WO2017056674A1 - 低熱膨張超耐熱合金及びその製造方法 - Google Patents
低熱膨張超耐熱合金及びその製造方法 Download PDFInfo
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Definitions
- the present invention relates to a high strength low thermal expansion super heat resistant alloy having oxidation resistance suitable for a large member used at high temperature such as a thermal power plant and a method for producing the same.
- Well-known Fe-based alloys with low thermal expansion include Fe-Ni and Fe-Ni such as Fe-36% Ni, Fe-42% Ni, Fe-29% Ni-17% Co, etc. -Co-based alloy. These alloys exhibit a very low coefficient of thermal expansion near room temperature due to the Invar effect. Further, low thermal expansion alloys having high strength are disclosed in Japanese Patent Publication No. 41-2767 (Patent Document 1), Japanese Patent Application Laid-Open No. 59-56563 (Patent Document 2) and Japanese Patent Application Laid-Open No. 4-218642 (Patent Document 3). It is disclosed. These alloys can obtain a high strength and a relatively low coefficient of thermal expansion not only at room temperature but also up to a certain high temperature. Further, low thermal expansion alloys having high strength and improved oxidation resistance at high temperatures are disclosed in Japanese Patent Laid-Open Nos. 53-6225 (Patent Document 4) and 2001-234292 (Patent Document 5). .
- Fe-Ni and Fe-Ni-Co alloys such as Fe-36% Ni, Fe-42% Ni, and Fe-29% Ni-17% Co have low strength at room temperature and high temperature. It is difficult to apply to applications that require strength. In addition, since it does not contain elements contributing to the improvement of oxidation resistance such as Cr, Al, Ti, etc., it is easy to oxidize at high temperatures and is not suitable for use at high temperatures.
- the alloy shown in Patent Document 1 is a low thermal expansion alloy having high strength, but has a high notch sensitivity at a temperature of about 500 to 650 ° C., and has a large notch creep rupture strength and smooth creep rupture strength at high temperatures. There was a difference and it was a problem.
- the alloy shown in Patent Document 2 has better notch creep rupture strength than the alloy shown in Patent Document 1, the coefficient of thermal expansion is slightly larger than the alloy of Patent Document 1, so from the viewpoint of low thermal expansion. Was not necessarily enough.
- the alloy shown in Patent Document 3 has a notch creep rupture strength better than the alloy shown in Patent Document 1, and has a lower thermal expansion coefficient than the alloys shown in Patent Document 1 and Patent Document 2, It is an alloy with a good balance of properties such as high strength and low thermal expansion.
- Patent Document 1 Patent Document 2, and Patent Document 3 do not contain elements such as Cr that contribute to the improvement of oxidation resistance, they are easily oxidized at high temperatures and are oxidized in the atmosphere at high temperatures. There were limits to use in the environment.
- Patent Document 4 and Patent Document 5 have high strength and at the same time improve the oxidation resistance by adding Cr, and are considered for use in a high-temperature oxidizing atmosphere. Since the addition amount is large, the low thermal expansion alloy has a large thermal expansion coefficient, which is insufficient from the viewpoint of the thermal expansion coefficient as compared with the alloys disclosed in Patent Document 1, Patent Document 2, and Patent Document 3.
- An object of the present invention is a low thermal expansion super heat resistant alloy having high strength, good notch creep rupture strength, low thermal expansion coefficient, oxidation resistance at use temperature and capable of producing large parts, and a method for producing the same Is to provide.
- the present inventors have intensively studied an Fe—Ni—Co alloy containing Al, Ti, and Nb.
- the ratio of Fe, Ni, and Co that provides low thermal expansion
- the appropriate range of Al, Ti, and Nb that provides high strength at room temperature and high temperature
- intermetallic compounds containing Si, Nb, and Ni are discontinuously precipitated at the grain boundaries of the austenite matrix, and a large amount of Ni, Al, Ti, and Nb is contained in the austenite matrix.
- the present inventors have found that it is effective to obtain a structure having a fine intermetallic compound, and have reached the present invention. Further, in order to stably satisfy the above-described good low thermal expansion characteristics and mechanical characteristics, it has been found that it is effective to perform a solution treatment and an aging treatment at a relatively low temperature, and the present invention has been achieved. .
- the present invention in mass%, C: 0.1% or less, Si: 0.1 to 1.0%, Mn: 1.0% or less, Ni: 25 to 32%, Co: more than 18% and more than 24 %, Al: more than 0.25% and 1.0% or less, Ti: 0.5-1.5%, Nb: more than 2.1% and less than 3.0%, B: 0.001-0.
- a preferable composition of the low thermal expansion superalloy is, by mass%, C: 0.05% or less, Si: 0.2 to 0.7%, Mn: 0.5% or less, Ni: 26 to 29%, Co: 18% to 22%, Al: 0.3 to 0.6%, Ti: 0.6% to less than 1.2%, Nb: 2.5% to less than 3.0%, B: 0.001 -0.01%, Mg: 0.0005-0.01%, balance Fe and inevitable impurities, Mg / S ⁇ 1, 52.9% ⁇ 1.235Ni + Co ⁇ 55.8%, Al + Ti + Nb: 3.
- the low thermal expansion super heat resistant alloy preferably contains 0.1% or more and less than 1.7% Cr by mass%, and more preferably contains 0.4 to 1.6% Cr by mass%.
- the drawing in the room temperature tensile test in the solution treatment state can be 50% or more.
- the low thermal expansion super heat resistant alloy has an average thermal expansion coefficient of 8.1 ⁇ 10 ⁇ 6 / ° C. or less at 30 to 500 ° C. in an aging treatment state, a tensile strength at room temperature of 780 MPa or more, and a tensile strength at 550 ° C.
- a composite creep test under a stress of 510 MPa at 650 ° C. with a stress of 600 MPa or more there is no detachment of the oxide film in an oxidation test for 100 hours in an atmosphere at 600 ° C. with an elongation at break of 10% or more.
- the increase in oxidation can be 1.3 mg / cm 2 or less.
- the present invention is a method for producing a low thermal expansion superalloy having the above composition, wherein after the low thermal expansion superalloy is vacuum induction melted to obtain an ingot, the ingot is used one or more times. After hot plastic working, solution treatment at 850 to 1080 ° C., aging treatment including holding at 580 to 700 ° C. for 8 to 100 hours is performed at least once, and Si, Precipitating a granular intermetallic compound containing one or more elements of Nb and Ni alone or in total of 36% by mass or more, and containing Ni, Al, Ti, Nb in a concentration higher than the concentration in the alloy, and having an average diameter It is desirable to deposit an intermetallic compound of 50 nm or less in the austenite matrix. More preferably, after the vacuum induction melting, it is desirable to produce an ingot by electroslag remelting and / or vacuum arc remelting.
- the low thermal expansion super heat-resistant alloy of the present invention is used for applications such as large gas turbine parts, joined parts with ceramics, glass, etc., joined parts with cemented carbide, etc. Can be kept small, and relatively good oxidation resistance and stable high strength can be obtained, so that higher reliability is achieved.
