EP1805340B1 - Creep-resistant, martensitically hardenable, heat-treated steel - Google Patents
Creep-resistant, martensitically hardenable, heat-treated steel Download PDFInfo
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- EP1805340B1 EP1805340B1 EP05795177A EP05795177A EP1805340B1 EP 1805340 B1 EP1805340 B1 EP 1805340B1 EP 05795177 A EP05795177 A EP 05795177A EP 05795177 A EP05795177 A EP 05795177A EP 1805340 B1 EP1805340 B1 EP 1805340B1
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
Definitions
- the invention relates to martensitic-hardenable steels with increased nitrogen contents, which are characterized by a very good combination of properties, in particular by a high resistance to creep and good ductility.
- Martensite-hardenable steels based on 9-12% chromium are widely used materials in power plant technology. It is known that the addition of chromium in the abovementioned range not only provides good resistance to atmospheric corrosion but also complete through-hardenability of thick-walled forgings, for example as monobloc rotors or as rotor disks in gas and steam turbines. Proven alloys of this type usually contain about 0.08 to 0.2% carbon, which in solution allows the setting of a hard martensitic structure.
- a good combination of heat resistance and ductility of martensitic steels is made possible by a tempering treatment in which Forming a particle-stabilized subgrain structure by the precipitation of carbon in the form of carbides with simultaneous recovery of the dislocation substructure.
- the tempering behavior and the resulting properties can be effectively influenced by the choice and proportionate tuning of specific carbide formers such as Mo, W, V, Nb and Ta.
- Strengths above 850 MPa for 9-12% chromium steels can be adjusted by keeping the tempering temperature low, typically in the range 600 to 650 ° C.
- the use of low tempering temperatures leads to high transition temperatures from the brittle to the ductile state (above 0 ° C), with which the material exhibits brittle fracture behavior at room temperature.
- Significantly improved ductilities can be achieved if the tempered strength is lowered below 700 MPa. This is achieved by raising the tempering temperature to over 700 ° C.
- the use of increased tempering temperatures has the advantage that the set structural states are stable for longer times at elevated temperatures.
- a typical representative who has found widespread use in steam power plants, in particular as rotor steel, is the German steel X20CrMoV12.1 known under DIN.
- the ductility at a strength level of 850 MPa can be significantly improved by alloying nickel.
- nickel by alloying about 2 to 3% nickel, even after a tempering treatment at temperatures of 600 to 650 ° C, the transition temperature from brittle to ductile state is still below 0 ° C, resulting in a significantly improved overall combination of strength and ductility.
- Such alloys are therefore widely used where significantly higher demands are placed on both strength and ductility, typically as disk materials for gas turbine rotors.
- a typical representative of such alloys, which in the gas turbine technology, in particular as a material for rotor disks width Has found use is known under DIN German steel X12CrNiMo12.
- EP 0 931 845 A1 a nickel-containing 12% chromium steel similar in structure to the German steel X12CrNiMo12, in which the element molybdenum is reduced compared to the known steel X12 CrNiMo12, but an increased content of tungsten was added.
- DE 198 32 430 A1 is a further optimization of the X12CrNiMo12 similar steel with the name M152 disclosed in which by the addition of rare earth elements, the embrittlement tendency in the temperature range between 425 and 500 ° C is limited.
- EP 0 866 145 A2 describes a new class of martensitic chromium steels with nitrogen contents in the range 0.12 to 0.25%.
- the entire structure of the structure is determined by the Formation of Sonderitriden, in particular controlled by Vanadiumnitriden, which can be distributed by the forging treatment, by the austenitization, by a controlled cooling treatment or by a tempering treatment in a variety of ways.
- the high ductility setting in this patent application is aimed at by the distribution and morphology of the nitrides, but especially by limiting grain coarsening during forging and solution heat treatment. This is achieved in the cited document by an increased volume fraction as well as by a high particle coarsening resistance of sparingly soluble nitrides, so that a dense dispersion of nitrides is still capable of effectively limiting grain growth even at austenitizing temperatures of 1150 to 1200 ° C.
- nitrides are only one factor for achieving maximum ductility.
- Another factor is the effect of dissolved substitution elements such as nickel and manganese.
- Manganese is known from carbon steels to be embrittling rather than promoting ductility. In particular, it causes embrittlement when the alloy is subjected to long-term annealing at temperatures in the range of 350 to 500 ° C. It is also known that nickel in carbon steels improves ductility but tends to lower high temperature hot strength as well. This is related to reduced carbide stability in nickel-containing steels.
- a martensitic-hardenable tempering steel having the following chemical composition is known (in% by weight): 9 to 12 Cr, 0.001 to 0.25 Mn, 2 to 7 Ni, 0.001 to 8 Co, at least one of W and Mo in the sum between 0.5 and 4, 0.5 to 0.8, at least one of Nb, Ta, Zr Hf in the Sum between 0.001 to 0.1, 0.001 to 0.05 Ti, 0.001 to 0.15 Si, 0.01 to 0.1 C, 0.12 to 0.18 N, max. 0.025 P, max. 0.015 S, max. 0.01 Al, max. 0.0012 Sb, max. 0.007 Sn, max.
