This review article summarizes the extensive research works carried out on ferrous alloys and critically examine several aspects of FSW in these materials. Particularly suitable tool materials, tool geometry, effect of tool geometry in metallurgical and mechanical properties of weldment were being discussed. Ever since The Welding Institute (TWI) developed the Friction Stir Welding (FSW) process, extensive studies were being carried out by joining different materials in various laboratory. Initially FSW process was developed for aluminium alloys slowly the technique is adopted for other softer materials such as magnesium, lead and zinc. Later, improvement in tool material lead to use of the eco-friendly welding process (FSW) to other hard materials such as copper, brass, stainless steel, hardened steel and superalloys. Even though several studies shows the capacity of FSW process to join hard materials, the process creates high stress and temperature at the stir zone (approximately 1300°C) which endorses fast tool degradation is the major concern during the process. High tool cost due to fast tool degradation, makes commercial application of FSW on hard metal as challenging. Introduction of polycrystalline cubic boron nitride (PCBN) and tungsten alloys tool materials made FSW possible on stainless steel, hardened steel and superalloys with outstanding results in terms of weld strength and microstructural properties. © 2017 Elsevier Ltd.