Method for hardening and straightening high alloy tool steels

Abstract

The invention relates to a method for straightening components made of high-alloy, martensitic materials, wherein the straightening is carried out by plastic deformation after hardening and before tempering.

Description

[0001] The invention relates to a method for hardening and straightening high-alloy tool steels, in particular corrosion-resistant steels for long, low-stress components with elevated operating temperatures. State of the art Introduction: High-alloy tool steels

[0002] High-alloy steels are frequently used in a wide variety of tools. They are often divided into five groups: hot-work steels, cold-work steels, high-speed steels, knife steels, and plastic mold steels.

[0003] Hot-work tool steels are typically used at higher temperatures for extrusion, forming, or molding. To withstand the alternating stresses at high temperatures, they are single-phase, free of carbides, and have a high degree of purity in non-metallic inclusions. To achieve a fine structure and minimize the number of inclusions, they are often remelted in a vacuum or under slag. They obtain their high-temperature strength from the alloying elements carbon, chromium, molybdenum, and vanadium. In contrast, cold-work tool steels and high-speed tool steels are usually ledeburitic, meaning they have a high proportion of carbides and are multiphase.

[0004] Cold-work steels are frequently used as punches, mandrels, cutting tools, and press dies. The temperature load is manageable, but their cutting edge retention and edge stability are required. They are alloyed with the same alloying elements as hot-work steels, but have significantly higher carbon and chromium contents to form the required carbides. High-speed steels, on the other hand, are exposed to high thermal stress during machining, such as turning, milling, or drilling. In terms of alloying, the required properties are achieved by adding high levels of special carbide formers such as tungsten, molybdenum, vanadium, and niobium. High cutting edge retention is also necessary for knife steels. Here, the temperature load is less pronounced. Instead, a certain degree of corrosion resistance is usually required, which is achieved by increasing the alloying content of chromium and slightly reducing the carbon content.

[0005] Plastic mold steels are frequently used in plastics processing and have similar property requirements to knife steels, which is why they are alloyed similarly. Both groups include steels with low to high corrosion resistance and with no to high carbide contents. Highly alloyed, corrosion-resistant and wear-resistant plastic mold steels are produced using powder metallurgy.

[0006] High-alloy tool steels are heat treated, and their performance properties are achieved through hardening and tempering.

[0007] Machining is often performed in the annealed state. They are then hardened and immediately tempered to achieve the desired properties. Final machining is performed by hard turning or grinding.

[0008] If the hardness is low after heat treatment—hardening and tempering—the production sequence can also be reversed. Hardening and tempering can be performed before machining. These materials are then referred to as quenched and tempered or pre-quenched. These materials can still be machined well, and no further heat treatment is required at the end of the manufacturing process. Corrosion-resistant ledeburitic tool steels Corrosion-resistant ledeburitic tool steels represent a special group of high-alloy tool steels. As already described, they have two particularly outstanding properties. Firstly, they are corrosion-resistant due to their high chromium content.On the other hand, in addition to chromium, they contain other carbide-forming elements such as vanadium, molybdenum, tungsten, niobium, and titanium. Together with their high carbon content, they form hard phases, primarily carbides, but in some alloys also nitrides, borides, or hybrids such as carbonitrides. After the final heat treatment, they have hardnesses of up to approximately 62 HRC. This high hardness, together with the hard phases, enables these steels to exhibit high wear resistance, cutting edge retention, edge stability, etc.

[0009] Due to their high hardness combined with their high carbides content, ledeburitic tool steels also have a significant disadvantage. These steels have low toughness and are relatively brittle. Due to their brittleness, impact toughness is measured on unnotched specimens rather than notched ones. But even with unnotched specimens, they only have toughness values ​​of around 10 joules to 70 joules. In tensile tests, plastic strain is around 1% to 3%. Some highly alloyed steels are even lower. This low toughness and plastic strain must be taken into account during production and application to prevent unwanted fractures and total failure of the components.

