Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon

Definitions

• the present invention relates to a Ni-base heat-resistant alloy and a method for producing the same.
• Fe-based alloys such as austenitic stainless steel have insufficient creep rupture strength. For this reason, it is essential to use a Ni-based alloy utilizing precipitation such as ⁇ ′ phase. Furthermore, since it is unavoidable that the steel pipe for a boiler / chemical industry is welded, it is required to have excellent weldability.
• Patent Document 1 discloses an austenitic heat-resistant alloy that is excellent in both weld crack resistance and toughness of HAZ and also excellent in creep strength at high temperatures.
• the present invention solves the above problems, and provides a Ni-base heat-resistant alloy that exhibits 0.2% proof stress and tensile strength at room temperature sufficient as a large structural member, and creep rupture strength at high temperature, and a method for producing the same.
• the purpose is to provide.
• the present invention has been made in order to solve the above-mentioned problems, and provides the following Ni-base heat-resistant alloy and its manufacturing method.
• the chemical composition of the alloy is mass%, C: 0.005 to 0.15%, Si: 2.0% or less, Mn: 3.0% or less, P: 0.030% or less, S: 0.010% or less, N: 0.030% or less, O: 0.030% or less, Ni: 40.0-60.0%, Co: 0.01-25.0%, Cr: 15.0% or more and less than 28.0%, Mo: 12.0% or less, W: less than 4.0%, B: 0.0005 to 0.006%, Al: 0 to 3.0%, Ti: 0 to 3.0%, Nb: 0 to 3.0%, REM: 0 to 0.1%, Mg: 0 to 0.02%, Ca: 0 to 0.02%, Balance: Fe and impurities, Satisfying the following formulas (i) to (iii): In the cross section perpendicular to the longitudinal direction of the alloy, the shortest distance from the center portion to the outer surface portion is 40 mm or more, The austenite grain size number in the outer surface portion is -2.0 to 4.0
• (Al + Ti + Nb) PB Total content of Al, Ti and Nb present as precipitates obtained by extraction residue analysis in the central portion (Al + Ti + Nb) PS : Al, Ti present as precipitates obtained by extraction residue analysis in the outer surface portion And Nb total content YS B : 0.2% yield strength at the center YS S : 0.2% yield strength at the outer surface TS B : Tensile strength at the center TS S : Tensile strength at the outer surface
• the chemical composition is mass%, Mg: 0.0001 to 0.02%, and Ca: 0.0001 to 0.02%, Containing one or two selected from The Ni-base heat-resistant alloy as described in (1) above.
• the 10,000-hour creep rupture strength at 700 ° C. in the longitudinal direction in the central portion is 150 MPa or more.
• the hot working is performed at least once in a direction substantially perpendicular to the longitudinal direction of the hot working.
• the Ni-based heat-resistant alloy of the present invention has little variation in mechanical properties depending on the part, and is excellent in creep rupture strength at high temperatures.
• C 0.005 to 0.15%
• C stabilizes the austenite structure, forms fine carbides at the grain boundaries, and improves the creep strength at high temperatures. Therefore, the C content needs to be 0.005% or more. However, when the content becomes excessive, the carbide becomes coarse and precipitates in a large amount, thereby lowering the ductility of the grain boundary, leading to a reduction in toughness and creep strength. Therefore, the C content is 0.15% or less.
• the C content is preferably 0.01% or more. Further, the C content is preferably 0.12% or less, and more preferably 0.10% or less.
• Si 2.0% or less Si is contained as a deoxidizing element. Si is an element effective for improving the corrosion resistance and oxidation resistance at high temperatures. However, if the Si content exceeds 2.0%, the stability of the austenite phase decreases, leading to a decrease in toughness and creep strength. Therefore, the Si content is 2.0% or less. The Si content is preferably 1.5% or less, and more preferably 1.0% or less. In addition, although it is not necessary to provide a minimum in particular about Si content, extreme reduction will not obtain a sufficient deoxidation effect, will deteriorate the cleanliness of an alloy, and will raise the manufacturing cost. Therefore, the Si content is preferably 0.02% or more, and more preferably 0.10% or more.
