Effect of Laves phase on the toughness of P92 weld metals

In this investigation, Laves phase was found to gradually precipitate from the tempered martensitic matrix of the two P92 weld metals (WMs) during the aging treatment. The particle size of Laves phase in the two WMs was ranged from 0.18 to 0.24 mu m and was larger than the M23C6 particle size (ranged from 0.09 to 0.13 mu m). The dislocation density of the two WMs was stable during aging. The hardness of the two WMs was stable during aging treatment, as the loss of solid solution strengthening was continuously compensated by the precipitation strengthening of Laves phase. The impact toughness of the two WMs declined gradually as the extending of aging time. The crack initiation zone and shear lip zone of the fracture surface were ductile fracture mode which consumed more fracture energy during impacting. The generation of Laves phase narrowed the crack initiation zone and shear lip zone and contributed to the decline of ductile fracture area percentage of aged WMs. The smaller ductile fracture area percentage contributed to the toughness reduction of aged WMs.