Steel for Induction Hardening

Abstract

A steel for induction hardening according to the present invention includes a chemical composition consisting of, in mass percent: C: 0.58 to 0.68%, Si: 0.70 to 1.40%, Mn: 0.20 to 1.40%, P: less than 0.020%, S: 0.025% or less, Al: more than 0.06% to 0.15%, N: 0.0020 to 0.0080%, O: 0.0015% or less, and Ca: 0.0005 to 0.005%, with the balance being Fe and impurities, and satisfies Formulae (1) to (3). The steel microstructure is made up of ferrite and pearlite. In the steel, a ratio of a number of composite inclusions to a total number of Al 2 O 3 inclusions and the composite inclusions is 20% or more. C+Si/7+Mn/5+Cr/9+Mo/2.5≤1.05  (1) C+Si/10+Mn/20+Cr/25≥0.70  (2) Cr/Si≤0.20  (3)

1 . A steel for induction hardening comprising
 a chemical composition consisting of, in mass percent:   C: 0.58 to 0.68%;   Si: 0.70 to 1.40%;   Mn: 0.20 to 1.40%;   P: less than 0.020%;   S: 0.025% or less;   Al: more than 0.06% to 0.15%;   N: 0.0020 to 0.0080%;   O: 0.0015% or less;   Ca: 0.0005 to 0.005%;   Cr: 0 to 0.15%;   Cu: 0 to 0.50%;   Ni: 0 to 0.30%;   Mo: 0 to 0.20%;   B: 0 to 0.0040%;   Ti: 0 to 0.050%;   V: 0 to 0.05%; and   Nb: 0 to 0.05%,   with the balance being Fe and impurities, and satisfying Formulae (1) to (3), wherein   a steel microstructure is made up of ferrite and pearlite, where an area fraction of the pearlite is 85% or more, and   in the steel, a ratio of a number of composite inclusions to a total number of Al 2 O 3  inclusions and the composite inclusions is 20% or more, and the composite inclusions contain, in mass percent, 2.0% or more of SiO 2  and 2.0% or more of CaO, with the 99% or more of the balance being Al 2 O 3 :
   C+Si/7+Mn/5+Cr/9+Mo/2.5≤1.05  (1)
 
   C+Si/10+Mn/20+Cr/25≥0.70  (2)
 
   Cr/Si≤0.20  (3)
 
   where, symbols of elements in Formulae (1) to (3) are to be substituted by contents of corresponding elements (mass percent).   
     
     
         2 . The steel for induction hardening according to  claim 1 , wherein the chemical composition contains one or more types selected from the group consisting of:
 Cr: 0.05 to 0.15%;   Cu: 0.03 to 0.50%;   Ni: 0.03 to 0.30%;   Mo: 0.01 to 0.20%; and   B: 0.0003 to 0.0040%.   
     
     
         3 . The steel for induction hardening according to  claim 1 , wherein the chemical composition contains Ti: 0.010 to 0.050%. 
     
     
         4 . (canceled) 
     
     
         5 . The steel for induction hardening according to  claim 2 , wherein the chemical composition contains Ti: 0.010 to 0.050%. 
     
     
         6 . The steel for induction hardening according to  claim 1 , wherein the chemical composition contains one or more types selected from the group consisting of:
 V: 0.01 to 0.05%; and   Nb: 0.01 to 0.05%.   
     
     
         7 . The steel for induction hardening according to  claim 2 , wherein the chemical composition contains one or more types selected from the group consisting of:
 V: 0.01 to 0.05%; and   Nb: 0.01 to 0.05%.   
     
     
         8 . The steel for induction hardening according to  claim 3 , wherein the chemical composition contains one or more types selected from the group consisting of:
 V: 0.01 to 0.05%; and   Nb: 0.01 to 0.05%.   
     
     
         9 . The steel for induction hardening according to  claim 5 , wherein the chemical composition contains one or more types selected from the group consisting of:
 V: 0.01 to 0.05%; and   Nb: 0.01 to 0.05%.