| 摘要 |
PURPOSE:To manufacture steel having high resistance against cracks by sulfide at low cost by repeating under special conditions produres such as hot processing, direct quenching, heating and quenching and then tempering in that order on steel of special composition in the form of austenite. CONSTITUTION:Steel meeting the composition formula by its ingredients such as C 0.15-0.45, Si less than 0.80, Mn more than 0.01- not less than 0.30, Cr 0.20- 1.50, 1 or 2 kinds of Mo and W Mo+1/2W 0.05-0.80, Nb 0.01-0.10, 1 or 2 kinds of Ti and Zr Ti+1/2Zr 0.005-0.050 and Al 0.01-0.10 in terms of weight percent and the balance of Fe and inevitable impurities (P less than 0.010, S less than 0.010) is hot-processed in the form of austenite. Immediately after this procedure, it is further hot-processed at a transformation point Ac3- (transformation point Ac3+200 deg.C). Next, it is directly quenched as it is in the form of austenite, and then is heated at a transformation point Ac3- (transformation point Ac3+200 deg.C) and quenching. These processes are further repeated more than once. Finally the steel is tempered at a transformation point of less than Ac3. |
