A study of hardness and the sensitization of nitrided martensitic stainless steel during cooling down process

This report presents the discussion on the sensitization of nitrided martensitic stainless steel grade AISI420 during cooling down process. It consists of project’s background, literature review, methodology, and all the relevant process and component related to this project. Basically, nitriding is one of the surface treatments where it involved diffusion of nitrogen into the grain boundaries. For this project, martensitic stainless steel is exposed to high temperature (above 1200°C) and low temperature (below 600°C) for 4 hours and 10 hours. The objectives of this project are to determine the effect of the gas nitriding process on the hardness and the microstructure of the AISI420 Martensitic Stainless Steel. Besides that, is to determine and compare the microstructure and sensitization of nitride martensitic stainless steel with different holding time. Metallography or microstructure of all the samples is observed by using Light Optical Microscope (LOM). Meanwhile for hardness, Vickers Hardness Testing is used and was plot in graph. Energy Dispersion X-Ray (EDX) examination and Scanning Electron Microscopy (SEM) are carried out to prove about the microstructure and new entities contain in the samples such as carbide chromium precipitation. The microstructure observed for the nitride sample show that high temperature of nitriding has more sensitization compared to low temperature. The precipitate along the grain boundaries can be seen clearly. At high temperature, the grain boundaries getting expand and bigger compare to as received samples and also low temperature samples. But low temperature of nitriding, the grain boundaries getting closer, dark and compact to each other. Highest value of hardness: 424.1HV is achieved from sample nitride at 1200°C. Diffusion of nitrogen into the samples content leads to higher hardness. EDX show analysis shows that the appearances of N increase the hardness of the material. Thus, as a conclusion, the objectives of the project are achieved successfully. Low temperature of nitriding shows less sensitize compare to high temperature.