COLD-ROLLED STEEL SHEET AND HOT DIP GALVANIZED STEEL SHEET WITH HIGH STRENGTH AND HIGH FORMABILITRY AND MANUFACTURING METHOD THEREOF

摘要

PURPOSE: A high-strength high-workability cold rolled steel sheet and a manufacturing method thereof are provided to offer economical efficiency of the cold rolled steel sheet having the elongation ratio of 28% or more. CONSTITUTION: A manufacturing method of a high-strength high-workability cold rolled steel sheet includes the following steps of: rolling steel slab at a temperature of A3 or more; cooling the steel slab at the speed of 70~110°C/second; winding the steel slab at the temperature of 100~300°C; and cold-rolling and annealing the steel slab with the reduction rate of 30% or less. In a cooling step, the martensite structure is formed. The particle size of the martensite is 100~1000nm.