CA2251805A1 - Martensitic-austentitic steel - Google Patents
Martensitic-austentitic steel Download PDFInfo
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- CA2251805A1 CA2251805A1 CA002251805A CA2251805A CA2251805A1 CA 2251805 A1 CA2251805 A1 CA 2251805A1 CA 002251805 A CA002251805 A CA 002251805A CA 2251805 A CA2251805 A CA 2251805A CA 2251805 A1 CA2251805 A1 CA 2251805A1
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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
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of 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
- C22C38/001—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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
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Abstract
This invention concerns a martensitic-austentitic steel consisting essentially (in wt%) of: 8 to 15 % chromium, 0.5 to 2.5 %
molybdenum, up to 2 % tungsten, 4 to 10 % cobalt, 0.5 to 6 % nickel, 2.5 to 8 % manganese, 0.1 to 1.0 % vanadium 0.05 to 0,25 %
nitrogen, up to 0.2 % carbon, the rest being iron with impurities. This martensitic-austentitic steel can be used, in particular, as material for rotors or rotor disks in gas turbines operating at temperatures above above 450 °C. The adjustment of the two phase martensitic-austentitic structure is done by heat treatment of the solution annealed and quenched steel structure in a temperature range between 550 °C and 650 °C.
molybdenum, up to 2 % tungsten, 4 to 10 % cobalt, 0.5 to 6 % nickel, 2.5 to 8 % manganese, 0.1 to 1.0 % vanadium 0.05 to 0,25 %
nitrogen, up to 0.2 % carbon, the rest being iron with impurities. This martensitic-austentitic steel can be used, in particular, as material for rotors or rotor disks in gas turbines operating at temperatures above above 450 °C. The adjustment of the two phase martensitic-austentitic structure is done by heat treatment of the solution annealed and quenched steel structure in a temperature range between 550 °C and 650 °C.
Description
- CA 022~180~ 1998-10-13 Martensitic-austenitic steel R~ CKG~OUND OF THE lN v~NllON
Field of the invention - The invention relates to a martensitic-austenitic steel, in particular for use as a material for creep-stressed components of gas turbines.
Discussion of background The use of hardenable and temperable chrome steels as a material for use in thermal power stations, in particular as a material for rotors or rotor wheels, is now state of the art. As compared with nickel-based super-alloys, hardenable and temperable chrome steels are distinguished in that they are more amenable to non-destructive testing. Furthermore, they have comparatively low coefficients of thermal expansion and high thermal conductivityi this enhances the resistance to thermal fatigue. At temperatures above 450 C, however, the hardened and tempered steels do not meet the demand, as desired, with respect to heat resistance, creep resistance and toughness.
A hardenable and temperable martensitic steel designated X12CrNiMol2 is known. In addition to iron, this steel contains 0.10-0.14% of C, 0.10-0.40% of Si, 0.5-0.9% of Mn, 11-12% of Cr, 2-2.6% of Ni, 1.3-1.8% of Mo, 0.2-0.35% of V and 0.02-0.05% of N as well as usual impurities. In the temperature range below 450 C, this steel has a relatively high high-temperature yield strength and a relatively high creep resistance.
However, the high-temperature yield strength and the creep behavior are inadequate at temperatures above 450 C. Furthermore, the steel shows a not inconsiderable tendency to embrittlement at higher temperatures.
AMENDED SHEET
- CA 022~180~ 1998-10-13 EP-A-481 377 discloses a high-strength martensitic-austenitic steel having a composition in %
by weight of 10 to 17% of chromium, less than 4% of molybdenum, up to 4% of cobalt, up to 8% of nickel, up to 10% of manganese, up to 1.0% of vanadium, up to 0.3%
of nitrogen, up to 0.15% of carbon, up to 6% of silicon and up to 4% of copper, the remainder being iron and mpurltles .
~ SUMMARY OF THE INVENTION-Accordingly, the object of the invention is to provide a martensitic-austenitic steel for use in gas turbine rotors or gas turbine rotor wheels having an adequate heat resistance and toughness for a temperature range from 450 C to at least 550 C.
According to the invention, this is achieved by the features of the first claim.
