Effect of Nitrogen on the Mechanical Properties of Drawing-Quality Aluminum-Killed Sheet Steel

Abstract

Full-sized ingots containing 0.004-0.019% nitrogen were made from a 0.025% aluminum-killed steel heat and processed to cold-roZled sheet under production conditions to evaluate sheet formability. This paper compares the mechanical properties obtained from the controlled nitrogen additions with those obtained for aluminum-killed steels that absorbed nitrogen during box annealing. It was found that increasing the nitrogen during steelmaking markedly increases hardness and yield strength and decreases the tensile elongation, whereas even larger amounts of nitrogen absorbed during annealing have a much smaller effect on these properties. Moreover, the experimental steels with soluble aluminum to soluble nitrogen ratios in approximately the 1.4-1.8 range have improved drawability, as indicated by r value, but large increases in nitrogen occurring during annealing da not affect r value.