Influence of nano carbide free bainitic transformation and retained austenite on toughness of railway wheels

The development of nano-carbide-free bainite (NCFB) through high silicon spring steel (EN45-compositions of steel are 0.551% C, 1.756% Si, 0.825% Mn, and 0.13% Cr). Silicon-rich steel avoids the precipitation of carbide. Heat treatment austenization temperature per sample 18 min heating at 900 °C. The desired microstructure of the treated samples was achieved through a heat treatment process at different austempering temperatures, such as 300 °C, 350 °C, and 400 °C, with holding times of 10, 20, and 30 min, after which they were shot peened for developed nano structure of bainite. In this study, material characterization studies through FESEM, the phase fraction, and retained austenite stability have been critically analysed with the help of X-ray diffraction and scanning electron microscopy. Toughness is analyzed through an impact testing machine under all conditions. The result 82.2% percent can be observed at 400 °C, 27.6 J to 50.3 J between 10 and 20 min, then gradually stabilized with a total increase of about 17%.