EP1249510B1 - Process for preparing tool steel articles by powder metallurgy - Google Patents

Process for preparing tool steel articles by powder metallurgy Download PDF

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Publication number
EP1249510B1
EP1249510B1 EP01890158A EP01890158A EP1249510B1 EP 1249510 B1 EP1249510 B1 EP 1249510B1 EP 01890158 A EP01890158 A EP 01890158A EP 01890158 A EP01890158 A EP 01890158A EP 1249510 B1 EP1249510 B1 EP 1249510B1
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Prior art keywords
powder
melt
temperature
process according
container
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German (de)
French (fr)
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EP1249510B2 (en
EP1249510A3 (en
EP1249510A2 (en
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Claes Dipl.-Ing. Tornberg
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Voestalpine Boehler Edelstahl GmbH
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Boehler Edelstahl GmbH
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    • 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
    • C22C33/00—Making ferrous alloys
    • C22C33/02—Making ferrous alloys by powder metallurgy
    • 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
    • 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
    • C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon
    • 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
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • B22F2009/0848—Melting process before atomisation
    • 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
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • B22F2009/0848—Melting process before atomisation
    • B22F2009/0852—Electroslag melting
    • 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
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • B22F2009/0896—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid particle transport, separation: process and apparatus
    • 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
    • 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
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
    • 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
    • C21D2241/00—Treatments in a special environment
    • C21D2241/01—Treatments in a special environment under pressure
    • C21D2241/02—Hot isostatic pressing
    • 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
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working

Definitions

  • the invention relates to a process for powder metallurgy production of tool steel articles having improved homogeneity, higher purity and improved properties.
  • the invention relates to a tool steel article with improved property profile.
  • Tool steels with high carbon concentrations and high levels of carbide-forming elements are used for cutting parts and components with high wear resistance. Because in a solidification of such alloys in molds inhomogeneities and coarse primary and eutectic carbides are formed which cause manufacturing problems and poor mechanical properties of the tools or components created therefrom, powder metallurgy production of such parts is advantageous.
  • Powder metallurgy production essentially involves atomizing a tool steel melt into metal powder, introducing and compacting the metal powder into a container, sealing the capsule, and heating and hot isostatically pressing the powder in the capsule into a dense homogeneous material.
  • melt atomization which is advantageously nitrogen-based in the prior art
  • small metal droplets having a high surface to volume ratio are formed in the gas stream, causing a high rate of cooling and solidification of the liquid metal and thereby small carbide particles in the powder grains.
  • the powder compacted at first by tapping in the capsule is then formed therein by hot isostatic pressing at temperatures generally above 1080 ° C, at a pressure of greater than 85 MPa, to form a completely dense metal body.
  • This as-HIPed metal body which can still be subjected to hot working, has an advantageously low carbide size of 1-3 on average, with a high carbide content um and good mechanical material properties in comparison with a melt metallurgical production on.
  • the invention seeks to remedy and sets itself the goal of eliminating the lack of quality of the state-of-the-art PM tool steel objects and to provide a method of the type mentioned above, with which an isostatically pressed metal body with the highest material isotropy and lowest content oxide inclusions can be produced.
  • the invention aims at a tool steel object with improved processing and service properties with increased service life.
  • the advantages achieved by the method according to the invention are essentially based on the fact that synergistically improved metallurgical work on a melt introduced into a metallurgical vessel whose oxidic purity significantly and the temperature is adjusted homogeneously to an advantageous overheating value, after which an atomization of the liquid metal takes place in that the mean grain diameter is 50 to 70 ⁇ m.
  • This ensures that on the one hand in the powder, the oxygen content is surprisingly low and on the other hand, the fine grain content is substantially increased in terms of achieving a high tapping and Jottelêt in the capsule.
  • An inventive distribution of the grain diameter with an average value in the range of 50 to 70 microns allows reaching an unexpectedly high powder density in the capsule, so that on the one hand their shrinkage in hot isostatic pressing is low and on the other hand there is a largely complete isotropy of the pressed dense metal body.
  • the parameters for the hot isostatic press cycle involve warming up the powder in the container with substantially the same increase in temperature and pressure, which has already been shown to increase the Material density and homogeneity can be achieved.
  • the subsequent pressing is carried out in the temperature range of 1100 ° C to 1180 ° C at a pressure of 90 MPa and greater with a period of at least three hours, followed by a slow cooling of the compact.
  • Lower pressing temperatures than 1100 ° C and pressures below 90 MPa and less pressing times than three hours can cause discontinuities in the material
  • the pressed body has a completely dense material structure after HIPing, so it can be processed into a tool in this state or after hot working.
  • a particularly significant increase in the quality of the article is achieved in its production by the process according to the invention, when the melt of an iron-based alloy containing in wt .-% Carbon (C) 0.52 to 3.74 Manganese (Mn) to 2.9 Chrome (Cr) to 21.0 Molybdenum (Mo) to 10.0 Nickel (Ni) optionally to 1.0 Cobalt (Co) to 20.8 Vanadin (V) to 14.9 Niobium (Nb) Tantalum (Ta) singly or in total to 2.0 Tungsten (W) to 20.0 Sulfur (S) to 0.5 and accompanying elements up to a cumulative concentration of 4.8 and impurities and iron as the remainder.
  • the above chemical composition of the tool steel includes particularly carbide-rich tool steels with high abrasion resistance and high cutting strength of the tools produced therefrom. Since high carbide contents usually worsen the mechanical properties of the material, their fundamental improvement by the method according to the invention is of particular importance. It has been found that these high mechanical properties, in particular the impact resistance of the material, are due to the small mean grain diameter of the powder, a homogeneous dense bed of the same in the capsule and the high degree of oxidic purity in isotropic structure of the hot isostatically pressed article ,
  • the oxidic purity of the liquid metal can be effectively improved by metallurgical work, when conditioning the melt in the metallurgical vessel at an induced turbulent flow thereof and at a complete coverage of the metal bath by liquid slag, which is heated in particular by direct passage of current, during a time of at least 15 minutes.
  • liquid slag which is heated in particular by direct passage of current, during a time of at least 15 minutes.
  • a release of oxygen compounds or oxides is promoted from the melt and a recording of the same in the hot slag, wherein the induced flow of the metal bath increases the efficiency.
  • the conditioned melt introduced through a nozzle body in the metallurgical vessel with a melt flow diameter of 4.0 to 10.0 mm in a Verdüsungshunt and in this with at least three successive nitrogen, with a purity of At least 99.999% nitrogen, formed gas jets is acted upon with the proviso that the last loading of the melt stream is effected by a gas jet, which at least in places has a speed which is greater than the speed of sound. Compliance with the melt flow diameter and the high kinetic energy of the gas flow of the metal stream cause a favorable particle size distribution and a desired fineness of the metal powder produced.
  • the conditioning and adjustment of the temperature of the liquid metal in the metallurgical vessel and the high degree of purity of the sputtering gas nitrogen are further the causes of a surprisingly high degree of purity or a low oxygen content of the powder and as a result of the H exertisostatisch gerpeßten block.
  • the diameter of the powder grains atomization technology is adjusted or classified to a maximum value of 500 microns.
  • the powder collected in a staging area is fluidized and mixed by nitrogen and, while maintaining the nitrogen atmosphere, in a container or capsule having a total weight greater than 0, 5 t introduced, by mechanical shocks compressed and sealed gas-tight.
  • the heat-soaking time can be shortened due to increased heat conduction and the powder mass can be precompressed with respect to a substantially complete block isotropy.
  • the further object of the invention to provide a tool steel article with improved processing and service properties with increased service life is in a powder metallurgy tool made of tool steel with improved material properties consisting of an iron-based alloy containing in wt .-% Carbon (C) 0.52 to 3.74 Manganese (Mn) to 2.9 Chromium (Ce) to 21.0 Molybdenum (Mo) to 10.0 Nickel (Ni) optionally to 1.0 Cobalt (Co) to 20.8 Vanadin (V) to 14.9 Niobium (Nb) Tantalum (Ta) singly or in total to 2.0 Tungsten (W) to 20.0 Sulfur (S) to 0.5 and accompanying elements up to a total concentration of 4.8 and impurities and iron as the remainder, which material according to DIN 50 602 has a K0-W of at most 3, achieved.
  • Tool steels have a wide range of the concentration of the respective alloying elements, which always interact and are seen in terms of carbon content.
  • Lower carbon contents than 0.52 wt .-% lead to a low carbide content and / or low matrix hardness in the thermally tempered state of the steel, whereas higher than 3.74 wt .-% carbon, even in a powder metallurgical production, the material largely preclude use as a tool due to the mechanical property profile.
  • the high affinity for carbon of the elements Mo, V, Nb / Ta and W causes in appropriate proportions a desired carbide and Mischkarbid produced in an alloyed matrix.
  • concentration values in wt% 10.0, 14.9; 2.0; 20.0 will not be exceeded because On the one hand a desired compensation behavior and on the other hand, the manufacturability and the intended mechanical properties of the materials can not be achieved.
  • Ni may optionally be present in the alloy without adverse effect up to a content of 1.0% by weight
  • Co increases the hot hardness and cutting strength of the tools, but has a property of 20.8 wt .-% property-degrading ..
  • Sulfur contents up to 0.5 wt .-% improve the machinability of the tool steel, but without affecting the degree of purity of the same disadvantageous, that the mechanical material values are lowered.
  • the tool steel has a defined according to DIN 50 602 K0 value of substantially at most 3.
  • This high degree of purity of the material not only causes a great improvement of the mechanical properties in the tempered state, for example, a significantly increased toughness of the material, but it also the performance characteristics, especially the cutting edge of fine-cut tools for hard objects are skyrocketed.
  • This increase in the quality of the powder metallurgy tool steel articles according to the invention has been found, in particular, to be due to the fact that the small proportion of smaller and the absence of larger non-metallic inclusions minimizes any crack initiation caused by them.
  • Powders prepared by a method according to the invention had a proportion of the total amount of 52% and a proportion of about 72% up to a particle size of up to 100 ⁇ m up to a particle diameter of 63 ⁇ m.
  • powders prepared according to the prior art have proportions of 21.7% and 36.2% for the same classes. If one compares the determined average particle size, this is 61 ⁇ m for powder production according to the invention, whereas in a powder production according to the prior art a more than twice as large average particle size of 141 ⁇ m was determined.
  • Fig. 1 Inventive manufacturing method
  • Fig. 2 Prior art production method
  • Fig. 2 shows, in the comparative powder (prior art) segregation areas with an accumulation of coarse powder grains 1 and 2 fine fractions.
  • the powder produced according to the invention given largely homogeneity.
  • Fig. 3 Powder preparation according to the invention
  • Fig. 4 Comparative powder
  • Tool steels of the type described can, as was surprisingly found from the investigations, be alloyed with sulfur according to the invention up to a content of 0.5 wt .-%, without the content of non-metallic inclusions is substantially increased and a DIN-K0 value of greater than 3 sets.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Manufacture Of Metal Powder And Suspensions Thereof (AREA)

