Technical field
[0001]The present invention is an austenitic alloy tube and a method for producing the same.
BACKGROUND
[0002](Herein referred to collectively oil and gas wells is referred to as "oil wells") oil wells and gas wells in oil well pipe is used. The types of oil well pipe, there is a casing or tubing and the like. Casing is inserted into the oil well. Between the casing and Anakabe cement is filled, the casing is fixed to the mine. Tubing is inserted into the casing, through the production fluid such as oil and gas inside.
[0003]
　Production fluids, hydrogen sulfide (H 2 which may contain S) gas. Therefore, many oil wells, a sour environment containing hydrogen sulfide with corrosive. In the present specification, the sour environment, means acidified environment containing hydrogen sulfide. Sour environments may not only hydrogen sulfide, carbon dioxide also contains. The oil well pipe used in such sour environment, excellent stress corrosion cracking resistance (Stress Corrosion Cracking Resistance: hereinafter, referred to as SSC resistance) is obtained.
[0004]
　Represented by austenitic stainless steel, austenitic alloy tube has excellent SCC resistance. Therefore, the austenitic alloy pipe is used as oil well pipes. Recently, however, the SCC resistance is demanded that more excellent.
[0005]
　Alloy tube for the purpose of improving SCC resistance, JP 58-6928 (Patent Document 1) and it has been proposed in JP 63-203722 (Patent Document 2).
[0006]
　OCTG disclosed in Patent Document 1 is manufactured in the following manner. In weight%, C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or or less, P: 0.030% or less, S: 0.005% or less, sol. Al: 0.5% or less, Ni: 25 ~ 60%, Cr: contain 22.5 ~ 30%, Mo: less than 8% and W: contain one or two of lower than 16%, It has the balance consisting of Fe and unavoidable impurities, and, Cr (%) + 10Mo (%) + 5W (%) ≧ 70%, 4% ≦ Mo (%) + W (%) / 2 <8%, the conditions of to prepare the alloy to meet the. The prepared alloy, the thickness reduction rate at below recrystallization temperature to hot working under conditions of 10% or more. The alloy after hot working, and 260logC (%) + 1300 with the calculated lower limit temperature (℃), 16Mo (%) + 10W (%) + 10Cr (%) in the range between the calculated upper limit temperature (℃) at + 777 a heat treatment under conditions of holding 2 hours or less at the temperature. The alloy after the heat treatment, cold working at 10-60% of the wall thickness reduction rate. With the above-described manufacturing process, an oil well pipe according to Patent Document 1 is manufactured.
[0007]
　Tubular member disclosed in Patent Document 2 is manufactured in the following manner. In weight%, C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or less, Ni: 30 ~ 60%, Cr: 15 ~ 30%, Mo: 1.5 ~ 12% , Cu: contains 0.01 to 3.0% to prepare alloy base tube the balance being Fe and impurities. Respect prepared alloy raw tube, 200 ° C. in a temperature range of-ambient temperature, added to plastic working at least 35% reduction of area. Against plastic working is applied alloy base pipe, following heating - cooling - implementing the cold working process at least once. Heating - cooling - the cold working process, it is heated and held at the recrystallization temperature just above the alloy base pipe. Thereafter, cooling the alloy mother pipe in air or cooling rate. Against the cooled alloy raw tube, out the cold working.
CITATION
Patent Document
[0008]
Patent Document 1: JP 58-6928 JP
Patent Document 2: JP 63-203722 JP
Summary of the Invention
Problems that the Invention is to Solve
[0009]
　Among the oil well pipe, the oil well pipe is not less than 170mm in diameter, often 110ksi grade (yield strength obtained in the tensile test 758 ~ 861MPa) or more high strength is required. Here, in the present specification, the diameter refers more OCTG 170mm to as a "large-diameter oil well pipe". In large-diameter oil well pipe, together with the superior SCC resistance, high yield strength of more than 758MPa is required.
[0010]
　Furthermore, recent oil well, such as conventional, well vertical well dug straight vertically downward, inclined wells has increased. Inclined wellbore is formed by drilling bent horizontally extending direction of the wellbore from the vertically downward. Inclined wellbore, by including a portion (horizontal well) which extends horizontally, it is possible to extensively cover the stratum production fluid such as oil and gas are buried, increase the production efficiency of the production fluid be able to.
[0011]
　When a large-diameter oil well pipes used in such an inclined wellbore, unlike when used in a vertical wellbore, it may stress loaded from a direction other than the tube axis direction becomes large. For example, the inclined wellbore, large diameter oil Ikan used in a portion curving from the vertical direction to the horizontal direction are subjected to stress from a different direction from the large-diameter oil well pipes used in the vertical portion. Thus, the large-diameter oil Ikan utilized in inclined wells, even when loaded stress from the direction other than the vertical direction, it it is preferably possible service. If suppression strength anisotropy of the large-diameter oil well pipe, since the curved portion of the inclined wellbore can also be useful, more accessible to the inclined wells.
[0012]
　Further, in a large-diameter oil well pipes, and external defects typified by surface flaws, it is preferable that the internal defects typified by porosity, etc. can be detected prior to use. Therefore, the ability to detect the ultrasonic flaw detection in a large-diameter oil well pipe is preferably higher.
[0013]
　Furthermore, the austenitic alloy tube, containing a large amount of alloy elements typified by Ni and Cr. Therefore, seizure, etc. are likely to occur during the manufacturing process. If seizing occurs, flaws remain on the surface of the austenitic alloy tube. The occurrence of such defects is preferably who can suppress.
[0014]
　The purpose of the present disclosure has a high yield strength, excellent in SCC resistance, strength anisotropy is suppressed, detectability of the ultrasonic flaw detection is high, to provide a austenitic alloy tube and a manufacturing method thereof is there.
Means for Solving the Problems
[0015]
　Austenitic alloy tube according to the present disclosure,
　the chemical composition,
　in
　mass%, C: 0.004
　~ 0.030%, Si: 1.00% or
　less, Mn: 0.30 ~
　2.00%, P: 0 .030% or
　less, S: 0.0020% or
　less,
　Al: 0.001 ~ 0.100%,
　Cu: 0.50 ~ 1.50%, Ni: 25.00 ~
　55.00%, Cr: 20.
　～
　30.00 Pasento 00, Mo: 2.00
　～ 10.00 Pasento, N: 0.005 ～ 0.100 Pasento,
　Ti: 0 ～ 0.800 Pasento, W: 0 ～ 0.30
　Pasento, Nb: 0
　0.050%

　Mg:~, 0 ~ 0.0100%, Nd: 0 ~ 0.050%, and,
　the balance: Fe and impurities, consists,
　austenite crystal grains of grain size number is 2.0 to 7.0 and not more than mixed grain ratio is 5%,
　The yield strength obtained by the compression test is defined as the compression YS (MPa), when defined as a tensile yield strength obtained by a tensile test YS (MPa), tensile YS is not less than 758 MPa, the compression YS / tensile YS is 0.85 to 1.10,
　is an outer diameter of 170mm or more.
[0016]
　Method of manufacturing an austenitic alloy tube according to the present disclosure includes a material production step, the raw tube manufacturing process, and between the intermediate cold working step, the grain refining step and a final cold working step.
　In material production process, produced by continuous casting, after heating the slab having the chemical composition described above in 1100 ~ 1350 ° C., in a range of 50.0 to 90.0%, and the formula (1 ) to produce the material by hot working at a reduction of area of Rd0 satisfying.
　The blank tube manufacturing process, after heating the material at 1100 ~ 1300 ° C., in a range of 80.0 to 95.0%, and then hot worked at reduction rate Rd1 satisfying the equation (1) producing a blank tube.
　In the intermediate cold working step, in a range of 10.0 to 30.0%, and to cold drawing the blank tube in reduction of area Rd2 satisfying the equation (1).
　The grain refining step, after holding for 1 to 30 minutes in the blank tube after between the intermediate cold working step 1000 ~ 1250 ° C., rapidly cooled.
　In the final cold working step, the outside diameter to produce a more austenitic alloy tube 170mm by cold drawing in the grain refining step reduction ratio mother tube of 20.0 to 35.0% after Rd3.
　5 × Rd0 + 10 × Rd1 + 20 × Rd2 ≧ 1300 (1)
The invention's effect
[0017]
　Austenitic alloy tube according to the present disclosure has a high yield strength, excellent in SCC resistance, it is suppressed strength anisotropy, a high detectability of the ultrasonic flaw detection. A method of manufacturing an austenitic alloy tube according to the present disclosure has a high yield strength, excellent in SCC resistance, strength anisotropy is suppressed, high detectability of the ultrasonic flaw detection, generation of surface flaws It can produce inhibition austenitic alloy tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
[1] Figure 1 is a diagram showing the grain size number of austenite crystal grains of austenitic alloy tube, the relationship between the detectability of the ultrasonic flaw detection.
FIG. 2 is a perspective view of the austenitic alloy tube.
FIG. 3 is a cross-sectional view of a sample of ultrasonic testing.
[4] FIG. 4 is a graph showing the grain size number of austenite crystal grains of austenitic alloy tube, and yield strength, the relationship between the strength anisotropy.
DESCRIPTION OF THE INVENTION
[0019]
　The present inventors have found that the strength of the outer diameter of 170mm or more austenitic alloy tube, SCC resistance, strength anisotropy, and, were investigated and examined detectability of ultrasonic flaw detection. As a result, we obtained the following findings. Hereinafter, in this specification, the outer diameter of the above austenitic alloy tube 170 mm, also referred to as "large diameter austenitic alloy tube".
