Properties optimization through enhanced cooling rate using liquid CO_2 in friction stir welding of medium carbon low alloy S45C steel

摘要

Grain refinement, which can simultaneously improve both strength and toughness, has several advantagessuch as avoiding additional alloying elements, skipping additional heat treatments like soft annealing,quenching and tempering, and high strain rate superplasticity at medium and elevated temperatures whencompared with the high strength quenched and tempered steels [1]. For various industrial applications,friction stir welding (FSW), in particular, is one of the essential processing steps to achieve finedmicrostructure. Recently, Fujii et al. [2] reported that both strength and ductility improves by theenhanced cooling rate using liquid CO2 during the FSW of high carbon steel when performed below theA1 temperature. In their study, detailed investigations of the microstructure evolution in conjunction withthe mechanical properties are lacking. Therefore, this study emphasizes this issue in the FSW of mediumcarbon low alloy S45C steel sheets.