EP0396185B1 - Process for preparing semi-finished creep resistant products from high melting metal - Google Patents

Process for preparing semi-finished creep resistant products from high melting metal Download PDF

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EP0396185B1
EP0396185B1 EP90201056A EP90201056A EP0396185B1 EP 0396185 B1 EP0396185 B1 EP 0396185B1 EP 90201056 A EP90201056 A EP 90201056A EP 90201056 A EP90201056 A EP 90201056A EP 0396185 B1 EP0396185 B1 EP 0396185B1
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hot
forming
finished products
producing semi
alloys
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EP0396185A1 (en
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Ralf Dr. Eck
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Metallwerk Plansee GmbH
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Metallwerk Plansee GmbH
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C1/00Making non-ferrous alloys
    • C22C1/10Alloys containing non-metals
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C32/00Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
    • C22C32/001Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
    • C22C32/0015Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
    • C22C32/0031Matrix based on refractory metals, W, Mo, Nb, Hf, Ta, Zr, Ti, V or alloys thereof
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18High-melting or refractory metals or alloys based thereon

Definitions

  • the invention relates to a process for the production of semi-finished products or molded parts of high creep resistance from sintered or melted precursors from alloys of the high-melting metals vanadium, niobium, tantalum, chromium, molybdenum, tungsten, which are solidified by dispersoidal inclusions of oxides, carbides, silicides, borides and / or nitrides , individually, in groups or as a main component with other metal components.
  • hot forming results in the best possible hot creep strength values in immediately successive, as large as possible forming steps up to very high degrees of deformation of 90% and more. They are like this Formed materials undergo a final recrystallization annealing in order to form a stack structure that is as pronounced as possible. These processes with a large number of forming steps and annealing are very lengthy and expensive, but according to the prevailing teaching opinion, they are essential to achieve the highest hot creep strength.
  • the hot forming to 60-80% forming takes place in a single operation, if necessary with intermediate heating of the workpiece, if, for example, the forming process to the desired degree of deformation or to the desired workpiece shape cannot be carried out quickly enough and without excessive cooling.
  • the heat resistance values of alloys manufactured in this way are significantly lower than the values when a stacked structure is formed.
  • the method is nevertheless said to provide higher heat resistance values, in particular higher heat creep resistance, even at temperature values around and above three quarters of the melting temperature of the main constituent of the alloy, than known materials.
  • the object is achieved by a method according to the present invention, in which sintered or melted preliminary products from the materials mentioned at the outset are processed into semi-finished products, in that the preliminary products are subsequently subjected to two to four times at hot forming temperatures in the range of 900 ° C. which are customary for the respective metallic main component and 1600 ° C by 3 - 25%, but a total of a maximum of 75% thermomechanically and by intermediate annealing between the individual forming steps at temperatures ranging from about the respective hot forming temperature to the respective recrystallization temperature for 1 and 6 hours.
  • semi-finished products are, for. B. to understand forged blanks, rods, circular blanks, sheets and wires.
  • molded parts are parts that are produced from semi-finished products by shaping processes such as machining, but without further influencing the metallic structure and the metallic properties; also those parts that are processed from pre-products in the course of hot forming into ready-to-use molded parts.
  • the most important alloy elements in question in addition to the main constituents mentioned are the metals of subgroup 4 of the periodic table, but also other elements already used in alloys of the refractory metals, in particular rhenium and platinum.
  • the oxides, and especially the rare earths cerium oxide, yttrium oxide, lanthanum oxide, in addition to thorium oxide, manganese oxide, titanium oxide and zirconium oxide have proven particularly effective.
  • carbides, silicides, borides and nitrides are successfully used as dispersoids in high-melting metals.
  • Alkaline earth metals, aluminum and silicon are hardly used in the present case because of their known disadvantages at very high material temperatures, but cannot be completely ruled out.
  • customary hot-forming temperatures is to be understood as the temperatures which are advantageously to be used in hot-forming by forging and / or hammering for the respective high-melting metal.
  • the most favorable temperature for the comparatively low-melting chromium is of course significantly lower than for tungsten, but in any case below the temperature at which recrystallization begins.
