Solving spring cracking

Sandvik Materials Technology’s duplex stainless steel grade, Sandvik SAF 2205 is being used for wire springs in electrical contact systems on railway locomotives. An electrical rail contact system was designed for a passenger railway in South East Asia using standard stainless steel grade 316L wire springs to hold contact points in place between the locomotive and the rail. After some time in operation, cracking was found in the springs. The problem was due to stress corrosion cracking (SCC), emanating from the ambient humidity, and the materials mechanical strength. The combination of the two factors led to eventual spring breakage. Although breakage is not considered a major problem, there is the potential for arcing with the broken springs contacting the suspended rail. As a result, a review of possible alternative materials by the railway’s owners and operators led to the selection of Sandvik’s SAF 2205 duplex stainless steel. Sandvik SAF 2205 is characterised by high resistance to corrosion – particularly pitting and crevice corrosion. The pitting resistance of a steel is determined primarily by its chromium and molybdenum contents. Sandvik SAF 2205 is a 22% chromium, 3% molybdenum steel with a pitting resistance equivalent – a parameter for comparing the pitting resistance of different steels – of over 35.

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