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

Abstract

Two technique of coatings were performed by applying pack cementation technology, the first one was aluminizing diffusion coated low alloy steel substrate whereas the second one was single step simultaneous Co-deposition silicon-aluminum diffusion coated low alloy steel substrate. The pack mixture used for producing both coating systems in pack cementation process was composed of (30% Al, 2% NH 4 Cl and the filler 68% Al 2 O 3 ) , (30% Al , 5% Si , 2% NH4Cl and 63% Al 2 O 3 ) respectively. The pack temperature was 1000•C and the diffusion time was 3 hr. XRD exhibits the phases formed on both coated systems are Fe 2 Al 5 , FeAl 3 and FeSi . Uncoated low alloy steel substrate and the both two coating systems were subjected to exposure environment deposit salts mixture of (50%Na 2 SO 4 and 50%NaCl) with weight (2mg /cm 2 ), using cyclic oxidation method in the experiments at temperature of 750•C for 100hr each cycle of 5hr. It was found that the oxidation kinetic for uncoated low alloy steel will give evidence that the oxides formed on this alloy are nonprotective. The XRD analysis exhibited the phases are Fe 2 O 3 , Fe 3 O 4 . It was found they followed linear rate law, and spalling was observed. After these hot corrosion tests were undertaken, It was found that the oxidation kinetics for both coated systems in environment consist of salt mixture (50% NaCl +50% Na 2 SO 4 ) followed parabolic law (protective oxidation behavior). XRD exhibits the oxides formed on both coated systems are Al 2 O 3 , SiO 2 .