Method for hardening and straightening high alloy tool steels

Abstract

The invention relates to a method for straightening a component made of a high-alloy steel which has a real profile (2) in its longitudinal direction which deviates from the desired profile (3) of the component in the form of a bend, wherein the component is provided with a bent profile (5) by mechanical bending before carrying out a heat treatment in the form of an annealing step, which bent profile (5) is opposite to the original real profile (2), wherein subsequently, during the heat treatment, a new profile is established in the component as stresses are relieved, which is closer to the desired profile (3) than the original real profile (2) and the bent profile (5).

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 for a wide variety of tools. They are often classified into five groups: hot-work steels, cold-work steels, high-speed steels, knife steels, and plastic mold steels.

[0003] Hot-work steels are mostly used at higher temperatures for extrusion, forming, or other processes. To withstand the alternating stresses at these high temperatures, they are single-phase, carbide-free, and have a high degree of purity of non-metallic inclusions. For microstructure fineness and a low number of inclusions, they are often remelted under vacuum or slag. Their high-temperature strength is achieved through the alloying elements carbon, chromium, molybdenum, and vanadium.

[0004] In contrast, cold work steels and high-speed steels are mostly ledeburitic, meaning they have a high proportion of carbides and are multiphase.

[0005] Cold work steels are frequently used for punches, mandrels, cutting tools, and dies. Their temperature resistance is manageable, but their edge retention and stability are crucial. They are alloyed with the same elements as hot work steels but have significantly higher carbon and chromium contents to form the necessary carbides. High-speed steels, on the other hand, are subjected to high thermal stress during machining operations such as turning, milling, or drilling. The required properties are achieved by adding high concentrations of the special carbide formers tungsten, molybdenum, vanadium, and niobium. High edge retention is also essential for knife steels. Here, the temperature stress is not as pronounced. Instead, a certain degree of corrosion resistance is usually required, which is achieved through increased chromium content and a slightly reduced carbon content.

[0006] Plastic mold steels are frequently used in plastics processing and have similar property requirements to knife steels, which is why they are similarly alloyed. Both groups include steels with low to high corrosion resistance and with varying carbide content. Highly alloyed, corrosion-resistant, and wear-resistant plastic mold steels are produced using powder metallurgy.

[0007] What all high-alloy tool steels have in common is their heat treatment. Hardening and tempering give them their performance properties.

[0008] Machining is often performed on the soft-annealed workpieces. They are then hardened and immediately tempered to achieve the desired properties. Final machining is carried out by hard turning or grinding.

[0009] If the hardness is low after heat treatment – ​​hardening and tempering – the manufacturing sequence can be reversed. Hardening and tempering can be performed before machining. These are then referred to as tempered or pre-tempered materials. These can still be machined effectively, and no further heat treatment is required at the end of the manufacturing process. Corrosion-resistant ledeburitic tool steels represent a special group of high-alloy tool steels. As already described, they have two particularly outstanding properties. On the one hand, they are corrosion-resistant due to their high chromium content.On the other hand, in addition to chromium, they contain other carbide formers such as vanadium, molybdenum, tungsten, niobium, and titanium, and thus, with their high carbon content, form hard phases, primarily carbides, but in some alloys also nitrides, borides, or mixtures thereof such as carbonitrides. After final heat treatment, they achieve hardnesses of up to approximately 62 HRC. This high hardness, together with the hard phases, enables the high wear resistance, edge retention, edge stability, etc., of these steels.

[0010] Due to their high hardness combined with their high carbide content, ledeburitic tool steels also have a significant disadvantage: low toughness and relatively brittleness. Because of this brittleness, impact toughness is measured on unnotched specimens, not notched ones. However, even unnotched specimens only exhibit toughness values ​​of approximately 10 to 70 joules. In tensile tests, plastic elongation is around 1% to 3%. Some high-alloy steels exhibit even lower values. During manufacturing and application, these low toughness and plastic elongation must be taken into account to prevent unwanted fractures and total component failure.

