Temperature Measurement during Rapid Solidification of 18Cr-8Ni Stainless Steel and Its Initial Solidification Structure

A new measurement system using a silicon photo-diode was developed to investigate the precise thermal history during the initial solidification of stainless steel. From the measured cooling curve, it was confirmed there existed large undercooling before nucleation. Maximum undercooling obtained was 260 K. The undercooling increased with the cooling rate of a sample and has a strong linear dependence on the cooling rate. In the vicinity of the sample surface, the initial solidification layer was formed, which had cellular structure of metastable austenitic phase. Effect of undercooling on the micro and macro structure was also investigated quantitatively.