Steel for induction hardening

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%;

Al: 0.005 to 0.060%;

N: 0.0020 to 0.0080%;

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%; and

Ti: 0 to 0.050%;

with the balance being Fe and impurities,

the impurities including:

P: less than 0.020%;

S: less than 0.020%;

0: 0.0015% or less;

V: less than 0.01%; and

Nb: less than 0.01%,

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. The steel for induction hardening according to claim 2 , wherein the chemical composition contains Ti: 0.010 to 0.050%.