Abstract: It has been found that carbide-free bainite exists in an as-cast medium manganese steel (1.0%~1.8%C, 5.0%~9.0%Mn, 0.6%~1.5%Si) structure. The microstructure of the steel at room temperature consists of austenite and carbide when cooling rate I higher than 40℃/min, and of carbide-free bainite, pearlite, austenite and carbide when cooling rate is less than 20℃%/min. Carbide-free bainite mainly formed between 624~200℃ during cooling. A lot of carbide-free bainite is obtained in sand mold castings with sections thicker than 15mm. The hardness, toughness and wear resistance of the carbide-free bainite containing s cast medium manganese steel are very good.

Key words: 贝氏体, 锰钢, 铸态组织