Isothermal Trnsformation of Austenite to Bainite in an Eutectoid Steels

Bainite consists of aggregates of platelets or laths of ferrite separated by regions of phases such as austenite or martensite. Also, bainite is formed over a wide range of temperatures and has different morphologies at different transformation temperatures. The aim of the present work is determination of the kinetics of the austenite transformation over the temperature range 280-580 oC. Results showed that austenite, in the eutectoid steel, transformed to bainite over the range 280-555 oC, according to separate C-curves on the isothermal transformation diagram. It was shown that above 555 oC the microstructure is pearlitic and at the austenite stability region (bay) both pearlite and bainite coexisted together ≈ 555 oC. The microstructure at these region was spiky (stepwise) front. The chemistry of phases and distribution of alloying elements studied by using EDS technique. Finally, microhardness and Barkhausen jumps were also studied.