High-strength low alloy steels are a class of steels used in applications that require high strength and good weldability, including ship hulls, gas pipelines and oil industry. One way to build parts is fusion welding that create areas with a large grain size in the heat-affected zone and increased susceptibility to hydrogen cracking. One way to solve this problem is to use solid state friction stir welding (FSW (process. In this study, microstructure, mechanical and corrosion properties of high strength low alloy steel friction stir welding sections X-60 has been compared with gas metal arc welding (GMAW) method. The tool that used in this research for FSW is made of WC with 16mm shoulder diameter and 5mm pin diameter and for GMAW method the AWS ER70S has been used as the filler metal. Microstructural evaluation, mechanical and corrosion properties of friction stir welding X-60 cross sections examined by optical microscope, scanning electron microscopy, tensile and micro-hardness tests, open current potential, respectively. The results of the thermal history in the area of stir zone, indicating that temperature reach in stability of the austenite phase in the weld zone. Therefore, changing welding parameters and thereby, change the heat input during friction stir welding have a great impact on maximum temperature and cooling rate that cause creating ferrite and bainitic ferrite in the weld zone. This change in microstructure of weld zone cause to improve mechanical properties that increase yield strength from 380 MPa to 420 MPa. Also, the friction stir process cause increasing hardness of 220 Vickers to an average of 280 Vickers and uniform distribution of hardness in the cross-section of friction stir joints. In fusion welding the weld zone tensile strength and hardness compared with base metal has increased, but compared to the friction stir welding is less amounts.
