HIGH-STRENGTH STEEL FOR STEEL FORGINGS, AND STEEL FORGING

摘要

The high-strength steel for steel forgings according to the present invention has a composition that includes, as basic components, C: 0.35 mass% to 0.47 mass%; Si: 0 mass% to 0.4 mass%; Mn: 0.6 mass% to 1.5 mass%; Ni: more than 0 mass% up to 2.0 mass%; Cr: 0.8 mass% to 2.5 mass%; Mo: 0.10 mass% to 0.7 mass%; V: 0.035 mass% to 0.20 mass%; Al: 0.015 mass% to 0.050 mass%; N: 30 ppm to 100 ppm, and O: more than 0 ppm up to 30 ppm, the balance being Fe and inevitable impurities. The metal structure is mainly bainite, martensite or a mixed structure of bainite and martensite. Among cubic B1-type precipitates, the number of coherent precipitates having a diameter equal to or smaller than 30 nm is equal to or smaller than 50 /µm 2 .