In the present work, effect of deep cold rolling process known as deep rolling on near-surface microstructure and hardness of an austenitic stainless steel has been evaluated. Deep rolling process using a ball-point device was carried out on the barshaped AISI 316L stainless steel specimens. The process was performed at 15 and 26 passes with 0.2mm/s longitudinal rate and 22.4rpm bar rotation. Microstructure and hardness were investigated by feritscope, X-ray diffract meter, field emission scanning electron microscope and Vickers¬ micro-indenter at 0.1kgf. A composite microstructure, consisting of ultrafine and nano grains (200nm and 70nm), mechanical twins and strain-induced marten site, was observed in the near-surface regions. Surface hardness was increased from 210 to 450 and 500HV0.1 after 15 and 26 passes, respectively.

Influence of deep rolling prior to plasma nitriding on microstructure and hardness of the AISI 316L stainless steel was investigated in this paper. Deep rolling using 'ball-point' tool was conducted on the 316L stainless steel bar at multiple passes. Then, plasma nitriding was performed on the as-received and deep-rolled kinds at 450°C temperature for 5 h. Structural characterisation was done using optical microscope, field emission scanning electron microscope, feritscope, X-ray diffractometer, and glow discharge optical emission spectroscope as well as hardness measurement by a Vickers micro-hardness tester at 0.1 kgf. An ultrafine structure and a nitrogen-rich layer were, respectively, formed on the rolled and nitrided surfaces. Surface hardness was increased from 210 up to 450, 670 and 1050 HV 0.1 after the rolling, nitriding, and rollingnitriding processes, respectively. Thickness of the nitrided layer was increased from 12 to 20 lm and diffusion depth of nitrogen from 12 to 25 lm via conducting the deep rolling before the nitriding process. The rolling-nitriding process was resulted in rising of nitrogen concentration by a factor of about 3 at near-surface regions.