side panels, sills or pillars
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- Physics & Mathematics (AREA)
- Electrochemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Crystallography & Structural Chemistry (AREA)
- Combustion & Propulsion (AREA)
- Transportation (AREA)
- Heat Treatment Of Articles (AREA)
- Shaping Metal By Deep-Drawing, Or The Like (AREA)
Abstract
The invention relates to a method for producing a component for a vehicle, having the following steps: -(A) providing a workpiece made of a heat-treatable steel material, said workpiece being provided with a zinc-containing coating on both sides, -(B) at least partly heating the workpiece to a temperature above Ac1, -(C) introducing the at least partly heated workpiece into a hot-forming and/or press-hardening tool which comprises at least one punch and at least one die, -(D) closing the tool by moving the punch and/or the die relative to each other and hot-forming and/or press-hardening the workpiece, wherein at least one region of the heated workpiece is cooled in the closed tool such that a hardened microstructure is at least partly formed. The aim of the invention is to provide a method for producing a component for a vehicle, a component for a vehicle, and a use of the component, wherein together with an active corrosion protection, a sufficient component strength in the event of a crash and a sufficient service life expectancy can be ensured in particular with cyclical loading. This is achieved in that the workpiece has a first surface with a smaller layer thickness of the zinc-containing coating than the second surface of the workpiece. The workpiece is introduced into the hot-forming and/or press-hardening tool such that the first surface of the workpiece is positioned on the side which is largely loaded with pressure and/or tension during the component manufacturing process, in particular the tool side which has a largely concave shape.
Description
METHOD FOR PRODUCING A ZINC-COATED STEEL COMPONENT FOR A VEHICLE
The invention relates to a method of producing a component for a vehicle, comprising the following steps:
providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides, at least partly heating the workpiece to a temperature above Ad., inserting the at least partly heated workpiece into a hot-forming and/or press-hardening mold comprising at least one punch and at least one die, closing the mold by relative movement of the punch and/or the die toward one another and hot-forming and/or press-hardening the workpiece, with cooling of at least a region of the heated workpiece in the closed mold in such a way that there is at least partial formation of a hardened microstructure.
The invention further relates to a component, especially produced by the method of the invention, and to a corresponding use of the component.
Modern automobile construction without press-hardened components is hard to imagine.
Conventional steel components have been replaced by new high- and higher-strength steel materials, and the increase in strength or the high strength of the material has enabled a reduction in the material thickness with the same mechanical properties, such that a positive effect on a reduction in the total weight of the vehicle is possible and hence an associated reduction in the CO2 output is also possible. The steel material used is a heat-treatable steel, for example a manganese-boron steel, the most common representative at present being 22 MnB5. Press-hardened components are generally produced from coated formed blanks or from coated blanks which are first cold-formed to give preformed semifinished products. The coating may be organic in nature, but inorganic coatings based on aluminum or aluminum/silicon and based on zinc have become established in practice. In the case of coatings based on aluminum or aluminum/silicon, during the heating process (austenitization), diffusion of iron out of the base material (22MnB5) into the coating takes place and an AlSi-Fe layer is formed, which has what is called a barrier effect with regard to the anticorrosion properties. There is no active cathodic corrosion protection in the case of an aluminum-based
The invention relates to a method of producing a component for a vehicle, comprising the following steps:
providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides, at least partly heating the workpiece to a temperature above Ad., inserting the at least partly heated workpiece into a hot-forming and/or press-hardening mold comprising at least one punch and at least one die, closing the mold by relative movement of the punch and/or the die toward one another and hot-forming and/or press-hardening the workpiece, with cooling of at least a region of the heated workpiece in the closed mold in such a way that there is at least partial formation of a hardened microstructure.
The invention further relates to a component, especially produced by the method of the invention, and to a corresponding use of the component.
Modern automobile construction without press-hardened components is hard to imagine.
Conventional steel components have been replaced by new high- and higher-strength steel materials, and the increase in strength or the high strength of the material has enabled a reduction in the material thickness with the same mechanical properties, such that a positive effect on a reduction in the total weight of the vehicle is possible and hence an associated reduction in the CO2 output is also possible. The steel material used is a heat-treatable steel, for example a manganese-boron steel, the most common representative at present being 22 MnB5. Press-hardened components are generally produced from coated formed blanks or from coated blanks which are first cold-formed to give preformed semifinished products. The coating may be organic in nature, but inorganic coatings based on aluminum or aluminum/silicon and based on zinc have become established in practice. In the case of coatings based on aluminum or aluminum/silicon, during the heating process (austenitization), diffusion of iron out of the base material (22MnB5) into the coating takes place and an AlSi-Fe layer is formed, which has what is called a barrier effect with regard to the anticorrosion properties. There is no active cathodic corrosion protection in the case of an aluminum-based
2 coating. However, active cathodic corrosion protection is provided by zinc-based coatings. Diffusion of iron out of the base material (22MnB5) into the coating does again take place during the heating process (austenitization). The diffusion does raise the melting point of the iron-enriched zinc coating, but formation of liquid zinc phases (also known as "liquid embrittlement") cannot be completely suppressed. Liquid embrittlement, in the course of subsequent hot forming and/or press hardening, according to the degree of forming that results from the forming at the surface of the coating, results in formation of cracks which can propagate further in the direction of the base material owing to the material stress (compression-tension) and extend into the base material. The propagation of the cracks is due to the presence of liquid zinc phases at the particle boundaries of the material, which weaken the material and promote propagation of cracks in the coating by virtue of the compressive/tensile stress down to the base material. Press-hardened components of this kind that are afflicted by cracking can cause a strength reduction in the component in the event of a crash and shortening of the expected lifetime, especially under cyclical stress.
The phenomenon of crack formation in the hot forming of zinc-coated blanks is disclosed, for example, in the following publication: Drillet et al. "Study of cracks propagation inside the steel on press hardened steel zinc based coatings", La Metallurgia Italiana - n. 1/2012, pages 3-8). Studies were conducted on an omega-shaped profile cross section which was to be hot-formed and press-hardened. It was found that cracks promoted by pockets of liquid zinc present in the material as a result of heating, particularly in the region of the frame to be produced (critical region), can arise at first owing to compressive stress and/or subsequent tensile stress on the side facing the die and can extend into the base material. The more complex the degree of forming, especially in the frame region, the higher the propensity to stress cracking and, associated with this, the deeper the crack that can be formed in the base material.
