Nickel alloy steel 06Ni7DR submerged-arc welding method for low-temperature pressure vessel

Abstract

The invention belongs to the technical field of submerged-arc welding, and discloses a submerged-arc welding method for nickel alloy steel 06Ni7DR for a low-temperature pressure vessel, which comprises the following welding process steps: S1, groove processing: forming a V-shaped groove with the groove angle of 40 degrees + / -5 degrees from a non-flame edge, and forming a truncated edge of 0-3mm; s2, cleaning before welding; s3, assembling the test plates; s4, preheating before welding: preheating the assembled test piece before welding; a submerged-arc welding process is adopted, the polarity of welding current is alternating current, a welding material is a nickel-based alloy welding material, and the interlayer temperature is controlled; in the first pass, shielded metal arc welding small heat input is used for bottoming, in the second pass, heat input lower than a specified value is adopted for submerged-arc welding, and the same welding parameters are used for submerged-arc welding in the third pass to the capping pass. According to the welding method, large-heat-input submerged-arc welding of the nickel alloy steel 06Ni7DR is achieved, a welded joint has good obdurability, cold bending performance and cold crack resistance, the related standards are met, industrial application is facilitated, and the production efficiency is high.

Description

Technical Field

[0001] The invention belongs to the technical field of submerged arc welding, and in particular relates to a submerged arc welding method for nickel alloy steel 06Ni7DR for low-temperature pressure vessels. Background Art

[0002] As the global energy structure accelerates its transition to low-carbonization, liquefied natural gas (LNG) has gradually become an important bridge for the transition from fossil energy to renewable energy with its high calorific value, low pollution and convenient storage and transportation. LNG storage tanks need to serve under ultra-low temperature conditions of -162°C, which places high demands on the low-temperature performance of materials. Compared with 9% Ni steel, 06Ni7DR has the advantage of lower cost in LNG storage tanks and good low-temperature toughness, making it a good choice for LNG storage tanks. However, due to the high alloy content, 06Ni7DR has the risk of hot cracking during welding, and the large heat input will seriously reduce the impact toughness of the 06Ni7DR welded joint, which seriously restricts the promotion and use of 06Ni7DR. Only through submerged arc welding process testing and evaluation, the tensile properties, bending properties and impact properties of the welded joints are good, can the requirements for large-scale LNG cryogenic storage tank construction be met.

[0003] Patent CN118478074A discloses a welding method for 5.5% Ni low-temperature steel, which is specifically designed for 5.5% Ni steel welding to achieve high-quality welding of 5.5% Ni steel. However, only the weld impact performance test was performed, and impact tests on weak locations such as the fusion line and heat-affected zone were not performed. In addition, the low-temperature impact performance is lower than that of 06Ni7DR. Summary of the invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a submerged arc welding method for nickel alloy steel 06Ni7DR for low-temperature pressure vessels, wherein the steel plate thickness is 50 mm, and V-shaped groove butt joint is adopted. By strictly controlling the preheating temperature, interlayer temperature, heat input, post-weld dehydrogenation treatment and other processes, the tensile strength of the welded joint is guaranteed to be 680-820 MPa; d=50 mm, 180° side bend is qualified; the impact energy of the weld, fusion zone, and heat-affected zone at -196°C is ≥80 J.

[0005] The technical scheme adopted by the present invention is: a submerged arc welding method for nickel alloy steel 06Ni7DR for low-temperature pressure vessels, the chemical composition weight percentage of the steel is: C≤0.08%, Si: 0.05%-0.30%, Mn: 0.30%-0.80%, Ni: 6.50%-7.50%, P≤0.008%, S≤0.003%, Cr≤0.50%, Cu≤0.50%, Mo≤0.30%, Nb≤0.030%, V≤0.01%, Alt≥0.015%, the balance is Fe and unavoidable impurities, characterized in that the steel plate thickness is 50mm, the yield strength is ≥550MPa, the tensile strength is 680-820MPa, the elongation after fracture is ≥18%, and the impact energy at -196℃ is ≥80J. The welding process steps include:

[0006] S1: Bevel processing: V-shaped bevel from the non-flame side, bevel angle 40°±5, 0-3mm blunt edge;

