Steel part for machine structural use and manufacturing method thereof

摘要

The present invention provides a steel part for machine structural use whose fatigue strength and toughness are improved and a manufacturing method thereof. A steel part made of a steel containing, 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: exceeding 0.20 to 0.25%, Cr: 0.01 to 1.00%, Al: 0.001 to 0.500%, and N: 0.0080 to 0.0200%, and a balance being composed of Fe and inevitable impurities, in which 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.

主权项

1. 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 0.40%,Mn: 0.75 to 3.00%,P: 0.001 to 0.050%,S: 0.001 to 0.200%,V: exceeding 0.20 to 0.25%,Cr: 0.01 to 0.35%,Al: 0.001 to 0.500%, andN: 0.0080 to 0.0200%, andoptionally 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 0.18%, andoptionally Nb: 0.001 to 0.200%,a balance being composed of Fe and inevitable impurities, whereina 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, andan area ratio of V carbide in the bainite structure is 0.18% or more.