Austenite alloy material

Abstract

An austenite alloy material having a chemical composition of, in mass%, 0.005-0.050% of C, 0.05-0.50% of Si, 0.05-1.00% of Mn, 0.025% or less of P, 0.0020% or less of S, 33.00-41.00% of Ni, 20.00-30.00% of Cr, 0.20-1.00% of Nb, 0.11-0.30% of N, 0.01-0.10% of Al, 0.0035% or less of B, and 0.010% or less of O, the remaining portion being Fe and impurities, wherein 0.30≤[Cr]ER / [Nb]ER is satisfied.

Description

Austenitic alloy

[0001] This invention relates to austenitic alloy materials.

[0002] In recent years, clean energy from solar power generation has been attracting attention. In particular, because solar power generation does not emit carbon dioxide, its importance in preventing global warming is increasing year by year. Incidentally, when manufacturing solar power generation equipment, polycrystalline silicon is often used as the power generation element. Polycrystalline silicon is manufactured by repeatedly distilling and refining liquid trichlorosilane as a raw material.

[0003] In the reaction tower used to produce polycrystalline silicon, the environment is extremely harsh, with reaction gas pressures exceeding 100 MPa and temperatures exceeding 600°C. Therefore, there is a need for materials with excellent high-temperature strength that can be used in such environments. Patent documents 1 and 2 disclose alloy materials containing Nb.

[0004] Japanese Patent Publication No. 2017-57461 Japanese Patent Publication No. 2024-25945

[0005] To improve high-temperature strength, it is effective to incorporate Nb and precipitate fine nitrides containing Nb (e.g., Z phase). However, welding alloy materials with high Nb content can cause liquefaction cracking in the heat-affected zone. Therefore, there is a need for alloy materials that contain a predetermined amount of Nb while exhibiting excellent resistance to liquefaction cracking. Patent documents 1 and 2 do not address liquefaction cracking in the heat-affected zone.

[0006] The present invention aims to solve the above problems and provide an austenitic alloy material with excellent resistance to liquefaction cracking.

[0007] This invention was made to solve the above problems, and its essence lies in the austenitic alloy material described below.

[0008] (1) An austenitic alloy material having a chemical composition in mass percent of: C: 0.005 to 0.050%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0020% or less, Ni: 33.00 to 41.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.11 to 0.30%, Al: 0.01 to 0.10%, B: 0.0035% or less, O: 0.010% or less, the remainder being Fe and impurities, and satisfying the following formula (i): 0.30 ≤ [Cr] ＥＲ / [Nb] ＥＲ ... (i) However, [Cr] in equation (i) above ＥＲ and [Nb] ＥＲ This refers to the Cr and Nb content (mass %) in the residue obtained by extraction residue analysis.

[0009] (2) An austenitic alloy material having a chemical composition in mass percent of: C: 0.005 to 0.050%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0020% or less, Ni: 33.00 to 41.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.11 to 0.30%, Al: 0.01 to 0.10%, B: 0.0035% or less, O: 0.010% or less, and further containing one or more elements selected from the groups A, B, and C below, with the remainder being Fe and impurities, and satisfying the following formula (i): 0.30 ≤ [Cr] ＥＲ / [Nb] ＥＲ ... (i) However, [Cr] in equation (i) above ＥＲ and [Nb] ＥＲThis refers to the Cr and Nb content (mass%) in the residue obtained by extraction residue analysis. [Group A] One or more selected from the group consisting of Mo: 3.00% or less, W: 3.00% or less, Cu: 1.00% or less, Co: 1.00% or less, V: 0.50% or less, Ti: 0.10% or less, Ta: 0.50% or less, Zr: 0.10% or less, and Hf: 0.10% or less [Group B] One or more selected from the group consisting of Sn: 0.010% or less and Zn: 0.010% or less [Group C] One or more selected from the group consisting of Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.050% or less

[0010] (3) The austenitic alloy material according to (2) above, wherein the chemical composition contains one or more elements selected from group A.

[0011] (4) The austenitic alloy material according to (2) above, wherein the chemical composition contains one or more elements selected from group B.

[0012] (5) The austenitic alloy material according to (2) above, wherein the chemical composition contains one or more elements selected from the C group.

[0013] (6) An austenitic alloy material as described in any of (1) to (5) above, satisfying the following formula (ii): Nb × N ≤ 0.130 ... (ii) where the element symbols in the above formula represent the content (mass %) of each element contained in the alloy material.

