Pearlitic steel rail having excellent wear resistance and method of producing the same

Abstract

This invention is directed to improve a wear resistance and a damage resistance required for a rail of a sharply curved zone of a heavy load railway, comprising more than 0.85 to 1.20% of C, 0.10 to 1.00% of Si, 0.40 to 1.50% of Mn and if necessary, at least one member selected from the group consisting of Cr, Mo, V, Nb, Co and B, and retaining high temperature of hot rolling or a steel rail heated to a high temperature for the purpose of heat-treatment, the present invention provides a pearlitic steel rail having a good wear resistance and a good damage resistance, and a method of producing the same, wherein a head portion of the steel rail is acceleratedly cooled at a rate of 1° to 10° C./sec from an austenite zone temperature to a cooling stop temperature of 700° to 500° C. so that the hardness of the head portion is at least Hv 320 within the range of a 20 mm depth.

1. A pearlitic steel rail, having a good wear resistance, comprising more than 0.85 to 1.20%, in terms of percent by weight, of carbon, characterized in that the structure of said steel rail is a pearlite, a pearlitic lamella space of said pearlite is not more than 100 nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite is at least 0.15. 
     
     
       2. A pearlite steel rail, having a good wear resistance, comprising more than 0.85 to 1.20%, in terms of percent by weight, of carbon, characterized in that the structure within the range of a depth of 20 mm from the surface of a rail head portion of said steel rail with said head surface being the start point is pearlite, a pearlite lamella space of said pearlite is not more than 100 nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite is at least 0.15. 
     
     
       3. A pearlite type steel rail, having a good wear resistance, comprising, in terms of percent by weight:
 C: more than 0.85 to 1.20%    Si: 0.10 to 1.00%    Mn: 0.40 to 1.50%, and    the balance consisting of iron and unavoidable impurities, said steel rail characterized in that the structure of said steel rail is pearlite, a pearlite lamella space of said pearlite is not more than 100 nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite is at least 0.15.    
     
     
       4. A pearlitic steel rail, having a good wear resistance, comprising, in terms of percent by weight:
 C: more than 0.85 to 1.20%    Si: 0.10 to 1.00%    Mn: 0.40 to 1.50%, and    the balance consisting of iron and unavoidable impurities, said steel rail characterized in that the structure within the range of a depth of 20 mm from the surface of a rail head portion of said steel rail with said head surface being the start point is pearlite, a pearlite lamella space of said pearlite is not more than 100 nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite is at least 0.15.    
     
     
       5. A pearlitic steel rail having a good wear resistance, comprising, in terms of percent by weight:
 C: more than 0.85 to 1.20%    Si: 0.10 to 1.00%    Mn: 0.40 to 1.50%,    at least one member selected from the group consisting of: 
 Cr: 0.05 to 0.50%,  
 Mo: 0.01 to 0.20%,  
 V: 0.02 to 0.30%.,  
 Nb: 0.002 to 0.05%,  
 Co: 0.10 to 2.00%,  
 B: 0.0005 to 0.005%, and  
 the balance consisting of iron and unavoidable impurities,  
   
       said steel rail characterized in that the structure of said steel rail is pearlite, a pearlite lamella space in said pearlite is not more that 100 nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite structure is at least 0.15. 
     
     
       6. A pearlitic steel rail having a good wear resistance, comprising, in terms of percent by weight:
 C: more than 0.85 to 1.20%,    Si: 0.10 to 1.00%,    Mn: 0.40 to 1.50%,    at least one member selected from the group consisting of: 
 Cr: 0.05 to 0.50%,  
 Mo: 0.01 to 0.20%,  
 V: 0.02 to 0.30%.,  
 Nb: 0.002 to 0.05%,  
 Co: 0.10 to 2.00%,  
 B: 0.0005 to 0.005%, and  
 the balance consisting of iron and unavoidable impurities,  
   
       said steel rail characterized in that the structure within the range of a depth of 20 mm from the surface of a rail head portion of said steel rail with said head surface being the start point is pearlite, a pearlite lamella space of said pearlite is not more than 100 nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite is at least 0.15. 
     
