PREPARATION OF ZINC HOT DIPPING HIGH TENSILE STEEL SHEET EXCELLENT IN COLD WORKING PROPERTY AND AGING HARDENING PROPERTY

摘要

PURPOSE:To obtain the above mentioned sheet having a large mixing structure of working property and aging hardening property, by carrying out Zn hot dipping and cooling at a fixed speed and moreover, carrying out over aging treatment at lower temperature than that of cooling at a fixed speed after heating the thin sheet at the temperature of Ac1-Ac3. CONSTITUTION:Thin steel sheet composed of C;0.005-0.15%, Mn;0.25-2.0%, Si; not more than 1.0%, P; not more than 0.15%, S; not more than 0.025%, Al; not more than 0.1%, Fe; balance and innevitable impurities. Next, the above sheet is cooled at the cooling speed more than the critical cooling speed CR1 by the formula II necessary to obtain mixing structure at the temperature from 700 deg.C to 450- 550 deg.C of Zn plating finish after heating in the extent of (alpha+gamma) region heating temperature, that is, Ac1-Ac3. But, ME1 in the formula II is shown in the formula I. Next, cooling is carried out at the critical cooling speed CR2 by the formula necessary to obtain mixing structure at the temperature from the above mentioned 450-550 deg.C of Zn plating finish to not more than 300 deg.C. But, Me2 in the formula IV is shown in the formula III. As a result, Zn hot dipping high tensile sheet having superior cold working property and painting sintering hardening property, is able to obtain.