Nowadays, many applications are utilizing bainite as, for instance, lightweight design of car bodies. Bainite phase has higher hardness compared with ferrite, pearlite and austenite, but still retain better toughness than martensite. To create a bainite, however, a specific method called austempering is needed where the steel is quenched in the temperature below pearlite formation and held for a certain time. The optimalization of the quench temperature and holding time become very important. In this study, series of heat treatment processes have been carried out on the S45C steel to form bainite structure. The heat treatment processes include variations of transformation temperature from 200 -400°C, and holding time from 1 -5 hours, The lower salt-bath temperature and longer holding time generated larger amounts of bainite. In average, the highest hardness result was achieved on 5 hours holding time at 200°C with 42 HRC, and the lowest hardness was on 1 hour holding time at 400°C with 22 HRC.