Correlation of Microstructure with Mechanical Behavior of HSLA-100 Weld Metal Produced By GTAW Method

In this study, welding of high strength low alloy steel, HSLA-100 was performed using three fillers metals, cut from base metal (HSLA-100), ER100S-G and ER120S-G by GTAW procedure. Microstructural studies were conducted using optical and scanning electron microscopes. Tensile, impact and hardness tests were also used to evaluate the mechanical properties of the joint. The results showed that the microstructure of HSLA-100 weld metal included granular bainite and polygonal ferrite, ER100S-G weld metal consisted of acicular, Widmannstatten and grain boundary ferrites and ER120S-G weld metal comprised of acicular, polygonal and quasi-polygonal ferrites. Furthermore, the formation of a secondary phase (constituent) of martensite / austenite (M / A) was observed in the microstructure of all weld metals. The predominant form of this phase in HSLA-100 and ER100S-G weld metals was blocky type and formed along the prior austenite grain boundries and in ER120S-G weld metal was in the form of stringer type. The results of mechanical tests demonstrated that among weld metals, ER120S-G weld metal had the highest tensile strength (859 MPa), percent elongation (22%), impact toughness (45 joule) and hardness (294.7 HV30). whilst, the ER100S-G weld metal had the lowest tensile strength (775 MPa) and hardness (268.4 HV30) and the HSLA-100 weld metal had the lowest impact toughness (25 Joule).