[0007] S2: Cleaning before welding: Grind the iron oxide scale and rust on the upper and lower surfaces of the groove and the plate near the groove until the metallic luster is exposed, and use anhydrous ethanol or acetone to remove oil and iron filings on the groove and the surrounding area;

[0008] S3: Test plate assembly: spot weld two test plates together, control the gap at the base of the test plates to 1-2 mm, and fix the two ends of the test plates with arc-starting plates and arc-extinguishing plates;

[0009] S4: Preheating before welding: Preheat the assembled test pieces before welding;

[0010] S5: Welding: Submerged arc welding is used, the polarity of the welding current is AC, and the interlayer temperature is controlled; the first pass uses arc welding with a small heat input for base laying, and the second pass uses a heat input lower than the specified value for submerged arc welding. The same welding parameters are used for submerged arc welding from the third pass to the covering pass.

[0011] Furthermore, the preheating temperature of step S3 is ≥50°C.

[0012] Furthermore, in step S5, the interlayer temperature is controlled to be 50-100°C.

[0013] Further, step S5, for a welding process with a heat input of 15 to 25 kJ / cm, the first pass has a welding current of 100 to 120 A, an arc voltage of 20 to 23 V, a welding speed of 12 to 14 cm / min, and a line energy of 10 to 12 kJ / cm; the second pass has a welding current of 330 to 420 A, an arc voltage of 29 to 34 V, a welding speed of 42 to 50 cm / min, and a line energy of 12 to 21 kJ / cm; the third to cover pass has a welding current of 340 to 450 A, an arc voltage of 29 to 34 V, a welding speed of 33 to 42 cm / min, and a line energy of 15 to 25 kJ / cm, and the weld excess height is controlled to be 1 to 2 mm.

[0014] Further, step S5, for a welding process with a heat input of 26 to 35 kJ / cm, the first pass has a welding current of 100 to 120 A, an arc voltage of 20 to 23 V, a welding speed of 12 to 14 cm / min, and a line energy of 10 to 12 kJ / cm; the second pass has a welding current of 410 to 460 A, an arc voltage of 31 to 34 V, a welding speed of 37 to 40 cm / min, and a line energy of 19 to 26 kJ / cm; the third to cover pass has a welding current of 450 to 560 A, an arc voltage of 30 to 34 V, a welding speed of 30 to 35 cm / min, and a line energy of 26 to 35 kJ / cm, and the weld excess height is controlled to be 1 to 2 mm.

[0015] Preferably, the welding rod model is ENiCrMo-6, with a diameter of 3.2 mm. The mechanical properties of the welding rod deposited metal are: tensile strength ≥620 MPa, yield strength ≥350 MPa, elongation ≥32%, -196°C impact energy ≥80 J; the main chemical components and weight percentages are: C≤0.1%, Si≤1.0%, Mn: 2.0%~4.0%, Cr: 12.0%~17.0%, Mo: 5.0%~9.0%, Ni≥55.0%, W: 1.0%~2.0%, Nb+Ta=0.5%~2.0%, P≤0.02%, S≤0.015%, and the remainder is Fe and unavoidable impurities.

[0016] Preferably, the welding wire model is ENiCrMo-4, with a diameter of 2.4 mm. The mechanical properties of the welding wire deposited metal are: tensile strength ≥690 MPa, yield strength ≥430 MPa, elongation ≥35%, -196°C impact energy ≥70 J; the main chemical components and weight percentages are: C≤0.03%, Si≤0.20%, Mn≤1.0%, Cr: 14.5%~16.5%, Mo: 15.0%~17.0%, Ni≥50.0%, W: 3.0%~4.5%, V≤0.35%, Cu≤0.50%, Co≤2.50%, P≤0.03%, S≤0.02%, and the balance is Fe and unavoidable impurities.

