The most obvious role of nitrogen in cast iron is to stabilize pearlite. The formation of ferrite can be effectively inhibited when w (N) =0.005~0.0175%. More than this range produces a strong stable carbide action, and even causes the casting to produce white tissue. In thick wall gray cast iron,w（N）>0.008% Some compact graphite can appear in 0.008%, the flake graphite becomes shorter and thicker, and the end of the flake is round and passivated.
Nitrogen has influence on the tensile strength of gray cast iron. The tensile strength can be improved by increasing nitrogen content in a suitable range.
w（N）<0.008%The elongation and impact value of 0.008% ductile iron castings will not change due to changes in nitrogen content. w (N) =0.008%~0.012% can reduce the elongation by 10%~15%. With the increase of nitrogen content, the decrease of elongation can reach 30%~50%.
Malleable cast iron w（N）>0.008%, the decomposition rate of cementite was decreased and the annealing time was significantly prolonged.