Pealite base rail excellent in wear resistance and ductility and method for production thereof

Abstract

The present invention is: a pearlitic steel rail excellent in wear resistance and ductility, characterized in that, in a steel rail having pearlite structure containing, in mass, 0.65 to 1.40% C, the number of the pearlite blocks having grain sizes in the range from 1 to 15 μm is 200 or more per 0.2 mm 2 of an observation field at least in a part of the region down to a depth of 10 mm from the surface of the corners and top of the head portion; and a method for producing a pearlitic steel rail excellent in wear resistance and ductility, characterized by, in the hot rolling of said steel rail, applying finish rolling so that the temperature of the rail surface may be in the range from 850° C. to 1,000° C. and the sectional area reduction ratio at the final pass may be 6% or more, and then applying accelerated cooling to the head portion of said rail at a cooling rate in the range from 1 to 30° C./sec. from the austenite temperature range to at least 550° C.

1 . A pearlitic steel rail excellent in wear resistance and ductility, characterized in that, in a steel rail having pearlite structures containing, in mass, 0.65 to 1.40% C, the number of the pearlite blocks having grain sizes in the range from 1 to 15 μm is 200 or more per 0.2 mm 2  of observation field at least in a part of the region down to a depth of 10 mm from the surface of the corners and top of the head portion.  
     
     
         2 . A pearlitic steel rail excellent in wear resistance and ductility, characterized in that, in a steel rail having pearlite structures containing, in mass, 0.65 to 1.40% C, 0.05 to 2.00% Si, and 0.05 to 2.00% Mn, the number of the pearlite blocks having grain sizes in the range from 1 to 15 μm is 200 or more per 0.2 mm 2  of observation field at least in a part of the region down to a depth of 10 mm from the surface of the corners and top of the head portion.  
     
     
         3 . A pearlitic steel rail excellent in wear resistance and ductility, characterized in that, in a steel rail having pearlite structures containing, in mass, 0.65 to 1.40% C, 0.05 to 2.00% Si, 0.05 to 2.00% Mn, and 0.05 to 2.00% Cr, the number of the pearlite blocks having grain sizes in the range from 1 to 15 μm is 200 or more per 0.2 mM 2  of observation field at least in a part of the region down to a depth of 10 mm from the surface of the corners and top of the head portion.  
     
     
         4 . A pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 1  to  3 , characterized in that the C content of the steel rail is over 0.85 to 1.40%.  
     
     
         5 . A pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 1  to  4 , characterized in that the length of the rail after hot rolling is 100 to 200 m.  
     
     
         6 . A pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 1  to  5 , characterized in that the hardness in the region down to a depth of at least 20 mm from the surface of the corners and top of the head portion is in the range from 300 to 500 Hv.  
     
     
         7 . A pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 1  to  6 , characterized by further containing, in mass, 0.01 to 0.50% Mo.  
     
     
         8 . A pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 1  to  7 , characterized by further containing, in mass, one or more of 0.005 to 0.50% V, 0.002 to 0.050% Nb, 0.0001 to 0.0050% B, 0.10 to 2.00% Co, 0.05 to 1.00% Cu, 0.05 to 1.00% Ni, and 0.0040 to 0.0200% N.  
     
     
         9 . A pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 1  to  8 , characterized by further containing, in mass, one or more of 0.0050 to 0.0500% Ti, 0.0005 to 0.0200% Mg, 0.0005 to 0.0150% Ca, 0.0080 to 1.00% Al, and 0.0001 to 0.2000% Zr.  
     
     
         10 . A pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 4  to  9 , characterized by reducing the amount of pro-eutectoid cementite structures forming in the web portion of the rail so that the number of the pro-eutectoid cementite network intersecting two line segments each 300 μm in length crossing each other at right angles (the number of intersecting pro-eutectoid cementite network, NC) at the center of the centerline in the web portion of the rail may satisfy the expression NC≦CE in relation to the value of CE defined by the following equation (1):  
         CE= 60([mass % C])+10([mass % Si])+10([mass % Mn])+500([mass % P])+50([mass % S])+30([mass % Cr])+50   (1).  
     
     
         11 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility, characterized by, in the hot rolling of a steel rail containing 0.65 to 1.40 mass % C: applying finish rolling so that the temperature of the rail surface may be in the range from 850° C. to 1,000° C. and the sectional area reduction ratio at the final pass may be 6% or more; then applying accelerated cooling to the head portion of said rail at a cooling rate in the range from 1 to 30° C./sec. from the austenite temperature range to a temperature not higher than 550° C.; and controlling the number of the pearlite blocks having grain sizes in the range from 1 to 15 μm so as to be 200 or more per 0.2 mm 2  of observation field at least in a part of the region down to a depth of 10 mm from the surface of the corners and top of the head portion.  
     
