ENDURANCE INVESTIGATION OF NITRIDE FERRITIC STAINLESS STEEL SS439 UNDER TORSIONAL LOADING

The author’s Final Year Project, which entitled Endurance investigation of
Nitrided Ferritic SS439 Stainless Steel under Torsional Load. The purpose of the project
is to investigate the effect of nitriding on the endurance of the nitride ferritic SS439
stainless steel under torsional loading condition. Nitriding is a thermochemical surface
treatment for strengthen steel purpose. In the process, nitrogen is transferred and may
diffuse into the steel at a certain temperature. Nitriding process recently becomes one of
the attractive case-hardening processes for steel due to its metallurgical achievement like
high surface hardness, improvement in fatigue life and increased wear resistance and
anti-galling properties.The scope of this project includes application of nitriding process
to the Ferritic Stainless Steel SS439 and endurance investigation for the samples before
and after the nitriding process. In this project, low and high temperature gas nitriding has
been applied to ferritic stainless steel SS439. Microstructure, hardness testing, and also
fatigue testing has been done to the base, low and high temperature nitride SS439 to
compare the phase changes happened to the SS439, and also to know the endurance of
the material after treated with the nitriding process. The overall result shown that high
temperature nitriding has higher efficiency than low temperature nitriding to the ferritic
stainless steel SS439. In hardness test, hardness value for high temperature nitride is
higher than low temperature nitride on SS439 on the sample surface and below the
surface. The torsional fatigue testing proved that the endurance of nitride SS439 has
been improved from the base SS439. High temperature nitride SS439 is higher
endurance compared to low temperature nitride SS439 with cycle to failure up to 500000
under 10N loading.