WO2021032893A1 - Acier à outils pour applications de travail à froid et à grande vitesse - Google Patents

Acier à outils pour applications de travail à froid et à grande vitesse Download PDF

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Publication number
WO2021032893A1
WO2021032893A1 PCT/EP2020/073652 EP2020073652W WO2021032893A1 WO 2021032893 A1 WO2021032893 A1 WO 2021032893A1 EP 2020073652 W EP2020073652 W EP 2020073652W WO 2021032893 A1 WO2021032893 A1 WO 2021032893A1
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Prior art keywords
temperature
steel material
steel
hardening
weight
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PCT/EP2020/073652
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German (de)
English (en)
Inventor
Alfred HACKL
Harald Leitner
Gert Kellezi
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Voestalpine Böhler Edelstahl Gmbh & Co. Kg
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Priority to EP20761235.9A priority Critical patent/EP4018006A1/fr
Publication of WO2021032893A1 publication Critical patent/WO2021032893A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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")
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/12—Both compacting and sintering
    • B22F3/14—Both compacting and sintering simultaneously
    • B22F3/15—Hot isostatic pressing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum
    • 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
    • C21D1/78—Combined heat-treatments not provided for above
    • C21D1/785—Thermocycling
    • 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
    • C21D6/02—Hardening by precipitation
    • 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 by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/02—Making ferrous alloys by powder metallurgy
    • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
    • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

  • the invention relates to a tool steel for cold work and high speed work applications and a method for its production.
  • High speed steels and modern cold work steels are used in many areas and often have a very high level of hardness and sufficient toughness. Such steels are used, for example, for tools that remove drilling, milling or cutting.
  • a high level of hot hardness is required especially for high-speed work applications, since these areas of application not only lead to strong heating of the workpiece, but also to very strong heating of the tool. In this respect, it is important that these steels maintain their mechanical characteristics even at higher working temperatures that may be attainable.
  • such steels are exposed to high pressures even in many cold work applications, so that high compressive strength is also required. This applies, for example, to fineblanking and punching, so that compressive strength is required here in order to avoid premature chipping.
  • high-strength tools and high-speed steels have sufficient toughness in order to achieve a long service life and, in particular, to avoid high brittleness, which can lead to premature tool damage.
  • the properties of tool steels are primarily determined by the alloy composition in addition to the manufacturing route.
  • suitable heat treatments can be used to influence the steel phases and thus also the mechanical parameters, in particular the toughness.
  • Known high-strength, high-performance tool steels for high-speed and cold work applications include alloys which, in addition to iron, contain, for example, 0.8-2.4% carbon, 4-6% chromium, 2-5% molybdenum, 2-9% vanadium, 1-15% tungsten and Contains up to 12% cobalt.
  • the essential part of these elements should ensure a high hardness, which is ensured on the one hand by the carbon, which allows the carbide formation, these carbides being formed with the alloy elements chromium, molybdenum, tungsten and vanadium.
  • the cobalt present does not serve as a carbide former, but leads to an increase in hardness via matrix strengthening.
  • Such a high-speed steel object is known from EP 1 249 511 B1 which is said to have high heat resistance and high toughness, this object being produced from a metal powder which is compressed at high temperatures and, if necessary, hot-worked.
  • This item contains particularly few inclusions and is of a high degree of purity and, in addition to carbon and other elements, has 3.5 - 4.5% chromium, 13.3 - 15.3% tungsten, 2 - 3% molybdenum and 10.5% 12% cobalt.
  • the ratio of the concentration of tungsten to molybdenum should be between 5.2 and 6.5, with the cobalt content not exceeding 70% of the value of tungsten and molybdenum.
  • This steel material has a high heat resistance, but there is room for improvement in terms of hardening.
  • the object of the invention is to create a high-strength high-speed and hot-work steel which has the hardness level of known very hard corresponding steels, but also has improved toughness properties, measured by means of impact tests, compared to known high-strength steel types.
  • the hardenability should be improved compared to known types of steel, measured with the dilatometer.
