Internal high hardness type pearlitic rail with excellent wear resistance, rolling contact fatigue resistance, and delayed fracture property and method for producing same

Abstract

An internal high hardness type pearlitic rail has a composition containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by mass Si, 0.3% to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005% to 0.012% by mass S, 0.2% to 1.3% by mass Cr, 0.005% to 0.12% by mass V, 0.0015% to 0.0060% by mass N, and the balance being Fe and incidental impurities, wherein the value of [% Mn]/[% Cr] is greater than or equal to 0.3 and less than 1.0, where [% Mn] represents the Mn content, and [% Cr] represents the Cr content, and the value of [% V]/[% N] is in the range of 8.0 to 30.0, where [% V] represents the V content, and [% N] represents the N content, and wherein the internal hardness of a rail head is defined by the Vickers hardness of a portion located from a surface layer of the rail head to a depth of at least 25 mm and is greater than or equal to 380 Hv and less than 480 Hv.

1 . An internal high hardness type pearlitic rail comprising a composition containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by mass Si, 0.3% to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005% to 0.012% by mass S, 0.2% to 1.3% by mass Cr, 0.005% to 0.12% by mass V, 0.0015% to 0.0060% by mass N, and the balance being Fe and incidental impurities, wherein [% Mn]/[% Cr] is greater than or equal to 0.3 and less than 1.0, where [% Mn] represents Mn content, and [% Cr] represents Cr content, and [% V]/[% N] is in the range of 8.0 to 30.0, where [% V] represents V content, and [% N] represents N content, and wherein internal hardness of a rail head is defined by Vickers hardness of a portion located from a surface layer of the rail head to a depth of at least 25 mm and is greater than or equal to 380 Hv and less than 480 Hv. 
     
     
         2 . The internal high hardness type pearlitic rail according to  claim 1 , wherein DI calculated from expression (1) is 5.6 to 8.6, and C eq  calculated from expression (2) is 1.04 to 1.27,
     DI =(0.548[% C] 1/2 )×(1+0.64[% Si])×(1+4.1[% Mn])×(1+2.83[% P])×(1−0.62[% S])×(1+2.23[% Cr])×(1+1.82[% V])  (1); and       C   eq =[% C]+([% Si]/11)([% Mn]/7)+([% Cr]/5.8)+[% V]  (2)   
       where [% C] represents C content, [% Si] represents Si content, [% Mn] represents Mn content, [% P] represents P content, [% S] represents S content, [% Cr] represents Cr content, and [% V] represents V content of the composition. 
     
     
         3 . The internal high hardness type pearlitic rail according to  claim 1 , wherein [% Si]+[% Mn]+[% Cr] is 1.55% to 2.50, where [% Si] represents Si content, [% Mn] represents Mn content, and [% Cr] represents Cr content of the composition. 
     
     
         4 . The internal high hardness type pearlitic rail according to  claim 1 , wherein the composition further contains one or more components selected from the group consisting of 1.0% by mass or less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5% by mass or less Mo. 
     
     
         5 . The internal high hardness type pearlitic rail according to  claim 1 , wherein lamellar spacing of a pearlite layer in a portion located from a surface layer of the rail head to a depth of at least 25 mm is 0.04 to 0.15 μm. 
     
     
         6 . A method of producing an internal high hardness type pearlitic rail comprising:
 hot-rolling a steel material having the composition according to  claim 1  to form a rail in such a manner that the finishing rolling temperature is in the range of 850° C. to 950° C.; and   slack-quenching a surface of the rail head from a temperature equal to or higher than a pearlite transformation starting temperature to 400° C. to 650° C. at a cooling rate of 1.2 to 5° C./s.   
     
     
         7 . The internal high hardness type pearlitic rail according to  claim 2 , wherein [% Si]+[% Mn]+[% Cr] is 1.55% to 2.50, where [% Si] represents Si content, [% Mn] represents Mn content, and [% Cr] represents Cr content of the composition. 
     
     
         8 . The internal high hardness type pearlitic rail according to  claim 2 , wherein the composition further contains one or more components selected from the group consisting of 1.0% by mass or less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5% by mass or less Mo. 
     
     
         9 . The internal high hardness type pearlitic rail according to  claim 3 , wherein the composition further contains one or more components selected from the group consisting of 1.0% by mass or less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5% by mass or less Mo. 
     
     
         10 . The internal high hardness type pearlitic rail according to  claim 7 , wherein the composition further contains one or more components selected from the group consisting of 1.0% by mass or less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5% by mass or less Mo. 
     
     
         11 . The internal high hardness type pearlitic rail according to  claim 2 , wherein lamellar spacing of a pearlite layer in a portion located from a surface layer of the rail head to a depth of at least 25 mm is 0.04 to 0.15 μm. 
     
     
         12 . The internal high hardness type pearlitic rail according to  claim 3 , wherein lamellar spacing of a pearlite layer in a portion located from a surface layer of the rail head to a depth of at least 25 mm is 0.04 to 0.15 μm. 
     
     
         13 . The internal high hardness type pearlitic rail according to  claim 4 , wherein lamellar spacing of a pearlite layer in a portion located from a surface layer of the rail head to a depth of at least 25 mm is 0.04 to 0.15 μm. 
     
     
         14 . The internal high hardness type pearlitic rail according to  claim 7 , wherein lamellar spacing of a pearlite layer in a portion located from a surface layer of the rail head to a depth of at least 25 mm is 0.04 to 0.15 μm. 
     
     
         15 . The internal high hardness type pearlitic rail according to  claim 10 , wherein lamellar spacing of a pearlite layer in a portion located from a surface layer of the rail head to a depth of at least 25 mm is 0.04 to 0.15 μm.