• Mn 3.0% or less Mn is an element that has a deoxidizing action like Si and contributes to stabilization of austenite. However, if the Mn content exceeds 3.0%, embrittlement is caused and the toughness and creep ductility are lowered. Therefore, the Mn content is 3.0% or less.
• the Mn content is preferably 2.5% or less, more preferably 2.0% or less, and even more preferably 1.5% or less. Although it is not necessary to provide a lower limit for the Mn content, an extreme decrease results in an insufficient deoxidation effect and deteriorates the cleanliness of the alloy, and increases the manufacturing cost. Therefore, the Mn content is preferably 0.02% or more, more preferably 0.10% or more, and further preferably 0.15% or more.
• P 0.030% or less
• P is an element contained in the alloy as an impurity, but segregates at the grain boundaries of HAZ during welding to increase liquefaction cracking sensitivity and adversely affect toughness after long-term use. is there. Therefore, although it is preferable to reduce as much as possible, extreme reduction leads to an increase in steelmaking cost. Therefore, the P content is 0.030% or less, and preferably 0.020% or less.
• S 0.010% or less S is an element contained in the alloy as an impurity, but segregates at the grain boundaries of HAZ during welding to increase liquefaction cracking sensitivity and adversely affect toughness after long-term use. is there. Therefore, although it is preferable to reduce as much as possible, extreme reduction leads to an increase in steelmaking cost. Therefore, the S content is 0.010% or less, and preferably 0.005% or less.
• N 0.030% or less
• N is an element effective for stabilizing the austenite phase.
• the Cr content of the present invention a large amount of fine nitriding is required during use at high temperatures if contained in excess. The substance is precipitated in the grains, resulting in a decrease in creep ductility or toughness. Therefore, the N content is 0.030% or less, preferably 0.020% or less, and more preferably 0.015% or less.
• the N content is preferably 0.0005% or more, more preferably 0.001% or more, and further preferably 0.005% or more.
• O 0.030% or less O is contained in the alloy as an impurity, but if it is excessively contained, it causes a decrease in hot workability, toughness and ductility. Therefore, the O content is 0.030% or less, preferably 0.020% or less, more preferably 0.010% or less, and still more preferably 0.005% or less. In addition, although it is not necessary to set a minimum in particular about content of O, an extreme fall invites the raise of manufacturing cost. Therefore, the O content is preferably 0.001% or more.
• Ni 40.0-60.0%
• Ni is an effective element for obtaining an austenite structure, and is an essential element for ensuring the structural stability after long-term use. Further, Ni combines with Al, Ti, and Nb to form a fine intermetallic compound phase, and also has an effect of increasing creep strength. In order to sufficiently obtain the above Ni effect within the Cr content range of the present invention, the Ni content needs to be 40.0% or more. However, since Ni is an expensive element, if its content exceeds 60.0%, the cost increases. Therefore, the Ni content is 40.0 to 60.0%.
• the Ni content is preferably 42.0% or more, more preferably 45.0% or more, further preferably 48.0% or more, and preferably 58.0% or less.
• Co 0.01-25.0%
• Co is an austenite-forming element and contributes to the improvement of creep strength by increasing the stability of the austenite phase.
• the Co content needs to be 0.01% or more.
• the Co content is preferably 0.1% or more, more preferably 2.0% or more, and even more preferably 8.0% or more. Further, the Co content is preferably 23.0% or less, more preferably 21.0% or less.
• Cr 15.0% or more and less than 28.0% Cr is an essential element for ensuring oxidation resistance and corrosion resistance at high temperatures.
• the Cr content needs to be 15.0% or more.
• the Cr content is preferably 17.0% or more, and more preferably 19.0% or more.
• it is preferable that Cr content is 26.0% or less, and it is more preferable that it is 24.0% or less.
• Mo 12.0% or less W: less than 4.0% Both Mo and W are elements that contribute to improvement in creep strength at high temperatures by dissolving in the austenite structure as a matrix. In order to obtain this effect, it is necessary to contain one or both of Mo and W. However, when the content of these elements is excessive, the stability of the austenite phase is decreased, and the creep strength is decreased. Therefore, the Mo content is 12.0% or less. The Mo content is preferably 10.0% or less.