It is an object of the present invention, proceeding from the prior art, to specify a method of producing a component for a vehicle, a component for a vehicle and a use of the component, wherein not only active corrosion protection but also sufficient component strength in the event of a crash and expected lifetime, especially under cyclical stress, can be assured.
The phenomenon of crack formation in the hot forming of zinc-coated blanks is disclosed, for example, in the following publication: Drillet et al. "Study of cracks propagation inside the steel on press hardened steel zinc based coatings", La Metallurgia Italiana - n. 1/2012, pages 3-8). Studies were conducted on an omega-shaped profile cross section which was to be hot-formed and press-hardened. It was found that cracks promoted by pockets of liquid zinc present in the material as a result of heating, particularly in the region of the frame to be produced (critical region), can arise at first owing to compressive stress and/or subsequent tensile stress on the side facing the die and can extend into the base material. The more complex the degree of forming, especially in the frame region, the higher the propensity to stress cracking and, associated with this, the deeper the crack that can be formed in the base material.
It is an object of the present invention, proceeding from the prior art, to specify a method of producing a component for a vehicle, a component for a vehicle and a use of the component, wherein not only active corrosion protection but also sufficient component strength in the event of a crash and expected lifetime, especially under cyclical stress, can be assured.
3 The object is achieved in a method of the invention in that the workpiece has a first surface having a smaller coating thickness of the zinc-containing coating compared to the second surface of the workpiece, wherein the workpiece is inserted into the hot-forming and/or press-hardening mold in such a way that the first surface of the workpiece is positioned on the side predominantly subjected to compression and/or tension in the component manufacture, especially the predominantly concave mold side.
The method of the invention for production of a component for a vehicle firstly comprises the step of providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides. Heat-treatable steels used are essentially manganese-boron steels. It is also conceivable to use other steel qualities in which a higher strength can be generated as a result of a heat treatment and by comparison with the condition as supplied. A further step comprises at least partial heating of the workpiece to a temperature above An, especially above Ac3. The workpiece is first heated partially or completely to austenitization temperature, and (partially) different microstructures or a homogeneous microstructure throughout can be established in the workpiece according to the requirement on the component to be produced and the end use thereof in the motor vehicle. This can be effected by means of appropriate furnaces and/or by means of appropriate hot-forming and/or press-hardening tools. If different microstructures in the workpiece have to be taken into account, this is referred to as "tailored tempering", meaning that at least one region having a hard microstructure and at least one region which has a soft microstructure and is more ductile compared to the hard microstructure are established. A
further step comprises the insertion of the at least partly heated workpiece into a hot-forming and/or press-hardening mold comprising at least one punch and at least one die. At least one side of the mold is predominantly concave, preferably the die, and at least one side of the mold is predominantly convex, preferably the punch. The closure of the mold by relative movement of the punch and/or the die toward one another and hot-forming and/or press-hardening of the workpiece comprises a further step, with cooling of at least one region of the heated workpiece in the closed mold in such a way that there is at least partial formation of a hardened microstructure. The workpiece is completely or at least partially hardened, which is effected by rapid cooling in a mold, especially an actively cooled mold, in the course of hot forming and press-hardening (direct hot
The method of the invention for production of a component for a vehicle firstly comprises the step of providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides. Heat-treatable steels used are essentially manganese-boron steels. It is also conceivable to use other steel qualities in which a higher strength can be generated as a result of a heat treatment and by comparison with the condition as supplied. A further step comprises at least partial heating of the workpiece to a temperature above An, especially above Ac3. The workpiece is first heated partially or completely to austenitization temperature, and (partially) different microstructures or a homogeneous microstructure throughout can be established in the workpiece according to the requirement on the component to be produced and the end use thereof in the motor vehicle. This can be effected by means of appropriate furnaces and/or by means of appropriate hot-forming and/or press-hardening tools. If different microstructures in the workpiece have to be taken into account, this is referred to as "tailored tempering", meaning that at least one region having a hard microstructure and at least one region which has a soft microstructure and is more ductile compared to the hard microstructure are established. A
further step comprises the insertion of the at least partly heated workpiece into a hot-forming and/or press-hardening mold comprising at least one punch and at least one die. At least one side of the mold is predominantly concave, preferably the die, and at least one side of the mold is predominantly convex, preferably the punch. The closure of the mold by relative movement of the punch and/or the die toward one another and hot-forming and/or press-hardening of the workpiece comprises a further step, with cooling of at least one region of the heated workpiece in the closed mold in such a way that there is at least partial formation of a hardened microstructure. The workpiece is completely or at least partially hardened, which is effected by rapid cooling in a mold, especially an actively cooled mold, in the course of hot forming and press-hardening (direct hot
4 forming) or in the course of press-hardening (indirect hot forming], with conversion of the microstructure of the at least partly austenitic region of the workpiece by abrupt cooling to a martensitic and/or bainitic microstructure, particular preference being given to the achievement of a martensitic microstructure.
The inventors have found that, surprisingly, the reduction in the coating thickness of the zinc-containing coating on the first surface of the workpiece, which is positioned on the side predominantly subjected to compression and/or tension in the component manufacture, especially the predominantly concave mold side, preferably contacted with the die of the mold, can reduce the cracks or crack depth in the critical region compared to coating thicknesses that are customary in practice to a degree which satisfies the demands on component strength in the event of a crash and the expected lifetime, especially under cyclical stresses. Crack formation cannot be entirely avoided owing to the aforementioned phenomenon. The lowering of the coating thickness also reduces the zinc supply, and hence a lower level of liquid zinc phases, which weaken the material, arises in the material during the heating process.
In a first configuration of the method of the invention, the workpiece, prior to the provision thereof, is separated from a steel material in strip form which has been provided with a zinc-containing coating applied electrolytically or by hot dip coating, which is especially applied in a continuous coating process. Continuous coating processes are firstly economically viable and, secondly, the required coating thicknesses can be established in a controlled manner. The way in which the application of the different coating thicknesses (differential coating) on the surfaces of the steel material in strip form is conducted is known in the art.
