Steel for machine structural use and induction-hardened steel component

Abstract

There is provided a steel for machine structural use including, as a chemical composition, by mass %, C: 0.40% to 0.70%, Si: 0.15% to 3.00%, Mn: 0.30% to 2.00%, Cr: 0.01% or more and less than 0.50%, S: 0.003% to 0.070%, Bi: more than 0.0001% and 0.0050% or less, N: 0.0030% to 0.0075%, Al: 0.003% to 0.100%, and P: 0.050% or less; and as necessary, B, Mo, Ni, Cu, Ca, Mg, Zr, Rem, Ti, Nb, V, Sb, Te, and Pb, a remainder including Fe and impurities, in which Expressions 290×C+50×Si+430≥620 and d+3σ<20 are satisfied, and a presence density of MnS having an equivalent circle diameter of smaller than 2.0 μm is 300 pieces/mm 2 or more in a cross section parallel to a longitudinal direction.

1 . A steel for machine structural use comprising, as a chemical composition, by mass %,
 C: 0.40% to 0.70%,   Si: 0.15% to 3.00%,   Mn: 0.30% to 2.00%,   Cr: 0.01% or more and less than 0.50%,   S: 0.003% to 0.070%,   Bi: more than 0.0001% and 0.0050% or less,   N: 0.0030% to 0.0075%,   Al: 0.003% to 0.100%,   P: 0.050% or less,   B: 0% to 0.0050%,   Mo: 0% to 0.20%,   Ni: 0% to 1.00%,   Cu: 0% to 1.00%,   Ca: 0% to 0.0050%,   Mg: 0% to 0.0050%,   Zr: 0% to 0.0050%,   Rem: 0% to 0.0050%,   Ti: 0% to 0.20%,   Nb: 0% to 0.20%,   V: 0% to 0.35%,   Sb: 0% to 0.015%,   Te: 0% to 0.20%,   Pb: 0% to 0.50%, and   a remainder comprising Fe and impurities,   wherein a following Expression (1a) and a following Expression (2a) are satisfied, and   a presence density of MnS having an equivalent circle diameter of smaller than 2.0 μm is 300 pieces/mm 2  or more in a cross section parallel to a longitudinal direction,
   290×C+50×Si+430≥620  (1a)
 
     d+ 3σ<<20  (2a)
 
   where,   C and Si in the Expression (1a) represent C and Si contents by mass %,   d in the Expression (2a) represents an average equivalent circle diameter of the MnS in an unit of μm having the equivalent circle diameter of 1.0 μm or greater, and   σ in the Expression (2a) represents a standard deviation of the equivalent circle diameter of the MnS having the equivalent circle diameter of 1.0 μm or greater.   
     
     
         2 . The steel for machine structural use according to  claim 1  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 B: 0.0003% to 0.0050%, 
 Mo: 0.01% to 0.20%, 
 Ni: 0.05% to 1.00%, and 
 Cu: 0.05% to 1.00%. 
 
     
     
         3 . The steel for machine structural use according to  claim 1  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Ca: 0.0003% to 0.0050%, 
 Mg: 0.0003% to 0.0050%, 
 Zr: 0.0003% to 0.0050%, and 
 Rem: 0.0003% to 0.0050%. 
 
     
     
         4 . The steel for machine structural use according to  claim 1  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Ti: 0.005% to 0.20%, 
 Nb: 0.005% to 0.20%, and 
 V: 0.005% to 0.35%. 
 
     
     
         5 . The steel for machine structural use according to  claim 1  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%. 
 
     
     
         6 . An induction-hardened steel component comprising, as a chemical composition, by mass %,
 C: 0.40% to 0.70%,   Si: 0.15% to 3.00%,   Mn: 0.30% to 2.00%,   Cr: 0.01% or more and less than 0.50%,   S: 0.003% to 0.070%,   Bi: more than 0.0001% and 0.0050% or less,   N: 0.0030% to 0.0075%,   Al: 0.003% to 0.100%,   P: 0.050% or less,   B: 0% to 0.0050%,   Mo: 0% to 0.20%,   Ni: 0% to 1.00%,   Cu: 0% to 1.00%,   Ca: 0% to 0.0050%,   Mg: 0% to 0.0050%,   Zr: 0% to 0.0050%,   Rem: 0% to 0.0050%,   Ti: 0% to 0.20%,   Nb: 0% to 0.20%,   V: 0% to 0.35%,   Sb: 0% to 0.015%,   Te: 0% to 0.20%,   Pb: 0% to 0.50%, and   a remainder comprising Fe and impurities,   wherein a following Expression (1b) and a following Expression (2b) are satisfied, and   a presence density of MnS having an equivalent circle diameter of smaller than 2.0 μm is 300 pieces/mm 2  or more in a cross section parallel to a longitudinal direction,
   290×C+50×Si+430≥620  (1b)
 
     d+ 3σ<20  (2b)
 
   where,   C and Si in the Expression (1b) represent C and Si contents by mass %,   d in the Expression (2b) represents an average equivalent circle diameter of the MnS in an unit of μm having the equivalent circle diameter of 1.0 μm or greater, and   σ in the Expression (2b) represents a standard deviation of the equivalent circle diameter of the MnS having the equivalent circle diameter of 1.0 μm or greater.   
     
     
         7 - 10 . (canceled) 
     
     
         11 . The steel for machine structural use according to  claim 2  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Ca: 0.0003% to 0.0050%, 
 Mg: 0.0003% to 0.0050%, 
 Zr: 0.0003% to 0.0050%, and 
 Rem: 0.0003% to 0.0050%. 
 
     
     
         12 . The steel for machine structural use according to  claim 2  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Ti: 0.005% to 0.20%, 
 Nb: 0.005% to 0.20%, and 
 V: 0.005% to 0.35%. 
 
     
     
         13 . The steel for machine structural use according to  claim 3  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Ti: 0.005% to 0.20%, 
 Nb: 0.005% to 0.20%, and 
 V: 0.005% to 0.35%. 
 
     
     
         14 . The steel for machine structural use according to  claim 11  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Ti: 0.005% to 0.20%, 
 Nb: 0.005% to 0.20%, and 
 V: 0.005% to 0.35%. 
 
     
     
         15 . The steel for machine structural use according to  claim 2  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%. 
 
     
     
         16 . The steel for machine structural use according to  claim 3  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%. 
 
     
     
         17 . The steel for machine structural use according to  claim 4  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%. 
 
     
     
         18 . The steel for machine structural use according to  claim 11  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%. 
 
     
     
         19 . The steel for machine structural use according to  claim 12  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%. 
 
     
     
         20 . The steel for machine structural use according to  claim 13  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%. 
 
     
     
         21 . The steel for machine structural use according to  claim 14  comprising, as the chemical composition, by mass %, one or more selected from the group consisting of
 Sb: 0.0003% to 0.015%, 
 Te: 0.0003% to 0.20%, and 
 Pb: 0.01% to 0.50%.