The core of the invention is the setting of a very fine two-phase microstructure comprising tempered martensite and thermodynamically stable austenite. The steel essentially comprises 8 to 15% of chromium, 4 to 10% of cobalt, 2.5 to 8% of manganese, 0.5 to 6% of nickel, 0.5 to 2.5% of molybdenum, up to 2% of tungsten, 0.1 to 0.5% of vanadium, 0.05 to 0.2% of carbon and 0.05 to 0.25% of nitrogen, the remainder being iron and usual impurities resulting from the smelting.
The advantages of the invention are to be seen above all in the fact that the steel formed in a duplex structure has, even at temperatures above 450 C, a high high-temperature yield strength and a high creep resistance and, due to its high structural stability, shows a low tendency to embrittlement.
Further advantageous embodiments result from the subclaims.
AMENDED SHEET
- CA 022~180~ 1998-10-13 DESCRIPTION OF THE PREFERRED EMBODIMENT
The steel, developed for the use according to the invention, essentially contains (measured in % by 5 weight) 8 to 15% of chromium, 4 to 10% of cobalt, 2.5 to 8% of manganese, 0.5 to 6% of nickel, 0.5 to 2.5% of molybdenum, up to 2% of tungsten, 0.1 to 1.0% of vanadium, 0.05 to 0.2% of carbon and 0.05 to 0.25% of nitrogen, and it can be produced by casting or by powder-metallurgical means.
Known and industrially accepted 9-12% chrome steels achieve their heat resistance and creep resistance via the stabilizing action of extremely fine precipitations upon the dislocation network formed in the tempered martensite. In the steel developed for use according to the invention, a cubic face-centered phase (austenite) in addition to the fine precipitations is introduced which, due to its low self-diffusion and the formation of phase boundaries, contributes to an increase in the heat res;stance and creep resistance.
Martensitic steels with austenite as a creep-improving second phase are known in the art. By comparison with the steel according to the invention, however, they differ by the fact that their austenite fraction is not thermodynamically stable, so that a high susceptibility to thermal fatigue arises.
Below, the particularly preferred quantities for each element and the reasons for the selected alloying ranges of the alloy according to the invention are displayed.
The oxidation resistance is increased by chromium dissolved in the solid solution. Via the formation of hexagonal chromium nitrides, Cr can also - contribute to the improvement in creep resistance. In order to achieve this, a minimum Cr content of 8% by weight is necessary. The chromium content should, however, not exceed 15% by weight, since otherwise ~-ferrite is formed which entails a reduction in AMENDED SHEET
CA 022~180~ 1998-10-13 ~ 4/10 toughness and high-temperature strength. An expedient range for chromium therefore ranges from about 8 to 15%
by weight, preferably from 9 to 12% by weight, and especially is about 10% by weight.
In the present steel, manganese is particularly effective in increasing the solubility of nitrogen in the austenite region. A mlnlmum Mn content of 2.5% by weight is desirable in order to dissolve the stable nitrides of the hexagonal type (Cr,V)2N and of the cubic type (V, Cr)N during the solution-annealing.
During the tempering treatment, manganese is concentrated in the austenite formed and decisively lowers its martensite start temperature, i.e. manganese stabilizes the austenite. For this reason also, the manganese content should be at least 2.5% by weight.
The Mn content should, however, not exceed 8% by weight, in order to prevent the alloy from becoming completely austenitic. An expedient range for manganese therefore extends from about 2.5 to 8% by weight, preferably from 3.5 to 6.5% by weight, and is especially about 5% by weight.
Nickel increases the toughness in martensitic chrome steels, for example because it effectively reduces the ~-ferrite content. In a manner similar to manganese, nickel stabilizes the austenitic phase in the duplex structure. For this reason, the alloy should contain at least 0.5% by weight of Ni. Above a nickel content of 6% by weight, the Ac3 point is lowered to an undue extent. An expedient range for nickel therefore extends from about 0.5 to 6% by weight, preferably from 2 to 5% by weight, and is especially about 3.7% by weight.
