Welding material and welding joint

Abstract

There is provided a welding material used for welding of SUS310 stainless steel base metal that contains at least one of Nb and V and is excellent in intergranular corrosion resistance, the chemical composition of the welding material consisting, by mass percent, of C: 0.02% or less, Si: 2% or less, Mn: 2% or less, Cr: 26 to 50%, N: 0.15% or less, P: 0.02% or less, S: 0.002% or less, and Ni: a content percentage satisfying [5NiCr14], and the balance of Fe and impurities. Also, there is provided a welding joint of an austenitic stainless steel, which consists of the base metal and a weld metal formed by using the welding material.

Claims

1. A welding joint of an austenitic stainless steel, consisting of: a base metal of an austenitic stainless steel consisting, by mass percent, of C: 0.02% or less, Si: 0.01 to 0.5%, Mn: 0.01 to 2%, Cr: 24 to 26%, Ni: 18 to 22%, Mo: more than 0.10% and less than 0.50%, N: more than 0.04% and 0.15% or less, P: 0.02% or less, and S: 0.002% or less, and one or two elements of Nb: 0.30% or less and V: 0.40% or less, and the balance of Fe and impurities, and a weld metal formed by using a welding material consisting, by mass percent, of C: 0.02% or less, Si: 2% or less, Mn: 0.51% or less, Cr: 32.10 to 50%, N: 0.15% or less, P: 0.02% or less, 5: 0.002% or less, and Ni: a content satisfying Formula (I), one or more elements selected from Mo: 1% or less, Nb: 0.5% or less, V: 1% or less, and REM: 0.05% or less, and the balance of Fe and impurities:
5NiCr21.64(I)
0.1Nb+V1(II) where each symbol of element in Formulas (I) and (II) represents the content (mass %) of each element contained in the welding material.

2. The welding joint of an austenitic stainless steel according to claim 1, wherein the welding joint is used for PLR pipe or a core material of a boiling water type nuclear power plant.

3. The welding joint of an austenitic stainless steel according to claim 2, wherein the core material is a shroud.

Description

EXAMPLE 1

(1) Two types of austenitic stainless steels each having the chemical compositions shown in Table 1 were melted, hot-forged, hot-rolled, and subjected to solid solution heat treatment at 1060 C. Thereafter, test pieces for restraint weld cracking test having a thickness of 12 mm, a width of 50 mm, and a length of 100 mm, in which a U-type groove having a root radius r of 1.5 mm, a root face b of 1.5 mm, and a groove angle of 40 in No. 14349 of JIS Z3001-1 (2008) and a V-type groove having a root face b of 1 mm and a groove angle of 60 in No. 14343, were prepared. By using the test pieces for restraint weld cracking test obtained as described above, the periphery thereof was subjected to restraint welding onto a commercially available steel plate of SM400C specified in JIS G3106 (2008) having a thickness of 25 mm, a width of 200 mm, and a length of 200 mm by using a covered electrode of ENi6182 specified in JIS Z3224 (2010).

(2) TABLE-US-00001 TABLE 1 Chemical composition (in mass %, balance: Fe and impurities) Base metal C Si Mn P S Cr Ni Nb V Mo N I 0.009 0.21 0.49 0.009 0.001 24.60 19.20 0.05 0.10 0.30 0.10 II 0.007 0.21 0.49 0.011 0.001 24.30 19.70 0.09 0.33 0.08

(3) Thereafter, root pass TIG welding was performed in the grooves by using four types of 1.2 mm-diameter spool welding materials given in Table 2. The heat input was set to 7.2 to 10.8 kJ/cm, and the feed rate of welding material was changed in the range of 316 to 700 mm/min. Subsequently, about a half length of root pass weld zone was left, and the remaining portion was subjected to multi-pass welding under the condition of heat input of 7.2 kJ/cm. At this time, the pass-to-pass temperature was controlled so as to be 150 C. or lower.

(4) After the above-described welding, from each of the test pieces, three test specimens for observing the cross-sectional micro-structure of the joint were sampled from a portion in which the root pass welding had been performed, and three test specimens therefor were sampled from a portion in which multi-pass welding had been performed. The cross section was mirror polished and thereafter was subjected to chromic acid electrolytic etching. Then, the presence of cracks was observed under an optical microscope having a magnification of 500. A crack found in the portion in which only the root pass welding had been performed is thought to be solidification cracking, and a crack found in the portion in which multi-pass welding had been performed is thought to be reheat cracking. Also, the central portion of weld metal sampled from the portion in which only the root pass welding had been performed was subjected to EPMA analysis and quantified, whereby the composition of the weld metal was measured. These results are shown in Tables 3 and 4.