- C reacts with Ti and Nb to form MC-type carbides, suppresses the coarsening of crystal grains during forging and solution treatment, and contributes to improvement in strength.
- C exceeds 0.1%, a large amount of carbides are generated, and not only the chain-like carbides are unevenly distributed to form a non-uniform macrostructure, but also Ti required for forming a precipitation strengthening phase during the aging treatment.
- the Nb content decreases, it becomes difficult to obtain a sufficient strength, so C is made 0.1% or less.
- it is 0.05% or less.
- the lower limit should be 0.005%.
- Si reacts with Fe and Nb to discontinuously produce a granular intermetallic compound containing at least 36 mass% of one or more of Si, Nb, and Ni at the austenite grain boundary, thereby strengthening the grain boundary. It is an element necessary for this.
- Si is less than 0.1%, the amount of intermetallic compounds precipitated at the grain boundaries is small, so that the contribution to grain boundary strengthening is reduced.
- Si exceeds 1.0%, metal is present in the grain boundaries and grains. Since not only the intermetallic compound is produced too much but the hot workability is lowered, but also the ductility is lowered in the tensile test at room temperature and high temperature, Si is made 0.1 to 1.0%.
- a preferable lower limit of Si is 0.2%, and a more preferable lower limit of Si is 0.3%.
- a preferable upper limit of Si is 0.7%, and a more preferable upper limit of Si is 0.6%.
- Mn is added as a deoxidizing agent and a desulfurizing agent, but also dissolves in the alloy. If Mn exceeds 1.0%, the coefficient of thermal expansion is increased, so Mn is 1.0% or less. Preferably it is 0.5% or less, More preferably, it is 0.3% or less, More preferably, 0.2% or less is good.
- Ni is a main element constituting the austenite matrix together with Fe, Co, and Cr.
- the amounts and proportions of Fe, Ni, and Co greatly affect the thermal expansion coefficient, it is necessary to appropriately control the amounts and proportions of Fe, Ni, and Co in order to obtain low thermal expansion.
- Ni is also an important element constituting the ⁇ 'phase, which is a precipitation strengthening phase, and is an element that greatly affects the strength. As described above, Ni stabilizes the austenite matrix and is also used to generate a precipitation strengthening phase ⁇ ′ phase. If Ni is less than 25%, the austenite phase becomes unstable and martensite tends to be formed, and the thermal expansion coefficient increases.
- Ni is set to 25 to 32%.
- the preferable lower limit of Ni is 26%, and the preferable upper limit of Ni is 29%.
- Co is an element that forms an austenite matrix with Fe, Ni, and Cr.
- the amounts and proportions of Fe, Ni, and Co greatly affect the thermal expansion coefficient, it is necessary to appropriately control the amounts and proportions of Fe, Ni, and Co in order to obtain low thermal expansion.
- Co is 18% or less, the Curie point decreases and the coefficient of thermal expansion increases rapidly at high temperatures, whereas when it exceeds 24%, the Curie point increases and the coefficient of thermal expansion extends over a wide temperature range from low temperature to high temperature. Therefore, Co exceeds 18% and is less than 24%.
- a preferable upper limit of Co is 22% or less.
- Ni and Co can obtain a low thermal expansion coefficient by optimizing their amounts and ratios.
- the amount and ratio of Ni and Co can be controlled by optimizing the value of 1.235Ni + Co. If the value of 1.235Ni + Co is 55.8% or more, the coefficient of thermal expansion becomes too high. On the other hand, if it is less than 52.9%, martensite is likely to be generated, and it becomes difficult to obtain a stable austenite structure. .9% ⁇ 1.235Ni + Co ⁇ 55.8%.
- the element symbol represents the content of the element symbol as it is.
- Al is an element constituting a ⁇ ′ phase (Ni 3 (Al, Ti, Nb)), which is an intermetallic compound that finely precipitates in austenite grains by aging treatment to increase the strength at room temperature and high temperature, and is essential It is an element.
- ⁇ ′ phase Ni 3 (Al, Ti, Nb)
- Al is 0.25% or less, the effect of increasing the strength is small.
- Al exceeds 1.0%, the thermal expansion coefficient is increased, so Al exceeds 0.25% and is 1.0% or less.
- a preferable lower limit of Al is 0.3%, and a preferable upper limit of Al is 0.6%.
- Ti is also an element constituting a ⁇ ′ phase (Ni 3 (Al, Ti, Nb)), which is an intermetallic compound that finely precipitates in austenite grains by aging treatment to increase the strength at room temperature and high temperature, It is an essential element. If Ti is less than 0.5%, the effect of increasing the strength is small. On the other hand, if it exceeds 1.5%, the thermal expansion coefficient is increased, so Ti is made 0.5 to 1.5%. The preferable lower limit of Ti is 0.6%, and the preferable amount of Ti with respect to the upper limit is less than 1.2%.
- Nb is also an element constituting a ⁇ ′ phase (Ni 3 (Al, Ti, Nb)), which is an intermetallic compound that is finely precipitated in austenite grains by aging treatment to increase the strength at room temperature and high temperature.
- Nb is an essential element because it is a constituent element of a granular intermetallic compound containing Ni, Si, and Nb as main constituent elements that precipitates at austenite grain boundaries to increase grain boundary strength and improve high temperature strength. It is. If Nb is 2.1% or less, the effect of improving the strength is small. On the other hand, if it is 3.0% or more, not only the thermal expansion coefficient is increased but also macro segregation is promoted, so Nb exceeds 2.1%. Less than 3.0%.
- a preferable lower limit of Nb is 2.5%, and a preferable Nb amount with respect to the upper limit is less than 3.0%.
- the strength at room temperature and high temperature increases as the total amount of Al + Ti + Nb increases.
- the value of Al + Ti + Nb is less than 3.5%, the amount of precipitated ⁇ ′ phase decreases, and sufficient strength cannot be obtained.
- it exceeds 5.5% the thermal expansion coefficient increases.
- the value of Al + Ti + Nb at which the coefficients can be appropriately balanced is 3.5% or more and less than 5.5%.
- a preferable upper limit of Al + Ti + Nb when importance is attached to a low thermal expansion coefficient is 4.7%.
- One of the objects of the present invention is to provide a low thermal expansion superalloy suitable for the manufacture of large products, but for that purpose it is necessary to manufacture a healthy large ingot.
- a healthy large ingot that is, a large ingot without macrosegregation during solidification
- it is effective to control the difference in density between the alloy liquid phase and the concentrated liquid phase, that is, the difference in molten metal density. If the density of the concentrated liquid phase is higher than that of the alloy liquid phase, the precipitation type Freckle segregation is likely to occur, and if the density of the concentrated liquid phase is lower than that of the alloy liquid phase, the floating type Freckle segregation is likely to occur.