  • the silicon content and the manganese content are slightly reduced compared to known types of steel, while the tungsten content is more in an upper known type Area is settled and the molybdenum content is increased.
  • the cobalt content is significantly reduced.
  • alloying elements in such steels act as follows:
  • Carbon is mainly used to set the desired level of strength.
  • the carbon content should not be too high, as this can lead to a high proportion of precipitates in the form of carbides, which could have a negative effect on the toughness and fatigue strength.
  • the upper limit according to the invention is therefore 2.50% by weight, preferably 2.30% by weight, particularly preferably 2.00% by weight.
  • the lower limit according to the invention is 1.50% by weight, preferably 1.70% by weight, particularly preferably 1.80% by weight.
  • Si is a solid solution hardener and not a carbide-forming element, but influences the carbide precipitation kinetics in steel. It stabilizes the carbon so that it is only available for the formation of carbides at higher temperatures. Silicon serves as a deoxidizer and is therefore present in low concentrations in almost all steels due to the manufacturing process. It increases the scaling resistance, the yield strength and the tensile strength without significantly reducing the elongation. On the other hand, a decrease in the silicon content leads to a reduction in the anisotropy of the mechanical properties. A low silicon content enables the initial formation of metastable M3C carbides. These act as a C reservoir for the subsequent precipitation of the desired MC carbides.
  • the upper limit according to the invention is therefore 1.00% by weight, preferably 0.75% by weight, particularly preferably 0.50% by weight, in particular 0.25% by weight. Silicon can also only be present as a production-related impurity, i.e. without conscious addition of alloys.
  • Manganese can influence the hardening behavior of the material, but is primarily to be seen together with the sulfur content, whereby sulfur and manganese are to be regarded as elements that improve the machinability of the steel due to the formation of sulfide inclusions.
  • sulfur and manganese are to be regarded as elements that improve the machinability of the steel due to the formation of sulfide inclusions.
  • manganese acts as a solid solution strengthener. This element increases the hardness, but too high a proportion can decrease the toughness.
  • the upper limit according to the invention is therefore 1.00% by weight, preferably 0.75% by weight, particularly preferably 0.40% by weight, in particular 0.10% by weight.
  • Manganese may also only be present as a manufacturing-related impurity, i.e. without deliberate addition.
  • chromium With a proportion of greater than 4.0% by weight, chromium leads to the desired solid solution. In general, chromium reduces the critical cooling rate and thus increases the hardenability. Furthermore, increased chromium contents can lead to carbide precipitation and thus increase the hardness. Thus, too high a chromium content can also have negative effects on toughness. In addition, too high a chromium content of more than 7.0% by weight can have negative effects on the residual austenite content during hardening.
  • the upper limit according to the invention is therefore 7.0% by weight, preferably 5.50% by weight, particularly preferably 5.00% by weight.
  • the lower limit according to the invention is 4.00% by weight, preferably 4.50% by weight, particularly preferably 4.70% by weight.
  • Molybdenum forms special carbides and, on the other hand, mixed carbides with iron. These are of the type M2C, M ⁇ C and MC. By adding molybdenum, the activation energy for the C diffusion in austenite is increased and thus the diffusion coefficient for C or C diffusion is reduced. This leads to a lower Bs temperature and reduced bainite formation. On the other hand, the addition of Mo leads to a refinement of the microstructure, ie a fine structure is predominant regardless of the cooling rate (1 ° C / s to 60 ° C / s). The grain coarsening remains low because of the slow dissolution rate and the high solution temperature of the carbides (carbides counteract the grain coarsening).
  • Austenitizing (solution annealing) at higher hardening temperatures can thus achieve improved tempering resistance, since more carbide-forming elements can be precipitated and more carbides are formed as a result.
  • the hard carbides also increase the hot yield strength and wear resistance.
  • Mo improves the scaling resistance of the steel. Too high a content worsens the machinability and, if it remains dissolved in the matrix, the thermal conductivity. It could also happen that embrittlement occurs during tempering due to the occupation of the former austenitic grain boundaries with carbides.