• W has a larger atomic weight than Mo, it needs to be contained in a larger amount in order to obtain the same effect as Mo, which is disadvantageous from the viewpoint of ensuring cost and phase stability. For this reason, the W content is less than 4.0%. It is not necessary to contain Mo and W in combination. When Mo or W is contained alone, the content is preferably 0.1% or more.
• B 0.0005 to 0.006%
• B is an element necessary for improving the creep strength by segregating at the grain boundary in use to strengthen the grain boundary and finely dispersing the grain boundary carbide. In addition, it has the effect of segregating at the grain boundaries to improve the fixing force and contribute to toughness improvement. In order to obtain these effects, the B content needs to be 0.0005% or more. However, when the B content increases and exceeds 0.006% in particular, a large amount of segregation occurs in the high-temperature HAZ near the melting boundary due to the welding heat cycle during welding, and overlaps with P to lower the melting point of the grain boundary. Enhances liquefaction cracking sensitivity of HAZ. Therefore, the B content is 0.0005 to 0.006%.
• the B content is preferably 0.001% or more, and preferably 0.005% or less.
• Al, Ti, and Nb are all elements that improve creep strength at high temperatures by binding to Ni and finely precipitating in the grains as intermetallic compounds. However, if the content is too large and exceeds 3.0% for any of the elements, the above effects are saturated and creep ductility and toughness after prolonged heating are reduced. Therefore, the content of each of Al, Ti, and Nb is set to 3.0% or less. The content of these elements is preferably 2.8% or less, and more preferably 2.5% or less.
• REM 0 to 0.1%
• Rare earth elements (REM) have a strong affinity with P, have a high melting point, and form a compound with P that is stable up to high temperatures, thereby fixing P and removing the adverse effects of P on liquefaction cracking and toughness of HAZ. .
• it is an element which precipitates as a carbide
• the content of REM becomes excessive and exceeds 0.1%, the effect of reducing the adverse effect of P is saturated, and in addition, a large amount of carbide precipitates, leading to a decrease in toughness. Therefore, the REM content is 0.1% or less.
• the REM content is preferably 0.08% or less, and more preferably 0.06% or less. In order to obtain the above effect, the REM content is preferably 0.001% or more, more preferably 0.005% or more, and further preferably 0.01% or more.
• REM refers to a total of 17 elements of Sc, Y and lanthanoid, and the content of REM means the total content of these elements.
• Mg 0 to 0.02% Mg has a strong affinity with S and has an effect of increasing hot workability, and also has an effect of reducing both the occurrence of liquefaction cracking of HAZ and a decrease in toughness due to S. Therefore, you may make it contain as needed.
• excessive addition of Mg causes a decrease in cleanliness due to bonding with oxygen.
• the content exceeds 0.02%, the cleanliness decreases significantly, and the hot workability is deteriorated. Therefore, the Mg content is 0.02% or less.
• the Mg content is preferably 0.01% or less.
• the Mg content is preferably 0.0001% or more, more preferably 0.0005% or more, and further preferably 0.001% or more.
• Ca 0 to 0.02%
• Ca has a strong affinity with S and has an effect of improving hot workability, and also has an effect of reducing both the occurrence of liquefaction cracking of HAZ and a decrease in toughness due to S. Therefore, you may make it contain as needed.
• excessive addition of Ca leads to a decrease in cleanliness due to bonding with oxygen.
• the content exceeds 0.02%, the cleanliness decreases remarkably, and hot workability is deteriorated. Therefore, the Ca content is 0.02% or less.
• the Ca content is preferably 0.01% or less.
• the Ca content is preferably 0.0001% or more, more preferably 0.0005% or more, and further preferably 0.001% or more.
• the alloy according to the present invention must satisfy the following formulas (i) to (iii) in addition to the content of each element being in the above range.
• the element symbols in the following formulas (i) to (iii) represent the content (% by mass) of each element.
• both Mo and W are elements that contribute to the improvement of creep strength at high temperatures by dissolving in the austenite structure that is a matrix.