- the F value is a negative value when the density of the concentrated liquid phase is larger, and a positive value when the density of the alloy liquid phase is larger, but in any case, the absolute value is closer to zero. Segregation is less likely to occur. If the absolute value of the F value is larger than 8%, it is easy to cause freckle segregation and it becomes difficult to produce a large ingot. Therefore, the absolute value of the F value is 8% or less. A preferable absolute value of the F value is 6% or less.
- B is an element that segregates at the austenite grain boundaries to increase the grain boundary strength, and increase hot workability, creep strength, and ductility. However, if B is less than 0.001%, the amount of B that segregates at the grain boundary decreases, and it is difficult to obtain sufficient grain boundary strength. On the other hand, if it exceeds 0.01%, a B compound is formed and hot workability is reduced. To prevent harm, B is made 0.001 to 0.01%. A preferable lower limit of B is 0.002%, and a preferable upper limit of B is 0.006%. A more preferable upper limit of B is 0.005%.
- Mg has an effect of improving the hot workability by combining with S segregated at the grain boundary to fix S. If Mg is less than 0.0005%, the effect is not sufficient. On the other hand, if it exceeds 0.01%, the amount of oxides and sulfides increases, and the purity decreases as inclusions, and a compound with Ni having a low melting point is present. Mg is limited to 0.0005 to 0.01% because it increases and decreases hot workability.
- a preferable lower limit of Mg is 0.001%, and a preferable upper limit of Mg is 0.007%. A more preferable upper limit of Mg is 0.005%.
- part or all of Mg may be replaced with Ca.
- (Mg + 0.6 ⁇ Ca) may be limited to the range of Mg alone.
- the purpose of adding Mg is to improve hot workability by fixing S of impurities that segregate at the grain boundaries, so the Mg content is defined according to the S content.
- Mg needs to have a mass ratio of 1: 1 or more with S, so the value of Mg / S is limited to 1 or more.
- (Mg + 0.6 ⁇ Ca) / S is preferably limited to 1 or more.
- Cr can be contained as a selective element in the present invention.
- Cr is dissolved in an austenite matrix mainly composed of Fe, Ni, and Co.
- Cr is an element that improves the oxidation resistance by solid solution in the oxide film mainly composed of Fe, Ni, Co, etc. formed on the surface when the alloy of the present invention is oxidized at high temperature. This is a selective element that can be added.
- Cr is preferably 0.1% or more, and when it is 1.7% or more, the Curie point is lowered to increase the thermal expansion coefficient. Above 1.7%.
- a preferable lower limit of Cr is 0.4, and a more preferable lower limit of Cr is 0.7%.
- a preferable upper limit of Cr is 1.6%, and a more preferable upper limit of Cr is 1.3%.
- the balance is Fe.
- impurities are included. Impurities P and S are easily segregated at the grain boundaries, leading to a decrease in high-temperature strength and hot workability. Therefore, it is preferable to limit P to 0.02% or less and S to 0.005% or less. About S, 0.003% or less is preferable and 0.002% or less is still more preferable.
- O and N combine with Al, Ti, Nb and the like to form oxide-based and nitride-based inclusions to reduce cleanliness and deteriorate fatigue strength. Since the amount of Al, Ti and Nb to be formed may be reduced to hinder the strength increase due to precipitation strengthening, it is preferable to keep it as low as possible.
- preferable O is 0.008% or less
- N is 0.004% or less
- more preferable O is 0.005% or less
- N is 0.003% or less.
- Ag, Sn, Pb, As, and Bi are also impurity elements that segregate at the austenite grain boundaries and cause a decrease in high-temperature strength. Ag, Sn, Pb, As, and Bi are limited to 0.01% or less in total. It is preferable.
- Nb is added, a small amount of Ta may be mixed as an impurity. In this case, 0.5 ⁇ Ta and Nb can be regarded as equivalent by mass%. Therefore, the range of Nb may be replaced with Nb + 0.5 ⁇ Ta.
- Zr segregates at the grain boundaries to improve hot workability, but if added or mixed excessively, a brittle compound is generated and hot workability is adversely affected. Therefore, Zr is 0.05% or less. Good. Moreover, since Cu, Mo, and W may increase the thermal expansion coefficient, they are each preferably 0.5% or less, more preferably 0.3% or less.
- an intermetallic compound (Laves phase) containing one or more elements of Si, Nb, and Ni alone or in total of 36% by mass or more is precipitated at the grain boundary of the austenite matrix by optimization of the chemical components described above. Can be obtained.
- An intermetallic compound containing one or more elements of Si, Nb, Ni alone or in total 36 mass% or more increases the grain boundary strength by suppressing the intergranular slip due to creep, and improves the creep strength and ductility.
- An intermetallic compound containing at least 36% by mass of one or more elements of Si, Nb, and Ni precipitates discontinuously in a granular manner at the grain boundary of the austenite matrix, and effectively strengthens the grain boundary.
- Si, Nb, and Ni contain one or more elements alone or in total, preferably 37% or more, and more preferably 40% by mass or more. The method for depositing this intermetallic compound will be described later.
- the quantitative analysis of the intermetallic compound is easy to analyze using, for example, an energy dispersive X-ray analyzer (EDX) during observation with a scanning electron microscope (SEM).
- EDX energy dispersive X-ray analyzer
- SEM scanning electron microscope
- the alloy of the present invention in order to obtain good high-temperature strength and ductility, particularly good creep strength and ductility, it is necessary to strengthen the austenite matrix (inside grains).
- the alloy of the present invention can finely disperse intermetallic compounds in which Ni, Al, Ti, and Nb are higher than the concentration in the alloy in the austenite matrix (inside the grains) by optimizing chemical components.
- This intermetallic compound is a precipitation strengthening phase called ⁇ ′ (gamma prime) phase, and the strength at room temperature and high temperature can be increased by fine precipitation of the ⁇ ′ phase.
- ⁇ ′ gamma prime
- the diameter is represented by the equivalent circle diameter that can be measured from cross-sectional observation.
- the diameter has a distribution, it is expressed using an average diameter.
- the diameter of the ⁇ ′ phase is preferably 30 nm or less, more preferably 20 nm or less.
- the method for precipitation of this ⁇ 'phase will be described later.
- the presence or absence of the ⁇ 'phase can be confirmed by SEM.
- a transmission electron microscope It is easy to analyze using EDX when observed with (TEM).
- TEM Transmission electron microscope
- the alloy of the present invention is characterized in that good tensile ductility can be obtained at room temperature in a state where it has been subjected to a solution treatment, and can be formed at room temperature. For that purpose, it is preferable that the fracture drawing by the tensile test at room temperature is 50% or more.
- the alloy of the present invention is characterized in that a low thermal expansion coefficient, high strength, low notch creep rupture sensitivity, and good oxidation resistance can be obtained in the state of aging treatment after solution treatment.
- the notch creep rupture sensitivity can be evaluated using a composite creep test piece having a notch and a smooth parallel portion in series in the axial direction of one test piece.
- An alloy with high notch sensitivity breaks in a relatively short time at the notch, whereas an alloy with low notch sensitivity shows good elongation at a smooth parallel part and fractures at a parallel part. Breaking at the point is a criterion for low notch sensitivity.