Preferably, the steel material in strip form, after the application of the zinc-containing coating, is subjected to a heat treatment at a temperature especially between 200 C and Act preferably between 350 C and An, for a period of time between 5 and 300 s, preferably between 20 and 240 s. The heat treatment (galvannealing) conducted additionally prior to the hot forming and/or press hardening enriches the coating with iron in a controlled manner, which raises the melting point of the zinc-containing coating and can reduce the formation of liquid zinc phases during the austenitization in the material. The heat treatment is preferably effected continuously, preferably inline after the coating process. The heat treatment can also alternatively be conducted on a steel material in strip form that has been wound up to form a coil, which, for example, is batch-annealed, in which case the heat treatment time may be several minutes to several hours and the temperature range is within the aforementioned order of magnitude.
In a preferred configuration of the process of the invention, a workpiece having a first surface having a coating thickness of < 4 gm, especially < 3.5 gm, more preferably <3 gm, and a second surface having a coating thickness > 4 gm, especially >
4.5 gm, more preferably? 5 gm, of the zinc-containing coating is used, in each case in the as yet non-press-hardened condition (condition as supplied). A reduction in the cracks or the crack depth, especially in the critical region, is perceptible essentially when the coating thickness is <4 gm on the first surface of the workpiece. In order to assure sufficient cathodic corrosion protection, the coating thickness on the first surface should be 1 gm, especially 1.5 gm, more preferably 2 gm. The coating thickness on the second surface is 5 25 gm, especially 5. 20 gm, more preferably 15 gm, in order to keep the diffusion pathway for iron enrichment in the applied layer short.
In a further configuration of the method of the invention, the workpiece, after being heated, is inserted as an essentially flat workpiece into a hot-forming and press-hardening mold (direct hot forming), or as an already cold-formed workpiece of near finished geometry into a press-hardening mold (indirect hot forming). Indirect hot forming offers the advantage that there are no liquid zinc phases in the material, and the cold (pre)forming to give a workpiece of near finished geometry results in barely any cracks or any significant propagation of cracks into the base material through the stress on the material, especially in the critical region during the cold forming.
After the austenitization, quenching and calibration are effected in the press-hardening mold, which may include a low degree of forming. The disadvantage is that an additional method step, namely the preforming of the workpiece, is required, and additional investment in plant is also associated therewith. Particular preference is given to using direct hot forming. A workpiece means either a flat steel sheet or a cold, preformed steel part that has yet to be hardened.
In an alternative configuration of the method of the invention, the workpiece is subjected to hot forming in a first mold and at least to partial press hardening in a second mold. The division of the "hot forming" and "press hardening" processes between two molds can advantageously increase the cycle time, with an associated enhancement in economic viability. However, the division of the process into two means that it is necessary to ensure that the temperature does not go below the Ms temperature (martensite start temperature) on insertion of the already hot-formed workpiece into the press-hardening mold. Preferably, the temperature on insertion is at least Ms+20K, especially Ms+50K.
In a further configuration of the method of the invention, the workpiece is trimmed in the hot-forming and/or press-hardening mold. This has the advantage that the workpiece, preferably in the still-hot state, can be trimmed relatively easily when the temperature has not yet gone below the Ms temperature. This makes it possible to dispense with additional mechanical cutting tools which, because of the high hardness in the finished workpiece (component), are prone to wear and have a short service life, or alternative separating apparatuses, for example costly hard trimming by laser.
In a further configuration of the method of the invention, a workpiece which is a tailored product is used. Tailored products are understood to mean tailored blanks or tailored welded blanks, tailored strips or tailored welded strips and tailored rolled blanks or tailored rolled strips, which are known in the art. Tailored blanks and tailored strips with different sheet thicknesses and tailored rolled blanks can additionally be used to save mass by comparison with workpieces having a uniform material thickness.
In the tailored blanks and tailored strips, as well as different sheet thicknesses, it is also possible to use different steel materials in order to take account of different microstructures in the workpiece, which are not established by the "tailored tempering"
already mentioned; in other words, a heat-treatable steel material which has a hard microstructure after the hardening is welded to at least one non-heat-treatable, non-hardenable steel material which, after hardening, essentially retains its soft microstructure, along the joining edge of each, preferably by means of butt laser welding. Complex delayering of the joining zone, which is absolutely necessary in the case of AlSi coatings, can be dispensed with in the case of zinc-containing coatings.
The heat-treatable steel is a magnesium-boron steel having a tensile strength of at least 1500 MPa in the hardened state. Its alloy constituents in % by weight are preferably limited as follows:
s0.5 Si s 0.7 Mn s.2.5 0.01 Al 0.015 Ti 5 0.05 Cr+Mo 5 1.0 .s0.05 balance: iron and unavoidable impurities.
In a further configuration of the method of the invention, a component having a profile cross section which is hat-shaped or omega-shaped at least in some regions is produced.
More particularly, the component produced has the form of a half shell. Half shells are components which, in the installed state, are preferably parts of an A, B, C, D pillar, of a door sill, of a longitudinal beam, of a transverse beam, of a crash box or of a chassis component.
In a second aspect of the invention, a component for a vehicle which has a profile cross section which is top hat-shaped or omega-shaped at least in some regions, and which has been at least partly press-hardened, especially produced by the process of the invention is specified, wherein the component has a first surface having a smaller coating thickness of a zinc-containing coating compared to the second surface of the component.
In order to avoid repetition, reference is made to the above statements at this point.
In a first configuration of the component of the invention, the component has been formed from a tailored product, in order especially to be able to influence the weight. If a component is to have different microstructures, it may have been produced alternatively or cumulatively by a "tailored tempering" process.
In a third aspect, the invention relates to use of the component of the invention as bodywork component of a vehicle, especially as part of an A, B, C, D pillar, door sill, longitudinal beam, transverse beam, crash box, or in the form of a chassis part of a vehicle, especially as part of a chassis component, more preferably in passenger vehicles, utility vehicles, heavy goods vehicles, specialty vehicles, buses, omnibuses, whether driven by a combustion engine and/or electrically, but also in rail-bound vehicles, for example trams or passenger-carrying wagons.
The invention is elucidated hereinafter with reference to a diagram that shows working examples. Identical parts are given identical reference numerals. The figures show:
Figure 1): a schematic sequence of steps for production of a component for a vehicle in a first configuration of a method of the invention, Figure 2): a partial cross-sectional view of a first working example of a component of the invention, Figure 3a, b): micrographs of the critical region, shown in fig. 2, of hot-formed and press-hardened components, wherein the coating thickness was 5 i.tm and 3 pm in the non-press-hardened condition (condition as supplied).
