Microstructure and mechanical properties of austempered high silicon cast steel

The influence of austempering treatment on the microstructure and mechanical properties of silicon alloyed cast steel has been studied. The experimental results show that an ausferrite structure consisting of bainitic ferrite and retained austenite can be obtained by austempering the high silicon cast steel in a large temperature range (240–400°C). No carbide would precipitate in the structure. The experimental results also indicate that a full ausferrite structure could be obtained by austempering the steel with a silicon content around 2.64%. Lower silicon would result in the formation of martensite, and excessive silicon would cause proeutectoid ferrite in the structure. The full ausferrite structure has high strength, toughness and hardness. With the increasing of silicon content, the strength decreases, the hardness keeps unchanged and the toughness firstly increases to a maximum value and then decreases. The material has also excellent work hardening ability.