Patent ID: 8916008

Claim:
A steel part for machine structural use made of a steel consisting of, in mass %, C: 0.05 to 0.20%, Si: 0.10 to 1.00%, Mn: 0.75 to 3.00%, P: 0.001 to 0.050%, S: 0.001 to 0.200%, V: 0.05 to 0.20%, Cr: 0.01 to 0.35%, Al: 0.001 to 0.500%, and N: 0.0080 to 0.0200%, and optionally Ca: 0.0003 to 0.0100%, optionally Mg: 0.0003 to 0.0100%, optionally Zr: 0.0005 to 0.1000%, optionally Mo: 0.01 to 1.00%, and optionally Nb: 0.001 to 0.200%, a balance being composed of Fe and inevitable impurities, wherein a steel structure contains a bainite structure having an area ratio of 95% or more, a bainite lath width is 5 μm or less, V carbide having an average grain diameter of not less than 4 nm nor more than 7 nm dispersedly exists in the bainite structure, and an area ratio of V carbide in the bainite structure is 0.18% or more.