| 摘要 |
<p>PURPOSE:To obtain a high carbon steel sheet having a metallic structure consisting of ferrite, graphite, and cementite and also having superior formability by graphitizing cementite in a high carbon steel having specific composition by subjecting this steel to hot rolling and subsequent annealing alone while obviating the necessity of cold rolling. CONSTITUTION:A steel having a composition which consists of, by weight, 0.30-1.10% C, <=0.20% Si, 0.10-0.50% Mn, 0.05-1.00% sol.Al, and the balance iron with inevitable impurities and in which the contents of P, S, and N as impurities are limited to <=0.020%, <=0.020%, and <=0.013%, respectively, is prepared. This steel is hot-rolled at 600-900 deg.C rolling finishing temp., cooled down to 400-650 deg.C at 5-40 deg.C/sec cooling rate, coiled, and subjected to soaking treatment at a temp. between 600 deg.C and the Ac1 transformation point, by which a metallic structure consisting of ferrite, graphite, and cementite is formed. If necessary, one or more kinds among 0.001-0.01% Ca and/or <=2.00% Ni and 0.0003-0.0050% B are added to the above composition.</p> |
