RESEARCH PAPER Experimental studies on controlling of process parameters in dissimilar friction stir welding of DH36 shipbuilding steel–AISI 1008 steel Pardeep Pankaj 1 & Avinish Tiwari 1 & Pankaj Biswas 1 & A. Gourav Rao 2 & Sukhomay Pal 1 Received: 3 September 2019 /Accepted: 6 March 2020 # International Institute of Welding 2020 Abstract 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. Keywords Microstructure . Mechanical properties . Z-force . DH36 steel . AISI 1008 steel . Thermal history 1 Introduction Friction stir welding (FSW) process is a solid-state pro- cess that was patented from The Welding Institute, UK, in 1991 by Thomas et al. [1]. In the FSW process, the fric- tional heat is generated between the tool shoulder and workpiece that leads to the excessive plastic deformation all over the tool results in the joining of the two sheets. FSW technique was firstly employed to join the aluminum alloys which are very difficult to be welded by fusion welding techniques. Later it becomes highly usable for joining high-temperature/high-strength alloys like titani- um, nickel, steels, and dissimilar metals [2–6]. However, the tool wear is an important issue during FSW of these high melting point alloys, despite some alternative tool materials that were used to overcome this issue [ 7]. FSW tool materials such as tungsten (W)-based alloys, polycrystalline cubic boron nitride (pcBN), and refractive materials (i.e., rhenium and iridium) are suggested for welding of such higher melting point alloys [8, 9]. FSW process has the potential to produce defect (i.e., blow- holes, porosity, and solidification cracking) free weld joints due to a solid state in nature [ 2 , 10 – 12 ]. Moreover, low heat input during the FSW process was expected to minimize the microstructural change in the heat-affected zone (HAZ) and limiting residual stress Recommended for publication by Commission III - Resistance Welding, Solid State Welding, and Allied Joining Process * Pardeep Pankaj pankajpardeep22@gmail.com Avinish Tiwari avit252@gmail.com Pankaj Biswas pankaj.panu012@gmail.com A. Gourav Rao gourav@nmrl.drdo.in Sukhomay Pal spal@iitg.ac.in 1 Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India 2 NMRL, Ambernath, India Welding in the World https://doi.org/10.1007/s40194-020-00886-3