Cobalt increases the nickel equivalent to such an extent that the alloy solidifies austenitically from the melt. As a result, nitrogen effusion and hence pore formation are avoided. The Co content should therefore be at least 4% by weight. However, the Co content should not exceed 10% by weight, so that the alloy still has a sufficiently high Ac3 temperature. An CORRECTED SHEET (RULE 91) ISA/EP
CA 022~l80~ l998-l0-l3 expedient range for cobalt therefore extends from about 4 to 10% by weight, preferably from 5 to 8% by weight, and is especially about 6% by weight.
Molybdenum promotes good tempering properties and the heat resistance, and a minimum content of 0.2%
by weight should therefore be maintained. The Mo content should not exceed 2.0% by weight, since otherwise a massive formation of Laves phases can occur. An expedient range for molybdenum therefore extends from 0. 5 to 2. 5% by weight, preferably from 1.0 to 2.0% by weight, and is especially about 1. 5% by weight.
Tungsten acts in a manner similar to molybdenum. Because of the risk of the formation of Laves phases, a content of 2% by weight should not be exceeded. The tungsten content is therefore within the range from 0 to 2% by weight, preferably below 1% by weight.
TogeLher with nitrogen and small fractions of chromium, vanadium forms a dense dispersion of coherent and partially coherent cubic nitrides which essentially determine the heat resistance and creep resistance. At least 0.1% by weight of V should be alloyed in. Since, however, vanadium promotes the tendency to form ~-ferrite, 1% by weight of V should not be exceeded.Preferably, the vanadium content is in the range from 0.15 to 0. 65% by weight.
In the atomically dissolved state, nitrogen promotes the diffusion-free martensitic conversion from the austenitic phase during cooling. This ensures the capacity for hardening and tempering. In addition, it forms the already mentioned nitrides with V and Cr and, if appropriate, also with Nb, Ti and Ta. Nitrogen should therefore be alloyed in approximately 3 5 stoichiometric quantities. Because of a possible N
effusion during solidification, an upper limit of 0.25%
by weight should not be exceeded. For this reason, the N content is in the range from about 0. 05 to 0. 25% by CORRECTED SHEET (RULE 91) ISA/EP
CA 022~180~ 1998-10-13 weight, preferably in the range from 0.07 to 0.15% by weight.
Together with chromium, carbon promotes the formation of carbides of the form Cr23C6. Owing to its stoichiometry, this carbide removes more chromium from the matrix than the Cr2N formed in the steel according to the invention. For this reason, the carbon content should not exceed 0.2% by weight, preferably 0.1% by weight.
Niobium, titanium, zirconium and tantalum are alloying elements which, together with vanadium, can form special nitrides of the MX type. Their effect is above all based on the fact that, even with small additions, they enhance the stability of V(N,C) precipitations. At unduly high contents, the stability of the nitrides is, however, so high that they cannot be dissolved during the solution-annealing treatment.
For this reason, the total content of these elements is to be limited to 0.5%.
Boron increases the coarsening resistance of precipitations. Since it tends to cause segregations, the content must be limited to 0.02%.
Among the usually occurring impurities, resulting from production, the elements such as phosphorus, sulfur, antimony, tin and arsenic should not exceed the contents indicated in Table 2 below.
This is necessary, in order to avoid embrittlement during tempering.
The steel according to the invention has a martensitic-austenitic microstructure which is produced by a hardening and tempering process. The hardening and tempering process comprises solution-annealing, hardening and subsequent tempering.
The solution-annealing should take place within the temperature range of 1050 C T 1250 C, preferably at 1100-C T 1230-C and especially at 1200 C, in order to dissolve all the nitrides of the form VN. The austenite content and the degree of hardening of the martensitic phase are set via the CA 022~l80~ l998-l0-l3 tempering treatment. In order to set a desired austenite fraction of 15 to 45%, a tempering temperature in the range of 550 C T 650-C should be selected, preferably 580 C T 630 C.
Embodiment example By way of example, a particularly preferred embodiment of the alloys described above is discussed in more detail below, and this is designated alloy 817.
The composition of the alloy 817 can be taken from Table 1 and also from Table 2. Table 2 here shows some maximum contents of possible impurities.
After solution-annealing and a quenching treatment, the alloy was tempered for 4 hours at 600-.
