Steel material for sliding members and method of manufacturing the same

Abstract

A steel material for sliding members with improved seizure resistance is provided. A steel material for sliding members has a chemical composition including, in mass %, 0.05 to 5.0% In, and a microstructure with metal In particles or particles of oxides mainly composed of In dispersed therein, those ones of the metal In particles which have diameters of 50 nm to 5 μm being in a number density not lower than 5000 particles/mm2 or those ones of the particles of oxides mainly composed of In which have diameters not smaller than 1 μm being in a number density not lower than 30 particles/mm2.

1 . A steel material for sliding members comprising:
 a chemical composition including, in mass %, 0.05 to 5.0% In; and   a microstructure with metal In particles or particles of oxides mainly composed of In dispersed therein,   those ones of the metal In particles which have diameters of 50 nm to 5 μm being in a number density not lower than 5000 particles/mm 2  or those ones of the particles of oxides mainly composed of In which have diameters not smaller than 1 μm being in a number density not lower than 30 particles/mm 2 .   
     
     
         2 . The steel material for sliding members according to  claim 1 , wherein the chemical composition comprises, in mass %:
 0.05 to 1.80% C;   up to 1.5% Si;   up to 2.0% Mn;   up to 0.10% P;   up to 0.10% S;   up to 0.10% Al;   up to 0.030% N;   0.05 to 5.0% In;   0 to 15.0% Cr;   0 to 0.50% Ni;   0 to 0.50% Cu;   0 to 0.050% Ti;   0 to 0.050% Nb;   0 to 2.5% V;   0 to 3.0% Mo;   0 to 6.0% W;   0 to 0.005% B; and   balance Fe and impurities.   
     
     
         3 . The steel material for sliding members according to  claim 1 , wherein those ones of the metal In particles which have diameters of 50 nm to 5 μm is in a number density not lower than 5000 particles/mm 2 . 
     
     
         4 . The steel material for sliding members according to  claim 3 , wherein the steel material includes an In concentration layer in a surface-layer portion. 
     
     
         5 . A method of manufacturing the steel material for sliding members according to  claim 3 , comprising:
 preparing raw material having a chemical composition including, in mass %, 0.05 to 5.0% In; and   subjecting the raw material to a quenching process in which the material is heated at 800 to 1200° C. for 5 to 30 minutes and then water cooled or oil cooled.   
     
     
         6 . The method of manufacturing the steel material for sliding members according to  claim 5 , further comprising: subjecting the quenched material to a tempering process in which the material is heated at 150 to 650° C. for 5 to 60 minutes and then air cooled or water cooled. 
     
     
         7 . The method of manufacturing the steel material for sliding members according to  claim 5 , wherein no tempering process is performed after the quenching process. 
     
     
         8 . The steel material for sliding members according to  claim 1 , wherein:
 the chemical composition includes an In content of, in mass %, 0.3 to 5.0%, and   those ones of the particles of oxides mainly composed of In which have diameters not smaller than 1 μm is in a number density not lower than 30 particles/mm 2 .   
     
     
         9 . The steel material for sliding members according to  claim 8 , wherein the number density of those ones of the particles of oxides mainly composed of In which have diameters not smaller than 1 μm satisfies the following expression, (i):
   M>80×In  (i),
 
 where M indicates the number density of those ones of the particles of oxides mainly composed of In which have diameters not smaller than 1 μm (particles/mm 2 ), and In indicates the In content in the steel (in mass %). 
 
     
     
         10 . A method of manufacturing the steel material for sliding members according to  claim 8 , comprising:
 preparing raw material having a chemical composition including, in mass %, 0.3 to 5.0% In;   subjecting the raw material to a quenching process in which the material is heated at 800 to 1200° C. for 5 to 30 minutes and then water cooled or oil cooled; and   subjecting the quenched material to a heat treatment in which the material is heated at 150 to 650° C. for 5 to 60 minutes and then furnace cooled.   
     
     
         11 . The method of manufacturing the steel material for sliding members according to  claim 10 , further comprising: heating the tempered material at 1000 to 1200° C. for 5 to 30 minutes and then cooling the material at an average cooling rate not higher than 300° C./h.