COLD ROLLED STEEL SHEET AND PLATED COLD ROLLED STEEL SHEET EACH HAVING EXCELLENT STRAIN AGE HARDENING CHARACTERISTIC AND FREE FROM DEGRADATION DUE TO ROOM- TEMPERATURE AGING, AND MANUFACTURING METHOD OF THEM

摘要

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet and a plated cold rolled steel sheet each having excellent workability and bake hardening property and minimal degradation due to room-temperature aging, and a manufacturing method of them. SOLUTION: A steel sheet after cold rolling in which N is added as a reinforcing element and Al content is controlled to a value within a proper range is box-annealed to decrease solid-solution C while securing solid-solution N. By this method, the cold rolled steel sheet and the plated cold rolled steel sheet which are soft during working and can provide high baking hardenability by heat treatment after the working and have minimal degradation due to room- temperature aging can be obtained.