[0017] Technical principle of the present invention:

[0018] The nickel alloy steel of the present invention adopts the submerged arc welding process to make the weld well-formed and defect-free; at the same time, a series of measures are taken to make the weld joint obtain good tensile, bending and -196°C impact properties:

[0019] (1) The Ni content of nickel-based alloy welding materials (such as ERNiCrMo-4) is usually greater than 50%, which is much higher than the 7% Ni of 06Ni7DR steel. It can effectively suppress the dilution effect of the parent material and avoid the formation of brittle martensite in the fusion zone due to carbon migration. High Ni content can also reduce the brittle temperature range of the weld metal and reduce crack sensitivity;

[0020] (2) The carbon content of nickel-based alloy welding materials is ≤0.1%, and the S / P content is extremely low, which can avoid the formation of low-melting-point eutectics (such as Ni-S, Ni-P) with Ni, significantly reducing the tendency of hot cracks. At the same time, the low-hydrogen design reduces the risk of cold cracks;

[0021] (3) The welding current adopts AC polarity, which effectively avoids the magnetic blow phenomenon that is very easy to occur during the welding process of high-nickel steel, ensuring the quality of the welded joint;

[0022] (4) Using a lower preheating temperature and strictly controlling the interlayer temperature can effectively prevent grain coarsening in the heat-affected zone of the weld joint and ensure the low-temperature impact performance of the weld joint;

[0023] (5) Multi-layer and multi-pass welding is used to avoid the formation of coarse bainite or martensite. At the same time, through the reheating of subsequent welds, the previous weld and HAZ are recrystallized to form fine equiaxed crystals, which significantly improves toughness.

[0024] The beneficial effects of the present invention are:

[0025] 1) The nickel alloy steel 06Ni7DR used in the present invention has better economy compared with 9% Ni commonly used in LNG storage tanks;

[0026] 2) The welding method proposed in the present invention realizes high heat input submerged arc welding of nickel alloy steel 06Ni7DR, and the welded joint has good toughness, cold bending, and cold crack resistance, which meets the relevant standards.

[0027] 3) At the same time, the welding method has strong process operability, is convenient for industrial application, and has high production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 It is a schematic diagram of welding joint pair;

[0030] Figure 2 This is the macroscopic metallographic image of the 15kJ / cm weld joint;

[0031] Figure 3 This is the macroscopic metallographic image of the 25kJ / cm weld joint;

[0032] Figure 4 This is the macroscopic metallographic diagram of the 35kJ / cm weld joint. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention performs submerged arc welding with different heat inputs on nickel alloy steel 06Ni7DR for low-temperature pressure vessels. The specific implementation method is illustrated by examples 1 to 3, and comparative example 1 is used for comparison with example 3.

[0035] The welding equipment used in the embodiment is a Lincoln double-wire submerged arc welding machine of model DC / AC1000.

[0036] The tensile test of the base material in the embodiment refers to the GB / T 228 standard, and the yield strength is determined using an extensometer; the tensile test of the welded joint refers to the GB / T 2651 standard.

[0037] The parent material impact test of the embodiment refers to GB / T 229 standard, and the impact test of the welded joint refers to GB / T 2650 standard.

[0038] Example The cold bending test of the welded joint was carried out according to GB / T 2653 standard.

[0039] The welding test plates of Examples 1 to 3 and Comparative Example 1 were taken from the same 06Ni7DR steel plate with a thickness of 50 mm; the components and weight percentages of the steel were: C: 0.04%, Si: 0.07%, Ni: 7.06%, Mn: 0.77%, P: 0.003%, S: 0.002%, Cr: 0.02%, Cu: 0.02%, Mo: 0.16%, Nb: 0.003%, V: 0.002%, Alt: 0.029%, and the balance was Fe and unavoidable impurities; its yield strength was 617 MPa, tensile strength was 717 MPa, elongation was 26.4%, and impact energy at -196°C was 233 J.

[0040] The base welding electrode model selected in Examples 1 to 3 is GEM-CM6 with a diameter of Φ3.2. The main chemical components and weight percentages of the electrode are: C: 0.042%, Si: 0.44%, Mn: 2.91%, Cr: 13.3%, Mo: 6.38%, Ni: 70.6%, W: 1.45%, Nb+Ta=1.35%, P: 0.008%, S: 0.003%, and the remainder is Fe and unavoidable impurities. The filling and covering submerged arc welding wire selected is OK Autrod NiCrMo-4, and its matching flux is OK FLUX 10.99. The main chemical components and weight percentages of the welding wire are: C: 0.003%, Si: 0.01%, Mn: 0.5%, Cr: 15.9%, Mo: 15.7%, Ni: 58.5%, W: 3.6%, V≤0.01%, Cu: 0.08%, Co: 0.014%, P: 0.004%, S<0.001%, and the balance is Fe and unavoidable impurities.