[0010] Corrosion-resistant ledeburitic tool steels are often divided into two steel groups: Knife steels and the workpieces made from them have high demands on wear resistance and edge retention, as well as certain requirements on corrosion resistance. Chromium contents of approximately 15 to 18% are typical for these steels. A large portion of this chromium content remains dissolved in the iron matrix after the final heat treatment through hardening and tempering. This makes it reactive and can react with the oxygen in the air on the workpiece surface. The resulting chromium oxide then forms a dense surface layer with a thickness of a few nanometers, which prevents further chemical reactions and thus corrosion.

[0011] Knife steels include both non-ledeburitic and some ledeburitic steels. At a carbon content of approximately 0.4% to 0.6%, the solubility limit is reached in the individual steels due to interaction with the respective carbide-forming alloying elements, which is why the first carbides form during solidification of the melt.

[0012] Ledeburitic knife steels include, among others, the steels X90CrMoV18, X105CrMo17, X105CrCoMo18-2, etc.

[0013] Through the powder metallurgical steel production route, there are also some ledeburitic plastic mold steels which, similar to knife steels, have a corrosion resistance tailored to the application.

[0014] In powder metallurgical steel production, the alloyed steel melt is first atomized into metal powder before being pressed into a dense block by hot isostatic pressing (HIPPing). Only then does it undergo forging or rolling.

[0015] Compared to knife steels, ledeburitic plastic mold steels have a significantly higher carbide content, made possible by the manufacturing process. Some important powder metallurgical plastic mold steels are ~X190CrVMo20-4, ~X270CrVMoW20-7, -X260CrVMo26-4, ~X230CrVMo14-9, ~X170CrVMo18-3, etc. Annealing

[0016] After forming, the steel bars of the various alloys are peeled and annealed at the steel manufacturer. During annealing, annealed carbides precipitate in the steel matrix. The matrix becomes depleted of alloying elements and becomes ferritic. In addition to the primary carbides formed during solidification and elongated by forming, ranging in size from a few micrometers to approximately 50 µm, the steel also contains annealed carbides with a size of approximately 100 nm to 500 nm. Depending on the alloy, the annealed steels have a hardness of approximately 250 HB to 300 HB.

[0017] This makes them soft enough to be machined to a near-net-shape shape by the processor through mechanical machining processes such as turning, milling, whirling, drilling, and grinding. To minimize residual stresses, machining involves rough roughing with high material removal and finishing with low material removal. Once the final dimensions of the workpiece are almost reached, the final heat treatment, consisting of stress relieving, hardening, and tempering, takes place. The temperatures for hardening and tempering are adapted to the required properties of the workpiece in use. Hardening and tempering

[0018] High-alloy, corrosion-resistant tool steels are hardened at temperatures above 1000°C. If hardening and tempering are not performed by the tool manufacturer itself but by contracting, the following hardening temperatures are typically available for hardening at contract hardening shops: 1030°C, 1070°C, and 1180°C. These temperatures are considered a compromise between the achievable properties and cost-effective hardening by keeping the furnaces as full as possible.

[0019] In order to keep thermal stresses and distortion caused by large temperature differences between the inside and outside to a minimum during heating, various holding temperatures are used during hardening to allow temperature equalization. During heating, the structure of the matrix also transforms from ferrite to austenite. During holding at hardening temperature, the annealing carbides formed during annealing go back into solution and the matrix becomes enriched with alloying elements again. After holding, the material is cooled quickly to keep the alloying elements in solution and prevent annealing carbides from forming again, and to prevent the austenite from transforming into ferrite, pearlite or bainite. However, some metallurgical processes can take place that can impair the properties of the steel, such as pro-eutectoid carbide precipitation, the formation of grain boundary martensite or unwanted carbide precipitation in the interior of the grain. At approx.The desired formation of martensite begins at temperatures between 300°C and 200°C, depending on the alloying layer. In high-alloy steels, martensite formation is not yet complete at room temperature, and large amounts of residual austenite are still present. In the microstructure, the austenite usually has a square or angular shape. Accumulations of residual austenite are often found in the area around the primary carbides, where higher alloy contents are found due to diffusion.