[0014] According to the present invention, an austenitic alloy material with excellent resistance to liquefaction cracking can be obtained.

[0015] Figure 1 is a diagram illustrating the evaluation method for liquefaction crack resistance. Figure 2 is a diagram illustrating the observation location for the presence or absence of cracks.

[0016] In order to solve the aforementioned problems, the inventors conducted a detailed investigation into liquefaction cracking resistance and obtained the following findings.

[0017] As mentioned above, to improve high-temperature strength, it is effective to include a large amount of Nb and precipitate fine nitrides containing Nb. In order to precipitate such nitrides during use in a high-temperature environment, it is necessary to include a large amount of Nb and then solidify the Nb by heat treatment. However, Nb does not completely solidify and often remains in the alloy material as Nb carbonitrides even after heat treatment. When such alloy materials are welded, liquefaction cracking occurs. This is thought to be due to the following mechanism. In the description of this invention, carbonitrides include carbides and nitrides.

[0018] When an alloy containing Nb carbonitride is heated by welding, the Nb carbonitride melts in the heat-affected zone of the alloy. Nb then concentrates in the matrix phase surrounding the Nb carbonitride, forming a localized Nb-enriched region. Because Nb significantly lowers the solidus temperature of the matrix phase, the Nb-enriched region melts locally. Subsequently, during the cooling process, tensile stress due to thermal contraction occurs around the Nb-enriched region. As a result, the Nb-enriched region opens up, making it easier to detect as liquefaction cracking in the heat-affected zone even after cooling.

[0019] Therefore, the inventors investigated a method to suppress liquefaction cracking in the heat-affected zone while incorporating Nb into the alloy material. As a result, they found that modifying the Nb carbonitride and increasing the Cr content in the carbonitride is effective. Specifically, they found that liquefaction cracking can be suppressed by controlling the composition of the precipitate obtained by extraction residue analysis so that the ratio of Cr content to Nb content in the precipitate is 0.30 or higher. This is thought to be because Cr does not lower the solidus temperature of the matrix phase as much as Nb, so even if an Nb carbonitride containing a lot of Cr dissolves, local melting around the Nb carbonitride is suppressed compared to when an Nb carbonitride without Cr dissolves.

[0020] In this way, by controlling the chemical composition of the carbonitride, excellent resistance to liquefaction cracking can be obtained.

[0021] This invention is based on the above findings. The requirements of this invention will be described in detail below.

[0022] (A) The reasons for limiting the chemical composition of each element are as follows. In the following explanation, "%" for content refers to "mass%".

[0023] C: 0.005-0.050% Carbon (C) is an element necessary to ensure the high-temperature strength of the alloy. However, C combines with Nb to form Nb carbonitrides, which can cause liquefaction cracking. Furthermore, if C is included in excess, a large amount of carbides are generated during the solidification process, reducing hot workability and degrading manufacturability. Therefore, the C content should be 0.005-0.050%. A C content of 0.010% or more is preferable. A C content of 0.045% or less is preferable, and 0.040% or less is more preferable.

[0024] Si: 0.05-0.50% Si is an element that has a deoxidizing effect. However, if Si is included in excess, the resistance to liquefaction cracking in the heat-affected zone decreases. Therefore, the Si content should be 0.05-0.50%. Preferably, the Si content should be 0.10% or more, and more preferably 0.20% or more. Furthermore, preferably, the Si content should be 0.45% or less, and more preferably 0.40% or less.

[0025] Mn: 0.05-1.00% Mn is an element that has a deoxidizing effect. However, if Mn is included in excess, the stability of the austenite phase decreases and the high-temperature strength decreases. For this reason, the Mn content should be 0.05-1.00%. Preferably, the Mn content should be 0.10% or more, and more preferably 0.20% or more. Furthermore, preferably, the Mn content should be 0.95% or less, and more preferably 0.90% or less.

[0026] P: 0.025% or less. P is an element contained as an impurity. Therefore, the P content should be 0.025% or less. Preferably, the P content should be 0.020% or less, and more preferably 0.015% or less. It is preferable to reduce the P content as much as possible, and it may even be 0%, but an extreme reduction in the P content will lead to an increase in manufacturing costs. Therefore, it is preferable that the P content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.005% or more.

