Influence of Aging Treatment on the Microstructure Evolution and Mechanical Properties of 316H Weld Metals with Different C Contents

Abstract

The influence of 600°C aging treatment on the microstructure and mechanical properties of 316H stainless steel weld metals with different C contents have been studied. The results indicated that during the aging process, the rapid precipitation of M₂₃C₆ carbide occurred in δ-ferrite firstly owing to the high diffusion rate of C. After the C is depleted by precipitation of M₂₃C₆, the residual δ-ferrite transforms into σ phase through eutectoid transformation (δ-ferrite → σ phase + γ). Furthermore, after a long enough aging time, the transformation from M₂₃C₆ to σ phase occurred. The C content has a significant influence on the δ-ferrite transformation behavior, δ-ferrite in the low and medium C weld metals transforms into M₂₃C₆ and σ phase successively, while δ-ferrite in high C weld metal only transforms into M₂₃C₆ carbides. The variations of mechanical properties with aging conditions depended mainly on the microstructures at different aging conditions. For the low C weld metal, as the aging time increased, the increasing σ phase content improved the strength obviously. For the medium and high C weld metals, as the aging time increased, first the depletion of the solid solution C as a result the M₂₃C₆ precipitation deteriorated the strength, then the formation of σ phase improved the strength. Furthermore, with the increasing of the aging time, the precipitation of M₂₃C₆ and σ phase deteriorated the elongation and impact energy.