[0020] For environmental reasons, hardening was switched from salt baths to vacuum furnaces. The vacuum furnace offers the following additional advantages over other technologies: bright surface of the components, low distortion with adjusted flow conditions, high reproducibility of the hardening result, automation of the hardening cycle, flexible, adaptable production, and high cooling rates thanks to multi-chamber systems, strong circulation, and high gas pressure. Tempering takes place immediately after hardening and when temperatures below approximately 60°C are reached to prevent stabilization of the residual austenite and the associated embrittlement of the workpieces (state of the art in heat treatment). The residual austenite must be completely transformed to avoid subsequent dimensional changes.Tempering is carried out several times at temperatures in the range of the secondary hardness maximum – slightly above for maximum toughness, slightly below or well below to achieve high corrosion resistance, and exactly in the range of the maximum for the highest possible hardness. When held at tempering temperature, the martensite relaxes and forms secondary hardness carbides. These can occur in various morphologies. Most often, regularly distributed globular particles with a diameter of 3 to 10 nm form. In other areas, they have an elongated appearance with a thickness of 2 nm to 3 nm. Their quantity correlates with the number of dissolved alloying elements. Even at the highest resolution in electron microscopes, no interfaces can be identified between the secondary hardness carbides and the surrounding matrix. The carbides are therefore completely coherent, whereas the primary carbides are incoherent and exhibit a clear interface.During cooling after holding at tempering temperature, a further large portion of the retained austenite can transform into martensite. After two or three tempering cycles, the retained austenite disappears.

[0021] After heat treatment, a high-alloy ledeburitic tool steel has a microstructure with a matrix of tempered, tough martensite, incoherent primary carbides in the µm range, and coherent secondary hardening carbides in the nm range. The steels then typically have a hardness in the range of approximately 60 HRC.

[0022] Once hardening and tempering are complete, the workpieces are finished by grinding and polishing. Dimensional change and distortion

[0023] Another important issue during hardening is dimensional change and distortion. Conventionally produced tool steels exhibit pronounced anisotropy of dimensional change during hardening due to the longitudinal arrangement of the carbides in the rolling direction during hot forming. Powder metallurgical steels have a more homogeneous distribution of carbides and are therefore nearly isotropic in their dimensional change.

[0024] Pre-processing through mechanical removal, the machining strategy—how many roughing and finishing operations are performed—and the number and timing of stress relief annealing operations all play a role. Even the initial condition of the steel bar soft-annealed at the steel manufacturer—what was its temperature-time profile, how was the furnace charged—influences the distortion behavior.

[0025] Furthermore, when heated for hardening, the matrix of annealed steels is ferritic and only transforms into austenite at higher temperatures above around 700°C. Upon cooling, the matrix then becomes austenitic. While ferrite has a thermal expansion coefficient of approximately 12µm / mK, the expansion coefficient of austenite is significantly higher at around 17µm / mK. Carbides have significantly lower expansion coefficients of approximately 5 to 6µm / mK. The expansion coefficients vary depending on the alloy and the alloy content or the composition of the carbides. At hardening temperature, the structural stresses are greatly reduced due to the high mobility of the atoms. Quenching after holding at hardening temperature then leads to high internal structural stresses due to the different expansion coefficients. The carbides exhibit high compressive stresses.The iron matrix, especially in the area of ​​large elongated carbides, has high tensile stresses and is prone to plastic deformation.

[0026] When producing abrasive tools such as milling cutters, drills, knives, etc., high dimensional accuracy is essential for long service life. This is often achieved by taking appropriate measurements before hardening and tempering, and then final grinding to achieve the exact required dimensions. Straightening long components

[0027] For long components, such as plasticizing screws, long knives, broaches, etc., deflection is also a major issue. Due to the high dimensional deviations, a simple allowance of a few tenths of a millimeter is usually not sufficient to ensure dimensional accuracy during final machining. Complex process steps—so-called straightening—are necessary to straighten the long, thin workpieces. However, these also introduce new stresses into the workpieces.