  • the degrees of deformation to be used per forming step are to be limited to the area of critical forming, ie to the area in which grain growth occurs due to subsequent temperature treatment. Extrusion and drawing can be mentioned as further applicable hot forming processes.
  • An important advantage of the high-melting alloys produced by the inventive method is the high hot creep resistance values, even in temperature ranges which are around three quarters of the respective melting temperature, where others Process creep-resistant alloys already drop sharply in the corresponding values.
  • Another advantage of the method is that in addition to the heat creep resistance, the other heat resistance values, namely tensile strength with sufficient residual elongation, are comparatively favorable.
  • Dispersion-strengthened alloys according to the present invention are preferably used as molding tools in forging or pressing tools for the high-temperature shaping of metallic moldings, in particular in isothermal high-temperature forging.
  • Another area of application is rotating anodes for X-ray tubes.
  • the ZHM-molybdenum alloy used for comparison was brought to the same overall degree of deformation of approximately 70%, but in a single step, without intermediate annealing after small degrees of deformation according to the invention.
  • the TZM-molybdenum alloy which had long been the leader in terms of high creep resistance, could no longer be cited for comparison, since a corresponding sample under the load values mentioned would crack in less than a minute.
  • Molybdenum metal powder with a grain size of approx. 5 ⁇ m was mixed with fine-grained powder additives, namely with 1.2% by weight Hf, 0.4% by weight Zr, 0.15% by weight C and 1.0% by weight CeO2 with a grain size of approx. 0.8 ⁇ m mixed, the mixture filled in a rubber tube, shaken tightly and cold isostatically pressed with a pressure of 2500 bar under water.
  • the isostatically pressed rod was turned green to a diameter of 75 mm on a lathe and then cut to a height of 55 mm.
  • the cylinders were sintered in a dry H2 atmosphere (TP ⁇ - 35 ° C) for 5 hours at 2000 ° C.
  • the sintered density was 9.50 g / cm3.
  • the forming process involved heating the sintered body to 1200 ° C in an H2-flooded furnace for 20 minutes, further compressing it to a height of 43 mm, the two-period annealing first at 2000 ° C for 1 hour and then at 1500 ° C for 1 hour. This is followed by heating in the forging furnace to 1200 ° C for 20 minutes and forging at approx. 10 degrees of deformation to a height of 39 mm.
  • Annealing and forging are repeated two more times: annealing at 2000 ° C, 1 hour and 1500 ° C, 1 hour, placing in the forging furnace, forging at a height of 35 mm, annealing at 2000 ° C, 1 hour and 1500 ° C 1 Hour, heating to 1200 ° C for 20 minutes and finish forging to a height of 12 mm.
  • Example 1 The process according to Example 1 is repeated with the following alloy composition: Mo - 1.2% by weight Hf, 0.4% by weight Zr, 0.15% by weight C and, deviating from above, 1% by weight Y2O3 with a grain size of 0.25 ⁇ m.
  • Tungsten metal powder which was obtained by H2 reduction of blue tungsten oxide and had a grain size of 3.80 ⁇ m, was with 1.20 wt.% Hf, 0.40 wt.% Zr, 0.10 wt.% C and with 1 wt.% CeO2 of grain size 0.8 microns, mixed in a compulsory mixer and pressed in a die pressing tool with a diameter of 105 mm to a height of 55 mm.
  • the blanks were sintered for 7 hours at 2500 ° C in dry H2 with a dew point of -35 ° C and reached a density of 17.7 g / cm3. After sintering, the dimensions of the blanks were approximately 90 mm in diameter x 48 mm in height.
  • the blanks were first warmed at 1550 ° C. for 20 minutes and then upset to a height of 43 mm by hot forging. There followed an intermediate annealing of the blanks for 2 hours at 1550 ° C in an H2 atmosphere. The blanks were then again heated at 1550 ° C. for 20 minutes and deformed at this temperature in a second forging pass by approx. 10% to a height of 39 mm. The subsequent annealing was again carried out at 1550 ° C for 2 hours in an H2 atmosphere. For the third pass, heating was again carried out at 1550 ° C. for 20 minutes and then forging to a height of 35 mm. Finally, the round blanks were annealed for a fourth time for 2 hours at 1550 ° C. and after a final warming over 20 minutes at 1550 ° C. at 17 mm height, they were forged and cooled from the forging heat in the furnace to room temperature overnight.

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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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Description

Die Erfindung betrifft ein Verfahren zur Herstellung von Halbfabrikaten oder Formteilen hoher Warmkriechfestigkeit aus gesinterten oder erschmolzenen Vorprodukten aus durch dispersoide Einlagerungen von Oxiden, Karbiden, Siliziden, Boriden und/oder Nitriden verfestigten Legierungen der hochschmelzenden Metalle Vanadium, Niob, Tantal, Chrom, Molybdän, Wolfram, einzeln, zu mehreren oder als Hauptbestandteil mit anderen Metallanteilen.The invention relates to a process for the production of semi-finished products or molded parts of high creep resistance from sintered or melted precursors from alloys of the high-melting metals vanadium, niobium, tantalum, chromium, molybdenum, tungsten, which are solidified by dispersoidal inclusions of oxides, carbides, silicides, borides and / or nitrides , individually, in groups or as a main component with other metal components.

