Local probing study of corrosion behaviour of a martensitic stainless steel

摘要

With increasing use of plastic components in many applications, new challenges are encountered by plastic component manufacturing industries, and tooling is one of the important issues. Moulding materials used for shaping the molten plastic into products should possess good corrosion resistance and wear resistance, good polishability and high hardness, etc. Martensitic stainless steels are generally used as plastic moulding materials due to their relatively good corrosion resistance and wear resistance, etc. In this work, corrosion resistance of a martensitic stainless steel (AISI 420 Modified) was studied using microscopic and electrochemical techniques. After a hardening heat treatment, samples were tempered at 250°C. The micros true ture was characterised by using LOM and SEM. The corrosion behaviour of the samples was investigated through cyclic potentiodynamic polarisation in 0.1M NaCl solution. The corroded area of the samples was examined by using SEM. Moreover, in-situ AFM measurements were performed in the solution to monitor the corrosion process. The LOM and SEM results revealed phases present in the steel. The polarisation tests and post-analysis showed localized dissolution of the material in the solution, and local attack occurred on regions around the carbide phase. The in-situ AFM imaging showed preferential dissolution along carbide phase boundary, which can be attributed to chromium depletion from the matrix due to the chromium carbide precipitation.