     
         12 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility, characterized by, in the hot rolling of a steel rail containing, in mass, 0.65 to 1.40% C, 0.05 to 2.00% Si, and 0.05 to 2.00% Mn: applying finish rolling so that the temperature of the rail surface may be in the range from 850° C. to 1,000° C. and the sectional area reduction ratio at the final pass may be 6% or more; then applying accelerated cooling to the head portion of said rail at a cooling rate in the range from 1 to 30° C./sec. from the austenite temperature range to a temperature not higher than 550° C.; and controlling the number of the pearlite blocks having grain sizes in the range from 1 to 15 μm so as to be 200 or more per 0.2 mm 2  of observation field at least in a part of the region down to a depth of 10 mm from the surface of the corners and top of the head portion.  
     
     
         13 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility, characterized by, in the hot rolling of a steel rail containing, in mass, 0.65 to 1.40% C, 0.05 to 2.00% Si, 0.05 to 2.00% Mn, and 0.05 to 2.00% Cr: applying finish rolling so that the temperature of the rail surface may be in the range from 850° C. to 1,000° C. and the sectional area reduction ratio at the final pass may be 6% or more; then applying accelerated cooling to the head portion of said rail at a cooling rate in the range from 1 to 30° C./sec. from the austenite temperature range to a temperature not higher than 550° C.; and controlling the number of the pearlite blocks having grain sizes in the range from 1 to 15 μm so as to be 200 or more per 0.2 mm 2  of observation field at least in a part of the region down to a depth of 10 mm from the surface of the corners and top of the head portion.  
     
     
         14 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  13 , characterized in that, at the finish rolling in the hot rolling of said steel rail, continuous finish rolling is applied so that two or more rolling passes may be applied at a sectional area reduction ratio of 1 to 30% per pass and the time period between the passes may be 10 sec. or less.  
     
     
         15 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  13 , characterized by applying accelerated cooling to the head portion of said rail at a cooling rate in the range from 1 to 30° C./sec. from the austenite temperature range to a temperature not higher than 550° C. within 200 sec. after the end of the finish rolling in the hot rolling of said steel rail.  
     
     
         16 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  13 , characterized by applying accelerated cooling within 200 sec. after the end of the finish rolling in the hot rolling of said steel rail: to the head portion of said rail at a cooling rate in the range from 1 to 30° C./sec. from the austenite temperature range to a temperature not higher than 550° C.; and to the web and base portions of said rail at a cooling rate in the range from 1 to 10° C./sec. from the austenite temperature range to a temperature not higher than 650° C.  
     
     
         17 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by, in a reheating process for a bloom or slab containing aforementioned steel composition, reheating said bloom or slab so that: the maximum heating temperature (Tmax, ° C.) of said bloom or slab may satisfy the expression Tmax≦CT in relation to the value of CT defined by the following equation (2) composed of the carbon content of said bloom or slab; and the retention time (Mmax, min.) of said bloom or slab after said bloom or slab is heated to a temperature of 1,100° C. or above may satisfy the expression Mmax≦CM in relation to the value of CM defined by the following equation (3) composed of the carbon content of said bloom or slab:  
         CT= 1,500−140([mass % C])−80([mass % C]) 2    (2),  CM= 600−120([mass % C])−60([mass % C]) 2    (3).  
     
     
         18 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by applying accelerated cooling, after hot-rolling a bloom or slab containing aforementioned steel composition into the shape of a rail: within 60 sec. after the hot rolling, to the base toe portions of said steel rail at a cooling rate in the range from 5 to 20° C./sec. from the austenite temperature range to a temperature not higher than 650° C.; and to the head, web and base portions of said steel rail at a cooling rate in the range from 1 to 10° C./sec. from the austenite temperature range to a temperature not higher than 650° C.  
     
     
         19 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by applying accelerated cooling, after hot-rolling a bloom or slab containing aforementioned steel composition into the shape of a rail: within 100 sec. after the hot rolling, to the web portion of said steel rail at a cooling rate in the range from 2 to 20° C./sec. from the austenite temperature range to a temperature not higher than 650° C.; and to the head and base portions of said steel rail at a cooling rate in the range from 1 to 10° C./sec. from the austenite temperature range to a temperature not higher than 650° C.  
     
     
         20 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by applying accelerated cooling, after hot-rolling a bloom or slab containing aforementioned steel composition into the shape of a rail: within 60 sec. after the hot rolling, to the base toe portions of said steel rail at a cooling rate in the range from 5 to 20° C./sec. from the austenite temperature range to a temperature not higher than 650° C.; within 100 sec. after the hot rolling, to the web portion of said steel rail at a cooling rate in the range from 2 to 20° C./sec. from the austenite temperature range to a temperature not higher than 650° C.; and to the head and base portions of said steel rail at a cooling rate in the range from 1 to 10° C./sec. from the austenite temperature range to a temperature not higher than 650° C.  
     