Abstract

Production of thick deformed or non-deformed objects made from tool steel comprises pouring a melt into a metallurgical vessel; conditioning to improve the degree of purity; adjusting the temperature to a value above the formation temperature of primary precipitation in the alloy; forming a powder having an average grain size of 50-70 mu m from the melt at constant temperature by injection nitrogen; disintegrating in the nitrogen stream; grading the powder; collecting, mixing and pouring into a container and compacting by hot isostatic pressing. The parameters of the pressing cycle are adjusted so that the temperature and pressure in the heating process are elevated.

Description

Die Erfindung bezieht sich auf ein Verfahren zur pulvermetallurgischen Herstellung von Gegenständen aus Werkzeugstahl mit verbesserter Homogenität, höherer Reinheit und verbesserten Eigenschaften.The invention relates to a process for powder metallurgy production of tool steel articles having improved homogeneity, higher purity and improved properties.

Weiters bezieht sich die Erfindung auf einen Werkzeugstahl-Gegenstand mit verbessertem Eigenschaftsprofil.Furthermore, the invention relates to a tool steel article with improved property profile.

Werkzeugstähle mit hohen Kohlenstoffkonzentrationen und hohen Gehalten an karbidbildenden Elementen werden für Schneidteile und Komponenten mit hoher Verschleißfestigkeit eingesetzt. Weil nun bei einer Erstarrung derartiger Legierungen in Gießformen Inhomogenitäten sowie grobe primäre und eutektische Karbide gebildet werden, die Fertigungsprobleme und schlechte mechanische Eigenschaften der daraus erstellten Werkzeuge oder Komponenten bewirken, ist eine pulvermetallurgische Herstellung derartiger Teile vorteilhaft.Tool steels with high carbon concentrations and high levels of carbide-forming elements are used for cutting parts and components with high wear resistance. Because in a solidification of such alloys in molds inhomogeneities and coarse primary and eutectic carbides are formed which cause manufacturing problems and poor mechanical properties of the tools or components created therefrom, powder metallurgy production of such parts is advantageous.

Eine pulvermetallurgische Herstellung beinhaltet im wesentlichen ein Verdüsen einer Werkzeugstahlschmelze zu Metallpulver, ein Einbringen und Verdichten des Metallpulvers in einen Behäler bzw. eine Kapsel, ein Verschließen der Kapsel und ein Erwärmen und heißisostatisches Pressen des Pulvers in der Kapsel zu einem dichten homogenen Material.Powder metallurgy production essentially involves atomizing a tool steel melt into metal powder, introducing and compacting the metal powder into a container, sealing the capsule, and heating and hot isostatically pressing the powder in the capsule into a dense homogeneous material.

Bei einem Verdüsen der Schmelze, welches nach dem Stand der Technik vorteilhaft mit Stickstoff erfolgt, werden kleine Metalltröpfchen mit einem hohen Verhältnis von Oberfläche zu Volumen im Gasstrom gebildet, was eine große Abkühl- und Erstarrungsgeschwindigkeit des Flüssigmetalles und dadurch kleine Karbidteilchen in den Pulverkörnern bewirkt. Wie vorher erwähnt, wird in der Folge das zumeinst durch Klopfen in der Kapsel verdichtete Pulver in dieser durch heißisostatisches Pressen bei Temperaturen von zumeist über 1080°C mit einem Druck von größer als 85 MPa zu einem vollkommen dichten Metallkörper ausgeformt. Dieser as-HIPed Metallkörper, der noch einer Warmumformung unterworfen werden kann, weist bei hohem Karbidgehalt eine vorteilhaft geringe Karbidgröße von durchschnittlich 1-3 um und gute mechanische Materialeigenschaften im Vergleich mit einer schmelzmetallurgischen Herstellung auf.In melt atomization, which is advantageously nitrogen-based in the prior art, small metal droplets having a high surface to volume ratio are formed in the gas stream, causing a high rate of cooling and solidification of the liquid metal and thereby small carbide particles in the powder grains. As previously mentioned, the powder compacted at first by tapping in the capsule is then formed therein by hot isostatic pressing at temperatures generally above 1080 ° C, at a pressure of greater than 85 MPa, to form a completely dense metal body. This as-HIPed metal body, which can still be subjected to hot working, has an advantageously low carbide size of 1-3 on average, with a high carbide content um and good mechanical material properties in comparison with a melt metallurgical production on.

Pulvermetallurgisch hergestellte Gegenstände aus Werkzeugstahl besitzen zwar eine durchaus vorteilhafte Struktur mit feinverteilten Karbidphasen; einer unvollständigen Materialisotropie und eines schlechten Reinheitsgrades wegen kann jedoch das erreichbare hohe Gütepotential von PM-Werkstoffen nicht realisiert werden.Although powder metallurgically produced articles made of tool steel have a thoroughly advantageous structure with finely divided carbide phases; However, due to an incomplete material isotropy and a poor degree of purity, the achievable high quality potential of PM materials can not be realized.

