The role of tin in the hot-ductility deterioration of a low-carbon steel

The effect of tin on the hot ductility of a 0.15 wt pet C steel is investigated using a continuous-casting thermal simulator with three cooling rates: 5 degreesC/s, 10 degreesC/s, and 20 degreesC/s. Non equilibrium grain-boundary segregation of tin occurs during cooling and plays an important role in reducing the steel hot ductility. There is a critical cooling rate for the Sn segregation being between 5 degreesC/s and 20 degreesC/s. When the cooling rate is higher than the critical cooling rate, the segregation caused by diffusion of tin-vacancy complexes to the boundary is dominant, leading the boundary concentration of tin to increase with decreasing cooling rate. However, when the cooling rate is lower than the critical cooling rate, the desegregation caused by backward diffusion of tin away from the boundary also takes place during cooling, leading the boundary concentration of tin to decrease with decreasing cooling rate.