[0028] Various technologies are available for straightening and are widely used in the industry. However, all have their advantages and disadvantages.

[0029] In the soft-annealed state, when the steel parts can still be machined, they still have a high plastic formability of 5 to 10% or more. Therefore, they can still be easily straightened by mechanical deformation, usually using two support points and a punch.

[0030] Mechanical straightening introduces a great deal of stress into a steel bar. Therefore, the straightening process is often combined with stress relief annealing. Annealing largely relieves the stresses in the steel bar, but it also causes the bar to bend again. Approximately 50% of the straightness deviation can be reduced in the stress-relieved, annealed state per combination of straightening and stress relief annealing. Since a straight bar is required for further mechanical processing, further straightening is necessary.

[0031] If the machined bar is already near its net shape and goes to the final heat treatment—hardening and tempering—it becomes even more difficult to obtain a straight workpiece. Several processes are used here.

[0032] After hardening at approximately 200°C, the workpiece can be removed from the furnace and clamped in a hydraulic press to prevent any deviation in straightness. Plastic deformation does not occur; the steel is only elastically bent. High-alloy ledeburitic materials have very low martensite transformation temperatures. Upon cooling from 200°C to room temperature, martensite formation continues. Due to the prestressed state, the martensite laths arrange themselves in such a way that stress is reduced, making the parts straighter at room temperature than without this straightening step.

[0033] Another technology is "notch straightening." After hardening and tempering, local plastic deformations are introduced into the workpiece. A small punch is preferably used for this, which impacts the workpiece surface at high speed. It is important to set the correct geometry at the punch tip. If the tip is too blunt, the punch impact will have no effect. If the tip is too sharp, the punch penetrates deeply into the workpiece, making it difficult to restore an intact, smooth surface. The numerous small plastic deformations collectively cause the components to straighten.

[0034] Local plastic deformation can also be induced by the flame of an acetylene torch. The component is locally heated with the flame for so long that it becomes extremely hot. The resulting thermal expansion then causes a slight deformation of the workpiece. The technology is very complex.

[0035] In some cases, up to 60 flame straightening points must be created before the required straightness is achieved. Furthermore, local material damage occurs because the high temperatures change the heat treatment condition of the material. At temperatures above the tempering temperature, the steel initially loses its high hardness and becomes soft. When hardening temperatures are reached, re-hardening occurs. A hard, coin-sized point is then surrounded by a soft ring. With frequent load changes, such as in fast-running machines with cycle times of just a few seconds, cracks can form and grow, and the steel parts can break off. With a low number of load cycles and low stress, this damage caused by flame straightening is not significant.

[0036] Long components: Use at high temperatures Components that experience higher temperatures during use are particularly critical, as the stresses introduced by straightening steps after tempering can cause the components to bend again and therefore have a shorter service life.

[0037] Plasticizing screws, for example, convey plastic into a plasticizing cylinder and melt it at temperatures ranging from 220°C to 350°C (rarely 450°C). They have a length-to-diameter ratio of approximately 30 and a diameter clearance of a few tenths of a millimeter relative to the surrounding cylinder. Within this, they perform a rotating motion during metering – generating the plastic melt – and a linear motion under massive pressure of up to 2400 bar when injecting the plastic melt into the mold. Excessive stresses caused by straightening are critical here and can lead to reduced service life.

[0038] In the finished heat-treated state, further stress relief annealing at the usual temperatures of 550°C to 650°C is no longer possible, as even at temperatures above the tempering temperature, the favorable properties achieved would be lost. Therefore, stress relief and minimal distortion must be ensured throughout the entire workpiece manufacturing process – turning, milling, whirling, rough grinding, straightening, stress relief annealing, hardening, tempering, straightening, and finishing. Stresses and distortion cannot be avoided by these measures; they can only be minimized.

