Effect of annealing on mechanical properties and microstructure evolution of borated stainless steels

A borated stainless steel based on the composition of type 304 stainless steel containing different amount of boron was fabricated through a conventional ingot metallurgy-hot working process, and the relationship between the microstructure and mechanical properties was investigated. As the content of boron increases, the volume fraction of (Fe,Cr)₂B increases, as predicted by thermodynamic equilibrium calculations. As the annealing proceeds at 1180°C, the plate-like shape of (Fe,Cr)₂B turned into a spherical shape. In addition, brittle fracture of the boride was dominant before the heat-treatment, but ductile mode due to the formation of dimples in the austenite was dominant after heat-treatment. In the specimen containing 1.78 wt% of boron, the Cr and Ni contents of the austenite matrix were homogenized after annealing at 1180 °C for 192 h, and the strength and ductility were simultaneously improved.