Effects of Modified Inclusions and Precipitates Alloyed by Rare Earth Element on Corrosion and Impact Properties in Low Alloy Steel

This study has focused on the morphology and distribution of inclusions and precipitates modified by rare earth (RE) elements, which has a decisive influence on microstructure, corrosion properties and impact behaviors in Q355 low alloy steel. Characterized by the method of electrolytic extraction and ASPEX-scanning electron microscopy (ASPEX-SEM), small-sized spherical RE inclusions have been modified to replace elongated MnS and large-sized Al2O3. Q355RE steel after RE alloying has lower corrosion rate and higher value of α/γ, due to the formation of stable and dense rust layers. Q355RE steel also exhibits better resistance to fracture at low temperature, owing to the presence of RE modification to inclusions and its effects on reducing crack initiation and propagation. Nano-scale RE precipitates containing sulfur and phosphorus is observed along grain boundaries by transmission electron microscopy (TEM). The purification of grain boundaries by RE is beneficial to the improvement of corrosion and impact properties.