EP1263540B1 - Method for the production of thin-walled steel components and components produced therefrom - Google Patents

Abstract

A process for the production of thin walled parts of steel, wherein there are layers that are at least partly differently treatable relating to their strength and hardness qualities. This process can include creating a composite material from a plurality of different layers by connecting at least one core layer and at least one surface layer together. At least one layer of the core or surface layer is cast adjacent to another layer to form a composite material having an alloy gradient that is flat at each interface between any of the core layer or the surface layer. Next, the process can include deforming the composite material along a length of these layers. Finally the process can include heat treating the layers to transform the strength and hardness qualities of at least one of these layers.

Description

The present invention relates to a method for producing thin-walled Steel components, the layers of which different steel alloys exist according to The preamble of claim 1. The invention further comprises thin-walled components made of steel with a core layer and edge layers.

Thin-walled steel components with a wall thickness of less than 4 mm, for one particularly high durability is required, for example in machine and Vehicle construction, are first hot and / or cold formed, cutting or processed without cutting and then tempered by thermal treatment, namely martensitic or bainitic. Made from hardening steel a component with a uniform, high hardness, which however has a low toughness. A cheaper combination wear-resistant surfaces with high toughness in the core zone achieved the use of case-hardened steels. Through a carburizing treatment in a thermochemical hardening process produces hardened, hard surface layers, while the core layer continues to maintain high toughness. The beneficial one However, use properties are a relatively complex manufacturing process across from. Due to the relatively long case hardening time of, for example 180 minutes at 850-950 ° C and the subsequent quenching in an oil bath or in Gas flow is inevitably a delay in hardness. This causes dimensional and Shape deviations, which require extensive reworking, which significantly increases the manufacturing and cost expenditure. Also lies a relatively coarse hardness structure, which has an austenite grain size according to DIN 50601 of 5 or 6, for example. This creates a tendency to grain boundary cracks at the intergranular grain boundaries.

The use of roll-clad is still a substitute for case hardening Steel known, two or more, differently alloyed strips or sheets, preferably from cold rolled strip. By printing and the temperature, the core and outer layers are made of different alloys Steels intimately connected to one another in the roll gap on the surfaces. Through the Subsequent annealing results from the diffusion processes of the metallic composite. Such a roll cladding process is specified, for example, in DE 41 37 118 A1. However, this creates an abrupt, abrupt transition between the different layers of material. The hardship transition between paid and unrefined layers is therefore also correspondingly steep, so that due to the load-induced stress gradient produces relatively thick boundary layers Need to become. Due to the relative tensions there is also at the interface inevitably the latent danger that the edge zones when stressed by Flake the yield point in the joining area. This disadvantage can be like mentioned above, can only be countered by thicker edge layers, however, this in turn leads to an undesirably higher wall thickness of the components leads and also complicates the manufacture.

According to DE 196 31 999 A1 is already for the production of composite sheets proposed to combine core and surface layers in a continuous caster. This is to produce a steel layer material. The problem in the production of differently tempered or hardened layers however not taken up. A similar continuous casting process is described in DE 33 46 391 A1, in which laminated sheets are also embedded in a melt become. The problem with the realization of differently remunerated or however, hardened layers are also not addressed. The aforementioned Continuous casting processes and systems are obviously only for manufacturing relatively thick boards or sheets, and not for the production of thin-walled components. The situation is similar with that from US Pat. No. 3,457,984 emerging state of the art. This only refers to the cast strand to coat a continuous caster with sheet metal.

DE-A-198 15 007 and DE-A-198 50 213 describe methods and procedures manufactured thin metal tapes known, in which a core material an inexpensive material through a casting process with thin metal strips be cast in layers to form a composite material, the thin Metal strips for the production of corrosion-resistant and / or particularly smooth outer layers be used. A subsequent treatment is also in progress here on the influence of other properties of the composite material.

In view of this, the task for the present invention is a rational process for the production of thin-walled components made of steel with different Strength and / or hardness properties. Furthermore, a Component with layers of different strength and / or hardness properties be specified, which is particularly cheaper due to the reduced effort than can be produced so far.

The method according to the invention for the production of thin-walled components Steel that has an inner core layer and outer peripheral layers sees here before that the core and outer layers of different steel alloys exist and in a casting process to a composite material with flat Alloy gradients are connected at the interfaces and the composite deformed to the dimensions of the thin-walled components and heat-treated and the heat treatment becomes a martensitic or bainitic Not all harden, but at least one of the layers leads.

This gives components according to claim 23 or 25.