[0027] S: 0.0020% or less. S is an element that improves weldability by increasing penetration during welding. However, if S is present in excess, hot workability decreases and manufacturability deteriorates. Therefore, the S content should be 0.0020% or less. Preferably, the S content should be 0.0015% or less. There is no lower limit to the S content, and the S content may be 0%. On the other hand, if the effect of improving weldability due to S is to be obtained, it is preferable that the S content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0028] Ni: 33.00–41.00% Ni is an important element for stabilizing the austenite phase and maintaining high-temperature strength. However, excessive Ni content leads to a significant increase in manufacturing costs. Therefore, the Ni content is set to 33.00–41.00%. Preferably, the Ni content is 35.00% or more, 35.50% or more, 36.00% or more, or 36.50% or more, or 37.00% or more. Furthermore, it is preferable that the Ni content be 40.00% or less, and more preferably 39.00% or less.

[0029] Cr: 20.00-30.00% Cr forms a dense oxide film at high temperatures, which helps maintain oxidation resistance and / or corrosion resistance at high temperatures. Furthermore, in this invention, Cr is an important element because increasing the Cr content in the carbonitride can improve resistance to liquefaction cracking. However, excessive Cr content reduces the stability of the austenite phase and deteriorates the high-temperature strength. Therefore, the Cr content is set to 20.00-30.00%. Preferably, the Cr content is 22.00% or more, and more preferably 23.00% or more. Also, preferably, the Cr content is 29.00% or less, and more preferably 28.00% or less.

[0030] Nb: 0.20-1.00% Nb is an element that forms nitrides and is effective in improving high-temperature strength. However, excessive Nb content deteriorates resistance to liquefaction cracking. Therefore, the Nb content should be 0.20-1.00%. A Nb content of 0.40% or more is preferable. Furthermore, a Nb content of 0.80% or less is preferable.

[0031] N: 0.11-0.30% N is an effective element for forming nitrides and for improving high-temperature strength by solid dissolving in the austenite phase. However, N combines with Nb to form Nb carbonitrides, which can cause liquefaction cracking. Furthermore, excessive N content reduces hot workability and degrades manufacturability. Therefore, the N content should be 0.11-0.30%. Preferably, the N content is 0.13% or more, and more preferably 0.15% or more. Preferably, the N content is 0.28% or less, and more preferably 0.26% or less.

[0032] Al: 0.01-0.10% Al is an element that has a deoxidizing effect and contributes to improving high-temperature properties by reducing oxide inclusions. However, if Al is included in excess, Al will form Al nitrides, and the high-temperature strength will deteriorate. For this reason, the Al content should be 0.01-0.10%. It is preferable that the Al content be 0.03% or more. It is also preferable that the Al content be 0.08% or less.

[0033] B: 0.0035% or less. B has the effect of increasing high-temperature strength and / or hot workability. However, if B is included in excess, resistance to liquefaction cracking decreases. Therefore, the B content should be 0.0035% or less. Preferably, the B content is 0.0030% or less, and more preferably 0.0025% or less. There is no lower limit to the B content, and the B content may be 0%. On the other hand, if the effect of increasing high-temperature strength and / or hot workability due to B is to be obtained, preferably, the B content is greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0034] O: 0.010% or less. O is contained in the alloy as an impurity. Therefore, the O content is set to 0.010% or less. It is preferably 0.008% or less, and more preferably 0.006% or less. The O content is preferably reduced as much as possible and may be 0%, but an extreme reduction in the O content leads to an increase in manufacturing cost. For this reason, the O content is preferably more than 0%, more preferably 0.001% or more, and even more preferably 0.002% or more.

[0035] In the chemical composition of the alloy material of the present invention, the balance is Fe and impurities. Here, the impurities are components that are mixed in due to raw materials such as ores and scraps and other factors during the industrial production of the alloy material, and are those that are allowed within a range that does not adversely affect the alloy material according to the present invention.

[0036] Nb×N: 0.130 or less. Nb forms fine nitrides containing N together with N and is effective in improving high-temperature strength. However, when the Nb and N contents are excessive, a large amount of Nb carbonitrides are generated during the solidification process, and voids are generated at the interface between the Nb carbonitrides and the austenite phase during hot working, causing fracture and easily leading to a decrease in hot workability. In order to improve hot workability, it is preferable that the left side value of the following formula (ii) is 0.130 or less. Nb×N≦0.130 ··· (ii) However, the element symbols in the above formula represent the content (% by mass) of each element contained in the alloy material.