After this heat treatment, the microstructure was two-phase martensitic-austenitic with a content of about 37% of austenite phase and a phase region size of from 200 to 300 nm.
The properties of the alloy 817 according to the invention are compared in Table 3 with the previously mentioned alloy X12CrNiMol2.
According to Table 3, the alloy 817 iS
distinguished throughout by improved properties as compared with the alloy X12CrNiMol2. The high heat resistance and creep resistance allow use as rotor material or rotor wheel material for gas turbines at elevated temperatures of up to 550 C.
Element Cr Mo W Co Ni Mn V
% by wt. 10 0.5 1.5 6.0 3.7 5.0 0.5 Element Nb Ti Ta N C Fe % by wt. 0.01 0.01 0.01 0.12 0.01 rem.
Table 1 ....
CA 022~180~ 1998-10-13 Element P S Sb Sn As % by wt. 0.005 0.002 0.003 3.00r 0.005 Table 2 P~v_~L~ 817 y1~N~-' 12 Yield strength Rpo 2(RT), [MPa] 970 800 Yield strength Rpo 2(200'C), ~MPa] 920 730 Yield strength Rpo 2(300'C), [MPa] 860 690 0 Yield strength Rpo 2(400'C)[MPa] 850 650 Yield strength Rpo 2(500'C), [MPa~ 800 520 Yield strength Rpo 2(600'C), [MPa] 650 ---Elongation at break(RT), As[~] 20 12 Notched bar impact work, AV(RT), [ J] 80 30-50 15 FATT50, [ c] i Av/high position~ [J] -30; 80 ---Creep resistance, Rm/1OOOOOh/S00'C' [MPa~ -300 170 Table 3 Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
Field of the invention - The invention relates to a martensitic-austenitic steel, in particular for use as a material for creep-stressed components of gas turbines.
Discussion of background The use of hardenable and temperable chrome steels as a material for use in thermal power stations, in particular as a material for rotors or rotor wheels, is now state of the art. As compared with nickel-based super-alloys, hardenable and temperable chrome steels are distinguished in that they are more amenable to non-destructive testing. Furthermore, they have comparatively low coefficients of thermal expansion and high thermal conductivityi this enhances the resistance to thermal fatigue. At temperatures above 450 C, however, the hardened and tempered steels do not meet the demand, as desired, with respect to heat resistance, creep resistance and toughness.
A hardenable and temperable martensitic steel designated X12CrNiMol2 is known. In addition to iron, this steel contains 0.10-0.14% of C, 0.10-0.40% of Si, 0.5-0.9% of Mn, 11-12% of Cr, 2-2.6% of Ni, 1.3-1.8% of Mo, 0.2-0.35% of V and 0.02-0.05% of N as well as usual impurities. In the temperature range below 450 C, this steel has a relatively high high-temperature yield strength and a relatively high creep resistance.
However, the high-temperature yield strength and the creep behavior are inadequate at temperatures above 450 C. Furthermore, the steel shows a not inconsiderable tendency to embrittlement at higher temperatures.
AMENDED SHEET
- CA 022~180~ 1998-10-13 EP-A-481 377 discloses a high-strength martensitic-austenitic steel having a composition in %
by weight of 10 to 17% of chromium, less than 4% of molybdenum, up to 4% of cobalt, up to 8% of nickel, up to 10% of manganese, up to 1.0% of vanadium, up to 0.3%
of nitrogen, up to 0.15% of carbon, up to 6% of silicon and up to 4% of copper, the remainder being iron and mpurltles .
~ SUMMARY OF THE INVENTION-Accordingly, the object of the invention is to provide a martensitic-austenitic steel for use in gas turbine rotors or gas turbine rotor wheels having an adequate heat resistance and toughness for a temperature range from 450 C to at least 550 C.
According to the invention, this is achieved by the features of the first claim.
The core of the invention is the setting of a very fine two-phase microstructure comprising tempered martensite and thermodynamically stable austenite. The steel essentially comprises 8 to 15% of chromium, 4 to 10% of cobalt, 2.5 to 8% of manganese, 0.5 to 6% of nickel, 0.5 to 2.5% of molybdenum, up to 2% of tungsten, 0.1 to 0.5% of vanadium, 0.05 to 0.2% of carbon and 0.05 to 0.25% of nitrogen, the remainder being iron and usual impurities resulting from the smelting.