[0011] Corrosion-resistant ledeburitic tool steels are often divided into two groups: knife steels and the workpieces made from them have high demands on wear resistance and edge retention, as well as certain requirements for corrosion resistance. Chromium contents of 15 to 18% are typical for these steels. A large portion of this chromium remains dissolved in the iron matrix after the final heat treatment through hardening and tempering. This makes it reactive, allowing it to react with oxygen from the air on the workpiece surface. The resulting chromium oxide then forms a dense surface layer just a few nanometers thick, which prevents further chemical reactions and thus corrosion.

[0012] 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 interaction with the respective carbide-forming alloying elements in the individual steels, which is why the first carbides form as soon as the melt solidifies.

[0013] Ledeburitic knife steels include, among others, the steels X90CrMoV18, X105CrMo17, X105CrCoMo18-2, etc.

[0014] The powder metallurgy steelmaking route also offers some ledeburitic plastic mold steels which, similar to knife steels, exhibit corrosion resistance tailored to the application.

[0015] In powder metallurgy steel production, the alloyed steel melt is first atomized into metal powder before the steel is pressed back into a dense block by hot isostatic pressing (HIPPing). Only then does the forming process take place, such as forging or rolling.

[0016] Compared to knife steels, ledeburitic plastic mold steels have a significantly higher carbide content, made possible by the manufacturing process. Some important powder metallurgy plastic mold steels are ~X190CrVMo20-4, ~X270CrVMoW20-7, ~X260CrVMo26-4, ~X230CrVMo14-9, ~X170CrVMo18-3, etc. Soft annealing

[0017] After forming, the steel bars of the various alloys are peeled and annealed at the steel manufacturer. During annealing, annealed carbides precipitate from the steel matrix. The matrix becomes depleted of alloying elements and ferritic. In addition to the primary carbides, formed during solidification and elongated by forming, which range 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.

[0018] This makes them soft enough to be machined into near-net-shape using mechanical processes such as turning, milling, whirling, drilling, and grinding. To minimize residual stresses, machining is performed using a roughing operation with significant material removal followed by a finishing operation with minimal material removal. Once the workpiece is nearly at its final dimensions, it undergoes a final heat treatment consisting of stress-relief annealing, hardening, and tempering. The hardening and tempering temperatures are adjusted to meet the required properties of the workpiece in its intended application. Hardening and tempering

[0019] High-alloy, corrosion-resistant tool steels are hardened at temperatures above 1000°C. If the hardening and tempering are not carried out by the tool manufacturer but outsourced, the following hardening temperatures are typically available at contract hardening shops: 1030°C, 1070°C, and 1180°C. These temperatures represent a compromise between the achievable properties and cost-effective hardening through the highest possible furnace capacity.

[0020] To minimize thermal stresses and distortion caused by large temperature differences between the interior and exterior during heating, various holding temperatures are used during the hardening process to allow for temperature equalization. During heating, the matrix structure also transforms from ferrite to austenite. While holding at the hardening temperature, the annealing carbides formed during soft annealing dissolve again, and the matrix is ​​re-enriched with alloying elements. After holding, rapid cooling is performed to keep the alloying elements in solution and prevent the re-formation of annealing carbides, as well as to prevent the austenite from transforming into ferrite, pearlite, or bainite. Nevertheless, some metallurgical processes can occur that can impair the properties of the steels, such as pre-eutectoid carbide precipitation, the formation of grain boundary martensite, or unwanted carbide precipitates within the grains. At approximately...The desired formation of martensite begins between 200°C and 300°C, depending on the alloy composition. In high-alloy steels, martensite formation is not yet complete at room temperature, and significant amounts of retained austenite are still present. In the microstructure, the austenite usually exhibits an angular or angular shape. Accumulations of retained austenite are frequently found in the region around the primary carbides, as higher alloy contents are present there due to diffusion.

