Steel product for induction hardening, induction-hardened member using the same, and methods for production them

Abstract

The present invention provides a steel material for induction quenching, containing 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities. The steel material has a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, the thickness of the ferrite structure is 30 μm or less, and the average prior austenite grain diameter of a hard layer obtained by induction quenching is 12 μm or less. Since having superior machinability and superior fatigue strength after induction quenching, this steel material is suitable, for an automobile drive shaft, constant velocity joint, and the like.

1 . A steel material for induction quenching, comprising 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities, wherein the steel material has a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, the maximum thickness of the ferrite structure is 30 μm or less, and an average prior austenite grain diameter of a hard layer after induction quenching is 12 μm or less.  
     
     
         2 . The steel material for induction quenching according to  claim 1 , further comprising at least one element selected from the group consisting of 1.0% or less of Cu, 3.5% or less of Ni, 1.0% or less of Co, 0.1% or less of Nb, 0.1% or less of Ti, and 0.5% or less of V on a mass basis.  
     
     
         3 . The steel material for induction quenching according to  claim 1 , further comprising at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.  
     
     
         4 . The steel material for induction quenching according to  claim 2 , further comprising at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.  
     
     
         5 . An induction quenched member formed from the steel material for induction quenching according to  claim 1 , wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.  
     
     
         6 . An induction quenched member formed from the steel material for induction quenching according to  claim 2 , wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.  
     
     
         7 . An induction quenched member formed from the steel material for induction quenching according to  claim 3 , wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.  
     
     
         8 . An induction quenched member formed from the steel material for induction quenching according to  claim 4 , wherein the average prior austenite grain diameter of the hard layer after induction quenching is 12 μm or less.  
     
     
         9 . A method for manufacturing a steel material for induction quenching, comprising: 
 a step of hot working steel at a total reduction rate of 80% or more in a temperature region of more than 850° C. to 950° C., the steel comprising 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities, and    a step of cooling the steel treated by the hot working to 600° C. or less at a cooling rate of less than 0.6° C./sec.    
     
     
         10 . The method for manufacturing a steel material for induction quenching, according to  claim 9 , wherein the steel further comprises at least one element selected from the group consisting of 1.0% or less of Cu, 3.5% or less of Ni, 1.0% or less of Co, 0.1% or less of Nb, 0.1% or less of Ti, and 0.5% or less of V on a mass basis.  
     
     
         11 . The method for manufacturing a steel material for induction quenching according to  claim 9 , wherein the steel further comprises at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.  
     
     
         12 . The method for manufacturing a steel material for induction quenching according to  claim 10 , wherein the steel further comprises at least one element selected from the group consisting of 0.005% or less of Ca, 0.005% or less of Mg, 0.005% or less of Te, 0.5% or less of Bi, 0.5% or less of Pb, and 0.01% or less of Zr on a mass basis.  
     
     
         13 . A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to  claim 1 , which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.  
     
     
         14 . A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to  claim 2 , which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.  
     
     
         15 . A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to  claim 3 , which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.  
     
     
         16 . A method for manufacturing a induction quenched member, comprising a step of performing induction quenching of the steel material for induction quenching according to  claim 4 , which is formed into a predetermined shape, in a heating temperature region of 800° C. to 1,000° C. for 5 seconds or less.