Efficiency of protective coatings on high creep resistant cast steel

paper presents results of research of multilayer aluminium-silicon coatings. Aluminium-silicon coatings were created on high- temperature creep resist cast iron using slurry method in air atmosphere. These coatings protect equipment against hot corrosion in carburizing atmosphere at thermal shocks conditions. Various technological parameters of coatings manufacturing were applied. Main technological parameters were: temperature and time of annealing and Al-Si ratio in the active mixture. The structure of obtained coatings is three-zonal. Phase composition of two external zones ensures protection against carburizing, but these zones are not resistant to cracking. The cracks form as a result of thermal shocks. The internal zone of the coatings situated next to substrate compensates for differences of thermal expansion of the coating and the substrate. The cracks are stopped in the internal zone and do not propagate into the substrate material. Protective efficiency of the coatings at carburizing conditions with thermal shocks was determined. Structure of the coatings before and after carburizing and thermal shocks is described in present paper. Thickness, chemical composition (EDS) and phase composition (XRD) of the coatings are determined. Correlation between the coatings structure and depth of carburized layer was determined.