A Novel Approach for Evaluating the Contraction of Hypo-Peritectic Steels during Initial Solidification by Surface Roughness.

The contraction of peritectic steels in the initial solidification has an important influence on the formation of surface defects of continuously cast slabs. In order to understand the contraction behavior of the initial solidification of steels in the mold, the solidification process and surface roughness in a commercial hypo-peritectic and several non-peritectic steels were investigated using Confocal Scanning Laser Microscope (CSLM). The massive transformation of delta-Fe (δ) to austenite (γ) was documented in the hypo-peritectic steel, which caused surface wrinkles and greatly increases the surface roughness of samples in the experiments. Surface roughness (Ra(δ→γ)) was calculated to evaluate the contraction level of the hypo-peritectic steel due to δ–γ transformation. The result shows that the surface roughness method can facilitate the estimation of the contraction level of peritectic transformation over a wide range of cooling rates.