The method according to the invention is characterized by core and edge layers made of steel materials with different strength and / or hardness properties, namely in particular different martensitic hardenability properties, to combine with each other so that thin-walled components are available be made, which the respective advantages of case hardening and Combine roll cladding.

In detail, the heat treatment according to the invention with respect to the Strength and / or hardness properties of the composite material a strength distribution generated with the generally regarded as particularly advantageous Case hardening history is comparable. In contrast to case hardening occurs with the invention However, there is practically no delay in the process, so that a precise, dimensionally and formally accurate component is made available without dimensional corrections required are. Furthermore, by the flat according to the invention Alloy gradients at the interfaces between the layers form the formation of internal material notches, as used in roll cladding, as mentioned at the beginning, are inevitable avoided. Thanks to the optimized hardness and strength gradient there is no longer any risk that the boundary layers through Yield point exceeded in the joining area, i.e. at the interface, at high Chipping off the load voltage.

The individual layers are preferably made of steel alloys with different martensitic hardenability properties, i.e. different grades formed on carbon, chromium and manganese, the subsequent influencing the strength and / or hardness properties due to martensitic or bainitic Heat treatment takes place, i.e. a heat treatment with the steps of heating-quenching-tempering. Specifically, they consist of their strength and / or Hardness properties of layers of higher alloy, i.e. carbon-rich steel than that not in their strength and / or hardness properties influenceable layers. In the area of the flat alloy gradient becomes a correspondingly flat carbon gradient in this case realized. This transition zone between higher and lower carbon Layers extends with a wall thickness of the components of less than 4 mm over less than 20%, preferably less than 15% of the wall thickness. On in any case, the range of the flat alloy or carbon gradient is wider than 0.1 mm, i.e. more than an order of magnitude wider than the known one Walzplattierverfahren.

Preferably, the strength and / or hardness properties can be influenced Layers the edge layers of the components, which are hard as a surface are and get a hardness curve, which is roughly the case hardening equals. The disadvantage of case hardening is that due to the long residence time A relatively coarse grain structure occurs in the marginal zones, which leads to an increased Micro-crack sensitivity is caused by the layer arrangement according to the invention however avoided. Because of the relatively short dwell times, the Edge layers also have a wear-resistant fine grain structure with high toughness the edge zone, which leads to a particularly low sensitivity to microcracks. Prefers components with a wall thickness can be made using the method according to the invention less than 4 mm. The strength of the wall thickness and / or hardness properties of influenceable layers, i.e. the martensitic hardened layers, a cross-sectional proportion of about 10% to 50%. alternative can also the core layer of the components in their strength and / or hardness properties be influenced, for example hardened, while the outer layers Steel alloys which cannot be influenced in their strength and / or hardness properties or stainless steels.

The layers which can be influenced in their strength and / or hardness properties Materials such as C 55, C 67 or other steels from EN, 100 Cr 6 or X 20 Cr13, X 35 CrMo 17 advantageously form the boundary layers, while the core layers cannot be influenced in their strength and / or hardness properties Materials such as DC 01 or C 10 exist. For certain Applications can be influenced in their strength and / or hardness properties However, layers also form the core layers, for example one Spring steel core made of C 60, C 67 or C 75, while the outer layers made of easily deformable Steels such as C 10 or DC 01, or also made of rust-resistant Steels like X 5 CrNi 1810.

The alloy gradient according to the invention between the surface and core layers can be produced in that for the production of the composite material for the Edge layers Boards made of martensitic hardenable steel parallel and spaced apart be arranged and the core layer between them with molten, low-carbon steel is cast. To train the Surface layers become, for example, cold or surface treated hot strip used with predetermined chemical analysis, especially high carbon content. Due to the molten core material cast in between, the has a lower carbon content, local melting occurs of the boards at the material interfaces, which is due to diffusion processes a flat alloy or carbon gradient, with a depth of about 0.1 - 0.3 mm. These properties are due to the invention Connection by means of a casting process close to the final dimensions.

The boards are preferably at the casting wheels or the casting mold Pouring the molten core material cooled from the outside. This can even with thin blanks, the width of the alloy gradient can be controlled that it is in the range of 0.1 mm and thereby up to 10% of the total cross section is.

It is particularly advantageous that the blanks as strip steel at the edge of the casting gap be fed to a continuously operating casting plant. Alternatively, you can the casting plant can be a continuous casting plant with a fixed continuous mold or for Carrying out a continuous casting and rolling process with the casting gap delimiting rotating rollers (casting wheels). According to the invention the tape that forms the edge layers on both sides along the rollers or copper jaws inserted into the casting gap at the edge of the melt sump. At least on the inside, where the liquid core material is poured in, the Tapes are bare, scale and oxide free due to the appropriate surface treatment as well as roughened if necessary.