- V / N 0.012 As, balance Fe and common impurities, and the proviso that the weight ratio of vanadium to nitrogen V / N ranges between 3.5 and 4.2.
- These alloys are characterized by a very good combination of impact energy at room temperature and heat resistance at 550 ° C, especially at higher Cr contents.
- the relatively high N content increases the creep rupture strength.
- V and N are in the specified range in nearly stoichiometric proportions. This achieves optimum solubility and coarsening resistance of the vanadium nitrides.
- the high solubility is required to dissolve as much of the precipitation hardening vanadium nitride as possible, while a high resistance to coarsening of the nitrides is needed in order to have the finest possible fine structure in the EP 1 158 067 A1 To achieve the described heat treatment.
- the invention has for its object to provide a martensitic-hardenable tempering steel with high ductility in the temperature range between 350 and 500 ° C and good creep resistance in the temperature range up to 550 ° C.
- Core of the invention is a martensitic-hardenable tempering steel having the following composition (in wt .-%): 8.5 to 9.5 Cr, 0.15 to 0.25 Mn, 2 to 2.7 Ni, 0.5 to 2.5 Mo, 0.4 to 0.8 V, 0.02 to 0.04 Nb , 0.001 to 0.15 Si, 0.06 to 0.1 C, 0.11 to 0.15 N, maximum 0.007 P, maximum 0.005 S, maximum 0.01 Al, balance iron and common impurities, and the requirement that the weight ratio of vanadium to nitrogen V / N in the range between 4.3 and 5.5.
- the advantage of the invention is that in the said alloy, a compensation structure is set, which is characterized by a tough matrix and the presence of heat-resistant nitrides, at the same time a tendency to embrittlement in the range between 350 and 500 ° C is suppressed.
- the toughness of the base matrix is adjusted by the presence of substitution elements, preferably nickel.
- the contents of the substitution elements are determined so as to allow optimum unfolding of both martensite hardening and particle hardening by means of special nitrides, preferably vanadium nitrides, to provide high creep strength coupled with good ductility.
- the embrittlement tendency of the inventive steel in the temperature range of 350 to 500 ° C due to precipitation of the ⁇ 'Cr phase is suppressed by the low compared to the prior art, the Cr content and moderate N content.
- a weight content of 8.5 to 9.5% chromium allows a reasonable hardenability of thick-walled components and ensures sufficient oxidation resistance up to a temperature of 550 ° C.
- a weight fraction below 8.5% impairs the through-hardenability. Contents above 9.5% lead to the accelerated formation of the ⁇ 'Cr phase during the tempering process, which leads to embrittlement of the material.
- the range to be specified should be between 0.15 and 0.25% for manganese and between 0.001 and 0.15% for silicon, taking into account the possibilities of ladle metallurgy.
- Nickel is used as an austenite stabilizing element to suppress delta ferrite. In addition, it is said to improve ductility as a dissolved element in the ferritic matrix. Nickel contents between 2 to 2.7 wt .-% are optimal, since on the one hand, the nickel is homogeneously dissolved in the matrix, on the other hand, there is still no increased proportion of retained austenite or tempering austenite in the tempered martensite.
- This element improves creep strength by solid solution hardening as a partially dissolved element and precipitation hardening during a long-term stress.
- an excessively high proportion of this element leads to embrittlement during a long-term aging, which is due to the excretion and coarsening of the sigma phase.
- the maximum proportion of Mo must be limited to 2.5%.
- a preferred range is about 1.4 to 1.6%.
- microstructural forms are optimal when the elements vanadium and nitrogen are alloyed in a slightly more than stoichiometric V / N ratio.
- a slightly more than stoichiometric ratio also increases the stability of the vanadium nitride over that of the chromium nitride.
- a V / N ratio in the range between 4.3 to 5.5 is preferred.
- the specific content of nitrogen and vanadium nitrides depends on the optimum volume fraction of the vanadium nitrides, which are to remain as insoluble primary nitrides during the solution annealing.
- niobium is a preferred element among the special nitride formers.
- the preferred range is 0.02 to 0.04% by weight.
- the grain coarsening resistance in solution annealing is increased and the stability of primary and excrete V8N, C) nitrides is increased by partial substitution of V.
- these elements together with silicon and manganese, these elements increase the embrittlement of long-term aging in the range between 350 and 500 ° C. These elements should therefore be limited to the minimum tolerable levels.
- This element is a strong nitride former, which already sets nitrogen in the melt and thus strongly affects the effectiveness of the added nitrogen.
- the aluminum nitrides formed in the melt are very coarse and reduce the ductility. Aluminum must therefore be limited to a weight fraction of 0.01%.