The advantages of the invention are to be seen above all in the fact that the steel formed in a duplex structure has, even at temperatures above 450 C, a high high-temperature yield strength and a high creep resistance and, due to its high structural stability, shows a low tendency to embrittlement.
Further advantageous embodiments result from the subclaims.
AMENDED SHEET
- CA 022~180~ 1998-10-13 DESCRIPTION OF THE PREFERRED EMBODIMENT
The steel, developed for the use according to the invention, essentially contains (measured in % by 5 weight) 8 to 15% of chromium, 4 to 10% of cobalt, 2.5 to 8% of manganese, 0.5 to 6% of nickel, 0.5 to 2.5% of molybdenum, up to 2% of tungsten, 0.1 to 1.0% of vanadium, 0.05 to 0.2% of carbon and 0.05 to 0.25% of nitrogen, and it can be produced by casting or by powder-metallurgical means.
Known and industrially accepted 9-12% chrome steels achieve their heat resistance and creep resistance via the stabilizing action of extremely fine precipitations upon the dislocation network formed in the tempered martensite. In the steel developed for use according to the invention, a cubic face-centered phase (austenite) in addition to the fine precipitations is introduced which, due to its low self-diffusion and the formation of phase boundaries, contributes to an increase in the heat res;stance and creep resistance.
Martensitic steels with austenite as a creep-improving second phase are known in the art. By comparison with the steel according to the invention, however, they differ by the fact that their austenite fraction is not thermodynamically stable, so that a high susceptibility to thermal fatigue arises.
Below, the particularly preferred quantities for each element and the reasons for the selected alloying ranges of the alloy according to the invention are displayed.
The oxidation resistance is increased by chromium dissolved in the solid solution. Via the formation of hexagonal chromium nitrides, Cr can also - contribute to the improvement in creep resistance. In order to achieve this, a minimum Cr content of 8% by weight is necessary. The chromium content should, however, not exceed 15% by weight, since otherwise ~-ferrite is formed which entails a reduction in AMENDED SHEET
CA 022~180~ 1998-10-13 ~ 4/10 toughness and high-temperature strength. An expedient range for chromium therefore ranges from about 8 to 15%
by weight, preferably from 9 to 12% by weight, and especially is about 10% by weight.
In the present steel, manganese is particularly effective in increasing the solubility of nitrogen in the austenite region. A mlnlmum Mn content of 2.5% by weight is desirable in order to dissolve the stable nitrides of the hexagonal type (Cr,V)2N and of the cubic type (V, Cr)N during the solution-annealing.
During the tempering treatment, manganese is concentrated in the austenite formed and decisively lowers its martensite start temperature, i.e. manganese stabilizes the austenite. For this reason also, the manganese content should be at least 2.5% by weight.
The Mn content should, however, not exceed 8% by weight, in order to prevent the alloy from becoming completely austenitic. An expedient range for manganese therefore extends from about 2.5 to 8% by weight, preferably from 3.5 to 6.5% by weight, and is especially about 5% by weight.
Nickel increases the toughness in martensitic chrome steels, for example because it effectively reduces the ~-ferrite content. In a manner similar to manganese, nickel stabilizes the austenitic phase in the duplex structure. For this reason, the alloy should contain at least 0.5% by weight of Ni. Above a nickel content of 6% by weight, the Ac3 point is lowered to an undue extent. An expedient range for nickel therefore extends from about 0.5 to 6% by weight, preferably from 2 to 5% by weight, and is especially about 3.7% by weight.
Cobalt increases the nickel equivalent to such an extent that the alloy solidifies austenitically from the melt. As a result, nitrogen effusion and hence pore formation are avoided. The Co content should therefore be at least 4% by weight. However, the Co content should not exceed 10% by weight, so that the alloy still has a sufficiently high Ac3 temperature. An CORRECTED SHEET (RULE 91) ISA/EP
CA 022~l80~ l998-l0-l3 expedient range for cobalt therefore extends from about 4 to 10% by weight, preferably from 5 to 8% by weight, and is especially about 6% by weight.
