Assessment of Strain Age Cracking in Fusion Welded Additively Manufactured Ni-Superalloy Sub-Components

Gas tungsten arc welding (GTAW) of additively manufactured Haynes® 282 (H282) and Inconel® 740H (IN740H) sub-components, produced via laser-powder bed fusion (L-PBF), may be necessary for manufacturing or assembly of primary heat exchangers (PHX). Aging post weld heat treatment (PWHT) at 790-840°C is required to improve strength via gamma prime (γ’) precipitation, but strain age cracking (SAC), or reheat cracking, can occur during this process, particularly in the heat affected zone (HAZ). This study evaluates the susceptibility of L-PBF H282 and IN740H HAZ to SAC during PWHT at 800°C utilizing a Gleeble® 3500. Experiments were conducted on both vertically and horizontally L-PBF built components, with heating rates ranging from 40 to 3480°C/h and strains from 1 to 10%, representing various levels of weld-induced residual stress/strain. Additionally, wrought GTAW H282 samples were tested and compared to L-PBF H282 HAZ. Fractography and metallurgical characterization were conducted to supplement the test results. Generally, SAC failed samples exhibited migrated grain boundaries, and crack propagation through creep void formation was observed along precipitate-denuded regions at grain boundaries. The study discusses the lessons learned and insights from published literature on the implications of PWHT, such as the benefits of faster heating rates, for H282 and IN740H welded components.