(5) TABLE-US-00002 TABLE 2 Welding Chemical composition (in mass %, balance: Fe and impurities) material C Si Mn P S Cr Ni Nb V Mo N REM.sup. A 0.009 0.20 0.48 0.008 0.001 32.20 11.25 0.08 B 0.008 0.22 0.49 0.008 0.001 32.10 10.46 0.05 0.10 0.31 0.08 C 0.008 0.20 0.51 0.006 0.001 31.50 10.82 0.08 0.013 D 0.011 0.23 0.50 0.026* 0.001 27.25 17.23* 0.10 *indicates that chemical composition does not satisfy the range defined by the present invention. .sup.REM corresponds to La + Ce.

(6) TABLE-US-00003 TABLE 3 Base Welding Weld Groove Heat Solidification Reheat metal material metal No. shape input Feed rate cracking cracking I A A1 U-type 7.2 kJ 316 mm/min 0/3 0/3 Inventive A2 U-type 7.2 kJ 490 mm/min 0/3 0/3 Examples A3 U-type 7.2 kJ 700 mm/min 0/3 0/3 A4 V-type 10.8 kJ 490 mm/min 0/3 0/3 B B1 V-type 10.8 kJ 490 mm/min 0/3 0/3 C C1 V-type 10.8 kJ 490 mm/min 0/3 0/3 D* D1 U-type 7.2 kJ 316 mm/min 1/3 2/3 Comparative D2 U-type 7.2 kJ 490 mm/min 1/3 2/3 Examples D3 U-type 7.2 kJ 700 mm/min 0/3 1/3 D4 V-type 10.8 kJ 490 mm/min 0/3 1/3 II A A5 V-type 10.8 kJ 490 mm/min 0/3 0/3 Inventive B B2 V-type 10.8 kJ 490 mm/min 0/3 0/3 Examples D* D5 U-type 7.2 kJ 490 mm/min 0/3 2/3 Comp. Ex. *indicates that chemical composition does not satisfy the range defined by the present invention.

(7) TABLE-US-00004 TABLE 4 Weld Base Welding metal Chemical composition (in mass % balance: Fe and impurities) metal material No. C Si Mn P S Cr Ni Nb V Mo N REM.sup. I A A1 0.009 0.21 0.49 0.008 0.001 26.54 17.17 0.04 0.07 0.22 0.09 A2 0.009 0.21 0.49 0.008 0.001 27.00 16.69 0.03 0.07 0.21 0.09 A3 0.009 0.21 0.49 0.007 0.001 28.08 15.56 0.03 0.05 0.16 0.09 A4 0.009 0.20 0.48 0.006 0.001 30.03 13.52 0.01 0.03 0.09 0.09 B B1 0.008 0.22 0.49 0.008 0.001 29.93 12.99 0.05 0.1 0.31 0.09 C C1 0.008 0.20 0.50 0.007 0.001 29.43 13.33 0.02 0.03 0.09 0.09 0.010 D* D1 0.009 0.21 0.49 0.012 0.001 25.03 18.88 0.04 0.08 0.25 0.10 D2 0.009 0.21 0.49 0.013 0.001 25.21 18.75 0.04 0.08 0.23 0.10 D3 0.010 0.22 0.49 0.014 0.001 25.45 18.57 0.03 0.07 0.20 0.10 D4 0.011 0.23 0.50 0.023 0.001 25.71 18.23 0.01 0.02 0.06 0.10 II A A5 0.008 0.20 0.48 0.009 0.001 29.91 13.70 0.03 0.10 0.08 B B2 0.008 0.22 0.49 0.009 0.001 29.84 13.14 0.06 0.07 0.32 0.08 D* D5 0.010 0.22 0.50 0.022 0.001 26.39 17.95 0.03 0.10 0.09 *indicates that chemical composition does not satisfy the range defined by the present invention. .sup.REM corresponds to La + Ce.

(8) The numerical value in the columns of solidification cracking and reheat cracking in Table 3 represents the number of test specimens in which the occurrence of cracks was found/the number of test specimens whose cross sections were microscopically observed. Concerning the evaluation of the crack tests conducted in this observation, the weld metal in which the occurrence of at least one crack was found was made unacceptable, and the weld metal in which the occurrence of no crack was found was made acceptable.

(9) When welding materials A to C in which the chemical composition satisfied the definition of the present invention were used, in any test piece, neither solidification cracking nor reheat cracking occurred in the weld metal regardless of welding conditions, whereas when welding material D in which the chemical composition deviated from the definition of the present invention was used, in all test pieces, a weld crack was found in the weld metal.

(10) As is apparent from the above, by using a welding material having a proper chemical composition, a welding joint having excellent solidification crack resistance and reheat crack resistance can be obtained.

INDUSTRIAL APPLICABILITY

(11) Because having excellent intergranular corrosion resistance and weld crack resistance, the welding joint using the welding material for an austenitic stainless steel of the present invention is suitable for a welded structural material that is used as a PLR pipe or a core material such as a shroud, which have risks of corrosion damage at grain boundaries in a nuclear power plant.