PRODUCTION OF GALVANIZED COLD-ROLLED STEEL SHEET HAVING EXCELLENT WORKABILITY

摘要

PURPOSE:To produce a galvanized cold-rolled steel sheet having excellent workability and adhesion of a plating layer by subjecting a low-carbon cold-rolled steel sheet to a heat treatment and galvanizing treatment under specific conditions. CONSTITUTION:The aluminum killed cold-rolled steel sheet which does not contain N in a solid soln. state by fixing preliminarily the nitrogen contained therein in the form of AlN or BN and contains 0.01-0.08% C is heated to 750-850 deg.C in a reducing atmosphere to reduce the oxide on the surface. The steel sheet is then slowly cooled down to 720-650 deg.C and is quickly cooled to a 200-350 deg.C temp. region at a cooling rate of >=20 deg.C/sec and is held at said temp. for 10- 60sec. The steel sheet is in succession heated up to 430-470 deg.C at a temp. elevating rate of >=5 deg.C/sec and is dipped in a galvanizing bath to form a galvanizing layer by molten Zn on the surface. The galvanized sheet is taken out of the galvanizing bath and is quickly cooled down to <=400 deg.C at a cooling rate of >=5 deg.C/sec; in succession, the steel sheet is subjected to a treatment for precipitation of solid soln. carbon for 2-10min at 220-400 deg.C. The galvanized cold- rolled steel sheet having excellent workability and adhesion of the plating layer is thus obtd.