AISI 420 martensitic stainless steel corrosion resistance enhancement by low-temperature plasma carburizing

Abstract

Abstract Corrosion resistance of plasma carburized AISI 420 martensitic stainless steel was evaluated by cyclic polarization test in 3.5% NaCl solution. Two distinct treatment groups were studied with the purpose of evaluating the influence of the carburizing temperature and time on the corrosion behavior of treated material (one at 350–500\u202f°C temperature range for 8, and 12\u202fh times; and other one at 400\u202f°C for 12–48\u202fh time range, and at 450\u202f°C for 4–16\u202fh time range). To support the discussions on electrochemical test results, microstructural characterization was carried out using metallographic analysis and XRD techniques. Microstructural characterization results show that low temperature and short time treatments produce outer layer composed by α′C and Fe3C phases. High temperature and/or long time treatments promote outer layer Cr7C3 and Cr23C6 phases precipitation. Corrosion test results show improved carburized samples resistance, which is related to chromium-carbides precipitation-free outer layer formation. The Cr-carbides formation promotes a reduction on carburized samples corrosion resistance due to depletion of Cr in the solid solution of carburized layer. Finally, by confronting the behavior of untreated and carburized samples, it is verified the potentialities of the low-temperature plasma carburizing to enhance the corrosion resistance of AISI 420 MSS.