- the preferred properties are that the average thermal expansion coefficient at 30 to 500 ° C. is 8.1 ⁇ 10 ⁇ 6 / ° C. or less, the tensile strength at room temperature is 780 MPa or more, the tensile strength at 550 ° C. is 600 MPa or more, and 510 MPa at 650 ° C.
- the average coefficient of thermal expansion at 30 to 500 ° C. is preferably low, and can be lowered by combining the composition and the production method in a well-balanced manner.
- the average coefficient of thermal expansion at 30 to 500 ° C. is preferably 7.9 ⁇ 10 ⁇ 6 / ° C. or less, more preferably 7.7 ⁇ 10 ⁇ 6 / ° C. or less, and still more preferably 7.5 ⁇ 10 ⁇ 6 / ° C. or less.
- a preferable oxidation increase is less than 1.2 mg / cm ⁇ 2 >, More preferably, it is 1.0 mg / cm ⁇ 2 > or less.
- “there is no peeling of the oxide film” means that the peeled off oxide film that can be visually observed after the oxidation resistance test is not observed around the test piece.
- the alloy composition is as described above, and the melting is preferably performed by vacuum induction melting (VIM) in order to reduce impurities.
- VAR vacuum induction melting
- VAR vacuum arc remelting
- VAR vacuum induction melting
- ESR electroslag remelting
- ESR melting since S can be efficiently reduced by using ESR melting, it is preferable to employ ESR melting in the case of the alloy of the present invention in which S is desired to be limited to a low level.
- an ingot larger than electroslag remelting can be produced by using vacuum arc remelting with a high solidification rate.
- vacuum arc remelting or electroslag remelting is applied after vacuum induction melting, a consumable electrode is prepared by vacuum induction melting, and the ingot is prepared by vacuum arc remelting or electroslag remelting using the consumable electrode. Will be manufactured.
- a consumable electrode is produced by vacuum induction melting
- an ingot is produced by electroslag remelting using the consumable electrode, and further vacuum arc remelting is performed using the ingot, thereby producing a more homogeneous ingot.
- Can do if a consumable electrode is produced by vacuum induction melting, an ingot is produced by electroslag remelting using the consumable electrode, and further vacuum arc remelting is performed using the ingot, thereby producing a more homogeneous ingot. Can do.
- the solution treatment is performed at 850 to 1080 ° C.
- the lower limit of the preferable solution treatment temperature is 900 ° C.
- the upper limit of the preferable solution treatment temperature is 960 ° C.
- the cooling after the solution treatment is preferably performed at a cooling rate higher than that of air cooling. Oil cooling is preferable, and water cooling is more preferable.
- an aging treatment at 580 to 700 ° C. for 8 to 100 hours is performed at least once, so that Ni, Al, Ti, and Nb are concentrated in the austenite matrix and the diameter is 50 nm or less.
- the ⁇ ′ phase can be finely precipitated, and a high strength and a low thermal expansion coefficient can be obtained.
- the aging treatment temperature is set to 580 to 700 ° C.
- the upper limit of the preferable aging temperature is 680 ° C, more preferably 650 ° C. Since good characteristics can be obtained by holding for 8 to 100 hours, the aging treatment time is 8 to 100 hours. It is preferably 20 to 70 hours, more preferably 30 to 60 hours.
- the aging treatment may be performed once, or may be performed twice or more by changing the temperature within a range of 580 to 700 ° C. Further, for example, even after the first aging treatment is performed for a short time of about 730 ° C. or less and about 730 ° C. or less for about 10 hours or less, the second or subsequent aging treatment is performed at 580 to 700 ° C. When an aging treatment is performed for 8 to 100 hours within the range, a ⁇ ′ phase of 50 nm or less can be precipitated in the austenite crystal grains. Further, for example, after the first aging treatment is performed for a short time of about 10 hours or less at a temperature of 730 ° C.
- the ⁇ ′ phase becomes fine, and a ⁇ ′ phase of 50 nm or less comparable to that obtained by performing the aging treatment only once for a long time at 580 to 700 ° C. can be obtained. . Specific examples will be shown in examples described later.
- a 10 kg ingot was prepared by vacuum induction melting.
- Tables 1 and 2 Alloy Nos. In the composition range defined by the present invention were prepared. 1-5 and comparative alloy no. 21 to 24 chemical components are shown. Alloy No. 1 to 5 have an absolute value of F value of 8% or less, and can be manufactured without problems of macrosegregation when large ingots are manufactured by vacuum arc remelting or electroslag remelting after vacuum melting in mass production. . The balance is Fe and impurities.
- the ingots shown in Table 1 and Table 2 were homogenized at 1180 ° C. for 20 hours, and then subjected to hot forging (hot plastic working) to finish a bar having a cross section of 30 mm ⁇ 30 mm. Since both the alloy within the range of the composition defined in the present invention and the comparative alloy had Mg / S of 1 or more, hot forging could be performed without a problem of cracking. In the alloy having the composition defined in the present invention, no freckle segregation was observed. Then, after hold
- the aging treatment conditions are the following six conditions. (1) 720 ° C. ⁇ 8 h ⁇ (50 ° C./h) ⁇ 620° C. ⁇ 8 h, air cooling (2) 670 ° C. ⁇ 50 h, air cooling (3) 700 ° C. ⁇ 50 h, air cooling (4) 720 ° C. ⁇ 8 h ⁇ (50 ° C. / H) ⁇ 620 ° C. ⁇ 8 h, air-cooled + 600 ° C. ⁇ 50 h, air-cooled (5) 600 ° C. ⁇ 50 h, air-cooled (6) 620 ° C. ⁇ 50 h, air-cooled In Tables 5 and 6, only numbers with () are indicated. Of the aging treatments shown in the above (1) and (4), those shown as “(50 ° C./h)” show the cooling rate per hour.
- the component analysis of the ⁇ ′ phase was measured by cutting out a thin film sample and performing observation and EDX analysis using a TEM.
- the ⁇ ′ phase is described as “intragranular precipitate” and “intragranular precipitation” in Tables 4 and 5.
- a test piece having a diameter of 5 mm and a length of 20 mm was taken along the longitudinal direction of the bar, and the average thermal expansion coefficient up to 500 ° C. was measured by differential thermal expansion measurement based on 30 ° C. .
- a round bar test piece having a parallel part of 6.0 mm and a distance between gauge points of 30 mm was taken along the longitudinal direction of the bar, and tested according to JIS at room temperature and 550 ° C., 0.2% Yield strength, tensile strength, elongation and drawing were measured.
- a test piece having a diameter of 10 mm and a length of 20 mm was taken along the longitudinal direction of the bar, and the test piece was inserted into an electric furnace in an atmospheric atmosphere maintained at 600 ° C., taken out after 100 hours of exposure, and brought to room temperature. The amount of increase in oxidation was measured by air cooling and measuring the weight before and after heating.
