Influence of heat input on post weld microstructure and mechanical properties of friction stir welded HSLA-65 steel

The present study focuses on the correlations of microstructures, mechanical properties and heat inputs in friction stir welded HSLA-65 steel. A new approach via Orientation Imaging Microscopy (OIM™) is developed to acquire quantitative microstructural data including bainite lath/packet and prior austenite grain size (PAG). A linear relationship between heat input and quantitative microstructural data in the weld has been established. Mechanical properties exhibit a linear relationship with heat input. Yield strength is highly dependent on grain/lath size, which follows Hall-Petch relations. These correlations can be used to determine FSW weld parameters for desired mechanical properties welds.