Figure 1 shows, in schematic form, a sequence (E) of steps for production of a component for a vehicle in a first configuration of a method of the invention.
The method of the invention firstly comprises the step (A) of providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides. The coating has a first surface 3 having a coating thickness < 4 p.m, especially <
3.5 pm, more preferably < 3 pm, and a second surface 4 having a coating thickness of? 4 pm, especially? 4.5 pm, more preferably? 5 pm, of the zinc-containing coating, in each case in the as yet non-press-hardened condition (condition as supplied).
What is not shown here is that the workpiece, prior to provision thereof, is separated from a steel material in strip form, which has been provided with a zinc-containing coating applied electrolytically or by hot dip coating, which has especially been applied in a continuous coating process. Heat-treatable steel materials are essentially manganese-boron steels. A further step (B) comprises at least partial heating, preferably complete heating, of the workpiece to a temperature above Ad, especially above Ac3. The workpiece is first partially or completely heated to austenitization temperature, and different microstructures or a homogeneous microstructure throughout can be established in the workpiece according to the requirement on the component to be produced and the end use thereof in the motor vehicle. This can be effected by means of appropriate furnaces. Workpieces used include monolithic steel materials having a homogeneous material thickness, for example having material thicknesses between 0.5 and 6 mm, especially between 0.8 and 4 mm, or tailored products.
The temperature for heating (through-heating), preferably in a furnace (continuous furnace), is, for example, 850 to 930 C with a residence time, for example, between 3 and 12 min. The heating is followed by the insertion of the at least partly, preferably completely, heated workpiece into a hot-forming and/or press-hardening mold (step C) comprising at least one punch and at least one die. It has to be ensured that the workpiece having a first surface having a lower coating thickness of the zinc-containing coating compared to the second surface of the workpiece is inserted into the hot-forming and/or press-hardening mold in such a way that the first surface of the workpiece is brought into contact with the predominantly concave side of the mold, preferably with the die of the mold, and the second surface of the workpiece with the predominantly convex side of the mold, preferably with the punch of the mold.
This can be verified, for example, by suitable means that are not shown here, for example measurement systems, for example thermal imaging cameras etc., namely at an early stage in the region of charging of the furnace and/or at the outlet of the furnace and/or prior to the insertion into the mold, in order to avoid incorrect insertion.
The reduction in the coating thickness of the zinc-containing coating on the first surface 3 of the workpiece, which is preferably brought into contact with the die of the mold, can reduce the cracks or excessively high crack depths in the critical region 1 by comparison with coating thicknesses that are customary in practice to a degree which meets the demands on component strength in the event of a crash and the expected lifetime, especially under cyclical stresses. The lowering of the coating thickness also reduces the zinc supply and hence a lower level of liquid zinc phases, which weaken the material, forms during the heating process in the material.
The closure of the mold by relative movement of the punch and/or the die relative to one another and hot forming and/or press hardening of the workpiece are encompassed by a further step (D), wherein at least one region of the hot workpiece in the closed mold is cooled in such a way that there is at least partial formation of a hardened microstructure. The workpiece is at least completely or partially hardened, which is effected by rapid cooling in a mold, especially an actively cooled mold, in the course of hot forming and press-hardening (direct hot forming) or in the course of press-hardening (indirect hot forming), with conversion of the microstructure of the at least partly austenitic region of the workpiece by abrupt cooling to a martensitic and/or bainitic microstructure, particular preference being given to the achievement of a martensitic microstructure. If different microstructures in the workpiece are required, it is possible by the "tailored tempering" process or alternatively through the use of, for example, a tailored blank composed at least of one heat-treatable steel material and at least one non-heat-treatable steel material, to establish at least one region having a hard microstructure and at least one region which has a soft microstructure and is more ductile compared to the hard microstructure.
Particular preference is given to direct hot forming.
By differential coating, the workpiece is used to produce, by the indirect and preferably direct hot forming, components which have a top hat-shaped or omega-shaped profile cross section 5 in some regions. More particularly, the component produced has the form of a half shell. Half shells are components which, in the installed state, are preferably parts of an A, B, C, D pillar, of a door sill, of a longitudinal beam, of a transverse beam, of a crash box or of a chassis component.
What is not shown here is that hot-formed parts can also have other profile cross sections which are used, for example, as attachments, especially as part of a wheel rim, preferably as the wheel disk of a wheel rim. Figure 2 shows a partial cross-sectional view of a first working example of a component of the invention, for example in the form of a B pillar. What is shown is a cross section along an axis of the component F, where the component may be formed symmetrically about the axis F at least in this cross section. A B pillar has a cross section of variable length along its component axis. Especially in the case of direct hot forming, which is preferred, the first surface 3 of the workpiece, which is in contact with the die during the hot forming and press hardening, experiences high compressive/tensile stress, as a result of which cracks with high crack depths which extend into the base material form in the critical region (1) by virtue of the liquid zinc phases, which weaken the material, that result from the heating. The second surface 4 of the workpiece, which is in contact with the punch during the hot forming and press hardening, experiences lower compressive/tensile stress compared to the first surface, as a result of which there is no risk of excessively deep crack formation on the side facing the aunch.
Components or half shells of this kind are preferably joined to further components or half shells to form a profile having a cavity. The first surface 3 of the component having the reduced coating thickness of the zinc-containing coating (in the condition as supplied) accordingly has an external side for component-related reasons. The second surface 4, having a higher coating thickness of the zinc-containing coating compared to the first surface 3, accordingly has an internal side present within the cavity for component-related reasons. Especially in cavities, in the case of entry of a corrosive medium, there can be elevated risk of corrosion. In general, secondary measures, for example cavity sealing by means of wax, are undertaken in these regions. With a corresponding (higher) coating thickness of the zinc-containing coating on the second surface 4, it is possible in accordance with the invention to provide active long-term corrosion protection.
For the purpose of studying the formation of cracks, two samples were taken from the critical region 1 of hot-formed and press-hardened components 5, the coating 7 having been enriched with iron for temperature-related reasons after the annealing treatment and the subsequent hot forming and press hardening, in order to be able to create micrographs. The furnace temperature was 880 C with a residence time of 6 min.
