WO2013073423A1 - 継目無オーステナイト系耐熱合金管 - Google Patents

継目無オーステナイト系耐熱合金管 Download PDF

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WO2013073423A1
WO2013073423A1 PCT/JP2012/078788 JP2012078788W WO2013073423A1 WO 2013073423 A1 WO2013073423 A1 WO 2013073423A1 JP 2012078788 W JP2012078788 W JP 2012078788W WO 2013073423 A1 WO2013073423 A1 WO 2013073423A1
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tube
content
resistant alloy
seamless
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PCT/JP2012/078788
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English (en)
French (fr)
Japanese (ja)
Inventor
佳奈 浄徳
伊勢田　敦朗
岡田　浩一
平田　弘征
吉澤　満
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新日鐵住金株式会社
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Priority to PL12850463T priority Critical patent/PL2781612T3/pl
Priority to EP12850463.6A priority patent/EP2781612B1/en
Priority to CN201280056250.6A priority patent/CN103946403B/zh
Priority to IN3492DEN2014 priority patent/IN2014DN03492A/en
Priority to KR1020147015980A priority patent/KR101632520B1/ko
Publication of WO2013073423A1 publication Critical patent/WO2013073423A1/ja

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    • 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
    • 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
    • C22C19/053—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 30% but less than 40%
    • 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
    • C22C19/058—Alloys based on nickel or cobalt based on nickel with chromium without Mo and 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
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C22C30/02—Alloys containing less than 50% by weight of each constituent containing copper
    • 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 seamless austenitic heat-resistant alloy tube. Specifically, it can be used as a member for high-temperature equipment by directly fillet welding the outer surface of the pipe, such as a pipe constituting the furnace wall of a power generation boiler (hereinafter referred to as “furnace wall pipe”).
  • the present invention relates to a seamless austenitic heat-resistant alloy tube. More specifically, it is a seamless alloy pipe made of an austenitic heat-resistant alloy with excellent high-temperature strength, sufficient stress corrosion cracking resistance, and low thermal expansion coefficient.
  • the present invention relates to a seamless austenitic heat-resistant alloy pipe capable of suppressing the occurrence of cracks in HAZ.
  • Non-Patent Document 1 shows a chart in which the horizontal axis indicates the Cr content of the material and the vertical axis indicates the temperature at an allowable stress of 49 MPa, with the increase in Cr content. It is stated that the temperature on the vertical axis, and hence the creep strength as the high temperature strength, is increased.
  • Non-Patent Document 2 shows a diagram arranged for practical heat-resistant materials with the Ni content of the material on the horizontal axis and the crack sensitivity on the vertical axis, and as the Ni content increases, It is shown that the crack sensitivity on the vertical axis is reduced, and the corrosion resistance at high temperatures (stress corrosion cracking resistance) is increased.
  • Patent Documents 1 to 3 disclose heat-resistant alloys in which the content of Cr and Ni is increased and at least one of Mo and W is contained to improve the creep rupture strength as high-temperature strength.
  • Patent Documents 4 to 7 contain 28% to 38% Cr, 35% to 60% Ni in mass%.
  • a heat-resistant alloy that further improves the creep rupture strength by utilizing precipitation of an ⁇ -Cr phase having a body-centered cubic structure mainly composed of Cr is disclosed.
  • Patent Document 8 and Patent Document 9 Mo and / or W is included to enhance solid solution, and Al and Ti are included to form a ⁇ ′ phase that is an intermetallic compound, specifically, Ni. 3 Ni-based alloys are disclosed that are used in the severe environment described above by utilizing precipitation strengthening of (Al, Ti).
  • Patent Document 10 proposes a high Ni austenitic heat-resistant alloy in which the creep strength is improved by adjusting the range of the content of Al and Ti and precipitating the ⁇ 'phase.
  • HAZ weld heat-affected zone
  • austenitic heat-resistant alloys used as members of various structures are required to satisfy both prevention of cracking in HAZ during welding and welded joint performance.
  • Patent Document 11 includes a specific amount of Fe, and by adjusting the range of the effective B amount, austenite-based heat resistance capable of ensuring workability at high temperatures and preventing cracks in HAZ during butt welding.
  • An alloy is disclosed.