- Table 1 shows the chemical composition (in% by weight) of a preferred alloy according to the invention (DM13) and of comparative alloys: Table 1: Chemical composition DM13A-2 St13TNiEL alloy Type "D" C 12:08 12:12 12:04 Cr 9.0 11.5 11.2 Mn 12:19 Max. 0.25 12:05 Ni 2.4 2.3 3:06 Co 4:02 Not a word 1.4 1.5 1.83 V 0.6 12:25 0.61 Nb 12:04 12:03 Si 12:13 12:25 ⁇ 00:02 N 0117 0035 0156 al 0008 ⁇ 00:02 P Max. 0.025 0004 S Max. 0.015 0002 V / N 5.13 7.24 3.91
- Table 2 contains experimental data for determining the notched impact energy at room temperature: Table 2: Notch energy for various differently treated alloys alloy conditions Notch energy in J DM13A-2 Initial state after the above heat treatment 76 Outsourced at 400 ° C / 1032h 90 Outsourced at 480 ° C / 1032h 58 St13TNiEL Initial state after the above heat treatment > 40 (required) Alloy "D" Initial state after the above heat treatment 106 Outsourced at 300 ° C / 5000h 57 Outsourced at 380 ° C / 5000h 36 Outsourced at 450 ° C / 5000h 21 Outsourced at 500 ° C / 5000h 54
- the alloy according to the invention is distinguished by a high heat resistance at 550 ° C., as well as by a high ductility and a good modulus of elasticity.
- the voltage for 1% creep at 550 ° C for the alloys DM13A-2 and St13TNiEL is shown as a function of time.
- the advantage of the alloy according to the invention comes into play at high removal times.
- the invention is not limited to the embodiment described.
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Abstract
Description
Die Erfindung bezieht sich auf martensitisch-härtbare Stähle mit erhöhten Stickstoffgehalten, welche sich durch eine sehr gute Eigenschaftskombination, insbesondere durch einen hohen Widerstand gegen Kriechen und eine gute Duktilität, auszeichnen.The invention relates to martensitic-hardenable steels with increased nitrogen contents, which are characterized by a very good combination of properties, in particular by a high resistance to creep and good ductility.
Martensitisch-härtbare Stähle auf der Basis 9-12 % Chrom sind weitverbreitete Werkstoffe der Kraftwerkstechnik. Es ist bekannt, dass die Zugabe von Chrom im obengenannten Bereich nicht nur eine gute Beständigkeit gegen atmosphärische Korrosion, sondern auch die vollständige Durchhärtbarkeit von dickwandigen Schmiedestücken ermöglicht, so wie sie etwa als Monoblockrotoren oder als Rotorscheiben in Gas- und Dampfturbinen Anwendung finden. Bewährte Legierungen dieser Art enthalten gewöhnlich etwa 0.08 bis 0.2 % Kohlenstoff, welcher in Lösung die Einstellung einer harten martensitischen Struktur ermöglicht. Eine gute Kombination von Warmfestigkeit und Duktilität martensitischer Stähle wird durch eine Anlassbehandlung ermöglicht, in welcher sich durch die Ausscheidung von Kohlenstoff in Form von Karbiden unter gleichzeitiger Erholung der Versetzungssubstruktur eine teilchenstabilisierte Subkornstruktur bildet. Das Anlassverhalten und die hieraus resultierenden Eigenschaften können wirksam durch die Wahl und das mengenanteilsmässige Abstimmen spezieller Karbidbildner wie zum Beispiel Mo, W, V, Nb und Ta beeinflusst werden.Martensite-hardenable steels based on 9-12% chromium are widely used materials in power plant technology. It is known that the addition of chromium in the abovementioned range not only provides good resistance to atmospheric corrosion but also complete through-hardenability of thick-walled forgings, for example as monobloc rotors or as rotor disks in gas and steam turbines. Proven alloys of this type usually contain about 0.08 to 0.2% carbon, which in solution allows the setting of a hard martensitic structure. A good combination of heat resistance and ductility of martensitic steels is made possible by a tempering treatment in which Forming a particle-stabilized subgrain structure by the precipitation of carbon in the form of carbides with simultaneous recovery of the dislocation substructure. The tempering behavior and the resulting properties can be effectively influenced by the choice and proportionate tuning of specific carbide formers such as Mo, W, V, Nb and Ta.
Festigkeiten über 850 MPa von 9-12 % Chromstählen können eingestellt werden, indem die Anlasstemperatur tief, typischer Weise im Bereich 600 bis 650 °C, gehalten wird. Die Anwendung tiefer Anlasstemperaturen führt jedoch zu hohen Übergangstemperaturen vom spröden in den duktilen Zustand (über 0 °C), womit der Werkstoff bei Raumtemperatur sprödes Bruchverhalten entfaltet. Deutlich verbesserte Duktilitäten können erreicht werden, wenn die vergütete Festigkeit unter 700 MPa abgesenkt wird. Dies wird durch ein Anheben der Anlasstemperatur auf über 700 °C erreicht. Die Anwendung erhöhter Anlasstemperaturen hat dabei den Vorteil, dass die eingestellten Gefügezustände bei erhöhten Temperaturen über längere Zeiten stabil sind. Ein typischer Vertreter, welcher in Dampfkraftwerken, insbesondere als Rotorstahl breite Verwendung gefunden hat, ist der unter DIN bekannte deutsche Stahl X20CrMoV12.1.Strengths above 850 MPa for 9-12% chromium steels can be adjusted by keeping the tempering temperature low, typically in the range 600 to 650 ° C. However, the use of low tempering temperatures leads to high transition temperatures from the brittle to the ductile state (above 0 ° C), with which the material exhibits brittle fracture behavior at room temperature. Significantly improved ductilities can be achieved if the tempered strength is lowered below 700 MPa. This is achieved by raising the tempering temperature to over 700 ° C. The use of increased tempering temperatures has the advantage that the set structural states are stable for longer times at elevated temperatures. A typical representative who has found widespread use in steam power plants, in particular as rotor steel, is the German steel X20CrMoV12.1 known under DIN.
