Effect of Pack Cementation Coating on Hot Corrosion Resistance of Low Alloy Steel


Two technique of coatings were performed by applying pack cementationtechnology, the first one was aluminizing diffusion coated low alloy steel substratewhereas the second one was single step simultaneous Co-deposition silicon- aluminumdiffusion coated low alloy steel substrate. The pack mixture used for producing bothcoating systems in pack cementation process was composed of (30% Al, 2% NH4Cl andthe filler 68% Al2O3) , (30% Al , 5% Si , 2% NH4Cl and 63% Al2O3 ) respectively. Thepack temperature was 1000◦C and the diffusion time was 3 hr. XRD exhibits the phasesformed on both coated systems are Fe2Al5 , FeAl3 and FeSi . Uncoated low alloy steelsubstrate and the both two coating systems were subjected to exposure environmentdeposit salts mixture of (50%Na2SO4 and 50%NaCl) with weight (2mg /cm2), usingcyclic oxidation method in the experiments at temperature of 750◦C for 100hr eachcycle of 5hr. It was found that the oxidation kinetic for uncoated low alloy steel will giveevidence that the oxides formed on this alloy are non – protective. The XRD analysisexhibited the phases are Fe2O3 , Fe3O4. It was found they followed linear rate law, andspalling was observed. After these hot corrosion tests were undertaken, It was found thatthe oxidation kinetics for both coated systems in environment consist of salt mixture(50% NaCl +50% Na2SO4) followed parabolic law (protective oxidation behavior). XRDexhibits the oxides formed on both coated systems are Al2O3, SiO2.