Effect of welding speed on friction stir welds of GL E36 shipbuilding steel

Abstract

The aim of this study was to characterize mechanical and microstructural characteristics of friction-stir-welded GL E36 shipbuilding steel. The tool rotational speed was kept constant at 500 rpm and different welding speeds were used (1, 2 and 3 mm/s) to achieve different heat inputs. Thermal cycles were monitored by thermocouples placed near the weld face. The welded joints showed a very good esthetics and homogeneous surface quality that indicate a stability of the considered process parameters. The welded joints properties were analyzed by metallography and mechanical tests such as microhardness, tensile and bending. Macrostructural observations were done at the beginning, middle and ending of the welded length. In addition, radiographic inspection was carried out. The pcBN tool exhibited good wear behavior even after welding around 8.5 m where no apparent loss in dimensions and geometrical features of the probe and shoulder were found. The macrographs displayed different microstructural features and material flow pattern among the heat inputs achieved. A large microstructure gradient was observed, especially within the stirred zone. All the tensile samples broke at the base material showing that the joints achieved higher strength. Microhardness peaks of about 400 HV were also encountered in all the joints. Finally, for welding speeds of 2–3 mm/s the thermocouples presented the most uniform thermal profiles.