  • Patent Document 12 by adjusting the content of impurity elements such as Sn and Pb in addition to P and S, cracking in HAZ can be prevented at the time of butt welding and long-time use at high temperatures.
  • An austenitic heat-resistant alloy that is also capable of being excellent in creep strength is disclosed.
  • austenitic heat-resistant alloys are generally assembled into various structures by welding. In recent years, there has been a movement to use these austenitic heat-resistant alloy tubes for furnace wall tubes of power generation boilers.
  • carbon steel or 1% Cr steel that does not need to be preheated and postheated has been generally used from various viewpoints such as workability.
  • the conventionally used carbon steel or 1% Cr steel has insufficient high-temperature strength. For this reason, neither the above-mentioned carbon steel nor 1% Cr steel can be used as the material for the furnace wall tube of the “next generation ultra super critical pressure boiler”.
  • austenitic stainless steel has a large coefficient of linear thermal expansion as shown in Non-Patent Document 4. For this reason, in austenitic stainless steel, thermal deformation becomes large at the time of welding, which causes a problem at the time of manufacturing the furnace wall.
  • the furnace wall is composed of a panel in which a plurality of furnace wall tubes are arranged in parallel and welded to a fin plate or a fin bar for connecting the furnace wall tubes. For this reason, unlike butt welding in which machined groove surfaces are welded, it is necessary to fillet weld the outer surface of the as-manufactured pipe directly to the fin plate or fin bar.
  • an austenitic heat-resistant alloy tube with an increased Ni content that can be suitably used for the furnace wall tube of the “next generation ultra super critical pressure boiler”, that is, excellent high temperature strength and sufficient stress corrosion cracking resistance.
  • seamless alloy pipes made of austenitic heat-resistant alloys with a low thermal expansion coefficient Ni content that is excellent in weld crack resistance and can suppress cracking in HAZ during welding Developing an improved seamless austenitic heat-resistant alloy tube has become an urgent issue.
  • Patent Documents 1 to 10 described above disclose austenitic heat-resistant alloys with improved creep rupture strength, but have not been studied from the viewpoint of “weldability” when assembled as a structure, There is no consideration of welding the outer surface of the tube directly. Therefore, it is impossible to use the tube made of the austenitic heat-resistant alloy proposed in each of the above patent documents as the furnace wall tube of the “next generation ultra super critical pressure boiler”.
  • the austenitic heat-resistant alloy proposed by the present inventors in Patent Document 11 is used as products such as tubes, plates, rods and forged products used for heat-resistant pressure-resistant members for power generation boilers, chemical industries, etc., particularly as large products. It is suitable for. And this austenitic heat-resistant alloy can remarkably improve the high temperature workability at the time of manufacturing the above-mentioned products and when using the actual machine, the resistance to weld cracking, and the decrease in ductility due to high temperature aging.
  • the austenitic heat-resistant alloy proposed by the present inventors in Patent Document 12 can prevent cracks in HAZ, can also prevent defects caused by welding workability that occurs during welding work, and can also be used at high temperatures. Excellent creep strength. For this reason, this austenitic heat-resistant alloy can be suitably used as a raw material for high-temperature equipment such as a power generation boiler and a chemical industrial plant.
  • the present invention has been made in view of the above-mentioned present situation.
  • an austenitic heat-resistant alloy that can be used as a member of a high-temperature apparatus by directly fillet welding the outer surface of the tube.
  • This is a seamless alloy pipe made of an austenitic heat-resistant alloy with excellent thermal cracking resistance, sufficient stress corrosion cracking resistance, and low thermal expansion coefficient.
  • An object of the present invention is to provide a seamless austenitic heat-resistant alloy pipe capable of suppressing the occurrence of cracks in HAZ.
  • the present inventors conducted various investigations in order to solve the problems described above.
  • austenitic heat-resistant alloy pipes various austenitic heat-resistant alloy seamless pipes containing B (hereinafter sometimes simply referred to as “austenitic heat-resistant alloy pipes”).
  • the cracks generated in the above HAZ are mechanically influenced by the toe angle of the surging.
  • the toe angle is indirectly influenced by the oxide layer formed on the outer surface of the austenitic heat-resistant alloy tube.
