Influences of alloying elements and solidification modes on the nitrogen content of nitrogenous stainless steel

The effects of Mn,Cr and Ni on the solidification mode and nitrogen content of as-cast stainless steel were studied by smelting experiments. The key influencing factors on nitrogen content were explored. The coefficients of interaction between alloying elements and nitrogen were analyzed in molten steel and solidified steel. The results show that the nitrogen content is determined by both the solubility of nitrogen in molten steel and the solidification mode. When the solubility of nitrogen increases and the solidification mode changes according to the sequence of F→FA→AF→A,the solid solubility of nitrogen in the primary crystal enhances and the emission of nitrogen gas lessens during solidification. With the increase of Mn content,the nitrogen content increases monotonically.However,the nitrogen content varies with the Cr and Ni content in the above processes non-monotonically. The content of Mn does not change the solidification mode which is always FA,and the interaction coefficient is-0.0286,similar to that in molten steel; whereas the increase of Cr and Ni changes the solidification mode according to the routine of F→FA→AF→A and FA→AF→A,respectively,the interaction coefficients between alloying elements and nitrogen in the steel are not a fixed value,E_N^Cr=-0.046 and-0.011,E_N^Ni=-0.011 and 0.033,respectively.