Hier will die Erfindung Abhilfe schaffen und setzt sich zum Ziel, den Gütemangel der nach dem Stand der Technik hergestellten Gegenständen aus PM-Werkzeugstahl zu beseitigen und ein Verfahren der eingangs genannten Art anzugeben, mit welchem ein isostatisch gepreßter Metallkörper mit höchster Werkstoffisotropie und geringstem Gehalt an oxidischen Einschlüssen herstellbar ist.Here, the invention seeks to remedy and sets itself the goal of eliminating the lack of quality of the state-of-the-art PM tool steel objects and to provide a method of the type mentioned above, with which an isostatically pressed metal body with the highest material isotropy and lowest content oxide inclusions can be produced.

Weiters zielt die Erfindung auf einen Werkzeugstahl-Gegenstand mit verbesserten Bearbeitungs- und Gebrauchseigenschaften bei erhöhter Einsatzstandzeit ab.Furthermore, the invention aims at a tool steel object with improved processing and service properties with increased service life.

Dieses Ziel wird durch das Verfahren gemäß Anspruch 1 erreicht.This object is achieved by the method according to claim 1.

Die mit dem erfindungsgemäßen Verfahren erreichten Vorteile sind im wesentlichen darin begründet, daß synergetisch vorerst durch metallurgische Arbeit an einer in ein metallurgisches Gefäß eingebrachten Schmelze deren oxidischer Reinheitsgrad entscheidend verbessert und deren Temperatur homogen auf einen vorteilhaften Überhitzungswert eingestellt werden, wonach eine Verdüsung des Flüssigmetalles derart erfolgt, daß der mittlere Korndurchmesser 50 bis 70 µm beträgt. Dadurch wird erreicht, daß einerseits im Pulver der Sauerstoffgehalt überraschend niedrig anfällt und andererseits auch der Feinkornanteil wesentlich im Hinblick auf ein Erreichen einer hohen Klopf- und Rütteldichte in der Kapsel erhöht ist. Wenn nun, wie erfindungsgemäß vorgesehen, das Metallpulver unter Aufrechterhaltung der Stickstoffatmosphäre klassiert, gesammelt, in einen Behälter eingebracht, in diesem verdichtet und der Behälter verschlossen wird, kann keine Oxidation oder Physisorption von Sauerstoff an der Pulverkornoberfläche entstehen.The advantages achieved by the method according to the invention are essentially based on the fact that synergistically improved metallurgical work on a melt introduced into a metallurgical vessel whose oxidic purity significantly and the temperature is adjusted homogeneously to an advantageous overheating value, after which an atomization of the liquid metal takes place in that the mean grain diameter is 50 to 70 μm. This ensures that on the one hand in the powder, the oxygen content is surprisingly low and on the other hand, the fine grain content is substantially increased in terms of achieving a high tapping and Rütteldichte in the capsule. Now, as classified according to the invention, the metal powder classified while maintaining the nitrogen atmosphere, collected, placed in a container, compressed in this and the container is sealed, no oxidation or physisorption of oxygen at the powder grain surface can arise.

Eine erfindungsgemäße Verteilung der Korndurchmesser mit einem Mittelwert im Bereich von 50 bis 70 µm ermöglicht ein Erreichen einer unerwartet hohen Pulverdichte in der Kapsel, so daß einerseits deren Schwindmaß beim heißisostatischen Pressen gering ist und andererseits eine weitgehend vollständige Isotropie des gepreßten dichten Metallkörpers vorliegt. Diese Vorteile werden auch bei Behältergrößen mit einem Durchmesser oder einer Dicke von mehr als 300 mm und einer Länge von größer als 1000 mm erreicht.An inventive distribution of the grain diameter with an average value in the range of 50 to 70 microns allows reaching an unexpectedly high powder density in the capsule, so that on the one hand their shrinkage in hot isostatic pressing is low and on the other hand there is a largely complete isotropy of the pressed dense metal body. These advantages are also achieved with container sizes with a diameter or thickness of more than 300 mm and a length greater than 1000 mm.

Die Parameter für den heißisostatischen Preßzyklus beinhalten ein Aufwärmen des Pulvers im Behälter bei im wesentlichen gleichen Anstieg von Temperatur und Druck, wodurch schon in dieser Phase, wie sich gezeigt hat, eine Erhöhung der Materialdichte und Homogenität erreicht werden. Der anschließende Preßvorgang erfolgt im Temperaturbereich von 1100°C bis 1180°C bei einem Druck von 90 MPa und größer mit einer Zeitdauer von mindestens drei Stunden, gefolgt von einer langsamen Abkühlung des Preßkörpers. Niedrigere Preßtemperaturen als 1100°C und Drücke unter 90 MPa sowie geringere Preßzeiten als drei Stunden können Ungänzen im Werkstoff bewirkenThe parameters for the hot isostatic press cycle involve warming up the powder in the container with substantially the same increase in temperature and pressure, which has already been shown to increase the Material density and homogeneity can be achieved. The subsequent pressing is carried out in the temperature range of 1100 ° C to 1180 ° C at a pressure of 90 MPa and greater with a period of at least three hours, followed by a slow cooling of the compact. Lower pressing temperatures than 1100 ° C and pressures below 90 MPa and less pressing times than three hours can cause discontinuities in the material

Der Preßkörper weist nach dem HIPen eine vollständig dichte Materialstruktur auf, kann also in diesem Zustand oder nach einer Warmumformung zu einem Werkzeug verarbeitet werden.The pressed body has a completely dense material structure after HIPing, so it can be processed into a tool in this state or after hot working.

Für die hohe Güte des nach dem Verfahren gemäß der Erfindung pulvermetallurgisch hergestellten Werkzeugstahl- Gegenstandes ist dessen niedriger Gehalt an Einschlüssen sowie die geringe Einschlußgröße kennzeichnend. Der hohe oxidische Reinheitsgrad, der mit einem K0-Wert nach DIN 50 602 von im wesentlichen höchstens 3 dokumentiert ist, führt nicht nur zu stark verbesserten mechanischen Eigenschaften, insbesondere bei erhöhten Einsatztemperaturen, des Werkstoffes in allen Beanspruchungsrichtungen. sondern verbessert auch dessen Gebrauchseigenschaften, vorzugsweise die Schneidhaltigkeit von Feinschnitt-Werkzeugen, in hohem Maße.For the high quality of the powder metallurgically produced by the process according to the invention tool steel object whose low content of inclusions and the low inclusion size is characteristic. The high degree of oxidic purity, which is documented with a K0 value according to DIN 50 602 of substantially at most 3, not only leads to greatly improved mechanical properties, in particular at elevated operating temperatures, of the material in all directions of stress. but also improves its performance properties, preferably the cutting edge of fine-cut tools, to a great extent.

Eine besonders markante Gütesteigerung des Gegenstandes wird bei dessen Herstellung nach dem erfindungsgemäßen Verfahren erreicht, wenn die Schmelze aus einer Eisenbasislegierung enthaltend in Gew.-% Kohlenstoff (C) 0,52 bis 3,74 Mangan (Mn) bis 2,9 Chrom (Cr) bis 21,0 Molybdän (Mo) bis 10,0 Nickel (Ni) gegebenenfalls bis 1,0 Kobalt (Co) bis 20,8 Vanadin (V) bis 14,9 Niob(Nb) Tantal (Ta) einzeln oder in Summe bis 2,0 Wolfram (W) bis 20,0 Schwefel (S) bis 0,5 sowie Begleitelemente bis zu einer Summenkonzentration von 4,8 und Verunreinigungen und Eisen als Rest, gebildet ist.
Obige chemische Zusammensetzung des Werkzeugstahles beinhaltet besonders karbidreiche Werkzeugstähle mit hoher Abriebfestigkeit und hoher Schneidhaltigkeit der daraus gefertigten Werkzeuge. Da hohe Karbidanteile in der Regel die mechanischen Eigenschaften des Werkstoffes verschlechtern, ist deren grundsätzliche Verbesserung durch das erfindungsgemäße Verfahren von besonderer Bedeutung. Es hat sich gezeigt, daß diese hohen mechanischen Kennwerte, insbesondere die der Schlagbiegezähigkeit des Materials, synergetisch durch den kleinen mittleren Korndurchmesser des Pulvers, eine homogene dichte Schüttung desselben in der Kapsel und durch den hohen oxidischen Reinheitsgrad bei isotroper Struktur des heißisostatisch gepreßten Gegenstandes begründet sind.A particularly significant increase in the quality of the article is achieved in its production by the process according to the invention, when the melt of an iron-based alloy containing in wt .-% Carbon (C) 0.52 to 3.74 Manganese (Mn) to 2.9 Chrome (Cr) to 21.0 Molybdenum (Mo) to 10.0 Nickel (Ni) optionally to 1.0 Cobalt (Co) to 20.8 Vanadin (V) to 14.9 Niobium (Nb) Tantalum (Ta) singly or in total to 2.0 Tungsten (W) to 20.0 Sulfur (S) to 0.5 and accompanying elements up to a cumulative concentration of 4.8 and impurities and iron as the remainder.
The above chemical composition of the tool steel includes particularly carbide-rich tool steels with high abrasion resistance and high cutting strength of the tools produced therefrom. Since high carbide contents usually worsen the mechanical properties of the material, their fundamental improvement by the method according to the invention is of particular importance. It has been found that these high mechanical properties, in particular the impact resistance of the material, are due to the small mean grain diameter of the powder, a homogeneous dense bed of the same in the capsule and the high degree of oxidic purity in isotropic structure of the hot isostatically pressed article ,