To prevent undesirable oxidation of the wall surface by heating To prevent feed in the casting gap, it is advantageous to the incoming Feed steel strip or the blanks under an anti-oxidation cover. This can preferably be a protective gas atmosphere. Such a protective glass bell is generated by supplying inert gases or inert gas mixtures.

As soon as the melt of the core material comes into contact with the strip surface, this is heated to over 950 ° C, so that the diffusion welding Melt with the strip surface a metallic joint with the invention flat alloy gradients. By forming the boundary layers Strip (hot strip) the heat is passed on to the copper rolls or the mold walls released so that the tapes do not melt completely, which is not desirable would. The consequence of this casting compound in the wall thickness area close to the final dimensions is an increase in casting performance because the heat dissipation through the heating of the supplied boundary layers, that is, the casting gap is through the cold material supplied is cooled.

The aforementioned casting is preferably followed by a hot rolling process. Due to the prevailing temperatures of above 950 ° C due to the high surface pressure and deformation ensures that complete welding of the layers safely achieved in the manner desired according to the invention will, even if the metallic joining when the Melt with the belt surface should not have been sufficient. It forms then at the latest a flat material transition gradient between the layers which is in the 0.1 mm range. The surface of the rolling stock receives one Condition poor in rolling scars and scales without flaming or finishing operations.

The composite material is then rolled by hot and / or cold rolling Rolling degree of regularly more than 30% rolled to a thickness of 1 to 5 mm. The final, preferably cold rolling true-to-shape design to the wall thickness of the components, which range up to 4.0 mm, with the surface having the smallest depths of defects and high freedom from pores has what the prerequisite for later use for highly stressed Components, for example machine components. If necessary, the final Shaping multiple cold rolling and intermediate annealing may be required.

Before further processing by bending, punching or the like, the is on Dimensionally rolled composite material preferably a recrystallization or soft annealing subjected to about 730 ° C. In this soft annealed condition is suitable the composite material is good for cold forming, for example of machine components.

Finally, the composite molded material is used to influence its Strength and / or hardness properties subjected to a heat treatment at which results in a martensitic hardening of the hardenable layers. By itself known sequence of process steps heating-quenching-tempering the differently hardenable layers, for example the outer layers, are martensitic hardened, while the lower alloyed areas have lower hardness and keep their toughness.

By partial heat treatment, for example by means of laser or electron radiation, can have a locally limited influence on the strength and / or Hardness properties, that is, hardening take place. Alternatively, an influencing the strength and / or hardness properties take place in the short-term continuous process, preferably in a protective gas oven. This enables a particularly rational Production of functionally optimized strip material and components.

A particularly advantageous application has one according to the aforementioned Process-manufactured, thin-walled steel component with a soft core layer and martensitic hardened surface layers, which consists of a cold-formed, hardened multi-layer composite material, which is carbon-rich, martensitic hardened surface layers and a relatively lower-carbon core layer The carbon gradient between the layers is flat. This component according to the invention is characterized in that it is The hardness curve and distribution of strength come close to a case-hardened steel component. By using a multi-layer composite material from different However, martensitic curable layers can have material properties which cannot be achieved with other hardening processes are. Thanks to the flat transition zone, there is an approximation of the reference stress conditions given to the load voltage profile in cross section. Corresponding there is a more rational production with optimized functional properties, like a pore-free and decarburization-free surface without edge oxidation of the grain boundaries with an austenite grain size finer than 8 according to DIN 50601. Alternatively, the component also boundary layers which cannot be influenced in their strength and / or hardness properties, for example made of stainless steel alloys, and a tempered core layer have, for example made of spring steel.

The wall thickness of the component according to the invention is preferably up to 4.0 mm. The carbon gradient in the transition area extends over approximately 10 up to 30% of the wall thickness, in any case over 0.1 mm.

The materials for the outer and core layers are preferably one on the other matched that the hardness of the core layer at least 30% to 50% of the hardness corresponds to the boundary layers.

The component can consist of two different materials, for example from a low-alloy core layer and high-alloy outer layers. The chemical composition of the outer layers can, however, if necessary also be different, so that a total of at least three layers with different Material properties are present. This allows one more achieve improved functional optimization of the components, such as corrosion protection or fusion weldability.

Furthermore, asymmetrical components can be made in components manufactured according to the invention Realize spring travel or self-adjusting spring travel or forces.

