Experimental studies on controlling of process parameters in dissimilar friction stir welding of DH36 shipbuilding steel–AISI 1008 steel

In the present work, DH36 steel and AISI 1008 steel sheets were joined using friction stir welding (FSW) process to investigate the influence of the rotational speed, traverse speed, and tool offset on temperature distribution, z-force, microstructure, and mechanical properties of the welded specimens. At a traverse speed (v) of 50 mm/min with a rotational speed (ω) of 600 rpm and tool offset of 2 mm, the maximum impact toughness and hardness were obtained due to higher grain refinement. The transverse tensile test specimens fractured in the weaker material (i.e., AISI 1008 steel) and exhibited the ultimate tensile strength values at least on the level of the weaker material. The impact toughness and hardness were highly dependent on the grain size variation. The effect of pitch ratio (ω/v) on grain size variation was more as compared with that on tool offset. Increasing the pitch ratio reduced the grain size and improved the impact toughness and hardness. Stir zone exhibited the acicular-shaped bainitic ferrite in DH36 steel and Widmanstatten ferrite grains in AISI 1008 steel. The higher hardness values were observed in thermo-mechanically affected zone of both steels due to significant grain refinement. Increasing the rotational speed and decreasing the traverse speed result in a higher welding temperature, which reduced the z-force.