Microstructure development and mechanical properties of medium carbon carbide-free bainite steels

摘要

This paper concerns with a further development of low temperature carbide-free bainite steels by decreasing its carbon content aiming at both, accelerating the bainite transformation reaction and obtaining a wider range of mechanical properties. For this purpose, three medium carbon steels containing 0.32, 0.42 and 0.56 % C were cast. Dilatometric measurements were performed to design the suitable heat-treatment parameters of these alloys. The structure was characterized using light optical microscopy, scanning electron microscopy and x-ray diffractometry. Decreasing the carbon content has facilitated accelerating the bainite transformation and obtaining the desired fine-structure in shorter time frames. Additionally, decreasing the carbon content below the eutectoid composition enabled introducing the polygonal ferrite phase in the structure which results in a wider window for the design of mechanical properties. The best alloy for producing a wide range of heat treatment parameters and hence a wide range of mechanical properties is that containing 0.42 % C.