A Comparative Study of Microstructures and Properties of Two Types of Nickel-Base Alloy Covered Electrodes

Two types of nickel-base alloy covered electrodes, ENiCrMo-6 and ENiCrFe-9, were investigated and compared among their deposited metal compositions, microstructures, strengths, and cryogenic impact values. They all exhibited dendritic microstructures which were composed of dendritic fcc nickel-base solid solution, interdendritic phases, and grain boundary carbides. The molybdenum in the deposited metals tended to migrate and aggregate toward the edges of the dendrite arms during solidification. The niobium preferred to form oxide and/or carbide and aggregate in the interdendritic regions. The grain boundaries were filled with the continuous carbides and oxides. The differences in the tensile mechanical properties of the deposited metals of the two types of electrodes were relatively minor. The impact values of ENiCrMo-6 at −196 °C were above 80 J; while that of ENiCrFe-9 were in the range of 54-66 J. The relatively high level of carbon and sulfur and more grain boundary precipitates should be responsible for the lower cryogenic impact value of the ENiCrFe-9 covered electrode.