Analysis of Local Strain Evolution during Electron Beam Welding of Hot Crack Sensitive Nickel Base Conventionally Cast Alloy 247 LC CC

Abstract

Among different joining methods, the electron beam welding is recently applied for manufacturing of turbine components from temperature-resistant nickel-based conventionally cast Alloy 247 LC CC. However, the high tendency to hot cracking, in particular the formation of solidification cracks, remains a major challenge. Experiments indicate a significant reduction in hot cracks if the welding is performed outside the common welding parameter range. To understand these observations, a study of local thermo-mechanical conditions during electron beam welding of Alloy 247 samples was carried out using numerical simulations. The results were subsequently compared with reference test welds. For this purpose, a finite element model for coupled transient thermal and mechanical analysis was created and used. The work presents a comparative analysis of the evolution of strain components in brittle temperature range during cooling, considering the distribution and orientation of the cracks. Various relations between local strain kinetics and crack appearance, with notable influence of the plastic strain vector, were observed. Finally, the aspects of assessment of hot crack susceptibility with aid of thermo-mechanical welding simulation are discussed.