Molybdenum promotes good tempering properties and the heat resistance, and a minimum content of 0.2%
by weight should therefore be maintained. The Mo content should not exceed 2.0% by weight, since otherwise a massive formation of Laves phases can occur. An expedient range for molybdenum therefore extends from 0. 5 to 2. 5% by weight, preferably from 1.0 to 2.0% by weight, and is especially about 1. 5% by weight.
Tungsten acts in a manner similar to molybdenum. Because of the risk of the formation of Laves phases, a content of 2% by weight should not be exceeded. The tungsten content is therefore within the range from 0 to 2% by weight, preferably below 1% by weight.
TogeLher with nitrogen and small fractions of chromium, vanadium forms a dense dispersion of coherent and partially coherent cubic nitrides which essentially determine the heat resistance and creep resistance. At least 0.1% by weight of V should be alloyed in. Since, however, vanadium promotes the tendency to form ~-ferrite, 1% by weight of V should not be exceeded.Preferably, the vanadium content is in the range from 0.15 to 0. 65% by weight.
In the atomically dissolved state, nitrogen promotes the diffusion-free martensitic conversion from the austenitic phase during cooling. This ensures the capacity for hardening and tempering. In addition, it forms the already mentioned nitrides with V and Cr and, if appropriate, also with Nb, Ti and Ta. Nitrogen should therefore be alloyed in approximately 3 5 stoichiometric quantities. Because of a possible N
effusion during solidification, an upper limit of 0.25%
by weight should not be exceeded. For this reason, the N content is in the range from about 0. 05 to 0. 25% by CORRECTED SHEET (RULE 91) ISA/EP
CA 022~180~ 1998-10-13 weight, preferably in the range from 0.07 to 0.15% by weight.
Together with chromium, carbon promotes the formation of carbides of the form Cr23C6. Owing to its stoichiometry, this carbide removes more chromium from the matrix than the Cr2N formed in the steel according to the invention. For this reason, the carbon content should not exceed 0.2% by weight, preferably 0.1% by weight.
Niobium, titanium, zirconium and tantalum are alloying elements which, together with vanadium, can form special nitrides of the MX type. Their effect is above all based on the fact that, even with small additions, they enhance the stability of V(N,C) precipitations. At unduly high contents, the stability of the nitrides is, however, so high that they cannot be dissolved during the solution-annealing treatment.
For this reason, the total content of these elements is to be limited to 0.5%.
Boron increases the coarsening resistance of precipitations. Since it tends to cause segregations, the content must be limited to 0.02%.
Among the usually occurring impurities, resulting from production, the elements such as phosphorus, sulfur, antimony, tin and arsenic should not exceed the contents indicated in Table 2 below.
This is necessary, in order to avoid embrittlement during tempering.
The steel according to the invention has a martensitic-austenitic microstructure which is produced by a hardening and tempering process. The hardening and tempering process comprises solution-annealing, hardening and subsequent tempering.
The solution-annealing should take place within the temperature range of 1050 C T 1250 C, preferably at 1100-C T 1230-C and especially at 1200 C, in order to dissolve all the nitrides of the form VN. The austenite content and the degree of hardening of the martensitic phase are set via the CA 022~l80~ l998-l0-l3 tempering treatment. In order to set a desired austenite fraction of 15 to 45%, a tempering temperature in the range of 550 C T 650-C should be selected, preferably 580 C T 630 C.
Embodiment example By way of example, a particularly preferred embodiment of the alloys described above is discussed in more detail below, and this is designated alloy 817.
The composition of the alloy 817 can be taken from Table 1 and also from Table 2. Table 2 here shows some maximum contents of possible impurities.
After solution-annealing and a quenching treatment, the alloy was tempered for 4 hours at 600-.
After this heat treatment, the microstructure was two-phase martensitic-austenitic with a content of about 37% of austenite phase and a phase region size of from 200 to 300 nm.
The properties of the alloy 817 according to the invention are compared in Table 3 with the previously mentioned alloy X12CrNiMol2.