The press-hardened components were produced from a manganese-boron steel (22MnB5) having a zinc-containing coating applied electrolytically at least on the first surface 3 and having a coating thickness of 3 pm (figure 3a) and 5 pm (figure 3b) prior to the press hardening in the condition as supplied. In the iron-enriched coating, it can be seen in the micrographs that, with coating thicknesses of the zinc-containing coating > 4 pm (in the condition as supplied), there are cracks with high crack depths 6', which extend down to the base material 2. The crack depths 6' in the base material are > 10 jun (figure 3b), which means that it is no longer possible to assure sufficient component strength in the event of a crash and expected lifetime, especially under cyclical stress.
Crack formation behavior is different with low coating thicknesses of the zinc-containing = 12 coating < 4 pm (in the condition as supplied). The crack depth 6 in the base material 2 can be reduced to a maximum of 10 pm, which means that it is possible to assure sufficient component strength in the event of a crash and expected lifetime, especially under cyclical stress. In order to ensure sufficient cathodic corrosion protection, the coating thickness on the first surface 3 is ?_ 1 p.m, especially 1.5 gm, more preferably 2 m, in the as yet non-press-hardened condition (in the condition as supplied). The coating thickness on the second surface 4 is restricted to 5. 25 pm, especially 5. 20 pm, more preferably 15 m.
List of reference signs A, B, C, D step sequence, method steps process direction component axis 1 critical region 2 heat-treatable steel material, base material 3 first surface of the steel material 4 second surface of the steel material press-hardened component 6, 6' crack depth 7 coating after the annealing treatment and the subsequent hot forming and press hardening
The inventors have found that, surprisingly, the reduction in the coating thickness of the zinc-containing coating on the first surface of the workpiece, which is positioned on the side predominantly subjected to compression and/or tension in the component manufacture, especially the predominantly concave mold side, preferably contacted with the die of the mold, can reduce the cracks or crack depth in the critical region compared to coating thicknesses that are customary in practice to a degree which satisfies the demands on component strength in the event of a crash and the expected lifetime, especially under cyclical stresses. Crack formation cannot be entirely avoided owing to the aforementioned phenomenon. The lowering of the coating thickness also reduces the zinc supply, and hence a lower level of liquid zinc phases, which weaken the material, arises in the material during the heating process.
In a first configuration of the method of the invention, the workpiece, prior to the provision thereof, is separated from a steel material in strip form which has been provided with a zinc-containing coating applied electrolytically or by hot dip coating, which is especially applied in a continuous coating process. Continuous coating processes are firstly economically viable and, secondly, the required coating thicknesses can be established in a controlled manner. The way in which the application of the different coating thicknesses (differential coating) on the surfaces of the steel material in strip form is conducted is known in the art.
Preferably, the steel material in strip form, after the application of the zinc-containing coating, is subjected to a heat treatment at a temperature especially between 200 C and Act preferably between 350 C and An, for a period of time between 5 and 300 s, preferably between 20 and 240 s. The heat treatment (galvannealing) conducted additionally prior to the hot forming and/or press hardening enriches the coating with iron in a controlled manner, which raises the melting point of the zinc-containing coating and can reduce the formation of liquid zinc phases during the austenitization in the material. The heat treatment is preferably effected continuously, preferably inline after the coating process. The heat treatment can also alternatively be conducted on a steel material in strip form that has been wound up to form a coil, which, for example, is batch-annealed, in which case the heat treatment time may be several minutes to several hours and the temperature range is within the aforementioned order of magnitude.
In a preferred configuration of the process of the invention, a workpiece having a first surface having a coating thickness of < 4 gm, especially < 3.5 gm, more preferably <3 gm, and a second surface having a coating thickness > 4 gm, especially >
4.5 gm, more preferably? 5 gm, of the zinc-containing coating is used, in each case in the as yet non-press-hardened condition (condition as supplied). A reduction in the cracks or the crack depth, especially in the critical region, is perceptible essentially when the coating thickness is <4 gm on the first surface of the workpiece. In order to assure sufficient cathodic corrosion protection, the coating thickness on the first surface should be 1 gm, especially 1.5 gm, more preferably 2 gm. The coating thickness on the second surface is 5 25 gm, especially 5. 20 gm, more preferably 15 gm, in order to keep the diffusion pathway for iron enrichment in the applied layer short.
In a further configuration of the method of the invention, the workpiece, after being heated, is inserted as an essentially flat workpiece into a hot-forming and press-hardening mold (direct hot forming), or as an already cold-formed workpiece of near finished geometry into a press-hardening mold (indirect hot forming). Indirect hot forming offers the advantage that there are no liquid zinc phases in the material, and the cold (pre)forming to give a workpiece of near finished geometry results in barely any cracks or any significant propagation of cracks into the base material through the stress on the material, especially in the critical region during the cold forming.
After the austenitization, quenching and calibration are effected in the press-hardening mold, which may include a low degree of forming. The disadvantage is that an additional method step, namely the preforming of the workpiece, is required, and additional investment in plant is also associated therewith. Particular preference is given to using direct hot forming. A workpiece means either a flat steel sheet or a cold, preformed steel part that has yet to be hardened.
In an alternative configuration of the method of the invention, the workpiece is subjected to hot forming in a first mold and at least to partial press hardening in a second mold. The division of the "hot forming" and "press hardening" processes between two molds can advantageously increase the cycle time, with an associated enhancement in economic viability. However, the division of the process into two means that it is necessary to ensure that the temperature does not go below the Ms temperature (martensite start temperature) on insertion of the already hot-formed workpiece into the press-hardening mold. Preferably, the temperature on insertion is at least Ms+20K, especially Ms+50K.
In a further configuration of the method of the invention, the workpiece is trimmed in the hot-forming and/or press-hardening mold. This has the advantage that the workpiece, preferably in the still-hot state, can be trimmed relatively easily when the temperature has not yet gone below the Ms temperature. This makes it possible to dispense with additional mechanical cutting tools which, because of the high hardness in the finished workpiece (component), are prone to wear and have a short service life, or alternative separating apparatuses, for example costly hard trimming by laser.