Es ist ferner bekannt, dass die Duktilität auf einem Festigkeitsniveau von 850 MPa durch das Zulegieren von Nickel deutlich verbessert werden kann. So ist etwa bekannt, dass durch das Zulegieren von etwa 2 bis 3 % Nickel selbst nach einer Anlassbehandlung bei Temperaturen von 600 bis 650 °C die Übergangstemperatur vom spröden in den duktilen Zustand noch unter 0 °C liegt, womit sich insgesamt eine deutliche verbesserte Kombination von Festigkeit und Duktilität einstellen lässt. Solche Legierungen finden daher dort eine breite Verwendung, wo deutlich höhere Anforderungen an sowohl Festigkeit wie auch Duktilität gestellt werden, typischer Weise als Scheibenwerkstoffe für Gasturbinenrotoren. Ein typischer Vertreter derartiger Legierungen, welcher in der Gasturbinentechnik, insbesondere als Werkstoff für Rotorscheiben breite Verwendung gefunden hat, ist der unter DIN bekannte deutsche Stahl X12CrNiMo12.It is also known that the ductility at a strength level of 850 MPa can be significantly improved by alloying nickel. For example, it is known that by alloying about 2 to 3% nickel, even after a tempering treatment at temperatures of 600 to 650 ° C, the transition temperature from brittle to ductile state is still below 0 ° C, resulting in a significantly improved overall combination of strength and ductility. Such alloys are therefore widely used where significantly higher demands are placed on both strength and ductility, typically as disk materials for gas turbine rotors. A typical representative of such alloys, which in the gas turbine technology, in particular as a material for rotor disks width Has found use is known under DIN German steel X12CrNiMo12.
In der vergangenen Zeit wurden verschiedene Anstrengungen unternommen, um spezielle Eigenschaften dieser Stähle zu verbessern. So wird beispielsweise in der Veröffentlichung von
Speziell für Gasturbinenanwendungen wurden auf der anderen Seite Anstrengungen unternommen, um entweder die Zeitstandfestigkeiten im Bereich von 450 bis 500°C auf hohem Duktilitätsniveau zu verbessern oder die Versprödungsneigung bei Temperaturen zwischen 425 und 500 °C zu reduzieren. So beschreibt die europäische Patentanmeldung
Ein möglicher Ansatz zur Verbesserung der Warmfestigkeit bei gleichzeitig hoher Duktilität wurde mit der Entwicklung von Stählen mit erhöhten Stickstoffgehalten vorgeschlagen. In
Ein optimierter Ausbildungszustand von Nitriden ist jedoch nur ein Faktor zur Erreichung einer maximalen Duktilität. Ein weiterer Einflussfaktor ist durch die Wirkung von gelösten Substitutionselementen wie Nickel und Mangan zu erwarten. Von Mangan ist von den Kohlenstoffstählen her bekannt, dass dieses Element eher versprödend als duktilitätsfördernd wirkt. Insbesondere bewirkt es eine Versprödung, wenn die Legierung einer langzeitigen Glühung bei Temperaturen im Bereich 350 bis 500 °C ausgesetzt wird. Es ist ferner bekannt, dass Nickel in Kohlenstoffstählen die Duktilität verbessert, tendenziell aber auch die Warmfestigkeit bei hohen Temperaturen senkt. Dies wird mit einer reduzierten Karbidstabilität in nickelhaltigen Stählen in Beziehung gesetzt.However, an optimized formation state of nitrides is only one factor for achieving maximum ductility. Another factor is the effect of dissolved substitution elements such as nickel and manganese. Manganese is known from carbon steels to be embrittling rather than promoting ductility. In particular, it causes embrittlement when the alloy is subjected to long-term annealing at temperatures in the range of 350 to 500 ° C. It is also known that nickel in carbon steels improves ductility but tends to lower high temperature hot strength as well. This is related to reduced carbide stability in nickel-containing steels.
Aus
Es ist bekannt, dass sich bei Stählen mit ca. 12 % Chrom und einem erhöhten Anteil an N nachteilig im Temperaturbereich von etwa 425 bis 500 °C die α'Cr-Phase ausscheidet, welche zur Versprödung des Stahles führt. Zwar werden durch diese Ausscheidungen die Festigkeitseigenschaften erhöht, aber die Werte für Duktilität, Kerbschlagzähigkeit und Korrosionsbeständigkeit sinken. Damit sind derartige Stähle für den Einsatz in Verdichtern oder Turbinen im Kraftwerksbereich nur bedingt einsetzbar. Die Bildung von VN in derartigen Stählen verstärkt noch die Neigung zur Ausscheidung der α'Cr-Phase und damit die Versprödungsneigung im genannten Temperaturbereich.It is known that in steels with about 12% chromium and an increased proportion of N adversely affects the α'Cr phase in the temperature range of about 425 to 500 ° C, which leads to embrittlement of the steel. Although these precipitates increase the strength properties, the ductility, notched impact strength and corrosion resistance values decrease. Thus, such steels are only of limited use for use in compressors or turbines in the power plant area. The formation of VN in such steels further enhances the tendency to precipitate the α'Cr phase and hence the embrittlement tendency in said temperature range.
