| 摘要 |
PURPOSE:To improve strength and ductility in equil. through addition of less alloy elements by controlling the cumulative draft in an unrecrystallized austenite region according to the alloy component composition of steel in a hot rolling process at the time of producing a high strength cold-rolled steel plate. CONSTITUTION:A steel input contg. 0.01-0.2% C, 1.0-2.5% Mn, <1.0% Si, or further containing specific small amounts of Cr, Ni, Mo, Cu, P, Ca and one or two or more kinds of Ca and Cl or Mg or specific small amounts of Nb, V and one or two or more kinds of Ti or Zr or contg. both of these is used as a raw material. At the time of hot rolling the steel ingot, it is so performed that the cumulative draft at <=950 deg.C becomes >=50%, and the rolling finish temp. is kept at above the Ar3 point. The plate is wound at <=550 deg.C temperatures. This hot-rolled steel plate is coled-rolled to intended thickness and is wound to a coil, after which it is subjected to box type annealing at two-phase region temperatures of ferrite and austenite. The cold-rolled steel plate of composite structure type of superior strength and ductility is obtained. |
