Microstructure and mechanical properties of ultrasonic assisted underwater wet welding joints

•A new weld method, ultrasonic assisted underwater wet welding process was studied to achieve high-performance joints.•Arc stability and mechanical properties enhanced obviously when the ultrasonic applied.•The fracture occurrence of the welded joint during tensile testing was transferred from the joint to the base metal.•The maximum angle of bending testing was increased from 21 ° to 84 °.

A new weld method, ultrasonic assisted underwater wet welding process (U-FCAW), was explored in order to achieve high performance welding joints. The addition of ultrasonic can form an acoustic field between the workpiece and the ultrasonic radiator. The joints were welded by ultrasonic assisted underwater wet welding process (U-FCAW) and underwater flux cored arc welding (FCAW), respectively. The effect of ultrasonic on the arc stability, microstructure and mechanical properties, such as tensile, bending and hardness distribution, was investigated. The results indicated that arc stability improved when ultrasonic was applied. The amount of martensite (M) and upper bainite (BU) was decreased, while the granular bainite (BG) and acicular ferrite (AF) increased, when ultrasonic was applied during welding. The tensile strength and the bending properties were substantially enhanced. The fracture occurrence of the welded joints during tensile testing was transferred from the joint to base metal, compared to FCAW. A 46% and 48% increase was found in the tensile strength of the upper and lower layers, respectively. The maximum angle during bending test was increased from 21° to 84°.

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