Diffusion coatings for high temperature corrosion protection of 9–12%Cr steels

AbstractSteels containing 9–12%Cr are of great interest for application as heat-exchanger tubes in power stations. Indeed they possess a high thermal conductivity and favourable mechanical properties at temperatures up to 650°C. However, from a mechanical point of view, even though conventional ferritic-martensitic 9–12%Cr steels are designed for service temperatures up to 650°C, their use at such high temperatures is rather limited in corrosive environments. One solution may be to protect these steels by suitable corrosion-resistant coatings. Pack cementation is one of the easiest and cheapest coating processes for high temperature applications. However, for ferritic-martensitic steels, the maximum coating temperature is limited to 650°C. Above this limit, the decomposition of martensite would be accelerated, to the detriment of the mechanical properties of the material. The objective of the present work was to use pack cementation to coat the 9%Cr steel P91 and the 12%Cr steel HCM12A without modifying t...