Für Halbfabrikate, insbesondere aber für Formteile aus hochschmelzenden Metallen, besteht der Bedarf nach verbesserten Warmfestigkeitseigenschaften, vor allem nach höherer Warmkriechfestigkeit. Die Festigkeits-Eigenschaften derartiger Metalle werden nebeneinander gleichermaßen durch Legieren, Umformverfestigung, Alterungsprozesse und Dispersionshärtung erzielt. Unter den Verfahren zur Herstellung kriechfester Legierungen haben sich besonders Dotierungs- und Umformverfahren mit dem Ziel bewährt, ein Stapelgefüge im Metall zu erzeugen, d. h. ein Gefüge, bei dem die einzelnen metallischen Körner ein Streckungsverhältnis von mindestens 1:2 aufweisen. Lange Zeit wurden hochschmelzende Metalle zu diesem Zweck vor allem mit Kalium, Aluminium und Silizium dotiert. In den letzten Jahren hat die Dotierung mit Dispersoiden auf oxidischer und karbidischer Basis vermehrt an Bedeutung gewonnen. Derartige Legierungen sind beispielsweise in der AT-PS 386 612 beschrieben.For semi-finished products, but especially for molded parts made of refractory metals, there is a need for improved heat resistance properties, especially for higher heat creep resistance. The strength properties of such metals are achieved in parallel by alloying, strain hardening, aging processes and dispersion hardening. Among the processes for producing creep-resistant alloys, doping and forming processes have proven particularly useful with the aim of producing a stacked structure in the metal, i. H. a structure in which the individual metallic grains have an aspect ratio of at least 1: 2. For a long time, high-melting metals were mainly doped with potassium, aluminum and silicon. In recent years, doping with dispersoids based on oxides and carbides has become increasingly important. Such alloys are described for example in AT-PS 386 612.

Unter den bekannten Verfahren zur Herstellung warmkriechfester Materialien ergibt die Warmumformung in unmittelbar aufeinanderfolgenden, möglichst großen Umformschritten bis auf sehr hohe Verformungsgrade von 90 % und mehr die besten Warmkriechfestigkeitswerte. Dabei werden die so umgeformten Werkstoffe einer abschließenden Rekristallisationsglühung unterzogen, um ein möglichst ausgeprägtes Stapelgefüge zu formieren. Diese Verfahren mit einer Vielzahl von Umformschritten und Glühungen sind sehr langwierig und kostspielig, nach der herrschenden Lehrmeinung aber unumgänglich, um höchste Warmkriechfestigkeiten zu erreichen. Alternativ erfolgt die Warmumformung auf 60 - 80 % Umformung in einem einzigen Arbeitsgang, ggf. unter Zwischenwärmen des Werkstücks, falls beispielsweise der Umformprozeß auf den gewünschten Umformgrad oder in die gewünschte Werkstückform nicht rasch genug und ohne zu starke Abkühlung erfolgen kann. Die Warmfestigkeitswerte derart gefertigter Legierungen liegen deutlich unter den Werten bei Ausbildung einer Stapelgefügestruktur.Among the known processes for the production of hot creep-resistant materials, hot forming results in the best possible hot creep strength values in immediately successive, as large as possible forming steps up to very high degrees of deformation of 90% and more. They are like this Formed materials undergo a final recrystallization annealing in order to form a stack structure that is as pronounced as possible. These processes with a large number of forming steps and annealing are very lengthy and expensive, but according to the prevailing teaching opinion, they are essential to achieve the highest hot creep strength. Alternatively, the hot forming to 60-80% forming takes place in a single operation, if necessary with intermediate heating of the workpiece, if, for example, the forming process to the desired degree of deformation or to the desired workpiece shape cannot be carried out quickly enough and without excessive cooling. The heat resistance values of alloys manufactured in this way are significantly lower than the values when a stacked structure is formed.

Aufgabe vorliegender Erfindung ist danach die Bereitstellung eines Verfahrens zur Herstellung dispersionsverfestigter Halbfabrikate oder Formteile aus hochschmelzenden Metallen, welches sich von den üblicherweise verwendeten Verfahren durch eine geringere Anzahl von Verfahrensschritten sowie höhere Wirtschaftlichkeit unterscheidet. Das Verfahren soll gleichwohl höhere Warmfestigkeitswerte, insbesondere höhere Warmkriechfestigkeit auch noch bei Temperaturwerten um und oberhalb drei Viertel der Schmelztemperatur des Hauptbestandteiles der Legierung, erbringen, als bekannte Werkstoffe.It is an object of the present invention to provide a process for producing dispersion-strengthened semifinished products or moldings from high-melting metals, which differs from the commonly used processes in that it has a smaller number of process steps and is more economical. The method is nevertheless said to provide higher heat resistance values, in particular higher heat creep resistance, even at temperature values around and above three quarters of the melting temperature of the main constituent of the alloy, than known materials.