[0021] For environmental reasons, salt bath hardening was switched to vacuum furnaces. The vacuum furnace offers several additional advantages over other technologies: a bright surface finish on the components, minimal distortion under optimized flow conditions, high reproducibility of the hardening result, automation of the hardening cycle, flexible and adaptable manufacturing, and high cooling rates thanks to multi-chamber systems, strong circulation, and high gas pressure. Immediately after hardening and once temperatures drop below approximately 60°C, tempering takes place to prevent the stabilization of the retained austenite and the associated embrittlement of the workpieces (state of the art in heat treatment). The retained austenite must be completely transformed to prevent subsequent dimensional changes.Tempering is performed several times at temperatures near the secondary hardening maximum – slightly above for maximum toughness, slightly below or far below for high corrosion resistance, and precisely at the maximum for the highest possible hardness. When held at tempering temperature, the martensite expands and forms secondary hardening carbides. These can form in various morphologies. Most commonly, they are regularly distributed globular particles with a diameter of 3 to 10 nm. In other cases, they have an elongated appearance with a thickness of 2 to 3 nm. Their quantity correlates with the number of dissolved alloying elements. Even at the highest resolution in electron microscopes, no interfaces between the secondary hardening carbides and the surrounding matrix can be discerned. The carbides are therefore completely coherent, whereas the primary carbides are incoherent and exhibit a distinct interface.Upon cooling after being held 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.

[0022] After heat treatment, a high-alloy ledeburitic tool steel has a microstructure with a matrix of tempered, tough martensite, incoherent primary carbides in the micrometer range, and coherent secondary hardening carbides in the nanometer range. These steels typically have a hardness of approximately 60 HRC.

[0023] Once the hardening and tempering processes are complete, the workpieces are finished by grinding and polishing. Dimensional changes and delays

[0024] Another important aspect of hardening is dimensional change and distortion. Conventionally manufactured tool steels exhibit pronounced anisotropy in dimensional change during hardening due to the longitudinal arrangement of carbides in the rolling direction during hot forming. Powder metallurgy steels have a more homogeneous distribution of carbides and are therefore nearly isotropic in their dimensional change.

[0025] Pre-processing through mechanical material removal, the machining strategy – how many roughing and finishing operations are performed – and the number and timing of stress-relief annealing processes all play a role. Even the initial condition of the steel bar annealed at the steel manufacturer – its temperature-time profile and furnace charge – influences the distortion behavior.

[0026] Furthermore, during heating for hardening, the matrix of soft-annealed steels is ferritic and only transforms into austenite at higher temperatures above approximately 700°C. Upon cooling, the matrix is ​​then austenitic. While ferrite has a coefficient of thermal expansion of approximately 12 µm / mK, the coefficient of expansion of austenite is significantly higher, at around 17 µm / mK. Carbides have considerably lower coefficients of expansion, ranging from approximately 5 to 6 µm / mK. These coefficients of expansion vary depending on the alloy and its alloy content, or the composition of the carbides. At hardening temperature, the high mobility of the atoms significantly reduces the microstructural stresses. However, quenching after holding at hardening temperature results in high internal stresses due to the differing coefficients of expansion. Carbides exhibit high compressive stresses.The iron matrix, especially in the area of ​​large longitudinally elongated carbides, has high tensile stresses and is prone to plastic deformation.

[0027] When manufacturing cutting tools such as milling cutters, drills, knives, etc., high dimensional accuracy is essential for a long tool life. This is often achieved by adding a corresponding allowance before hardening and tempering, and then finishing with grinding to achieve the exact required dimensions. Straightening long components

[0028] For long components, such as plasticizing screws, long knives, broaching tools, etc., deflection is also a major concern. Due to the significant dimensional deviations, a simple allowance of a few tenths of a millimeter is usually insufficient to achieve the required dimensional accuracy during final machining. Complex process steps—known as straightening—are necessary to straighten these long, thin workpieces. However, these steps also introduce new stresses into the workpieces.

[0029] Various technologies are available for straightening and are widely used in industry. However, they all have their advantages and disadvantages.

[0030] In the soft-annealed state, when the steel parts can still be machined, they also retain a high plastic deformability of 5 to 10% or more. Therefore, they can still be straightened effectively by mechanical deformation, usually using two support points and a punch.

[0031] Mechanical straightening introduces many stresses into a steel bar. Therefore, the straightening process is often combined with stress-relief annealing. Annealing largely eliminates 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 with each combination of straightening and stress-relief annealing. Since a straight bar is necessary for further machining, a second straightening process is required.

[0032] If the machined bar is already close to its final contour before undergoing final heat treatment – ​​hardening and tempering – obtaining a straight workpiece again becomes significantly more complex. Several processes are employed here.

