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 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. 
     
     
       2. 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 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 than 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 pearlitic 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 steel rail having a good weldability and a good wear resistance according to  claim 3 , wherein said chemical components Si, Cr and Mn satisfy the relation Si+Cr+Mn=1.5 to 3.0% in terms of percent by weight. 
     
     
       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 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 said steel rail temperature reaches 700° to 500° C.; 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. 
     
     
       10. A method for producing a pearlitic steel rail as defined in any of  claims 1  to  6  having a good wear resistance, 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; 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 the temperature of the rail is 700 to 500° C.; and 
 thereafter recuperating heat from within the rail while leaving said steel rail to cool; cool, 
 
       wherein the hardness of said steel rail within the range of depth of 20 mm from the surface of a head portion of said steel rail is at least Hv 320,
 wherein said steel rail comprises, 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 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. 
 
     
     
       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 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 a gage corner portion of said steel rail reaches 700° to 500° C.; and 
 thereafter 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 harness of a head top portion is Hv 250 to 320. 
     
     
       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 
 thereafter 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   thereafter 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 wear resistance, 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, 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 the temperature of the rail is 700 to 500° C.; and   thereafter recuperating heat from within the rail while 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, and   wherein said steel rail comprises, 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 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.   
     
     
       15. A method for producing a pearlitic steel rail having a good weldability and good wear resistance according to claim 14,
 wherein said steel rail comprises a weld joint portion formed by welding a joint portion, and   wherein the difference of hardness between the weld joint portion and base metal in the joint portion prior to welding is not more than Hv 30.   
     
     
       16. A method for producing a pearlitic steel rail having a good weldability and good wear resistance according to claim 14, further comprising welding a joint portion to form a weld joint portion. 
     
     
       17. The method for producing a pearlitic steel rail having a good weldability and good wear resistance according to claim 16,
 wherein the weld joint portion has undergone flash butt welding.   
     
     
       18. A method for producing a pearlitic steel rail having a good weldability and good wear resistance according to claim 10,
 wherein said steel rail comprises a weld joint portion formed by welding a joint portion, and   wherein the difference of hardness between the weld joint portion and base metal in the joint portion prior to welding is not more than Hv 30.   
     
     
       19. A method for producing a pearlitic steel rail having a good weldability and good wear resistance according to claim 10, further comprising welding a joint portion to form a weld joint portion. 
     
     
       20. The method for producing a pearlitic steel rail having a good weldability and good wear resistance according to claim 19,
 wherein the weld joint portion has undergone flash butt welding.   
     
     
       21. A method for producing a pearlitic steel rail, having a good wear resistance, 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, 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 the temperature of the rail is 700 to 500° C.; and   thereafter recuperating heat from within the rail while 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,   wherein said steel rail comprises, 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: 0.05 to 0.50%,   at least one member selected from the group consisting of:
 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 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 the structure of said steel rail is pearlite, a pearlite lamella space in said pearlite is not more than 100 nm, and a ratio of a cementite thickness to a ferrite thickness in said pearlite structure is at least 0.15.   
     
     
       22. A method for producing a pearlitic steel rail, having a good wear resistance, 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, 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 the temperature of the rail is 700 to 500° C.; and   thereafter recuperating heat from within the rail while 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,   wherein said steel rail comprises, 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: 0.05 to 0.50%,   at least one member selected from the group consisting of:
 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 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 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.   
     
     
       23. 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,
 wherein said steel rail comprises, 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,   wherein a head portion of said steel rail does not contain a pro-eutectic cementite structure,   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,   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 more than 10 to 30° C./sec; 
 stopping said accelerated cooling at the point when pearlite transformation of a gage corner portion of said rail has proceeded at 70% and the temperature of rail is 700 to 500° C.; and 
 thereafter recuperating heat from within the rail while leaving said steel rail to cool, 
   wherein said steel rail comprises a weld joint portion formed by welding a joint portion, and   wherein the difference of hardness between the weld joint portion and base metal in the joint portion prior to welding is not more than Hv 30.   
     
     
       24. 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,
 wherein said steel rail comprises, 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,   wherein a head portion of said steel rail does not contain a pro-eutectic cementite structure,   wherein the hardness of a gage corner portion of said steel rail is at least Hv 360 and the hardness of a head top of portion is Hv 250 to 320,   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 more than 10 to 30° C./sec; 
 stopping said accelerated cooling at the point when pearlite transformation of said gage corner portion of said rail has proceeded at 70% and the temperature of rail is 700 to 500° C.; and 
 thereafter recuperating heat from within the rail while leaving said steel rail to cool, 
   wherein said steel rail comprises a weld joint portion formed by welding a joint portion, and   wherein the difference of hardness between the weld joint portion and base metal in the joint portion prior to welding is not more than Hv 30.