| 摘要 |
The invention provides a non-heat-treated steel for hot forging which can be converted into steel of a martensite-base structure by hot-forging and subsequent controlled cooling even though subsequent re-heating/quenching/tempering treatment is not conducted after the cooling and which can give high-strength and high-toughness steel parts excellent in machinability; and non-heat-treated steel hot forgings made from the steel. A martensitic non-heat-treated steel for hot forging, characterized by containing by mass C: 0.10 to 0.20%, Si: 0.10 to 0.50%, Mn: 1.0 to 3.0%, P: 0.001 to 0.1%, S: 0.005 to 0.80%, Cr: 0.10 to 1.50%, Al: more than 0.1 to 0.20%, and N: 0.0020 to 0.0080% with the balance consisting substantially of Fe and unavoidable impurities; and a non-heat-treated steel hot forging made from the steel, characterized in that the steel structure in the whole section of part or the whole of the hot forging is a substantially martensitic structure having an effective grain diameter of 15mum or below. |