In a further configuration of the method of the invention, a workpiece which is a tailored product is used. Tailored products are understood to mean tailored blanks or tailored welded blanks, tailored strips or tailored welded strips and tailored rolled blanks or tailored rolled strips, which are known in the art. Tailored blanks and tailored strips with different sheet thicknesses and tailored rolled blanks can additionally be used to save mass by comparison with workpieces having a uniform material thickness.
In the tailored blanks and tailored strips, as well as different sheet thicknesses, it is also possible to use different steel materials in order to take account of different microstructures in the workpiece, which are not established by the "tailored tempering"
already mentioned; in other words, a heat-treatable steel material which has a hard microstructure after the hardening is welded to at least one non-heat-treatable, non-hardenable steel material which, after hardening, essentially retains its soft microstructure, along the joining edge of each, preferably by means of butt laser welding. Complex delayering of the joining zone, which is absolutely necessary in the case of AlSi coatings, can be dispensed with in the case of zinc-containing coatings.
The heat-treatable steel is a magnesium-boron steel having a tensile strength of at least 1500 MPa in the hardened state. Its alloy constituents in % by weight are preferably limited as follows:
s0.5 Si s 0.7 Mn s.2.5 0.01 Al 0.015 Ti 5 0.05 Cr+Mo 5 1.0 .s0.05 balance: iron and unavoidable impurities.
In a further configuration of the method of the invention, a component having a profile cross section which is hat-shaped or omega-shaped at least in some regions is produced.
More particularly, the component produced has the form of a half shell. Half shells are components which, in the installed state, are preferably parts of an A, B, C, D pillar, of a door sill, of a longitudinal beam, of a transverse beam, of a crash box or of a chassis component.
In a second aspect of the invention, a component for a vehicle which has a profile cross section which is top hat-shaped or omega-shaped at least in some regions, and which has been at least partly press-hardened, especially produced by the process of the invention is specified, wherein the component has a first surface having a smaller coating thickness of a zinc-containing coating compared to the second surface of the component.
In order to avoid repetition, reference is made to the above statements at this point.
In a first configuration of the component of the invention, the component has been formed from a tailored product, in order especially to be able to influence the weight. If a component is to have different microstructures, it may have been produced alternatively or cumulatively by a "tailored tempering" process.
In a third aspect, the invention relates to use of the component of the invention as bodywork component of a vehicle, especially as part of an A, B, C, D pillar, door sill, longitudinal beam, transverse beam, crash box, or in the form of a chassis part of a vehicle, especially as part of a chassis component, more preferably in passenger vehicles, utility vehicles, heavy goods vehicles, specialty vehicles, buses, omnibuses, whether driven by a combustion engine and/or electrically, but also in rail-bound vehicles, for example trams or passenger-carrying wagons.
The invention is elucidated hereinafter with reference to a diagram that shows working examples. Identical parts are given identical reference numerals. The figures show:
Figure 1): a schematic sequence of steps for production of a component for a vehicle in a first configuration of a method of the invention, Figure 2): a partial cross-sectional view of a first working example of a component of the invention, Figure 3a, b): micrographs of the critical region, shown in fig. 2, of hot-formed and press-hardened components, wherein the coating thickness was 5 i.tm and 3 pm in the non-press-hardened condition (condition as supplied).
Figure 1 shows, in schematic form, a sequence (E) of steps for production of a component for a vehicle in a first configuration of a method of the invention.
The method of the invention firstly comprises the step (A) of providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides. The coating has a first surface 3 having a coating thickness < 4 p.m, especially <
3.5 pm, more preferably < 3 pm, and a second surface 4 having a coating thickness of? 4 pm, especially? 4.5 pm, more preferably? 5 pm, of the zinc-containing coating, in each case in the as yet non-press-hardened condition (condition as supplied).
What is not shown here is that the workpiece, prior to provision thereof, is separated from a steel material in strip form, which has been provided with a zinc-containing coating applied electrolytically or by hot dip coating, which has especially been applied in a continuous coating process. Heat-treatable steel materials are essentially manganese-boron steels. A further step (B) comprises at least partial heating, preferably complete heating, of the workpiece to a temperature above Ad, especially above Ac3. The workpiece is first partially or completely heated to austenitization temperature, and different microstructures or a homogeneous microstructure throughout can be established in the workpiece according to the requirement on the component to be produced and the end use thereof in the motor vehicle. This can be effected by means of appropriate furnaces. Workpieces used include monolithic steel materials having a homogeneous material thickness, for example having material thicknesses between 0.5 and 6 mm, especially between 0.8 and 4 mm, or tailored products.
The temperature for heating (through-heating), preferably in a furnace (continuous furnace), is, for example, 850 to 930 C with a residence time, for example, between 3 and 12 min. The heating is followed by the insertion of the at least partly, preferably completely, heated workpiece into a hot-forming and/or press-hardening mold (step C) comprising at least one punch and at least one die. It has to be ensured that the workpiece having a first surface having a lower coating thickness of the zinc-containing coating compared to the second surface of the workpiece is inserted into the hot-forming and/or press-hardening mold in such a way that the first surface of the workpiece is brought into contact with the predominantly concave side of the mold, preferably with the die of the mold, and the second surface of the workpiece with the predominantly convex side of the mold, preferably with the punch of the mold.
This can be verified, for example, by suitable means that are not shown here, for example measurement systems, for example thermal imaging cameras etc., namely at an early stage in the region of charging of the furnace and/or at the outlet of the furnace and/or prior to the insertion into the mold, in order to avoid incorrect insertion.
The reduction in the coating thickness of the zinc-containing coating on the first surface 3 of the workpiece, which is preferably brought into contact with the die of the mold, can reduce the cracks or excessively high crack depths in the critical region 1 by comparison with coating thicknesses that are customary in practice to a degree which meets the demands on component strength in the event of a crash and the expected lifetime, especially under cyclical stresses. The lowering of the coating thickness also reduces the zinc supply and hence a lower level of liquid zinc phases, which weaken the material, forms during the heating process in the material.
