HIGH-Ni ALLOY THICK STEEL PLATE HAVING EXCELLENT WELD HIGH-TEMPERATURE CRACKING RESISTANCE, AND METHOD FOR PRODUCING SAME

Abstract

A high-Ni alloy steel plate excellent in weld hot cracking resistance includes in mass %: C≤0.15%, Si: 0.05-1.0%, Mn: 0.05-2.0%, P≤0.035%, S≤0.0015%, Cr: 16-28%, Ni: 18-65%, Al: 0.01-1.0%, Ti: 0.15-1.5%, B: 0.0002-0.0030%, N≤0.05%, O≤0.003%, Mo: 0.01-10%, Cu: 0.01-4.0%, Co: 0.01-3.0%, V: 0.01-0.5%, Mg≤0.0050%; and a balance consisting of Fe and impurities, in which a grain size number G defined by JIS G0552 is 1.0 or more and a standard deviation of a concentration distribution of solid solute Ti in a thickness direction is 0.045% or less. A manufacturing method of a high-Ni alloy steel plate excellent in weld hot cracking resistance includes conducting a high-temperature long-time heat treatment at a temperature of 1200 degrees C. or more for eight hours or more in a step prior to a final hot rolling.

1 . A high-Ni alloy thick steel plate excellent in weld hot cracking resistance, comprising, in mass %:
 C: 0.15% or less, Si: 0.05 to 1.0%, Mn: 0.05 to 2.0%, P: 0.035% or less, S: 0.0015% or less, Cr: 16 to 28%, Ni: 18 to 65%, Al: 0.01 to 1.0%, Ti: 0.15 to 1.5%, B: 0.0002 to 0.0030%, N: 0.05% or less, O: 0.003% or less, Mo: 0.01 to 10%, Cu: 0.01 to 4.0%, Co: 0.01 to 3.0%, V: 0.01 to 0.5%, Mg: 0.0050% or less; and a balance consisting of Fe and impurities, wherein   a grain size number G defined by JIS G0552 is 1.0 or more and a standard deviation of a concentration distribution of solid solute Ti in a thickness direction is 0.045% or less.   
     
     
         2 . The high-Ni alloy thick steel plate excellent in weld hot cracking resistance according to  claim 1 , further comprising, in mass %, in place of a part of Fe, one or two elements selected from the group consisting of A group and B group below: 
       A group:
 one or more of Ca: 0.0003 to 0.0050%, Sn: 0.0001 to 0.05%, Zn+Pb+Bi: 0.0010% or less, Zr: 0.0001 to 0.5%, Hf: 0.0001 to 0.5%, and La+Ce+Nd+Pr: 0.0001 to 0.0050%; and 
 
       B group:
 one or more of W: 0.01 to 3.0%, Nb: 0.001 to 4.0%, and Ta: 0.001 to 1.0%. 
 
     
     
         3 . The high-Ni alloy thick steel plate excellent in weld hot cracking resistance according to  claim 1 , wherein the high-Ni alloy thick steel plate is used in a welded structure. 
     
     
         4 . A manufacturing method of the high-Ni alloy thick steel plate excellent in weld hot cracking resistance according to  claim 1 , the method comprising:
 preparing a steel ingot produced by continuous cast and having a thickness of 160 mm or more and a ratio of a slab thickness to a product thickness being 3.0 or more; and   conducting a high-temperature long-time heat treatment at a temperature of 1200 degrees C. or more for eight hours or more in a step prior to a final hot rolling.   
     
     
         5 . A manufacturing method of the high-Ni alloy thick steel plate excellent in weld hot cracking resistance according to  claim 3 , the method comprising:
 preparing a steel ingot produced by continuous cast and having a thickness of 160 mm or more and a ratio of a slab thickness to a product thickness being 3.0 or more; and   conducting a high-temperature long-time heat treatment at a temperature of 1200 degrees C. or more for eight hours or more in a step prior to a final hot rolling.   
     
     
         6 . The high-Ni alloy thick steel plate excellent in weld hot cracking resistance according to  claim 2 , the high-Ni alloy thick steel plate is used in a welded structure. 
     
     
         7 . A manufacturing method of the high-Ni alloy thick steel plate excellent in weld hot cracking resistance according to  claim 2 , the method comprising:
 preparing a steel ingot produced by continuous cast and having a thickness of 160 mm or more and a ratio of a slab thickness to a product thickness being 3.0 or more; and   conducting a high-temperature long-time heat treatment at a temperature of 1200 degrees C. or more for eight hours or more in a step prior to a final hot rolling.   
     
     
         8 . A manufacturing method of the high-Ni alloy thick steel plate excellent in weld hot cracking resistance according to  claim 6 , the method comprising:
 preparing a steel ingot produced by continuous cast and having a thickness of 160 mm or more and a ratio of a slab thickness to a product thickness being 3.0 or more; and   conducting a high-temperature long-time heat treatment at a temperature of 1200 degrees C. or more for eight hours or more in a step prior to a final hot rolling.