Fig. 1 -

einen Querschnitt durch ein erfindungsgemäßes Bauteil;

Fig. 2 -

eine schematische Darstellung einer Gießanlage zur Herstellung von erfindungsgemäßem Bandmaterial.

Further features and advantages of the present invention will become clear from the following description of preferred exemplary embodiments with reference to the accompanying figures. Show in it

Fig. 1 -

a cross section through an inventive component;

Fig. 2 -

is a schematic representation of a casting plant for the production of strip material according to the invention.

Fig. 1 shows a section through a cold-formed, martensitic surface layer hardened Component 1. This is preferably made of strip material with a total thickness of 5 formed, which is in the range of 0.3 to 4.0 mm.

The component shown consists of steel layer material with several layers. These include in particular a core area B made of low carbon alloy and outer layers A made of carbon-rich, martensitic hardened steel. The Core layer B consists for example of Ck10, DC01, C 10, C 35 or C 53. Die outer edge layers consist, for example, of Ck67, C 55, C 67, or also 102 Cr6, x5 Cr Ni 1810 or the like. The boundary layers A can in turn also consist of steel alloys with different analyzes.

The peculiarity of the component 1 shown is that the layers A, B, A even before cold forming to the final dimension 5 according to the invention Processes have been interconnected so that wide at the layer boundaries Transition zones G have been formed, which are indicated by hatching and in which a flat surface is formed by carbon diffusion between the layer materials Has formed a carbon gradient that is in the range of several 1/10 mm.

The entire component 1 (FIG. 1) is, after which it becomes, for example, a machine component has been cold formed, subjected to a martensitic hardening process Service. As a result, the outer layers A are hardened, while the core B is a relative one maintains great toughness. Thanks to the flat carbon gradient according to the invention G there is a flat voltage curve at the layer boundaries, so that there is no danger chipping of the outer layers A from the core layer B is like this for example in the case of the roll-clad strip according to the prior art is. With martensitic hardening, there is practically no delay in hardness, that is, no undesired hardening Shape and size change on, so that the component 1 before the hardening process can be brought to the final dimension 5 and no rework required is, as is the case with case hardening. By choosing the layer materials however, an advantageous strength and hardness profile is achieved, which is comparable or better with case hardening. The hardening of the outer layers A in the layered material according to the invention can namely with a Short-term heat treatment take place, i.e. with a significantly shorter austenitization time than case hardening. This gives the outer layers A a finer grain size Hardness structure than would be achievable by case hardening. A possible crack progress is therefore not intercrystalline, but transcrystalline, which is a significant improvement in toughness and a corresponding increase in service life brings with it.

Alternatively, the component 1 according to the invention as shown in FIG Core layer B, which is hardened in particular martensitic or bainitic, and relative have not or less tempered outer layers, whereby it consists of a cold-formed, in its strength and / or hardness properties influenceable multilayer composite consists of a carbon-rich, in their strength and / or Core layer B which can be influenced by hardness properties and relatively low-carbon in relation thereto Has boundary layers A, the zone of the carbon gradient G, such as explained above, runs flat between the layers A, B. Here are to Production of spring elements with particularly interesting material combinations a spring steel that can be influenced in its strength and / or hardness properties in the core and low corrosion, for example stainless alloys in the Edge layers A conceivable. This allows, for example, an asymmetrical suspension travel or specify a self-adjusting spring force.

Fig. 2 shows schematically a continuously operating two-roll casting and rolling system. This has two rotating, water-cooled copper rollers 2, which have a casting gap Limit from 1 - 5 mm wide. From above, the melt sump 3 is over Dip tube 4 charged with molten material B. Along the edges of the Casting nip is fed from strip material A from supply coils. With the one in the casting gap encapsulated core material B is there the connection between the as a steel hot band supplied material A and the molten material B instead. Due to the high surface pressure at temperatures above 950 ° C in hot rolling there is definitely an optimal metallic joining.

In the system shown, the heat dissipation via the copper rollers 2 ensures that Steel warmer A through that the carbon gradient G is the steel warmer A does not penetrate too far. In any case, it remains sufficiently thick Boundary layer of the carbon-rich, martensitic hardenable boundary material A is present, around components in the subsequent heat treatment and hardening processes with the hardness curve shown or the strength distribution.

With the system according to the invention shown, steel layer materials can be with extremely different properties in terms of strength and / or hardness properties of the individual layers. The cold-formable composite can be processed particularly well and efficiently to final dimensions. in the Contrary to the known methods, neither occurs during the subsequent hardening to a disadvantageous delay in hardness, there is still the risk of flaking off Surface layers. This is because they have a fine, tough structure, which not to break the component even under high loads or short-term overload leads.

