Pearlitic rail and method for manufacturing pearlitic rail
A pearlitic rail includes a composition including in % by mass: 0.70% to 0.90% of C; 0.1% to 1.5% of Si; 0.01% to 1.5% of Mn; 0.001% to 0.035% of P; 0.0005% to 0.030% of S; 0.1% to 2.0% of Cr, remainder of the composition consisting of Fe and inevitable impurities. Surface hardness of a rail top is not less than HB 430, and hardness at a depth of 25 mm from a surface of the rail top is not less than HB 410.
1. A method of manufacturing a pearlitic rail, the method comprising:
hot rolling a billet having a composition including in % by mass: 0.70% to 0.90% of C; 0.1% to 1.5% of Si; 0.01% to 1.5% of Mn; 0.001% to 0.035% of P; 0.0005% to 0.030% of S; 0.1% to 2.0% of Cr, remainder of the composition consisting of Fe and inevitable impurities, so as to achieve a finishing rolling temperature of not lower than 900° C. to form a rail material; and
cooling the rail material in an accelerated manner at a cooling rate of 2° C./s to 30° C./s from a temperature of 770° C. to 500° C., reheating the rail material or subjecting the rail material to secondary heating to a temperature within a range of 530° C. to 580° C., holding the rail material within the range of 530° C. to 580° C. for 20 s to 100 s, and cooling the rail material in an accelerated manner at a cooling rate of 2° C./s to 10° C./s to a temperature within a range of not higher than 450° C.
2. The method of manufacturing a pearlitic rail according to claim 1 , further comprising terminating the accelerated cooling performed at a cooling rate of 2° C./s to 10° C./s, at a temperature within a range of 350° C. to 450° C., and then slowly cooling the rail material at a cooling rate of not more than 0.5° C./s.
3. The method of manufacturing a pearlitic rail according to claim 1 , wherein the composition of the billet further includes in % by mass one or both of: not more than 0.010% of Ca; and not more than 0.1% of REM.
4. The method of manufacturing a pearlitic rail according to claim 3 , further comprising terminating the accelerated cooling performed at a cooling rate of 2° C./s to 10° C./s, at a temperature within a range of 350° C. to 450° C., and then slowly cooling the rail material at a cooling rate of not more than 0.5° C./s.
5. The method of manufacturing a pearlitic rail according to claim 1 , wherein the composition of the billet further includes in % by mass at least one of: not more than 0.15% of V; not more than 0.030% of Nb; not more than 1.0% of Cu; not more than 0.5% of Ni; and not more than 0.5% of Mo.
6. The method of manufacturing a pearlitic rail according to claim 5 , further comprising terminating the accelerated cooling performed at a cooling rate of 2° C./s to 10° C./s, at a temperature within a range of 350° C. to 450° C., and then slowly cooling the rail material at a cooling rate of not more than 0.5° C./s.
7. The method of manufacturing a pearlitic rail according to claim 5 , wherein the composition of the billet further includes in % by mass one or both of: not more than 0.010% of Ca; and not more than 0.1% of REM.
8. The method of manufacturing a pearlitic rail according to claim 7 , further comprising terminating the accelerated cooling performed at a cooling rate of 2° C./s to 10° C./s, at a temperature within a range of 350° C. to 450° C., and then slowly cooling the rail material at a cooling rate of not more than 0.5° C./s.