Die Aufgabe wird durch ein Verfahren gemäß vorliegender Erfindung gelöst, bei dem gesinterte oder erschmolzene Vorprodukte aus den eingangs genannten Werkstoffen zu Halbfabrikaten verarbeitet werden, indem die Vorprodukte in Folge zwei- bis viermal bei für den jeweiligen metallischen Hauptbestandteil gebräuchlichen Warmumformungstemperaturen im Bereich von 900°C und 1600°C um jeweils 3 - 25 %, insgesamt jedoch maximal um 75 % thermomechanisch verformt werden und indem die Vorprodukte zwischen den einzelnen Umformschritten bei Temperaturen im Bereich von etwa der jeweiligen Warmumformungstemperatur bis zur jeweiligen Rekristallisationstemperatur 1 und 6 Stunden lang zwischengeglüht werden.The object is achieved by a method according to the present invention, in which sintered or melted preliminary products from the materials mentioned at the outset are processed into semi-finished products, in that the preliminary products are subsequently subjected to two to four times at hot forming temperatures in the range of 900 ° C. which are customary for the respective metallic main component and 1600 ° C by 3 - 25%, but a total of a maximum of 75% thermomechanically and by intermediate annealing between the individual forming steps at temperatures ranging from about the respective hot forming temperature to the respective recrystallization temperature for 1 and 6 hours.

Unter dem Begriff Halbfabrikate sind z. B. Schmiederohlinge, Stäbe, Ronden, Bleche und Drähte zu verstehen. Formteile sind demgegenüber solche Teile, die aus Halbfabrikaten durch Formgebungsverfahren wie Zerspanung, aber ohne weitere Beeinflussung des metallischen Gefüges und der metallischen Eigenschaften hergestellt werden; weiterhin auch solche Teile, die aus Vorprodukten im Zuge der Warmumformung gleichzeitig zu anwendungsfertigen Formteilen verarbeitet werden.The term semi-finished products are, for. B. to understand forged blanks, rods, circular blanks, sheets and wires. In contrast, molded parts are parts that are produced from semi-finished products by shaping processes such as machining, but without further influencing the metallic structure and the metallic properties; also those parts that are processed from pre-products in the course of hot forming into ready-to-use molded parts.

Die wichtigsten, in Frage kommende Legierungselemente neben den genannten Hauptbestandteilen sind die Metalle der 4. Nebengruppe des Periodensystems, aber auch sonstige in Legierungen der hochschmelzenden Metalle bereits verwendete Elemente, insbesondere Rhenium und Platin. Unter den Dispersoiden für hochschmelzende Metalle haben sich die Oxide, und dort wieder vor allem die Seltenen Erden Ceroxid, Yttriumoxid, Lanthanoxid, neben Thoriumoxid Manganoxid, Titanoxid und Zirkonoxid besonders bewährt. Daneben werden Karbide, Silizide, Boride und Nitride als Dispersoide in hochschmelzenden Metallen erfolgreich eingesetzt. Erdalkalimetalle, Aluminium und Silizium werden wegen ihrer bekannten Nachteile bei sehr hohen Werkstoff-Einsatztemperaturen im vorliegenden Fall kaum angewendet, sind aber nicht vollständig auszuschließen.The most important alloy elements in question in addition to the main constituents mentioned are the metals of subgroup 4 of the periodic table, but also other elements already used in alloys of the refractory metals, in particular rhenium and platinum. Among the dispersoids for high-melting metals, the oxides, and especially the rare earths cerium oxide, yttrium oxide, lanthanum oxide, in addition to thorium oxide, manganese oxide, titanium oxide and zirconium oxide have proven particularly effective. In addition, carbides, silicides, borides and nitrides are successfully used as dispersoids in high-melting metals. Alkaline earth metals, aluminum and silicon are hardly used in the present case because of their known disadvantages at very high material temperatures, but cannot be completely ruled out.

Unter dem Begriff "gebräuchliche Warmformungstemperaturen" sind die bei der Warmumformung durch Schmieden und/oder Hämmern für das jeweilige hochschmelzende Metall günstigerweise anzuwendenden Temperaturen zu verstehen. Dabei ist eine qualitativ hochwertige, z. B. rißfreie Ausbringung, ebenso Bedingung wie die Wirtschaftlichkeit des Verfahrens. Die günstigste Temperatur liegt selbstverständlich für das vergleichsweise niedrig schmelzende Chrom deutlich niedriger als etwa für Wolfram, in jedem Fall aber unter der Temperatur, bei welcher Rekristallisation einsetzt. Die je Umformschritt anzuwendenden Umformgrade sind auf den Bereich der kritischen Umformung, d. h. auf den Bereich, bei dem durch anschließende Temperaturbehandlung ein Kornwachstum auftritt, zu beschränken.
Als weitere anwendbare Warmumformverfahren sind das Strangpressen und das Ziehen zu nennen.
The term “customary hot-forming temperatures” is to be understood as the temperatures which are advantageously to be used in hot-forming by forging and / or hammering for the respective high-melting metal. A high quality, e.g. B. crack-free application, condition as well as the economy of the process. The most favorable temperature for the comparatively low-melting chromium is of course significantly lower than for tungsten, but in any case below the temperature at which recrystallization begins. The degrees of deformation to be used per forming step are to be limited to the area of critical forming, ie to the area in which grain growth occurs due to subsequent temperature treatment.
Extrusion and drawing can be mentioned as further applicable hot forming processes.

