Rail having excellent fatigue crack propagation resistance characteristics, and method of producing same

Abstract

A rail has excellent fatigue crack propagation resistance characteristics, wherein the rail has a component composition including C: 0.80 to 1.30 mass %, Si: 0.10 to 1.20 mass %, Mn: 0.20 to 1.80 mass %, P: not more than 0.035 mass %, S: 0.0005 to 0.012 mass %, Cr: 0.20 to 2.50 mass % and the remainder being Fe and inevitable impurities and satisfying CP represented by equation (1) being not more than 2500: CP=X/R A   (1) and X ={(10×[% C])+([% Si]/12)+([% Mn]/24)+([% Cr]/21)} 5   (2), where [% Y] is content of an element Y (mass %), and R A is a prior austenite grain size (μm).

1 - 5 . (canceled) 
     
     
         6 . A rail having excellent fatigue crack propagation resistance characteristics, wherein
 the rail has a component composition comprising C: 0.80 to 1.30 mass %, Si: 0.10 to 1.20 mass %, Mn: 0.20 to 1.80 mass %, P: not more than 0.035 mass %, S: 0.0005 to 0.012 mass %, Cr: 0.20 to 2.50 mass % and the remainder being Fe and inevitable impurities and satisfying CP represented by equation (1) being not more than 2500:
     CP=X/R   A   (1) and
 
     X ={(10×[% C])+([% Si]/12)+([% Mn]/24)+([% Cr]/21)} 5   (2),
 
   
       where [% Y] is content of an element Y (mass %), and R A  is a prior austenite grain size (μm). 
     
     
         7 . The rail according to  claim 6 , wherein the component composition further contains at least one selected from V: not more than 0.30 mass %, Cu: not more than 1.0 mass %, Ni: not more than 1.0 mass %, Nb: not more than 0.05 mass %, and Mo: not more than 2.0 mass %. 
     
     
         8 . The rail according to  claim 6 , wherein the component composition further contains at least one selected from Al: not more than 0.07 mass %, W: not more than 1.0 mass %, B: not more than 0.005 mass %, Ti: not more than 0.05 mass %, and Sb: not more than 0.05 mass %. 
     
     
         9 . A method of producing a rail having excellent fatigue crack propagation resistance characteristics, wherein a raw steel material having a component composition according to  claim 6  is heated to not higher than 1350° C. and hot-rolled such that a finish temperature is not lower than 900° C. 
     
     
         10 . The method according to  claim 9 , wherein, after the hot rolling, accelerated cooling is conducted at a cooling rate of 0.4 to 3° C./s from 900° C. to 750° C. and at a cooling rate of 1 to 10° C./s from 750° C. to a cooling stop temperature of 400 to 600° C. 
     
     
         11 . The rail according to  claim 7 , wherein the component composition of the raw steel material further contains at least one selected from Al: not more than 0.07 mass %, W: not more than 1.0 mass %, B: not more than 0.005 mass %, Ti: not more than 0.05 mass %, and Sb: not more than 0.05 mass %. 
     
     
         12 . The method according to  claim 9 , wherein the component composition of the raw steel material further contains at least one selected from V: not more than 0.30 mass %, Cu: not more than 1.0 mass %, Ni: not more than 1.0 mass %, Nb: not more than 0.05 mass %, and Mo: not more than 2.0 mass %. 
     
     
         13 . The method according to  claim 9 , wherein the component composition of the raw steel material further contains at least one selected from Al: not more than 0.07 mass %, W: not more than 1.0 mass %, B: not more than 0.005 mass %, Ti: not more than 0.05 mass %, and Sb: not more than 0.05 mass %. 
     
     
         14 . The method according to  claim 12 , wherein the component composition of the raw steel material further contains at least one selected from Al: not more than 0.07 mass %, W: not more than 1.0 mass %, B: not more than 0.005 mass %, Ti: not more than 0.05 mass %, and Sb: not more than 0.05 mass %. 
     
     
         15 . The method according to  claim 12 , wherein, after the hot rolling, accelerated cooling is conducted at a cooling rate of 0.4 to 3° C./s from 900° C. to 750° C. and at a cooling rate of 1 to 10° C./s from 750° C. to a cooling stop temperature of 400 to 600° C. 
     
     
         16 . The method according to  claim 13 , wherein, after the hot rolling, accelerated cooling is conducted at a cooling rate of 0.4 to 3° C./s from 900° C. to 750° C. and at a cooling rate of 1 to 10° C./s from 750° C. to a cooling stop temperature of 400 to 600° C. 
     
     
         17 . The method according to  claim 14 , wherein, after the hot rolling, accelerated cooling is conducted at a cooling rate of 0.4 to 3° C./s from 900° C. to 750° C. and at a cooling rate of 1 to 10° C./s from 750° C. to a cooling stop temperature of 400 to 600° C.