Influence of heat treatments and chemical composition on SCC susceptibility during repairing procedure of overlaying of Inconel 182 by laser surface melting

Abstract

A practical repairing technique using laser surface melting (LSM) was developed to remove the stress corrosion cracking (SCC) in overlaying of Inconel 182. Influence of microstructure of different heat treatments performed during repairing process on intergranular cracking/intergranular stress corrosion cracking (IGC/IGSCC) susceptibility was discussed. The intergranular precipitate was identified as M₂₃ C₆ by TEM. The microstructure with no intergranular precipitate and refiner sub-grain after LSM process shows excellent IGC/IGSCC resistance. The stress relief heat treatment induced severe microstructure of high IGC/IGSCC susceptibility, owing to the semicontinuous intergranular precipitation. The influence of Nb/C ratio on IGC/IGSCC susceptibility of three nickel based superalloys after LSM process was also investigated. For both of the Inconel 182 alloys with different Nb content, the microstructure after LSM process and following sensitisation treatment showed precipitation free grain boundary. The results of corrosion tests also indicated that the material with higher Nb/C ratio showed higher IGC/IGSCC resistance after LSM process and following sensitisation treatment.