  • the upper limit according to the invention is therefore 5.0% by weight, preferably 3.50% by weight, particularly preferably 3.00 Wt%.
  • the lower limit according to the invention is 1.00% by weight, preferably 1.50% by weight, particularly preferably 2.00% by weight.
  • the upper limit according to the invention is 7.0% by weight, preferably 6.00% by weight, particularly preferably 5.00% by weight.
  • the lower limit according to the invention is 3.00% by weight, preferably 4.00% by weight, particularly preferably 4.50% by weight.
  • Tungsten is a ferrite-stabilizing element. It is a very strong carbide former and is used to increase wear resistance. The addition of tungsten improves the hot hardness and tempering resistance, therefore it is used as an additive in high-speed steel and hot-work steel. However, tungsten is also an expensive alloy element.
  • the upper limit according to the invention is therefore 16.0% by weight, preferably 15.50% by weight, particularly preferably 15.00% by weight. In order to ensure the above-mentioned effects, the lower limit according to the invention is 12.00% by weight, preferably 13.00% by weight, particularly preferably 13.50% by weight.
  • Cobalt is an austenite-stabilizing element. It does not form carbides, but remains dissolved in the matrix and thus influences the carbon diffusion. This leads to an increase in hot hardness and improved hot brittleness.
  • the upper limit according to the invention is therefore 8.0% by weight, preferably 7.50% by weight, particularly preferably 7.00% by weight.
  • the lower limit is 6.00% by weight, preferably 6.30% by weight, particularly preferably 6.50% by weight.
  • the tungsten equivalent W eq which is defined as W + 2Mo, shows the hot hardness and tempering resistance as well as a measure of the structure.
  • the W eq should be less than 21% by weight, since otherwise the toughness is reduced and the tendency towards brittle fracture increases. This value is preferably between 14 and 20.8% by weight, particularly preferably between 17 and 19.5% by weight, since this can be advantageous for both the machinability and the hot hardness.
  • this setting of W eq can also have a positive influence on the structure, since the carbide content is high enough to achieve a high level of hardness and excellent wear resistance and at the same time is not unnecessarily high, which would negatively affect the toughness.
  • the steel material is preferably processed by powder metallurgy.
  • molten steel is generally atomized into powder. This powder is filled into a capsule, sealed airtight and then hot isostatically pressed (HIP process).
  • HIP process hot isostatically pressed
  • This already dense and homogeneous material can then be fed to a forming process and, in particular, it can be rolled or forged to the required dimensions.
  • the hot isostatically pressed block is brought to a temperature range of 1100 ° C - 1180 ° C for the deformation, the holding time being selected accordingly so that the entire material is heated through.
  • the delivery to the customer takes place typically in the soft annealed condition, whereby the soft annealing takes place in that the material is brought to a temperature of 820 ° C - 880 ° C.
  • the holding period can be, for example, 2 - 5 hours.
  • the material In order to ensure complete soft annealing, the material must also be completely heated through, followed by slow, controlled furnace cooling to a temperature range of 720 ° C - 780 ° C and held here for 2 - 5 hours, for example.
  • the cobalt content is lowered, specifically to a range in which the person skilled in the art would expect a significantly reduced hardness level. According to the invention, it was found that this does not occur despite the reduction in the cobalt content.
  • the inventors explain this with the fact that cobalt is not a carbide former but remains dissolved in the matrix. Cobalt increases the hardness, but reduces the toughness. In high-speed steels, cobalt is to be permitted to a greater extent, especially in view of its higher hot hardness. yaws, whereby it was recognized according to the invention that in very many applications this higher hot hardness is not relevant at all.
  • FIG. 1 shows the possible steel compositions according to the invention
  • FIG. 2 shows the production route in a highly schematic manner
  • FIG. 3 is a comparison table showing two known steel materials and the material according to the invention.