[0020]
　(1) the chemical composition of the large diameter austenitic alloy tube, in mass%, C: 0.004 ~ 0.030%, Si: 1.00% or less, Mn: 0.30 ~ 2.00%, P: 0.030% or less, S: 0.0020% or less, Al: 0.001 ~ 0.100%, Cu: 0.50 ~ 1.50%, Ni: 25.00 ~ 55.00%, Cr: 20 .00 ~ 30.00%, Mo: 2.00 ~ 10.00%, N: 0.005 ~ 0.100%, Ti: 0 ~ 0.800%, W: 0 ~ 0.30%, Nb: 0 ~ 0.050%, Ca: 0 ~ 0.0100%, Mg: 0 ~ 0.0100%, Nd: 0 ~ 0.050%, and the balance: Fe and impurities, and chemical composition consisting of. In this case, assuming that it meets the other conditions described later (the following items (2) to (4)), a tensile test piece prescribed in ASTM E8M-16a (the parallel portion diameter 6 mm, parallel part length 30 mm) using a room temperature (25 ° C.), a tensile test by the obtained yield strength in the air (hereinafter, referred to as a tensile YS. units MPa) can be a 110ksi grade (tensile YS is 758 ~ 861MPa) and higher, and , it is possible to obtain an excellent SCC resistance.
[0021]
　(2) In the large-diameter austenitic alloy pipe having the chemical composition of the above (1), if the grain size number of austenite crystal grains conforming to ASTM E112 2.0 above, increases the detectability of the ultrasonic flaw detection . Hereinafter, in this specification, the grain size number of austenite crystal grains means the crystal grain size number conforming to ASTM E112.
[0022]
　Figure 1 is a diagram showing the grain size number austenite grains of large diameter austenitic alloy tube, the relationship between the detectability of ultrasonic testing (signal intensity ratio). Figure 1 was obtained by the following method.
[0023]
　Outer diameter is at 170mm or more, has a chemical composition of the above (1), and were prepared a plurality of large diameter austenitic alloy tube having various grain size number. Figure 2 shows a perspective view of a large diameter austenitic alloy tube. As shown in FIG. 2, the austenitic alloy tube comprises a first tube end region 110, a second tube end region 120, a body region 100. The first tube end region 110 is in the range of 500mm toward the center from the first tube end 11 in the axial direction of the austenitic alloy tube. That is, the axial length of the first tube end region 110 is 500 mm. The second tube end region 120, the first tube end 11 in the range of 500mm toward the center in the axial direction of the austenitic alloy tube from the second tube end 12 located on the opposite side. That is, the axial length of the second tube end region 120 is 500 mm. Body region 100 is a portion excluding the first tube end region 110 and the second tube end region 120 from the large-diameter austenitic alloy tube.
[0024]
　The body region 100 of each large-diameter austenitic alloy tube axial direction (longitudinal direction: Longitudinal Direction) in 5 equally divided. From each section, the axial length of the large diameter austenitic alloy tube samples were taken annular becomes 100 mm. As shown in FIG. 3, the axially central portion of the inner peripheral surface of each sample were prepared artificial flaw 200 is a cylindrical bore extending radially (direction of thickness). The diameter of the artificial flaw 200 was 3 mm.
[0025]
　Using an ultrasonic flaw detector, the outer surface of the sample toward the artificial flaw 200 outputs (incident) ultrasound, receives the ultrasound reflected by the artificial flaw 200, was observed as an echo. Ultrasonic intensity incident was either identical. Obtained a sample of each segment, the average of the echo of the signal strength of the artificial flaw 200 (total of five) was defined as the signal strength at the large diameter austenitic alloy tube.
[0026]
　Test No. 1 in Table 1 below (grain size number is 5.7) defines the signal strength at the large diameter austenitic alloy tube with 100. That has the chemical composition described above, the crystal grain size number is relative to the signal intensity of the echo reflected by the artificial flaws formed on the inner surface of the large diameter austenitic alloy pipe of the present embodiment as a 5.7. Then, the signal intensity obtained by the large diameter austenitic alloy tube of various grain size number defined a ratio of signal intensities obtained in large austenitic alloy tube of test No. 1 the signal intensity ratio (%) . If the signal intensity ratio exceeds 50.0% was judged to be excellent in the detectability of the ultrasonic flaw detection. The resulting signal intensity ratio (%) and based on the grain size number was created to FIG.
[0027]
　Referring to FIG. 1, it is less than the grain size number is 2.0, the signal intensity ratio becomes less than 50.0%, the signal intensity ratio is greatly reduced with decreasing grain size number. However, the grain size number is at least 2.0, with an increase of grain size number, the signal strength ratio is significantly increased. The grain size number is at 7.0 or higher, the signal intensity ratio becomes 100% saturated. That is, the relationship between the detectability of grain size number and the ultrasonic flaw detection had an inflection point in the grain size number = 2.0 vicinity.
[0028]
　Based on the above findings, there is an outer diameter of 170mm or more, in large austenitic alloy pipe having the chemical composition of the above (1), the austenite grains in the 2.0 to 7.0 in grain size number if, on the condition that satisfies the other conditions (the above-mentioned items (1) and the following item (4)), the detection capability of the ultrasonic flaw detection increases remarkably.
[0029]
　Note that in the large diameter austenitic alloy tube, the grain size number is greater than 7.0, in the manufacturing process, surface defects are likely to occur in large diameter austenitic alloy tube. Therefore, the 7.0 the upper limit of grain size number.
[0030]
　(3) If the grain size number of austenite crystal grains of large diameter austenitic alloy pipe having the chemical composition of the above (1) 2.0 to 7.0, not only the ability to detect ultrasonic flaw detection is enhanced , it is possible to suppress the strength anisotropy.
[0031]
　Figure 4 is a grain size number austenite grains of large diameter austenitic alloy pipe having the chemical composition of the above (1), and the yield strength (tensile YS), and strength anisotropy (compression YS / tensile YS) is a diagram showing the relationship. Mark (□) figures vicinity in FIG. 4 shows the grain size number at that mark. Figure 4 is determined by the following method.
[0032]
　A yield strength obtained by a tensile test Tensile YS (MPa) was determined by the following method. An outer diameter of 170 ~ 296 mm, having a chemical composition of the above (1), and were prepared a plurality of large diameter austenitic alloy tube having various grain size number. The body region 100 shown in FIG. 2, was divided into five equal parts in the axial direction of the alloy tube. Then, the thick central portion of each segment, tensile test piece prescribed in ASTM E8M-16a (the parallel portion diameter 6 mm, parallel part length 30 mm) was collected. Parallel portion of the tensile test specimen was parallel to the axial direction of the large diameter austenitic alloy tube. Using the collected tensile specimens, and a tensile test at room temperature (25 ° C.) in air, it was determined yield strength. Yield strength was 0.2% proof stress. The average yield strength obtained in each segment, the yield strength obtained by the tensile test (tensile YS, units MPa) was.
[0033]
　A yield strength obtained by the compression test compression YS (MPa) was determined by the following method. From the thickness center of each segment is divided into five equal parts in the axial direction of the body region 100 of the large diameter austenitic alloy tube described above, it was taken cylindrical compression test piece. The diameter of the compression test piece is 6.35 mm, was 12.7mm long. The length direction of the compression test piece was parallel to the axial direction of the austenitic alloy tube. Using the collected compression test pieces, in the air, at room temperature (25 ° C.), to implement the compression test according to ASTM E9-09, to obtain a yield strength. The average yield strength obtained in each segment, obtained yield strength by compression test (compression YS, the unit is MPa) was defined. Yield strength was 0.2% proof stress.
[0034]
　Using the obtained tensile YS and compression YS, based on the following equation to determine the anisotropy index AN.
　Anisotropy index AN = compression YS / tensile YS
[0035]
　And the obtained anisotropic index AN (= compression YS / tensile YS), based on the grain size number, and tensile YS, created the FIG. The vertical axis of FIG. 4 is anisotropic index AN (= compression YS / tensile YS), the horizontal axis represents the tensile YS (MPa). More compression YS / tensile YS is close to 1.00, which means that the strength anisotropy is suppressed. Incidentally, the grain size number of the large-diameter austenitic alloys of the marks was determined according to the method described in Examples set forth below.
[0036]
　Referring to FIG. 4, the tensile YS cases not less than 758 MPa, if the grain size number of 2.0 or more, anisotropy indices AN (= compression YS / tensile YS) of 0.85 to 1.10 falls within the range, the strength anisotropy is suppressed.
[0037]
　Based on the above findings, there is an outer diameter of 170mm or more, in large austenitic alloy pipe having the chemical composition of the above (1), the grain size number of austenite grains at 2.0 to 7.0 if, on the condition that satisfies the other conditions (the above-mentioned items (1) and the following item (4)), as well as the ability to detect ultrasonic flaw detection increases significantly the strength anisotropy can be suppressed. Specifically, ASTM E8M-16a tensile obtained by a tensile test in conformity yield strength (tensile YS) compressive yield strength obtained by the compression test according to ASTM E9-09 for the ratio of the (compression YS) (= compression YS / tensile YS) is 0.85 to 1.10.
[0038]
　(4) has a chemical composition of the above (1), comprising a strength grade 110 ksi (tensile YS is 758 MPa) or more, in large austenitic alloy tube grain size number is 2.0 to 7.0 Furthermore, the microstructure are substantially the sizing, excellent in SCC resistance.
[0039]
　In other words, the large diameter austenitic alloy pipe having the chemical composition of the above (1), even to 7.0 grain size number of 2.0, microstructure if mixed grain, grain SCC is likely to occur in different crystal grain boundaries of size.
[0040]
　Above chemical composition, strength, and the large diameter austenitic alloy tube having a grain size number, out of 20 samples taken by the below-mentioned method, the proportion of the number of samples "mixed grain" has occurred (mixed if the particle ratio) is less than 5%, the microstructure of the large diameter austenitic alloy tube is substantially sized, have excellent SCC resistance.
[0041]
　Diameter austenitic alloy tube having (5) above configuration, for example, it can be prepared by proceeding as in the following manufacturing method. This manufacturing method includes a material production step, the raw tube manufacturing process, and between the intermediate cold working step, the grain refining step and a final cold working step. In material production process, the production of material cast slab produced by continuous casting and hot working. The blank tube manufacturing process, to produce a mother tube with hot working the material. In the intermediate cold working step, cold drawing the blank tube.
