Size distribution of inclusions in 12%Cr stainless steel with a wide range of solidification cooling rates

The effect of solidification cooling rate on the size and distribution of inclusions in 12%Cr stainless steel was investigated. A wide range of solidification cooling rates (from 0.05 to 106 K·s^-1) was achieved using various solidification processes, including conventional casting, laser remelting, and melt spinning. The size and distribution of inclusions in the steel were observed and statistically collected. For comparison, mathematical models were used to calculate the sizes of inclusions at different solidification cooling rates. Both the statistical size determined from observations and that predicted from calculations tended to decrease with increasing cooling rate; however, the experimental and calculated results did not agree well with each other at excessively high or low cooling rate. The reasons for this discrepancy were theoretically analyzed. For the size distribution of inclusions, the effect of cooling rate on the number densities of large-sized (> 2 μm) inclusions and small-sized (≤ 2 μm) inclusions were distinct. The number density of inclusions larger than 1 µm was not affected when the cooing rate was less than or equal to 6 K·s^-1 because inclusion precipitation was suppressed by the increased cooling rate.