Effect of solution annealing on weldability of aged alloy 800/25Cr–35Ni steel dissimilar welds

Dissimilar welding of the aged alloy 800 and the as cast 25Cr–35Ni (wt-%) heat resistant steel was investigated. Microstructures, mechanical properties and weldability of the dissimilar welds were characterised using optical microscopy, scanning electron microscopy and transition electron microscopy equipped by energy dispersive X-ray spectroscopy, and Varestraint test. Since such dissimilar welding was susceptible to crack formation in the heat affected zone of the aged part, the effects of a preweld solution annealing, heat input, interpass temperature and type of filler metal on the weldability of two alloys were investigated. It was found that during the solution treatment, the precipitates produced in the service stage were decomposed and that TiC was formed. In addition, tensile strength and hardness were reduced, but ductility and toughness increased. It was concluded that the most important step to improve weldability and to reduce cracking susceptibility was solution annealing. A suitable annealing treatment was then proposed. The best weldability was found under conditions of solution annealing, low heat input, low interpass temperature and using Inconel 82 or 617 for filler metals.