Effect of N on the Softness of Continuous Annealed Tinplate

Effect of the amount of total and solute nitrogen on the softness of continuous annealed tinplate was experimentally investigated.(1) Reduction of total N and lowering the slab reheating temperature are effective on softening.(2) Hardness of soft temper tinplate does not depend on total N and slab reheating temperature but on solute N in hot rolled sheets, if other conditions are the same. The smaller the amount of solute N is, the lower the hardness of tinplate becomes.(3) T-1 of temper degree requires to keep solute N in hot rolled sheets below about 15ppm.(4) The phenomenon of softening due to the reduction of solute N in hot rolled sheets cannot be explained by the reduction of its solution hardening, but by the reduction of its pinning effect to grain growth in annealing and by coarse grain structure of annealed sheets.