Assessment of Properties on AISI 316LN Austenitic Stainless Steel Material under Low Temperature Liquid Nitriding Processes
Ram.Subbiah1, S. Satheesh2, Shoan C. Sunny3, G. Kishor4, K. Fahad5, R. Rajavel6

1Ram Subbiah, Assistant Professor, Department of Mechanical Engineering, TJS Engineering College, Chennai (Tamil Nadu), India.
2S.Satheesh, Final Year, Department of Mechanical Engineering, TJS Engineering College, Chennai (Tamil Nadu), India.
3Shoan C Sunny, Final Year, Department of Mechanical Engineering, TJS Engineering College, Chennai (Tamil Nadu), India.
4G.Kishor, Final Year, Department of Mechanical Engineering, TJS Engineering College, Chennai (Tamil Nadu), India.
5K.Fahad, Final Year, Department of Mechanical Engineering, TJS Engineering College, Chennai (Tamil Nadu), India.
6R.Rajavel, Professor & Head, Department of Mechanical Engineering, Velammal Engineering College, Chennai (Tamil Nadu), India.
Manuscript received on 13 February 2014 | Revised Manuscript received on 20 February 2014 | Manuscript Published on 28 February 2014 | PP: 69-71 | Volume-3 Issue-9, February 2014 | Retrieval Number: I1484023914/14©BEIESP
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Abstract: Austenitic stainless steels have been widely used in highly corrosive environments for power generation, chemical, fertilizer, marine, and food and petrochemical reactors. These materials are well known for their good corrosion resistance and mechanical properties like strength etc. However, because of its low hardness and wear resistance their applications are greatly limited. Nevertheless, the performance of these alloys can improved further for both aqueous and high temperature applications and environments by case hardening techniques like carburizing, nitriding and so on. These surface hardening processes offer high corrosion resistance in addition to, improved hardness and wear resistance. In the present study, the effect of gas nitriding on the properties like micro hardness, corrosion resistance and wear resistance of type AISI 316LN grade austenitic stainless steels were investigated. The salt bath nitriding was carried out at a temperature of 5000C for durations of 60, 90 and 120 minutes with a post oxidation process for a period of 30 minutes and named as SBN1, SBN2, SBN3 respectively. The resultant inter metallic phases were analyzed with optical microscope and micro hardness tester for micro hardness, micro structural changes, nature and compositions of the diffused elements. It has been found that the matrix element interacted with alloying elements and formed a ‘ξ ‘ phase or ‘s’ phase consisting of hard complex Fe-Cr nitrides. These phases showed significant influence on the properties. From the experiment results, it was observed that gas nitriding increases the micro hardness to a considerable amount. A maximum of 1410Hv could be obtained on the austenitic grade stainless steel specimens, which were investigated among the various specimens, in order to improve the wear resistance. The untreated specimens were compared with the nitride specimen.. The reason for the increase in the micro hardness could be attributed to the presence of the Mo and the other alloying elements in the solid solution. The value of hardness at the surface level increases with the diffusion time up to a certain level. Beyond this, limit further increase in diffusion duration does not have any impact on the surface hardness. To evaluate the effect of post-oxidation on nitrided specimen’s corrosion and tribological properties were determined. From the results, it was observed that post- oxidation has no significant effect on the hardness but improves the corrosion resistance in comparison with non-oxidized specimen in a larger factor. Also it was observed that the change in the properties was due to the formation iron oxide layer on the specimen and especially during the subsequent treatment in the oxidizing bath. From the micro structural analysis of the nitrided specimens, the case depths were observed to be about 20 -50 microns (μm).
Keywords: Stainless Steels, Nitriding, Micro Hardness, Corrosion Resistance, Microstructure.

Scope of the Article: Materials Engineering