Rail and method for producing the same

Abstract

A rail includes a foot, a web, and a head. The web has a chemical composition containing C: 0.70 to 1.20 mass%, Si: 0.20 to 1.20 mass%, Mn: 0.20 to 1.50 mass%, P: 0.035 mass% or less, and Cr: 0.20 to 2.50 mass%, with the balance being Fe and incidental impurities. The area fraction of pearlite in the web is 95% or more, and the average size of pearlite blocks is 60 µm or less.

1 . A rail comprising a foot, a web, and a head, wherein the web has a chemical composition comprising: 
 C: 0.70 to 1.20 mass%,   Si: 0.20 to 1.20 mass%,   Mn: 0.20 to 1.50 mass%,   P: 0.035 mass% or less,   S: 0.0005 to 0.012 mass%, and   Cr: 0.20 to 2.50 mass%, with the balance being Fe and incidental impurities,   an area fraction of pearlite in the web is 95% or more, and   an average size of pearlite blocks is 60 µm or less.   
     
     
         2 . The rail according to  claim 1 , wherein the chemical composition further comprises one or two or more selected from Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.05 mass% or less, Mo: 1.0 mass% or less, V: 0.005 to 0.10 mass%, W: 1.0 mass% or less, and B: 0.005 mass% or less. 
     
     
         3 . The rail according to  claim 1 , wherein a crack growth rate da/dN (m/cycle) in the web at a stress intensity factor ΔK = 20 MPa·m ½  is 8.0 × 10 -8  or less. 
     
     
         4 . A rail production method for producing a rail from a slab having the chemical composition according to  claim 1 , the method comprising:
 performing finish rolling at a finishing temperature of 1000° C. or lower in such a manner that a reduction in area of a web is 10% or more; and   after finish rolling, cooling the web at a cooling rate of 1 to 5° C./s from a temperature higher than or equal to a pearlite transformation start temperature to a temperature range of 400° C. to 600° C.   
     
     
         5 . The rail production method according to  claim 4 , wherein the finishing temperature in finish-rolling the web is in a range of 800 to 900° C. 
     
     
         6 . The rail according to  claim 2 , wherein a crack growth rate da/dN (m/cycle) in the web at a stress intensity factor ΔK = 20 MPa·m ½  is 8.0 × 10 -8  or less. 
     
     
         7 . A rail production method for producing a rail from a slab having the chemical composition according to  claim 2 , the method comprising:
 performing finish rolling at a finishing temperature of 1000° C. or lower in such a manner that a reduction in area of a web is 10% or more; and   after finish rolling, cooling the web at a cooling rate of 1 to 5° C./s from a temperature higher than or equal to a pearlite transformation start temperature to a temperature range of 400° C. to 600° C.   
     
     
         8 . The rail production method according to  claim 7 , wherein the finishing temperature in finish-rolling the web is in a range of 800 to 900° C.