Citation: Ahmed, M.S.I.; Ahmed, M.M.Z.; Abd El-Aziz, H.M.; Habba, M.I.A.; Ismael, A.F.; El-Sayed Seleman, M.M.; Abd El-Aty, A.; Alamry, A.; Alzahrani, B.; Touileb, K.; et al. Cladding of Carbon Steel with Stainless Steel Using Friction Stir Welding: Effect of Process Parameters on Microstructure and Mechanical Properties. Crystals 2023, 13, 1559. https://doi.org/10.3390/ cryst13111559 Academic Editor: Indrajit Charit Received: 13 September 2023 Revised: 9 October 2023 Accepted: 17 October 2023 Published: 1 November 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). crystals Article Cladding of Carbon Steel with Stainless Steel Using Friction Stir Welding: Effect of Process Parameters on Microstructure and Mechanical Properties Mahmoud S. I. Ahmed 1 , Mohamed M. Z. Ahmed 2,3 , Hussein M. Abd El-Aziz 1 , Mohamed I. A. Habba 4 , Ashraf F. Ismael 1 , Mohamed M. El-Sayed Seleman 3 , Ali Abd El-Aty 2,5, * , Ali Alamry 2 , Bandar Alzahrani 2 , Kamel Touileb 2 and Wael M. Fathy 1 1 Department of Mining and Petroleum Engineering, Faculty of Engineering, Al-Azhar University, Cairo 11651, Egypt; eng.mah.soliman@gmail.com (M.S.I.A.); dr_eng_hussein@yahoo.com (H.M.A.E.-A.); ashrafismael1193.el@azahr.edu.eg (A.F.I.); waelfathy.12@azhar.edu.eg (W.M.F.) 2 Department of Mechanical Engineering, College of Engineering at Al Kharj, Prince Sattam bin Abdulaziz University, Al Kharj 11942, Saudi Arabia; moh.ahmed@psau.edu.sa (M.M.Z.A.); a.alamry@psau.edu.sa (A.A.); ba.alzahrani@psau.edu.sa (B.A.); k.touileb@psau.edu.sa (K.T.) 3 Department of Metallurgical and Materials Engineering, Faculty of Petroleum and Mining Engineering, Suez University, Suez 43512, Egypt; mohamed.elnagar@suezuniv.edu.eg 4 Mechanical Department, Faculty of Technology and Education, Suez University, Suez 43518, Egypt; mohamed.atia@suezuniv.edu.eg 5 Mechanical Engineering Department, Faculty of Engineering-Helwan, Helwan University, Cairo 11795, Egypt * Correspondence: a.hassibelnaby@psau.edu.sa Abstract: The aim of this study is to investigate friction stir welding (FSW) to join A304 austenitic stainless steel and low carbon steel A283 Gr. C in-lap configuration to clad the carbon steel with highly corrosion-resistant stainless steel. Thus, a wide range of FSW parameters were investigated such as FSW tool rotation rate from 200 to 400 rpm, tool traverse speed from 25 to 75 mm/min, and vertical forces of 20 to 32 KN. The FSW parameters combination of high welding rotation rate (400 rpm) and high vertical forces (32 KN) results in rejected joints in terms of surface appearance and clear surface defects. On the other hand, rotation rates of 200 and 300 rpm with different welding speeds and vertical forces resulted in some sound joints that were further investigated for microstructure and mechanical properties. The sound lap joints were examined via optical microstructure, SEM, and EDS investigations. For the mechanical properties, both tensile shear testing and hardness testing were used. The transverse macrographs showed intermixing between the two dissimilar materials with an almost irregular interface. The hardness profile in both materials showed a significant increase across the different regions from the Base Material (BM) to the nugget zone, with a maximum value of 260 Hv in the stainless steel and 245 Hv in the carbon steel. This increase is mainly attributed to the grain refining in the weld region due to the dynamic recrystallization and transformations upon the thermomechanical cycle. The tensile shear load of the joints varied from 20 to 27 KN for the FSWed joints, with the highest joint tensile shear load of 27 KN for that produced at 300 rpm tool rotation and 25 mm/min welding speed. Keywords: carbon steel; stainless steel; friction stir welding; lap joint; mechanical properties 1. Introduction Friction stir welding (FSW) is a distinct solid-state welding technique. Unlike tra- ditional fusion welding methods that melt materials, FSW operates by generating heat through friction to soften the workpieces without reaching their melting point [1]. This process involves using a specialized non-consumable rotating tool with two primary com- ponents: a pin, which penetrates the workpieces, and a shoulder, which rests on the surface of the welded materials [2]. As the tool rotates and traverses along the joint line, the Crystals 2023, 13, 1559. https://doi.org/10.3390/cryst13111559 https://www.mdpi.com/journal/crystals