Role of detonation gun spray Cr 3 C 2 –NiCr coating in improving high temperature corrosion resistance of SAE–213–T22 and SAE–347H steel in presence of Na 2 SO 4 –82%Fe 2 (SO 4 ) 3 salt deposits

Abstract

Cr₃C₂–NiCr coatings were sprayed on SAE–213–T22 and SAE–347H boiler steels by detonation gun spray process. High temperature corrosion studies were conducted on the uncoated as well as detonation gun sprayed specimens in a molten salt environment at 700°C under cyclic conditions. The molten salt comprising Na₂SO₄–82%Fe₂(SO₄)₃ was applied on the specimens as a deposit. The weight change technique was used to establish kinetics of the corrosion. X-ray diffraction, field emission scanning electron microscopy/energy dispersive spectroscopy and X-ray mapping techniques were used to analyse the corrosion products. SAE–213–T22 steel suffered an accelerated corrosion in the form of intense spalling of its oxide scale, whereas SAE–347H steel exhibited only marginal spallation in the form of fine powder. The Cr₃C₂–NiCr coating showed good adherence to the boiler steels during the exposure with no tendency for spallation of its oxide scale. The coating was found to be successful in developing resistance against hot corrosion in the molten salt environment, which may be attributed to the formation of oxides of nickel and chromium.