[0041] The welding materials used for base, filling and covering in Comparative Example 1 are ER309L and matching flux. The main chemical components and weight percentages of the welding wire are: C: 0.005%, Si: 0.35%, Mn: 2.1%, P≤0.022%, S<0.015%, Cr: 24.2%, Ni: 13.0%, and the balance is Fe and unavoidable impurities.

[0042] Embodiment 1:

[0043] Welding heat input is 15kJ / cm Nickel alloy steel 06Ni7DR submerged arc welding specific steps:

[0044] 1) Bevel processing: straight-edge single V-shaped bevel, one side has a bevel angle of 40°, 0-3mm blunt edge, and one side is straight without bevel.

[0045] 2) Pretreatment: Grind the iron oxide and rust on the groove and the upper and lower surfaces near the groove of the plate until the metallic luster is exposed, and use anhydrous ethanol / acetone to remove the oil and iron filings on the groove and the surrounding area. Spot weld the two test plates together, control the gap at the root of the test plates to 1-2mm, and fix the two ends of the test plates with arc-starting plates and arc-extinguishing plates.

[0046] 3) Preheating: Preheating is performed before welding, the preheating temperature is ≥50°C, and electric heating is used.

[0047] 4) Welding: Use submerged arc welding technology, the welding current polarity is AC, and the interlayer temperature is controlled at 50-100℃; see the welding joint group diagram Figure 1 , 15kJ / cm welding joint weld schematic diagram see Figure 2 , the key welding process parameters are shown in Table 1.

[0048] Embodiment 2:

[0049] The specific steps of submerged arc welding of nickel alloy steel 06Ni7DR with a welding heat input of 25kJ / cm are as follows:

[0050] 1) Bevel processing: straight-edge single V-shaped bevel, one side has a bevel angle of 40°, 0-3mm blunt edge, and one side is straight without bevel.

[0051] 2) Pretreatment: Grind the iron oxide and rust on the groove and the upper and lower surfaces near the groove of the plate until the metallic luster is exposed, and use anhydrous ethanol / acetone to remove the oil and iron filings on the groove and the surrounding area. Spot weld the two test plates together, control the gap at the root of the test plates to 1-2mm, and fix the two ends of the test plates with arc-starting plates and arc-extinguishing plates.

[0052] 3) Preheating: Preheating is performed before welding, the preheating temperature is ≥50°C, and electric heating is used.

[0053] 4) Welding: Use submerged arc welding technology, the welding current polarity is AC, and the interlayer temperature is controlled at 50-100℃; see the welding joint group diagram Figure 1 , 25kJ / cm welding joint weld schematic diagram see Figure 3 , the key welding process parameters are shown in Table 2.

[0054] Embodiment 3:

[0055] Welding heat input is 35kJ / cm Nickel alloy steel 06Ni7DR submerged arc welding specific steps:

[0056] 1) Bevel processing: straight-edge single V-shaped bevel, one side has a bevel angle of 40°, 0-3mm blunt edge, and one side is straight without bevel.

[0057] 2) Pretreatment: Grind the iron oxide and rust on the groove and the upper and lower surfaces near the groove of the plate until the metallic luster is exposed, and use anhydrous ethanol / acetone to remove the oil and iron filings on the groove and the surrounding area. Spot weld the two test plates together, control the gap at the root of the test plates to 1-2mm, and fix the two ends of the test plates with arc-starting plates and arc-extinguishing plates.

[0058] 3) Preheating: Preheating is performed before welding, the preheating temperature is ≥50°C, and electric heating is used.

[0059] 4) Welding: Use submerged arc welding technology, the welding current polarity is AC, and the interlayer temperature is controlled at 50-100℃; see the welding joint group diagram Figure 1 , 35kJ / cm welding joint weld schematic diagram see Figure 4 , the key welding process parameters are shown in Table 3.

