| 摘要 |
PURPOSE:To obtain a cold rolled steel plate of about 40-55kg/mm.<2> tensile strengths having a high (r) value and quench hardenability by performing annealing after hot rolling and cold rolling of Al killed steel of an increased content of Si in a batch tupe annealing furnace. CONSTITUTION:Steel consisting of 0.005-0.02 C by %, 1.0-2.0 Si, 0.03-0.5 Mn, <=0.1 P, 0.02-0.08 Al, 0.002-0.020 N and the balance Fe and unavoidable impurities is hot rolled, and after it is coiled at below 600 deg.C, it is cold rolled. The resultant steel plate is annealed in a continuous heat treatment furnace in coil units such as an open coil or tight coil type box annealing furnace. Here, below the lower limit of C, quench hardenability is low. If Si is below the lower limit, the strength of levels cannot be obtained and the effect that it gives on the quench hardenability is less. In excess of the upper limit, an (r) value decreases considerably; at the same time, crystal grains coarsen, resulting in an increased rate of surface roughening. If the Mn exceeds the upper limit, the (r) value decreases considerably. |
