Steel for welded structures excellent in high temperature strength and low temperature toughness and method of production of same

Abstract

By heating a steel material comprising C: 0.003 to 0.05%, Si: 0.60% or less, Mn: 0.6 to 2.0%, P: 0.020% or less, S: 0.010% or less, Cr: 0.20 to 1.5%, Nb: 0.005 to 0.05%, Al: 0.060% or less, and N: 0.001 to 0.006%, further limiting, as an impurity, Mo to 0.03% or less, having a balance of iron and unavoidable impurities, and having a weld cracking parameter P CM value defined by P CM =C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B of 0.22% or less, to 1000 to 1300° C. in temperature, finishing the hot rolling at 800° C. or more in temperature, then cooling, steel for welded structures excellent in high temperature strength and low temperature toughness can be inexpensively provided.

1 . A method of production of steel for welded structures excellent in high temperature strength and low temperature toughness characterized by comprising heating a steel material comprising, by mass %,
 C: 0.003 to 0.05%,   Si: 0.60% or less,   Mn: 0.6 to 2.0%,   P: 0.020% or less,   S: 0.010% or less,   Cr: 0.20 to 1.5%,   Nb: 0.005 to 0.05%,   Al: 0.060% or less, and   N: 0.001 to 0.006%,   
       further limiting, as an impurity, Mo to 0.03% or less, having a balance of iron and unavoidable impurities, and having a weld cracking parameter P CM  value defined by
 P CM =C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B of 0.22% or less, to 1000 to 1300° C. in temperature, finishing the hot rolling at a temperature of 800° C. or more, and then cooling. 
 
     
     
         2 . A method of production of steel for welded structures excellent in high temperature strength and low temperature toughness as set forth in  claim 1 , characterized by, after finishing said hot rolling, starting accelerated cooling from 750° C. or more in temperature, and stopping the accelerated cooling at 550° C. or less. 
     
     
         3 . A method of production of steel for welded structures excellent in high temperature strength and low temperature toughness as set forth in  claim 1  characterized by further containing, by mass %, one or both of
 V: 0.01 to 0.10% and 
 Ti: 0.005 to 0.025%. 
 
     
     
         4 . A method of production of steel for welded structures excellent in high temperature strength and low temperature toughness as set forth in  claim 1 , characterized by further containing, by mass %, one or more of
 Ni: 0.05 to 0.50%,   Cu: 0.05 to 0.50%,   B: 0.0002 to 0.003%, and   Mg: 0.0002 to 0.005%.   
     
     
         5 . A method of production of steel for welded structures excellent in high temperature strength and low temperature toughness as set forth in  claim 1 , characterized by further containing, by mass %, one of
 Ca: 0.0005 to 0.004% and   an REM: 0.0005 to 0.008%.   
     
     
         6 . A steel for welded structures excellent in high temperature strength and low temperature toughness characterized by being obtained by heating a steel material comprising, by mass %,
 C: 0.003 to 0.05%,   Si: 0.60% or less,   Mn: 0.6 to 2.0%,   P: 0.020% or less,   S: 0.010% or less,   Cr: 0.20 to 1.5%,   Nb: 0.005 to 0.05%,   Al: 0.060% or less, and   N: 0.001 to 0.006%,   
       further limiting, as an impurity, Mo to 0.03% or less, having a balance of iron and unavoidable impurities, and having a weld cracking parameter P CM  value defined by
 P CM =C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B of 0.22% or less, to 1000 to 1300° C. in temperature, finishing the hot rolling at a temperature of 800° C. or more, and then cooling.