STEEL FOR MACHINE STRUCTURAL USE AND INDUCTION-HARDENED STEEL COMPONENT
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%.