[0033] After hardening at approximately 200°C, the workpiece can be removed from the hardening furnace and clamped in a hydraulic press so that it is pre-stressed to counteract any straightness deviations. No plastic deformation occurs; the steel is only elastically bent. The high-alloy ledeburitic materials have very low martensitic transformation temperatures. During cooling from 200°C to room temperature, martensite formation continues. Due to the pre-stressed state, the martensite lattices align themselves in such a way that stress reduction occurs, resulting in parts that are straighter at room temperature than they would be without this straightening step.

[0034] Another technology is "kerfing." After hardening and tempering, local plastic deformations are introduced into the workpiece. A small punch is preferably used for this, striking 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 impact of the punch 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 straighten the components.

[0035] Local plastic deformation can also be induced by the flame of an acetylene burner. The component is heated locally with the flame until it reaches a high temperature. The associated thermal expansion then causes a slight deformation of the workpiece. This technology is very complex. In some cases, up to 60 flame straightening points must be created to achieve the required straightness. Furthermore, local material damage occurs because the high temperatures alter the heat-treated state 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 spot is then surrounded by a soft ring. With frequent load changes, such as in high-speed machines with cycle times of just a few seconds, cracks can form and propagate, and the steel parts can break.With a low number of load cycles and low stress, this damage caused by flame straightening is irrelevant. Long components: Use at high temperatures

[0036] Components that experience higher temperatures during operation are particularly critical, as the stresses introduced by straightening steps after tempering can cause the components to bend again and therefore have shorter service lives.

[0037] Plasticizing screws, for example, convey plastic within a plasticizing cylinder and melt it at temperatures of 220°C to 350°C, rarely 450°C. They have a length-to-diameter ratio of approximately 30 and a diameter clearance to the surrounding cylinder of a few tenths of a millimeter. Within this cylinder, they perform a rotary motion during metering—generating the plastic melt—and a linear motion under immense 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 tool life.

[0038] In the fully heat-treated state, further stress-relief annealing at the usual temperatures of 550°C to 650°C is no longer possible, as the favorable properties achieved would be lost again even at these temperatures above the tempering temperature. Therefore, throughout the entire manufacturing process – turning, milling, whirling, rough grinding, straightening, stress-relief annealing, hardening, tempering, straightening, and finishing – attention must be paid to stress reduction and minimizing distortion. These measures cannot completely eliminate stress and distortion; they can only keep them to a minimum.

[0039] Summary State of the Art The tool steels are machined mechanically in the soft-annealed state (turning, milling, grinding, polishing). Straightening ("making straight") the parts in the soft-annealed state is also done mechanically. A jig is placed underneath at two positions, and a hammer is used to press down on the center until the worms are straight. During the subsequent stress-relief annealing, they then bend back to approximately half the original arc length. After the workpieces have been mechanically shaped (turning, milling, etc.), the desired material properties are achieved by hardening and tempering. In hardening practice, it is state of the art that tempering should be carried out as soon as possible after hardening to prevent retained austenite stabilization and a significant reduction in toughness. Furthermore, ledeburitic materials are generally very brittle in the hardened state only and tend to break.For use as screws, the long and thin workpieces, with a length-to-diameter ratio of approximately 30, must be straightened because they rotate within the surrounding cylinder of mass, resulting in a diameter clearance of a few tenths of a millimeter between the two components. In this state, mechanical straightening is no longer possible due to the material's brittleness. To straighten the screws, the process involved, among other methods, local heating 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 process and a hardening device for a longitudinal section of a deformed, rod-shaped workpiece, wherein the workpiece is clamped in a pressure device during both heating and quenching. Object of the invention

[0041] A straightening process ("straightening") for long components, such as screws, without causing local damage, is to be developed. (In addition, the straightening should be able to be done automatically, mechanically on a straightening machine.)

[0042] 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 existing stresses at the increased temperatures in the injection molding process and thus wear out.

[0043] In particular, a method according to claim 1 is proposed to solve the problem.

[0044] In one embodiment, a method is provided for straightening a component made of a high-alloy steel which has a real shape in its longitudinal direction that deviates from the target shape of the component in the form of a bend, wherein the component is provided with a bent shape by mechanical bending before carrying out a heat treatment in the form of an annealing step, which is opposite to the original real shape, wherein subsequently, during the heat treatment, a new shape is established in the component as stresses are relieved, which is closer to the target shape than the original real shape and the bent shape.

