Determination of strength mismatch states of 316LN-HGH4169-Inconel 718 dissimilar welds at cryogenic temperature through a digital image correlation technique

Abstract 316LN steel and Inconel 718 alloy was proposed for the outer components of the magnet container and the toroidal field (TF) coils respectively, which inevitably requires welding connection resulting in strength mismatch between different base materials (BMs) and welding filler. However, local tensile properties of 316LN-HGH4169-Inconel 718 dissimilar welds at cryogenic temperature have not been characterized currently. Global tensile properties of dissimilar welds at both room temperature (300 K) and cryogenic temperature (6 K) were evaluated through the digital image correlation (DIC) technique and the electronic extensometer synchronously to verify the reliability of the DIC technique when used for dissimilar welds. Then we obtained the regional boundaries of the weld zone (WZ), the heated affected zone (HAZ), and the BM of dissimilar welds by macroscopic observations and microhardness measurements. Finally, local tensile properties of dissimilar welds at 300 K and 6 K were characterized by the localized optical DIC for the determination of strength mismatch states of 316LN-HGH4169-Inconel 718 dissimilar welds at 300 K and 6 K. This work could be applied for characterization of local property and then determination of strength mismatch states of all the dissimilar welds from room temperature to cryogenic temperature.