[0042]
　It is defined as a reduction of area of ​​Rd0 the area reduction rate in the material production process. It is defined as a reduction of area of ​​Rd1 the area reduction rate in the base pipe manufacturing process. Is defined as a reduction rate Rd2 the reduction rate in the intermediate cold working step. The reduction of area in the final cold working step is defined as a reduction of area of ​​Rd3. By adjusting the reduction rate Rd0 ~ Rd3 within a proper range, to adjust the grain size number of the large-diameter austenitic alloy tube, and can be sized microstructure. For example, if reduction of area Rd1 of reduction of area Rd0 and base pipe manufacturing process of material production process is too low, even if increasing the reduction rate Rd2 in the intermediate cold working step, 2.0 or more grain size number although can be adjusted to, it may not be possible to sizing. Further, if too high the reduction rate Rd2 in the intermediate cold working step, seizure occurs at a die, scratches on the surface of the final cold austenitic alloy tube after machining process will remain.
[0043]
　Therefore, in this embodiment, the reduction of area Rd0 in material production step was 50.0 to 90.0%, the reduction rate Rd1 in base pipe manufacturing process and from 80.0 to 95.0%, and, the reduction of area Rd2 in the intermediate cold working step was 10.0 to 30.0%, further 20.0 to the reduction of area Rd3 in the final cold working process after the grain refining step 35.0 % to.
[0044]
　Further, in this embodiment, reduction rate Rd0 in material production process, reduction of area at base pipe manufacturing process Rd1 and, reduction rate Rd2 in the intermediate cold working step is adjusted to satisfy the equation (1) to.
　5 × Rd0 + 10 × Rd1 + 20 × Rd2 ≧ 1300 (1)
　Here, "Rd0" in the formula (1) is a reduction of area of Rd0 (%) in the material production process is assigned. The "Rd1" is area reduction rate in the base pipe manufacturing process Rd1 (%) is substituted. The "Rd2" is area reduction rate in the intermediate cold working step Rd2 (%) is substituted. When defined as F1 = 5 × Rd0 + 10 × Rd1 + 20 × Rd2, rounding off the first decimal place of the value of the resulting F1.
[0045]
　In this case, the austenitic alloy tube of the chemical composition, grain size number is within the range of 2.0 to 7.0, and mixed grain ratio is 5% or less, further, the excessive reduction of area of ​​Rd2 by suppressing the seizure is suppressed occurrence of scratches on the surface of austenitic alloy tube is suppressed. Furthermore, in the final cold working step, by adjusting the intensity in the range of 20.0 to 35.0% of the reduction of area Rd3, tensile YS austenitic alloy tube becomes more 758 MPa, and anisotropic index AN (= compression YS / tensile YS) is within a range from 0.85 to 1.10.
[0046]
　Austenitic alloy tube according to the present embodiment has been completed based on the above findings,
　the chemical composition,
　in
　mass%, C: 0.004
　~ 0.030%, Si: 1.00% or
　less, Mn: 0.30
　2.00% ~, P: 0.030% or
　less, S: 0.0020% or
　less,
　Al: 0.001 ~ 0.100%, Cu: 0.50
　~ 1.50%, Ni: 25.00 ~
　Pasento
　55.00,
　Cr: 20.00 ～ 30.00 Pasento, Mo: 2.00 ～ 10.00 Pasento,
　N: 0.005 ～ 0.100 Pasento, Ti: 0 ～ 0.800
　Pasento, W: 0
　0.30%

　Nb:~, 0 ~ 0.050%, Ca: 0 ~ 0.0100%,
　Mg: 0 ~ 0.0100%, Nd: 0 ~ 0.050%, and,
　the balance: Fe and impurities, made,
　the crystal grain size number of austenite crystal grains is 2.0 to 7.0, and mixed grain ratio It is 5% or less,
　The yield strength obtained by the compression test is defined as the compression YS (MPa), when defined as a tensile yield strength obtained by a tensile test YS (MPa), tensile YS is not less than 758 MPa, the compression YS / tensile YS is 0.85 to 1.10,
　is an outer diameter of 170mm or more.
[0047]
　The chemical composition of the austenitic alloy tube described
　above, Ti:
　0.005 ~ 0.800%, W: 0.02 ~ 0.30%,
　and, Nb: 0.001 ~ 0.050%, from the group consisting of it may contain one or two or more kinds selected.
[0048]
　The chemical composition of the austenitic alloy tube described
　above,
　Ca: 0.0003 ~ 0.0100%, Mg: 0.0005 ~ 0.0100%,
　and, Nd: 0.010 ~ 0.050%, from the group consisting of it may contain one or two or more kinds selected.
[0049]
　Method of manufacturing an austenitic alloy tube according to the present embodiment includes a material production step, the raw tube manufacturing process, and between the intermediate cold working step, the grain refining step and a final cold working step.
　In material production process, produced by continuous casting, after heating the slab having the chemical composition described above in 1100 ~ 1350 ° C., in a range of 50.0 to 90.0%, and the formula (1 ) to produce the material by hot working at a reduction of area of Rd0 satisfying.
　The blank tube manufacturing process, after heating the material at 1100 ~ 1300 ° C., in a range of 80.0 to 95.0%, and then hot worked at reduction rate Rd1 satisfying the equation (1) producing a blank tube.
　In the intermediate cold working step, in a range of 10.0 to 30.0%, and to cold drawing the blank tube in reduction of area Rd2 satisfying the equation (1).
　The grain refining step, after holding for 1 to 30 minutes in the blank tube after between the intermediate cold working step 1000 ~ 1250 ° C., rapidly cooled.
　In the final cold working step, the cold drawing the blank tube after grain refining step at from 20.0 to 35.0% of the reduction of area Rd3, outer diameter to produce a more austenitic alloy tube 170mm .
　5 × Rd0 + 10 × Rd1 + 20 × Rd2 ≧ 1300 (1)
[0050]
　It described in detail below austenitic alloy pipe of the present embodiment. In the description of the present specification, "%" related to elements, unless otherwise specified, means mass%.
[0051]
　[About the outer diameter of the austenitic alloy tube]
　austenitic alloy pipe of the present embodiment is directed to an alloy tube of the so-called large diameter. Specifically, the diameter of the austenitic alloy pipe of the present embodiment is 170mm or more. A preferred lower limit of the diameter of the austenitic alloy tube is, for example, a 180 mm, and more preferably 190 mm, more preferably from 200 mm, more preferably from 210 mm, more preferably from 220 mm. The upper limit of the diameter of the austenitic alloy pipe of the present embodiment is not particularly limited, for example, is 350 mm. The preferable upper limit of the diameter of the austenitic alloy tube is, for example, a 340 mm, more preferably from 320 mm. The thickness of the austenitic alloy tube according to the present embodiment is not particularly limited, for example, a 7 ~ 40 mm.
[0052]
　[Chemical Composition of Austenitic alloy tube]
　chemical composition of the large diameter austenitic alloy pipe of the present embodiment contains the following elements.
[0053]
　[Essential
　element] C: 0.004 ~ 0.030%
　carbon (C) increases the strength of the large diameter austenitic alloy tube. If C content is less than 0.004% or above effect is not sufficiently obtained. On the other hand, C content if it exceeds 0.030%, Cr carbides are generated in the grain boundaries. Cr carbide enhances the susceptibility to cracking at the grain boundaries. As a result, the SCC resistance of the large-diameter austenitic alloy tube is lowered. Therefore, C content is 0.004 to 0.030%. A preferred lower limit of the C content is 0.006%, more preferably 0.007%, still more preferably 0.008%. The preferable upper limit of the C content is 0.024%, more preferably 0.023%, still more preferably 0.020%.
[0054]
　Si: 1.00% or less
　silicon (Si) is inevitably contained. Therefore, Si content is over 0%. Si is used for deoxidizing alloy, the result is contained in large diameter austenitic alloy tube. If the Si content exceeds 1.00%, the hot workability of the large diameter austenitic alloy tube is lowered. Therefore, Si content is 1.00% or less. The preferable upper limit of the Si content is 0.80%, more preferably 0.60%, more preferably 0.50%. The lower limit of Si content is not particularly limited. However, excessive reduction of Si content increases the manufacturing cost. Therefore, considering the operation of industrial, preferable lower limit of Si content is 0.0005%, more preferably 0.005%, more preferably 0.10%, more preferably 0. it is 20%.
[0055]
　Mn: 0.30 ~ 2.00%
　manganese (Mn) is an austenite forming element, which stabilizes austenite in the alloy. Mn further increase the solubility of N into the alloy. Therefore, Mn is particularly suppresses when many N content in order to increase the strength of the alloy, a pinhole in the vicinity of the surface of the large diameter austenitic alloy tube occurs. If Mn content is less than 0.30%, these effects can not be sufficiently obtained. On the other hand, Mn content if it exceeds 2.00%, hot workability of the large diameter austenitic alloy is lowered. Therefore, Mn content is 0.30 to 2.00%. The preferable lower limit of the Mn content is 0.40%, more preferably 0.45%, more preferably from 0.50%. The preferable upper limit of the Mn content is 1.50%, more preferably 1.20%, more preferably 0.90%, more preferably 0.80%.
[0056]
　P: 0.030% or less
　Phosphorus (P) is an impurity which is inevitably contained. That, P content is over 0%. P increases the stress corrosion cracking susceptibility resulting resistance of the alloy under sour environment. Accordingly, P content is 0.030% or less. The preferable upper limit of the P content is 0.028%, more preferably 0.025%. P content is preferably as small as possible. However, an extreme reduction in P content increases the manufacturing cost. Therefore, when considering industrial production, preferable lower limit of the P content is 0.0001%, more preferably 0.0005%, more preferably from 0.001%.
