Improved oxidation resistance of the Zr-alloyed layer formed on 420 stainless steel by plasma surface alloying

A Zr-alloyed layer is prepared on the 420 stainless steel by plasma surface alloying technique in order to improve its poor elevated temperature property. The oxidation behavior of the Zr-alloyed stainless steel is studied in the paper. It is found that the Zr-alloyed layer with approximately 5 pm in thickness is bonded strongly to the steel substrate and consists of ZrC, Cr23C6 and metallic Zr. The result of a cycling oxidation at 1000 degrees C indicates that the mass gain of Zr-alloyed specimens is only 0.9 mg/cm(2) after exposure for 100 h in air, exhibiting an excellent oxidation resistance. A thin oxide scale formed on the alloyed stainless steel is compact and strongly adheres to the oxidized substrate. The improvement of the oxidation resistance for the Zr-alloyed 420 steel is attributed to the formation of a stable outer ZrO2-rich layer and the Cr2O3-rich layer between the inner Fe3O4+Cr2O3 oxide and the substrate. (C) 2012 Elsevier B.V. All rights reserved.