Steel material for carbonitriding and carbonitrided steel material

Abstract

The present invention relates to a steel material for carbonitriding treatment, containing: C, Si, Mn, P, S, Cu, Ni, Cr, Mo, Al, and N with a balance being Fe and inevitable impurities, satisfying Expression 1 of 0.6 to 1.4 and Expression 2 of >560 when subjected to carbonitriding, Expression 1: Surface C concentration (mass %)+12/14×Surface N concentration (mass %), and Expression 2: 129.7805×[Cr (mass %)]−76.9797×[Cr (mass %)]2+339.3375×[Surface N concentration (mass %)]−539.345×[Surface N concentration (mass %)]2+181.4983×[Cr (mass %)]×[Surface N concentration (mass %)]+437.6799, and providing a carbonitrided steel material having a hardness of 560 HV or more at a portion from a surface thereof to a depth of 0.05 mm when subjected to a tempering treatment at 500° C. after the carbonitriding.

1 . A steel material for carbonitriding treatment, comprising:
 C at 0.1 mass % to 0.3 mass %;   Si at 0.3 mass % or less;   Mn at 0.4 mass % to 2.0 mass %;   P at 0.03 mass % or less;   S at 0.03 mass % or less;   Cu at 0.3 mass % or les;   Ni at 2.5 mass % or less;   Cr at 0.5 mass % to 3.0 mass %;   Mo at 0.001 mass % to 1.0 mass %;   Al at 0.01 mass % to 0.08 mass %; and   N at 0.005 mass % to 0.03 mass %;   with a balance being Fe and inevitable impurities,   satisfying the following Expression 1 of 0.6 to 1.4 and Expression 2 of >560 when subjected to carbonitriding,
   Surface C concentration(mass %)+12/14×Surface N concentration(mass %),  Expression 1:
 
   129.7805×[Cr(mass %)]−76.9797×[Cr(mass %)] 2 +339.3375×[Surface N concentration(mass %)]−539.345×[Surface N concentration (mass %)] 2 +181.4983×[Cr(mass %)]×[Surface N concentration(mass %)]+437.6799, and  Expression 2:
 
   providing a carbonitrided steel material having a hardness of 560 HV or more at a portion from a surface thereof to a depth of 0.05 mm when subjected to a tempering treatment at 500° C. after the carbonitriding.   
     
     
         2 . The steel material for carbonitriding treatment according to  claim 1 , further comprising at least one selected from the group consisting of:
 Nb at 0.001 mass % to 0.08 mass %;   V at 0.5% mass % or less;   Ti at 0.05% mass % or less; and   B at 0.0005 mass % to 0.003 mass %.   
     
     
         3 . The steel material for carbonitriding treatment according to  claim 1 , comprising:
 C at 0.15 mass % to 0.25 mass %;   Si at 0.01 mass % to 0.24 mass %;   Mn at 0.5 mass % to 1.8 mass %;   Cu at 0.001 mass % to 0.3 mass %;   Ni at 0.01 mass % to 0.6 mass %;   Cr at 0.6 mass % to 1.8 mass %;   Mo at 0.01 mass % to 0.8 mass %;   Al at 0.02 mass % to 0.05 mass %;   N at 0.01 mass % to 0.025 mass %; and   at least one selected from the group consisting of:
 Nb at 0.0015 mass % to 0.06 mass %; 
 V at 0.25 mass % or less; 
 Ti at 0.012 mass % to 0.04 mass %; and 
 B at 0.0006 mass % to 0.0025 mass %, 
   with a balance being Fe and inevitable impurities, and   providing, by performing the carbonitriding, a carbonitrided steel material that satisfies the following Expression 1 being 0.7 to 1.2:
   Surface C concentration(mass %)+12/14×Surface N concentration(mass %),  Expression 1:
 
   
     
     
         4 . The steel material for carbonitriding treatment according to  claim 1 , comprising:
 Cu at 0.03 mass % to 0.3 mass %.   
     
     
         5 . The steel material for carbonitriding treatment according to  claim 1 , comprising:
 Si at 0.01 mass % to 0.17% mass %.   
     
     
         6 . The steel material for carbonitriding treatment according to  claim 1 , comprising:
 Cu at 0.03 mass % to 0.25 mass %.   
     
     
         7 . A carbonitrided steel material obtained by carbonitriding the steel material for carbonitriding treatment according to  claim 1 ,
 satisfying the following Expression 1 of 0.6 to 1.4 and Expression 2 of >560,
   Surface C concentration(mass %)+12/14×Surface N concentration(mass %),  Expression 1:
 
   129.7805×[Cr(mass %)]−76.9797×[Cr(mass %)] 2 +339.3375×[Surface N concentration(mass %)]−539.345×[Surface N concentration (mass %)]2+181.4983×[Cr(mass %)]×[Surface N concentration(mass %)]+437.6799, and  Expression 2:
 
   having a hardness of 560 HV or more at a portion from a surface thereof to a depth of 0.05 mm when subjected to a tempering treatment at 500° C.