[0057]
　S: 0.0020% or less
　Sulfur (S) is an impurity which is inevitably contained. That, S content is over 0%. S decreases the hot workability of the alloy. Thus, S content is 0.0020%. The preferable upper limit of S content is 0.0015%, more preferably 0.0012%, more preferably 0.0009%, more preferably 0.0008%. S content is preferably as small as possible. However, an extreme reduction in P content increases the manufacturing cost. Therefore, when considering industrial production, preferable lower limit of the P content is 0.0001%, more preferably 0.0003%, more preferably 0.0005%.
[0058]
　Al: 0.001 ~ 0.100%
　of aluminum (Al), the deoxidizing alloy. Al is oxygen and fixed to form oxides, suppresses the generation of Si oxides and Mn oxides. This increases the hot workability of the alloy. If Al content is less than 0.001%, this effect can not be obtained sufficiently. On the other hand, Al content if it exceeds 0.100%, the Al oxide is excessively produced, hot workability of the alloy is rather reduced. Therefore, Al content is from 0.001 to 0.100%. A preferable lower limit of Al content is 0.005%, more preferably 0.010%, still more preferably 0.012%. The preferable upper limit of Al content is 0.080%, more preferably 0.060%, still more preferably 0.050%.
[0059]
　Cu: 0.50 ~ 1.50%
　copper (Cu) is under sour environment, increase the SCC resistance of the alloy. If Cu content is less than 0.50%, this effect can not be obtained sufficiently. On the other hand, Cu content if it exceeds 1.50%, decreases the hot workability of the alloy. Therefore, Cu content is 0.50 to 1.50% in mass%. The preferable lower limit of Cu content is 0.60%, more preferably 0.65%, more preferably 0.70%. The preferable upper limit of Cu content is 1.40%, more preferably 1.20%, more preferably 1.00%.
[0060]
　Ni: 25.00 ~ 55.00%
　nickel (Ni) is an austenite forming element, which stabilizes austenite in the alloy. Ni is further to form a Ni sulfide film on the surface of the alloy, increasing the SSC resistance of the alloy. If Ni content is less than 25.00%, these effects can not be sufficiently obtained. On the other hand, if it exceeds Ni content 55.00%, and N solid solution limit is reduced to decrease the strength of the austenitic alloy tube. Therefore, Ni content is 25.00 to 55.00%. A preferable lower limit of Ni content is 27.00%, more preferably 28.00%, more preferably 29.00%. The preferable upper limit of the Ni content is 53.00%, more preferably 52.0%, more preferably 51.00%.
[0061]
　Cr: 20.00 ~ 30.00%
　chromium (Cr), in the presence of a Ni, enhancing the SSC resistance of the alloy. Cr further enhance the strength of the alloy by solid solution strengthening. If Cr content is less than 20.00%, these effects can not be sufficiently obtained. On the other hand, Cr content if it exceeds 30.00% decreases the hot workability of the alloy. Therefore, Cr content is 20.00 to 30.00%. A preferable lower limit of the Cr content is 21.00%, more preferably 22.00%, even more preferably 23.00%. The preferable upper limit of the Cr content is 29.00%, more preferably 27.00%, even more preferably 26.00%.
[0062]
　Mo: 2.00 ~ 10.00%
　molybdenum (Mo), in the presence of the Cr and Ni, increase the SCC resistance of the alloy. Mo further enhances the strength of the alloy by solid solution strengthening. If Mo content is less than 2.00%, these effects can not be sufficiently obtained. On the other hand, Mo content if it exceeds 10.00%, decreases the hot workability of the alloy. Therefore, Mo content is from 2.00 to 10.00%. A preferable lower limit of Mo content is 2.20%, more preferably 2.40%, more preferably 2.50%. The preferable upper limit of the Mo content is 9.50%, more preferably 9.00%, more preferably 7.00%.
[0063]
　N: 0.005 ~ 0.100%
　nitrogen (N) increases the strength of the alloy by solid solution strengthening. The austenitic alloy tube according to the present embodiment, the C content in order to improve the SCC resistance is suppressed low. Therefore, by containing a large amount of N instead and C, increasing the strength of the alloy. If N content is less than 0.005%, these effects can not be sufficiently obtained. On the other hand, if the N content is it exceeds 0.100% pinholes are easily generated in the vicinity of the surface of the alloy during solidification of the alloy. N content further if it exceeds 0.100% lowers the hot workability of the alloy. Therefore, N content is 0.005 to 0.100%. The preferable lower limit of the N content is 0.008%, more preferably 0.010%. The preferable upper limit of the N content is 0.095%, more preferably 0.090%.
[0064]
　The remainder of the chemical composition of the austenitic alloy tube according to the present embodiment is composed of Fe and impurities. Here, the impurities, in producing a large-diameter austenitic alloy tube industrially, ore as a raw material, there is to be mixed etc. Scrap or manufacturing environment, austenitic alloy pipe of the present embodiment means what is allowed in a range which does not give a significant adverse effect on the effect of the.
[0065]
　The above-mentioned impurities, which may O (oxygen) is included. If O is contained as an impurity, the upper limit of the O content is, for example, as follows.
　O: 0.0010% or less
[0066]
　[Optional elements]
　The present embodiment further chemical composition of the austenitic alloy tube by, Ti, W, and may contain one or two or more selected from the group consisting of Nb. Both of these elements increases the strength of the alloy.
[0067]
　Ti: 0 ~ 0.800%
　titanium (Ti) is an optional element and may not be contained. That, Ti content may be 0%. If contained, Ti, in the presence of the C and N, to promote grain refinement. Ti further enhance the strength of the alloy by precipitation hardening. However, Ti content if it exceeds 0.800%, decreases the hot workability of the alloy. Therefore, Ti content is from 0 to 0.800% in mass%. A preferable lower limit of the Ti content is 0 percent, more preferably 0.005%, still more preferably 0.030%, still more preferably 0.050%. The preferable upper limit of the Ti content is 0.750%, and still more preferably 0.700%.
[0068]
　W: 0 ~ 0.30%
　of tungsten (W) is an optional element and may not be contained. That, W content may be 0%. If contained, W is in the presence of the Cr and Ni, increase the SCC resistance of the alloy. W further enhance the strength of the alloy by solid-solution strengthening. However, W content if it exceeds 0.30%, decreases the hot workability of the alloy. Therefore, W content is 0 to 0.30% in mass%. The preferable lower limit of the W content is 0%, and more preferably from 0.02%, more preferably 0.04%. The preferable upper limit of the W content is 0.25%, more preferably 0.20%.
[0069]
　Nb: 0 ~ 0.050%
　niobium (Nb) is an optional element and may not be contained. That, Nb content may be 0%. If contained, Nb is in the presence of the C and N, to promote grain refinement. Nb further enhance the strength of the alloy by precipitation hardening. However, if the Nb content is too high, decrease the hot workability of the alloy. Therefore, Nb content is from 0 to 0.050 percent. The preferable lower limit of Nb content is 0 percent, more preferably 0.001%, still more preferably 0.008%, more preferably 0.010%. The preferable upper limit of Nb content is 0.045%, more preferably 0.040%.
[0070]
　This embodiment further chemical composition of the austenitic alloy tube according to, Ca, Mg, and may contain one or more members selected from the group consisting of Nd. Both of these elements enhances the hot workability of the alloy.
[0071]
　Ca: 0 ~ 0.0100%
　calcium (Ca) is an optional element and may not be contained. That, Ca content may be 0%. If contained, Ca combines with S to form sulfides, reducing solid solution S. Thus, Ca improves the hot workability of the alloy. However, Ca content if it exceeds 0.0100% coarse oxides are generated, the hot workability of the alloy is rather reduced. Therefore, Ca content is from 0 to 0.0100%. The preferable lower limit of the Ca content is 0%, and more preferably 0.0003%, more preferably 0.0005%. The preferable upper limit of the Ca content is 0.0080%, more preferably 0.0060%.
[0072]
　Mg: 0 ~ 0.0100%
　magnesium (Mg) is an arbitrary element, may not be contained. That, Mg content may be 0%. If contained, Mg, like Ca, combines with S to form sulfides, reducing solid solution S. Thus, Mg improves the hot workability of the alloy. However, Mg content if it exceeds 0.0100% coarse oxides are generated, the hot workability of the alloy is rather reduced. Thus, Mg content is from 0 to 0.0100%. A preferable lower limit of the Mg content is 0 percent, more preferably 0.0005%, more preferably 0.0007%. The preferable upper limit of the Ca content is 0.0080%, more preferably 0.0060%, more preferably 0.0050%.
[0073]
　Nd: 0 ~ 0.050%
　neodymium (Nd) is optional element and may not be contained. That, Nd content may be 0%. If contained, Nd, like Ca and Mg, combined with S to form sulfides, reducing solid solution S. Thus, Nd improves the hot workability of the alloy. However, Nd content if it exceeds 0.050% coarse oxides are generated, the hot workability of the alloy is rather reduced. Therefore, Nd content is from 0 to 0.050 percent. The preferable lower limit of the Nd content is greater than 0%, more preferably 0.010%, still more preferably 0.020%. The preferable upper limit of the Nd content is 0.040%, and still more preferably 0.035%.
[0074]
　[Grain size for]
　In the microstructure of austenitic alloy pipe of the present embodiment, the grain size number that complies with the austenite grain of ASTM E112 is 2.0 to 7.0. Further, in the microstructure of austenitic alloy pipe of the present embodiment, mixed grain ratio is 5% or less.