[0060] Comparative Example 1:

[0061] The specific steps of submerged arc welding of nickel alloy steel 06Ni7DR with welding heat input of 35kJ / cm are as follows:

[0062] 1) Bevel processing: straight-edge single V-shaped bevel, one side has a bevel angle of 40°, 0-3mm blunt edge, and one side is straight without bevel.

[0063] 2) Pretreatment: Grind the iron oxide and rust on the groove and the upper and lower surfaces near the groove of the plate until the metallic luster is exposed, and use anhydrous ethanol / acetone to remove the oil and iron filings on the groove and the surrounding area. Spot weld the two test plates together, control the gap at the root of the test plates to 1-2mm, and fix the two ends of the test plates with arc-starting plates and arc-extinguishing plates.

[0064] 3) Preheating: Preheating is performed before welding, the preheating temperature is ≥50°C, and electric heating is used.

[0065] 4) Welding: Submerged arc welding technology is adopted, the welding current polarity is DC reverse connection, the interlayer temperature is controlled at 100-150°C, and the key welding process parameters are shown in Table 4.

[0066] Table 1 Key welding process parameters of Example 1

[0067]

[0068] Table 2 Key welding process parameters of Example 2

[0069]

[0070] Table 3 Key welding process parameters of Example 3

[0071]

[0072]

[0073] Table 4 Key welding process parameters of comparative example 1

[0074]

[0075] Various tests and inspections were conducted on the samples of Example 1, Example 2, Example 3 and Comparative Example 1:

[0076] 1. Test plate flaw detection: After the welded test plate passed the appearance inspection, an ultrasonic inspection was performed according to GB / T 11345 standard. The results of Examples 1-3 and Comparative Example 1 were all qualified.

[0077] 2. Mechanical properties of welded joints:

[0078] (1) Welded joint tensile test: This test adopts full thickness tensile test at two locations. The tensile test results are listed in Table 5.

[0079] (2) Bending test: In this test, samples were taken transversely, and 4 side bending samples were used for the side bending test: d = 50 mm, the bending angle was 180°, and the test was carried out at room temperature. After the test, the outer side of the bending part of the sample was checked with the naked eye to see if there were any defects such as cracks or delamination. The tests of Examples 1-3 were all qualified, and Comparative Example 1 was unqualified. The test results are shown in Table 6.

[0080] (3) Impact test: The impact specimens were standard Charpy V-notch specimens with a specimen size of 10 mm × 10 mm × 55 mm. In this test, impact specimens were taken at the center of the joint weld, the fusion line, and the heat-affected zone. The impact test temperature was -196°C. The impact values ​​of Examples 1-3 met the standards, while the impact value of Comparative Example 1 was lower than the standard requirements. The impact test results are shown in Table 7.

[0081] Table 5 Transverse stretching results of Examples 1 to 3 and Comparative Example 1

[0082]

[0083] Table 6 Side bending test results of Examples 1 to 3 and Comparative 1

[0084]

[0085]

[0086] Table 7 -196℃ Charpy impact test results of Examples 1 to 3 and Comparative Example 1

[0087]

[0088]

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A submerged arc welding method for nickel alloy steel 06Ni7DR for low-temperature pressure vessels, wherein the chemical composition of the steel is as follows by weight: C≤0.08%, Si: 0.05%-0.30%, Mn: 0.30%-0.80%, Ni: 6.50%-7.50%, P≤0.008%, S≤0.003%, Cr≤0.50%, Cu≤0.50%, Mo≤0.30%, Nb≤0.030%, V≤0.01%, Alt≥0.015%, the remainder being Fe and unavoidable impurities, characterized in that: The thickness of the steel plate is 50mm, the yield strength is ≥550MPa, the tensile strength is 680~820MPa, the elongation after fracture is ≥18%, and the impact energy at -196℃ is ≥80J. The welding process steps include: S1: Bevel processing: V-shaped bevel from the non-flame side, bevel angle 40°±5, 0-3mm blunt edge; S2: Cleaning before welding: Grind the iron oxide scale and rust on the upper and lower surfaces of the groove and the plate near the groove until the metallic luster is exposed, and use anhydrous ethanol or acetone to remove oil and iron filings on the groove and the surrounding area; S3: Test plate assembly: spot weld two test plates together, control the gap at the base of the test plates to 1-2 mm, and fix the two ends of the test plates with arc-starting plates and arc-extinguishing plates; S4: Preheating before welding: Preheat the assembled test pieces before welding; S5: Welding: Submerged arc welding process is adopted, the welding current polarity is AC, the welding material is nickel-based alloy welding material, and the interlayer temperature is controlled; the first pass uses arc welding with a small heat input for base laying, and the second pass uses a heat input lower than the specified value for submerged arc welding. The same welding parameters are used for submerged arc welding from the third pass to the covering pass.

