Investigation of abnormal corrosion of 10.5 – 12.5 chromium ferritic stainless steel used to fabricate railway coal wagons

Abstract

The 10.5 – 12.5 per cent chromium ferritic stainless steel has attained success as a material used to manufacture and refurbish coal wagons. It was designed to be a low-cost material making use of the minimum chromium content required to impart acceptable corrosion resistance. There was a sudden occurrence of uniform corrosion of coal wagons manufactured between the year 2015 and 2016. This study focuses on investigating abnormally corroded wagons that are manufactured using the ferritic stainless steels. Furthermore, the exposure and salt spray tests were conducted on different consignments. The optical microscope was used to conduct a metallographic examination and chemical analysis was conducted to compare different consignments ferritic stainless steel. The root cause analysis on the plate from in-service wagon indicated that the material was indeed ferritic stainless steel and the surface roughness test showed some presence of pits on the surface of the plate. The experimental results of the different consignments indicated that one plate was dark grey which corroded quite significant during corrosion testing, whilst the other was bright grey which showed a lower corrosion rate.