An investigation of microstructural evolution in electron beam welded RAFM steel and 316LN SS dissimilar joint under creep loading conditions

Microstructural evolution in creep tested electron beam welded Reduced Activation Ferritic Martensitic (RAFM) steel and 316LN stainless steel dissimilar weld joints has been studied at 823 K under different stress levels. The rupture life of the weld joints spanned between 17,596 and 190 h with variation in applied stress from 160 to 220 MPa. Failure of the weld joints occurred in the RAFM steel side at all stress levels. Microstructural examination showed that the failure location shifted from the unaffected base metal region of the RAFM steel to the 'soft region' within the heat affected zone (HAZ) in the RAFM steel side with decrease in applied stress. The strength mismatch between various regions within the HAZ of RAFM steel and the microstructural instability of 'soft region' in the RAFM steel are the two important factors which dictate the failure location and rupture life of the joints.