Der oxidische Reinheitsgrad des Flüssigmetalles kann durch eine metallurgische Arbeit wirkungsvoll verbessert werden, wenn eine Konditionierung der Schmelze im metallurgischen Gefäß bei einer induzierten turbulenten Strömung derselben und bei einer vollständigen Abdeckung des Metallbades durch flüssige Schlacke, welche insbesondere mittels direkten Stromdurchganges beheizt wird, während einer Zeit von mindestens 15 Minuten erfolgt. Dabei wird eine Abgabe von Sauerstoffverbindungen bzw. Oxiden aus der Schmelze und eine Aufnahme derselben in die heiße Schlacke gefördert, wobei die induzierte Strömung des Metallbades die Effizienz steigert. Per se ist bekannt, eine Strömung von Flüssigmetall in einem metallurgischen Gefäß mittels Einleitens von Argon-Spülgas durch mindestens einen bodenseitig angeordneten gasdurchlässigen Spülstein zu erreichen. Es ist jedoch wichtig, um eine Reoxidation der Schmelze zu verhindern, daß deren Abdeckung durch flüssige Schlacke auch bei Schmelzenbewegungen vollständig erhalten bleibt. Um Probleme beim Einsatz eines Spülsteines im Hinblick auf die Zuverlässigkeit einer Ausbildung einer kontrollierten und effizienten Metallströmung sowie um Schwierigkeiten bei der Spül- bzw. Rührgaszufuhr, wobei kleine Gasmengen wenig metallurgische Wirkung zeigen, jedoch hohe Gasmengen Oberflächenteile der Schmelze schlackenfrei erstellen und oxidieren sowie Schlackenpartikel in den Stahl einmischen können, zu vermeiden, ist es bevorzugt, elektromagnetische Mittel, zum Beispiel elektromagnetische Rührspulen, für eine Induzieren einer turbulenten Strömung im Flüssigmetall einzusetzen. Höchst vorteilhaft kann dabei auch eine Einstellung und gleichmäßige Verteilung der Temperatur des Metallbades mittels einer Einbringung von Wärmeenergie in die Schlacke durch elektrischen Stromdurchgang erfolgen.The oxidic purity of the liquid metal can be effectively improved by metallurgical work, when conditioning the melt in the metallurgical vessel at an induced turbulent flow thereof and at a complete coverage of the metal bath by liquid slag, which is heated in particular by direct passage of current, during a time of at least 15 minutes. In this case, a release of oxygen compounds or oxides is promoted from the melt and a recording of the same in the hot slag, wherein the induced flow of the metal bath increases the efficiency. It is known per se to achieve a flow of liquid metal in a metallurgical vessel by introducing argon purge gas through at least one gas permeable purge plug arranged on the bottom side. However, it is important to prevent reoxidation of the melt that their coverage by liquid slag is completely retained even during melting movements. Problems with the use of a purging plug with regard to the reliability of formation of a controlled and efficient metal flow and difficulties in the purging or stirring gas supply, with small amounts of gas show little metallurgical effect, but high levels of gas create surface elements of the melt without slag and oxidize and slag particles in to prevent the steel from being mixed in, it is preferable to use electromagnetic means, for example electromagnetic stirring coils, for inducing a turbulent flow in the liquid metal. In this case, adjustment and uniform distribution of the temperature of the metal bath by means of introduction of thermal energy into the slag by electrical current passage can also be extremely advantageous.

In einer weiteren Ausgestaltung der Erfindung ist vorgesehen, daß die konditionierte Schmelze durch einen Düsenkörper im metallurgischen Gefäß mit einem Schmelzenstromdurchmesser von 4,0 bis 10,0 mm in eine Verdüsungskammer eingebracht und in dieser mit mindestens drei aufeinander folgenden aus Stickstoff, mit einem Reinheitsgrad von mind. 99,999% Stickstoff, gebildeten Gasstrahlen mit der Maßgabe beaufschlagt wird, daß die letzte Beaufschlagung des Schmelzenstromes durch einen Gasstrahl erfolgt., der zumindest stellenweise eine Geschwindigkeit aufweist, die größer als die Schallgeschwindigkeit ist. Eine Einhaltung des Schmelzenstromdurchmessers und die hohe kinetische Energie der Gasbeaufschlagung des Metallstromes bewirken eine günstige Kornverteilung und eine gewünschte Feinheit des erstellten Metallpulvers. Die Konditionierung und die Einstellung der Temperatur des Flüssigmetalles im metallurgischen Gefäß sowie der hohe Reinheitsgrad des Zerstäubungsgases Stickstoff sind weiters die Ursachen für einen überraschend hohen Reinheitsgrad bzw. einen geringen Sauerstoffanteil des Pulvers und in der Folge des heißisostatisch gerpeßten Blockes.In a further embodiment of the invention it is provided that the conditioned melt introduced through a nozzle body in the metallurgical vessel with a melt flow diameter of 4.0 to 10.0 mm in a Verdüsungskammer and in this with at least three successive nitrogen, with a purity of At least 99.999% nitrogen, formed gas jets is acted upon with the proviso that the last loading of the melt stream is effected by a gas jet, which at least in places has a speed which is greater than the speed of sound. Compliance with the melt flow diameter and the high kinetic energy of the gas flow of the metal stream cause a favorable particle size distribution and a desired fineness of the metal powder produced. The conditioning and adjustment of the temperature of the liquid metal in the metallurgical vessel and the high degree of purity of the sputtering gas nitrogen are further the causes of a surprisingly high degree of purity or a low oxygen content of the powder and as a result of the Heißisostatisch gerpeßten block.

Weil auch geringe Anteile an Grobkorn im Metallpulver, insbesondere beim Befüllen der Kapsel und beim Verdichten des Pulvers in dieser, Entmischungen bewirken können, ist von Vorteil, wenn der Durchmesser der Pulverkörner verdüsungstechnisch auf einen Maximalwert von 500 µm eingestellt oder klassiert wird.Because even small amounts of coarse grain in the metal powder, in particular during filling of the capsule and during compacting of the powder in this, can cause segregation, is advantageous if the diameter of the powder grains atomization technology is adjusted or classified to a maximum value of 500 microns.

Allenfalls kann zur Sicherstellung einer homogenen Schüttung und zur Gütesteigerung des Erzeugnisses nach der Erfindung vorgesehen sein, daß das in einem Bereitstellungsraum gesammelte Pulver durch Stickstoff fluidisiert und gemischt und bei Aufrechterhaltung der Stickstoffatmosphäre in einen Behälter bzw. eine Kapsel mit einem Gesamtgewicht von größer als 0,5 t eingebracht, durch mechanische Stöße verdichtet und gasdicht eingeschlossen wird.At best, to ensure a homogeneous bed and increase the product of the invention, it may be provided that the powder collected in a staging area is fluidized and mixed by nitrogen and, while maintaining the nitrogen atmosphere, in a container or capsule having a total weight greater than 0, 5 t introduced, by mechanical shocks compressed and sealed gas-tight.