[0037] The left side value of formula (ii) is preferably 0.120 or less, and more preferably 0.110 or less. The lower limit of the left side value of formula (ii) is not particularly limited. However, if the left side value of formula (ii) is too low, the nitrides containing Nb will decrease and the high-temperature strength will deteriorate. Therefore, the left side value of formula (ii) is preferably more than 0, and more preferably 0.050 or more.

[0038] In the chemical composition of the alloy material of the present invention, in order to improve the high-temperature strength, one or more selected from Mo, W, Cu, Co, V, Ti, Ta, Zr, and Hf may be contained within the following ranges. Note that since these elements are not necessarily essential in the alloy material, the lower limit of the content of these elements is 0%. The reasons for limiting each element will be explained.

[0039] Mo: 3.00% or less. Mo dissolves in the austenite phase and greatly contributes to the improvement of high-temperature strength. Therefore, Mo may be contained as necessary. However, if Mo is contained in excess, the σ phase is generated, and the hot workability and toughness decrease. Therefore, the Mo content is set to 3.00% or less. The Mo content is preferably less than 3.00%, 2.90% or less, 2.80% or less, 2.70% or less, 2.60% or less, or 2.50% or less, and more preferably 2.00% or less. In order to more surely obtain the above effects, the Mo content is preferably more than 0%, more preferably 0.10% or more, and still more preferably 0.50% or more.

[0040] W: 3.00% or less. W dissolves in the austenite phase and greatly contributes to the improvement of high-temperature strength. Therefore, W may be contained as necessary. However, even if W is contained in excess, the effect saturates. Also, since W is an expensive element, containing W in excess causes an increase in cost. Therefore, the W content is set to 3.00% or less. The W content is preferably 2.50% or less, and more preferably 2.00% or less. In order to more surely obtain the above effects, the W content is preferably more than 0%, more preferably 0.01% or more, and still more preferably 0.10% or more.

[0041] Cu: 1.00% or less. Cu is an austenite-forming element and contributes to improved high-temperature strength by enhancing phase stability. For this reason, Cu may be included as needed. However, excessive Cu content leads to a decrease in hot workability. Therefore, the Cu content should be 1.00% or less. Preferably, the Cu content should be 0.80% or less, and more preferably 0.60% or less. If the above effects are to be obtained more reliably, it is preferable that the Cu content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.05% or more.

[0042] Co: 1.00% or less. Co is an austenite-forming element that enhances phase stability and contributes to improved high-temperature strength. For this reason, Co may be included as needed. However, since Co is an extremely expensive element, excessive Co content will lead to a significant increase in costs. Therefore, the Co content should be 1.00% or less. Preferably, the Co content should be 0.80% or less, and more preferably 0.60% or less. If the above effects are to be obtained more reliably, it is preferable that the Co content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.05% or more.

[0043] V: 0.50% or less. V has the effect of forming fine nitrides and improving high-temperature strength. For this reason, V may be included as needed. However, if V is included in excess, a large amount of carbonitride containing V will be generated during the solidification process, reducing hot ductility and leading to deterioration of manufacturability. Therefore, the V content should be 0.50% or less. Preferably, the V content should be 0.45% or less, and more preferably 0.40% or less. If the above effect is to be obtained more reliably, it is preferable that the V content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.05% or more.

[0044] Ti: 0.10% or less. Ti precipitates within the grains as fine carbonitrides, contributing to improved high-temperature strength. For this reason, Ti may be included as needed. However, excessive Ti content leads to the precipitation of large amounts of coarse Ti nitrides, resulting in a decrease in toughness. Therefore, the Ti content should be 0.10% or less. Preferably, the Ti content is 0.08% or less, and more preferably 0.06% or less. If the above effects are to be obtained more reliably, it is preferable that the Ti content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0045] Ta: 0.50% or less. Ta forms fine nitrides and acts as a solid solution strengthening element, improving high-temperature strength. For this reason, Ta may be included as needed. However, if Ta is included in excess, a large amount of carbonitride containing Ta will be generated during the solidification process, reducing hot ductility and leading to a deterioration in manufacturability. Also, since Ta is an expensive element, including too much Ta will increase costs. Therefore, the Ta content should be 0.50% or less. Preferably, the Ta content should be 0.45% or less, and more preferably 0.40% or less. If the above effects are to be obtained more reliably, it is preferable that the Ta content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0046] Zr: 0.10% or less. Zr has the effect of improving high-temperature strength as a grain boundary strengthening element. For this reason, Zr may be included as needed. However, if Zr is included in excess, a large amount of coarse Zr nitride will precipitate, leading to a decrease in toughness. Therefore, the Zr content should be 0.10% or less. Preferably, the Zr content should be 0.08% or less, and more preferably 0.06% or less. If the above effect is to be obtained more reliably, it is preferable that the Zr content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0047] Hf: 0.10% or less. Hf contributes to precipitation strengthening as a carbonitride and improves high-temperature strength. For this reason, Hf may be included as needed. However, excessive Hf content will impair workability and weld crack resistance. Therefore, the Hf content should be 0.10% or less. Preferably, the Hf content should be 0.08% or less, and more preferably 0.06% or less. If the above effects are to be obtained more reliably, it is preferable that the Hf content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0048] In the chemical composition of the alloy material of the present invention, in order to improve weldability, one or more elements selected from Sn and Zn may be further included within the range shown below. Since these elements are not necessarily essential in the alloy material, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0049] Sn: 0.010% or less. Sn has the effect of improving weldability by increasing penetration during welding. For this reason, Sn may be included as needed. However, if Sn is included in excess, the hot workability will decrease. Therefore, the Sn content should be 0.010% or less. Preferably, the Sn content should be 0.008% or less, and more preferably 0.006% or less. If the above effects are to be obtained more reliably, it is preferable that the Sn content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.003% or more.

