The present work deals with the enhancement of the surface characteristics of stainless steel 316L as a result of shot peening treatment using ceramic balls. In accordance with our own research and information available in literature, as a result of shot peening process, the shot balls can penetrate to the surface layer (permanently depositing) and modify the mechanical performance and the corrosion resistance in the products being treated in this way. Shot peening leads to a significant change to the surface hardness and topography, and consequently, to the change in corrosion behaviour dependent on the choice of processing parameters. Therefore, in this paper, steel samples were treated using two variable parameters of peening pressure (0.3 and 0.4 MPa) and peening time (30 and 60s). In the research, the reference surface were the samples subjected to mechanical polishing. The surface morphology of the samples was investigated by scanning electron microscopy (SEM). The potentiodynamic polarization tests were performed with 1 mV/s scan rate in 0.9% NalCl solution. The improved corrosion resistance (lowest current density Icorr=0.35µA/cm2 and highest corrosion potential Ecorr=-0.164V) was obtained for specimens with longer time (60s) and higher pressure of shot peening treatment (0.4MPa). Greater changes in surface roughness were observed with an increase in peening pressure than with an increase in the processing time. The treatment of the surface with ceramic shots results in an increase in the hardness of the treated surface by more than 110% (for sample 316L/0.4/60) compared to the reference surface. Moreover, an increase in average hardness values was recorded for all surfaces after shot peening (by more than 42% relative to reference samples).
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Purpose: Plasma Transferred Arc surfacing is increasingly used in applications where enhancement of wear, corrosion and heat resistance of materials surface is required. The shape of weld bead geometry affected by the PTA Welding process parameters is an indication of the quality of the weld. In the paper the modelling, analysis and optimization of weld bead parameters of nickel based overlay deposited by plasma transferred arc surfacing are made. Design/methodology/approach: The experiments were conducted based on a five factor, five level central composite rotatable design and a mathematical model was developed using multiple regression technique. The direct and interaction effects of input process parameters of PTA Hardfacing on weld bead geometry are discussed. Finally, Microsoft Excel Solver has been used to optimize the process parameter with a view to economize the powder and achieve the desirable bead dimensions. Findings: Penetration, dilution and total area are increased when the welding current is increased but reinforcement marginally increases and then decreases. Penetration, weld width, dilution and total area decrease when travel speed is increased. Reinforcement increases slightly and then decreases. Practical implications: The developed mathematical models can be used to predict the dimensions of the weld bead and dilution. Originality/value: This paper highlights the development of a mathematical model correlating various process parameters to weld bead geometry in PTA hardfacing of Colmonoy 5, a Nickel based alloy over Stainless steel 316 L plates.
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