Prior severe surface plastic deformation (SSPD) treatments have proven beneficial to low-temperature nitriding to achieve a thicker nitride layer, improved hardness, and wear resistance. Although extensive work has been reported on SSPD followed by nitriding; however, cyclic treatment of SSPD and low-temperature nitriding on austenitic steels (ASS) is not reported. Also, the role of deformation on nitridation kinetics was not well understood.
In the present work, at first, ultra-sonic shot peening (USP) and low-temperature liquid nitriding (LN) are performed in cycles on 316 ASS. Comparison is made among cyclic treated, liquid nitrided, and one-time shot-peened and nitrided sample conditions.
From the results of this study (optical, electron microscopy and hardness depth profile at the cross-section, XRD depth profiling by sequential removal of layers from the treated surface to the core to know the phases formed with depth), we have extended our research to know the role of deformation on the kinetics of nitridation for various ASS.
The ASS are subjected to LN at 425 ℃ for 4 hours before and after the deformation (USP and cryo-rolling). The treated sample surfaces and cross-sections are characterized using X-ray diffraction and scanning electron microscopy, respectively.
It is observed that the role of deformation in enhancing the nitrided layer thickness is dependent on the material chemistry along with the phases present in it. All the possible causes are analyzed and discussed.
Further, to establish links between the deformation and nitriding kinetics for various phases with the same chemistry, the experimental tests are followed by Thermo-Calc studies.
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