Abstract
The failure of Ethan cracking tubes in radiant chambers after four years service has been analyzed. The microstructure evolution during solution annealing and its affect on the mechanical properties and repair welding of 35Cr–45Ni heat resistant alloy was studied by means of optical and electron microscopy and by mechanical testing in samples welded both by GTAW and SMAW process. HAZ cracking after welding of cracked or creeped tubes due to formation of continuous brittle carbide network was overcome by localized solution heat treatment. Analysis revealed that dissolution of continuous brittle secondary carbide precipitates promoted an increase in ductility of about 20% which is enough to accommodate the thermal stresses during thermal fluctuations at service.
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