Derart kann sichergestellt werden, daß, wenn in wirtschaftlich günstiger Weise das homogenisierte Pulver in einen Behälter bzw. in eine Kapsel mit einem Durchmesser bzw. einer Dicke von gleich oder größer 400 mm und einer Länge von mindestens 1000 mm eingebracht wird, bei Anwendung der vorhin genannten Parameter für den heißisostatischen Preßzyklus der hergestellte Block Homogenität und vollkommene Materialdichte erlangt.It can thus be ensured that, when the homogenized powder is introduced in an economically favorable manner into a container or into a capsule with a diameter or a thickness of equal to or greater than 400 mm and a length of at least 1000 mm, using the above said parameters for the hot isostatic pressing cycle of the produced block obtained homogeneity and perfect material density.

Wenn die pulvergefüllte Kapsel im kalten Zustand in eine HIP-Einrichtung eingebracht wird und eine darauffolgende Erwärmung der Pulverkapsel unter allseitigem Umgebungsdruck erfolgt, kann einerseits die Durchwärmungszeit auf Grund einer angehobenen Wärmeleitung verkürzt und die Pulvermasse im Hinblick auf eine weitgehend vollständige Isotropie des Blockes vorverdichtet werden.If the powder-filled capsule is introduced into a HIP device in the cold state and subsequent heating of the powder capsule under ambient atmospheric pressure, on the one hand the heat-soaking time can be shortened due to increased heat conduction and the powder mass can be precompressed with respect to a substantially complete block isotropy.

Es kann, wie sich gezeigt hat, in bestimmten Fällen zur Unterstützung der Konsolidierung günstig sein, wenn die Anwärmung und/oder der Preßvorgang des Pulvers bei konstanter, gegebenenfalls sich gleichmäßig ändernder, um einen Mittelwert pendelnder Temperaturbeaufschlagung durchgeführt wird und der Preßvorgang bei einer Temperatur von mindestens 1140°C, höchstens jedoch von 1170°C, erfolgt.It may be found to be beneficial in certain cases to assist in consolidation when the heating and / or pressing of the powder is carried out at constant, possibly uniformly varying, averaging temperature application and the pressing at a temperature of at least 1140 ° C, but not more than 1170 ° C.

Auf Grund der verbesserten Materialeigenschaften ist es möglich und es kann insbesondere zur Kostenminimierung vorteilhaft sein, wenn der erfindungsgemäß pulvermetallurgisch hergestellte Block im Zustand as-HIPed oder bei geringster, aus wirtschaftlichen Gründen durchzuführender Verformung als Vormaterial für Werkzeuge oder Werkzeugteile eingesetzt wird.Due to the improved material properties, it is possible and it may be particularly advantageous for cost minimization, if the invention powder-metallurgically produced block in the as-HIPed state or with minimal, carried out for economic reasons deformation is used as a starting material for tools or tool parts.

Das weitere Ziel der Erfindung, einen Werkzeugstahlgegenstand mit verbesserten Bearbeitungs- und Gebrauchseigenschaften bei erhöhter Einsatzstandzeit zu schaffen, wird bei einem pulvermetallurgisch hergestellten Gegenstand aus Werkzeugstahl mit verbesserten Werkstoffeigenschaften bestehend aus einer Eisenbasislegierung enthaltend in Gew.-% Kohlenstoff (C) 0,52 bis 3,74 Mangan (Mn) bis 2,9 Chrom (Ce) bis 21,0 Molybdän (Mo) bis 10,0 Nickel (Ni) gegebenenfalls bis 1,0 Kobalt (Co) bis 20,8 Vanadin (V) bis 14,9 Niob (Nb) Tantal (Ta) einzeln oder in Summe bis 2,0 Wolfram (W) bis 20,0 Schwefel (S) bis 0,5 sowie Begleitelemente bis zu einer Summenkonzentration von 4,8 und Verunreinigungen und Eisen als Rest, welcher Werkstoff nach DIN 50 602 einen K0-W von höchstens 3 aufweist, erreicht.The further object of the invention to provide a tool steel article with improved processing and service properties with increased service life, is in a powder metallurgy tool made of tool steel with improved material properties consisting of an iron-based alloy containing in wt .-% Carbon (C) 0.52 to 3.74 Manganese (Mn) to 2.9 Chromium (Ce) to 21.0 Molybdenum (Mo) to 10.0 Nickel (Ni) optionally to 1.0 Cobalt (Co) to 20.8 Vanadin (V) to 14.9 Niobium (Nb) Tantalum (Ta) singly or in total to 2.0 Tungsten (W) to 20.0 Sulfur (S) to 0.5 and accompanying elements up to a total concentration of 4.8 and impurities and iron as the remainder, which material according to DIN 50 602 has a K0-W of at most 3, achieved.

Werkzeugstähle haben ein breites Spektrum der Konzentration der jeweiligen Legierungselemente, wobei diese immer in Wechselwirkung stehen und im Hinblick auf den Kohlenstoffgehalt zu sehen sind. Geringere Kohlenstoffgehalte als 0,52 Gew.-% führen zu einem niedrigen Karbidanteil und/oder zu einer geringen Matrixhärte im thermisch vergüteten Zustand des Stahles, wohingegen höhere Gehalte als 3,74 Gew.-% Kohlenstoff, auch bei einer pulvermetallurgischen Herstellung, den Werkstoff für eine Verwendung als Werkzeug auf Grund des mechanischen Eigenschaftsprofiles weitgehend ausschließen.Tool steels have a wide range of the concentration of the respective alloying elements, which always interact and are seen in terms of carbon content. Lower carbon contents than 0.52 wt .-% lead to a low carbide content and / or low matrix hardness in the thermally tempered state of the steel, whereas higher than 3.74 wt .-% carbon, even in a powder metallurgical production, the material largely preclude use as a tool due to the mechanical property profile.

Von besonderer Bedeutung für eine gute Härtbarkeit und die erreichbaren mechanischen und chemischen Eigenschaften der Gegenstände sind die Elemente Mn und Cr, wobei Gehalte über 2 Gew.-% Mn und über 21 Gew.-% Cr zu einem Abfall der für die Werkzeuge erforderlichen Materialwerte führen.Of particular importance for good hardenability and the achievable mechanical and chemical properties of the articles are the elements Mn and Cr, wherein contents of more than 2 wt .-% Mn and over 21 wt .-% Cr lead to a decrease in the material values required for the tools ,

Die hohe Affinität zu Kohlenstoff der Elemente Mo, V, Nb/Ta und W bewirkt in entsprechenden Anteilen eine gewünschte Karbid- und Mischkarbidausbildung in einer legierten Matrix. In der obigen Reihenfolge der Elemente sollen jedoch die Konzentrationswerte in Gew.-% 10,0;14,9; 2,0; 20,0 nicht überschritten werden, weil dadurch einerseits ein gewünschtes Vergütungsverhalten und andererseits die Herstellbarkeit und die vorgesehenen mechanischen Eigenschaften der Werkstoffe nicht erreicht werden können.
Ni kann gegebenenfalls ohne nachteilige Wirkung bis zu einem Gehalt von 1,0 Gew.-% in der Legierung vorliegen
Co steigert die Warmhärte und Schneidhaltigkeit der Werkzeuge , wirkt jedoch ab einem Gehalt von 20,8 Gew.-% eigenschaftsverschlechternd.. Schwefelgehalte bis 0,5 Gew.-% verbessern die Zerspanbarkeit des Werkzeugstahles, ohne jedoch den Reinheitsgrad desselben derartig nachteilig zu beeinflussen, daß die mechanischen Materialwerte erniedrigt sind.The high affinity for carbon of the elements Mo, V, Nb / Ta and W causes in appropriate proportions a desired carbide and Mischkarbidausbildung in an alloyed matrix. In the above order of the elements, however, the concentration values in wt% 10.0, 14.9; 2.0; 20.0 will not be exceeded because On the one hand a desired compensation behavior and on the other hand, the manufacturability and the intended mechanical properties of the materials can not be achieved.
Ni may optionally be present in the alloy without adverse effect up to a content of 1.0% by weight
Co increases the hot hardness and cutting strength of the tools, but has a property of 20.8 wt .-% property-degrading .. Sulfur contents up to 0.5 wt .-% improve the machinability of the tool steel, but without affecting the degree of purity of the same disadvantageous, that the mechanical material values are lowered.

