Steel for nitrocarburizing, nitrocarburized steel part, and producing method of nitrocarburized steel part

1. A nitrocarburized steel part, comprising:

a nitrocarburized portion present on a surface of the nitrocarburized steel part; and

a non-nitrocarburized portion surrounded by the nitrocarburized portion, wherein the non-nitrocarburized portion includes, by mass %:

C: 0% to less than 0.15%;

Si: 0.01% to 1.00%;

Mn: 0.01% to 1.00%;

S: 0.0001% to 0.050%;

Al: 0.0001% to 0.050%;

Ti: more than 0.50% to 1.50%;

N: 0.0005% to 0.0100%; and

a balance consisting of Fe and inevitable impurities,

in which P is limited to 0.050% or less;

O is limited to 0.0060% or less; and

an amount of Ti [Ti %], an amount of C [C %], an amount of N [N %], and an amount of S [S %] satisfy 0.48<[Ti %]−47.9×([C %]/12+[N %]/14+[S %]/32)≤1.20; and

in the nitrocarburized portion, a hardness HV at a depth of 50 μm away from the surface is 600 to 1050, a depth where a hardness HV becomes 550 is 0.4 mm or more, and a thickness of an acicular compound layer is 30 μm or less.

2. The nitrocarburized steel part according to claim 1 , wherein the non-nitrocarburized portion further includes at least one of, by mass %:

Cr: 0.01% to less than 0.30%;

Mo: 0.01% to 1.00%;

V: 0.005% to 0.50%;

Nb: 0.005% to 0.10%;

Cu: 0.05% to 2.00%;

Ni: 0.05% to less than 2.00%; and

B: 0.0005% to 0.0050%.

3. A producing method of a nitrocarburized steel part, the method comprising:

processing a steel having a chemical composition according to claim 1 or 2 into a desired product shape, and then performing a nitrocarburizing to the steel while being held in 550° C. to 650° C. for 60 minutes or longer.

4. The producing method of the nitrocarburized steel part according to claim 3 ,

wherein the steel is further held in 580° C. to 700° C. for 5 minutes or longer in an atmosphere other than a nitriding atmosphere after the nitrocarburizing.