[0045] It is preferred that heat treatment is the last heat treatment step that the component undergoes before its completion.

[0046] It is preferred that the component is pre-bent at an angle of 180° against the direction of the deviation of the original real path.

[0047] It is preferred that the bending is carried out to such an extent that the deviation of the bent shape from the target shape is in the range of 30 to 100% of the deviation of the original actual shape from the target shape.

[0048] It is preferred that the bending is carried out to such an extent that the deviation of the bent shape from the target shape is in the range of 50 to 80% of the deviation of the original actual shape from the target shape.

[0049] It is preferred that the deviation of the curved path over the entire longitudinal extent of the component is a mirror image of the original deviation of the original real path to the target path, to an extent of 30% to 100% of the original deviation.

[0050] It is preferred that the deviation of the curved path over the entire longitudinal extent of the component is mirror-image to the original deviation of the original real path to the target path, to an extent of 50% to 80% of the original deviation.

[0051] It is preferred that the bending to the curved profile takes place after hardening and before tempering, wherein the tempering process is or includes heat treatment in the form of an annealing step and the component is stress-free and straight after the tempering process.

[0052] In one version, the component is made of a martensitic tool steel. In another version, the component is made of a ledeburitic tool steel. In another version, the component is made of a corrosion-resistant martensitic steel. In another version, the component is made of a corrosion-resistant ledeburitic tool steel.

[0053] Preferably, the component is made of one of the steels X105CrMo17, X105CrCoMo18-2, ~X190CrVMo20-4 or -X270CrVMoW20-7.

[0054] Preferably, the component is 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 for an arc of about one millimeter, they are pre-bent to a negative arc of about 0.5 mm – half the value of the straightness deviation.

[0055] In reality, a value higher often proves even more advantageous. Pre-bending, ideally mirroring the straightness deviation (not just the maximum bend, but the entire length), to 50 to 80% (rarely 100%) of the initial value is recommended. The component's history, the manufacturing process, and its geometry also influence the optimal value. This value must be determined empirically during series production. The long components then go into the furnace for stress-relief annealing. With optimal pre-bending, they emerge from the furnace almost straight.

[0056] The components are thus made stress-free and straight by overpressing the bars and subsequent stress-relief annealing.

[0057] Corrosion-resistant steels exhibit a unique behavior with regard to their properties after hardening, particularly their toughness. In contrast to ledeburitic cold-work or high-speed steels, which show no or only minimal plastic deformability, tensile tests reveal a low yield strength of approximately 700 MPa and a plastic deformability of about 1% to 2%. This is attributed to altered behavior of the retained austenite and a significantly reduced brittleness of the newly formed martensite due to the high chromium content. The high chromium content allows dislocations to slide more easily. Furthermore, chromium also reduces the stabilization of the retained austenite. Measurements show that even if a week passes between hardening and tempering, no decrease in impact toughness or plastic elongation is observed in tensile tests.

[0058] This behavior can be used to employ pre-bending even 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, such that a straightness deviation of 100% is reduced to 50% or more in the opposite direction.

[0059] The subsequent tempering process achieves the same effect as stress-relief annealing. It can be used to straighten the component, eliminating any remaining or introduced stresses. Additionally, the associated microstructural transformations described above during tempering reduce stress. Therefore, after complete heat treatment, the components are straight and stress-free or have low stress levels.

[0060] The invention is illustrated using figures. Fig. 1 schematically illustrates a screw bent by 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 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-only condition of a ledeburitic cold work steel (little or no plastic deformability) and a corrosion-resistant, ledeburitic tool steel (low yield strength and 1% to 2% plastic deformability). Microstructures in each case: martensite, retained austenite, primary carbides.

[0061] Fig. 1Figure 1 illustrates 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.

[0062] Fig. 2 illustrates the problem, or the initial state of the component before the application of the method in question.

[0063] The component exhibits an actual profile 2, which deviates from the target profile 3. The deviation is perpendicular to the longitudinal direction or length of the component.

[0064] The maximum deviation 4 is usually found in the middle area of ​​the component, but in the case of worm gears, due to geometry, it is often also found to the side of it.

[0065] Fig. 3Figure 1 illustrates a mechanical device for aligning the actual path 2 of the component with the target path 3. This involves two support points at the ends of the component and a punch in the middle section of the component.