According to Table 3, the alloy 817 iS
distinguished throughout by improved properties as compared with the alloy X12CrNiMol2. The high heat resistance and creep resistance allow use as rotor material or rotor wheel material for gas turbines at elevated temperatures of up to 550 C.
Element Cr Mo W Co Ni Mn V
% by wt. 10 0.5 1.5 6.0 3.7 5.0 0.5 Element Nb Ti Ta N C Fe % by wt. 0.01 0.01 0.01 0.12 0.01 rem.
Table 1 ....
CA 022~180~ 1998-10-13 Element P S Sb Sn As % by wt. 0.005 0.002 0.003 3.00r 0.005 Table 2 P~v_~L~ 817 y1~N~-' 12 Yield strength Rpo 2(RT), [MPa] 970 800 Yield strength Rpo 2(200'C), ~MPa] 920 730 Yield strength Rpo 2(300'C), [MPa] 860 690 0 Yield strength Rpo 2(400'C)[MPa] 850 650 Yield strength Rpo 2(500'C), [MPa~ 800 520 Yield strength Rpo 2(600'C), [MPa] 650 ---Elongation at break(RT), As[~] 20 12 Notched bar impact work, AV(RT), [ J] 80 30-50 15 FATT50, [ c] i Av/high position~ [J] -30; 80 ---Creep resistance, Rm/1OOOOOh/S00'C' [MPa~ -300 170 Table 3 Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
Claims (5)
LETTERS PATENT OF THE UNITED STATES IS:
1. A martensitic-austenitic steel, comprising:
(measured in % by weight) from 8 to 15% of chromium, 0.5 to 2.5% of molybdenum, up to 2% of tungsten, 4 to 10% of cobalt, 0.5 to 6% of nickel, 2.5 to 8% of manganese, 0.1 to 1.0% of vanadium, 0.05 to 0.25% of nitrogen and up to 0.2% of carbon, the remainder being iron and impurities, and optionally furthermore up to a maximum of 0.02% of boron and/or optionally furthermore up to a maximum of 0.5% in total of the elements niobium, titanium, zirconium and tantalum.
(measured in % by weight) from 8 to 15% of chromium, 0.5 to 2.5% of molybdenum, up to 2% of tungsten, 4 to 10% of cobalt, 0.5 to 6% of nickel, 2.5 to 8% of manganese, 0.1 to 1.0% of vanadium, 0.05 to 0.25% of nitrogen and up to 0.2% of carbon, the remainder being iron and impurities, and optionally furthermore up to a maximum of 0.02% of boron and/or optionally furthermore up to a maximum of 0.5% in total of the elements niobium, titanium, zirconium and tantalum.
2. The martensitic-austenitic steel as claimed in claim 1, wherein chromium is present in the range from 9 to 12% and/or molybdenum is present in the range from 1.0 to 2.0% and/or cobalt is present in the range from 5 to 8% and/or nickel is present in the range from 2 to 5% and/or manganese is present in the range from 3.5 to 6.5% and/or 1.0% of tungsten is present and/or vanadium is present in the range from 0.15 to 0.65% and/or nitrogen is present in the range from 0.07 to 0.15%
and/or up to 0.1% of carbon is present.
and/or up to 0.1% of carbon is present.
3. The use of the martensitic-austenitic steel as claimed in either of claims 1 and 2 as a heat- and creep-resistant material in thermal power stations.
4. A heat treatment process for the martensitic-austenitic steel as claimed in either of claims 1 and 2, which comprises tempering the alloy steel in the solution-annealed and quenched state in the temperature range from 550 C to 650 C in such a way that a microstructure having a volume fraction of from 20% to 50% of austenite is formed.