[0075]
　In austenitic alloy tube of the aforementioned chemical composition, grain size number of austenite crystal grains is less than 2.0, as shown in FIG. 4, the anisotropy of the strength increases. Specifically, tensile for the obtained yield strength by the test (tensile YS), the ratio of the obtained yield strength by compression test (compression YS) (= compression YS / tensile YS) is less than 0.85. In this case, there is a case where the austenitic alloy tube is not suitable for use as OCTG inclined wellbore applications. Furthermore, as shown in FIG. 1, the detection capability of the ultrasonic flaw detection is significantly decreased. On the other hand, if the grain size number of the crystal grains exceeds 7.0, a high reduction rate in cold working is required, defects such as seizure is likely to occur on the surface of the austenitic alloy tube during the manufacturing process . Austenitic alloy pipe of the present embodiment, the crystal grain size number that complies with the austenite grain of ASTM E112 is 2.0 to 7.0. Therefore, small anisotropy in strength, particularly tensile for the obtained yield strength by the test (tensile YS), the ratio of the obtained yield strength by compression test (compression YS) (= compression YS / tensile YS ) is 0.85 to 1.10. Therefore, even if it takes how stress is used in various different environments, it shows excellent resistance. Furthermore, excellent detectability of the ultrasonic flaw detection. Furthermore, during the manufacturing process, the generation of flaws such as seizure on the surface of austenitic alloy tube is suppressed. A preferred lower limit of the grain size number is 2.1, still more preferably 2.5, still more preferably 2.7, still more preferably 3.0. The preferable upper limit of the grain size number is 6.9, more preferably 6.8, still more preferably 6.7.
[0076]
　[Measurement method of grain size number]
　Measurement method of austenite crystal grains in austenitic alloy tube grain size number is as follows. The body region 100 shown in FIG. 2 to 5 equal parts in the axial direction of the alloy tube. In each section, to select the sampling position 90 degree pitch in the circumferential direction of the pipe. Taking samples from the thick central portion of the selected sampling position. Viewing surface of the sample, and a cross-section perpendicular to the axial direction of the austenitic high alloy tube (the longitudinal direction), the area of the viewing surface, for example, 40 mm 2 and.
[0077]
　By the method described above, four samples in each segment, taking samples of 20 with all wedges (4 5 Groups ×). The observation surface of the samples taken, corroded with curling etchant, thereby revealing the grain boundaries of the austenite of the surface. Observe corroded observation surface, in compliance with ASTM E112, obtaining the grain size number of austenite crystal grains.
[0078]
　Austenite grains obtained in 20 samples the average value of the grain size number is defined as the grain size number conforming to ASTM E112 in the austenitic alloy tube.
[0079]
　[For mixed grain ratio]
　Furthermore austenitic alloy pipe of the present embodiment, the microstructure is substantially sized. More specifically, among the 20 samples taken from the wall thickness central part of the austenitic alloy tube, the proportion of the number of samples "mixed grain" has occurred (mixed grain ratio) is 5% or less .
[0080]
　If the mixed grain ratio exceeds 5%, a large variation in the grain size of austenitic alloy tube. In this case, in the austenitic high alloy of the chemical composition, the SCC resistance is lowered.
[0081]
　Mixed grain proportion of the microstructure of austenitic alloy tube of the present embodiment is 5% or less, a substantially sized. Therefore, having a chemical composition described above, even the outside diameter is a diameter austenitic alloy tube above 170 mm, has excellent SCC resistance. Preferred mixed grain ratio is 0%.
[0082]
　[Measurement method of mixed grain ratio]
　mixed grain ratio can be determined by the following method. The body region 100 shown in FIG. 2 to 5 equal parts in the axial direction (longitudinal direction) of the alloy tube. In each section, to select the sampling position 90 degree pitch in the circumferential direction of the pipe. Taking samples from the thick central portion of the selected sampling position. Viewing surface of the sample, and a cross-section perpendicular to the axial direction of the austenitic high alloy, the area of the viewing surface, for example, 40 mm 2 and.
[0083]
　By the method described above, four samples in each section, to collect 20 samples in all categories. The observation surface of the samples taken, corroded with curling etchant, thereby revealing the grain boundaries of the surface. Observe corroded observation surface, in compliance with ASTM E112, determines the grain size number.
[0084]
　At this time, the observation surface of each sample, to identify the crystal grains of 3 or more different grain size number of crystal grains of grain size number with a maximum frequency as "foreign grain". In the observation plane, if the heterogeneous grain area ratio is 20% or more, it is identified as "mixed grains" occurs in the sample.
[0085]
　In the 20 samples, the samples mixed grain occurs is defined as "mixed grain sample". As shown in the following equation, defined duplex grain total number of samples for the total number of samples (20) the ratio of (number) mixed grain rate (%).
　Mixed grain ratio (%) = mixed grain total number of samples / total number of samples × 100
[0086]
　As described above, in 20 of each sample taken from the thickness center of the austenitic alloy tube, determine the grain size number conforming to ASTM E112, the observation surface of the sample, the crystal grains of grain size number with a maximum frequency when the area of ​​crystal grains of 3 or more different grain size number was defined as mixed grains sample sample of 20% or more, it is defined as a mixed grain ratio of a percentage of the total number of samples of mixed grain sample number.
[0087]
　The austenitic alloy pipe of the present embodiment, mixed grain ratio is 5% or less. In other words, it is almost sized. If it exceeds mixed grain ratio is 5%, the SCC resistance is low. For mixed grain ratio of the austenitic alloy pipe of the present embodiment is less than 5%, on the assumption that meet other requirements, excellent SCC resistance.
[0088]
　[Yield strength and compression YS / tensile YS]
　In austenitic alloy pipe of the present embodiment, when defining the yield strength obtained by a tensile test as "tensile YS", tensile YS is not less than 758 MPa. Furthermore, when the yield strength obtained by the compression test was defined as "compression YS" compression YS / tensile YS is 0.85 to 1.10.
[0089]
　Austenitic alloy tube of the present embodiment, 110Kis grade (tensile YS is 758 ~ 861MPa) has a yield strength of at least. Then, while having a yield strength of at least 110ksi grade, anisotropy indices AN (compression YS / tensile YS) is from 0.85 to 1.10. Therefore, large diameter austenitic alloy tube diameter of at least 170mm in this embodiment, the load is the stress distribution for use in various different environments are possible useful.
[0090]
　A preferred lower limit of the tensile YS is 760 MPa, more preferably from 770 MPa, more preferably from 780 MPa. The upper limit of the tensile YS is not particularly limited, for example, 1000 MPa. The upper limit of the tensile YS, for example, may be a 965MPa.
[0091]
　A preferred lower limit of the compression YS / tensile YS is 0.86, further preferably 0.87, more preferably 0.88. The preferable upper limit of the compression YS / tensile YS is 1.08, more preferably 1.07, still more preferably 1.06.
[0092]
　Tensile YS is measured by the following methods. The body region 100 shown in FIG. 2 to 5 equal parts in the axial direction of the alloy tube. From the thick center of each section, to collect the tensile test piece. Tensile specimens conform to prescribed in ASTM E8M-16a, the diameter of the parallel portion and 6 mm, and 30mm length of the parallel portion. Parallel portion of the tensile test specimen shall be parallel to the axial direction of the austenitic alloy tube (the longitudinal direction). Tensile test in compliance with ASTM E8M-16a, carried at room temperature in air (25 ° C.). The average of five yield strength obtained, a tensile obtained yield strength by the test (tensile YS, the unit is MPa) to define. Here, the yield strength means the 0.2% proof stress.
[0093]
　Compression YS is measured in the following manner. The body region 100 shown in FIG. 2 to 5 equal parts in the axial direction of the alloy tube. From the thickness center of each segment, taking a compression test piece. Compression test piece is a cylindrical, a diameter of 6.35 mm, is 12.7mm long. Longitudinal compression test piece is parallel to the axial direction of the austenitic alloy tube (the longitudinal direction). Using an Instron type compression tester, in air, at room temperature (25 ° C.), to implement the compression test according to ASTM E9-09. The average of five yield strength obtained, resulting yield strength by compression test (compression YS, the unit is MPa) to define. Here, the yield strength means the 0.2% proof stress.
[0094]
　Using the obtained tensile YS and compression YS, determine the anisotropy index AN (= compression YS / tensile YS).
[0095]
　[Manufacturing Method]
　An example of a manufacturing method of austenitic alloy pipe of the present embodiment will be described. The manufacturing method of austenitic alloy pipe of the present embodiment is not limited to this production method.
[0096]
　Method of manufacturing an austenitic alloy pipe of the present embodiment includes a material production step, the raw tube manufacturing process, and between the intermediate cold working step, the grain refining step and a final cold working step. In the production method of the present embodiment, reduction rate Rd0 in material production process, reduction of area at base pipe manufacturing process Rd1, reduction rate in the intermediate cold working step Rd2, and, in the final cold working step the reduction of area Rd3 respectively adjusted, and reduction of area of ​​Rd0 ~ Rd2 is adjusted to satisfy a specific relationship. Hereinafter, detail of each steps of the method of manufacturing the present embodiment.
[0097]
　[Material manufacturing process]
　The material production process, the production of material cast slab produced by continuous casting and hot working. Materials produced in the material production process is, for example, the round billet. The following describes the material manufacturing process.
[0098]
　In material production process, first, heating the prepared slab. Heating of the slab, for example, it is carried out in a heating furnace or soaking furnace. The heating temperature is, for example, 1100 ~ 1350 ° C.. Holding time at the heating temperature is, for example, from 2.0 hours to 5.0 hours. The heated slab to produce a material with hot working. Hot working may be a slabbing with blooming mill, forging machine may be a hot forging using.
[0099]
　Is defined as the area of the Acc vertical cross section (cross section) in the axial direction of the hot working before slab of material production process (longitudinal) axis direction (longitudinal direction of the material after hot working of the material manufacturing process is defined as Arm the area of the cross section perpendicular (cross section) in). In this case, reduction of area of Rd0 in hot working of the material production process (%) is defined by the following equation.
　Reduction of area Rd0 = {1- (Arm / Acc )} × 100
[0100]
　Reduction of area Rd0 in hot working a material manufacturing process is 50.0 to 90.0%. If reduction rate Rd0 is less than 50.0%, even meet the other manufacturing conditions, might grain size number of austenite alloy tube after the final cold working process is less than 2.0, or, it is in the range grain size number of 2.0 to 7.0, sometimes mixed grain ratio exceeds 5%. Therefore, reduction of area Rd0 is 50.0% or more. A preferred lower limit of the reduction rate Rd0 is 55.0%, still more preferably 60.0%.
