Effect of Ni content on microstructure and mechanical properties evolutions of 9Cr high Si heat resistant steel deposited metals

Abstract

This work presents the effect of Ni content on the morphology of microstructure and changes of mechanical properties of high Si 9Cr heat resistant steel deposited metals with different states: as-welded, as-post weld heat treated (750 °C/2.5 h) and as-aged (550 °C/3000 h). With the increase of Ni content, the martensitic laths are refined improving the overall mechanical properties. δ ferrite deteriorates the impact toughness. During aging process, Ni facilitates the formation of M6X. Therefore the overall mechanical properties of deposited metal decreases as the Ni content increases after long-term aging owing to the formation of chain-like precipitates consisted mainly of M6X. The process of post weld heat treatment improves the negative effect of small-sized δ ferrite on impact toughness.