COLD-ROLLED SHEET AND HOT-GALVANIZED, COLD-ROLLED SHEET, BOTH EXCELLENT IN BAKE HARDENING, COLD NONAGING AND FORMING PROPERTIES, AND PROCESS FOR PRODUCING THE SAME.

摘要

A cold-rolled sheet or a hot-galvanized, cold-rolled sheet having high paint bake hardening and cold nonaging properties and being excellent in the forming properties such as an average r value (deep drawing characteristics) and elongation (bulging characteristics) is produced by annealing an ultralow-carbon steel itself or one containing at least either titanium or niobium above the Ac₃ transformation point to thereby give thereto a single-phase structure of low-temperature transformation product. As regards the paint bake hardening properties, it is possible to realize a BH value as high as about 10 kgf/mm².