[0039] Summary of the state of the art The tool steels are mechanically machined in the annealed state (turning, milling, grinding, polishing). The straightening ("straightening") of the parts in the annealed state is also performed mechanically. A trestle is placed at two positions, and a hammer is applied to the center of the worms until they are straight. During the subsequent stress-relieving annealing, they then bend back to approximately half their previous arc. After mechanical shaping (turning, milling, etc.) of the workpieces, the desired material properties are achieved through hardening and tempering. In hardening practice, it is state of the art to temper as soon as possible after hardening to prevent residual austenite stabilization and a significant deterioration in toughness. Furthermore, ledeburitic materials are generally very brittle in the merely hardened state and prone to fracture.For use as screws, the long and thin workpieces, with a length-to-diameter ratio of approximately 30, must be straightened, as they rotate within the surrounding mass cylinder, and there is a diameter gap of a few tenths of a millimeter between the two components. In this state, mechanical straightening is no longer possible due to brittleness. To straighten the screws, one of the methods used to straighten them was to heat them locally with an acetylene torch. The thermal expansion caused a sufficient local change in length to straighten the screws. This so-called "flame straightening" is a laborious manual process and leads to local material damage to the already hardened and tempered parts.

[0040] DE 699 14 433 T2 describes a hardening method and a hardening device for a longitudinal section of a deformed, rod-shaped workpiece, wherein the workpiece is clamped in a pressure device during heating and quenching. Object of the invention

[0041] A straightening process ("straightening") for long components, such as screws, without local damage must be developed.

[0042] (In addition, the straightening should be able to be done automatically, mechanically on an automatic straightening machine.)

[0043] The straightening process must be carried out in such a way that the screws are straight and at the same time as stress-free as possible, so that they do not bend again due to excessive stress at the increased temperatures in the injection molding process and thus wear out.

[0044] To solve the problem, a method according to claim 1 is proposed in particular.

[0045] In one embodiment, a method is provided for straightening a component made of a high-alloy steel which has a real profile in its longitudinal direction which deviates from the desired profile of the component in the form of a bend, wherein the component is provided with a bent profile by mechanical bending before carrying out a heat treatment in the form of an annealing step, which bent profile is opposite to the original real profile, wherein subsequently during the heat treatment, with the reduction of stresses in the component, a new profile is established which is closer to the desired profile than the original real profile and the bent profile.

[0046] It is preferred that the heat treatment is the last heat treatment step that the component undergoes before its completion.

[0047] It is preferred that the component is pre-bent at an angle of 180° against the direction of the deviation of the original real course.

[0048] It is preferred that the bending is carried out to such an extent that the deviation of the bent course from the desired course is in the range of 30 to 100% of the deviation of the original real course from the desired course.

[0049] It is preferred that the bending is carried out to such an extent that the deviation of the bent course from the desired course is in the range of 50 to 80% of the deviation of the original real course from the desired course.

[0050] It is preferred that the deviation of the curved course over the entire longitudinal extent of the component is a mirror image of the original deviation of the original real course from the target course, to an extent of 30% to 100% of the original deviation.

[0051] It is preferred that the deviation of the curved course over the entire longitudinal extent of the component is a mirror image of the original deviation of the original real course from the target course, to an extent of 50% to 80% of the original deviation.

[0052] It is preferred that the bending to the curved shape takes place after hardening and before tempering, wherein the tempering process is or includes the heat treatment in the form of an annealing step and the component is stress-free and straight after the tempering process.

[0053] In one variant, the component is made of a martensitic tool steel. In another variant, the component is made of a ledeburitic tool steel. In another variant, the component is made of a corrosion-resistant, martensitic steel. In another variant, the component is made of a corrosion-resistant, ledeburitic tool steel.

[0054] It is preferred that the component is made of one of the steels X105CrMo17, X105CrCoMo18-2, -X190CrVMo20-4 or ~X270CrVMoW20-7.

[0055] It is preferred that the component be a plasticizing screw. The first step to improving the existing straightening process is to pre-bend the long rods. A value of approximately 50% is a good starting point for pre-bending. This means that with a bend of approximately one millimeter, they are pre-bent to a negative bend of approximately 0.5 mm – half the straightness deviation.

