Page 389 - Failure Analysis Case Studies II

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Fig. 1. Schematic view of catalyst reduction reactor (bottom section).

2.2. Metallographic examination
The two extremities of the crack were prepared for microstructural replication, polished to a 1
pm diamond finish and etched with 2% nital. Examination of the replicated micrograph in the
laboratory showed the microstructure of the HAZ to consist of tempered martensite/bainite. The
crack path was inter-granular in form, following the prior austenite grain boundaries (see Figs 2
and 3). The nature and location of the crack was typical of re-heat cracking of a low-alloy Cr-Mo
steel, rather than a fatigue crack.

2.3. Hardness
Hardness measurements were taken across the cracked zone on one of the polished replicated
areas using a “Microdur” portable hardness tester. The results showed generally acceptable hardness