Behavior of M23C6 phase in Inconel 617B superalloy during welding

The room/high temperature mechanical property of the Inconel 617B joined by multi-layer narrow gap tungsten arc welding technology (NG-TIG) is investigated, and thermal simulation is utilized to reveal the behavior of M23C6 phase in Inconel 617B superalloy during welding. Eutectic microstructures and micro fissures resulting from constitutional liquation due to thermal exposure in welding occur in the heat affected zone (HAZ), which leads to slight softening in the HAZ after welding. Room/high temperature tensile tests show that little adverse effects on the mechanical strength of joint has been caused by the welding process. It is shown by the thermal simulation that constitutional liquation of this micro-scale M23C6 carbides would occur when the peak temperature (T-p) reached 1300 degrees C. The behavior of the micro-sized M23C6 in multi-layer welding cycle could be described as: M23C6 + (gamma-Ni) -> liquid -> M23C6 + gamma-Ni -> M23C6 + gamma-Ni + secondary M23C6.