Behaviors of novel manufacturing 1215MS+Bi steel in casting thermal processes

Currently, the effects of cooling and heating rates on the sizes and morphologies of impurities and grains in the typical Bi-bearing 1215 MS steels in the manufacturing processes have never been studied, so this work aims to deduce their solidification and heating behaviors. The in-situ heating experiments were carried out using a high-temperature laser confocal microscope. Results show that bismuth could refine the dendrite arm spacing. Liquid Bi segregates at the solidification interface of grain boundary and inhibits the growth of grains. The surface tension of Bi-MnS is smaller than Bi-Fe. A big heating rate aggravated the thermal vibration of grains in local areas and resulted in large local temperature difference. Slow heating and heat preservation are helpful for sulfides to absorb heat and for achieving large grains. To sum up, this study broadens the recognition of free-cutting steels and further contributes to the development of new steel grade.