| 摘要 |
PURPOSE:To make the production of a high-strength zinc hot dipped steel plate having a low yield ratio, and excellent strength-elongation balance and stretch- flangability in the production of a zinc hot dipped steel plate by forming the structure of the steel plate into specific 3-phase composite structure. CONSTITUTION:An ingot contg. 0.005-0.15% C, <1% Si, 0.7-2.5% Mn, <0.1% P or further <0.5% Cr is hot and cold rolled to a cold-rolled steel plate. After the steel plate is annealed in a direct firing type heating furnace of a non- oxidative atmosphere at 900-1,100 deg.C and a radiation heating furnace of a reducing atmopshere, the steel plate is passed through a slow cooling zone, a quick cooling zone and a cooling control furnace then through the inside of a zinc hot dipping bath of about 500 deg.C, whereby zinc hot dipping is applied thereon. The ferrite-bainite-martensite 3-phase structure contg. 5-50% area rate of bainite and 1-20% area rate of martensite is formed, and the high strength zinc hot dipped steel plate of the composite structure having a low yield ratio and excellent strength-elongation balance and stretch-flangability is obtained. |
