A Comparison Between Friction Stir Welded and Submerged Arc Welded DH36 Steel Thin Plate

The adoption of the friction stir welding process into the shipbuilding industry is being considered as a medium term issue. Currently the data on friction stir welded mild steels tends to be fragmented, with critical areas being short on specific data e.g. toughness.

This work has been put in place to directly compare friction stir welded and submerged arc welded thin plate. The plate thicknesses used were 4, 6 and 8mm thick DH36 grade steel, which are commonly used in the construction of vessels such and destroyers and frigates.

Friction stir welding was carried out using the currently most established parameters for a single sided process.

Distortion was found to be lower in friction stir welded steel, but the 4mm thick was still showing significant distortion. No issues were identified with weld metal strength, and toughness at -20^OC was found to be comparable but more uniform across the weld area than with the submerged arc welded material.

Microstructural observations have been linked to hardness, toughness and fatigue test data. The fatigue data includes the observation of preferential crack initiation relative to the trailing/leading side of the welding process.

An assessment on the feasibility of the process in a shipbuilding environment will be included based on the data presented.