Method for producing high-carbon steel rails excellent in wear resistance and ductility

Abstract

Disclosed are methods of producing steel rails having a high carbon content and being excellent in wear resistance and ductility from the slabs for rails. One method involves producing a steel rail having a high content of carbon, comprising finish rolling the rail in two consecutive passes, with a reduction rate per pass of a cross-section of the rail of 2-30%, wherein the conditions of the finish rolling satisfy the following relationship: S≦800/(C×T), wherein S is the maximum rolling interval time (seconds), C is the carbon content of the steel, wherein the carbon content is 0.85-1.40 mass %, and T is the maximum surface temperature (° C.) of the rail head. Another method involves producing a steel rail with a high content of carbon, comprising: finish rolling the rail in three or more passes, with a reduction rate per pass of a cross-section of the rail of 2-30%, wherein the conditions of the finish rolling satisfy the following relationship: S≦2400/(C×T×P), wherein S is the maximum rolling interval time (seconds), C is the carbon content of the steel rail, wherein the carbon content is 0.85˜1.40 mass %, T is the maximum surface temperature (° C.) of a rail head, and P is the number of passes, which is 3 or more. In addition to above, controlled additional amounts of V, Nb, N may be added to the steel rail and/or controlled rapid cooling of the rail after rolling may be accomplished to provide further improvements.

1 . A method for producing a steel rail having a high content of carbon, wherein the rail contains, in mass %, 
 C: more than 0.85% but less than or equal to 1.40%,    Si: 0.05 to 2.00%,    Mn: 0.05 to 2.00%,    B: 0.0001 to 0.0050%,    optionally one or more selected from    Cr: 0.05 to 2.00%,    Mo: 0.01 to 0.50%,    Co: 0.003 to 2.00%,    Cu: 0.01 to 1.00%,    Ni: 0.01 to 1.00%,    Ti: 0.0050 to 0.0500%,    Mg: 0.0005 to 0.0200%,    Ca: 0.0005 to 0.0150%,    Al: 0.0100 to 1.00%,    Zr: 0.0001 to 0.2000%,    N: 0.0060 to 0.0200%,    V: 0.005 to 0.500% and    Nb: 0.002 to 0.050%, and    the balance being Fe and unavoidable impurities, comprising:    finish rolling said rail in two consecutive passes, with a reduction rate per pass of a cross-section of said rail of 2-30%,    wherein conditions of said finish rolling satisfy the following relationship:      S≦CPT1    wherein CPT1 is the value expressed by the following expression 1        CPT 1=800/( C×T )  (expression 1)    wherein 
 S is the maximum rolling interval time (seconds), and  
 (C×T) is defined as follows;  
 C is the carbon content of the steel in mass %, and T is the maximum surface temperature (° C.) of a rail head.  
   
   
   
       2 . A method for producing a steel rail having a high content of carbon in mass %, 
 C: more than 0.85% but less than or equal to 1.40%,    Si: 0.05 to 2.00%,    Mn: 0.05 to 2.00%,    B: 0.0001 to 0.0050%,    optionally one or more selected from    Cr: 0.05 to 2.00%,    Mo: 0.01 to 0.50%,    Co: 0.003 to 2.00%,    Cu: 0.01 to 1.00%,    Ni: 0.01 to 1.00%,    Ti: 0.0050 to 0.0500%,    Mg: 0.0005 to 0.0200%,    Ca: 0.0005 to 0.0150%,    Al: 0.0100 to 1.00%,    Zr: 0.0001 to 0.2000%,    N: 0.0060 to 0.0200%,    V: 0.005 to 0.500% and    Nb: 0.002 to 0.050%, and    the balance being Fe and unavoidable impurities, comprising:    finish rolling said rail in three or more passes, with a reduction rate per pass of a cross-section of said rail of 2-30%,    wherein conditions of said finish rolling satisfy the following relationship:      S≦CPT2    wherein CPT2 is the value expressed by the following expression 2,        CPT 2=2400/( C×T×P )  (expression 2)    wherein 
 S is the maximum rolling interval time (seconds), and  
 (C×T×P) is defined as follows;  
 C is the carbon content of the steel rail in mass %, and  
 T is the maximum surface temperature (° C.) of a rail head, and P is the number of passes, which is 3 or more.  
   
   
   
       3 - 12 . (canceled)  
   
   
       13 . The method according to  claim 1 , wherein chemical composition(s) included in said rail meet the following relationship:  
       0.30≧V (mass %)+10×Nb (mass %)+5×N (mass %)≧0.04  
   
   
       14 . The method according to  claim 1 , further comprising: 
 immediately after said finish rolling, cooling the surface of said rail head at a cooling rate of 2-30° C./sec. until the surface temperature reaches 950-750° C.    
   
   
       15 . The method according to  claim 14 , further comprising: 
 after said cooling step, when the temperature of the rail head is more than 700° C., cooling the surface of the rail head at a cooling rate of 2-30° C./sec. until the surface temperature reaches at least 600° C.; and then    allowing the rail to further cool at room temperature.    
   
   
       16 . The method according to  claim 1 , further comprising: 
 after said finish rolling process, when the temperature of the rail head is more than 700° C., cooling the surface of the rail head at a cooling rate of 2-30° C./sec. until the surface temperature reaches at least 600° C., and then    allowing the rail to further cool at room temperature.    
   
   
       17 . The method according to  claim 2 , wherein chemical composition(s) included in said rail meet the following relationship:  
       0.30≧V (mass %)+10×Nb (mass %)+5×N (mass %)≧0.04  
   
   
       18 . The method according to  claim 2 , further comprising: 
 immediately after said finish rolling, cooling the surface of said rail head at a cooling rate of 2-30° C./sec. until the surface temperature reaches 950-750° C.    
   
   
       19 . The method according to  claim 18 , further comprising: 
 after said cooling step, when the temperature of the rail head is more than 700° C., cooling the surface of the rail head at a cooling rate of 2-30° C./sec. until the surface temperature reaches at least 600° C.; and then    allowing the rail to further cool at room temperature.    
   
   
       20 . The method according to  claim 2 , further comprising: 
 after said finish rolling process, when the temperature of the rail head is more than 700° C., cooling the surface of the rail head at a cooling rate of 2-30° C./sec. until the surface temperature reaches at least 600° C., and then    allowing the rail to further cool at room temperature.