Wed, 28 April, 2021
In 2020, TWI held a successful webinar on friction stir welding of steel to showcase our latest developments.
In a continuation of the testing being performed on the new tools developed by Element Six for friction stir welding steel, multiple tools from several different production batches have now each reached an accumulated weld distance in excess of 60m.
The welds are being performed as multiple, five metre long welds in 6mm thick S355 steel, at a welding speed of 300mm/min.
After reaching 60m of weld, a number of the tools were used to make butt weld samples for metallography and mechanical testing to ensure that the weld quality remained good. The cross weld tensile test pieces failed in a ductile manner in the parent metal some distance from the weld and HAZ as can be seen in the figure below. This is consistent with previous experience of friction stir welds made in steel.
The mean ultimate tensile strength of the tested samples was 562 MPa. No parent metal was tested but EN 10025-3 for S355 steel in the fine grained, rolled condition specifies a minimum UTS requirement of 520 MPa for steel less than 40mm in thickness. As the welded samples failed in the parent metal, it can only be stated that the weld strength was at least equal to 562 MPa and exceeded the minimum parent metal requirement.
Cross weld tensile test pieces in 6mm thick S355 steel showing ductile failure in the parent metal away from the weld zone.