- the state of peeling of the oxide film was confirmed visually.
- the composite rupture test is based on ASTM, using both test pieces having a parallel part diameter and a notch bottom diameter of 4.52 mm, a notch outer diameter of 6.35 mm, a notch radius of 0.13 mm, and a parallel part length of 19.05 mm.
- the test was carried out under a stress of 650 ° C. and 510 MPa, and the breaking time, breaking position, breaking elongation and breaking drawing were measured. The results are shown in Tables 4-7.
- No. in the composition range defined in the present invention It can be seen that all of Nos. 1 to 5 have good moldability because the drawing at break in the room temperature tensile test in the solution treatment state is 50% or more. Comparative Example No. Nos. 22 to 24 also show good fracture drawing. No. 21 has a fracture drawing of less than 50%, which is slightly worse than an alloy having a formability within the composition range defined in the present invention. Since this contains a large amount of Nb, a large amount of intermetallic compounds containing Si, Nb, and Ni are also present in the grains before the aging treatment.
- Table 5 shows invention alloy Nos. With different aging treatment conditions. 3 shows the component analysis value of the grain boundary precipitate, the component analysis value of the ⁇ 'phase (intragranular fine precipitate), and the average diameter.
- the total amount of Si, Nb, and Ni in the grain boundary precipitate is 36% or more. It has become. Further, the amounts of Ni, Al, Ti and Nb in the ⁇ ′ phase are not only concentrated higher than the values in the alloy, but also the average diameter is 50 nm or less.
- the alloy No. 1 of the present invention which was subjected to aging treatment under the condition (4).
- No. 3 shows the average equivalent circle diameter of the ⁇ ′ phase as a result of the final (third) aging treatment being performed at 600 ° C. for 50 hours despite the first aging treatment being performed at 720 ° C. for 8 hours. Is 10.4 nm.
- the average equivalent circle diameter of the ⁇ ′ phase was much finer than that in the condition (1) where the aging treatment was not performed at 600 ° C. for 50 hours, and was equivalent to the equivalent circle diameter in the condition (5). . From this result, it can be seen that the last aging treatment condition greatly affects the size of the ⁇ ′ phase in the austenite grains.
- Comparative Alloy No. 23 had a large amount of Ni, the solid solubility of the intermetallic compound was large, and the intermetallic compound containing Si, Nb, and Ni was not sufficiently precipitated at the grain boundaries.
- Comparative alloy No. No. 24 has a large amount of Al, the amount of precipitated ⁇ ′ phase is increased, the balance of the matrix phase composition is lost, and the matrix phase is transformed into a martensite structure ( ⁇ ′ phase), so that the thermal expansion coefficient is greatly increased.
- Comparative Alloy No. 21 since the value of Al + Ti + Nb exceeds the specified upper limit value, the precipitation strengthening amount is large, but the ductility is lowered, and the drawing value is lower than that of the alloy of the present invention.
- the alloy of the present invention satisfies an increase in oxidation after heating at 600 ° C. for 100 hours in the air at 1.3 mg / cm 2 .
- the alloy No. Nos. 3 to 5 have a smaller oxidation increase and have good oxidation resistance.
- Comparative Alloy No. No. 22 is an alloy No. 22 of the present invention.
