Steel for induction hardening with excellent fatigue properties
A steel for induction hardening includes as a chemical composition, by mass %, C: 0.45% to 0.85%, Si: 0.01% to 0.80%, Mn: 0.1% to 1.5%, Al: 0.01% to 0.05%, REM: 0.0001% to 0.050%, O: 0.0001% to 0.0030%. Ca: 0.0050% or less as necessary, Ti: less than 0.005%, N: 0.015% or less, P: 0.03% or less, S: 0.01% or less, and the balance consists of Fe and impurities. The steel for induction hardening also includes a composition inclusion which is an inclusion containing REM, O, S, and Al, or an inclusion containing REM, Ca, O, S, and Al, to which TiN is adhered.
1. A steel for induction hardening, comprising as a chemical composition, by mass%:
C: 0.45% to 0.85%;
Si: 0.01% to 0.80%;
Mn: 0.1% to 1.5%;
Al: 0.01% to 0.05%;
REM: 0.0001% to 0.050%;
O: 0.0001% to 0.0030%;
Ti: less than 0.005%;
N: 0.015% or less;
P: 0.03% or less;
S: 0.01% or less; and
the balance comprising Fe and impurities,
wherein the steel for induction hardening includes a composite inclusion which is an inclusion containing REM, O, S, and Al, to which TiN is adhered, and
the sum of a number density of TiN having a maximum diameter of 1 μm or more which independently exists without adhesion to the inclusion, and a number density of MnS having a maximum diameter of 10 μm or more is 5 pieces/mm 2 or less.
2. A steel for induction hardening, comprising as a chemical composition, by mass %:
C: 0.45% to 0.85%;
Si: 0.01% to 0.80%;
Mn: 0.1% to 1.5%;
Al: 0.01% to 0.05%;
Ca: 0.0050% or less;
REM: 0.0001% to 0.050%;
O: 0.0001% to 0.0030%;
Ti: less than 0.005%;
N: 0.015% or less;
P: 0.03% or less;
S: 0.01% or less; and
the balance comprising Fe and impurities,
wherein the steel for induction hardening includes a composite inclusion which is an inclusion containing REM, Ca, O, S, and Al, to which TiN is adhered, and
the sum of a number density of TiN having a maximum diameter of 1 μm or more which independently exists without adhesion to the inclusion, and a number density of MnS having a maximum diameter of 10 μm or more is 5 pieces/mm 2 or less.
3. The steel for induction hardening according to claim 1 or 2 , further comprising as the chemical composition, one or more kinds of elements selected from the group consisting of, by mass %:
Cr: 2.0% or less;
V: 0.70% or less;
Mo: 1.00% or less;
W: 1.00% or less;
Ni: 3.50% or less;
Cu: 0.50% or less;
Nb: less than 0.050%; and
B: 0.0050% or less.