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

摘要

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 M_(23)C_(6) carbide occurred in δ -ferrite firstly owing to the high diffusion rate of C. After the C is depleted by precipitation of M_(23)C_(6), 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 M_(23)C_(6) 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 M_(23)C_(6) and σ phase successively, while δ -ferrite in high C weld metal only transforms into M_(23)C_(6) 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 M_(23)C_(6) precipitation deteriorated the strength, then the formation of σ phase improved the strength. Furthermore, with the increasing of the aging time, the precipitation of M_(23)C_(6) and σ phase deteriorated the elongation and impact energy.