Der Erfindung liegt die Aufgabe zugrunde, einen martensitisch-härtbaren Vergütungsstahl mit hoher Duktilität im Temperaturbereich zwischen 350 und 500 °C und guter Kriechfestigkeit im Temperaturbereich bis 550 °C zu schaffen.The invention has for its object to provide a martensitic-hardenable tempering steel with high ductility in the temperature range between 350 and 500 ° C and good creep resistance in the temperature range up to 550 ° C.
Kern der Erfindung ist ein martensitisch-härtbarer Vergütungsstahl mit folgender Zusammensetzung (Angaben in Gew.-%): 8.5 bis 9.5 Cr, 0.15 bis 0.25 Mn, 2 bis 2.7 Ni, 0.5 bis 2.5 Mo, 0.4 bis 0.8 V, 0.02 bis 0.04 Nb, 0.001 bis 0.15 Si, 0.06 bis 0.1 C, 0.11 bis 0.15 N, maximal 0.007 P, maximal 0.005 S, maximal 0.01 Al, Rest Eisen und übliche Verunreinigungen, und der Massgabe, dass das Gewichtsverhältnis von Vanadium zu Stickstoff V/N im Bereich zwischen 4.3 und 5.5 liegt.Core of the invention is a martensitic-hardenable tempering steel having the following composition (in wt .-%): 8.5 to 9.5 Cr, 0.15 to 0.25 Mn, 2 to 2.7 Ni, 0.5 to 2.5 Mo, 0.4 to 0.8 V, 0.02 to 0.04 Nb , 0.001 to 0.15 Si, 0.06 to 0.1 C, 0.11 to 0.15 N, maximum 0.007 P, maximum 0.005 S, maximum 0.01 Al, balance iron and common impurities, and the requirement that the weight ratio of vanadium to nitrogen V / N in the range between 4.3 and 5.5.
Bevorzugte Bereiche für die einzelnen Legierungselemente der erfindungsgemässen Zusammensetzung sind in den Unteransprüchen enthalten.Preferred ranges for the individual alloying elements of the inventive composition are contained in the subclaims.
Der Vorteil der Erfindung besteht darin, dass bei der genannten Legierung ein Vergütungsgefüge eingestellt wird, das sich durch eine zähe Grundmatrix und durch die Anwesenheit warmfestigkeitsbringender Nitride auszeichnet, wobei gleichzeitig eine Versprödungsneigung im Bereich zwischen 350 und 500 °C unterdrückt wird. Die Zähigkeit der Grundmatrix wird durch die Anwesenheit von Substitionselementen, vorzugsweise durch Nickel, eingestellt. Die Gehalte der Substitutionselemente sind so bestimmt, dass sie eine optimale Entfaltung von sowohl der Martensithärtung wie auch der Teilchenhärtung durch Sondernitride, vorzugsweise Vanadiumnitride, zur Einstellung einer hohen Kriechfestigkeit bei gleichzeitig guter Duktilität ermöglichen. Die Versprödungsneigung des erfindungsgemässen Stahles im Temperaturbereich von 350 bis 500 °C infolge Ausscheidung der α'Cr-Phase wird dabei durch den im Vergleich zum bekannten Stand der Technik geringen Cr-Gehalt und moderaten N-Gehalt unterdrückt.The advantage of the invention is that in the said alloy, a compensation structure is set, which is characterized by a tough matrix and the presence of heat-resistant nitrides, at the same time a tendency to embrittlement in the range between 350 and 500 ° C is suppressed. The toughness of the base matrix is adjusted by the presence of substitution elements, preferably nickel. The contents of the substitution elements are determined so as to allow optimum unfolding of both martensite hardening and particle hardening by means of special nitrides, preferably vanadium nitrides, to provide high creep strength coupled with good ductility. The embrittlement tendency of the inventive steel in the temperature range of 350 to 500 ° C due to precipitation of the α'Cr phase is suppressed by the low compared to the prior art, the Cr content and moderate N content.
Nachfolgend werden die bevorzugten Mengen in Gewichtsprozenten für jedes Element und die Gründe für die gewählten erfindungsgemässen Legierungsbereiche in ihrem Zusammenhang mit den hieraus resultierenden Möglichkeiten der Wärmebehandlungen aufgezeigt.Hereinafter, the preferred amounts in weight percent for each element and the reasons for the selected according to the invention Alloy areas shown in their context with the resulting possibilities of heat treatments.
Ein Gewichtsanteil von 8.5 bis 9.5 % Chrom ermöglicht eine vertretbare Durchhärtbarkeit dickwandiger Bauteile und stellt eine hinreichende Oxidationsbeständigkeit bis zu einer Temperatur von 550 °C sicher. Ein Gewichtsanteil unter 8.5 % beeinträchtigt die Durchvergütbarkeit. Gehalte oberhalb 9.5 % führen zur beschleunigten Bildung der α'Cr-Phase während des Anlassvorgangs, welche zur Versprödung des Materials führt.A weight content of 8.5 to 9.5% chromium allows a reasonable hardenability of thick-walled components and ensures sufficient oxidation resistance up to a temperature of 550 ° C. A weight fraction below 8.5% impairs the through-hardenability. Contents above 9.5% lead to the accelerated formation of the α'Cr phase during the tempering process, which leads to embrittlement of the material.
