TWI

Butt joints were fabricated by friction stir welding (FSW) in 4340 steel (0.43%C, 0.69%Mn, 0.76%Cr, 1.76%Ni, 0.24%Mo, 0.43%V, 0.16%Cu) and between 4340 steel and Inconel 718 (Ni, 17-21%Cr, 4.7-5.5%Nb, 2.8-3.3%Mo) and their microstructure and mechanical properties were investigated. The FSW procedure incorporated preheating at 320-330 deg.C, complete FSW at the preheat temperature and a post-FSW thermal cycle designed to optimise mechanical properties. Weld nugget and thermomechanically affected zone microstructures were observed by optical microscopy and SEM. Mechanical properties were characterised by hardness measurements, tensile tests and side-bend tests. Premature failure of dissimilar joints during side-bend testing was studied by microstructural analysis of the interface morphology and nano-indentation hardness testing.

12th International Symposium, 26-28 Jun 2018, Session 7B: High Temperature II, Paper 01