[0050] Zn: 0.010% or less. Zn has the effect of improving weldability by increasing penetration during welding. For this reason, Zn may be included as needed. However, if Zn is included in excess, the hot workability will decrease. Therefore, the Zn content should be 0.010% or less. Preferably, the Zn content should be 0.008% or less, and more preferably 0.006% or less. If the above effects are to be obtained more reliably, it is preferable that the Zn content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.003% or more.

[0051] In the chemical composition of the alloy material of the present invention, in order to improve hot workability, one or more elements selected from Ca, Mg, and REM may be further included within the ranges shown below. Since these elements are not necessarily essential in the alloy material, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0052] Ca: 0.0050% or less. Ca forms compounds with S, reducing the amount of S in the austenite phase and improving hot workability. For this reason, Ca may be included as needed. However, excessive Ca content will actually degrade hot workability. Therefore, the Ca content should be 0.0050% or less. Preferably, the Ca content is 0.0045% or less, and more preferably 0.0040% or less. If the above effect is to be obtained more reliably, it is preferable that the Ca content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0053] Mg: 0.0050% or less. Like Ca, Mg forms compounds with S, reducing the amount of S in the austenite phase and improving hot workability. For this reason, Mg may be included as needed. However, excessive Mg content will actually degrade hot workability. Therefore, the Mg content should be 0.0050% or less. Preferably, the Mg content should be 0.0045% or less, and more preferably 0.0040% or less. If the above effect is to be obtained more reliably, it is preferable that the Mg content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0054] REM: 0.050% or less. REM forms a compound with S, similar to Ca, reducing the amount of S in the austenite phase and having the effect of improving hot workability. Therefore, REM may be contained as necessary. However, if REM is contained in excess, the productivity will deteriorate significantly. Thus, the REM content is set to 0.050% or less. It is preferably 0.045% or less, and more preferably 0.040% or less. In addition, when it is desired to more surely obtain the above effects, the REM content is preferably more than 0%, more preferably 0.001% or more, and still more preferably 0.005% or more.

[0055] Here, REM is a general term for a total of 17 elements including Sc, Y, and lanthanoids, and the REM content means the total amount of these elements. Incidentally, lanthanoids are industrially added in the form of mischmetal.

[0056] (B) Electrolytic extraction residue As described above, liquefaction cracking can be suppressed by precipitating Nb carbonitride rich in Cr that satisfies the following formula (i). 0.30 ≤ [Cr] ＥＲ / [Nb] ＥＲ ... (i) However, [Cr] in the above formula (i) ＥＲ and [Nb] ＥＲ mean the contents (mass%) of Cr and Nb in the residue obtained by extraction residue analysis.

[0057] When the right-hand side value of the above formula (i) is less than 0.30, since the Cr content in the precipitate is low, local melting accompanying the concentration of Nb cannot be suppressed, and good liquefaction cracking resistance cannot be obtained. Therefore, the right-hand side value of the above formula (i) is 0.30 or more. The right-hand side value of the above formula (i) is preferably 0.40 or more, and more preferably 0.50 or more.

[0058] The upper limit of the right-hand side value of the above formula (i) is not particularly limited. Under the chemical composition defined in the present application and the manufacturing conditions described later, the upper limit of the right-hand side value of the above formula (i) is 0.90 or less, or 0.85 or less.