- the alloy of the present invention can produce a large ingot without worrying about macro segregation, can be formed in a solution treatment state, and has a low coefficient of thermal expansion and is high at room temperature to high temperature if properly subjected to aging treatment. Because tensile strength, good oxidation resistance, and good creep ductility can be obtained, the alloy of the present invention can be used for joining parts such as large gas turbine parts, ceramics, glass, and cemented carbides. When used, the clearance between components from room temperature to high temperature can be kept small, and relatively good oxidation resistance and stable high strength can be obtained, so that higher reliability is achieved.
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Abstract
Description
特許文献1に示される合金は、高強度を有する低熱膨張合金であるが、500~650℃付近の温度において、切欠き感受性が高く、高温での切欠きクリープ破断強度と平滑クリープ破断強度に大きな差があり、問題となっていた。
特許文献2に示される合金は、特許文献1に示される合金に比べて良好な切欠きクリープ破断強度を有するものの、熱膨張係数が特許文献1の合金よりやや大きいことから、低熱膨張という観点からは、必ずしも十分とは言えなかった。
特許文献3に示される合金は、特許文献1に示される合金より良好な切欠きクリープ破断強度を有し、かつ特許文献1、特許文献2に示される合金より低い熱膨張係数を有することから、高強度、低熱膨張等の特性バランスが良好な合金である。しかし、特許文献1、特許文献2、特許文献3に示される合金は、Cr等の耐酸化性向上に寄与する元素を含まないので、高温で酸化しやすく、高温での大気中のような酸化環境での使用には限界があった。
本発明の目的は、高強度、良好な切欠きクリープ破断強度、低い熱膨張係数、使用温度での耐酸化性を有し、かつ大型部品の製造が可能な低熱膨張超耐熱合金及びその製造方法を提供することである。
また、上記の良好な低熱膨張特性と機械的特性を安定して満足させるためには、比較的低温での固溶化処理と時効処理を行うことが有効であることを見出し、本発明に至った。
前記低熱膨張超耐熱合金は、質量%で0.1%以上1.7%未満のCrを含むことが望ましく、質量%で0.4~1.6%のCrを含むことが更に望ましい。
また、前記低熱膨張超耐熱合金は、時効処理状態で30~500℃の平均熱膨張係数が8.1×10-6/℃以下、室温の引張強さが780MPa以上、550℃での引張強さが600MPa以上、650℃で510MPaの応力下での複合クリープ試験において平行部において破断し、かつ破断伸びが10%以上、600℃の大気中で100時間の酸化試験において酸化膜の剥離がなく、酸化増量が1.3mg/cm2以下とすることができる。
更に好ましくは、前記真空誘導溶解の後、エレクトロスラグ再溶解または/および真空アーク再溶解によってインゴットを製造することが望ましい。
Cは、Ti、Nbと反応してMC型炭化物を形成し、鍛造時や固溶化処理時の結晶粒の粗大化を抑制し、強度の向上に寄与する。しかし、Cが0.1%を超えると炭化物が多く生成し、連鎖状の炭化物を偏在させて不均一なマクロ組織となるだけでなく、時効処理時に析出強化相を形成するために必要なTi、Nb量が減少するため十分な強度が得られにくくなることから、Cは0.1%以下とする。好ましくは0.05%以下がよい。Cによる効果を確実にするには、その下限を0.005%とすると良い。
Mnは、脱酸剤、脱硫剤として添加されるが、合金中にも固溶する。Mnは、1.0%を超えると熱膨張係数を増加させることから、Mnは1.0%以下とする。好ましくは0.5%以下がよく、更に好ましくは0.3%以下、より一層好ましくは0.2%以下がよい。
NiとCoは、前述したように、その量と割合を適正化することによって低い熱膨張係数を得ることが出来る。CoはNiの1.235倍で熱膨張係数の低下に寄与することから、1.235Ni+Coの値を適正化することによって、NiとCoの量及び割合を制御することができる。1.235Ni+Coの値が55.8%以上では熱膨張係数が高くなりすぎ、一方、52.9%より小さいとマルテンサイトを生成しやすくなり、安定したオーステナイト組織が得られにくくなることから、52.9%≦1.235Ni+Co<55.8%とする。なお、前述の関係式については、元素記号はそのまま元素記号の含有量も表すものである。
Tiもまた、時効処理によってオーステナイト粒内に微細析出して室温及び高温での強度を上昇させる金属間化合物であるγ’相(Ni3(Al,Ti,Nb))を構成する元素であり、必須元素である。Tiは、0.5%より少ないと強度上昇への効果が小さく、一方1.5%を超えると熱膨脹係数を増加させることから、Tiは0.5~1.5%とする。好ましいTiの下限は0.6%であり、上限に関して好ましいTi量は1.2%未満である。
γ’相を構成する元素のうち、Al、Ti、Nbについては、その総量であるAl+Ti+Nbの値が大きい方が室温及び高温での強度は高くなる。Al+Ti+Nbの値が3.5%より少ないと析出するγ’相の量が少なくなり、十分な強度が得られなくなる一方、5.5%より多くなると熱膨脹係数が増加することから、強度と熱膨張係数が適度にバランスできるAl+Ti+Nbの値は3.5%以上5.5%未満である。低い熱膨張係数を重視する場合の好ましいAl+Ti+Nbの上限は4.7%である。
本発明者らは低熱膨張超耐熱合金の溶湯密度差を求め、溶湯密度差に影響する化学成分の影響を鋭意検討した結果、F値=0.0014Ni+0.6Co-6.8Al+7.6Ti-5.3Nb-0.11Feで算出されるF値が溶湯密度差とよい相関を示すことを新規に見出した。F値は、濃化液相の密度の方が大きい場合マイナスの値に、合金液相の密度の方が大きい場合プラスの値となるが、何れの場合も絶対値がゼロに近い方がフレックル偏析を起こしにくくなる。F値の絶対値は、8%より大きいとフレックル偏析を起こしやすくなり大型インゴットの製造が難しくなることから、F値の絶対値は8%以下とした。好ましいF値の絶対値は6%以下である。
Cを0.1%以下に低く抑えた場合に、粒界析出炭化物の量が少なくなりすぎることにより、粒界へ偏析したSを固定できなくなり、粒界へのS偏析による熱間加工性の低下が起こりやすくなるため、Mgは、粒界偏析したSと結合してSを固定して、熱間加工性を改善する効果を有する。Mgは0.0005%より少ないと効果が十分でなく、一方0.01%を超えると酸化物や硫化物が多くなり、介在物として清浄度を低下させたり、低融点のNiとの化合物が多くなり、熱間加工性を低下させることから、Mgは0.0005~0.01%に限定する。好ましいMgの下限は0.001%であり、好ましいMgの上限は0.007%である。更に好ましいMgの上限は0.005%である。なお、Mgの一部または全てをCaに置換してもよく、その場合は(Mg+0.6×Ca)をMg単独の範囲に限定すればよい。
Mgの添加の目的は、粒界偏析する不純物のSの固定により熱間加工性を向上させることであるため、S含有量に応じてMg含有量が規定される。Sを有効に固定するためには、MgはSとの質量比で1:1以上となることが必要であることから、Mg/Sの値を1以上に限定する。Mgの一部または全てをCaに置換した場合は、(Mg+0.6×Ca)/Sを1以上に限定するのが好ましい。
不純物であるP、Sは粒界に偏析しやすく、高温強度や熱間加工性の低下を招くことから、Pは0.02%以下、Sは0.005%以下に限定することが良い。Sについては、0.003%以下が好ましく、0.002%以下が更に好ましい。また、O、Nは、Al、Ti、Nb等と結合して酸化物系、窒化物系の介在物を形成して清浄度を低下させ、疲労強度を劣化させるだけでなく、γ’相を形成するAl、Ti、Nb量を低減して析出強化による強度上昇を阻害する恐れがあることから、できるだけ低く抑えることが好ましい。このため、好ましいOは0.008%以下、Nは0.004%以下がよく、更に好ましいOは0.005%以下、Nは0.003%以下がよい。また、Ag、Sn、Pb、As、Biもオーステナイト粒界に偏析して高温強度の低下を招く不純物元素であり、Ag、Sn、Pb、As、Biは合計で0.01%以下に制限することが好ましい。
