Cr diffusion coatings on a ferritic-martensitic steel for corrosion protection in KCl-rich biomass co-firing environments

•Lifetime of X20CrMoV12-1 substantially enhanced by Cr and Ni + Cr diffusion coatings•Addition of KCl to sulphate salt accelerates degradation of substrates and coatings•Increased corrosion rates are a result of different synergetic corrosion mechanisms•Chlorides accelerate scale dissolution by active oxidation and chromate formation•Ni increases incubation time but promotes formation of detrimental Ni-S eutectic