[0059] The content (mass %) of each element in the residue analyzed as electrolytic extraction residue in the above formula can be measured by the following procedure. Specifically, first, a test piece of a predetermined size is taken from the alloy material, excluding the welded area and the heat-affected zone. Then, using an electrolyte of 10 vol% acetylacetone - 1 mass% tetramethylammonium chloride - methanol, an aqueous solution of 20 mA / cm² is used. ２ The test specimen is electrolyzed at the specified current density. After electrolysis, the solution is filtered through a 0.2 μm filter, and the residue is acid-decomposed. The content (mass%) of Cr and Nb is then measured using an ICP (inductively coupled plasma) emission spectrometer, and their ratio is calculated.

[0060] (D) Dimensions of the alloy material The alloy material according to the present invention includes alloy tubes, alloy plates, etc. The dimensions of the alloy material according to the present invention are not particularly limited. For example, in the case of an alloy tube, the outer diameter of the alloy tube is preferably 12 to 600 mm and the wall thickness is preferably 1.5 to 50 mm. In the case of an alloy plate, the plate thickness is preferably 5 to 100 mm.

[0061] (E) Manufacturing Method A preferred manufacturing method for the alloy material according to the present invention will be described. The alloy material according to the present invention can obtain the effects described above regardless of the manufacturing method, as long as it has the above-described structure, but it can be manufactured stably by, for example, the following manufacturing method. The preparation step, the first heat treatment step, the hot working step, and the second heat treatment step will be described in detail.

[0062] <Preparation Process> First, a material having the above-mentioned chemical composition is prepared. The material may be an ingot, slab, bloom, or billet. When manufacturing the material, for example, it may be manufactured by the following method: For example, molten steel having the above-mentioned chemical composition is manufactured by a well-known method using an electric furnace, an AOD (Argon Oxygen Decarburization) furnace, a VOD (Vacuum Oxygen Decarburization) furnace, etc. An ingot is manufactured using the manufactured molten steel by the ingot-making method. Alternatively, slabs, blooms, or billets may be manufactured using the manufactured molten steel by the continuous casting method. Billets may be manufactured by hot working the manufactured ingots, slabs, or blooms.

[0063] <First Heat Treatment Step> In the first heat treatment step, the material prepared in the preparation step is held for 4 hours or more at a first heat treatment temperature T1 that satisfies the following equation (I). By setting the first heat treatment temperature T1 to be equal to or greater than the left-hand side value of the following equation (I), the ingot can be homogenized while dissolving precipitates such as coarse Nb carbonitrides. Therefore, the first heat treatment temperature T1 must satisfy the following equation (I). There is no particular upper limit to the first heat treatment temperature T1. However, if the first heat treatment is performed at an excessively high temperature, regions with high concentrations of various elements will melt locally due to solidification segregation. Therefore, it is preferable that the first heat treatment temperature T1 be 1300°C or less. 450 × Nb × N + 1175 ≤ T1 ... (I) However, the element symbols in the above equation represent the content (mass %) of each element contained in the alloy material.

[0064] By holding the ingot at the first heat treatment temperature T1 for 4 hours or more, the solidification segregation inside the ingot is homogenized, allowing for control of the precipitate composition in subsequent processes. Therefore, the holding time at the first heat treatment temperature T1 should be 4 hours or more. There is no particular upper limit to the holding time at the first heat treatment temperature T1. However, if the holding time at the first heat treatment temperature T1 is extended, the above effect will saturate, and it will actually lead to a decrease in productivity. Therefore, it is preferable to hold the ingot at the first heat treatment temperature T1 for 24 hours or less.

[0065] <Hot Working Process> In the hot working process, after heating the material following the first heat treatment process, the material is subjected to hot working such as hot forging, hot rolling, hot extrusion, hot punching, and perforation rolling. The heating temperature before hot working is not particularly limited, but it should be between 1150 and 1250°C. Furthermore, in order to suppress the decrease in hot ductility and the occurrence of defects during hot working, it is preferable to carry out the hot working in a temperature range of 900°C or higher.