• the content of these elements is excessive, On the other hand, the stability of the austenite phase is lowered and the creep strength is lowered. Therefore, the total content of Mo and W needs to satisfy the above formula (i).
• the middle value of the formula (i) is preferably 1.0 or more, and preferably 10.0 or less.
• P and B are elements that segregate at the grain boundaries of the HAZ in the vicinity of the melting boundary during the heat cycle during welding, thereby lowering the melting point and increasing the susceptibility to liquefaction cracking of the HAZ.
• P segregated at the grain boundaries decreases the fixing force of the grain boundaries, whereas B conversely strengthens the grain boundaries, so P adversely affects toughness and B is reversed.
• Cr is an element that affects the grain boundary segregation behavior of P and B, and indirectly affects their performance.
• the value on the left side of the formula (iii) is preferably 0.030 or less.
• the lower limit of the left side value of the formula (iii) is not particularly limited, but the content of P as an impurity is extremely low, and is close to 0.0015 when Cr is 15.0% and B is 0.0005%. It may be a value.
• the balance is Fe and impurities.
• impurities are components mixed in due to various factors of raw materials such as ores and scraps and manufacturing processes when the alloy is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.
• Grain size Austenite grain size number in the outer surface -2.0 to 4.0 If the austenite grain size in the outer surface portion is too coarse, the 0.2% proof stress and tensile strength at room temperature will be low, while if too fine, it will not be possible to maintain high creep rupture strength at high temperatures. Therefore, the austenite grain size number in the outer surface portion is set to -2.0 to 4.0.
• the crystal grain size number is determined by the intersecting line segment (grain size) defined in JIS G 0551 (2013).
• the crystal grain size number of the outer surface portion after the final heat treatment can be set to the above range by appropriately adjusting the heat treatment temperature and holding time after the hot working and the cooling method. .
• the Ni-base heat-resistant alloy according to the present invention exhibits 0.2% proof stress and tensile strength at room temperature sufficient for a large structural member, and creep rupture strength at high temperature. That is, the effect of the present invention is remarkably exhibited for a thick member.
• the shortest distance from the center portion to the outer surface portion is set to 40 mm or more in the cross section perpendicular to the longitudinal direction.
• the shortest distance from the center portion to the outer surface portion is preferably 80 mm or more, and more preferably 100 mm or more.
• the shortest distance from the center portion to the outer surface portion is, for example, a radius of the cross section (mm) when the alloy is cylindrical, and a length (mm) that is half the short side of the cross section when the alloy is a quadrangular prism. It becomes.
• the heat-resistant alloy according to the present invention is obtained, for example, by subjecting a steel ingot or a cast piece obtained by continuous casting to hot working such as hot forging or hot rolling, as will be described later.
• the longitudinal direction of the heat-resistant alloy is generally the direction connecting the top and bottom portions of the steel ingot when using a steel ingot, and the length direction when using a slab.
• an insoluble ⁇ ′ phase (Ni 3 (Al, Ti, Nb)) is generated mainly in the grains after the heat treatment after hot working.
• the cooling rate is slower at the center of the alloy than at the outer surface, the amount of undissolved ⁇ ′ phase tends to increase. Therefore, the precipitation amount of Al, Ti, and Nb precipitated as ⁇ 'at the central portion with respect to the outer surface portion of the alloy increases, and when the value of (Al + Ti + Nb) PB / (Al + Ti + Nb) PS exceeds 10.0, High creep rupture strength cannot be maintained.
• the lower limit value of (Al + Ti + Nb) PB / (Al + Ti + Nb) PS is not required, but is preferably 1.0 or more because the central portion tends to increase the amount of precipitates more than the outer surface portion.
• the precipitate obtained by the extraction residue analysis is an insoluble ⁇ ′ phase contained in the alloy.
• the extraction residue analysis is performed according to the following procedure. First, a test piece for measuring the ⁇ ′ phase is collected from the center portion and the outer surface portion in a cross section perpendicular to the longitudinal direction of the alloy sample. After obtaining the surface area of the above test piece, only the base material of the heat-resistant alloy is completely electrolyzed in an electrolysis condition of 20 mA / cm 2 in a 1% tartaric acid-1% ammonium sulfate aqueous solution. And the solution after electrolysis is filtered with a 0.2 micrometer filter, and deposits are extracted as a residue.
