Available online at w.sciencedirect.com *-@0 =I0 ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTEF3'JATIONAL. 2010, 17(10): 68-74 Microstructure Tensile and Impact Toughness Properties of Friction Stir Welded Mild Steel A K Lakshminarayanan' , V Balasubramanian' , M Salahuddin' (1. Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar 608002, Tamil Nadu, India; 2. Clean Technology Division, Ministry of Environment and Forests, New Delhi 110003, India) Abstract: Microstructure, tensile and impact toughness properties and fracture location of friction stir welded AISI 1018 mild steel were revealed. The AISI 1018 mild steel plates with thickness of 5 mm were friction stir welded by tungsten based alloy tool with tool rotational speed of 1000 r/min and welding speed of 50 mm/min. Tensile strength of stir zone is higher (8%) compared to that of the base metal. This may be due to the formation of finer grains in the weld nugget region under the stirring action of the rotating tool. The ductility and impact toughness of the joints are decreased compared to those of the base metal owing to the inclusion of tungsten particles in the weld region. Key words: friction stir welding; tensile property; impact toughness; mild ,steel Friction stir welding (FSW) is a relatively new solid state joining process and is the focus of con- stant attention in joining low and high temperature materials"'. FSW has appeared as an easy, ecological and promising productive welding method that re- duces material waste and avoids radiation and harm- ful gas emissions, usually associated with the fusion welding processesC2'. FSW technology has been ex- tensively implemented in the fabrication of alumin- ium structure components for space vehicles, air- craft, automotive, and naval applications. Though FSW process is successful in joining these relatively soft materials and expanding the application of this process to harder, stronger materials such as carbon steels, stainless steels, and titanium alloys, it has proven difficult owing to the propensity of the tool to degrade during the welding processC3]. Much of the degradation may be attributed to the high heat (temperature of around 1 200 "C 1 and stresses gener- ated during friction stir welding of these high- strength However, the development of wear resistant tool materials will benefit the FSW process and pave way for the rapid implementation in the fabrication of ferrous structures and struc- tures made from other refractory materials. Biography:A K Lakshrninarayanan(1980-), Male, Doctor Candidate; Recently, there has been considerable interest in exploring the use of FSW for joining steels and other higher-melting temperature materials. Many fundamental aspects of the process still remain unan- swered, e. g. the bonding nature of joint and materi- als flow pattern during weldingC5]. Few papersC6-'23 are available on friction stir welded carbon steels, but there is a need for further experimental research to understand the fundamental mechanisms associat- ed with the weld formation process and the welding quality. Hence, this preliminary investigation was carried out to understand the microstructural chan- ges, tensile and impact toughness properties and fracture location of friction stir welded AISI 1018 mild steel. 1 Experimental The rolled plates of AISI 1018 steel with thick- ness of 5 mm were cut to the required dimensions (300 mmX 150 mm) by abrasive cutting. A noncon- sumable rotating tool made of tungsten based alloy shown in Fig. 1 was used to fabricate FSW joints. The tool was manufactured through power metallurgy route having a shoulder diameter of 20 mm and a ta- pered pin, tapering from 9 mm at the shoulder to 7 mm E-mail: akln2k2@yahoo. corn; Received Date: October 15, 2009