Improved Understanding of Varestraint Testing—Nickel-Based Superalloys

By Varestraint testing, the susceptibility of an alloy to hot cracking during welding can be evaluated on test plates when they are bent at the same time as welding takes place. The strains imposed by welding can thus be augmented by the strains imposed by the bending action to find the strain limits when hot cracks appear and also the sensitivity to hot cracking by counting the number and measuring the length of the individual cracks as a means to differentiate between the weldability of different alloys. Supports are usually recommended to avoid hinging and to use test plates thicker than 10 mm in order to minimize the influence of the compression strains (lower part of the bent specimen) on the weld cracking at the bending. The cracking response of two precipitation hardening Nickel-based superalloys—ATI 718Plus^® and Haynes^® 282^®—was analysed in the context of the actual tensile/compression ratio imposed and measured by strain gauges attached to the upper and lower surface of the test plates. It was found that no influence of the compressive strains on the cracking response in Varestraint testing takes place. It was also seen that the hot cracking susceptibility of Haynes^® 282^® is lower compared to that of ATI 718Plus^®.