Effects of Rare Earth Elements on Inclusions and Impact Toughness in a Weathering Steel

The effects of rare earth (RE) elements on inclusions and impact toughness of a weathering steel (Q355NHBRE) were studied in this paper. The microstructures, inclusions and impact fractures were observed by optical microscopy, scanning electron microscopy and auger electron spectroscopy. The results showed that the addition of RE elements increased the content of pearlite and modified elongated MnS and irregularly shaped composite inclusions into fine spherical RE inclusions. The segregation of RE elements towards grain boundaries reduced the segregation of impurity elements (P, S), thus purifying grain boundaries and improving grain boundary binding force. After RE alloying, Q355NHBRE steel had greater upper shelf energy and lower ductile–brittle transition temperature, which improved the low temperature impact toughness.