Inclusions and solidification structures of high pure ferritic stainless steels dual stabilized by niobium and titanium

Abstract

As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the quality of ingots. Niobium and titanium are usually used to react with carbon and nitrogen to improve the properties of ferritic stainless steels. In this research, combined with thermodynamic calculation, effects of niobium and titanium on the inclusions and solidification structures in three kinds of high pure ferritic stainless steels with different titanium additions were investigated by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy disperse spectrometer (EDS). Results show that Al2O3 and a few (Nb,Ti)N particles form when titanium addition is 0.01 %. Furthermore, inclusions are mainly TiN and Al2O3–TiOx–TiN duplex inclusions when titanium addition is more than 0.10 %. Those two types of inclusions are in well distribution, and can afford nuclei to the solidification process. Therefore, the ratio of equiaxed zone increases with the increase of titanium addition. The ratio increases from 42.1 % to 64.0 % with the titanium addition increasing from 0.01 % to 0.10 %, and it increases to 85.7 % when the titanium addition reaches 0.34 %.