Assessment of fatigue life and crack growth resistance of friction stir welded AISI 409M ferritic stainless steel joints

Fatigue life and fatigue crack growth behaviour of friction stir welded AISI 409M grade ferritic stainless steel joints in comparison with the base metal was studied. The fatigue life and fatigue crack growth behaviour were evaluated using hourglass and centre cracked tension specimens, respectively. A 100 kN servo hydraulic controlled fatigue testing machine was used to test the specimens under constant amplitude uniaxial tensile load with a stress ratio of 0.1 and a frequency of 15 Hz. It is found that, the joint fabricated by the friction stir welding process showed superior fatigue life and fatigue crack growth resistance compared to that of the base metal. This was mainly due to the synergetic effect of dual phase ferritic–martensitic microstructure, superior tensile properties and favourable residual stress, which inhibited the growth of cracks compared with that of the single phase ferritic stainless steel base metal.