The closure of the mold by relative movement of the punch and/or the die relative to one another and hot forming and/or press hardening of the workpiece are encompassed by a further step (D), wherein at least one region of the hot workpiece in the closed mold is cooled in such a way that there is at least partial formation of a hardened microstructure. The workpiece is at least completely or partially hardened, which is effected by rapid cooling in a mold, especially an actively cooled mold, in the course of hot forming and press-hardening (direct hot forming) or in the course of press-hardening (indirect hot forming), with conversion of the microstructure of the at least partly austenitic region of the workpiece by abrupt cooling to a martensitic and/or bainitic microstructure, particular preference being given to the achievement of a martensitic microstructure. If different microstructures in the workpiece are required, it is possible by the "tailored tempering" process or alternatively through the use of, for example, a tailored blank composed at least of one heat-treatable steel material and at least one non-heat-treatable steel material, to establish at least one region having a hard microstructure and at least one region which has a soft microstructure and is more ductile compared to the hard microstructure.
Particular preference is given to direct hot forming.
By differential coating, the workpiece is used to produce, by the indirect and preferably direct hot forming, components which have a top hat-shaped or omega-shaped profile cross section 5 in some regions. More particularly, the component produced has the form of a half shell. Half shells are components which, in the installed state, are preferably parts of an A, B, C, D pillar, of a door sill, of a longitudinal beam, of a transverse beam, of a crash box or of a chassis component.
What is not shown here is that hot-formed parts can also have other profile cross sections which are used, for example, as attachments, especially as part of a wheel rim, preferably as the wheel disk of a wheel rim. Figure 2 shows a partial cross-sectional view of a first working example of a component of the invention, for example in the form of a B pillar. What is shown is a cross section along an axis of the component F, where the component may be formed symmetrically about the axis F at least in this cross section. A B pillar has a cross section of variable length along its component axis. Especially in the case of direct hot forming, which is preferred, the first surface 3 of the workpiece, which is in contact with the die during the hot forming and press hardening, experiences high compressive/tensile stress, as a result of which cracks with high crack depths which extend into the base material form in the critical region (1) by virtue of the liquid zinc phases, which weaken the material, that result from the heating. The second surface 4 of the workpiece, which is in contact with the punch during the hot forming and press hardening, experiences lower compressive/tensile stress compared to the first surface, as a result of which there is no risk of excessively deep crack formation on the side facing the aunch.
Components or half shells of this kind are preferably joined to further components or half shells to form a profile having a cavity. The first surface 3 of the component having the reduced coating thickness of the zinc-containing coating (in the condition as supplied) accordingly has an external side for component-related reasons. The second surface 4, having a higher coating thickness of the zinc-containing coating compared to the first surface 3, accordingly has an internal side present within the cavity for component-related reasons. Especially in cavities, in the case of entry of a corrosive medium, there can be elevated risk of corrosion. In general, secondary measures, for example cavity sealing by means of wax, are undertaken in these regions. With a corresponding (higher) coating thickness of the zinc-containing coating on the second surface 4, it is possible in accordance with the invention to provide active long-term corrosion protection.
For the purpose of studying the formation of cracks, two samples were taken from the critical region 1 of hot-formed and press-hardened components 5, the coating 7 having been enriched with iron for temperature-related reasons after the annealing treatment and the subsequent hot forming and press hardening, in order to be able to create micrographs. The furnace temperature was 880 C with a residence time of 6 min.
The press-hardened components were produced from a manganese-boron steel (22MnB5) having a zinc-containing coating applied electrolytically at least on the first surface 3 and having a coating thickness of 3 pm (figure 3a) and 5 pm (figure 3b) prior to the press hardening in the condition as supplied. In the iron-enriched coating, it can be seen in the micrographs that, with coating thicknesses of the zinc-containing coating > 4 pm (in the condition as supplied), there are cracks with high crack depths 6', which extend down to the base material 2. The crack depths 6' in the base material are > 10 jun (figure 3b), which means that it is no longer possible to assure sufficient component strength in the event of a crash and expected lifetime, especially under cyclical stress.
Crack formation behavior is different with low coating thicknesses of the zinc-containing = 12 coating < 4 pm (in the condition as supplied). The crack depth 6 in the base material 2 can be reduced to a maximum of 10 pm, which means that it is possible to assure sufficient component strength in the event of a crash and expected lifetime, especially under cyclical stress. In order to ensure sufficient cathodic corrosion protection, the coating thickness on the first surface 3 is ?_ 1 p.m, especially 1.5 gm, more preferably 2 m, in the as yet non-press-hardened condition (in the condition as supplied). The coating thickness on the second surface 4 is restricted to 5. 25 pm, especially 5. 20 pm, more preferably 15 m.
List of reference signs A, B, C, D step sequence, method steps process direction component axis 1 critical region 2 heat-treatable steel material, base material 3 first surface of the steel material 4 second surface of the steel material press-hardened component 6, 6' crack depth 7 coating after the annealing treatment and the subsequent hot forming and press hardening
Claims (12)
1. A method of producing a component for a vehicle, comprising:
(A) providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides, wherein the workpiece has a first surface having a smaller coating thickness of the zinc-containing coating compared to a second surface of the workpiece, the first surface having a coating thickness < 4 µm and the second surface having a coating thickness >=4 µm of the zinc-containing coating, in each case in an as yet non-press-hardened condition;
(B) at least partly heating the workpiece to a temperature above Ac1;
(C) inserting the at least partly heated workpiece into at least one of a hot-forming and press-hardening mold comprising at least one punch and at least one die, in such a way that the first surface of the workpiece is positioned on a side contacted with the die of the mold; and (D) closing the mold by relative movement of at least one of the punch and the die toward one another and at least one of hot-forming and press-hardening the workpiece, with cooling of at least one region of the heated workpiece in the closed mold in such a way that there is at least partial formation of a hardened microstructure.
(A) providing a workpiece composed of a heat-treatable steel material provided with a zinc-containing coating on both sides, wherein the workpiece has a first surface having a smaller coating thickness of the zinc-containing coating compared to a second surface of the workpiece, the first surface having a coating thickness < 4 µm and the second surface having a coating thickness >=4 µm of the zinc-containing coating, in each case in an as yet non-press-hardened condition;
(B) at least partly heating the workpiece to a temperature above Ac1;
(C) inserting the at least partly heated workpiece into at least one of a hot-forming and press-hardening mold comprising at least one punch and at least one die, in such a way that the first surface of the workpiece is positioned on a side contacted with the die of the mold; and (D) closing the mold by relative movement of at least one of the punch and the die toward one another and at least one of hot-forming and press-hardening the workpiece, with cooling of at least one region of the heated workpiece in the closed mold in such a way that there is at least partial formation of a hardened microstructure.