[0101]
　Incidentally, reduction ratio Rd0 is too high, reduction of area in hot working of the material manufacturing process is too high. Therefore, scratches are likely to occur on the surface of the element tube after hot working. In this case, there are cases where the final cold austenitic surface of the alloy tube after process step flaw remains. Therefore, the upper limit of the reduction rate Rd0 is 90.0%. The preferable upper limit of the reduction rate Rd0 is 88.0%, still more preferably 85.0%.
[0102]
　[Mother tube production process]
　The base pipe manufacturing process for producing hot-worked to base pipe a (Hollow Shell) material. Specifically, heating the prepared material. Heating the material, for example, it is carried out in a heating furnace or soaking furnace. The heating temperature of the material is, for example, 1100 ~ 1300 ° C..
[0103]
　Hot working may be adopted Mannesmann method, it may be adopted hot extrusion represented by a Ugine Sejournet-Sejurune method. When employing the Mannesmann process, using a plurality of inclined rolls, a piercing mill and a plug, to produce a mother tube by puncturing and rolling material. Further with respect to base pipe produced by the drilling machine, it may be carried out elongation rolling using a mandrel mill or the like. Further, with respect to base tube after elongation rolling may be carried out constant-radius rolling with sizers or Redeyusa like.
[0104]
　The area of the cross section of the prior hot working mother pipe manufacturing process material is defined as Arm, and the area of the perpendicular to the axial direction of the element tube after hot working mother pipe manufacturing step sectional (cross section) Ahs1 Define. In this case, reduction of area in hot working mother pipe manufacturing process Rd1 (%) is defined by the following equation.
　Reduction of area Rd1 = {1- (Ahs1 / Arm )} × 100
[0105]
　Reduction of area Rd1 in hot working in base pipe manufacturing process is 80.0 to 95.0%. If reduction rate Rd1 is less than 80.0%, even meet the other manufacturing conditions, might final cold grain size number of austenite alloy tube after processing is less than 2.0, or even within the crystal grain size number of 2.0 to 7.0, sometimes mixed grain ratio exceeds 5%. Furthermore, even meet the other manufacturing conditions, in some cases tensile YS is less than 758 MPa. Therefore, reduction of area Rd1 is 80.0% or more. A preferred lower limit of the reduction rate Rd1 is 82.0%, still more preferably 85.0%.
[0106]
　On the other hand, if reduction of area Rd1 is too high, reduction of area in hot working mother pipe manufacturing process is too high. In this case, flaws are easily generated on the surface of the base pipe. As a result, the final cold surface of the austenitic alloy tube after processing steps which may scratch remains. Therefore, the upper limit of the reduction rate Rd1 is 95.0%. The preferable upper limit of the reduction rate Rd1 is 93.0%, still more preferably 90.0%.
[0107]
　Intermediate cold working step]
　In the intermediate cold working step further with respect to manufactured raw tube, out the cold working. Thereby introducing distortion into base pipe, causing recrystallization in grain refinement steps follows step, refining the crystal grains. Cold working is a cold drawing.
[0108]
　The area of the cross section of the intermediate cold working step cold working before the element tube is defined as Ahs1, the area of the cross section of the base pipe after cold working the intermediate cold working step is defined as Ahs2. In this case, the area reduction rate in cold working the intermediate cold working step Rd2 (%) is defined by the following equation.
　Reduction of area Rd2 = {1- (Ahs2 / Ahs1 )} × 100
[0109]
　Reduction of area Rd2 in cold working with intermediate cold working step is 10.0 to 30.0%. If reduction rate Rd2 is less than 10.0%, even meet the other manufacturing conditions, might grain size number of austenite alloy tube after the final cold working process is less than 2.0, there is a case in which the tensile YS is less than 758MPa. Therefore, reduction rate Rd2 is 10.0% or more. A preferred lower limit of the reduction rate Rd2 is 11.0%, still more preferably 13.0%.
[0110]
　On the other hand, if reduction of area Rd2 is too high, an excessive load is applied to the die cold drawing. In this case, seizure occurred in the die, scratches on the surface of the mother tube after between the intermediate cold working step is formed. As a result, scratches in the final cold austenitic surface of the alloy tube after machining process will remain. Therefore, the upper limit of the reduction rate Rd2 is 30.0%. The preferable upper limit of the reduction rate Rd2 is 29.0%, more preferably 28.0%, more preferably 26.0%.
[0111]
　[Grain refining step]
　implementing the grain refinement process to the intermediate cold raw tube after processing. Specifically, heating the mother pipe after between the intermediate cold work. The heating temperature is 1000 ~ 1250 ° C.. If the heating temperature is below 1000 ° C., there are cases where the SCC resistance of the blank tube is reduced. On the other hand, when the heating temperature exceeds 1250 ° C., will be recrystallized grains are coarsened, the final cold grain size number of austenite alloy tube after processing is less than 2.0. Therefore, the heating temperature in the grain refinement process is 1000 ~ 1250 ° C.. A preferred lower limit of the heating temperature in the grain refinement process is 1050 ° C.. Preferred upper limit of the heating temperature in the grain refinement process is 1200 ° C., more preferably from 1150 ° C.. Holding time at the heating temperature is 1 to 30 minutes. If the retention time is too short, the recrystallization is not sufficiently promoted. On the other hand, if the retention time is too long, will be recrystallized grains are coarsened, the final cold grain size number of austenite-based alloy tube after machining process is less than 2.0. In addition, there is a case in which the tensile YS is less than 758MPa. Therefore, the holding time at the heating temperature is 1 to 30 minutes.
[0112]
　After the retention time, quenching the blank tube to room temperature (25 ° C.). The cooling rate is, for example, is 1 ° C. / sec or more. Cooling method is not particularly limited, for example, it is water cooled. Water cooling method, for example, a method of cooling by dipping the raw tube in a water bath, a method in which quenching the blank tube by the shower water cooling. Base tube may be quenched by other methods.
[0113]
　[Final cold working step]
　Further with respect to base pipe after grain refinement process, by carrying out the cold working, the outer diameter to produce a more austenitic alloy tube 170 mm. The final cold working step is intended to adjust the outer diameter and yield strength of the austenitic alloy tube.
[0114]
　Final cold area of the cross section of the cold working before the raw tube processing steps is defined as Ahs2, final cold axial cross section perpendicular austenitic alloy tube after cold working process step (cross-section) If the area is defined as Ahs3, area reduction rate in cold working of the final cold working step Rd3 (%) is defined by the following equation.
　Reduction of area Rd3 = {1- (Ahs3 / Ahs2 )} × 100
[0115]
　Reduction of area Rd3 in cold working in the final cold working step is 20.0 to 35.0%. If reduction rate Rd3 is less than 20.0%, even meet the other manufacturing conditions, the final cold yield strength obtained by a tensile test of austenitic alloy tube after machining (MPa) is less than 758MPa If there is a. On the other hand, if reduction of area Rd3 is it exceeds 35.0% excessive load is applied to the die cold drawing. In this case, seizure occurs in the die, flaws are formed on the final cold blank tube surface after processing steps. Furthermore, crystal grains extend in the axial direction, the anisotropy becomes strong. In this case, there is a case where an anisotropic index AN (= compression YS / tensile YS) is less than 0.85. Therefore, reduction of area Rd3 in the final cold working step is 20.0 to 35.0%. A preferred lower limit of the reduction rate Rd3 is 22.0%, still more preferably 24.0%. The preferable upper limit of the reduction rate Rd3 is 33.0%, more preferably, 31.0% and more preferably 29.0%.
[0116]
　[For formula (1)]
　Further in the above production process, reduction of area in the material production process Rd0, area reduction rate in the base pipe manufacturing process Rd1, and reduction of area Rd2 in the intermediate cold working step has the formula ( to satisfy 1).
　5 × Rd0 + 10 × Rd1 + 20 × Rd2 ≧ 1300 (1)
　Here, "Rd0" in the formula (1) is a reduction of area of Rd0 (%) in the material production process is assigned. The "Rd1" is area reduction rate in the base pipe manufacturing process Rd1 (%) is substituted. The "Rd2" is area reduction rate in the intermediate cold working step Rd2 (%) is substituted.
[0117]
　In large diameter austenitic alloy pipe of the present embodiment, finer austenite grain size, and, in order to suppress the generation of mixed grain than the requirements for each production step, the grain refining step before three of the manufacturing process of (material manufacturing process, raw tube manufacturing process, and an intermediate cold working step) in so as to satisfy the equation (1), to adjust the reduction rate Rd0, Rd1 and Rd2. Thus, in the large diameter austenitic alloy pipe having the chemical composition described above, the crystal grain size number is within the range of 2.0 to 7.0, and mixed grain ratio is 5% or less.
[0118]
　Is defined as F1 = 5 × Rd0 + 10 × Rd1 + 20 × Rd2. Reduction of area Rd0 is 50.0 to 90.0%, and reduction of area Rd1 is the 80.0 to 95.0%, and reduction of area Rd2 is at 10.0 to 30.0% even if F1 is less than 1300, the grain refinement process, the crystal grains are not sufficiently fine. As a result, the grain size number of austenite crystal grains is less than 2.0, and mixed grain ratio exceeds 5%. The reduction of area Rd0 and 50.0 to 90.0%, and the reduction of area Rd1 and 80.0 to 95.0%, and the reduction of area Rd2 and 10.0 to 30.0%, further , by setting the 1300 than F1, the grain size number of austenite crystal grains in the microstructure of the large diameter austenitic alloy tube described above can be set to 2.0 or more, and a mixed grain ratio below 5% can do. A preferred lower limit of F1 is 1350, more preferably from 1370. The numerical values ​​of F1 is rounded to the first decimal place of the value obtained by calculation.
