Steel material for sliding part and method of manufacturing steel material for sliding part

Abstract

A steel material for a sliding part with improved slidability and workability is provided. A steel material for a sliding part includes a steel material with a C content of 0.30 to 0.60 mass %, having a microstructure including (a) at least one of tempered martensite and bainite and (b) an iron carbide, the volume fraction of the tempered martensite and bainite combined being not lower than 80% and the volume fraction of the iron carbide being not lower than 2.0%, the Vickers hardness being not lower than 300 and not higher than 600, the volume fraction of the iron carbide, X, and the Vickers hardness, Hv, satisfying the following relational expression, (1):X≥-0.0⁢65×Hv+36.5,(1)where X is in % and Hv is in Hv.

1 . A steel material for a sliding part including a steel material with a C content of 0.30 to 0.60 mass %,
 having a microstructure including (a) at least one of tempered martensite and bainite and (b) an iron carbide, a volume fraction of the tempered martensite and the bainite combined being not lower than 80% and a volume fraction of the iron carbide being not lower than 2.0%,   a Vickers hardness being not lower than 300 and not higher than 600,   the volume fraction of the iron carbide, X, and the Vickers hardness, Hv, satisfying the following relational expression, (1):   
       
         
           
             
               
                 
                   
                     
                       X 
                       ≥ 
                       
                         
                           
                             - 
                             
                               0 
                               . 
                               0 
                             
                           
                           ⁢ 
                           65 
                           × 
                           Hv 
                         
                         + 
                         36.5 
                       
                     
                     , 
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         where X is in % and Hv is in Hv. 
       
     
     
         2 . The steel material for a sliding part according to  claim 1 , wherein the steel material has a chemical composition of, in mass %:
 0.30 to 0.60% C;   0.01 to 2.00% Si;   0.10 to 2.00% Mn;   up to 0.060% Al;   up to 0.020% N;   up to 0.10% P;   up to 0.20% S;   0 to 0.50% Cr; and   balance Fe and impurities.   
     
     
         3 . The steel material for a sliding part according to  claim 1 , wherein an average minor-axis length of particles of the iron-carbide is not larger than 0.027 μm. 
     
     
         4 . The steel material for a sliding part according to  claim 1 , including none of a nitriding layer, a carburization layer and a carbonitriding layer on a surface. 
     
     
         5 . The steel material for a sliding part according to  claim 1 , wherein a Vickers hardness at a surface is not lower than 300 and not higher than 600, and the volume fraction of the iron carbide, X, and the Vickers hardness at the surface, Hv, satisfy the relational expression (1). 
     
     
         6 . The steel material for a sliding part according to  claim 1 , wherein the Vickers hardness is not lower than 300 and not higher than 550. 
     
     
         7 . A method of manufacturing the steel material for a sliding part according to  claim 1 , comprising:
 holding a material at a temperature not lower than 830° C. and not higher than 1100° C. and then quenching the material by cooling at a cooling rate not lower than 300° C./s in a range from the holding temperature down to 300° C.; and   tempering the quenched material by holding at a temperature not lower than 200° C. and not higher than 600° C.