EP4556579A2 - Procédé pour durcir et dresser des aciers d'outils fortement alliés - Google Patents

Procédé pour durcir et dresser des aciers d'outils fortement alliés Download PDF

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EP4556579A2
EP4556579A2 EP25164074.4A EP25164074A EP4556579A2 EP 4556579 A2 EP4556579 A2 EP 4556579A2 EP 25164074 A EP25164074 A EP 25164074A EP 4556579 A2 EP4556579 A2 EP 4556579A2
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Prior art keywords
hardening
straightening
steels
tempering
component
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German (de)
English (en)
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EP4556579A3 (fr
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Gottfried Pöckl
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D3/00—Straightening or restoring form of metal rods, metal tubes, metal profiles, or specific articles made therefrom, whether or not in combination with sheet metal parts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D3/00—Straightening or restoring form of metal rods, metal tubes, metal profiles, or specific articles made therefrom, whether or not in combination with sheet metal parts
    • B21D3/10—Straightening or restoring form of metal rods, metal tubes, metal profiles, or specific articles made therefrom, whether or not in combination with sheet metal parts between rams and anvils or abutments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D3/00—Straightening or restoring form of metal rods, metal tubes, metal profiles, or specific articles made therefrom, whether or not in combination with sheet metal parts
    • B21D3/14—Recontouring
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C21D1/30—Stress-relieving
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/10—Modifying the physical properties of iron or steel by deformation by cold working of the whole cross-section, e.g. of concrete reinforcing bars
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/01—Selection of materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/20—Making tools by operations not covered by a single other subclass
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/007—Ledeburite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr

Definitions

  • 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.
  • 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.
  • 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.
  • 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 are exposed to high thermal stress during machining, such as turning, milling, or drilling.
  • the required alloying elements are These properties are achieved by alloying high levels of special carbide formers such as tungsten, molybdenum, vanadium, and niobium.
  • High cutting edge retention is also required for knife steels.
  • the thermal stress is less pronounced. Instead, a certain degree of corrosion resistance is usually required, which is achieved by increasing the alloy's chromium content and slightly reducing the carbon content.
  • 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.
  • High-alloy tool steels are heat treated, and their performance properties are achieved through hardening and tempering.
  • 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.
  • 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. On the one hand, they are corrosion-resistant due to their high chromium content.
  • chromium in addition to chromium, they also contain other carbide formers such as vanadium, Molybdenum, tungsten, niobium, and titanium, combined with their high carbon content, 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.
  • carbide formers such as vanadium, Molybdenum, tungsten, niobium, and titanium
  • 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 this. 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.
  • 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.
  • Ledeburitic knife steels include, among others, the steels X90CrMoV18, X105CrMo17, X105CrCoMo18-2, etc.
  • 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.
  • HIPPing hot isostatic pressing
  • Some important powder metallurgical plastic mold steels are ⁇ X190CrVMo20-4, ⁇ X270CrVMoW20-7, -X260CrVMo26-4, ⁇ X230CrVMo14-9, ⁇ X170CrVMo18-3, etc.
  • the steel bars of the various alloys are peeled and annealed at the steel manufacturer.
  • annealed carbides precipitate in the steel matrix.
  • the matrix becomes depleted of alloying elements and becomes ferritic.
  • the steel also contains annealed carbides with a size of approximately 100 nm to 500 nm.
  • the annealed steels have a hardness of approximately 250 HB to 300 HB.
  • 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 contract hardening, 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.
  • various holding temperatures are used during hardening to allow for temperature equalization.
  • the matrix structure also transforms from ferrite to austenite.
  • the annealing carbides formed during soft annealing dissolve again, and the matrix becomes enriched with alloying elements.
  • the material is rapidly cooled to keep the alloying elements in solution and prevent the formation of annealing carbides, and to prevent the austenite from transforming into ferrite, pearlite, or bainite. Nevertheless, some metallurgical processes may occur.
  • the desired formation of martensite begins at approximately 300°C to 200°C.
  • martensite formation is not yet complete at room temperature, and large amounts of retained austenite are still present.
  • the austenite usually has a square or angular shape. Accumulations of retained austenite are often found in the area around the primary carbides, as higher alloy contents are found there due to diffusion.
  • 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, the ability to automate 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 performed several times at temperatures in the range of the secondary hardness maximum – slightly above for maximum toughness, slightly below or far below to achieve high corrosion resistance, and precisely in the range of the maximum for the highest possible hardness.
  • the martensite relaxes and forms secondary hardening carbides. These can occur in various morphologies. Usually, they form regularly distributed globular particles with a diameter of 3 to 10 nm. 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 detected between the secondary hardening carbides and the surrounding matrix.
  • the carbides are therefore completely coherent, while the primary carbides are incoherent and exhibit a distinct interface.
  • Upon 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.
  • a high-alloy ledeburitic tool steel After heat treatment, a high-alloy ledeburitic tool steel has a microstructure with a matrix of tempered, tough martensite, incoherent primary carbides in the ⁇ m range, and coherent secondary hardening carbides in the nm range.
  • the steels then typically have a hardness in the range of approximately 60 HRC.
  • the workpieces are finished by grinding and polishing.
  • 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.
  • the matrix of the soft-annealed steels is ferritic and only transforms at higher Temperatures above around 700°C convert to austenite. Upon cooling, the matrix then becomes austenitic. While ferrite has a thermal expansion coefficient of approximately 12 ⁇ m/mK, the expansion coefficient of austenite is significantly higher at around 17 ⁇ m/mK. Carbides have significantly lower expansion coefficients of approximately 5 to 6 ⁇ m/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.
  • the workpiece 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.
  • notch dressing Another technology is "notch dressing.” After hardening and tempering, local plastic deformations are introduced into the workpiece. A small punch is preferably used for this, which is pressed onto 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 will penetrate deeply into the workpiece, making it difficult to restore an intact, smooth surface. The numerous small plastic deformations collectively cause the components to straighten.
  • Plasticising screws for example, convey plastic into a plasticising 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 of surrounding cylinder of a few tenths of a millimeter. Within this cylinder, they perform a rotating motion during dosing – 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 shortened service life.
  • 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.
  • a method 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.
  • the heat treatment is the last heat treatment step that the component undergoes before its completion.
  • the component is pre-bent at an angle of 180° against the direction of the deviation of the original real course.
  • 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.
  • 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.
  • 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.
  • the deviation of the curved course over the entire longitudinal extent of the component is mirror-image to the original deviation of the original real course to the Target course is present and this to an extent of 50% to 80% of the original deviation.
  • 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.
  • 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.
  • the component is made of one of the steels X105CrMo17, X105CrCoMo18-2, -X190CrVMo20-4 or ⁇ X270CrVMoW20-7.
  • 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.
  • 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.
  • the components are thus made stress-relieved and straight by over-pressing the bars and subsequent stress relieving.
  • 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.
  • 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.
  • 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.
  • Fig. 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.
  • Fig. 2 illustrates the problem or the initial state of the component before the application of the procedure in question.
  • 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.
  • 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.
  • Fig. 3 illustrates a mechanical device for adjusting the actual profile 2 of the component to the desired profile 3.
  • two support points are provided at the ends of the component and a stamp in the central area of the component.
  • Fig. 4 illustrates the straightening of the component in the method according to the invention.
  • 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.
  • the component has a real curve 2 before bending, which deviates from the target curve 3.
  • 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%.
  • the bending then takes place against the maximum deviation 4.
  • 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.
  • the component is removed from the bending device and subjected to heat treatment in the form of an annealing step.
  • the component preferably undergoes a heat treatment in the temperature range of 600°C to 800°C for a duration of 1 to 5 hours.
  • bending takes place between hardening and tempering.
  • the temperatures of the annealing step must be reduced to the tempering temperatures, as 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.
  • 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.
  • 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.
  • 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.
  • Fig. 5 illustrates 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.

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EP25164074.4A 2023-02-20 2024-02-13 Procédé pour durcir et dresser des aciers d'outils fortement alliés Pending EP4556579A3 (fr)

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DE102023104087.1A DE102023104087A1 (de) 2023-02-20 2023-02-20 Verfahren zum Härten und Richten hochlegierter Werkzeugstähle
EP24157313.8A EP4417336B1 (fr) 2023-02-20 2024-02-13 Procédé pour durcir et dresser des aciers d'outils fortement alliés

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69914433T2 (de) 1998-10-12 2004-07-15 Neturen Co. Ltd. Zwangsabschreck - und Wärmebehandlungsverfahren und -vorrichtung für verzogene stabförmige Werkstücke

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DE567578C (de) * 1930-07-09 1933-01-05 Fritz Foedisch Vorrichtung zum Vorbiegen von im warmen Zustande aus dem Walzwerk kommenden Schienen u. dgl. auf dem Kuehlbett, damit sie sich beim Erkalten geradeziehen
CN113894185B (zh) * 2021-11-23 2024-05-14 成都先进金属材料产业技术研究院股份有限公司 钛合金带筋管的矫直方法

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69914433T2 (de) 1998-10-12 2004-07-15 Neturen Co. Ltd. Zwangsabschreck - und Wärmebehandlungsverfahren und -vorrichtung für verzogene stabförmige Werkstücke

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EP4556579A3 (fr) 2025-10-29

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