Claims (29)

1. Procedure for the production of thin-walled parts made of steel, which show an inner core layer and outer surface layers, in which the core layer and the surface layers consist of differential steel alloys and are connected together by a casting procedure to a composite material with alloy gradient going flatly at the interfacials and the composite material is deformed to the size of the thin-walled parts and heat treated and wherein the heat treatment results in a martensitic or a bainitic hardening not of all, but at least of one of the layers.
2. Procedure according to claim 1, characterized in that the hardened layer(s) consist of higher alloyed steel than the layers, which are not changed in their strength and/or hardness qualities.
3. Procedure according to one of the claims 1 to 2, characterized in that the core layers and the surface layers include hardened layers and stainless layers.
4. Procedure according to one of the claims 1 to 3, characterized in that the hardened layers form the surface layers.
5. Procedure according to one of the claims 1 to 4, characterized in that the hardened layers own a wear resistant fine grain structure with high toughness and little microcrack sensitivity.
6. Procedure according to one of the claims 1 to 5, characterized in that the hardened layers form the core layers.
7. Procedure according to one of the claims 1 to 6, characterized in that the parts show a wall thickness of less than 4 mm.
8. Procedure according to one of the claims 1 to 7, characterized in that the hardened layers show a quota of the cross section of 10 to 50% of the wall thickness.
9. Procedure according to one of the claims 1 to 8, characterized in that the area of the alloy gradient is broader than 0,1 mm.
10. Procedure according to one of the claims 1 to 9, characterized in that the alloy gradient extends on about 10-25 % of the wall thickness.
11. Procedure according to one of the claims 1 to 10, characterized in that for the production of the composite material for the surface layers blanks made of martensitic or bainitic hardenable steel are arranged parallel by far to each other and the core layer situated in between these is spilled with glaze liquid, carbon poorer steel.
12. Procedure according to claim 11, characterized in that the blanks are cooled from outside.
13. Procedure according to claim 11 or 12, characterized in that the blanks are brought as steel hoops to the edge of the casting gap of a casting plant working continuously.
14. Procedure according to claim 13, characterized in that the rope casting plant has a firm open-ended mould.
15. Procedure according to claim 13, characterized in that the casting plant has cooled rotating rolls limiting the casting gap.
16. Procedure according to one of the claims 1 to 15, characterized in that the deformation of the composite material is carried out by a hot-rolling process.
17. Procedure according to one of the claims 1 to 15, characterized in that the deformation of the composite material is carried out by a cold-rolling process.
18. Procedure according to one of the claims 1 to 17, characterized in that the composite material, which is deformed to the measure of the parts is soft-annealed and afterwards deformed to parts.
19. Procedure according to one of the claims 1 to 18, characterized in that the hardening is carried out by a short-time heat treatment.
20. Procedure according to one of the claims 1 to 29, characterized in that the composite material, which is formed to measure, is treated by a heat treatment for the martensitic or bainitic hardening of the hardened layers.
21. Procedure according to one of the claims 1 to 21, characterized in that a locally determined change is carried out at the hardened layers.
22. Procedure according to one of the claims 1 to 21, characterized in that the martensitic or bainitic hardening of the layers is carried out in a continuous operation.
23. Thin-walled part made of steel, produced according to a procedure according to one or more of the claims 1 to 22, characterized in that it consists of a cold-rolled multilayer composite material, which owns hardened surface layers and a not hardened core layer.
24. Thin-walled part made of steel according to claim 23, characterized in that the martensitic or bainitic hardened surface layers are carbon rich and the core layer is relatively carbon poor, in which the carbon gradient goes flatly between the layers.
25. Thin-walled part made of steel, produced according to a procedure according to one or more of the claims 1 to 22, characterized in that it consists of a cold-rolled multilayer composite material, which owns not hardened surface layers and a hardened core layer.
26. Part according to one of the claims 23 to 25, characterized in that the wall thickness of the part is less than 4 mm.
27. Part according to one of the claims 23 to 26, characterized in that the carbon gradient extends in the region of about 10 to 30% of the wall thickness of the part.
28. Part according to one of the claims 23 to 27, characterized in that the carbon gradient extends about more than 0.1 mm.
29. Part according to one of the claims 23 to 28, characterized in that it owns in the surface zone a wear resistant fine grain structure with high toughness and little microcrack sensitivity.

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