Microstructural Investigation of SPA-C Steel Sheets Used in Railway Vehicles in Resistance Spot Welding

This paper presents an experimental study on resistance spot welding of SPA-C steel sheets used in side wall and roof in rail vehicles. SPA-C steel sheets having 2.3 mm thicknesses were joined by using resistance spot welding as lap joint. A timer and current controlled resistance spot welding machine having 120 kVA capacity and a pneumatic application mechanism with a single lever was used to prepare the specimens. Welding periods were chosen as 5, 10, 15, 20, 25 and 30 cycles and also welding currents were increased from 6 kA up to 14 kA by rise of 0.5 kA. The electrode force was kept constant at 6 kN. The micro and macro-structures of prepared welding specimens were investigated by means of an optical microscope and scanning electron microscope (SEM) in order to see the joinability of SPA-C steel sheets by resistance spot welding.