| 摘要 |
PURPOSE:To manufacture the steel material excellent in ductility having a very fine ferritic crystalline structure, by hot-working steel containing the specified amounts of C and alloying elements other than C but not-containing Nb, Ta, Mo or W under a specified condition. CONSTITUTION:Steel containing C <=0.3% and alloying elements other than C <=3% but not substantially containing Nb, Ta, Mo or W is hot-worked on the way of cooling it from a temp. above its transformation point Ac3. At the final stage, reduction is applied to it in a manner such that the ratio of total sectional reduction by one pass or by two or more passes is made above 50%, most pref. above 75%, within 1sec in a temp. range of (Ar1+50 deg.C)-(Ar3+100 deg.C). In a temp. range including a high-temp. one above 600 deg.C on the way of cooling after the completion of the working, forcible cooling with a cooling speed above 20 deg.C/sec is performed. Accordingly, very fine grains of about 3-4mu can be obtained. |
