| 摘要 |
PURPOSE:To produce a high-tensile steel plate of an excellent spring property and ductility by subjecting a steel contg. specific ratios of C, Si and Mn successively to heating, cooling, isothermal holding, cooling, cold rolling and aging treatment under specific conditions. CONSTITUTION:The steel consisting, by wt.%, of 0.40-0.85% C, 1.40-2.50% Si, 0.30-1.00% Mn, and the balance Fe and inevitable impurities is heated to the temp. above the Ac3 point and is thereby completely austenitized. The steel is then cooled in a 380-480 deg.C range at the cooling rate (about >=10 deg.C/sec) higher than the rate to pass the nose of a TTT diagram and is isothermally held until 65-85% of supercooled austenite makes bainite transformation. The steel is further cooled down to room temp. at the air cooling or higher cooling rate (about 1-1,000 deg.C/sec) to form the two-phase steel consisting of 65-85% bainite phase and the balance residual austenite phase. This two-phase steel is cold rolled at 10-25% draft and is further subjected to the aging treatment for >=10min and <=10hr at 180-420 deg.C.
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