     
       7. A pearlite steel rail having a good weldability and a high wear resistance according to  claim 1 , wherein the difference of hardness between a weld joint portion and a base metal is not more than Hv 30. 
     
     
       8. A pearlite type  pearlitic steel rail, having a good weldability and a good wear resistance according to  claim 3 ,  resistance, wherein a structure of said steel rail is pearlite, a pearlite lamella space of said pearlite is not more than  100  nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite is at least  0 . 15 , 
       
         said steel rail comprising, in terms of percent by weight:  
           C:  0 . 86  to  1 . 20   % ,    
           Si:  0 . 10  to  1 . 00   % ,    
           Mn:  0 . 40  to  1 . 50   % ,    
         whereinCr and the balance consisting of iron and unavoidable impurities, 
         said chemical components Si, Cr and Mn satisfy the relation Si+Cr+Mn=1.5 to 3.0% in terms of percent by weight and wherein a head portion of said steel rail does not contain a pro- eutectic cementite structure.    
       
     
     
       9. A method for producing a pearlitic steel rail as defined in any of  claims 1  to  6  ,
 said method comprising the steps of:  
 hot rolling a melted and cast steel to provide a steel rail, with said steel rail retaining rolling heat immediately after hot rolling;  
 cooling in an accelerated manner said steel retaining rolling heat immediately after hot rolling or cooling in an accelerated manner said steel rail heated for heat treatment , said accelerated cooling taking place from an austenite temperature at a cooling rate of 1° to 10° C./sec;  
 stopping said accelerated cooling at the point when said steel rail temperature reaches 700° to 500° C.; and  
 thereafter leaving said steel rail to cool;  
 wherein said steel rail has a head portion and the hardness of said steel rail within the range of a depth of 20 mm from the  a surface of a  said head portion of said steel rail is at least Hv  320 and wherein said steel comprises:    
     0 . 86  to  1 . 20   % , in terms of percent by weight, of carbon, characterized in that the structure of said steel rail is a pearlite, a pearlite lamella space of not more than  100  nm, and with a ratio of a cementite thickness to a ferrite thickness in said pearlite of at least  0 . 15 , and wherein said head portion does not contain a pro - eutectic cementite structure.   
 
     
     
       10. A method for producing a pearlitic steel rail as defined in any of  claims 1  to  6 , said method comprising the steps of:
 hot rolling a melted and cast steel to provide a steel rail, with said steel rail retaining rolling heat immediately after hot rolling;    cooling in an accelerated manner said steel rail retaining rolling heat immediately after hot rolling or cooling in an accelerated manner said steel rail heated for heat treatment, said accelerated cooling taking place from an austenite temperature at a cooling rate of more than 10° C./sec and up to 30° C./sec;    stopping said accelerated cooling at the point when pearlite transformation of said steel rail has proceeded at least 70%; and    thereafter leaving said steel rail to cool;    
       wherein the hardness of said steel rail within the range of a depth of 20 mm from the surface of a head portion of said steel rail is at least Hv 320. 
     
     
       11. A method for producing a pearlitic steel rail as defined in any of  claims 1  to  6 ,
 said method comprising the steps of:  
 hot rolling a melted and cast steel to provide a steel rail, with said steel rail retaining rolling heat immediately after hot rolling;  
 cooling in an accelerated manner said steel retaining rolling heat immediately after hot rolling or cooling in an accelerated manner said steel rail heated for heat treatment , said accelerated cooling taking place from an austenite temperature at a cooling rate of 1° to 10° C./sec:  
 stopping said accelerated cooling at the point when the temperature of a gage corner portion of said steel rail reaches 700° to 500° C.; and  
 thereafter leaving said steel rail to cool;  
 wherein said steel rail has a head portion and the hardness of said gage corner portion of said steel rail is at least Hv 360 and the harness  hardness of a head top portion is Hv 250 to 320 and wherein said steel comprises:  
     0 . 86  to  1 . 20   % , in terms of percent by weight, of carbon, characterized in that the structure of said steel rail is a pearlite, a pearlite lamella space of not more than  100  nm, and with a ratio of a cementite thickness to a ferrite thickness in said pearlite of at least  0 . 15 , and wherein said head portion does not contain a pro - eutectic cementite structure.   
 