Es war nun angesichts der bisher praktizierten Lehrmeinung völlig überraschend, daß die Umformung in kleinen prozentuellen Stufen und bis auf insgesamt maximal 75 %, in der Regel aber wesentlich weniger, in Verbindung mit den angeführten Zwischenglühprozessen so günstige Warmkriechfestigkeits-Eigenschaften ergibt. Bisher war davon ausgegangen worden, daß zur Erzielung höchstmöglicher Warmkriechfestigkeit bei den genannten Werkstoffen eine Umformung von mindestens 90 %, in der Regel sogar weit mehr unumgänglich ist.It was now completely surprising in view of the previously held doctrine that the forming in small percentage steps and up to a maximum of 75% in total, but as a rule significantly less, in combination with the intermediate annealing processes mentioned, gives such favorable creep resistance properties. It had previously been assumed that in order to achieve the highest possible creep resistance for the materials mentioned, a deformation of at least 90%, as a rule even much more, is unavoidable.

Ebenso überraschend und nicht vorhersehbar war, daß nach dem erfindungsgemäßen Verfahren hergestellte, hochschmelzende Legierungen nicht zwingend zur Ausbildung eines Stapelgefüges gebracht werden müssen und sich gleichwohl höhere Warmkriechfestigkeiten erzielen lassen, als bisher für vergleichbare hochschmelzende Legierungen mit Stapelgefüge bekannt geworden ist.
Dessen ungeachtet konnten Spitzenwerte für die Warmfestigkeit, insbesondere für die Warmkriechfestigkeit, bei einzelnen Legierungen hochschmelzender Metalle dann erreicht werden, wenn in Abwandlung des erfindungsgemäßen Grundverfahrens die Zwischenglühungen nach den einzelnen Umformschritten etwa während der Hälfte der vorgesehenen Gesamtglühzeit bei Temperaturen oberhalb der Rekristallisationstemperatur des jeweiligen Werkstoffes, d. h. bei 1300°C bis 2100°C vorgenommen wurde und anschließend während der zweiten zeitlichen Hälfte bei etwa der Warmumformungstemperatur geglüht wurde, welche Temperatur grundsätzlich unterhalb der Rekristallisationstemperatur für den jeweiligen Werkstoff liegt. Mittels dieser zweigeteilten, im Unterschied zur einheitlichen Zwischenglühung lassen sich Stapelgefüge erzielen, welche die Warmkriechfestigkeit entsprechender Werkstoffe nochmals wesentlich erhöhen.
It was just as surprising and unforeseeable that high-melting alloys produced by the process according to the invention do not necessarily have to be brought to the formation of a stack structure, and nevertheless higher hot creep strengths can be achieved than has previously been known for comparable high-melting alloys with a stack structure.
Notwithstanding this, peak values for the heat resistance, in particular for the heat creep resistance, could be achieved for individual alloys of refractory metals if, in a modification of the basic process according to the invention, the intermediate annealing after the individual shaping steps took place for about half of the intended total annealing time at temperatures above the recrystallization temperature of the respective material, ie at 1300 ° C to 2100 ° C and then annealed during the second half of the time at approximately the hot forming temperature, which temperature is generally below the recrystallization temperature for the respective material. By means of this two-part, in contrast to the uniform intermediate annealing, stacking structures can be achieved, which further increase the warm creep resistance of corresponding materials.

Ein wichtiger Vorteil bei den nach dem erfinderischen Verfahren hergestellten hochschmelzenden Legierungen sind die hohen Warmkriechfestigkeitswerte selbst in Temperaturbereichen, die etwa bei drei Viertel der jeweiligen Schmelztemperatur liegen, wo nach anderen Verfahren hergestellte warmkriechfeste Legierungen in den entsprechenden Werten bereits stark abfallen. Ein weiterer Vorteil des Verfahrens besteht darin, daß neben der Warmkriechfestigkeit auch die anderen Warmfestigkeitswerte, nämlich Zugfestigkeit bei ausreichender Restdehnung, vergleichsweise günstig liegen.An important advantage of the high-melting alloys produced by the inventive method is the high hot creep resistance values, even in temperature ranges which are around three quarters of the respective melting temperature, where others Process creep-resistant alloys already drop sharply in the corresponding values. Another advantage of the method is that in addition to the heat creep resistance, the other heat resistance values, namely tensile strength with sufficient residual elongation, are comparatively favorable.

