Effect of Rare Earth on Microstructure and Properties of Super Ferritic Stainless Steel

Scanning Electron Microscopy (SEM), Optical Microscopy (OM), image analysis, room-temperature impact test and potentiodynamic polarization technique were used to evaluate the influence of different rare earth (RE) quantity on grain size, second phase separation, mechanical properties and corrosion resistance of super ferritic stainless steel (SFSS). The results show that a proper amount of RE can refine grains, increasing the grain grade from 6.9 to 8.6. The percentage of precipitation phase was significantly decreased in the annealing at 930℃ and no chain structure was observed. RE can increase the solid solubility of carbon and nitrogen, thus suppressing carbonitride precipitation. The impact energy of SFSS containing 0.106% RE was 45.25 J, rising by 217% compared with the steel without RE. Meanwhile, RE promoted the impact fracture mechanism to transit from brittle fracture to ductile. With the content of sulfur reducing and the inclusions improved, the pitting corrosion resistance was enhanced effectively. The steel containing 0.106% RE exhibited the lowest corrosion rate.