Effect of Deformation-induced Martensite on the Toughness of Fe–Ni–Cr Austenitic Weld Metal

The effect of the deformation-induced martensite (α') with varying carbon content on the toughness was investigated in metastable γ-phase weld metals, which were Fe–0.05C–27Ni–3Cr and Fe–0.44C–25Ni–3Cr. The toughness was measured using a Charpy impact test and a three-point bending test. The microstructures were characterized by means of scanning electron microscope. The correlations between α' phase, crack propagation and toughness studied using electron backscatter diffraction. The crack initiation was suppressed by the formation of α' phase, and the toughness improved at -100°C in Fe–0.05C–27Ni–3Cr weld metal. The toughness was reduced by the brittle fracture of the hard α' phase in the Fe–0.44C–25Ni–3Cr weld metal. It is clear that the formation of the α' phase particles with high toughness is important to improve toughness by transformation induced plasticity in the weld metals.