Dispersionsverfestigte Legierungen gemäß vorliegender Erfindung finden bevorzugt Anwendung als Formwerkzeuge in Schmiede- oder Preßwerkzeugen für die Hochtemperatur-Umformung metallischer Formstücke, insbesondere beim isothermen Hochtemperaturschmieden. Ein weiteres Anwendungsgebiet sind Drehanoden für Röntgenröhren.Dispersion-strengthened alloys according to the present invention are preferably used as molding tools in forging or pressing tools for the high-temperature shaping of metallic moldings, in particular in isothermal high-temperature forging. Another area of application is rotating anodes for X-ray tubes.

Unter den Hochtemperatur-Metallegierungen hoher Warmkriechfestigkeit hatten schon bisher Molybdänlegierungen mit Zusätzen von Zirkonium, Hafnium und etwas Kohlenstoff besonders günstige Warmfestigkeits-Eigenschaften gezeigt. Diese Legierungen sind als ZHM-Legierungen bekannt geworden und stellen eine Weiterentwicklung der als TZM bekannt gewordenen Molybdänlegierungen dar. Die nachfolgende Tabelle belegt eindrucksvoll, daß entsprechend vorliegender Erfindung hergestellte oxiddispersionsverfestigte ZHM-Legierungen deutlich bessere Warm-, insbesondere Warmkriechfestigkeitswerte, erreichen als nach üblichen Verfahren hergestellte ZHM-Legierungen.Among the high-temperature metal alloys with high creep resistance, molybdenum alloys with additions of zirconium, hafnium and some carbon had previously shown particularly favorable heat resistance properties. These alloys have become known as ZHM alloys and represent a further development of the molybdenum alloys which have become known as TZM. The following table impressively shows that oxide dispersion-strengthened ZHM alloys produced in accordance with the present invention achieve significantly better hot values, in particular hot creep strength values, than those produced by conventional processes ZHM alloys.

Die zum Vergleich dienende ZHM-Molybdänlegierung wurde auf denselben Gesamtumformgrad von ca. 70 % gebracht, jedoch in einem einzigen Arbeitsschritt, ohne Zwischenglühung nach kleinen Umformgraden gemäß Erfindung.
Die hinsichtlich hoher Warmkriechfestigkeit lange Zeit führende TZM-Molybdänlegierung konnte gar nicht mehr zum Vergleich angeführt werden, da eine entsprechende Probe unter den genannten Belastungswerten bereits in weniger als einer Minute reißen würde.

Figure imgb0001
The ZHM-molybdenum alloy used for comparison was brought to the same overall degree of deformation of approximately 70%, but in a single step, without intermediate annealing after small degrees of deformation according to the invention.
The TZM-molybdenum alloy, which had long been the leader in terms of high creep resistance, could no longer be cited for comparison, since a corresponding sample under the load values mentioned would crack in less than a minute.
Figure imgb0001

Beispiel 1example 1

Molybdänmetallpulver von ca. 5µm Korngröße wurde mit feinkörnigen Pulverzusätzen, und zwar mit 1,2 Gew.% Hf, 0,4 Gew.% Zr, 0,15 Gew.% C und 1,0 Gew.% CeO₂ der Korngröße von ca. 0,8µm vermischt, die Mischung in einen Gummischlauch gefüllt, dicht gerüttelt und kaltisostatisch mit einem Druck von 2500 bar unter Wasser gepreßt. Der isostatisch gepreßte Stab wurde grün auf einen Durchmesser von 75 mm auf einer Drehbank gedreht und anschließend auf 55 mm Höhe abgelängt. Die Zylinder wurden in trockener H₂-Atmosphäre (TP<- 35°C) 5 Stunden lang bei 2000°C gesintert. Die Sinterdichte betrug 9,50 g/cm³. Der Umformvorgang umfaßte das Aufwärmen des Sinterlings auf 1200°C in einem H₂-gefluteten Ofen während 20 Minuten, weiters das Stauchen auf 43 mm Höhe, das zweiperiodische Glühen zunächst während 1 Stunde bei 2000°C und anschließend während 1 Stunde bei 1500°C. Es folgen das Anwärmen im Schmiedeofen auf 1200°C während 20 Minuten und Schmieden bei ca. 10 Umformgrad auf 39 mm Höhe. Das Glühen und Schmieden wird noch weitere zweimal wiederholt: Glühen bei 2000°C, 1 Stunde sowie 1500°C, 1 Stunde, Einlegen in den Schmiedeofen, Schmieden auf 35 mm Höhe, Glühen bei 2000°C, 1 Stunde sowie 1500°C 1 Stunde, Anwärmen während 20 Minuten auf 1200°C und Fertigschmieden auf eine Höhe von 12 mm.Molybdenum metal powder with a grain size of approx. 5 µm was mixed with fine-grained powder additives, namely with 1.2% by weight Hf, 0.4% by weight Zr, 0.15% by weight C and 1.0% by weight CeO₂ with a grain size of approx. 0.8µm mixed, the mixture filled in a rubber tube, shaken tightly and cold isostatically pressed with a pressure of 2500 bar under water. The isostatically pressed rod was turned green to a diameter of 75 mm on a lathe and then cut to a height of 55 mm. The cylinders were sintered in a dry H₂ atmosphere (TP <- 35 ° C) for 5 hours at 2000 ° C. The sintered density was 9.50 g / cm³. The forming process involved heating the sintered body to 1200 ° C in an H₂-flooded furnace for 20 minutes, further compressing it to a height of 43 mm, the two-period annealing first at 2000 ° C for 1 hour and then at 1500 ° C for 1 hour. This is followed by heating in the forging furnace to 1200 ° C for 20 minutes and forging at approx. 10 degrees of deformation to a height of 39 mm. Annealing and forging are repeated two more times: annealing at 2000 ° C, 1 hour and 1500 ° C, 1 hour, placing in the forging furnace, forging at a height of 35 mm, annealing at 2000 ° C, 1 hour and 1500 ° C 1 Hour, heating to 1200 ° C for 20 minutes and finish forging to a height of 12 mm.

