Effect of Austempering Time and Temperature on the Microstructure and Hardness of Bainitic Silicon Steel

In this research, the effect of austempering heat treatment time and temperature on the mechanical properties and microstructure of high silicon steel were investigated. The melting process of this alloy was carried out in an induction furnace with the capacity of 20 kg followed by casting in a Y-block mold cavity. After cutting, the samples were austenitized for 2 hours at 1150ºC and austempered at 250 and 300ºC temperatures for 2 to 72 hours. The achieved microstructure showed nanometer layers of bainitic-ferrite, and retained-austenite between them. Increasing the austempering time led to the increment of the amount of bainitic-ferrite. The amount of bainitic-ferrite in samples, austempered at 250ºC, was 84% and in the maximum state was about 91%. A maximum hardness value of 611 HV was obtained in samples austempered at 250ºC for 72 hours.