5. The heat treatment process as claimed in claim 4, wherein the alloy steel is solution-annealed in the temperature range of 1050 C < T< 1250-C.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE1996114407 DE19614407A1 (en) | 1996-04-12 | 1996-04-12 | Martensitic-austenitic steel |
| DE19614407.8 | 1996-04-12 | ||
| PCT/CH1997/000123 WO1997039158A1 (en) | 1996-04-12 | 1997-03-25 | Martensitic-austentitic steel |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2251805A1 true CA2251805A1 (en) | 1997-10-23 |
Family
ID=7791041
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002251805A Abandoned CA2251805A1 (en) | 1996-04-12 | 1997-03-25 | Martensitic-austentitic steel |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0907758A1 (en) |
| JP (1) | JP2000510904A (en) |
| CN (1) | CN1216073A (en) |
| CA (1) | CA2251805A1 (en) |
| DE (1) | DE19614407A1 (en) |
| NO (1) | NO984756D0 (en) |
| PL (1) | PL329050A1 (en) |
| WO (1) | WO1997039158A1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2329646T3 (en) * | 1999-07-12 | 2009-11-30 | Mmfx Steel Corporation Of America | LOW CARBON STEEL OF SUPERIOR MECHANICAL AND CORROSION PROPERTIES. |
| DE10063117A1 (en) * | 2000-12-18 | 2003-06-18 | Alstom Switzerland Ltd | Conversion controlled nitride precipitation hardening tempering steel |
| CN1333098C (en) * | 2005-06-24 | 2007-08-22 | 寇生瑞 | Iron base rare earth high chromium steel impellor blade |
| CN102154592B (en) * | 2011-03-04 | 2012-11-21 | 燕山大学 | Micro-alloying martensite stainless steel for blades of water turbine and manufacturing method thereof |
| CN102242313B (en) * | 2011-07-18 | 2012-12-26 | 山东建筑大学 | High-hardness silver-bearing martensite antibacterial stainless steel |
| CN103526131B (en) * | 2013-10-31 | 2015-07-22 | 万宝力不锈钢制品（东莞）有限公司 | High-strength stainless steel coffee pot material and preparation method thereof |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE959681C (en) * | 1943-08-14 | 1957-03-07 | Eisen & Stahlind Ag | Blades and similarly stressed components of gas turbines and other similarly or similarly stressed objects |
| DE1082739B (en) * | 1953-05-29 | 1960-06-02 | Nyby Bruk Ab | Use of non-precipitation-hardening, overheating-insensitive alloys |
| JPS63171856A (en) * | 1987-01-09 | 1988-07-15 | Hitachi Ltd | Heat-resisting steel and gas turbine using same |
| JPH04154921A (en) * | 1990-10-16 | 1992-05-27 | Nisshin Steel Co Ltd | Manufacture of high strength stainless steel strip having excellent shape |
| CN1044388C (en) * | 1994-01-26 | 1999-07-28 | 川崎制铁株式会社 | Method of manufacturing stainless steel sheet of high corrosion resistance |
| JPH07216451A (en) * | 1994-01-31 | 1995-08-15 | Nisshin Steel Co Ltd | Production of stainless steel material having high welding softening resistance, high strength, and high ductility |
| JPH07268561A (en) * | 1994-03-29 | 1995-10-17 | Nisshin Steel Co Ltd | High strength stainless steel excellent in hot workability and free from welding softening |
-
1996
- 1996-04-12 DE DE1996114407 patent/DE19614407A1/en not_active Withdrawn
-
1997
- 1997-03-25 EP EP97906971A patent/EP0907758A1/en not_active Withdrawn
- 1997-03-25 JP JP09536615A patent/JP2000510904A/en active Pending
- 1997-03-25 CN CN 97193736 patent/CN1216073A/en active Pending
- 1997-03-25 PL PL97329050A patent/PL329050A1/en unknown
- 1997-03-25 CA CA002251805A patent/CA2251805A1/en not_active Abandoned
- 1997-03-25 WO PCT/CH1997/000123 patent/WO1997039158A1/en not_active Application Discontinuation
-
1998
- 1998-10-12 NO NO984756A patent/NO984756D0/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| NO984756L (en) | 1998-10-12 |
| DE19614407A1 (en) | 1997-10-16 |
| JP2000510904A (en) | 2000-08-22 |
| EP0907758A1 (en) | 1999-04-14 |
| WO1997039158A1 (en) | 1997-10-23 |
| PL329050A1 (en) | 1999-03-01 |
| CN1216073A (en) | 1999-05-05 |
| NO984756D0 (en) | 1998-10-12 |
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