Page 156 - Failure Analysis Case Studies II

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Fig. 2. Typical fracture through the centre of the weld and along the piston rod. The location of one of the rosette welds can
be seen.

nominal steel grades. A 0.2 wt% excess of Mn was noted in one steel, but this was not deemed
relevant to the failures.
Vickers microhardness tests showed that the weld metal had a hardness of 350-370 Hv. The
region immediately adjacent to the fusion line had a hardness of 220 Hv, which decreased rapidly
to 200 Hv. The carburised case of the adapter plug had a hardness in the region of 350 Hv.

3.3. Metallography and fractography
Sections of the weld were mounted in resin, polished and etched. The microstructure comprised
large, elongated grains of a duplex ferrite/austenite nature (Fig. 3) with large carbides both within

Fig. 3. Optical micrograph of one of the E312 welds showing austenite/ferrite duplex structure and a hairline crack (centre
of photograph) (etchant: Vilella's etch).