Abstract
The weld heat affected zone (HAZ) of tungsten inert gas (TIG) welded cast IN 738 superalloy has been examined. HAZ microfissuring was observed in alloy welded in solution treated and overaged conditions. Closer and careful microstructural examination by analytical scanning electron microscopy revealed the liquation of boride, sulphocarbide, MC type carbides, γ′ precipitate particles and γ-γ′ eutectic, which were present in the preweld alloy, and the formation of resolidified constituents along the microfissured HAZ grain boundaries, thereby indicating that HAZ cracking in this alloy involves liquation cracking. Liquation of these phases, as well as characteristics of the intergranular liquid film contributing to the low resistance to HAZ cracking of the alloy have been examined and are discussed.
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