Die derart hergestellten Proben wurden auf ihre Warmfestigkeits-Eigenschaften hin untersucht. Die Versuchsergebnisse sind in der Tabelle dargestellt.The samples produced in this way were examined for their heat resistance properties. The test results are shown in the table.

Beispiel 2Example 2

Das Verfahren nach Beispiel 1 wird mit folgender Legierungszusammensetzung wiederholt:
Mo - 1,2 Gew.% Hf, 0,4 Gew.% Zr, 0,15 Gew. % C und abweichend von oben 1 Gew.% Y₂O₃ der Korngröße 0,25 µm.
The process according to Example 1 is repeated with the following alloy composition:
Mo - 1.2% by weight Hf, 0.4% by weight Zr, 0.15% by weight C and, deviating from above, 1% by weight Y₂O₃ with a grain size of 0.25 µm.

Beispiel 3Example 3

Wolfram-Metallpulver, das durch H₂-Reduktion von blauem Wolframoxid gewonnen wurde und eine Korngröße von 3,80µm aufwies, wurde mit 1,20 Gew.% Hf, 0,40 Gew.% Zr, 0,10 Gew.% C sowie mit 1 Gew.% CeO₂ der Korngröße 0,8µm versetzt, in einem Zwangsmischer gemischt und in einem Matrizenpreßwerkzeug mit 105 mm Durchmesser auf Höhe 55 mm gepreßt. Die Ronden wurden 7 Stunden lang bei 2500°C in trockenem H₂ mit einem Taupunkt -35°C gesintert und erreichten eine Dichte von 17,7 g/cm³. Nach dem Sintern betrugen die Abmessungen der Ronden ca. 90 mm Durchmesser x 48 mm Höhe.Tungsten metal powder, which was obtained by H₂ reduction of blue tungsten oxide and had a grain size of 3.80 µm, was with 1.20 wt.% Hf, 0.40 wt.% Zr, 0.10 wt.% C and with 1 wt.% CeO₂ of grain size 0.8 microns, mixed in a compulsory mixer and pressed in a die pressing tool with a diameter of 105 mm to a height of 55 mm. The blanks were sintered for 7 hours at 2500 ° C in dry H₂ with a dew point of -35 ° C and reached a density of 17.7 g / cm³. After sintering, the dimensions of the blanks were approximately 90 mm in diameter x 48 mm in height.