  • FIG. 4 shows a diagram showing dilatometer examinations at different l values
  • FIG. 5 shows a diagram according to FIG. 4 with two comparison materials
  • FIG. 6 shows the hardness profile as a function of the tempering temperature of the comparison materials and of the material according to the invention
  • FIG. 7 shows the impact bending work in joules, depending on the tempering temperature of the comparison materials and the material according to the invention
  • FIG. 8 comparison of the impact bending work of the invention with comparative examples
  • FIG. 9 shows the moduli of elasticity of the material according to the invention and of the comparison materials
  • FIG. 10 shows the compressive strength Rpo2 in MPa of the comparison materials and of the material according to the invention
  • FIG. 11 shows the temperature profile during flaring in detail
  • FIG. 12 shows the temperature profile during hardening and tempering
  • FIG. 13 an exemplary structure according to the invention.
  • FIG. 14 shows an exemplary structure of a conventional tool steel.
  • FIG. 1 the analysis area can be seen within which the invention can be carried out and the effects according to the invention are reliably achieved.
  • the silicon content and the manganese content in particular are between 0 and a maximum of 1% and are thus lower than known types of steel.
  • the cobalt content is between 6 and 8% and in particular around 7% and is therefore significantly lower than in the known solutions.
  • a corresponding steel melt is atomized, in particular with nitrogen or other inert gases, to form a powder.
  • This powder is classified by sifting or sieving, if necessary, and the classified powder is then combined to form a desired particle size band, filled into a corresponding capsule which is welded and is then compressed by hot isostatic pressing. A material converted in this way can accordingly then be fed to the hot forming.
  • the dense and homogeneous material obtained by hot isostatic pressing can be rolled or forged to the required dimensions in a forming process.
  • the powder-metallurgical route is particularly chosen when highly wear-resistant materials are to be achieved or tools made from these materials. This is because this makes it possible to increase the carbon content and thus the concentration of the carbide-forming elements with a view to increasing the carbide content and thus the wear resistance and hardness of the material.
  • conventional processing does not always allow such an increase, so that the powder metallurgical route is used here, in which homogenization and compacting of the material is easily possible even with high carbon-carbide contents.
  • a block produced in this way is then brought to a temperature range of 1100 ° C - 1180 ° C for the deformation, the holding time being selected depending on the size of the block in order to ensure that the entire material is heated through.
  • the Soft annealing where a lower hardness is set so that the material is softer and can be processed by the customer.
  • this final annealing step the so-called soft annealing, is described, in which the material is brought to a temperature of 820 ° C.-880 ° C. and is maintained accordingly.
  • the holding time must be chosen so that the material is completely heated. In order to ensure that the strength does not increase again when the furnace cools, it is necessary to ensure a slowly controlled furnace cooling to a temperature range of 720 ° C - 780 ° C, whereby the holding time is set to the defined temperature 2 to 5 hours.
  • the composition of the steel material according to the invention is shown, which is in the range of the composition of Figure 2 and represents an embodiment of the steel mate rials.
  • This steel material is compared with two other embodiments, namely REF 1 and REF 2, which compared to the known embodiments, the silicon and manganese content are significantly reduced and in particular the cobalt content is also very different and in particular is reduced.
  • the good through-hardenability according to the invention cannot be reliably achieved with the areas disclosed in the prior art.
  • I values define cooling rates and denote the time it takes to cool steel from 800 ° C to 500 ° C, in units of hectoseconds.
  • I values of 3, 5.5 and 8 were maintained and the relative change in length was recorded within a temperature range of 0.500 ° C., which allows conclusions to be drawn about the martensite and bainite transformation.
  • test material was first brought to a temperature of 1180 ° C., warmed up completely and then held for 180 s and then cooled in a defined manner.
  • the change in length shows when a phase transition or phase separation takes place.
  • the kink in the curve in the region of approx. 150 ° C results from the martensite formation.
  • the material according to the invention therefore only has bainite at significantly slower cooling speeds, which in turn means that the hardenability of the material according to the invention is significantly higher.