[0056] In reality, a higher value often proves even more advantageous. Pre-bending, ideally mirroring the straightness deviation (not just the maximum runout, but the entire length), to 50 to 80% (rarely 100%) of the initial value is desirable. The component's history, production route, and geometry also influence the optimal value. It should be determined empirically in series production. The long components then go into the furnace for stress relief annealing. With optimal pre-bending, they emerge from the annealing furnace almost straight.

[0057] The components are thus made stress-relieved and straight by over-pressing the bars and subsequent stress relieving.

[0058] Corrosion-resistant steels exhibit exceptional properties after hardening, particularly their toughness. Tensile tests reveal a low yield strength of around 700 MPa and a plastic deformability of around 1% to 2%, in contrast to ledeburitic cold-work steels or high-speed steels, which exhibit no or only minimal plastic formability. This is due to altered behavior of the retained austenite and significantly reduced brittleness of the freshly formed martensite due to the high chromium content. The high chromium content allows dislocations to slip more easily. Furthermore, chromium also reduces the stabilization of the retained austenite. Measurements show that even if a week elapses between hardening and tempering, no decrease in impact toughness or plastic elongation can be observed in the tensile test.

[0059] This behavior can be exploited to implement pre-bending during the hardening and tempering cycle. The hardening / tempering cycle is interrupted, and the long workpieces are plastically deformed at room temperature after hardening by mechanical pre-bending, reducing a straightness deviation from 100% to 50% or more in the opposite direction.

[0060] The subsequent tempering process has the same effect as stress relief. It can be used to straighten the component again from the remaining or introduced stresses. In addition, tempering has the effect of stress reduction due to the associated microstructural transformations described above. Thus, after the complete heat treatment, the components are straight and stress-free or low-stress.

[0061] The invention is illustrated by figures. Fig. 1 schematically illustrates a screw bent due to stress. Fig. 2 schematically illustrates the deflection of a long component after heat treatment. Fig. 3 schematically illustrates mechanical straightening on a hydraulic press: two support points, one punch. Fig. 4 schematically illustrates pre-bending of the straightness deviation to 50% in the opposite direction (180° from the initial straightness deviation). Fig. 5 illustrates a comparison of tensile specimens in the hardened state of a ledeburitic cold-work tool steel (little or only low plastic deformability) and a corrosion-resistant, ledeburitic tool steel (low yield strength and 1% to 2% plastic deformability). Microstructure in each case: martensite, retained austenite, primary carbides.

[0062] Fig. 1illustrates a long, thin component in the form of a plasticizing screw 1, which exhibits a bend. The object of the invention is to provide a straightening process for the component, in particular the plasticizing screw 1, so that it becomes straight and, at the same time, as stress-free as possible.

[0063] Fig. 2 illustrates the problem or the initial state of the component before the application of the procedure in question.

[0064] The component has an actual profile 2 that deviates from the target profile 3. The deviation is perpendicular to the longitudinal direction or the length of the component.

[0065] The maximum deviation 4 is usually in the middle area of ​​the component, but in the case of screws, due to their geometry, it is often also to the side.

[0066] Fig. 3illustrates a mechanical device for adjusting the actual profile 2 of the component to the desired profile 3. For this purpose, two support points are provided at the ends of the component and a stamp in the central area of ​​the component.

[0067] Fig. 4 illustrates the straightening of the component in the method according to the invention.

[0068] Straightening is carried out by mechanical bending prior to an annealing step. This is carried out using a bending device which is known in the art and which is Fig. 3 explained principle can work.

[0069] As illustrated, the component has a real curve 2 before bending, which deviates from the target curve 3.

[0070] The maximum deviation 4, which usually occurs approximately in the middle of the component, represents the basis for determining the bending of the component and is specified as 100%.

