Effect of welding sequence of a multi-pass temper bead in gas-shielded flux-cored arc welding process: hardness, microstructure, and impact toughness analysis

Abstract

Welding is used in ships, military, buildings, industrial machinery, automobiles, and many other industries. Problems associated with welding are common issues encountered in these fields. This paper investigated the weld profile, impact toughness, microhardness, and microstructure of a JIS SS400 structural multi-layer welding joint using gas-shielded flux-cored arc welding (FCAW-G). It further examined the effects of temper bead welding (TBW) made with two different welding processes, namely with 4 Layers 4 Passes (4L4P) and 4 Layers 10 Passes (4L10P). Thermocouples were fixed to measure the thermal cycles, and the temperature distribution curves along the weld seams were measured by infrared radiation (IR) images. All welded samples were checked using nondestructive phased array ultrasonic testing (PAUT) to ensure defect-free samples before the experiments commenced. The Charpy impact tests were finished at 20 and −20 °C, respectively. Vickers microhardness measurement was carried out at room temperature. The 4L4P welding process was found to improve the impact toughness of the welding joints. Ferrite (F) and acicular ferrite (AF) were observed via an optical microscope (OM) analysis of the 4L4P welding process, which was more effective in tempering the heat-affected zone (HAZ). In addition, it was found that the 4L4P welding process produced an overall lower hardness than the 4L10P welding process. The microstructure of the welding joints as well as the mechanical properties including impact toughness and microhardness were studied by using a scanning electron microscope (SEM) attached with an energy-dispersive spectrometer (EDS) and an OM.