Microanalysis of inclusion/matrix interfaces in weld metals

The effects of non‐metallic inclusions on the microstructure of as‐deposited C–Mn weld metals have been investigated in a series of welds produced using different electrode coatings to obtain inclusions of different chemical compositions. The inclusions were analysed on carbon extraction replicas or in thin foils in a 120 kV (scanning) transmission electron microscope (TEM (STEM)) equipped with energy dispersive x‐ray microanalysis facilities. Both x‐ray microanalysis and convergent beam diffraction techniques, with probe sizes down to 10 nm, were used to characterize the inclusions and the inclusion/matrix interfaces. It was found that the ‘cores’ of the inclusions were mainly oxides, such as MnSiO3 or MnAl2O4. The surfaces of the inclusions were either coated with thin layers of copper sulphide, or mixtures of copper sulphide and titanium carbonitride when both copper and titanium were present as impurities in the welds. Effects of non‐metallic inclusions on weld metal microstructure are discussed with respect to the above‐mentioned coatings and the heterogeneous nucleation of the fine acicular ferrite microconstituent.