[0119]
　Above by the manufacturing process, the outer diameter can be produced over a large diameter austenitic alloy tube 170 mm. Diameter austenitic alloy tube produced, despite a large diameter pipe is more than 170mm diameter, a ~ 7.0 grain size number of austenite crystal grains is 2.0, and the mixed grain ratio 5% or less. In addition, tensile YS is greater than or equal to 758MPa, compression YS / tensile YS is 0.85 to 1.10. Therefore, high detection capability of the ultrasonic flaw detection, and have a high strength of at least 110ksi grade (758MPa ~ 861MPa), can be suppressed anisotropy. Furthermore, since the microstructure is substantially sized, exhibits excellent SCC resistance. Furthermore, even though the grain size number is 2.0 to 7.0, scratches on the surface is unlikely to occur.
[0120]
　The manufacturing method described above is an example, large diameter austenitic alloy pipe of the present embodiment may be manufactured by other manufacturing methods. That has the chemical composition described above, the crystal grain size number of austenite crystal grains is 2.0 to 7.0, and not more than mixed grain ratio is 5%, the tensile YS is not less than 758 MPa, compression YS / tensile YS is the 0.85 to 1.10, if production of large diameter austenitic alloy pipe of the present embodiment in which the outer diameter is 170mm or more, the production method is not particularly limited. The above production method is a preferred example of manufacturing a large diameter austenitic alloy pipe of the present embodiment.
Example
[0121]
　Hereinafter, more detailed explanation of the effect of the large diameter austenitic alloy pipe of the present embodiment by way of example. Conditions in Examples is an example of conditions adopted for confirming the workability and effects of the large diameter austenitic alloy pipe of the present embodiment. Therefore, large diameter austenitic alloy pipe of the present embodiment is not limited to this single example of conditions.
[0122]
　[Manufacturing Method]
　were produced bloom or ingot having the chemical composition of Table 1.
[0123]
[Table 1]

[0124]
　With bloom or ingot, material production process, raw tube manufacturing process, an intermediate cold working step, grain refinement step, and, by implementing the respective steps in order of the final cold working step, the outer diameter shown in Table 2 It was produced austenitic alloy tube dimensions (mm).
[0125]
[Table 2]

[0126]
　Table 2 in the "material production process" column "material" field of "CC" is material, means that a bloom produced by continuous casting. "It" means that the material is an ingot. In material production process, any of the bloom heating temperature 1270 ° C. for the test numbers, any and heating temperature 1270 ° C. ingot Test No. was a retention time 2.0-5.0 hours. Test Nos. 1 to Test No. 12, to implement the slabbing against bloom and ingot after heating the test numbers 15 to Test No. 27 was prepared round billets. Reduction of area Rd0 by slabbing for each test number (%) were as shown in Table 2. Incidentally, with respect to the round billet test numbers 11 and 12, by carrying out cutting, to form a through hole in the central axis of the round billet.
[0127]
　The blank tube manufacturing process, with respect to the material produced in the material production process (round billet) was performed hot working by the production method shown in Table 2. In any of the test numbers, the heating temperature of the material was 1100 ~ 1300 ° C.. Table 2 in the "mother tube manufacturing process" field "type", "MM" in the column for the material of the corresponding test number, which means that it has performed the hot working by the Mannesmann method. The Mannesmann process of this example was prepared a raw tube by carrying out piercing-rolling by the piercer. On the other hand, "US", relative to the material of the corresponding test number, which means that it has performed the hot extrusion according Ugine Sejournet-Sejurune method. Reduction of area Rd1 in hot working mother pipe manufacturing process was as shown in Table 2.
[0128]
　In the intermediate cold working step, with respect to manufactured raw tube by raw tube manufacturing process was carried out cold working the (cold drawing). Reduction of area Rd2 in the intermediate cold working step in each test number was as shown in Table 2.
[0129]
　The grain refining step, the blank tube for each test number was heated for 20 minutes at a heating temperature shown in Table 2 (° C.), then water cooled.
[0130]
　In the final cold working step, with respect to base tube after grain refining process, cold working the (cold drawn) was performed to produce a austenitic alloy tube. Reduction of area Rd3 in the final cold working step in each test number was as shown in Table 2.
[0131]
　With the above-described manufacturing process, to produce a austenitic alloy tube of the test numbers 1-27. Samples were taken from an arbitrary position of these austenitic alloy tube, it was carried out well-known component analysis. Specifically, C in the chemical composition, the combustion for S - quantified on the basis of the infrared absorption method (JIS G1121, JIS G1215), for the N, inert gas melt - based on the thermal conductivity (TCD) Method quantified Te, and other elements were determined based on ICP mass spectrometry (JIS G1256). As a result, the chemical composition of the austenitic alloy tube for each test number was as shown in Table 1.
[0132]
　[Evaluation Test]
　[grain size number measured Test
　in austenitic alloy tube for each test number, a body region 100 shown in FIG. 2 was divided into five equal parts in the axial direction of the alloy tube. In each segment, it was selected sampling locations in 90 degree pitch in the circumferential direction of the pipe. Samples were taken from the thick central portion of the selected sampling positions (four positions). Viewing surface of the sample, and a cross-section perpendicular to the axial direction of the austenitic high alloy, the area of the observation plane is 40 mm 2 was.
[0133]
　By the method described above, four samples in each segment were collected 20 samples in all categories. The observation surface of the samples taken, corroded with curling etchant was made to appear the crystal grain boundaries of the surface. Observe corroded observation surface, in compliance with ASTM E112, we were determined grain size number. The average value of the grain size number was determined in 20 samples was defined as the grain size number conforming to ASTM E112 in the austenitic alloy tube for each test number.
[0134]
　[Mixed grain ratio measurement test]
　The mixed grain ratio of austenitic alloy tube for each test number was determined by the following method. The body region 100 shown in FIG. 2 was divided into five equal parts in the axial direction of the alloy tube. In each segment, it was selected sampling locations in 90 degree pitch in the circumferential direction of the pipe. Samples were taken from the thick central portion of the selected sampling positions (four positions). Viewing surface of the sample, and a cross-section perpendicular to the axial direction of the austenitic alloy tube, the area of the observation plane is 40 mm 2 was.
[0135]
　By the method described above, four samples in each segment were collected 20 samples in all categories. The observation surface of the samples taken, corroded with curling etchant was made to appear the crystal grain boundaries of the surface. Observe corroded observation surface, decided grain size number. At this time, the observation surface of each sample, identified three or more different grain size number of the crystal grains from grain size number with a maximum frequency as "foreign grain". In the observation plane, if the heterogeneous grain area ratio is 20% or more was recognized as "mixed grains" it occurs in the sample.
[0136]
　In the above-mentioned 20 samples was defined samples mixed grain has occurred as "mixed grain sample". Then, as shown in the following equation, duplex grain total number of samples for the total number of samples (20) the ratio of (number) were defined mixed grain rate (%).
　Mixed grain ratio (%) = mixed grain total number of samples / total number of samples × 100
[0137]
　[Tensile Test]
　The tensile YS austenitic alloy tube for each test number was measured by the following method. The body region 100 shown in FIG. 2 was divided into five equal parts in the axial direction of the alloy tube. From the thick center of each segment, the tensile test specimens were taken. That is, the austenitic alloy tube for each test number, were taken five tensile specimens. Tensile test specimens having dimensions specified in ASTM E8M-16a, specifically, the diameter of the parallel portion of the tensile test specimen is 6 mm, the length of the parallel portion was 30 mm. Parallel portion of the tensile test specimen was parallel to the axial direction of the austenitic alloy tube (the longitudinal direction). Using five tensile specimens taken, in compliance with ASTM E8M-16a, was a tensile test at room temperature in air (25 ° C.). The average of the resulting five yield strength (0.2% proof stress), obtained by a tensile test was the yield strength (tensile YS, the unit is MPa) was defined.
[0138]
　[Compression Test
　compression YS austenitic alloy tube for each test number was measured by the following method. The body region 100 shown in FIG. 2 was divided into five equal parts in the axial direction of the alloy tube. From the thickness center of each segment, the compressed test pieces were taken. That is, the austenitic alloy tube for each test number, were taken five compression specimens. Compression test piece is a cylindrical, a diameter of 6.35 mm, length was 12.7 mm. Longitudinal compression test piece was parallel to the axial direction of the austenitic alloy tube (the longitudinal direction). Relative collected five compression test specimens using an Instron type compression tester, in air, at room temperature (25 ° C.), it was performed to a compression test in compliance with ASTM E9-09. The average of the resulting five yield strength (0.2% proof stress), the resulting yield strength by compression test (compression YS, the unit is MPa) was defined.
[0139]
　Using a tensile YS and compression YS obtained by tensile test and compression test above, it was determined anisotropy index AN = compression YS / tensile YS, the.
[0140]
　[Ultrasonic flaw detectability measurement test]
　The body region 100 of the austenitic alloy tube for each test number was divided into five equal parts in the axial direction of the alloy tube. From each section, the axial length of the alloy tube was collected annular sample 100 mm. As shown in FIG. 3, the axially central portion of the inner peripheral surface of the samples were prepared artificial flaw (hole) 200 extending in the thickness direction. The diameter of the artificial flaw 200 was 3 mm.
[0141]
　Using an ultrasonic flaw detector, the outer surface of the sample toward the artificial flaw outputs (incident) ultrasound, receives the ultrasound reflected by the artificial flaws were observed as an echo. Ultrasonic intensity incident was the same in any of the test numbers.
[0142]
　Obtained in samples taken at each section, the average of the echo of the signal strength of the artificial flaw (total of five) was defined as the signal strength at its austenitic alloy tube.
[0143]
　Table 1 Test No. 1 (grain size number is 5.7) defines the signal strength in the austenitic alloy tube with 100. Then, the signal intensity obtained in austenitic alloy tube for each test number was defined the ratio signal strength of the test No. 1 the signal intensity ratio (%). If the signal intensity ratio exceeds 50.0% was judged to be excellent in the detectability of the ultrasonic flaw detection.
