Influence of austenite grain size on the transformation product and hardness in the HAZ for micro-alloyed steel S700MC

摘要

Austenite grain size (AGS) is a microstructural parameter that highly influences austenite decompositions during cooling from an austenitizing temperature. Since the precipitates coarsening and dissolution are key parameter for austenite grain growth, the precipitation kinetics therefore, indirectly causes the variation of transformation products in the HAZ. The phase constituents have a big contribution to the hardness or to the tensile strength of the material. Therefore, the transformation products from austenite are very important to be investigated in the HAZ. In this study, a HAZ is physically simulated using Dilatometer. Dilatometer samples are heated to peak temperatures in the range between 700 and 1300X employing the heating rate of about 450-500℃/s and subsequently cooled down by controlling t_(8/5) time of 10s. The metallography is then conducted using conventional metallographic technique and the microstructures have been investigated. A significant change in the transformation products is observed from the fine grained to the coarse grained region. The fine grained region is dominated by ferrite andferritic bainite, whereas mainly bainitic microstructure is developed in the coarse grained region.