The effect of alloy content on the microstructure of as-deposited weldmetal in 9Cr-based ferrous weldments

The more widespread use of 9Cr-1Mo-based steels (modified and un-modified) is limited, in part, by a lack of understanding of the welding behaviour of this class of materials. A series of weldments, based on modified 9Cr-1Mo alloy steels, with varying Si and Mn contents was investigated using transmission electron microscopy (TEM). All as-deposited samples were found to consist of laths of heavily dislocated martensite separated by an interlath phase. Addition of Si was found to increase the amount of retained austenite (γ) present in the interlath region, whilst increasing Mn content promoted carbide formation. At high levels of both additions, a banded structure containing both phases was formed. These additions had little effect on the carbides (M23C6 type) present within the laths