1School of Mechanical Engineering, SRM University, Chennai, India, 603203.
2DMI College of Engineering, Chennai, India, 600115.
3Indira Gandhi Center for Atomic Research, Kalpakkam, India, 603203.
4Department of Production Technology, MIT Campus, ANNA University, Chennai, India, 600044.
*Corresponding Author
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Austenitic stainless steels have been widely used in highly corrosive environments for power generation, chemical, fertilizer, marine, and food and petrochemical reactors. However, their low hardness and poor wear resistance impose strong limitations in cases. Nevertheless, the performance of these alloys can be improved further for both aqueous and high temperature applications by case hardening. In the present study, the effect of nitriding time on the properties like microhardness and corrosion resistance of AISI type 316LN grade austenitic stainless steel was investigated. The gas nitriding was carried out at a temperature of 823K for a period of 8 hrs. 9 hrs and 11 hrs respectively with a flow rate of 8 cum/hr. The resulting microstructural changes and intermetallic phases in surface and subsurface were studied with optical microscope, microhardness and XRD analysis. It has been found that the matrix element interacted with alloying elements and formed ‘ξ’ phase or ‘s’ phase consisting of hard complex Fe-Cr nitrides. The thickness of the diffused layer varied with the nitriding time. A maximum surface hardness value of 1210VHN and case depths varying from 58 microns to 73 microns could be obtained. The reason for the increase in the microhardness could be attributed to the presence of the hard complex iron chromium nitrides in the diffused layer.
nitriding, stainless steels, surface hardness, case depth, corrosion resistance