Erfindungsgemäß weist der Werkzeugstahl einen nach DIN 50 602 definierten K0-Wert von im wesentlichen höchstens 3 auf. Dieser hohe Reinheitsgrad des Werkstoffes bewirkt nicht nur eine große Verbesserung der mechanischen Eigenschaften im vergüteten Zustand, beispielsweise eine wesentlich gesteigerte Zähigkeit des Materials, sondern es sind auch die Gebrauchseigenschaften, insbesondere die Schneidhaltigkeit von Feinschnitt- Werkzeugen für harte Gegenstände sprunghaft angehoben. Diese Gütesteigerung der erfindungsgemäßen pulvermetallurgisch hergestellten Gegenstände aus Werkzeugstahl ist, wie gefunden wurde, insbesondere darin begründet, daß der geringe Anteil an kleineren und das Fehlen von größeren nichtmetallischen Einschlüssen eine von diesen bewirkte Rißinitiation minimiert.According to the tool steel has a defined according to DIN 50 602 K0 value of substantially at most 3. This high degree of purity of the material not only causes a great improvement of the mechanical properties in the tempered state, for example, a significantly increased toughness of the material, but it also the performance characteristics, especially the cutting edge of fine-cut tools for hard objects are skyrocketed. This increase in the quality of the powder metallurgy tool steel articles according to the invention has been found, in particular, to be due to the fact that the small proportion of smaller and the absence of larger non-metallic inclusions minimizes any crack initiation caused by them.

Im folgenden wird die Erfindung anhand von Untersuchungsergebnissen näher erläutert:

  • Von Kaltarbeitsstählen und Schnellarbeitsstählen mit Kohlenstoffgehalten C von größer als 2,2 Gew.-%, ca 12,5 Gew.-% Cr und über 4,0 Gew.-% V bzw. 1,1 bis 1,4 Gew.-% C, ca 4,3 Gew.-% Cr, ca 5 Gew.-% Mo, 3 bis 5 Gew.-% V, 5,8 bis 6,5 Gew.-% W, gegebenenfalls bis 9 Gew.-% Co Rest jeweils Eisen und Verunreinigungen wurden zur Erprobung 50 Stück 8 t Chargen geschmolzen, in ein mit einer Verdüsungskammer verbundenes metallurgisches Gefäß eingebracht, mit reaktiver Schlacke abgedeckt und diese mittels Elektroden bei direktem Stromdurchgang beheizt. In einem Zeitraum von 15 bis 45 Minuten erfolgte ein Konditionieren der Schmelze bei einem induktiven turbulenten Rühren derselben, wobei der Schmelzenspiegel immer mit heißer Schlacke abgedeckt war. Danach wurde eine Bohrung in einem Düsenkörper des metallurgischen Gefäßes freigesetzt und ein in die Verdüsungskammer eintretender Schmelzenstrom mit einem Durchmesser von 4,0 bis 10,0 mm mittels aufeinanderfolgenden Stickstoff-Gasstrahlen beaufschlagt, wobei der letzte Gasstrahl mit Überschallgeschwindigkeit aus der Düse austrat, auf das Flüssigmetall gerichtet war und dieses in Tröpfchen zerteilte. In der Verdüsungskammer erfolgte eine Erstarrung der Tröpfchen zu Pulverkörnern in Stickstoff mit einem Reinheitsgrad von 99,999 %. Die Stickstoffatmosphäre über dem Pulver wurde auch bei einem Klassieren und Sammeln desselben aufrechterhalten, wobei aus dem Sammelbehälter jeweils Proben zur Klassierung der Pulverpartikel gezogen wurden.
The invention will be explained in more detail below on the basis of examination results:
  • Cold work steels and high speed steels with carbon contents C greater than 2.2% by weight, approx. 12.5% by weight Cr and above 4.0% by weight V or 1.1 to 1.4% by weight C, about 4.3 wt.% Cr, about 5 wt.% Mo, 3 to 5 wt.% V, 5.8 to 6.5 wt.% W, optionally up to 9 wt Residual ferrous and impurities were melted for testing 50 pieces 8 t batches, placed in a metallurgical vessel connected to a Verdüsungskammer, covered with reactive slag and heated by means of electrodes in direct current passage. In a period of 15 to 45 minutes took place Conditioning the melt with inductive turbulent stirring thereof, the melt level always being covered with hot slag. Thereafter, a bore was released in a nozzle body of the metallurgical vessel, and a 4.0 to 10.0 mm diameter melt stream entering the atomization chamber was impinged by successive nitrogen gas jets, with the last gas jet emerging from the nozzle at supersonic velocity Liquid metal was directed and this divided into droplets. In the atomization chamber, the droplets solidified into powder grains in nitrogen with a purity of 99.999%. The nitrogen atmosphere over the powder was also maintained in classifying and collecting it, drawing samples from each of the collection containers to classify the powder particles.

Vom Sammelbehälter erfolgte ein Einbringen des Pulvers in einen Behälter bzw. eine Kapsel aus unlegiertem Stahl, wobei durch ein Rütteln bzw. Beklopfen desselben bzw. derselben eine Verdichtung der Pulverfüllung und nachfolgend ein Verschließen der Kapsel vorgenommen wurden. Die mit verdichtetem Legierungspulver gefüllte Kapsel mit einem Durchmesser von 420 mm⌀ und einer Länge von 2000 mm wurde im kalten Zustand in die HIP-Anlage eingebracht, wonach der Druck und die Temperatur gleichzeitig erhöht wurden. Ein heißisostatisches Pressen erfolgte bei einer Temperatur von 1155°C mit einem Druck von 105 MPa in einer Zeitspanne von 3,85 Stunden, wonach der Preßkörper langsam abgekühlt wurde. Nach einer Warmumformung mit 0,2-fachen bis 8,1-fachem Verformungsgrad erfolgte aus den Schmiedestücken eine Entnahme von Proben.An introduction of the powder into a container or a capsule made of unalloyed steel was carried out from the collecting container, a compaction of the powder filling and subsequently a closure of the capsule being carried out by shaking or tapping thereof. The compacted alloy powder capsule with a diameter of 420 mm⌀ and a length of 2000 mm was placed in the cold state in the HIP system, after which the pressure and the temperature were simultaneously increased. A hot isostatic pressing was carried out at a temperature of 1155 ° C with a pressure of 105 MPa in a period of 3.85 hours, after which the compact was slowly cooled. After hot forming with 0.2 to 8.1 times the degree of deformation, the forgings were sampled.

Die bei Verwendung des erfindungsgemäßen Verfahrens aus dem Sammelbehälter entnommenen 50 Pulverproben wurden einer Siebanalyse unterworfen. Die Ergebnisse und zwar der jeweilig durchschnittliche Pulveranteil in den einzelnen Partikelklassen ist in der Tabelle 1 ( Kornverteilung der Metallpulver) in Gegenüberstellung mit 92 Ergebnissen bei Verwendung von Verfahren nach dem Stand der Technik wiedergegeben. Tab. 1 :Kornverteilung der Metallpulver, Anteil der Partikelklassen im Metallpulver, mittlere Partikelgröße Partikelklasse Mikron Verfahren gemäß der Erfindung Anteil in % Vergleichsverfahren Stand der Technik Anteil in % 0-45 31,5 12,7 46-63 20,5 9,0 64-75 8,7 5,3 76-100 11,0 9,2 101-125 7,6 9,8 126-180 9,5 14,0 181-250 6,0 13,2 251-355 3,7 12,8 355-500 1,5 14,0 Mittlere Partikelgröße 61µm 141µm The 50 powder samples taken from the collection container using the method according to the invention were subjected to sieve analysis. The results, namely the respective average powder content in the individual particle classes, are given in Table 1 (grain distribution of the metal powders) in comparison with 92 results using methods according to the prior art. Tab. 1: Grain distribution of the metal powders, proportion of particle classes in the metal powder, mean particle size Particle class micron Process according to the invention Share in% Comparative method Prior art Share in% 0-45 31.5 12.7 46-63 20.5 9.0 64-75 8.7 5.3 76-100 11.0 9.2 101-125 7.6 9.8 126-180 9.5 14.0 181-250 6.0 13.2 251-355 3.7 12.8 355-500 1.5 14.0 Mean particle size 61μm 141μm

