Fire resistant steel and method of production of same

Abstract

The present invention provides first resistant steel superior in fire resistance having less variation in material quality and exhibiting a yield strength of ⅔ or more of that at ordinary temperature even at 600° C. and a method of production of the same, that is, fire resistant steel characterized by containing, by mass %, C: 0.01 to 0.03%, Mn: 0.2 to 1.7%, Si: 0.5% or less, Cu: 0.7 to 2%, Mo: 0.8% or less, Nb: 0.01 to 0.3%, Ti: 0.005 to 0.03%, N: 0.006% or less, B: 0.0003 to 0.003%, V: 0.2% or less, Cr: 1% or less, Al: 0.1% or less, P: 0.03% or less, and S: 0.02% or less, containing Ni by mass ratio of Ni/Cu of 0.6 to 0.9, and comprising a balance of Fe and unavoidable impurities, and having a yield strength at 600° C. of 60% of the yield strength at 21° C.

1 . Fire resistant steel characterized by containing, by mass %,
 C: 0.01 to 0.03%,   Mn: 0.2 to 1.7%,   Si: 0.5% or less,   Cu: 0.7 to 2%,   Mo: 0.8% or less,   Nb: 0.01 to 0.3%,   Ti: 0.005 to 0.03%,   N: 0.006% or less,   B: 0.0003 to 0.003%,   V: 0.2% or less,   Cr: 1% or less,   Al: 0.1% or less,   P: 0.03% or less, and   S: 0.02% or less,   
     containing Ni by mass ratio of Ni/Cu of 0.6 to 0.9, and comprising a balance of Fe and unavoidable impurities, and having a yield strength at 600° C. of 60% of the yield strength at 21° C. 
   
   
       2 . Fire resistant steel as set forth in  claim 1  characterized by further containing, by mass %, one or more of any of
 Ca: 0.0005 to 0.005%,   Mg: 0.0005 to 0.01%, and   REM: 0.0005 to 0.01%,   
     and comprising a balance of Fe and unavoidable impurities. 
   
   
       3 . Fire resistant steel as set forth in  claim 1  or  2  characterized in that said steel material is section steel. 
   
   
       4 . A method of production of fire resistant steel characterized by heating a steel slab containing, by mass %,
 C: 0.01 to 0.03%,   Mn: 0.2 to 1.7%,   Si: 0.5% or less,   Cu: 0.7 to 2%,   Mo: 0.8% or less,   Nb: 0.01 to 0.3%,   Ti: 0.005 to 0.03%,   N: 0.006% or less,   B: 0.0003 to 0.003%,   V: 0.2% or less,   Cr: 1% or less,   Al: 0.1% or less,   P: 0.03% or less, and   S: 0.02% or less,   
     containing Ni by mass ratio of Ni/Cu of 0.6 to 0.9, and comprising a balance of Fe and unavoidable impurities to a temperature range of 200 to 1350° C., then starting rolling and, after finishing rolling, cooling by a cooling rate of an average of 0.1° C./s or more in the temperature range of 800° C. to 500° C. 
   
   
       5 . A method of production of fire resistant steel as set forth in  claim 4 , characterized by heating a steel slab further containing, by mass %,
 Ca: 0.0005 to 0.005%,   Mg: 0.0005 to 0.01%, and   REM: 0.0005 to 0.01%   
     and comprising a balance of Fe and unavoidable impurities to a temperature range of 1200 to 1350° C., then starting rolling and, after finishing rolling, cooling by a cooling rate of an average of 0.1° C./s or more in the temperature range of 800° C. to 500° C. 
   
   
       6 . A method of production of fire resistant steel as set forth in  claim 4  or  5  characterized by rolling to produce section steel.