2. The method as claimed in claim 1, wherein the workpiece, prior to the provision thereof, is separated from a steel material in strip form which has been provided with the zinc-containing coating applied electrolytically or by hot dip coating.
3. The method as claimed in claim 2, wherein the steel material in strip form, after the application of the zinc-containing coating, is subjected to a heat treatment at a temperature between 200°C and Ac1 for a period of time between 5 and 300 s.
4. The method as claimed in any one of claims 1 to 3, wherein the first surface of the workpiece has a coating thickness < 3.5 µm and the second surface has a coating thickness >=4.5 µm of the zinc-containing coating is used, in each case in the as yet non-press-hardened condition.
5. The method as claimed in any one of claims 1 to 4, wherein the workpiece, after being heated, is inserted as an essentially flat workpiece into the at least one of hot-forming and press-hardening mold, or as an already cold-formed workpiece of near finished geometry into a press-hardening mold.
6. The method as claimed in any one of claims 1 to 4, wherein the workpiece is hot-formed in a first mold and at least partly press-hardened in a second mold.
7, The method as claimed in any one of claims 1 to 6, wherein the workpiece is trimmed in the at least one of hot-forming and the press-hardening mold.
8. The method as claimed in any one of claims 1 to 7, wherein the workpiece is a tailored product.
9. The method as claimed in any one of claims 1 to 8, wherein a component having a profile cross section which is top hat-shaped or omega-shaped at least in some regions is produced as part of at least one of an A, B, C, D pillar, a door sill, a longitudinal beam, a transverse beam, a crash box and a chassis component.
10. A component for a vehicle which has a profile cross section which is top hat-shaped or omega-shaped at least in some regions, and which has been at least partly press-hardened, produced according to any one of claims 1 to 9, wherein the first surface of the component has a smaller coating thickness of a zinc-containing coating compared to the second surface of the component.
11. The component as claimed in claim 10, wherein the component has been formed from a tailored product.
12. The use of a component as claimed in any one of claims 10 and 11 as bodywork component of a vehicle as part of at least one of an A, B, C, D pillar, a door sill, a longitudinal beam, a transverse beam, a crash box, and a chassis component.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102015220347.6A DE102015220347B4 (en) | 2015-10-20 | 2015-10-20 | Method for producing a component for a vehicle |
| DE102015220347.6 | 2015-10-20 | ||
| PCT/EP2016/073709 WO2017067782A1 (en) | 2015-10-20 | 2016-10-05 | Method for producing a steel component for a vehicle |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2999634A1 CA2999634A1 (en) | 2017-04-27 |
| CA2999634C true CA2999634C (en) | 2019-09-24 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2999634A Expired - Fee Related CA2999634C (en) | 2015-10-20 | 2016-10-05 | Method for producing a zinc-coated steel component for a vehicle |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US20180282835A1 (en) |
| EP (1) | EP3365469B1 (en) |
| JP (1) | JP2019500215A (en) |
| KR (1) | KR20180073621A (en) |
| CN (1) | CN108138254A (en) |
| CA (1) | CA2999634C (en) |
| DE (1) | DE102015220347B4 (en) |
| ES (1) | ES2770304T3 (en) |
| MX (1) | MX2018004812A (en) |
| WO (1) | WO2017067782A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102018203727B4 (en) | 2018-03-13 | 2023-08-31 | Audi Ag | component composite |
| DE102018132171A1 (en) * | 2018-12-13 | 2020-06-18 | Thyssenkrupp Steel Europe Ag | Battery case and usage |
| DE102018222063A1 (en) * | 2018-12-18 | 2020-06-18 | Volkswagen Aktiengesellschaft | Steel substrate for the production of a hot-formed and press-hardened sheet steel component as well as a hot-forming process |
| DE102020130543A1 (en) | 2020-11-19 | 2022-05-19 | Voestalpine Stahl Gmbh | Steel material and method for its manufacture |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102009003508B4 (en) * | 2009-02-19 | 2013-01-24 | Thyssenkrupp Steel Europe Ag | Process for producing a press-hardened metal component |
| DE102009017326A1 (en) * | 2009-04-16 | 2010-10-21 | Benteler Automobiltechnik Gmbh | Process for producing press-hardened components |
| DE102013010025A1 (en) * | 2013-06-17 | 2014-12-18 | Muhr Und Bender Kg | Method for producing a product from flexibly rolled strip material |
| EP2848715B1 (en) | 2013-09-13 | 2018-10-31 | ThyssenKrupp Steel Europe AG | Method for producing a steel component with an anti-corrosive metal coating |
-
2015
- 2015-10-20 DE DE102015220347.6A patent/DE102015220347B4/en not_active Expired - Fee Related
-
2016
- 2016-10-05 CN CN201680061237.8A patent/CN108138254A/en active Pending
- 2016-10-05 EP EP16785377.9A patent/EP3365469B1/en active Active
- 2016-10-05 MX MX2018004812A patent/MX2018004812A/en unknown
- 2016-10-05 CA CA2999634A patent/CA2999634C/en not_active Expired - Fee Related
- 2016-10-05 ES ES16785377T patent/ES2770304T3/en active Active
- 2016-10-05 JP JP2018519951A patent/JP2019500215A/en not_active Withdrawn
- 2016-10-05 KR KR1020187014133A patent/KR20180073621A/en unknown
- 2016-10-05 WO PCT/EP2016/073709 patent/WO2017067782A1/en active Application Filing
- 2016-10-05 US US15/768,788 patent/US20180282835A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| CA2999634A1 (en) | 2017-04-27 |
| EP3365469A1 (en) | 2018-08-29 |
| EP3365469B1 (en) | 2020-01-01 |
| JP2019500215A (en) | 2019-01-10 |
| WO2017067782A1 (en) | 2017-04-27 |
| MX2018004812A (en) | 2018-08-01 |
| CN108138254A (en) | 2018-06-08 |
| DE102015220347B4 (en) | 2018-06-21 |
| US20180282835A1 (en) | 2018-10-04 |
| KR20180073621A (en) | 2018-07-02 |
| ES2770304T3 (en) | 2020-07-01 |
| DE102015220347A1 (en) | 2017-04-20 |
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