Variation of High Temperature Gas Nitriding Time on Duplex Stainless Steels

This report presents the discussion on solution nitriding of duplex stainless steel. It
consists of project's background, literature review, methodology, and all the relevant
process and component related to this project. Nitriding is a surface-hardening heat
treatment which introduces nitrogen into the surface of the duplex stainless steels at
certain temperature range. The objectives of this project are to investigate the hardness
and the changes on the surface microstructure of nitrided duplex stainless steel. During
nitriding sample will exposed to a constant high temperature at 11 00°C with varying the
time which is at lh, 2.5 h, 4.5h and 6 h. Metallographic study, XRD examination and
assessment of the sample's hardness will be performed to examine the hardness of the
treated sample. Scanning Electron Micrograph (SEM) and optical microscope will be
used to do an assessment of the microstructure of the sample before nitriding and after
nitriding process to be conducted. Weight of the nitrided sample at constant temperature
11 00°C are increasing as the nitriding time increase. The microstructure observed for the
nitrided sample shows that the grain course of austenite phases are increasing as longer
time nitriding were conducted as compared to ferrite phases. It shows that austenite
phases react more in nitrogen diffusion compared to ferrite. Highest value of hardness:
448.2HV is achieved from sample nitrided at 1100 oc for 6 hours. Diffusion of nitrogen
content leads to higher hardness. XRD analysis also shows that the appearance of FeN
increase the hardness of the material. Hence as a conclusion, the objectives of the project
are achieved successfully. High Temperature Gas Nitriding at ll00°C has successfully
improved the hardness of the material due to more nitrogen diffused in it.