[0066] When manufacturing alloy sheets, it is preferable to hot forge or hot roll the material (ingot, slab, bloom) after the first heat treatment process to produce alloy sheets of the above dimensions. When manufacturing alloy tubes, it is preferable to machine a through hole along the central axis of the billet in the material (billet) after the first heat treatment process. Hot extrusion, such as the Eugène Séjournay method, is performed on the billet with the through hole to produce alloy tubes of the above dimensions. Hot punching may be used instead of hot extrusion. Alternatively, drilling and rolling may be performed using the Mannesmann method. When drilling and rolling is performed, the heated billet can be drilled and rolled using a drilling machine in a well-known manner.

[0067] <Second Heat Treatment Step> In the second heat treatment step, the alloy material after the hot working step is held for 30 min or more at a second heat treatment temperature T2 that satisfies the following equation (II). When the second heat treatment temperature T2 is less than or equal to the right-hand side value of the following equation (II), Nb carbonitrides containing more Cr are more stable than Nb carbonitrides, and therefore Nb carbonitrides containing more Cr can be precipitated. For this reason, the second heat treatment temperature T2 must satisfy the following equation (II). The lower limit of the second heat treatment temperature T2 is not particularly limited. However, if the second heat treatment temperature T2 is low, a significant mixed grain structure may be formed, which may lead to a decrease in high-temperature strength. For this reason, it is preferable that the second heat treatment temperature T2 be 1180°C or higher. T2 ≤ 350 × Nb × N + 1200 ... (II) However, the element symbols in the above equation represent the content (mass %) of each element contained in the alloy material.

[0068] By holding the material at the second heat treatment temperature T2 for more than 30 minutes, sufficient Cr-rich Nb carbonitride can be precipitated. Therefore, the holding time at the second heat treatment temperature T2 should be more than 30 minutes. There is no particular upper limit to the holding time at the second heat treatment temperature T2. However, if the holding time at the second heat treatment temperature T2 is extended, the above effect will saturate, and it will actually lead to a decrease in productivity. Therefore, it is preferable to keep the holding time at the second heat treatment temperature T2 to 150 minutes or less.

[0069] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0070] A 50 kg ingot having the chemical composition shown in Table 1 was melted in the laboratory. After a first heat treatment at the first heat treatment temperature T1 and holding time shown in Table 2, the ingot was hot-rolled to produce an alloy sheet with a thickness of 18 mm. Hot rolling was performed at a temperature of 1000°C or higher on an ingot heated to 1250°C. Then, a second heat treatment was performed at the second heat treatment temperature T2 and holding time shown in Table 2.

[0071]

[0072]

[0073] <Electrolytic Extraction Residue> The content (mass%) of each element in the residue analyzed as electrolytic extraction residue was measured using the following procedure. Specifically, first, a test piece measuring 20 mm in width, 15 mm in length, and 5 mm in thickness was machined from the center of the width and thickness of the alloy plate. Then, 10 vol% acetylacetone - 1 mass% tetramethylammonium chloride - methanol was used to analyze it at 20 mA / cm². ２ The test specimens were electrolyzed at the specified current density. The solution of the electrolyzed sample was then filtered through a 0.2 μm filter, and the residue was acid-decomposed. The content (mass%) of Cr and Nb was then measured using an ICP emission spectrometer, and their ratios were calculated.

[0074] <Liquefaction Cracking Resistance> The liquefaction cracking resistance was evaluated using the following procedure. Figure 1 is a diagram illustrating the evaluation method for liquefaction cracking resistance. Figure 1(a) shows the shape of the test piece 1, (b) is an enlarged view of the V-groove, and (c) is a diagram illustrating the welding area. First, from each of the alloy plates mentioned above, a test piece 1 with a width of 50 mm, a length of 100 mm, and a thickness of 12 mm was machined as shown in Figure 1(a). Then, as shown in Figures 1(a) and (b), a V-groove was made on one side of the long edge of the test piece 1 so that the root surface 2 was 1 mm and the bevel angle was 30°. Two test pieces 1 of the same material were prepared and placed on an SS400 steel plate 3 with a width of 150 mm, a length of 150 mm, and a thickness of 30 mm so that the root surfaces 2a and 2b of test pieces 1a and 1b were in contact (see Figure 1(c)).

[0075] Using shielded metal arc welding, the area 4 shown by the dashed line in Figure 1(c) was welded in a constrained position. Then, the V-groove 5 was melt-run welded using TIG welding at a current of 150A, a voltage of 13V, and a welding speed of 10cm / min. After that, three passes of welding were performed using a commercially available Alloy 625 shielded metal arc welding rod (rod diameter: 4mm) at a current of 160A and a voltage of 25V.