[0066] Fig. 4 illustrates the straightening of the component in the method according to the invention.

[0067] Straightening is achieved by mechanical bending prior to an annealing step. This is done using a bending device known from the prior art and according to the relevant regulations. Fig. 3 The explained principle can work.

[0068] As illustrated, the component has a real shape 2 before bending, which deviates from the target shape 3.

[0069] The maximum deviation 4, which usually occurs approximately in the middle of the component, forms the basis for determining the bending of the component and is specified as 100%.

[0070] The bending then occurs in the opposite direction to the maximum deviation 4. This means that the component is bent in the opposite direction to the original real path 2, mirroring its shape, until a new path in the form of the bent path 5 results. The bent path 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%, particularly 50 and 80%, of the original maximum deviation 4, for example, 50% as shown. Preferably, the bent path 5 has a deviation at every point along its longitudinal direction which corresponds to the deviation of the original real path 2 at the same point, in the range of 30 to 100%, particularly 50 to 80%. Preferably, the ratio between the original deviation of the original real path 2 and the deviation of the bent path 5 along the longitudinal direction of the component is at least approximately constant.

[0071] 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.

[0072] 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 takes place between hardening and tempering. The following are involved:

[0073] The annealing temperature must be reduced to the tempering temperature, as otherwise the required performance properties, especially the high hardness, would be lost. The annealing process 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-reducing effect.

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

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

[0076] In one implementation variant, 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. 5Figure 8 illustrates a comparison of tensile specimens in the hardened-only state of a ledeburitic cold work steel 7 (hardly or only slight plastic deformability) and a corrosion-resistant, ledeburitic tool steel 8 (low yield strength and 1% to 2% plastic deformability). The microstructure comprises martensite, retained austenite and primary carbides in each case.

Claims

1. A method for directing a component made of high-alloy steel, which in its longitudinal direction has an actual course (2) which deviates from the target course (3) of the component by a bend, characterised in that the component is provided with a bent course (5) by mechanical bending prior to the execution of a heat treatment by an annealing step, which bent course (5) is opposing the original actual course (2), wherein a new course, which is closer to the target course (3) than both the original actual course (2) and the bent course (5), subsequently manifests itself during the heat treatment with strain relief in the component.

2. The method of claim 1, characterised in that the heat treatment is the last heat treatment step the component undergoes before its completion.

3. The method of claim 1 or 2, characterised in that the component is pre-bent at a 180° angle counter to the direction of the deviation of the original actual course (2).

4. The method of claim 3, characterised in that the extent of bending is such that the deviation of the bent course (5) from the target course (3) ranges from 30% to 100% of the deviation of the original actual course (2) from the target course (3).

5. The method of claim 3, characterised in that the extent of bending is such that the deviation of the bent course (5) from the target course (3) ranges from 50% to 80% of the deviation of the original actual course (2) from the target course (3).

6. The method of claim 3, characterised in that the deviation of the bent course (5) is symmetrical to the original deviation of the original actual course (2) from the target course (3) in a dimension of 30% to 100% of the original deviation across the entire longitudinal extension of the component.

7. The method of claim 3, characterised in that the deviation of the bent course (5) is symmetrical to the original deviation of the original actual course (2) from the target course (3) in a dimension of 50% to 80% of the original deviation across the entire longitudinal extension of the component.

8. The method of any one of claims 1 to 7, characterised in that the bending to the bent course (5) is done after curing and prior to tempering, wherein the tempering process is or comprises the heat treatment by an annealing step and the component is low-strain and straight after the tempering process.

9. The method of any one of claims 1 to 8, characterised in that the component is made of a martensitic tool steel.

10. The method of claim 9, characterised in that the component is made of a ledeburitic tool steel.

11. The method of claim 3, characterised in that the component is made of a corrosion-resistant, martensitic steel.

12. The method of claim 10, characterised in that the component is made of a corrosion-resistant, ledeburitic tool steel.

13. The method of claim 12, characterised in that the component is made of one of steels X105CrMo17, X105CrCoMo18-2, ~X190CrVMo20-4 and ~X270CrVMoW20-7.

14. The method of any one of claims 1 to 13, characterised in that the component is a plasticising screw (1).

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