• the content (mass%) of Al, Ti and Nb contained as an undissolved ⁇ ′ phase is measured by ICP-AES measurement after acid decomposition of the extraction residue, and based on the measured value (Al + Ti + Nb ) PB / (Al + Ti + Nb) Determine the value of PS .
• the Ni-base heat-resistant alloy according to the present invention satisfies the above formulas (v) and (vi) in mechanical properties at room temperature.
• both formulas (v) and (vi) are set to 1.0 or more. It is preferable.
• the 0.2% proof stress and tensile strength were determined by cutting a round bar tensile test piece with a parallel part length of 40 mm from the center part and outer surface part of the alloy in parallel with the longitudinal direction, and conducting a tensile test at room temperature. It asks by carrying out.
• the tensile test is performed according to JIS Z 2241 (2011).
• the Ni-base heat-resistant alloy of the present invention is used in a high-temperature environment, a high high-temperature strength, particularly a high creep rupture strength is required. Therefore, the alloy of the present invention needs to have a 10,000 hour creep rupture strength at 700 ° C. in the longitudinal direction of 150 MPa or more at the center.
• Creep rupture strength is obtained by the following method. First, a round bar creep rupture test piece having a diameter of 6 mm and a gauge distance of 30 mm described in JIS Z 2241 (2011) is cut out by machining from the center of the alloy in parallel with the longitudinal direction. Then, a creep rupture test is performed in the atmosphere at 700 ° C., 750 ° C., and 800 ° C., and the creep rupture strength at 700 ° C. for 10,000 hours is obtained using the Larson-Miller parameter method. The creep rupture test is performed in accordance with JIS Z 2271 (2010).
• Ni-base heat-resistant alloy of the present invention is manufactured by subjecting a steel ingot or slab having the above-described chemical composition to hot working.
• the treatment is performed so that the longitudinal direction of the final shape of the alloy coincides with the longitudinal direction of the steel ingot or slab as the raw material.
• the hot working may be performed only in the longitudinal direction, the hot working is performed once or more in the direction substantially perpendicular to the longitudinal direction in order to provide a higher degree of working and a more homogeneous structure. You may give it. Moreover, you may further give hot processing of different methods, such as hot extrusion, as needed after the said hot processing.
• the final heat treatment described below is performed in order to suppress the variation in the metal structure and mechanical properties of each part and maintain high creep rupture strength. Apply.
• the hot-worked alloy is heated to a heat treatment temperature T (° C.) in the range of 1070 to 1220 ° C., and within that range, 1150 D / T to 1500 D / T (min) is maintained.
• T heat treatment temperature
• D is, for example, a diameter (mm) of the alloy when the alloy is cylindrical, and a diagonal distance (mm) when the alloy is square. That is, D is the maximum value (mm) of the linear distance between an arbitrary point on the outer edge of the cross section and another arbitrary point on the outer edge in a cross section perpendicular to the longitudinal direction of the alloy.
• the heat treatment temperature is lower than 1070 ° C.
• the insoluble ⁇ ′ phase increases and the creep rupture strength decreases.
• the ductility is lowered due to melting of the grain boundary or markedly coarsening of the crystal grains.
• the heat treatment temperature is more preferably 1100 ° C. or higher, and more preferably 1200 ° C. or lower.
• the holding time is less than 1150 D / T (min)
• the ⁇ ′ phase in the central portion increases, and (Al + Ti + Nb) PB / (Al + Ti + Nb) PS is outside the range defined in the present invention.
• the crystal grains in the outer surface portion become coarse, and the austenite grain size number falls outside the range specified in the present invention.
• An alloy having the chemical composition shown in Table 1 was melted in a high-frequency vacuum melting furnace to form a steel ingot having an outer diameter of 550 mm and a weight of 3 t.
• the obtained steel ingot was processed into a cylindrical shape having an outer diameter of 200 to 480 mm by hot forging and subjected to final heat treatment under the conditions shown in Table 2 to obtain an alloy member sample.