     
         21 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by, after hot-rolling a bloom or slab containing aforementioned steel composition into the shape of a rail: within 60 sec. after the hot rolling, raising the temperature at the base toe portions of said steel rail to a temperature 50° C. to 100° C. higher than the temperature before the temperature rising; and also applying accelerated cooling to the head, web and base portions of said steel rail at a cooling rate in the range from 1 to 10° C./sec. from the austenite temperature range to a temperature not higher than 650° C.  
     
     
         22 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by, after hot-rolling a bloom or slab containing aforementioned steel composition into the shape of a rail: within 100 sec. after the hot rolling, raising the temperature at the web portion of said steel rail to a temperature 20° C. to 100° C. higher than the temperature before the temperature rising; and also applying accelerated cooling to the head, web and base portions of said steel rail at a cooling rate in the range from 1 to 10° C./sec. from the austenite temperature range to a temperature not higher than 650° C.  
     
     
         23 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by, after hot-rolling a bloom or slab containing aforementioned steel composition into the shape of a rail: within 60 sec. after the hot rolling, raising the temperature at the base toe portions of said steel rail to a temperature 20° C. to 100° C. higher than the temperature before the temperature rising; within 100 sec. after the hot rolling, raising the temperature at the web portion of said steel rail to a temperature 20° C. to 100° C. higher than the temperature before the temperature rising; and also applying accelerated cooling to the head, web and base portions of said steel rail at a cooling rate in the range from 1 to 10° C./sec. from the austenite temperature range to a temperature not higher than 650° C.  
     
     
         24 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by, in the event of acceleratedly cooling the head portion of said steel rail from the austenite temperature range, applying the accelerated cooling so that the cooling rate (ICR, ° C./sec.) in the temperature range from 750° C. to 650° C. at a head inner portion 30 mm in depth from the head top surface of said steel rail satisfy the expression ICR≧CCR in relation to the value of CCR defined by the following equation (4) composed of the chemical composition of said steel rail:  
         CCR= 0.6+10×([% C]−0.9)−5×([% C]−0.9)×[% Si]−0.17[% Mn]−0.13[% Cr]  (4).  
     
     
         25 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  16 , characterized by, in the event of acceleratedly cooling the head portion of said steel rail from the austenite temperature range, applying the accelerated cooling so that the value of TCR defined by the following equation (5) composed of the respective cooling rates in the temperature range from 750° C. to 500° C. at the surfaces of the head top portion (TH, ° C./sec.), the head side portions (TS, ° C./sec.) and the lower chin portions (TJ, ° C./sec.) of said steel rail satisfy the expression 4CCR≧TCR≧2CCR in relation to the value of CCR defined by the following equation (4) composed of the chemical composition of said steel rail:  
         CCR= 0.6+10×([% C]−0.9)−5×([% C]−0.9)×[% Si]−0.17[% Mn]−0.13[% Cr]  (4),  TCR= 0.05 TH (° C./sec.)+0.10 TS (° C./sec.)+0.50 TJ (° C./sec.)   (5).  
     
     
         26 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  25 , characterized in that the C content of the steel rail is 0.85 to 1.40%.  
     
     
         27 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  26 , characterized in that the length of the rail after hot rolling is 100 to 200 m.  
     
     
         28 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  27 , characterized in that the hardness in the region down to a depth of at least 20 mm from the surface of the corners and top of the head portion of a pearlitic steel rail according to any one of  claims 1  to  10  is in the range from 300 to 500 Hv.  
     
     
         29 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  28 , characterized in that the steel rail further contains, in mass, 0.01 to 0.50% Mo.  
     
     
         30 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  29 , characterized in that the steel rail further contains, in mass, one or more of 0.005 to 0.50% V, 0.002 to 0.050% Nb, 0.0001 to 0.0050% B, 0.10 to 2.00% Co, 0.05 to 1.00% Cu, 0.05 to 1.00% Ni, and 0.0040 to 0.0200% N.  
     
     
         31 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  30 , characterized in that the steel rail further contains, in mass, one or more of 0.0050 to 0.0500% Ti, 0.0005 to 0.0200% Mg, 0.0005 to 0.0150% Ca, 0.0080 to 1.00% Al, and 0.0001 to 0.2000% Zr.  
     
     
         32 . A method for producing a pearlitic steel rail excellent in wear resistance and ductility according to any one of  claims 11  to  31 , characterized by reducing the amount of pro-eutectoid cementite structures forming in the web portion of the rail so that the number of the pro-eutectoid cementite network intersecting two line segments each 300 μm in length crossing each other at right angles (the number of intersecting pro-eutectoid cementite network, NC) at the center of the centerline in the web portion of the rail satisfy the expression NC≦CE in relation to the value of CE defined by the following equation (1):  
         CE= 60([mass % C])+10([mass % Si])+10([mass % Mn])+500([mass % P])+50([mass % S])+30([mass % Cr])+50   (1).