Diese Elemente fördern die Anlassversprödung und müssen daher auf kleinste Gehalte begrenzt werden. Der zu spezifierende Bereich sollte unter Berücksichtigung der pfannenmetallurgischen Möglichkeiten im Bereich zwischen 0.15 und 0.25 % für Mangan und zwischen 0.001 und 0.15 % für Silizium liegen.These elements promote temper embrittlement and must therefore be limited to the smallest amounts. The range to be specified should be between 0.15 and 0.25% for manganese and between 0.001 and 0.15% for silicon, taking into account the possibilities of ladle metallurgy.
Nickel wird als austenitstabilisierendes Element zur Unterdrückung von Delta-Ferrit eingesetzt. Darüber hinaus soll es als ein gelöstes Element in der ferritischen Matrix die Duktilität verbessern. Nickelgehalte zwischen 2 bis 2.7 Gew.-% sind optimal, da einerseits das Nickel homogen in der Matrix gelöst ist, andererseits noch kein erhöhter Anteil von Restaustenit beziehungsweise Anlassaustenit im vergüteten Martensit vorliegt.Nickel is used as an austenite stabilizing element to suppress delta ferrite. In addition, it is said to improve ductility as a dissolved element in the ferritic matrix. Nickel contents between 2 to 2.7 wt .-% are optimal, since on the one hand, the nickel is homogeneously dissolved in the matrix, on the other hand, there is still no increased proportion of retained austenite or tempering austenite in the tempered martensite.
Dieses Element verbessert die Kriechfestigkeit durch Mischkristallhärtung als partiell gelöstes Element und durch Ausscheidungshärtung während einer Langzeitbeanspruchung. Ein übermässig hoher Anteil dieses Elementes führt jedoch zu Versprödung während einer Langzeitauslagerung, welcher durch die Ausscheidung und Vergröberung der Sigma-Phase gegeben ist. Aus diesem Grund muss der maximale Anteil von Mo auf 2.5 % begrenzt werden. Ein bevorzugter Bereich liegt bei ca. 1.4 bis 1.6 %.This element improves creep strength by solid solution hardening as a partially dissolved element and precipitation hardening during a long-term stress. However, an excessively high proportion of this element leads to embrittlement during a long-term aging, which is due to the excretion and coarsening of the sigma phase. For this Reason, the maximum proportion of Mo must be limited to 2.5%. A preferred range is about 1.4 to 1.6%.
Diese beiden Elemente zusammen kontrollieren massgeblich die Korngrössenausbildung und die Ausscheidungshärtung. Die Gefügeausbildungsformen sind dann optimal, wenn die Elemente Vanadium und Stickstoff in einem leicht überstöchiometrischem V/N-Verhältnis zulegiert sind. Ein leicht überstöchiometrisches Verhältnis erhöht auch die Stabilität des Vanadiumnitrids gegenüber der des Chromnitrids. Insgesamt bevorzugt wird ein V/N Verhältnis im Bereich zwischen 4.3 bis 5.5. Der konkrete Gehalt an Stickstoff und Vanadiumnitriden richtet sich nach dem optimalen Volumenanteil der Vanadiumnitride, welche während der Lösungsglühung als unlösliche Primärnitride zurückbleiben sollen. Je grösser der Gesamtanteil von Vanadium und Stickstoff ist, umso grösser derjenige Anteil der Vanadiumnitride, welcher nicht mehr in Lösung geht und umso grösser die Kornfeinungswirkung. Der positive Einfluss der Kornfeinung auf die Duktilität ist jedoch begrenzt, da mit zunehmendem Volumenanteil von Primämitriden die Primärnitride selbst die Duktilität begrenzen. Da VN auch die Neigung zur Bildung der spröden α'Cr-Phase erhöht, sollte der bevorzugte Gehalt an Stickstoff im Bereich von 0.11 bis 0.12 Gew.- % und derjenige von Vanadium im Bereich zwischen 0.5 und 0.6 Gew.- % liegen. Denkbar sind Bereichen von 0.11 bis 0.15 Gew.- % für N und 0.4-0.8 Gew.- % V.Together, these two elements significantly control grain size formation and precipitation hardening. The microstructural forms are optimal when the elements vanadium and nitrogen are alloyed in a slightly more than stoichiometric V / N ratio. A slightly more than stoichiometric ratio also increases the stability of the vanadium nitride over that of the chromium nitride. Overall, a V / N ratio in the range between 4.3 to 5.5 is preferred. The specific content of nitrogen and vanadium nitrides depends on the optimum volume fraction of the vanadium nitrides, which are to remain as insoluble primary nitrides during the solution annealing. The greater the total amount of vanadium and nitrogen, the greater the proportion of vanadium nitrides which no longer dissolve and the greater the grain refining effect. However, the positive effect of grain refining on ductility is limited because with increasing volume fraction of primary nitrides, the primary nitrides themselves limit ductility. Since VN also increases the tendency to form the brittle α'Cr phase, the preferred content of nitrogen should be in the range of 0.11 to 0.12% by weight and that of vanadium should be in the range of 0.5 to 0.6% by weight. Conceivable ranges are 0.11 to 0.15% by weight for N and 0.4-0.8% by weight V.
