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Demonstrating effectiveness of FSW steel for shipbuilding

TWI was among a group of eight organisations that collaborated on a project to investigate the viability of friction stir welding of steel for shipbuilding applications.

Friction stir welding (FSW) is a well-established process for joining lightweight aluminium and magnesium structures, its solid-state nature bringing a number of advantages over higher-temperature welding methods. These metals’ relatively low melting point makes them excellent candidates for the FSW technique.

Now research carried out for an EU project, HILDA (High-Integrity Low-Distortion Assembly), has shown how FSW can be used to join steel, a metal with a significantly higher softening point that makes much greater demands on the FSW tool.

Improved processes for the shipbuilding sector

This research was carried out with the shipbuilding industry in mind, so efforts focused on joining typical marine engineering steel, grade DH36. HILDA examined two aspects of the FSW technique: weld quality and its economic viability.

Efforts focused on characterising the microstructure of friction stir welds, and identifying its relationship with different weld parameters. Evaluation of the microstructure allowed a preliminary FSW parameter envelope to be identified, which was refined over the course of the project. The welding speeds attainable in typical 6mm-thick shipbuilding steel were increased from 100mm/min to 500mm/min, making the process competitive, in terms of production speed, with conventional fusion welding techniques.

Research showed that the welds produced have enhanced strength, toughness and fatigue life when compared with conventional arc or laser welds, and the process is also tolerant to defects.  A programme of classification compliance testing is currently being developed that recognises these property enhancements.

Increased performance and practicality

The case for using FSW in shipbuilding is further strengthened by its low weld-induced distortion,

excellent surface quality and potential to be carried out underwater. Results from the HILDA project, which ended in August 2015, are available on the European Commission Community Research and Development Information Service website.

For more information on our FSW expertise and how it could benefit your business, please email

Friction stir welding in half-inch-thick shipbuilding steel
Friction stir welding in half-inch-thick shipbuilding steel