Nb添加を行う場合に少量のTaが不純物として混入する場合があるが、その場合、質量%で0.5×TaとNbが等価とみなせる。そこでNbの範囲をNb+0.5×Taと置き換えても差し支えない。また、Zrは粒界に偏析して熱間加工性を改善するが、過度に添加または混入すると逆に脆い化合物を生成して熱間加工性を害することから、Zrは0.05%以下がよい。また、Cu、Mo、Wは熱膨脹係数を増加させる可能性があることから、それぞれ0.5%以下がよく、さらに好ましくは0.3%以下がよい。
本発明合金において、良好な高温強度、延性、特に良好なクリープ強度、延性を得るには、オーステナイト母相の粒界を強化することが必要である。本発明合金は、上述した化学成分の最適化によってオーステナイト母相の粒界にSi、Nb、Niの1種以上の元素を単独または合計で36質量%以上含む金属間化合物(ラーベス相)が析出した組織を得ることができる。Si、Nb、Niの1種以上の元素を単独または合計で36質量%以上含む金属間化合物はクリープによる粒界すべりを抑制することによって粒界強度を上昇させ、クリープ強度、延性を向上させ、特に切欠きクリープ破断感受性を大幅に改善する。Si、Nb、Niの1種以上の元素を単独または合計で36質量%以上含む金属間化合物は、オーステナイト母相の粒界に粒状に不連続に析出するため、粒界を有効に強化する。この金属間化合物はSi、Nb、Niが1種以上の元素を単独または合計で37%以上が好ましく、40質量%以上含むのが更に好ましい。この金属間化合物の析出方法は後述する。なお、前記金属間化合物の定量分析は、例えば、走査型電子顕微鏡(SEM)観察時にエネルギー分散型エックス線分析装置(EDX)を用いて分析するのが簡便である。
また、本発明合金は、固溶化処理後に時効処理を行った状態で、低熱膨張係数、高強度、低い切欠きクリープ破断感受性、良好な耐酸化性が得られることが特長である。ここで、切欠きクリープ破断感受性は、切欠きと平滑な平行部を1つの試験片の軸方向に直列に有する複合クリープ試験片を用いて評価することができる。切欠き感受性の高い合金は、切欠き部において比較的短時間で破断する一方、切欠き感受性の低い合金は平滑な平行部で良好な伸びを示して破断することから、複合クリープ試験において平行部において破断することが切欠き感受性が低いことの判断基準となる。好ましい特性は、30~500℃の平均熱膨張係数が8.1×10-6/℃以下、室温の引張強さが780MPa以上、550℃での引張強さが600MPa以上、650℃で510MPaの応力下での複合クリープ試験において平行部において破断し、かつ破断伸びが10%以上、600℃の大気中で100時間の酸化試験において酸化膜の剥離がなく、酸化増量が1.3mg/cm2以下である。30~500℃の平均熱膨張係数は低い方が好ましく、組成、製造方法をバランスよく組み合わせることによってより低い値とすることができる。好ましい30~500℃の平均熱膨張係数は7.9×10-6/℃以下、一層好ましくは7.7×10-6/℃以下、より一層好ましくは7.5×10-6/℃以下、更により一層好ましくは7.4×10-6/℃以下である。また、好ましい酸化増量は1.2mg/cm2未満であり、更に好ましくは1.0mg/cm2以下である。
なお、本発明の「酸化膜の剥離がない」とは、耐酸化試験後に目視で観察できる剥離して脱落した酸化膜が試験片の周辺に観察されないことを言う。
合金組成は前述したとおりであり、不純物低減のために溶解は真空誘導溶解(VIM)を行うのが好ましい。更に低い不純物レベルを量産規模の製造にて得るには、真空誘導溶解と真空アーク再溶解(VAR)の組み合わせで溶解してインゴットを製造するのが好ましい。更に経済性を考慮する場合には、真空誘導溶解(VIM)とエレクトロスラグ再溶解(ESR)の組み合わせで溶解してインゴットを製造するのが更に好ましい。また、ESR溶解を用いるとSを効率的に低減できることから、Sを低く制限したい本発明合金の場合はESR溶解を採用するのが好ましい。マクロ偏析のない、より大型のインゴットを製造したい場合には、凝固速度が速い真空アーク再溶解を用いれば、エレクトロスラグ再溶解より大きなインゴットを製造することができる。なお、真空誘導溶解の後に、真空アーク再溶解やエレクトロスラグ再溶解を適用する場合は、真空誘導溶解で消耗電極を作製し、その消耗電極を用いて真空アーク再溶解やエレクトロスラグ再溶解でインゴットを製造することになる。また、真空誘導溶解により消耗電極を作製し、その消耗電極を用いてエレクトロスラグ再溶解によりインゴットを作製し、さらにそのインゴットを用いて真空アーク再溶解を行えば、さらに均質なインゴットを作製することができる。
固溶化処理の後、580~700℃で8~100時間の時効処理を少なくとも1回行うことによって、オーステナイト母相中に、Ni、Al、Ti、Nbが合金中より濃化した直径50nm以下のγ’相を微細析出させることができ、高い強度と低い熱膨張係数を得ることができる。時効処理温度は、580℃より低いと、γ’相の析出量が減少して高強度が得られにくくなり、一方700℃より高いと析出相の量、形態、組成が変化し、低い熱膨張係数が得られにくくなることから、時効処理温度は580~700℃とする。好ましい時効温度の上限は680℃、さらに好ましくは650℃である。8~100時間の保持を行うことによって良好な特性を得ることができることから、時効処理時間は8~100時間とする。好ましくは20~70時間、更に好ましくは30~60時間がよい。時効処理は、1回で行ってもよいし、580~700℃の範囲内で温度を変えて2回以上に分けて行ってもよい。
また、例えば、1回目の時効処理を700℃を超えて730℃以下で10時間以下程度の短時間の時効処理を行った後であっても、2回目以降の時効処理を580~700℃の範囲内で8~100時間の時効処理を行うとオーステナイト結晶粒内に50nm以下のγ’相を析出させることができる。更に、例えば、1回目の時効処理を700℃を超えて730℃以下で10時間以下程度の短時間の時効処理を行った後に、580~700℃の範囲内で20~100時間の長時間の時効処理を行うと、γ’相が微細となって、580~700℃で長時間の1回のみの時効処理を行ったものに匹敵する50nm以下のγ’相とすることができる。。具体的な事例は後述の実施例で示す。
その後、930℃で1h保持後、空冷の固溶化処理を行い、室温(25℃)での引張試験を行った。引張試験は、棒材の長手方向に沿って平行部6.0mm、標点間距離30mmの丸棒試験片を採取し、室温にてJISに準拠して試験し、0.2%耐力、引張強さ、伸び、絞りを測定した。その結果を表3に示す。
(1)720℃×8h→(50℃/h)→620℃×8h、空冷
(2)670℃×50h、空冷
(3)700℃×50h、空冷
(4)720℃×8h→(50℃/h)→620℃×8h、空冷+600℃×50h、空冷
(5)600℃×50h、空冷
(6)620℃×50h、空冷
表4には上記の( )付き番号と共に具体的な処理条件を記し、表5及び表6には、( )付き番号のみを記す。
また、上記(1)と(4)で示す時効処理のうち、“(50℃/h)”として示すものは、1時間あたりの冷却速度を示すものである。
ミクロ観察は、棒材の長手方向に平行な面を研磨、エッチングし、粒界に析出した金属間化合物を光学顕微鏡およびSEMを用いて観察し、成分分析はSEMのEDX分析により測定した。また粒内に析出したをSEMを用いて観察した。各γ’相は必ずしも球状ではないため、直径は円相当径を用いて30個以上測定した。γ’相の成分分析は、薄膜試料を切り出し、TEMを用いて観察およびEDX分析を行い測定した。なお、γ’相については、表4及び5では「粒内析出物」「粒内析出」として記す。
熱膨張係数測定は、棒材の長手方向に沿って直径5mm、長さ20mmの試験片を採取し、示差熱膨張測定により、30℃を基準とした500℃までの平均熱膨張係数を測定した。
引張試験は、棒材の長手方向に沿って平行部6.0mm、標点間距離30mmの丸棒試験片を採取し、室温及び550℃にてJISに準拠して試験し、0.2%耐力、引張強さ、伸び、絞りを測定した。
酸化増量は、棒材の長手方向に沿って直径10mm、長さ20mmの試験片を採取し、600℃に保持した大気雰囲気の電気炉に試験片を挿入し、100時間暴露後に取り出し、室温まで空冷し、加熱前後の重量を測定することで酸化増量を測定した。酸化膜の剥離の状況は目視で確認した。