     
     
       12. A method for producing a pearlitic steel rail as defined in any of  claims 1  to  6 , said method comprising the steps of:
 hot rolling a melted and cast steel to provide a steel rail, with said steel rail retaining rolling heat immediately after hot rolling;    cooling in an accelerated manner said steel rail retaining rolling heat immediately after hot rolling or cooling in an accelerated manner said steel rail heated for heat treatment, said accelerated cooling taking place from an austenite temperature at a cooling rate of more than 10° C./sec and up to 30° C./sec.;    stopping said accelerated cooling at the point when pearlite transformation of a gage corner portion of said steel rail has proceeded at least 70%; and    trereafter leaving said steel rail to cool;    
       wherein the hardness of said gage corner portion of said steel rail is at least Hv 360 and the hardness of a head top portion is Hv 250 to 320. 
     
     
       13. A method for producing a pearlitic steel rail as defined in  claim 8 , said method comprising the steps of:
 hot rolling a melted and cast steel to provide a steel rail, with said steel rail retaining rolling heat immediately after hot rolling;    cooling in an accelerated manner said steel rail retaining rolling heat immediately after hot rolling or cooling in an accelerated manner said steel rail heated for heat treatment, said accelerated cooling taking place from an austenite temperature at a cooling rate of 1° to 10° C./sec.;    stopping said accelerated cooling at the point when the temperature of said rail reaches 700° to 500° C.; and    trereafter leaving said steel rail to cool;    
       wherein the hardness within the range of a depth of 20 mm from the surface of a head portion of said steel rail is at least Hv 320. 
     
     
       14. A method for producing a pearlitic steel rail having a good weldability and good wear resistance according to  claim 9  or  11 , wherein said steel rail is cooled in an accelerated manner only by air. 
     
     
       15. The pearlitic steel rail, having a good weldability and a good wear resistance according to  claim 8 , wherein the content of Mn is,
 Mn: 0.40 to 0.98% ,      
       in terms of percent by weight. 
     
     
       16. The pearlitic steel rail, having a good weldability and a good wear resistance according to  claim 8 , wherein the difference of hardness between a weld joint portion and a base metal is not more than Hv  30 . 
     
     
       17. The pearlitic steel rail, having a good weldability and a good wear resistance according to  claim 8 , comprising a weld joint portion. 
     
     
       18. The pearlitic steel rail, having a good weldability and a good wear resistance according to  claim 17 , wherein the weld joint portion has undergone flash butt welding. 
     
     
       19. A method for producing a pearlitic steel rail having a good weldability and good wear resistance according to  claim 9  or  11 , wherein the difference of hardness between a weld joint portion and a base metal is not more than Hv  30 . 
     
     
       20. A method for producing a pearlitic steel rail having a good weldability and good wear resistance according to  claim 9  or  11 , further comprising welding a joint portion to form a weld joint portion. 
     
     
       21. The method for producing a pearlitic steel rail having a good weldability and good wear resistance according to  claim 20 , wherein the weld joint portion has undergone flash butt welding. 
     
     
       22. A pearlitic steel rail, having a good weldability and a good wear resistance, wherein a structure of said steel rail is pearlite, a pearlite lamella space of said pearlite is not more than  100  nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite is at least  0 . 15 , 
       
         said steel rail comprising, in terms of percent by weight:  
           C:  0 . 86  to  1 . 20   % ,    
           Si:  0 . 10  to  1 . 00   % ,    
           Mn:  0 . 40  to  1 . 50   % ,    
         
           Cr and the balance consisting of iron and unavoidable impurities,  
         
           said chemical components Si, Cr and Mn satisfy the relation Si+Cr+Mn= 1 . 5  to  3 . 0   %  in terms of percent by weight and wherein a head portion of said steel rail does not contain a pro - eutectic cementite structure,    
         
           and wherein said pearlitic steel rail is prepared in a process comprising:  
           
             cooling in an accelerated manner said steel rail retaining rolling heat immediately after hot rolling, said accelerated cooling taking place from an austenite temperature at a cooling rate of  1 ° to  10 ° C./sec;  
           
           
             stopping said accelerated cooling at the point when said steel rail temperature reaches  700 ° C. to  500 ° C.