  • (G) B segregates at the grain boundaries of the HAZ near the melting boundary during the welding process due to the welding thermal cycle. Since B is an element that lowers the melting point of the grain boundary, the grain boundary where the B segregates during the welding is locally melted, and the melted portion is opened by welding thermal stress, so-called “liquefaction cracking”. Produce. Note that when the crystal grain size is large, the grain interface area per unit volume is small. Therefore, when the crystal grain size is large, the grain boundary segregation of B becomes remarkable and the stress applied to the specific grain interface becomes large, so that cracks in the HAZ are likely to occur.
  • the outer surface of the austenitic heat-resistant alloy tube was directly regarded as a fin plate (alloy plate having a chemical composition shown in Table 2 in the Example, having a thickness of 6 mm, a width of 15 mm, and a length of 200 mm) and fillet welding. Even in this case, it has been clarified that cracks in the HAZ can be prevented by taking the following measures (j) and (k).
  • the average crystal grain size d ( ⁇ m) at the thickness central portion of the alloy tube is adjusted to a range satisfying the following formula according to the amount of B contained in the alloy at 1000 ⁇ m or less.
  • d ⁇ 1500-2.5 ⁇ 10 5 ⁇ B B in the above formula represents the content (% by mass) of B.
  • the thickness of the oxide layer on the outer surface of the alloy tube is suppressed to 15 ⁇ m or less.
  • the present invention has been completed based on the above findings, and the gist thereof is a seamless austenitic heat-resistant alloy tube shown below.
  • Impurity refers to materials mixed from ore, scrap, or the production environment as raw materials when industrially producing austenitic heat-resistant alloys.
  • REM is a general term for a total of 17 elements of Sc, Y and lanthanoid, and the content of REM refers to the total content of one or more elements of REM.
  • the seamless austenitic heat-resistant alloy pipe of the present invention is excellent in weld crack resistance and can suppress the occurrence of cracks in the HAZ during welding. Therefore, the seamless austenitic heat-resistant alloy pipe of the present invention is a seamless alloy pipe made of an austenitic heat-resistant alloy having excellent high-temperature strength, sufficient stress corrosion cracking resistance, and a low thermal expansion coefficient. However, it can be suitably used as a member for high-temperature equipment such as a furnace wall tube of a power generation boiler.
  • C Chemical composition of the tube: C: 0.03-0.15%
  • C stabilizes austenite, forms fine carbides at grain boundaries, and improves creep strength at high temperatures.
  • a C content of 0.03% or more is necessary.
  • the carbide becomes coarse and precipitates in a large amount, so that the ductility of the grain boundary is lowered, and further, the toughness and the creep strength are also lowered. Therefore, an upper limit is set, and the C content is 0.03 to 0.15%.
  • the preferable lower limit of the C content is 0.04%, and the preferable upper limit is 0.12%.
  • Si 1% or less Si is an element that has a deoxidizing action and is effective for improving corrosion resistance and oxidation resistance at high temperatures. However, when Si is contained excessively, the stability of austenite is lowered, leading to a decrease in toughness and creep strength. Therefore, an upper limit is set for the Si content to 1% or less. The Si content is desirably 0.8% or less.
  • the desirable lower limit of the Si content is 0.02%.
  • Mn 2% or less Mn, like Si, has a deoxidizing action. Mn also contributes to stabilization of austenite. However, when the Mn content is excessive, embrittlement is caused, and the toughness and creep ductility are also reduced. Therefore, an upper limit is set for the Mn content to 2% or less. The Mn content is desirably 1.5% or less.
  • the desirable lower limit of the Mn content is 0.02%.
  • P 0.03% or less
  • P is an element which is contained in the alloy as an impurity and segregates at the grain boundary of HAZ during welding to increase the liquefaction cracking sensitivity. Therefore, an upper limit is set for the P content to 0.03% or less.
  • the content of P is desirably 0.02% or less.
  • the desirable lower limit of the P content is 0.0005%.
  • S 0.01% or less
  • S is an element which is contained in the alloy as an impurity like P and segregates at the grain boundaries of HAZ during welding to increase the liquefaction cracking sensitivity. Furthermore, S is an element that adversely affects toughness after long-term use. Therefore, an upper limit is set for the S content to 0.01% or less. The content of S is desirably 0.005% or less.
