Research has shown that the acicular ferrite microstructure in steel weld metal, which provides an optimum combination of strength and toughness, is indeed intragranularly nucleated bainite. It is possible to maximize the content of acicular ferrite by increasing the intragranular nucleation sites while maintaining a critical weld metal cooling rate and the steel hardenability. This paper highlights recent research related to nucleation and growth of acicular ferrite during decomposition of austenite.

The mechanism of acicular ferrite in weld deposits

Underwater Welding - A Review The paper describes principles of underwater welding and recent trends in research works undertaken for enhance welding technology and properties of underwater welds. Department of Materials Technology and Welding at Gdansk University of Technology (GUT) has been involved in underwater welding research for over 25 years. Investigations include technology of underwater welding, and weld properties examinations. All tests have been performed with the use of self designed stands allow to perform welds in shallow depths as well as the depths up to 1000 m. The main investigation directions performed at the Department of Materials Technology and Welding are presented: Weldability of HSLA steel and factors influencing susceptibility to cold cracking of welded joints. The effects of wet welding conditions on diffusible hydrogen amount in the welds. The effects of heat input, underwater welding depths and composition of shielded gases on welds toughness.

https://cyberleninka.org/article/n/1179315.pdf

Underwater Welding - A Review

Enhancement of the fatigue strength of underwater wet welds by grinding and ultrasonic impact treatment

The current status of and the perspectives for the development of underwater welding techniques are presented in this article. The most significant problems of welding in the aqueous environments are analysed and the directions of tasks undertaken so far aimed at taking control of this difficult process are pointed out.

Development of under-water welding techniques

Characterization of the underwater welding arc bubble through a visual sensing method

Underwater wet welding offers significant cost savings over other repair techniques for submerged structures, but the weld metal mechanical properties are not equal to those of surface welds. The problems of porosity and oxidation of the weld pool as underwater depths increased were addressed by additions of manganese, titanium, boron, and rare earth metals (REM) to the coating of a rutile-based SMAW electrode. A test matrix of 60 coating formulations was prepared and test welds were made at four depths: 70, 140, 200, and 300 ft (21, 43, 61, 91 m). With the addition of titanium, a strong deoxidant, it was possible to control weld metal chemical composition. Low porosity was associated with electrodes that deposited a slag with a basicity index approaching neutral (1.0). Slag basicity may influence transfer of hydrogen to the weld pool and, thus, influence porosity. Addition of titanium and boron produced a microstructure of 60 to 90 vol-% acicular ferrite. Tensile strength increased with the combined addition of manganese, titanium, and boron. The results of this investigation demonstrated some of the adverse effects of increasing underwater depth on weld metal quality can be mitigated by modifications to the electrode coatings.

S. Liu

Papers

The effect of ferro-alloy additions and depth on the quality of underwater wet welds