複合ラプチャー試験は、ASTMに基づき、平行部直径及び切欠き底部直径とも4.52mm、切欠き外部径6.35mm、切欠き半径0.13mm、平行部長さ19.05mmの試験片を用いて、650℃、510MPaの応力下で試験し、破断時間、破断位置、破断伸び、破断絞りを測定した。その結果を表4~表7に示す。
この結果から、最後に行う時効処理条件がオーステナイト粒内のγ’相のサイズに大きく影響していることがわかる。
本発明合金及びNo.21を除く比較合金は、Al+Ti+Nbの値が規定の下限値以上に入っているため、室温及び550℃での引張強さがそれぞれ780MPa及び600MPaを満足している。比較合金No.21は、Al+Ti+Nbの値が規定の上限値を超えているため、析出強化量が大きい一方で延性が低下しており、絞り値が本発明合金より低くなっている。
また、本発明合金は、大気中、600℃で100時間の加熱後の酸化増量が1.3mg/cm2を満足している。特にCrを含む本発明合金No.3~5は酸化増量が更に少なく、良好な耐酸化性を有している。比較合金No.22は、本発明合金No.1に比べて、Nbが多いため、酸化増量が大きく、耐酸化性が良くない。一方で母相組織がマルテンサイト組織である比較合金No.24は酸化増量が大きく、耐酸化性が良くない。複合ラプチャー試験を実施した合金は何れもSiを含み、Si、Nb、Niを含む金属間化合物が不連続に粒界を覆っており、粒界酸化による粒界破断を抑制できるため、平行部で10%以上の伸びを示して破断していることから、切欠き感受性が低いことがわかる。
Claims (8)
- 質量%でC:0.1%以下、Si:0.1~1.0%、Mn:1.0%以下、Ni:25~32%、Co:18%を超え24%未満、Al:0.25%を超え1.0%以下、Ti:0.5~1.5%、Nb:2.1%を超え3.0%未満、B:0.001~0.01%、Mg:0.0005~0.01%、残部Fe及び不可避的不純物からなり、Mg/S≧1、52.9%≦1.235Ni+Co<55.8%、Al+Ti+Nb:3.5%以上5.5%未満、F値=0.0014Ni+0.6Co-6.8Al+7.6Ti-5.3Nb-0.11Feで算出されるF値の絶対値が8%以下、を満足し、オーステナイト母相の粒界にSi、Nb、Niの1種以上の元素を単独または合計で36質量%以上を含む粒状の金属間化合物が析出し、かつ合金中の濃度より多いNi、Al、Ti、Nbを含み、平均値で直径50nm以下の金属間化合物がオーステナイト母相中に析出した組織を有することを特徴とする低熱膨張超耐熱合金。
- 前記低熱膨張超耐熱合金が、質量%でC:0.05%以下、Si:0.2~0.7%、Mn:0.5%以下、Ni:26~29%、Co:18%を超え22%以下、Al:0.3~0.6%、Ti:0.6%以上1.2%未満、Nb:2.5%以上3.0%未満、B:0.001~0.01%、Mg:0.0005~0.01%、残部Fe及び不可避的不純物からなり、Mg/S≧1、52.9%≦1.235Ni+Co<55.8%、Al+Ti+Nb:3.5~4.7%、F値=0.0014Ni+0.6Co-6.8Al+7.6Ti-5.3Nb-0.11Feで算出されるF値の絶対値が6%以下、を満足する組成を有することを特徴とする請求項1に記載の低熱膨張超耐熱合金。
- 前記低熱膨張超耐熱合金が、質量%で0.1%以上1.7%未満のCrを更に含むことを特徴とする請求項1または2に記載の低熱膨張超耐熱合金。
- 前記低熱膨張超耐熱合金が、質量%0.4~1.6%のCrを更に含むことを特徴とする請求項1または2に記載の低熱膨張超耐熱合金。
- 固溶化処理状態の前記低熱膨張超耐熱合金の室温引張試験における絞りが、50%以上であることを特徴とする請求項1乃至4の何れかに記載の低熱膨張超耐熱合金。
- 時効処理状態の前記低熱膨張超耐熱合金の30~500℃の平均熱膨張係数が、8.1×10-6/℃以下、室温の引張強さが780MPa以上、550℃での引張強さが、600MPa以上、650℃で510MPaの応力下での複合クリープ試験において平行部において破断し、かつ破断伸びが10%以上、600℃の大気中で100時間の酸化試験において酸化膜の剥離がなく、酸化増量が1.3mg/cm2以下であることを特徴とする請求項1ないし4のいずれかに記載の低熱膨張超耐熱合金。
- 請求項1乃至4の何れかに一項に記載の組成を有する低熱膨張超耐熱合金の製造方法であって、前記低熱膨張超耐熱合金の組成を満足するように真空誘導溶解を行ってインゴットを得た後、前記インゴットを用いて、1回以上の熱間塑性加工を行った後、850~1080℃で固溶化処理した後、580~700℃で8~100時間の保持を含む時効処理を少なくとも1回行い、オーステナイト母相の粒界にSi、Nb、Niの1種以上の元素を単独または合計で36質量%以上を含む粒状の金属間化合物を析出させ、かつ合金中の濃度より多いNi、Al、Ti、Nbを含み、平均値で直径50nm以下の金属間化合物をオーステナイト母相中に析出させることを特徴とする低熱膨張超耐熱合金の製造方法。
- 前記真空誘導溶解後、更にエレクトロスラグ再溶解または/および真空アーク再溶解を行って前記インゴットを得ることを特徴とする請求項7に記載の低熱膨張超耐熱合金の製造方法。
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CN109530697A (zh) * | 2018-12-28 | 2019-03-29 | 钢铁研究总院 | 一种高强度低密度低膨胀铁镍合金及其制备方法 |
WO2021192060A1 (ja) * | 2020-03-24 | 2021-09-30 | 新報国製鉄株式会社 | 低熱膨張鋳物及びその製造方法 |
WO2024084732A1 (ja) * | 2022-10-20 | 2024-04-25 | 横浜ゴム株式会社 | スチールワイヤおよびマリンホース並びにスチールワイヤの曲げ性能の評価方法 |
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CN116043149B (zh) * | 2022-12-16 | 2024-05-28 | 成都先进金属材料产业技术研究院股份有限公司 | 一种低膨胀高温合金组炉均质化处理方法 |
CN116043136A (zh) * | 2023-01-18 | 2023-05-02 | 上海材料研究所有限公司 | 一种低膨胀高强度合金钢及其制造方法与应用 |
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- 2016-07-29 JP JP2016575700A patent/JP6160942B1/ja active Active
- 2016-07-29 US US15/763,617 patent/US10633717B2/en active Active
- 2016-07-29 DE DE112016004410.0T patent/DE112016004410T5/de active Pending
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CN109530697A (zh) * | 2018-12-28 | 2019-03-29 | 钢铁研究总院 | 一种高强度低密度低膨胀铁镍合金及其制备方法 |
WO2021192060A1 (ja) * | 2020-03-24 | 2021-09-30 | 新報国製鉄株式会社 | 低熱膨張鋳物及びその製造方法 |
WO2024084732A1 (ja) * | 2022-10-20 | 2024-04-25 | 横浜ゴム株式会社 | スチールワイヤおよびマリンホース並びにスチールワイヤの曲げ性能の評価方法 |
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KR20180043361A (ko) | 2018-04-27 |
KR102048810B1 (ko) | 2019-11-26 |
JPWO2017056674A1 (ja) | 2017-10-05 |
JP6160942B1 (ja) | 2017-07-12 |
DE112016004410T5 (de) | 2018-06-21 |
US10633717B2 (en) | 2020-04-28 |
US20190048433A1 (en) | 2019-02-14 |
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