Study On Formation Mechanism Of Sheave-like Bainite In The High-carbon Silicon Steels

In this paper, high-carbon steel with high-silicon is taken as the research object. Thesamples were austenitized above Acm temperature and quenched at different temperatures fora short time (less than30min). Metallographic Analysis, X-Ray Diffraction (XRD),Mechanics Performance Testing and Transmission Electron Microscope (TEM) were used toresearch the formation of bainite sheaves, the mechanics performance of steel samples andfine structures of bainite sheaves. The formation characteristic of bainite sheaves and theirmechanics performance were studied also. At the same time, fine structures features andformation mechanism of bainite sheaves were researched.The experimental results show that, the induction period of bainite transformationdecreases with austenitizing temperature rising. Shortest incubation period changes from320sto200s, and tip-temperature change from280℃to250℃.Sheave-like bainite is composed ofbainite ferrite and retained austenite, but no carbide. Morphology of sheave-like bainite issingle needles in early stage, and then change to parallel sheaves with isothermal temperaturerising and isothermal time extending. And bainite transformation terminated nearly whenisothermal about30min, but an incomplete-reaction phenomenon is found.TEM research shows that, sheaves of bainite consist of more delicate structures, whosefine structures are high density dislocations, but no twin crystal. Growth steps are found in thefront of upper bainite sheaves formation temperature zone at280℃, and no boundary shapedistortion induced by stress field can be seen in TEM photograph. Contrast difference ofstrain field exists in lower bainite sheaves obtained by quenching at250℃. So it can beconcluded that, formation mechanism of sheaves in upper temperature formation area is like adiffusion mechanism, and formation mechanism of sheaves in lower temperature formationarea is like a shear mechanism.