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In this study, the use of Ultrasonic Peening Technology (UPT) on the of mill rollers graphite steel (GSH48) for enhancement of some of the surface mechanical properties was surveyed. One of the new technologies for severe plastic deformation is ultrasonic peening technology in which vibratory tool strikes the workpiece surface with continual reciprocating motions, resulting in severe plastic deformation on surface. This method improves mechanical properties like hardness, surface roughness, fatigue life and tension strength. With simulation and manufacturing of peening vibratory tool, preparation of process was accomplished including setting up the ultrasonic vibratory tool on lathe machine. The investigation of hardness tests, surface roughness, fatigue and tension strength on the pieces was performed in different conditions, before and after the process of ultrasonic peening with one, two and three passes. The results showed increase of hardness up to %36 in depth of 0.2 mm. Also, the surface roughness was reduced from Ra=1.376 µm to Ra= 0.545 µm. The most improvement in surface roughness and fatigue life was observed at the pieces with three passes of ultrasonic peening.

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In this study, a non-distractive method of x-ray diffraction (XRD) was used to determine residual stress of rolling mill rolls made of graphite steel (GSH48). This method utilizes the variations of distance between crystal planes as strain. The determination of residual stress was performed samples in different depths before and after conducting ultrasonic peening technology. In UPT process, impacts were exerted on the workpiece ball tool, resulting in the improvement of some mechanical properties such as residual stress by creating work hardening and compression. After the simulation and manufacturing of ultrasonic vibratory tool and then the installation of that on lathe machine, UPT operations were conducted on the prepared samples. Measuring residual stress from surface to 0.5 mm depth was performed before and after the UPT process. After the numerical simulation of the UPT, the distribution of experimental residual stress and numerical simulation was compared that the results suggested the increase of compressive residual stress about 0.4 mm from the surface after the UPT process. The rise of compressive residual stress in the rolling mill rolls leads to the increase of their strength and fatigue life and as a result, their working efficiency is boosted. After the UPT process, the grain size of the surface was calculated from the model of the x-ray diffraction using Viliamson-Hall relation that grain size was obtained 60.2 nm. The refinement of surface structure arises because of displacement arrangement again due to vibration with high frequency and severe plastic deformation after the UPT process.