Neben Vanadium ist Niob ein bevorzugtes Element unter den Sondemitridbildnern. Der bevorzugte Bereich liegt bei 0.02 bis 0.04 Gew.- %. In diesen kleinen Beimengungen wird der Kornvergröberungswiderstand beim Lösungsglühen erhöht und die Stabilität von primären und auszuscheidenden V8N,C)-Nitriden durch partielle Substitution von V erhöht.Besides vanadium, niobium is a preferred element among the special nitride formers. The preferred range is 0.02 to 0.04% by weight. In these small admixtures, the grain coarsening resistance in solution annealing is increased and the stability of primary and excrete V8N, C) nitrides is increased by partial substitution of V.
Diese Elemente verstärken zusammen mit Silizium und Mangan die Anlassversprödung bei Langzeitauslagerungen im Bereich zwischen 350 und 500°C. Diese Elemente sollten daher auf minimal tolerierbare Anteile begrenzt werden.Together with silicon and manganese, these elements increase the embrittlement of long-term aging in the range between 350 and 500 ° C. These elements should therefore be limited to the minimum tolerable levels.
Dieses Element ist ein starker Nitridbildner, welcher Stickstoff schon in der Schmelze abbindet und damit die Wirksamkeit des zulegierten Stickstoffs stark beeinträchtigt. Die in der Schmelze gebildeten Aluminiumnitride sind sehr grob und senken die Duktilität. Aluminium muss daher auf einen Gewichtsanteil von 0.01 % begrenzt werden.This element is a strong nitride former, which already sets nitrogen in the melt and thus strongly affects the effectiveness of the added nitrogen. The aluminum nitrides formed in the melt are very coarse and reduce the ductility. Aluminum must therefore be limited to a weight fraction of 0.01%.
Kohlenstoff bildet beim Anlassen Chromkarbide, welche für eine verbesserte Kriechfestigkeit förderlich sind. Bei zu hohen Kohlenstoffgehalten führt der hieraus resultierende erhöhte Volumenanteil von Karbiden jedoch zu einer Duktilitätsminderung, welche insbesondere durch die Karbidvergröberung während einer Langzeitauslagerung zum Tragen kommt. Der Kohlenstoffgehalt sollte daher nach oben auf 0.1 % begrenzt werden. Nachteilig ist auch die Tatsache, dass Kohlenstoff die Aufhärtung beim Schweissen verstärkt. Der besonders bevorzugte Kohlenstoffgehalt liegt im Bereich zwischen 0.06 und 0.08 Gew.- %.Carbon forms chromium carbides on tempering, which are conducive to improved creep resistance. At too high carbon contents, however, the resulting increased volume fraction of carbides leads to a ductility reduction, which comes into play in particular by the carbide coarsening during long-term storage. The carbon content should therefore be limited upwards to 0.1%. Another disadvantage is the fact that carbon increases the hardening during welding. The most preferred carbon content is in the range of 0.06 to 0.08% by weight.
In der Zeichnung ist ein Ausführungsbeispiel der Erfindung dargestellt. Die einzige Figur zeigt die Abhängigkeit der Spannung von der Zeit für das Erreichen einer Kriechdehnung von 1 % bei 550 °C für eine erfindungsgemässe Legierung und eine aus dem Stand der Technik bekannte Legierung.In the drawing, an embodiment of the invention is shown. The sole figure shows the dependence of the voltage on time for achieving a creep strain of 1% at 550 ° C for an alloy according to the invention and an alloy known from the prior art.
Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen und der Fig. 1 näher erläutert.The invention will be explained in more detail with reference to embodiments and FIG. 1.
Tabelle 1 gibt die chemische Zusammensetzung (in Gew.- %) einer bevorzugten erfindungsgemässen Legierung (DM13) und von Vergleichslegierungen wieder:
Typ "D"
Type "D"
Es wurden 10 kg Schmelzen in einem Induktionsofen erschmolzen und anschliessend geschmiedete Flachstäbe mit den Abmessungen 20mmx80mm hergestellt. Die folgenden Wärmebehandlungen wurden durchgeführt:
- DM13A-2:
1100°C/3h/schnelle Luftabkühlung (Ventilator) + 640°C/5h/Luftabkühlung - St13TNiEL:
1050-1080 °C/>0.5h/Öl + 630-650 °C/>2h/Luftabkühlung - Legierung "D":
1180°C/2h/Luftabkühlung + 640°C/2h/Luftabkühlung + 600°C/1h/Ofenabkühlung
- DM13A-2:
1100 ° C / 3h / fast air cooling (fan) + 640 ° C / 5h / air cooling - St13TNiEL:
1050-1080 ° C /> 0.5h / oil + 630-650 ° C /> 2h / air cooling - Alloy "D":
1180 ° C / 2h / air cooling + 640 ° C / 2h / air cooling + 600 ° C / 1h / furnace cooling
In Tabelle 2 sind experimentelle Daten zur Ermittlung der Kerbschlagenergie bei Raumtemperatur enthalten:
Man erkennt deutlich die Reduktion der Kerbschlagarbeit bei der Legierung "D" nach einer Auslagerung der Proben im Bereich zwischen 300 und 500°C. Dies ist in der Ausscheidung der α'Cr-Phase begründet. Bei der erfindungsgemässen Legierung DM13A-2 ist die Neigung zur Ausscheidung dieser Phase dagegen verringert, so dass auch die Versprödung im genannten Temperaturbereich geringer ausfällt.It can be clearly seen the reduction of impact energy in the alloy "D" after a swapping of the samples in the range between 300 and 500 ° C. This is due to the excretion of the α'Cr phase. In the case of the alloy DM13A-2 according to the invention, the tendency to precipitate this phase is opposed reduced, so that the embrittlement in the temperature range is lower.
