Effect of Cooling Rate on the Grain Morphology and Element Segregation Behavior of Fe-Mn-Al-C Low-Density Steel during Solidification

Abstract

Mold with diameter sizes of 140 mm, 80 mm, 40 mm and 15 mm were designed to obtain the ingot of Fe-30Mn-10Al-1.1C low-density steel under different cooling rates. The influence of cooling rate on the grain morphology and elemental segregation behavior during the steel solidification process was analyzed by methods including inductively coupled plasma, scanning electron microscope and energy dispersive spectroscopy. The solidification sequence of the low-density steel was calculated by JMatPro 7.0 thermodynamic software. The results show that the microstructure of the steel is mainly austenite and contains a small amount of ferrite. The solidification order in the steel is: L → α, L → γ and α → γ, L → γ + MC. As the cooling rate increases from 1.69 °C/s to 10.28 °C/s, the ferrite phase precipitation increases by 16.7%, and the grain size decreases significantly, and in particular, the austenitic grain size decreases by 26%. With the increase in cooling rate, the microscopic segregation value of aluminum decreases approximately to 1. Additionally, the microscopic segregation of manganese showed a trend of increasing first and then decreasing. Microscopic segregation of Al and Mn can be improved significantly by increasing the cooling rate.