The effects of pre- and post-weld heat treatment variables on the strain-age cracking in welded Rene 41 components

Rene 41, a precipitation-hardened nickel-base superalloy, is mostly used for hot section parts of jet aircraft engines. When cracks occur in these parts, welding is frequently utilized for crack repair to extend their service life. Rene 41 is very susceptible to strain-age cracking during welding and post-weld heat treatment because of its strengthening mechanism. The strengthening mechanism depends on the existence of gamma prime (gamma') phase and the morphology of carbides both of which are affected by heat treatment. In this study, the effects of pre- and post-weld heat treatment variables such as heating rate, holding temperature and time, and cooling rate on the strain-age cracking of Rene 41 during welding and post-weld heat treatment were investigated. An optimum combination of heat treatment variables was investigated to obtain a microstructure that would be less susceptible to strain-age cracking during welding and post-weld heat treatment. Pre- and post-weld solution heat treatments at 1080 degreesC for 30 min with 20 degreesC/min heating and 34 degreesC/min cooling rates produced optimum microstructures, and no cracks were observed in the Rene 41 samples after welding. MC carbides were dissolved lightly and distributed homogenously within the grains. M6C carbides precipitated as globules within the grains and in the grain boundaries. M23C6 carbides precipitated as chains of globules in the grain boundaries. (C) 2004 Elsevier Ltd. All rights reserved.