Zugversuche bei Raumtemperatur und bei 550°C der oben beschriebenen wärmebehandelten Proben (Ausgangszustand) brachten die in Tabelle 3 enthaltenen Ergebnisse:
Die erfindungsgemässe Legierung zeichnet sich sowohl durch eine hohe Warmfestigkeit bei 550 °C aus, als auch durch eine hohe Duktilität und einen guten E-Modul.The alloy according to the invention is distinguished by a high heat resistance at 550 ° C., as well as by a high ductility and a good modulus of elasticity.
In der einzigen Figur ist in Abhängigkeit von der Zeit die Spannung für 1 % Kriechdehnung bei 550 °C für die Legierungen DM13A-2 und St13TNiEL dargestellt. Der Vorteil der erfindungsgemässen Legierung kommt bei hohen Auslagerungszeiten zum Tragen.
Selbstverständlich ist die Erfindung nicht auf das beschriebene Ausführungsbeispiel beschränkt.In the single figure, the voltage for 1% creep at 550 ° C for the alloys DM13A-2 and St13TNiEL is shown as a function of time. The advantage of the alloy according to the invention comes into play at high removal times.
Of course, the invention is not limited to the embodiment described.
Claims (8)
- Maraging heat-treatment steel, characterized by the following chemical composition (details in % by weight): 8.5 to 9.5 Cr, 0.15 to 0.25 Mn, 2 to 2.7 Ni, 0.5 to 2.5 Mo, 0.4 to 0.8 V, 0.001 to 0.15 Si, 0.06 to 0.1 C, 0.11 to 0.15 N, 0.2 to 0.4 Nb, max 0.007 P, max 0.005 S, max 0.01 Al, remainder iron and standard impurities, with the proviso that the vanadium to nitrogen weight ratio V/N is in the range between 4.3 and 5.5.
- Maraging heat-treatment steel according to Claim 1, characterized by 8.5 to 9% Cr by weight.
- Maraging heat-treatment steel according to Claim 1, characterized by 0.2% by weight Mn.
- Maraging heat-treatment steel according to Claim 1, characterized by 2.3 to 2.6% by weight Ni.
- Maraging heat-treatment steel according to Claim 1, characterized by 1.4 to 1.6% Mo by weight.
- Maraging heat-treatment steel according to Claim 1, characterized by 0.5 to 0.6% by weight V.
- Maraging heat-treatment steel according to Claim 1, characterized by 0.11 to 0.12% N by weight.
- Maraging heat-treatment steel according to Claim 1, characterized by 0.06 to 0.08% C by weight.
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US20100037994A1 (en) * | 2008-08-14 | 2010-02-18 | Gopal Das | Method of processing maraging steel |
JP6128935B2 (en) * | 2012-05-22 | 2017-05-17 | キヤノン株式会社 | Substrate for liquid discharge head and liquid discharge head |
CN102912248A (en) * | 2012-10-13 | 2013-02-06 | 山东理工大学 | High-toughness wear resistant martensitic stainless steel and production method thereof |
CN104789894A (en) * | 2015-04-04 | 2015-07-22 | 王文姣 | Heat treatment method of high-strength automobile bumper and high-strength automobile bumper |
GB2546809B (en) * | 2016-02-01 | 2018-05-09 | Rolls Royce Plc | Low cobalt hard facing alloy |
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JPH01230713A (en) * | 1988-03-08 | 1989-09-14 | Nippon Steel Corp | Production of high-strength and high-toughness steel having excellent stress corrosion cracking resistance |
JPH0794687B2 (en) * | 1989-03-29 | 1995-10-11 | 新日本製鐵株式会社 | Method for producing HT80 steel excellent in high weldability, stress corrosion cracking resistance and low temperature toughness |
EP0411515B1 (en) | 1989-07-31 | 1993-09-08 | Mitsubishi Jukogyo Kabushiki Kaisha | High strength heat-resistant low alloy steels |
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US6045630A (en) * | 1997-02-25 | 2000-04-04 | Sumitomo Metal Industries, Ltd. | High-toughness, high-tensile-strength steel and method of manufacturing the same |
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US5906791A (en) * | 1997-07-28 | 1999-05-25 | General Electric Company | Steel alloys |
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