Haz microfissuring in EB welded allvac 718 plus™ alloy

Abstract

Weldability of two versions of newly developed 718 Plus alloy, HC49 and HC20 was studied and compared with that of Inconel 718. 5.0" × 0.5" × 0.5" thick plates were heat treated at 950° and 1050°C, water-quenched then EB welded. Microstructures of the base metal and welds were examined by optical and analytical electron microscopy. Intergranular microcracks were observed in HAZ in all the three alloys, and their susceptibility to cracking was established by measuring total and maximum crack lengths. It was observed that HC49, with higher B and P, suffered most cracking and Inconel 718 the least. HAZ cracking was observed to be associated with resolidified liquated phase suggesting it to be liquation cracking. The EDS analysis suggested that the grain boundary liquation was due to the constitutional liquation of NbC and due to the GB segregation of B during the pre-weld heat treatment. The increased cracking in 718 Plus as compared to Inconel 718 was attributed to the softer matrix of Inconel 718, which could withstand the welding stresses better. More severe cracking in higher B version of 718 Plus than in the lower B 718 Plus could be due to the increased segregation of B on its grain boundaries.