[0076] Figure 2 is a diagram illustrating the observation locations for checking for cracks. As shown by the dashed lines in Figure 2, the cross-sections of the specimen 1 were to be observed at the center line A in the longitudinal direction, and at a total of five locations 20 mm apart from the center line A. At each cross-section, the presence or absence of cracks in the heat-affected zone of the V-groove 5 was checked.

[0077] Furthermore, even if melting marks were observed at the grain boundaries in the heat-affected zone, if there was no opening, it was judged as "no cracks." If a crack occurred in even one cross-section, it was judged as "bad," and if no cracks were observed at all, it was judged as "excellent."

[0078] <Hot Workability> The hot workability was evaluated using the following procedure. Blocks were taken from the surface of each ingot as described above and subjected to heat treatment at 1220°C for 1 hour. Subsequently, a 10 mm diameter round bar test specimen was machined from near the surface of the ingot and a high-temperature tensile test was performed. Specifically, it was heated from room temperature to 1220°C in 60 seconds, held at 1220°C for 60 seconds, then cooled to 900°C at 20°C / s and held at 900°C for 60 seconds. After that, it was subjected to tensile fracture at a tensile speed of 20 mm / s. The diameter of the fracture surface of the test specimen after the test was measured with a digital caliper and the reduction in cross-sectional area was calculated. A reduction in cross-sectional area of ​​60% or more was considered excellent, and a reduction of less than 60% was considered bad.

[0079] Table 2 shows [Cr] ＥＲ / [Nb] ＥＲ The values, as well as the evaluation results for liquefaction cracking resistance and hot workability, are summarized below.

[0080] As shown in Table 2, tests No. 1 to 15, which fully satisfied the provisions of the present invention, showed excellent resistance to liquefaction cracking. In contrast, comparative examples No. 16 to 19 showed deteriorated resistance to liquefaction cracking.

[0081] According to the present invention, an austenitic alloy material with excellent resistance to liquefaction cracking can be obtained.

[0082] 1. Test specimen 2. Root surface 3. Steel plate 4. Region 5. V-groove

Claims

1. An austenitic alloy material having a chemical composition in mass percent of: C: 0.005–0.050%, Si: 0.05–0.50%, Mn: 0.05–1.00%, P: 0.025% or less, S: 0.0020% or less, Ni: 33.00–41.00%, Cr: 20.00–30.00%, Nb: 0.20–1.00%, N: 0.11–0.30%, Al: 0.01–0.10%, B: 0.0035% or less, O: 0.010% or less, the remainder being Fe and impurities, and satisfying the following formula (i): 0.30 ≤ [Cr] ＥＲ / [Nb] ＥＲ ... (i) However, [Cr] in equation (i) above ＥＲ and [Nb] ＥＲ This refers to the Cr and Nb content (mass %) in the residue obtained by extraction residue analysis.

2. An austenitic alloy material having a chemical composition in mass percent of: C: 0.005 to 0.050%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0020% or less, Ni: 33.00 to 41.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.11 to 0.30%, Al: 0.01 to 0.10%, B: 0.0035% or less, O: 0.010% or less, and further containing one or more elements selected from the groups A, B, and C below, with the remainder being Fe and impurities, and satisfying the following formula (i): 0.30 ≤ [Cr] ＥＲ / [Nb] ＥＲ ... (i) However, [Cr] in equation (i) above ＥＲ and [Nb] ＥＲ This refers to the Cr and Nb content (mass%) in the residue obtained by extraction residue analysis. [Group A] One or more selected from the group consisting of Mo: 3.00% or less, W: 3.00% or less, Cu: 1.00% or less, Co: 1.00% or less, V: 0.50% or less, Ti: 0.10% or less, Ta: 0.50% or less, Zr: 0.10% or less, and Hf: 0.10% or less [Group B] One or more selected from the group consisting of Sn: 0.010% or less and Zn: 0.010% or less [Group C] One or more selected from the group consisting of Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.050% or less 3. The austenitic alloy material according to claim 2, wherein the chemical composition contains one or more elements selected from group A.

4. The austenitic alloy material according to claim 2, wherein the chemical composition contains one or more elements selected from group B.

5. The austenitic alloy material according to claim 2, wherein the chemical composition contains one or more elements selected from the C group.

6. An austenitic alloy material according to any one of claims 1 to 5, satisfying the following formula (ii): Nb × N ≤ 0.130 ... (ii) where the element symbols in the above formula represent the content (mass %) of each element contained in the alloy material.

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