  • FIG. 6 shows the hardness curve at a tempering temperature of 1180 ° C, whereby it can be seen that the material according to the invention at higher tempering temperatures, in particular above 500 ° C, very quickly reaches hardness values that correspond to those of a known material, but with a significantly reduced cobalt content. If one also considers the impact bending energy, it can be seen from FIG. 7 that a significantly increased impact bending energy is achieved compared with the comparison material with the highest flare values according to FIG. 6, while the softer comparison material naturally achieves higher impact bending values. This also makes it clear, however, that the material according to the invention develops improved toughness with outstandingly high hardness values.
  • the F hardness according to FIG. 6 was determined at a hardness temperature of 1180 ° C. for F holding times of 180 seconds, measured after complete heating, the tempering treatment being carried out three times for 2 hours each and the entire heat treatment being carried out in vacuum. Especially with high-alloy tool steels that are hardened at high temperatures, a three-time tempering is necessary in order to do so the workpiece is then free of retained austenite and the structure is therefore completely martensitic including carbides.
  • the proportion of heating, holding and cooling is significantly reduced after each starting cycle.
  • up to three tempering cycles can be provided, since with each further tempering cycle a further proportion of the retained austenite turns into the desired martensite.
  • the proportion of retained austenite can be kept below 0.5%. The lowest possible proportion of retained austenite is therefore advantageous because it transforms in the event of a load and the corresponding part, e.g. a punch, can then tend to break brittle.
  • the low cooling rate of ⁇ 1 K / s can have an advantageous effect on the inherent stresses, so that these can be significantly reduced.
  • the impact bending tests according to FIG. 8 result clearly differ in the corresponding corresponding recognizable hardness values, while the material according to the invention has a very good toughness with a very high hardness, so that it is evident that it has been possible to reconcile two conflicting mechanical properties with one another.
  • the specified impact energy is referenced to the comparison material (REF 1).
  • the heating rate to 1180 ° C should take place as quickly as possible in order to make the process efficient.
  • the heating rate should therefore advantageously be selected to be ⁇ 5 K / s, preferably ⁇ 1 K / s.
  • the heating for the purpose of hardening is carried out in such a way that two holding periods or holding zones are present during heating for hardening.
  • the temperature is kept constant in the two holding periods until it is completely heated, the condition that the holding temperatures are at least 200 ° K apart and are overall over 200 ° C but below 800 ° C.
  • the first holding zone or first holding period can be at a temperature of> 440 ° C, in particular> 550 ° C
  • the second holding zone or holding period can be at a temperature of> 650 ° C, in particular> 750 ° C.
  • this temperature temperature held, for example, 10 to 30 minutes in order to achieve complete heating.
  • the duration depends on the size of the workpiece and the decisive factor is how much heating is achieved.
  • the heating according to the invention takes place, for example, as indicated in FIG. 12, initially heating to 650 ° C. in order to ensure thorough heating.
  • a second setpoint is reached at 850 ° C with a slightly shorter fold duration to also ensure that the temperature is fully heated.
  • nitrogen was switched to vacuum, this folding stage in this case being due to the duration of the vacuum drawing on the one hand and the sample size on the other.
  • the tempering treatment according to the invention provides for the tempering to be carried out immediately after the clarification th for at least 2 hours for each tempering cycle, the furnace being set to the tempering temperature as the setpoint.
  • a direct heating to this target value is carried out, this being done in a nitrogen atmosphere. It can be seen that each cycle was heated to the target temperature for 2 hours and then the heating was switched off when the nitrogen atmosphere was present. The final temperature was below 30 ° C. and when it was reached the next cycle was started. Three starting cycles are carried out. Of course, it is possible to carry out each starting cycle differently with regard to the tempering temperature or heating and cooling rates, but it can be advantageous to carry out each starting cycle identically.
  • the hardness / toughness advantage in particular at the specified F hardening temperature of around 1180 ° C., can be achieved if the specified heat treatment cycle is adhered to. Even slight downward deviations in the hardness temperature are not excluded, but the significant hardness-toughness advantages over the prior art are no longer guaranteed to the same extent.
  • temperatures above 1190 ° C there is a risk that the material may begin to melt, which is also undesirable.