• a specimen for observing the structure was collected from the outer surface, and the longitudinal section was polished with emery paper and buff, then corroded with mixed acid and observed with an optical microscope.
• the crystal grain size number on the observation surface was determined according to the determination method based on the intersection line segment (grain size) defined in JIS G 0551 (2013).
• a test piece for measuring the ⁇ ′ phase was collected from the center portion and the outer surface portion in the cross section perpendicular to the longitudinal direction of each sample. After determining the surface area of the above test piece, only the base material of the heat-resistant alloy was completely electrolyzed in an electrolysis condition of 20 mA / cm 2 in a 1% tartaric acid-1% ammonium sulfate aqueous solution. And the solution after electrolysis was filtered with a 0.2 micrometer filter, and the deposit was extracted as a residue.
• the content (mass%) of Al, Ti and Nb contained as an undissolved ⁇ ′ phase is measured by ICP-AES measurement after acid decomposition of the extraction residue, and based on the measured value (Al + Ti + Nb ) PB / (Al + Ti + Nb) The value of PS was determined.
• a tensile test piece having a parallel part length of 40 mm was cut out by machining from the center part and the outer surface part of each sample, and a tensile test was performed at room temperature. I asked for strength.
• a round bar creep rupture test piece having a diameter of 6 mm and a gauge distance of 30 mm described in JIS Z 2241 (2011) was cut out from the center of each sample in parallel with the longitudinal direction by machining.
• the creep rupture test was implemented in 700 degreeC, 750 degreeC, and 800 degreeC air
• Alloys 1 to 8 are examples of the present invention, and the alloy composition, grain size number, (Al + Ti + Nb) PB / (Al + Ti + Nb) PS , YS S / YS B , TS S / TS B , and creep rupture strength are defined by the present invention. The variation in mechanical properties was small, and the creep rupture strength was good.
• alloys A and B have substantially the same chemical composition as alloy 1 and have the same final shape by hot forging.
• the holding time at the time of heat treatment is outside the range of manufacturing conditions defined in the present invention.
• the grain size number of the outer surface portion of alloy A is outside the specified range of the present invention, and the values of YS S / YS B and TS S / TS B are out of the specified range of the present invention.
• the variation in mechanical properties increased depending on the part.
• the value of (Al + Ti + Nb) PB / (Al + Ti + Nb) PS was outside the specified range of the present invention, and the creep rupture strength was significantly lower than that of the alloy 1.
• Alloys C, D, and E have substantially the same chemical composition as alloy 2 and have the same final shape by hot forging. Since the heat treatment temperature of Alloy C is lower than the specified range of the present invention, the value of (Al + Ti + Nb) PB / (Al + Ti + Nb) PS and the crystal grain number of the outer surface part are outside the range specified by the present invention. Compared to 2, the creep rupture strength was extremely low. Since the heat treatment temperature of the alloy D is higher than the specified range of the present invention, the crystal grain size number of the outer surface portion and the values of YS S / YS B and TS S / TS B are outside the specified range of the present invention. Compared to Alloy 2, the creep rupture strength was remarkably low.
• the cooling method at the time of final heat treatment of alloy E is not water cooling but air cooling, and the cooling rate is extremely slow, so that the value of (Al + Ti + Nb) PB / (Al + Ti + Nb) PS falls outside the specified range of the present invention.
• the creep rupture strength was significantly lower than that of Alloy 3.
• Alloys F, G, and H are comparative examples whose chemical compositions deviate from the provisions of the present invention. Specifically, Alloy F is an example in which the W content is high, Alloy G has a high median value in equation (i), and Alloy H has a low median value in equation (ii). Therefore, in these examples, the creep rupture strength was reduced.
• the Ni-base heat-resistant alloy according to the present invention has little variation in mechanical properties depending on the part, and is excellent in creep rupture strength at high temperatures. Therefore, the Ni heat-resistant alloy of the present invention can be suitably used as large structural members such as boilers and chemical plants used in high temperature environments.

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• 2018
  • 2018-02-15 US US16/483,850 patent/US20200010931A1/en not_active Abandoned
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