  • the desirable lower limit of the S content is 0.0001%.
  • Ni 35-60%
  • Ni is an effective element for obtaining austenite, and is an essential element for ensuring the structural stability when used for a long time.
  • a Ni content of 35% or more is necessary.
  • Ni is an expensive element, and containing a large amount of Ni causes an increase in cost. Therefore, an upper limit is set so that the Ni content is 35 to 60%.
  • a desirable lower limit of the Ni content is 38%, and a desirable upper limit is 55%.
  • Cr 18-38% Cr is an essential element for securing oxidation resistance and corrosion resistance at high temperatures.
  • a Cr content of 18% or more is necessary.
  • the Cr content is 18 to 38%.
  • a desirable lower limit of the Cr content is 20%, and a desirable upper limit is 35%.
  • W 3-11% W is an element that contributes greatly to the improvement of creep strength at a high temperature exceeding 700 ° C. by dissolving in the matrix. In order to fully exhibit the effect, W content of at least 3% or more is necessary. However, even if W is excessively contained, the effect is saturated and the creep strength may be lowered. Furthermore, since W is an expensive element, excessive W content causes an increase in cost. Therefore, an upper limit is set so that the W content is 3 to 11%. A desirable lower limit of the W content is 5%, and a desirable upper limit is 10%.
  • Ti 0.01 to 1.2% Ti precipitates in the grains as fine carbonitrides and contributes to the creep strength at high temperatures. In order to obtain the effect, a Ti content of 0.01% or more is necessary. However, when the Ti content is excessive, it precipitates in large amounts as carbonitrides, leading to a decrease in creep ductility and toughness. Therefore, an upper limit is set so that the Ti content is 0.01 to 1.2%. A desirable lower limit of the Ti content is 0.05%, and a desirable upper limit is 1.0%.
  • Al 0.5% or less
  • Al is an element having a deoxidizing action.
  • an upper limit is set for the Al content to 0.5% or less.
  • the content of Al is desirably 0.3% or less.
  • the desirable lower limit of the Al content is 0.001%.
  • the lower limit of the Al content is more preferably 0.0015%.
  • B 0.0001 to 0.01%
  • B is an element necessary for improving the creep strength by segregating at the grain boundary during use at a high temperature to strengthen the grain boundary and finely dispersing the grain boundary carbide.
  • B has an effect of segregating at the grain boundary to improve the fixing force and contribute to improvement of toughness.
  • a B content of 0.0001% or more is necessary.
  • an upper limit is set so that the B content is 0.0001 to 0.01%.
  • a desirable lower limit of the B content is 0.0005%, and a desirable upper limit is 0.005%.
  • the crystal grain size of HAZ in the vicinity of the melting boundary increases, in other words, the grain interface area per unit volume decreases, and B Grain boundary segregation is promoted, and stress applied to a specific grain interface is increased, so that liquefaction cracking sensitivity is increased.
  • the average crystal grain size d ( ⁇ m) of the center thickness of the alloy tube is 1000 ⁇ m or less, and the following formula is satisfied according to the amount (%) of B contained in the alloy. If it adjusts to the range to perform, the increase in the liquefaction cracking sensitivity by the segregation of B can be suppressed.
  • d ⁇ 1500-2.5 ⁇ 10 5 ⁇ B B in the above formula represents the content of B in mass%.
  • N 0.02% or less N is an element effective for stabilizing austenite.
  • Cr content range of 18 to 38%, if N is contained excessively, a large amount of fine nitride precipitates in the grains during use at a high temperature, leading to a decrease in creep ductility and toughness. . Therefore, an upper limit is set for the N content to 0.02% or less.
  • the N content is desirably 0.015% or less.
  • the desirable lower limit of the N content is 0.0005%.
  • O 0.008% or less
  • O oxygen
  • an upper limit is set for the O content to 0.008% or less.
  • the content of O is desirably 0.005% or less.
  • the desirable lower limit of the O content is 0.0005%.
  • Zr 0.01 to 0.5%
  • Zr combines with C or N to form fine carbides or carbonitrides and contributes to the improvement of creep strength.
  • a Zr content of 0.01% or more is necessary.
  • an upper limit is set so that the Zr content is 0.01 to 0.5%.
