| 摘要 |
The present invention is directed to a steel product for machine structural use having excellent machinability and to a structural steel part for machinery manufactured from the steel product. More particularly, the invention is directed to a steel product for machine structural use having excellent machinability, particularly bringing about excellent "drill life" and exhibiting excellent "chip disposability" in the course of drilling, as well as to a structural steel part for machinery manufactured from the steel product. The steel product for machine structural use has a chemical composition comprising, in mass percent, C: 0.05% to 0.55%; Si: 0.50% to 2.5%; Mn: 0.01% to 2.00%; P: not greater than 0.035%; S: 0.005% to 0.2%; N: not greater than 0.0150%; elements to be added as needed: Cu, Ni, Cr, Mo, V, Nb, Ti, B, Al, Bi, Ca, Pb, Te, Nd, and Se; -23C + Si(5 - 2Si) - 4Mn + 104S - 3Cr - 9V + 10 ≥ 0; 3.2C + 0.8Mn + 5.2S + 0.5Cr - 120N + 2.6Pb + 4.1Bi - 0.001 alpha <2> + 0.13 alpha ≥ 3.0; and balance: Fe and incidental impurities; percentage of ferrite in microstructure being 10% to 80%; and Hv hardness being 160 to 350. In the above expressions, alpha represents the area percentage in % of a ferrite phase in the microstructure. The structural steel part for machinery can be manufactured relatively easily from the steel product for machine structural use through machining. <IMAGE> |
