Carbon diffusion in dissimilar joints between P91 and 12Cr1MoV steels welded by different consumables at high temperature

Three consumables: 9CrMoV(N), R31, and GTR-2CM are considered in welding P91 and 12Cr1MoV together. The stable phases and carbon activities of the involved materials were calculated by THERMO-CALC. Carbon diffusion after aging for varying times at 700°C was simulated by dispersed multiphase model in DICTRA. The usage of different weld metals causes different carbon concentration profiles near weld interfaces both on the P91 and 12Cr1MoV sides, driven by their carbon activity difference. Mole fractions of carbides varying with distance were investigated, showing that the formation of carbon-depleted zone (CDZ) and carbon-enriched zone (CEZ) is related to the dissolution and precipitation of M₂₃C₆ carbides. To validate the simulation results, the microstructure and hardness near the interface between P91 base and GTR-2CM weld metal were studied. Good agreements on the widths of CDZ and CEZ between modelled and experimental results were obtained.