Reheat Cracking Sensitivity of CGHAZ in Vanadium-Modified 2.25Cr1Mo Welds

Abstract

Over the past few years, some reheat cracks have been detected in the welding coarse grained heat affected zones (CGHAZ) of Vanadium-modified (V-mod) 2.25Cr1Mo reactor. Focusing on this problem, a series of Gleeble high temperature tensile tests were carried out on the simulation CGHAZ specimens of V-mod 2.25Cr1Mo at different temperature and strain rate, the reheat cracking sensitivity of CGHAZ has been assessed according to the reduction of area (RoA) of the specimens. Microstructural observation, hardness test and fractographic analysis also have been employed to ascertain possible causes for the effects of temperature and strain rate on the reheat cracking sensitivity. The results of tests show that the reheat cracking sensitivity of CGHAZ increases with a decreasing strain rate, it first increases and then decreases with a rising test temperature. The RoA presents a minimum value around 675°C, corresponding to the most sensitive temperature to reheat cracking. The comprehensive analysis reveals that the ductility of the simulated CGHAZ at elevated temperature is closely related to the tensile strength and the hardness of fractured tensile specimen. In the intermediate temperature range or at a slower strain rate, a relatively high hardness and relatively low tensile strength together results in a low RoA of the specimen and high reheat cracking sensitivity of CGHAZ metal.