Steel material superior in high temperature strength and toughness and method of production of same

Abstract

A steel material superior in high temperature characteristics and toughness is provided, the fire resistant steel material containing by mass %, C: 0.001% to 0.030%, Si: 0.05% to 0.50%, Mn: 0.40% to 2.00%, Nb: 0.03% to 0.50%, Ti: 0.005% to less than 0.040%, and N: 0.0008% to less than 0.0050%, restricting P: 0.030% or less and S: 0.020% or less, and having a balance of Fe and unavoidable impurities, where the contents of C and Nb satisfy C—Nb/7.74≦0.004, and Ti-based oxides of a grain size of 0.05 to 10 μm are present in a density of 30 to 300/mm 2 .

1 . A steel material superior in high temperature characteristics and toughness characterized by containing
 by mass %,   C: 0.001% to 0.030%,   Si: 0.05% to 0.50%,   Mn: 0.40% to 2.00%,   Nb: 0.03% to 0.50%,   Ti: 0.005% to less than 0.040%, and   N: 0.0008% to less than 0.0050%,   restricting   P: 0.030% or less and   S: 0.020% or less, and   having a balance of Fe and unavoidable impurities, where   the contents of C and Nb satisfy
   C—Nb/7.74≦0.004 
   
     and Ti-based oxides of a grain size of 0.05 to 10 μm are present in a density of 30 to 300/mm 2 . 
   
   
       2 . A steel material superior in high temperature characteristics and toughness as set forth in  claim 1  characterized by containing, by mass %, one or both of
 V: 0.10% or less and   Mo: less than 0.10%.   
   
   
       3 . A steel material superior in high temperature characteristics and toughness as set forth in  claim 1  characterized by containing, by mass %, one or more of
 Zr: 0.03% or less and   Hf: 0.01% or less.   
   
   
       4 . A steel material superior in high temperature characteristics and toughness as set forth in  claim 1  characterized by containing, by mass %, one or more of
 Cr: 1.5% or less,   Cu: 1.0% or less, and   Ni: 1.0% or less.   
   
   
       5 . A steel material superior in high temperature characteristics and toughness as set forth in  claim 1  characterized by containing, by mass %, one or more of
 Mg: 0.005% or less,   Al: 0.030% or less,   REM: 0.01% or less, and   Ca: 0.005% or less.   
   
   
       6 . A steel material superior in high temperature characteristics and toughness as set forth in  claim 1  characterized in that a mass concentration product of Nb and C is 0.0015 or more. 
   
   
       7 . A steel material superior in high temperature characteristics and toughness as set forth in  claim 1  characterized in that the steel material is a fire resistant steel material. 
   
   
       8 . A steel material superior in high temperature characteristics and toughness as set forth in  claim 1  characterized in that the steel material is extremely thick H-section steel with a flange thickness of 40 mm or more. 
   
   
       9 . A method of production of a steel material superior in high temperature characteristics and toughness characterized by adjusting steel comprised of ingredients as set forth in  claim 1  to a solute oxygen of 0.003 to 0.015 mass %, then adding Ti, melting, and casting to obtain a steel slab, and heating this to 1100 to 1350° C. and hot rolling. 
   
   
       10 . A method of production of a steel material superior in high temperature characteristics and toughness as set forth in  claim 9 , characterized by hot rolling by a cumulative reduction rate at 1000° C. and below of 10% or more. 
   
   
       11 . A method of production of a steel material superior in high temperature characteristics and toughness as set forth in  claim 9  characterized by hot rolling, then cooling from 800° C. to 500° C. temperature range by a 0.1 to 10° C./s average cooling speed.