2. The submerged arc welding method of nickel alloy steel 06Ni7DR for low-temperature pressure vessels according to claim 1, characterized in that: The preheating temperature in step S3 is ≥50°C.

3. The submerged arc welding method of nickel alloy steel 06Ni7DR for low-temperature pressure vessels according to claim 1, characterized in that: Step S5 controls the interlayer temperature to be 50-100°C.

4. The submerged arc welding method of nickel alloy steel 06Ni7DR for low-temperature pressure vessels according to claim 1, characterized in that: Step S5, for the welding process with heat input of 15-25kJ / cm, wherein the first welding current is 100-120A, the arc voltage is 20-23V, the welding speed is 12-14cm / min, and the line energy is 10-12kJ / cm, the second welding current is 330-420A, the arc voltage is 29-34V, the welding speed is 42-50cm / min, and the line energy is 12-21kJ / cm, the third to cover passes are 340-450A, the arc voltage is 29-34V, the welding speed is 33-42cm / min, and the line energy is 15-25kJ / cm, and the weld excess height is controlled to be 1-2mm.

5. The submerged arc welding method of nickel alloy steel 06Ni7DR for low-temperature pressure vessels according to claim 1, characterized in that: Step S5, for the welding process with heat input of 26-35kJ / cm, wherein the first welding current is 100-120A, the arc voltage is 20-23V, the welding speed is 12-14cm / min, and the line energy is 10-12kJ / cm; the second welding current is 410-460A, the arc voltage is 31-34V, the welding speed is 37-40cm / min, and the line energy is 19-26kJ / cm; the third to cover passes are welded with a current of 450-560A, an arc voltage of 30-34V, a welding speed of 30-35cm / min, and a line energy of 26-35kJ / cm, and the weld excess height is controlled to be 1-2mm.

6. A submerged arc welding method for nickel alloy steel 06Ni7DR for low-temperature pressure vessels according to claim 4 or 5, characterized in that: The welding rod model is ENiCrMo-6, and the diameter is 3.2mm. The mechanical properties of the welding rod deposited metal are as follows: tensile strength ≥620MPa, yield strength ≥350MPa, elongation ≥32%, and -196℃ impact energy ≥80J; the main chemical components and weight percentages are as follows: C≤0.1%, Si≤1.0%, Mn: 2.0%~4.0%, Cr: 12.0%~17.0%, Mo: 5.0%~9.0%, Ni≥55.0%, W: 1.0%~2.0%, Nb+Ta=0.5%~2.0%, P≤0.02%, S≤0.015%, and the balance is Fe and unavoidable impurities.

7. A submerged arc welding method for nickel alloy steel 06Ni7DR for low-temperature pressure vessels according to claim 4 or 5, characterized in that: The welding wire model is ENiCrMo-4, and the diameter is 2.4 mm. The mechanical properties of the weld metal of the welding wire are as follows: tensile strength ≥690 MPa, yield strength ≥430 MPa, elongation ≥35%, and impact energy at -196°C ≥70 J; the main chemical components and weight percentages are as follows: C≤0.03%, Si≤0.20%, Mn≤1.0%, Cr: 14.5%~16.5%, Mo: 15.0%~17.0%, Ni≥50.0%, W: 3.0%~4.5%, V≤0.35%, Cu≤0.50%, Co≤2.50%, P≤0.03%, S≤0.02%, and the balance is Fe and unavoidable impurities.

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