The object of the present investigations was to evaluate the effect of flash butt welding parameters on microstructures and mechanical properties of HSLA 590CL welded joints in wheel rims by adjusting welding parameters separately. The amount of Widmanstatten ferrites and bainite in the weld metal, and grain size were observed with the adjustment of welding parameters. The tensile strength of welded joints met the strength requirement of wheel rims steels, but the tensile strength and tensile fracture were different in different welding parameters. Micro-hardness distributions of welded joints in different welding parameters were similar, that is the maximum micro-hardness occurred in the weld and micro-hardness decreased from the weld to base metal. A certain degree of softening phenomenon was found in the heat affected zone (HAZ), which should result from the heat input in the flash butt welding. Two failure mechanisms of wheel rims in the expanding process were investigated. The first type fractured at the HAZ and showed ductile fracture characteristics, the crack initiation located at the thinning location. The second type fractured at the weld and showed brittle fracture characteristics.