  • a desirable lower limit of the Zr content is 0.015%, and a desirable upper limit is 0.4%.
  • Nb 0.01 to 0.5%
  • Nb combines with C or N to form fine carbides or carbonitrides and contributes to the improvement of creep strength.
  • an Nb content of 0.01% or more is necessary.
  • an upper limit is set so that the Nb content is 0.01 to 0.5%.
  • a desirable lower limit of the Nb content is 0.015%, and a desirable upper limit is 0.4%.
  • V 0.01 to 0.5%
  • V combines with C or N to form fine carbides or carbonitrides and contributes to the improvement of creep strength.
  • a V content of 0.01% or more is necessary.
  • an upper limit is set so that the V content is 0.01 to 0.5%.
  • a desirable lower limit of V content is 0.015%, and a desirable upper limit is 0.4%.
  • the above-mentioned Zr, Nb, and V can be contained alone or in combination of two or more.
  • the total amount when these elements are combined and contained may be 1.5%, but is preferably 1.2% or less.
  • One of the seamless austenitic heat-resistant alloy tubes of the present invention has a chemical composition comprising the above-mentioned elements, and the balance being Fe and impurities.
  • impurities refer to impurities mixed from ores, scraps, or production environments as raw materials when industrially producing austenitic heat-resistant alloys.
  • Another one of the seamless austenitic heat-resistant alloy pipes of the present invention is a chemistry containing one or more elements selected from Mo, Cu, Co, Ca, Mg and REM instead of a part of the above-mentioned Fe. Of composition.
  • Mo 1% or less Mo has an effect of improving creep strength. That is, Mo has a function of improving the creep strength at a high temperature by dissolving in the matrix. Therefore, you may contain Mo. However, when Mo is excessively contained, the stability of austenite is lowered, and instead the creep strength is lowered. For this reason, an upper limit is set for the amount of Mo in the case of inclusion, and the amount is made 1% or less.
  • the amount of Mo is preferably 0.1% or more.
  • Cu 1% or less Cu has an effect of improving creep strength. That is, Cu is an austenite-forming element like Ni and contributes to the improvement of creep strength by increasing phase stability. Therefore, Cu may be contained. However, when Cu is contained excessively, the hot workability is lowered. For this reason, when making it contain, the upper limit is provided in the quantity of Cu, and it is 1% or less.
  • the amount of Cu is preferably 0.02% or more.
  • Co 1% or less Co has the effect of improving the creep strength. That is, Co is an austenite-forming element, like Ni and Cu, and contributes to the improvement of creep strength by increasing phase stability. Therefore, Co may be contained. However, since Co is an extremely expensive element, excessive content of Co causes a significant cost increase. For this reason, the upper limit is set to the amount of Co in the case of making it contain, and it is 1% or less.
  • the amount of Co is preferably 0.02% or more.
  • the above-mentioned Mo, Cu and Co can be contained in only one of them or in combination of two or more.
  • the total amount when these elements are contained in combination may be 3%.
  • Ca 0.05% or less Ca has an effect of improving hot workability. For this reason, Ca may be contained. However, when the content of Ca is excessive, it combines with O to significantly reduce cleanliness, and on the other hand, deteriorate hot workability. For this reason, when making it contain, the upper limit is provided in the quantity of Ca, and it is 0.05% or less.
  • the amount of Ca is preferably 0.0005% or more.
  • Mg 0.05% or less Mg, like Ca, has an effect of improving hot workability. For this reason, you may contain Mg. However, if the Mg content is excessive, it combines with O to significantly reduce cleanliness, and on the contrary, deteriorate hot workability. For this reason, the upper limit is set to the amount of Mg in the case of containing 0.05% or less.
  • the amount of Mg is preferably 0.0005% or more.
  • REM 0.1% or less REM has an effect of improving hot workability. That is, REM has a strong affinity with S and contributes to improvement of hot workability. For this reason, you may contain REM. However, when the content of REM becomes excessive, it combines with O to significantly reduce cleanliness and, on the contrary, deteriorate hot workability. For this reason, an upper limit is set for the amount of REM in the case of inclusion, so that it is 0.1% or less.
  • the amount of REM is preferably 0.0005% or more.