  • a very narrow range of hardening treatment is sought, which is between 1170 ° C and 1190 ° C, in order to exclude negative influences or mechanical disadvantages.
  • the advantage of the invention is that the method according to the invention makes it possible to very reliably achieve mechanical properties that were previously not compatible with one another in this form.
  • very high values of over 69 HRc are achieved with toughness (measured as impact bending work of 10 to 30 J, preferably greater than 20 J), which previously could not be reliably achieved in this range with these materials in this form.
  • toughness measured as impact bending work of 10 to 30 J, preferably greater than 20 J
  • FIG. 13 shows a micrograph of the structure of the object according to the invention, taken by means of a scanning electron microscope with 1500-fold magnification.
  • the present carbide types are M ⁇ C - visible in the microstructure as white globular precipitates and the particularly hard MC carbides with excellent wear resistance are shown in gray.
  • the steel matrix is shown as a black background in this structure.
  • the extraordinarily high carbide content can be seen and that the two carbide types occur in roughly equal proportions. In total, there is a carbide content of 18-20%.
  • the fact that there are no carbide conglomerates can also be seen, which sometimes also shows the extraordinarily good combination of particularly high hardness with high abrasive wear resistance and yet greater toughness than conventional, comparable tool steels.
  • the rest of the structure consists of a martensitic matrix in which the carbides are bound.
  • FIG. 14 shows a structure of a conventional tool steel.
  • the first annealing treatment is carried out at 1180 ° C. for approx. 20-25 minutes. From the picture it can be seen that the long holding time leads directly to a significant coarsening of the grain.
  • the grain to be seen in the middle has a size in the millimeter range, while the structure according to the invention (FIG. 13) comprises fine grains of a few micrometers.
  • the undesired coarsening of the grain has a negative effect on the mechanical properties of the finished steel material and can no longer be influenced by subsequent tempering cycles.

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  • Powder Metallurgy (AREA)

Abstract

L'invention concerne un procédé de production d'un acier à outils pour des applications de travail à froid et de travail à chaud, dans lequel un matériau d'acier constitué des éléments d'alliage suivants : (tous les chiffres en % en poids) : carbone = 1,50 à 2,50 ; silicium = 0,25 à 1,0 ; Mn = 0,10 à 1,0 ; Cr = 4,0 à 7 ; W = 12 à 16 ; Mo = 1,0 à 5,0 ; V = 3,0 à 7,0 ; Co = 6,0 à 8,0 ; le reste étant du fer et des impuretés inévitables résultant de la fusion, est fondu et traité en une poudre par atomisation, et la poudre est ensuite soumise à une compression isostatique à chaud ou à une compression tridimensionnelle, et la poudre isostatique à chaud est ensuite traitée mécaniquement si nécessaire. Un traitement thermique suit, le traitement thermique étant effectué de telle sorte que le matériau est d'abord chauffé à une température de durcissement de 1 170°C-1 190 °C dans le noyau, puis maintenu à cette température de durcissement pendant 60 à 300 secondes, de préférence 100 à 200 secondes, puis refroidi à une vitesse de refroidissement de λ <= 3 à une température <= 50 °C, de préférence <= 30 °C, à des fins de durcissement, puis étiré, le traitement d'étirement comprenant au moins deux cycles dans lesquels le matériau est chauffé à une température de 400 °C à 600 °C et maintenu à cette température de 400 °C à 600 °C pendant au moins deux heures, puis refroidi à une vitesse de refroidissement de < 1 K/s à une température <= 50 °C, de préférence <= 30 °C. La présente invention concerne également un matériau d'acier produit par ce procédé et son utilisation.
PCT/EP2020/073652 2019-08-22 2020-08-24 Acier à outils pour applications de travail à froid et à grande vitesse WO2021032893A1 (fr)

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CN118028685A (zh) * 2024-04-11 2024-05-14 西安欧中材料科技股份有限公司 一种高端特钢钨基或钴基粉末高速钢的制备方法

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