Pulver, welche mit einem Verfahren nach der Erfindung erstellt waren, besaßen bis zu einem Korndurchmesser von 63 um einen Anteil an der Gesamtmenge von 52% und einen Anteil von ca 72% bis zu einer Korngröße bis 100µm. Pulver, hergestellt nach dem Stand der Technik, weisen hingegen für die gleichen Klassen Anteile von 21,7 % und 36,2 % auf. Vergleicht man die ermittelte mittlere Partikelgröße, so ist diese bei erfindungsgemäßer Pulverherstellung 61 µm, wohingegen bei einer Pulverfertigung nach dem Stand der Technik eine mehr als doppelt so große mittlere Partikalgröße von 141 µm ermittelt wurde.Powders prepared by a method according to the invention had a proportion of the total amount of 52% and a proportion of about 72% up to a particle size of up to 100 μm up to a particle diameter of 63 μm. By contrast, powders prepared according to the prior art have proportions of 21.7% and 36.2% for the same classes. If one compares the determined average particle size, this is 61 μm for powder production according to the invention, whereas in a powder production according to the prior art a more than twice as large average particle size of 141 μm was determined.

In Fig. 1 ( erfindungsgemäßes Herstellverfahren) und Fig. 2 ( Herstellverfahren nach dem Stand der Technik) sind Pulver in loser Schüttung dargestellt. Bei einer derartigen Schüttung treten, wie Fig. 2 zeigt, im Vergleichspulver (Stand der Technik) Entmischungsbereiche mit einer Häufung von groben Pulverkörnern 1 und feinen Fraktionen 2 auf. Hingegen ist beim erfindungsgemäß gefertigten Pulver weitgehend Homogenität gegeben. Gleiches gilt für Fig. 3 ( Pulvererstellung nach der Erfindung) und Fig. 4 ( Vergleichspulver) nach dem Stand der Technik.In Fig. 1 (Inventive manufacturing method) and Fig. 2 (Prior art production method) are shown in bulk powder. In such a bedding occur as Fig. 2 shows, in the comparative powder (prior art) segregation areas with an accumulation of coarse powder grains 1 and 2 fine fractions. On the other hand, the powder produced according to the invention given largely homogeneity. The same applies to Fig. 3 (Powder preparation according to the invention) and Fig. 4 (Comparative powder) according to the prior art.

Von den 50 Rohlingen mit jeweils unterschiedlicher chemischer Zusammensetzung, hergestellt nach dem erfindungsgemäßen Verfahren wurden nach einer Warmverformung Proben entnommen und deren Reinheitsgrad bzw. Gehalt an nichtmetallischen Einschlüssen nach DIN 50 602 und ASTM E 45 /85 Meth.D untersucht. Diese Ergebnisse wurden wiederum mit Ergebnissen von 92 Proben aus artgleichen Werkstoffen, jedoch hergestellt nach dem Stand der Technik, verglichen uns sind in Tabelle 2 ( Einschlußgehalt von PM-Werkzeugstählen K0) und Tabelle 4 ( Einschlußgehalt von PM-Werkzeugstählen nach ASTM-Wert) wiedergegeben. Tab.2: Einschlußgehalt von PM-Werkzeugstählen K0 ( DIN 50 602) Werkzeugstahl gem.Erfindung Werkzeugstahl gem.Stand der Technik K0 Anzahl der Proben Anteil % Anzahl der Proben Anteil % 0 28 56,0 15 16,3 1 18 36,0 28 30,4 2 3 6,0 19 20.7 3 1 2,0 12 13,0 4 7 7,6 5 2 2,2 6 3 3,3 7 1 1,1 8 9 10 11 12 1 1,1 13 1 1,1 14 1 1,1 15 1 1,1 16 17 18 1 1,1 19 20 Summe 50 100 92 100 Of the 50 blanks each having a different chemical composition prepared by the process according to the invention, samples were taken after a hot deformation and their degree of purity or content of non-metallic inclusions according to DIN 50 602 and ASTM E 45/85 Meth.D examined. These results were again compared to results from 92 samples of similar materials but made according to the prior art and are shown in Table 2 (inclusion content of PM tool steels K0) and Table 4 (inclusion content of PM tool steels according to ASTM value) , Table 2: Inclusion content of PM tool steels K0 (DIN 50 602) Tool steel gem.Erfindung Tool steel according to the state of the art K0 Number of samples Proportion of % Number of samples Proportion of % 0 28 56.0 15 16.3 1 18 36.0 28 30.4 2 3 6.0 19 20.7 3 1 2.0 12 13.0 4 7 7.6 5 2 2.2 6 3 3.3 7 1 1.1 8th 9 10 11 12 1 1.1 13 1 1.1 14 1 1.1 15 1 1.1 16 17 18 1 1.1 19 20 total 50 100 92 100

Bei einer Auswertung des Einschlußgehaltes im Werkstoff nach DIN 50 602 Verfahren K0 wurden bei Werkzeugstählen gemäß der Erfindung Gesamt-Summenkennwerte bis höchstens 3 mit einem Anteil bei diesem Wert von 2% ermittelt. Hingegen zeigten, wie aus Tabelle 2 ersichtlich ist, Werkzeugstähle, erstellt nach dem Stand der Technik, einen wesentlich höheren Gehalt an nichtmetallischen Einschlüssen mit vergleichsweise großem Durchmesser. Eine graphische Darstellung der Ergebnisse dieser Auswertung ist in Fig. 5 gezeigt, wobei auf der Abszisse die Summenkennwerte und auf der Ordinate deren Anteil in % aufgetragen sind. Daher zeigt die Kurve A den erfindungsgemäßen Werkstoff und die Kurve B einen Stahl hergestellt gemäß dem Stand der Technik.In an evaluation of the inclusion content in the material according to DIN 50 602 method K0 tool aggregates according to the invention total sum values were determined to a maximum of 3 with a share at this value of 2%. On the other hand, as shown in Table 2, tool steels made according to the prior art showed a much higher content of non-metallic inclusions with a comparatively large diameter. A graphical representation of the results of this evaluation is in Fig. 5 in which the abscissa represents the sum characteristic values and the ordinate their proportion in%. Therefore, curve A shows the material according to the invention and curve B shows a steel made according to the prior art.

Eine weitere Untersuchung des Gehaltes an nichtmetallischen Einschlüssen in pulvermetallurgisch hergestellten Werkzeugstählen erfolgte nach ASTM E 45/85 Meth.D.Further investigation of the content of non-metallic inclusions in tool steels produced by powder metallurgy was carried out according to ASTM E 45/85 Meth.D.

Wie aus der Tabelle 3 hervorgeht, wurde an 50 Mustern von erfindungsgemäß gefertigtem Material ( Kurve A) bei einer Probenanzahl 3 und einem Anteil von 6,0 % ein höchster ASTM-Wert von 1,5 ermittelt. Mit einem ASTM-Wert 0,5 lag der Anteil bei 68 %. Das Vergleichsmaterial, gefertigt nach dem Stand der Technik wies einen höheren Gehalt und gröbere Einschlüsse ( Kurve B) auf, was graphisch auch in Fig. 6 dargestellt ist, wobei auf der Abszisse wiederum der ASTM-Wert und auf der Ordinate der prozentuale Anteil aufgetragen wird. Tabelle 3: Einschlußgehalt von PM-Werkzeugstählen (ASTM E 45 /85 Meth. D) Werkzeugstahl gem. Erfindung Werkzeugstahl gem. Stand der Technik ASTM-Werte Anzahl Proben Anteil % Anzahl Proben Anteil % 0,5 34 68,0 24 26,1 1,0 13 26,0 35 38,0 1,5 3 6,0 22 23,9 2,0 6 6,5 2,5 4 4,4 3,0 1 1,1 Summe 50 100 92 100 As can be seen from Table 3, a maximum ASTM value of 1.5 was determined on 50 samples of material produced according to the invention (curve A) with a number of samples 3 and a proportion of 6.0%. With an ASTM value of 0.5, the proportion was 68%. The comparison material produced according to the prior art had a higher content and coarser inclusions (curve B), which is also shown graphically in FIG Fig. 6 is plotted on the abscissa again the ASTM value and on the ordinate the percentage fraction. Table 3: Inclusion content of PM tool steels (ASTM E 45/85 Meth. D) Tool steel acc. invention Tool steel acc. State of the art ASTM values Number of samples Proportion of % Number of samples Proportion of % 0.5 34 68.0 24 26.1 1.0 13 26.0 35 38.0 1.5 3 6.0 22 23.9 2.0 6 6.5 2.5 4 4.4 3.0 1 1.1 total 50 100 92 100

