Effects of Ce on the microstructure and properties of 27Cr-3.8Mo-2Ni super-ferritic stainless steels

Abstract

The effect of Ce on the microstructure, mechanical properties and corrosion resistance of 27Cr-3.8Mo-2Ni super-ferritic stainless steel were investigated by FactSage 7.2, OM and SEM. The results reveal that when the Ce content increases from 0.00 wt-% to 0.0498 wt-%, Al2O3 inclusions wrapped by irregular (TiNb)N are gradually modified into spheroidal CeAlO3, Ce2O3, and Ce2O2S inclusions, the rare earth inclusions are smaller than 1.0 × 10−6 m (1.0 μm) and dispersedly distributed. The diameter of recrystallized ferrite grain is decreased, the mechanical properties of super-ferritic stainless steels are well improved, impact fracture appearance transforms from pre-dominant cleavage to ductile fracture at 298 K (25°C), and the cleaving step of the fracture becomes smaller at 243 K (−30°C), the uniform corrosion resistance to H2SO4 of steels with is enhanced especially in 40 vol.-% H2SO4 at 333 K (60°C). In addition, the microstructure and properties could not be further improved with 0.0744 wt-% Ce content.