[0071] The bending then takes place against the maximum deviation 4. This means that the component is bent in the opposite direction to the original real profile 2, mirroring the original real profile 2, until a new profile in the form of the curved profile 5 results. The curved profile 5 preferably also has a maximum 6 at the location of the original maximum deviation 4. The maximum 6 is preferably between 30 and 100%, in particular 50 to 80%, of the original maximum deviation 4, for example 50% as shown. The curved profile 5 preferably has a deviation at every point in the longitudinal direction which corresponds to the range of 30 to 100%, in particular 50 to 80%, of the deviation of the original real profile 2 at the same point. The ratio between the original deviation of the original real profile 2 and the deviation of the curved profile 5 is preferably at least approximately constant over the longitudinal direction of the component.

[0072] When the desired curved profile 5 is achieved, the component is removed from the bending device and subjected to heat treatment in the form of an annealing step.

[0073] During the annealing step, the component preferably undergoes heat treatment in the temperature range of 600°C to 800°C for a duration of 1 to 5 hours. In one variant, bending occurs between hardening and tempering. The temperatures of the annealing step must be reduced to the tempering temperatures, otherwise the required performance properties, especially the high hardness, would be lost. The annealing step then takes place at temperatures of 250°C to 600°C for a duration of 1 to 4 hours. Since this involves significant structural changes due to an unstable initial state before tempering, even the lower temperatures are sufficient for a stress-relieving effect.

[0074] Due to the heat treatment, the component deforms from the curved profile 5 back towards the original real profile 2, so that a further profile is obtained which is at least closer to the target profile 3 than the other two profiles 2, 5.

[0075] A suitable extent of the deviation of the curved course 5 in relation to the deviation of the real course 2 depends, among other things, on the material of the component and its geometry, so that this can best be determined by experiment within the above-mentioned limits.

[0076] In one embodiment, the maximum deviation 4 of the component is measured and the measured value is multiplied by a factor in the range of 0.3 to 1 to determine the required maximum 6 of the bent profile. The punch of a bending device can then be moved according to the determined maximum.

[0077] Fig. 5illustrates a comparison of tensile specimens in the hardened state only of a ledeburitic cold work tool steel 7 (little or only low plastic formability) and a corrosion-resistant, ledeburitic tool steel 8 (low yield strength and 1% to 2% plastic formability). The microstructure in each case includes martensite, retained austenite and primary carbides.

Claims

1. Process for straightening components made of high-alloy, martensitic materials, characterized in that straightening by plastic deformation takes place after hardening and before tempering.

2. Method according to claim 1, characterized in that the martensitic materials have a low yield strength.

3. Method according to claim 1, characterized in that the martensitic materials have a yield strength below 1500 MPa.

4. Method according to claim 1, characterized in that the martensitic materials have a yield strength below 1000 MPa.

5. Method according to one of claims 1 to 4, characterized in that the components are long and thin and the straightening of the long, thin components is done by bending.

6. Method according to one of claims 1 to 5, characterized in that the components are stress-free or at least low in stress due to tempering after straightening and mechanical, plastic bending after the tempering process.

7. Method according to one of claims 1 to 6, characterized in that the components are made of a corrosion-resistant, martensitic tool steel.

8. Method according to one of claims 1 to 7, characterized in that the components are made of a corrosion-resistant, ledeburitic tool steel.

9. Method according to one of claims 1 to 8, characterized in that the long, thin components are pre-bent during straightening after hardening so that they are straight and stress-free or at least low-stress after tempering.

10. Method according to claim 9, characterized in that the deviation of the curved course (5) over the entire longitudinal extent of the component is mirror-symmetrical to the original deviation of the original real course (2) from the desired course (3), namely to an extent of 30% to 100% of the original deviation.

11. Method according to one of claims 1 to 10, characterized in thatthe component is made of one of the steels X35CrMoV15, X50CrNoV15, X39CrMo17, X60CrMo17, X80CrMo18, X90CrMo17, X105CrMo17, X105CrCoMo18-2, -X190CrVMo20-4 or ~X270CrVMoW20-7 or similar.

12. Method according to one of claims 1 to 11, characterized in that the component is made of one of the steels X90CrMo17, X105CrMo17, X105CrCoMo18-2, -X190CrVMo20-4 or ~X270CrVMoW20-7 or similar.

13. Method according to one of claims 1 to 12, characterized in that the component is a plasticizing screw (1).

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