Werkzeugstähle der bezeichneten Art können, wie aus den Ermittlungen überraschend gefunden wurde, erfindungsgemäß bis zu einem Gehalt von 0,5 Gew.-% mit Schwefel legiert sein, ohne daß der Gehalt an nichtmetallischen Einschlüssen wesentlich erhöht ist und sich ein DIN-K0-wert von größer als 3 einstellt.Tool steels of the type described can, as was surprisingly found from the investigations, be alloyed with sulfur according to the invention up to a content of 0.5 wt .-%, without the content of non-metallic inclusions is substantially increased and a DIN-K0 value of greater than 3 sets.

Claims (14)

  1. Process for the powder metallurgical production of dense, formed or unformed objects from highly pure tool steel having a K0 value in accordance with DIN 50 602 of substantially at most 3, wherein a melt is introduced into a metallurgical vessel and is conditioned therein, the oxidic purity thereof being improved and the temperature being adjusted to a value above the temperature at which primary deposits are formed in the alloy, after which, at a temperature that is held substantially constant, a powder having an average grain diameter of 50 to 70 µm is produced from this melt by atomisation in an atomising chamber by means of at least three successive gas jets with nitrogen having a purity of 99.999% N, said powder is disintegrated in the nitrogen stream and, whilst maintaining the nitrogen atmosphere, the powder is graded with a maximum grain diameter of 500 µm, collected, mixed, introduced into a container having a diameter or a thickness of greater than 300 mm and a length of greater than 1000 mm, compacted therein by mechanical impact and the container is sealed in a gas-tight manner, whereupon the powder-filled container or capsule is introduced in the cold state into the HIP installation and in a hot isostatic pressing cycle the parameters for said container or capsule are adjusted in such a way that in the heating-up process the temperature and pressure are raised, wherein an all-round pressure of at least 1 to 40 MPa acts in the powder body of the container or capsule, and thereafter an isostatic pressing operation is performed at a temperature of at least 1100°C, but at most 1180°C, under an isostatic pressure of at least 90 MPa and for a period of at least three hours, and then the HIP compact is cooled and this compact is optionally subsequently hot formed.
  2. Process according to claim 1, wherein the melt is formed from an iron-based alloy containing in wt.%: carbon (C) 0.52 to 3.74 manganese (Mn) to 2.9 chromium (Cr) to 21.0 molybdenum (Mo) to 10.0 nickel (Ni) optionally to 1.0 cobalt (Co) to 20.8 vanadium (V) to 14.9 niobium (Nb), tantalum (Ta) individually or in total to 2.0 tungsten (W) to 20.0 sulfur (S) to 0.5
    and accompanying elements up to a total concentration of 4.8 and impurities and iron as the remainder.
  3. Process according to claim 1 or 2, wherein a conditioning of the melt is performed in the metallurgical vessel with an induced, turbulent flow of said melt, preferably by electromagnetic means, and with the metal bath completely covered by liquid slag, said slag being heated in particular by means of the direct passage of current, for a period of at least 15 minutes.
  4. Process according to claim 1 to 3, wherein the conditioned melt is introduced into an atomising chamber through a nozzle body in the metallurgical vessel with a melt stream diameter of 4.0 to 10.0 mm and in said chamber it is acted upon by at least three successive gas jets formed from nitrogen, with the proviso that the last gas jet to act upon the melt stream has a speed which at least in places is greater than the speed of sound.
  5. Process according to one of claims 1 to 4, wherein the diameter of the powder grains is adjusted or graded to a maximum value of 500 µm by means of atomisation.
  6. Process according to one of claims 1 to 5, wherein the powder collected in a preparation chamber is fluidised with nitrogen and mixed together and whilst maintaining the nitrogen atmosphere is introduced into a container or capsule with a total weight of more than 0.5 t, compacted by mechanical impact and sealed in a gas-tight manner.
  7. Process according to one of claims 1 to 6, wherein the powder is introduced into a container or capsule having a diameter or thickness of greater than or equal to 400 mm and a length of at least 1500 mm.
  8. Process according to one of claims 1 to 7, wherein heating and/or pressing of the powder is performed at a constant temperature load, optionally a uniformly varying temperature load oscillating around a mean value, and pressing takes place at a temperature of at least 1140°C but at most 1170°C.
  9. Process according to one of claims 1 to 8, wherein the block produced by powder metallurgy is used in the as-HIP state or with a minimum of forming undertaken for economic reasons as a primary material for tools or tool components.
  10. Object produced by powder metallurgy from tool steel having improved material properties, preferably produced by a process according to one of the preceding claims, consisting of an iron-based alloy containing in wt.%: carbon (C) 0.52 to 3.74 manganese (Mn) to 2.9 chromium (Cr) to 21.0 molybdenum (Mo) to 10.0 nickel (Ni) optionally to 1.0 cobalt (Co) to 20.8 vanadium (V) to 14.9 niobium (Nb), tantalum (Ta) individually or in total to 2.0 tungsten (W) to 20.0 sulfur (S) to 0.5
    and accompanying elements up to a total concentration of 4.8 and impurities and iron as the remainder, said highly pure material having a K0 value in accordance with
    DIN 50 602 of at most 3 or an ASTM value in accordance with ASTM E 45/85 Method D of at most 1.5.
  11. Powder metallurgical object according to claim 10, formed from a material having a content of inclusions - in accordance with DIN 50 602 Method K0 - for the sum of characteristic values 1 and 0 in a proportion of over 80%.
  12. Powder metallurgical object according to claim 10, formed from a material having a content of inclusions - in accordance with DIN 50 602 Method K0 - for the characteristic value K0 in a proportion of over 50%.
  13. Powder metallurgical object according to claim 10, formed from a material having a content of inclusions - in accordance with ASTM E 45/85 Method D - for the sum of ASTM values 0.5 and 1 in a proportion of over 90%.
  14. Powder metallurgical object according to claim 10, formed from a material having a content of inclusions - in accordance with ASTM E 45/85 Method D - for the ASTM value of 0.5 in a proportion of over 60%.
EP01890158.7A 2001-04-11 2001-05-25 Process for preparing tool steel articles by powder metallurgy Expired - Lifetime EP1249510B2 (en)

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AT410448B (en) * 2001-04-11 2003-04-25 Boehler Edelstahl COLD WORK STEEL ALLOY FOR THE POWDER METALLURGICAL PRODUCTION OF PARTS
US20060249230A1 (en) * 2005-05-09 2006-11-09 Crucible Materials Corp. Corrosion and wear resistant alloy
CN103741042B (en) * 2013-12-19 2015-12-09 马鞍山市方圆材料工程有限公司 A kind of high abrasion cold roll alloy material and preparation method thereof
EP3608041A1 (en) * 2018-08-07 2020-02-12 BAE SYSTEMS plc Hot isostatic pressing consolidation of powder derived parts
WO2020030906A1 (en) * 2018-08-07 2020-02-13 Bae Systems Plc Hot isostatic pressing consolidation of powder derived parts
CN112279254B (en) * 2019-07-24 2022-07-15 比亚迪股份有限公司 Preparation method of silicon carbide powder and silicon carbide powder
CN111014704B (en) * 2020-01-03 2021-01-05 东南大学 Preparation method of powder metallurgy tool and die steel
CN116833409A (en) * 2021-11-29 2023-10-03 河冶科技股份有限公司 Method for preparing precipitation hardening high-speed steel by powder metallurgy process

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