  • REM is a generic name for a total of 17 elements of Sc, Y and lanthanoid, and the content of REM refers to the total content of one or more elements of REM.
  • REM is generally contained in misch metal. For this reason, for example, it may be added in the form of misch metal and contained so that the amount of REM falls within the above range.
  • the above-mentioned Ca, Mg and REM can be contained in only one of them, or in a combination of two or more.
  • the total amount when these elements are contained in combination may be 0.2%.
  • the average crystal grain size d ⁇ m at the wall thickness central portion of the tube is 1000 ⁇ m or less, and depending on the amount of B contained in the alloy, d ⁇ 1500-2.5 ⁇ 10 5 ⁇ B It must satisfy the expression expressed by In addition, B in said formula represents content of B in the mass%.
  • the toughness and ductility are significantly reduced. Furthermore, since the HAZ crystal grain size near the melting boundary also increases, in other words, the grain boundary area per unit volume decreases, so the upper limit of the B content contained in the tube is controlled to 0.01% as described above. However, liquefaction cracking due to segregation of B cannot be prevented.
  • the average crystal grain size d at the center of the thickness of the tube can be maintained by 0.5 to 5 hours in a temperature range of 1150 to 1250 ° C. Can be made to satisfy the above-mentioned formula of “d ⁇ 1500 ⁇ 2.5 ⁇ 10 5 ⁇ B”.
  • the thickness of the oxide layer on the outer surface of the tube The oxide film formed on the surface of the seamless austenitic heat-resistant alloy tube of the present invention having the chemical composition described in the item (A) has a high melting point. Moreover, the above oxide film deteriorates the wettability with the molten metal when fillet welding the outer surface of the pipe. For this reason, when the thickness of the oxide layer on the outer surface of the pipe is increased, the toe angle of the weld bead (excess) is increased and stress is easily concentrated on the HAZ, and liquefaction cracking is likely to occur. Therefore, an upper limit is set for the thickness of the oxide layer on the outer surface of the tube to be 15 ⁇ m or less. The thickness of the oxide layer on the outer surface of the tube is desirably 10 ⁇ m or less.
  • the outer surface of the tube can be stably formed by performing the solution heat treatment in the temperature range of 1150 to 1250 ° C. described in the above section (B) for 0.5 to 5 hours in a reducing gas such as hydrogen.
  • the thickness of the oxide layer can be 15 ⁇ m or less.
  • an oxide scale (oxide layer) is formed by performing the solution heat treatment described in the above section (B) in the atmosphere or in a combustion gas, treatments such as pickling, polishing, and shot blasting are performed.
  • the thickness of the oxide layer on the outer surface of the tube can be stably reduced to 15 ⁇ m or less.
  • the thickness of the oxide layer on the outer surface of the tube may be close to 0 ⁇ m by performing a solution heat treatment in reducing gas, pickling, polishing, shot blasting, or the like.
  • mechanical grinding may be performed to remove the oxide layer on the outer surface of the tube, thereby reducing the thickness of the oxide layer to zero.
  • the thickness of the oxide layer on the outer surface of the tube is desirably 0.1 ⁇ m or more, and more desirably 0.2 ⁇ m or more.
  • Each billet thus obtained was hot pierced and rolled using a model mill to produce a seamless tube having an outer diameter of 38 mm and a wall thickness of 9 mm.
  • Each seamless pipe having an outer diameter of 38 mm and a wall thickness of 9 mm was cut into a length of 200 mm, and the temperature was changed in the range of 1150 to 1280 ° C. and the holding time at the temperature in the range of 0.5 to 5 h.
  • a solution heat treatment was performed to prepare various test tubes having different average crystal grain diameters d at the center of the wall thickness.
  • the outer surface of the obtained test tube was polished to change the oxide layer thickness variously.
  • the average crystal grain size d at the center of the wall thickness and the oxide layer thickness on the outer surface of the tube were measured by the following methods.
  • the average crystal grain d ( ⁇ m) at the center of the wall thickness is based on the center of the 200 mm-long test tube, and before and after that, five test pieces are cut out so that the test surface has a cross section, and It was obtained by cutting into four pieces in the circumferential direction, mirror polishing, corroding with aqua regia and observing the central portion of the wall with an optical microscope.
