It is believed that particular phases found at the surface of inclusions in steel welds favour the formation of acicular ferrite. Such a microstructure increases tremendously the toughness of the weld deposits. Until now, it is not clear which phases are favourable, the uncertainty being partly due to the difficulty of characterizing phases with sizes of about 100nm at the periphery of inclusions. We compared characterization techniques including scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry and parallel electron energy-loss spectroscopy. We found that, in general, it is possible to identify the phases unambiguously by comparing the results of energy-dispersive spectrometry and electron diffraction patterns in the transmission electron microscope on samples prepared by carbon extraction replicas. For cases where the size is very small (<50nm) and/or when similarities in composition and crystal structure are difficult to differentiate, spectrum imaging using parallel electron energy-loss spectroscopy on samples prepared by ultramicrotomy is the most powerful characterization technique.