Elevated temperature failure of heat treatment furnace containers

Abstract

The present study characterises the failures that generally occur in heat treatment furnace containers, which are used for chromium deposition onto chain spindles. Containers are produced using austenitic stainless steel AISI 310S, with a wall thickness of 8 mm. When operating at temperatures of ∼970°C, cracks appear on the external surface, through the container wall. This occurs after periods as short as 1000 h and produces a lack of tightness, which renders the container useless. A structural analysis of the container wall reveals heavy carbonitride precipitation in a 1 mm layer close to the internal surface of the wall, producing sensitisation and intergranular corrosion. Cracks formed on the external wall surface, growing through the grain boundaries and close to large chromium carbides, were responsible for container failure. External cracks are the result of interacting creep–fatigue mechanisms, exacerbated by the coarsening of carbides and austenitic grains, caused by long periods at 970°C. Plastic deformation caused by hammering during the cooling cycle can contribute to the collapse of the container.