  • the oxide layer thickness on the outer surface of the tube was mirror-polished again on the 20 test pieces used for measuring the average crystal grain size d ( ⁇ m) of the above-mentioned thickness center for each test tube, This was determined by observation with an optical microscope in the state of polishing.
  • each test tube was observed at a magnification of 400 for every 20 test pieces, and the thickness of the oxide on the outer surface of the tube was measured. Subsequently, the value of the oxide thickness in 20 test pieces was arithmetically averaged to obtain the oxide layer thickness on the outer surface of the tube.
  • each test tube whose outer surface was polished after the solution heat treatment was used, and an alloy plate having a thickness of 6 mm and a width of 15 mm cut into a 200 mm length having the chemical composition shown in Table 2.
  • a constrained weld specimen was prepared that simulated fillet welding of a furnace wall tube shown in FIG.
  • test pieces were cut out from the four fillet welds so that the surface to be tested had a cross-section and mirror-polished.
  • the rate of occurrence of liquefaction cracks is defined as “(number of crack occurrence cross sections / 20) ⁇ 100 (%)”, and only test specimens with a liquefaction crack occurrence rate of 0 (zero) are judged as “pass”. Was judged as “failed”.
  • the alloys A to F having a chemical composition within the range specified in the present invention are used as the raw material, the average crystal grain size in the central portion of the tube or the oxide on the outer surface of the tube.
  • liquefaction cracking occurs in the HAZ, and it cannot be used for a furnace wall tube that directly fillet welds the outer surface of the tube.
  • the average crystal grain size d in the central portion of the wall thickness of the tube is less than 1000 ⁇ m, but d ⁇ 1500 ⁇ defined according to the amount of B contained in the alloy 2.5 ⁇ 10 5 ⁇ B
  • liquefaction cracking occurred in HAZ.
  • rate of occurrence of liquefaction cracks increased as the average crystal grain size d increased.
  • the average crystal grain size d at the center of the tube thickness exceeded 1000 ⁇ m, so that liquefaction cracking occurred in the HAZ.
  • the seamless austenitic heat-resistant alloy pipe of the present invention is excellent in weld crack resistance and can suppress the occurrence of cracks in the HAZ during welding. Therefore, the seamless austenitic heat-resistant alloy pipe of the present invention is a seamless alloy pipe made of an austenitic heat-resistant alloy having excellent high-temperature strength, sufficient stress corrosion cracking resistance, and a low thermal expansion coefficient. However, it can be suitably used as a member for high-temperature equipment such as a furnace wall tube of a power generation boiler.
PCT/JP2012/078788 2011-11-15 2012-11-07 継目無オーステナイト系耐熱合金管 WO2013073423A1 (ja)

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PL12850463T PL2781612T3 (pl) 2011-11-15 2012-11-07 Bezszwowa rura ze stopowej żaroodpornej stali austenitycznej
EP12850463.6A EP2781612B1 (en) 2011-11-15 2012-11-07 Seamless austenite heat-resistant alloy tube
CN201280056250.6A CN103946403B (zh) 2011-11-15 2012-11-07 奥氏体系无缝耐热合金管
IN3492DEN2014 IN2014DN03492A (ko) 2011-11-15 2012-11-07
KR1020147015980A KR101632520B1 (ko) 2011-11-15 2012-11-07 이음매 없는 오스테나이트계 내열 합금관

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JP6398277B2 (ja) * 2014-04-14 2018-10-03 新日鐵住金株式会社 Ｎｉ基耐熱合金溶接継手の製造方法
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JP6477252B2 (ja) * 2015-05-26 2019-03-06 新日鐵住金株式会社 オーステナイト系耐熱合金および耐熱耐圧部材
RU2581323C1 (ru) * 2015-06-01 2016-04-20 Байдуганов Александр Меркурьевич Жаропрочный сплав
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JP2018127672A (ja) * 2017-02-08 2018-08-16 新日鐵住金株式会社 オーステナイト系耐熱合金部材
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JP6825514B2 (ja) * 2017-08-01 2021-02-03 日本製鉄株式会社 オーステナイト系耐熱合金部材
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JPWO2018066579A1 (ja) * 2016-10-05 2019-07-11 日本製鉄株式会社 ＮｉＣｒＦｅ合金

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