Die Ronden wurden zunächst 20 Minuten lang bei 1550°C angewärmt und dann durch Warmschmieden auf 43 mm Höhe gestaucht. Es folgte eine Zwischenglühung der Ronden für 2 Stunden bei 1550°C in H₂-Atmosphäre. Dann wurden die Ronden wiederum bei 1550°C 20 Minuten lang angewärmt und bei dieser Temperatur in einem zweiten Schmiededurchgang um ca. 10 % auf 39 mm Höhe verformt. Die anschließende Glühung erfolgte wiederum bei 1550°C 2 Stunden lang in H₂-Atmosphäre. Für den dritten Schmiededurchgang wurde abermals bei 1550°C 20 Minuten lang angewärmt und dann auf 35 mm Höhe geschmiedet. Schließlich wurden die Ronden ein viertes Mal 2 Stunden lang bei 1550°C geglüht und nach einem letzen Anwärmen über 20 Minuten auf 1550°C auf 17 mm Höhe fertiggeschmiedet und von der Schmiedehitze im Ofen über Nacht auf Raumtemperatur abgekühlt.The blanks were first warmed at 1550 ° C. for 20 minutes and then upset to a height of 43 mm by hot forging. There followed an intermediate annealing of the blanks for 2 hours at 1550 ° C in an H₂ atmosphere. The blanks were then again heated at 1550 ° C. for 20 minutes and deformed at this temperature in a second forging pass by approx. 10% to a height of 39 mm. The subsequent annealing was again carried out at 1550 ° C for 2 hours in an H₂ atmosphere. For the third pass, heating was again carried out at 1550 ° C. for 20 minutes and then forging to a height of 35 mm. Finally, the round blanks were annealed for a fourth time for 2 hours at 1550 ° C. and after a final warming over 20 minutes at 1550 ° C. at 17 mm height, they were forged and cooled from the forging heat in the furnace to room temperature overnight.

Die so gefertigten Proben wurden untersucht und ergaben ein Kriechverhalten bei 1600°C, welches dasjenige von in einem einzigen Schmiedevorgang hergestellten W-Legierungen um ca. eine Zehnerpotenz übertraf.The samples produced in this way were examined and gave a creep behavior at 1600 ° C. which exceeded that of W alloys produced in a single forging process by approximately a power of ten.

Claims (9)

  1. Process for producing semi-finished products or shaped parts with a high resistance to creep under heat from sintered or molten primary products consisting of alloys, which are hardened by dispersoid inclusions of oxides, carbides, silicides, borides and/or nitrides, of the high-melting-point metals vanadium, niobium, tantalum, chromium, molybdenum, tungsten, either individually, in a plurality or as the main constituent with other metal constituents, characterised in that the primary products are thermomechanically formed by 3 - 25% in each case, although altogether by a maximum of 75%, between two and four times at hot-forming temperatures which are usual for the respective metallic main constituent and are in the range of 900°C and 1600°C, and in that the primary products are subjected to intermediate annealing between the individual forming steps at temperatures ranging from approximately the respective hot-forming temperature to the respective recrystallization temperature for between 1 and 6 hours.
  2. Process for producing semi-finished products according to claim 1, characterised in that individual or all the intermediate annealing operations are in each case carried out in two substeps, the first substep taking place over approximately half the intermediate annealing period at temperatures above the recrystallization temperature, i.e. at 1300°C to 2100°C, and the second substep taking place over approximately half the period employed for the basic process at the selected hot-forming temperature.
  3. Process for producing semi-finished products according to claim 1 or 2, characterised in that the hot forming takes place by hot forging.
  4. Process for producing semi-finished products according to claims 1 - 3, characterised in that alloys which contain dispersoids based on oxides and/or carbides are treated.
  5. Process for producing semi-finished products according to claim 4, characterised in that the dispersoids which are used are CeO₂, Y₂0₃, La₂0₃ and/or ThO₂.
  6. Process for producing semi-finished products according to claims 1 - 5, characterised in that a molybdenum alloy with additions of zirconium and hafnium and with oxides and carbides as finely divided dispersoids is used as the high-melting-point metal.
  7. Process for producing semi-finished products according to claim 6, characterised in that the hot forming takes place at temperatures of between 1250°C and 1350°C.
  8. Use of dispersion-hardened alloys produced according to one of claims 1 - 7 in forging or pressing tools for the high-temperature forming of metallic shaped parts.
  9. Use of dispersion-hardened alloys produced according to one of claims 1 - 7 in rotating anodes for X-ray tubes.
EP90201056A 1989-05-03 1990-04-26 Process for preparing semi-finished creep resistant products from high melting metal Expired - Lifetime EP0396185B1 (en)

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AT1059/89A AT392432B (en) 1989-05-03 1989-05-03 METHOD FOR THE PRODUCTION OF WARM-CRAWL-RESISTANT SEMI-FINISHED PRODUCTS OR MOLDED PARTS FROM HIGH-MELTING METALS

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DE102005033799B4 (en) * 2005-01-31 2010-01-07 Medicoat Ag Method for producing a rotating anode plate for X-ray tubes

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US6102979A (en) * 1998-08-28 2000-08-15 The United States Of America As Represented By The United States Department Of Energy Oxide strengthened molybdenum-rhenium alloy
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DE102004010600B4 (en) * 2004-03-02 2008-07-03 Thyssenkrupp Vdm Gmbh Process for primary oxide hardening of molten metals
DE102005033799B4 (en) * 2005-01-31 2010-01-07 Medicoat Ag Method for producing a rotating anode plate for X-ray tubes

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DE59002005D1 (en) 1993-08-26

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