[0144]
　[SCC resistance evaluation test (SSRT test)]
　from thick central portion of the body region 100 of the austenitic alloy tube for each test number, were taken two tensile test specimens. The tensile specimen corresponds to the test piece defined in NACE TM0198 (2016), the diameter of the parallel portion is 3.81 mm, the length of the parallel portion was 25.4 mm. Parallel portion of the tensile test specimen was parallel to the axial direction of the austenitic alloy tube (the longitudinal direction).
[0145]
　Against tensile test piece prepared by using a low strain rate tester (SSRT), while immersed specimen 25% NaCl solution, 200 ℃ (400 ° F) , 100psi of H 2 S gas atmosphere in, 4 × 10 -6 to a tensile test at a strain rate of / sec was determined breaking squeezing (%). The average fracture aperture of tensile test specimens were taken at each test number (two), it was defined as the diaphragm rupture of the test number (%). Moreover, the crack (secondary cracks) was visually confirmed whether or not occurred in the diaphragm of the two specimens. If in the throttle portion of any two specimens not cracks occur was recognized as no secondary cracking. If at least one or more cracks in the two specimens is occurring, it certified that there is secondary cracking. In SSRT test, fracture aperture is 60.0% or more, and, when the secondary cracking is not observed, was judged to be excellent in SCC resistance.
[0146]
　[Test Results]
　The test results are shown in Table 3.
[0147]
[table 3]

[0148]
　Table 3 with reference to, in the austenitic alloy tube of the test numbers 1 to 10, and 23-27, a chemical composition is appropriate production conditions was also suitable. Therefore, even outer diameter 170mm or more, the grain size number is 2.0 to 7.0, mixed grain ratio was 5% or less. Therefore, it is the signal intensity ratio 50.0% or more, excellent detectability of the ultrasonic flaw detection test. Further, in the SSRT test, fracture aperture is a 60.0% or more, the secondary cracks not occurred, it is excellent in SCC resistance. In addition, tensile YS was more than 758MPa. Further, the anisotropic index AN (= compression YS / tensile YS) is from 0.85 to 1.10, the strength anisotropy is suppressed. Additionally, surface defects were observed.
[0149]
　On the other hand, in Test No. 11, reduction of area Rd1 is too low in the raw tube manufacturing process, reduction rate Rd2 in the intermediate cold working step is too high. Therefore, the grain size number is greater than 7.0, surface defects were observed. For reduction of area Rd2 in the intermediate cold step is too high, seizure dies occurs, As a result, it is considered that surface defects occur.
[0150]
　In Test No. 12, reduction of area Rd1 in base pipe manufacturing process was too low. Therefore, although the grain size number was within the range of 2.0 to 7.0, mixed grain ratio exceeds 5%. As a result, in the SSRT test, fracture aperture is less than 60.0%, and the secondary cracks is confirmed, the SCC resistance was low.
[0151]
　In Test No. 13 and 14, without performing material production process, and reduction of area Rd2 in the intermediate cold working step was low. As a result, the grain size number is less than 2.0, mixed grain ratio exceeds 5%. Therefore, compression YS / tensile YS is less than 0.85, anisotropy was strong. Further, the signal intensity ratio is less than 50.0%, the detection capability of the ultrasonic flaw detection was low. Additionally, rupture diaphragm or secondary cracks less than 60.0% is generated in the SSRT test, the SCC resistance was low.
[0152]
　In Test No. 15 had lower reduction ratio Rd0 in material production process. Therefore, the grain size number is less than 2.0, mixed grain ratio exceeds 5%. Therefore, compression YS / tensile YS is less than 0.85, anisotropy was strong. Further, a signal strength is less than 50.0%, the detection capability of the ultrasonic flaw detection was low. Additionally, rupture diaphragm in SSRT test is less than 60.0%, the secondary cracks occur, the SCC resistance was low.
[0153]
　In Test No. 16 had lower reduction ratio Rd1 in raw tube manufacturing process. As a result, the grain size number is less than 2.0, and mixed grain ratio exceeds 5%. Therefore, compression YS / tensile YS is less than 0.85, anisotropy was strong. Further, a signal strength is less than 50.0%, the detection capability of the ultrasonic flaw detection was low. Additionally, rupture diaphragm in SSRT test is less than 60.0%, the SCC resistance was low. In addition, the tensile YS was less than 758MPa.
[0154]
　In Test No. 17, the area reduction rate Rd2 in the intermediate cold working step was high. Therefore, the grain size number is greater than 7.0, surface defects occurred.
[0155]
　In Test No. 18, the area reduction rate Rd2 in the intermediate cold working step was low. Therefore, the grain size number is less than 2.0, mixed grain ratio exceeds 5%. Therefore, compression YS / tensile YS is less than 0.85, the strength anisotropy was strong. Further, a signal strength is less than 50.0%, the detection capability of the ultrasonic flaw detection was low. Additionally, rupture diaphragm in SSRT test is less than 60.0%, the SCC resistance was low. In addition, the tensile YS was less than 758MPa.
[0156]
　In Test No. 19, the heating temperature in the grain refinement process was too high. Therefore, the grain size number is less than 2.0, and a tensile YS was less than 758 MPa. Therefore, compression YS / tensile YS is less than 0.85, anisotropy was strong. Further, a signal strength is less than 50.0%, the detection capability of the ultrasonic flaw detection was low.
[0157]
　In Test No. 20, reduction of area Rd3 in the final cold working step is too high. Therefore, the crystal grain size number is greater than 7.0. As a result, compression YS / tensile YS is less than 0.85, anisotropy was strong. Crystal grains is considered to be because too extending in the axial direction. In Test No. 20 In addition, surface flaws occurred.
[0158]
　In Test No. 21, reduction of area Rd3 in the final cold working step it was too low. Therefore, tensile YS was less than 758MPa.
[0159]
　In Test No. 22, F1 does not satisfy the equation (1). Therefore, the grain size number is less than 2.0, mixed grain ratio exceeds 5%. As a result, the compression YS / tensile YS is less than 0.85, the strength anisotropy was strong. Further, the signal intensity ratio is less than 50.0%, the detection capability of the ultrasonic flaw detection was low. Additionally, rupture diaphragm in SSRT test is less than 60.0%, the SCC resistance was low. In addition, the tensile YS was less than 758MPa.
[0160]
　It has been described an embodiment of the present invention. However, the above-described embodiment is merely an example for implementing the present invention. Accordingly, the present invention is not limited to the embodiments described above, it can be implemented by changing the above-described embodiments without departing from the scope and spirit thereof as appropriate.
DESCRIPTION OF SYMBOLS
[0161]
　11 a first end
　12 of the second tube end
　100 of the body field
　110 of an end field
　120 of the second tube end FIELD

The scope of the claims

[Requested item 1]A austenitic alloy tube,
　chemical composition,
　in
　mass%, C: 0.004
　~ 0.030%, Si: 1.00% or
　less, Mn: 0.30 ~
　2.00%, P: 0. 030% or
　less, S: 0.0020% or
　less,
　Al: 0.001
　~ 0.100%, Cu: 0.50 ~ 1.50%, Ni: 25.00
　~ 55.00%, Cr: 20.00
　30.00%
~,
　~ 10.00%, N: 0.005 ~ 0.100%,
　Ti: 0 ~ 0.800%, W: 0 ~
　0.30%, Nb: 0 ~
　% 0.050,
　Ca: 0 ~ 0.0100%,
　Mg: 0 ~ 0.0100%, Nd: 0 ~ 0.050%, and,
　the balance: Fe and impurities, consists,
　of austenite grain grain size number There was 2.0 to 7.0, and not more than mixed grain ratio is 5%,
　The yield strength obtained by the compression test is defined as the compression YS (MPa), when defined as a tensile yield strength obtained by a tensile test YS (MPa), tensile YS is not less than 758 MPa, the compression YS / tensile YS is 0.85 to 1.10,
　an outer diameter of 170mm or more, austenitic alloy tube.
[Requested item 2]
　A austenitic alloy pipe according to claim 1,
　wherein the chemical
　composition, Ti:
　0.005 ~ 0.800%, W: 0.02 ~ 0.30%,
　and, Nb: 0.001 ~ 0 .050%, containing one or more members selected from the group consisting of austenitic alloy tube.
[Requested item 3]
　A austenitic alloy pipe according to claim 1 or claim 2,
　wherein the chemical
　composition,
　Ca: 0.0003 ~ 0.0100%, Mg: 0.0005 ~ 0.0100%,
　and, Nd: 0 .010 to 0.050% containing one or more members selected from the group consisting of austenitic alloy tube.
[Requested item 4]
　A method for manufacturing austenitic alloy tube
　produced by the continuous casting method, after heating at 1100 ~ 1350 ° C. The cast slab having a chemical composition according to claim 1, the range of 50.0 to 90.0% a inner and the material production step of producing a material by hot working at a reduction of area of Rd0 satisfying the equation (1),
　after heating the material at 1100 ~ 1300 ℃, 80.0 ~ 95 . It is in the range of 0%, and the mother tube production step of producing a blank tube by hot working at a reduction of area of Rd1 satisfying the equation
　(1), in the range of 10.0 to 30.0% there are, and the formula (1) and between the intermediate cold working step of cold drawing said mother tube at reduction rate Rd2 satisfying,
　the one intermediate cold the mother tube after processing step at 1000 ~ 1250 ° C. ~ after 30 minutes holding, a grain refining step of quenching,
　the mother pipe after grain refining step Outer diameter was cold drawn at 20.0 to 35.0% of reduction ratio Rd3 a comprises a final cold working step of manufacturing the austenitic alloy tube above 170 mm, the manufacturing method of austenitic alloy tube .
　5 × Rd0 + 10 × Rd1 + 20 × Rd2 ≧ 1300 (1)