Looking for the Optimal Shot Peening Treatment on Quenched and Tempered Steels with Different Hardness Levels

Author:  V. Llaneza and F. J. Belzunce
Source:  Conf Proc 2014: ICSP-12 Goslar, Germany (pgs.49-54)
Doc ID:  2014049
Year of Publication:  2014
Abstract:  
Bars of a medium-carbon alloyed steel (AISI 4340), with a diameter of 16 mm, were subjected to different heat treatments (quenched and tempered between 200°C and 680°C) in order to achieve different mechanical properties. The bars were cut and machined to obtain fatigue specimens that were subjected to different shot peening treatments (diverse Almen intensities under 100% coverage) using cut wire shots of different sizes in a direct compressed air shot peening machine. X-ray diffraction (XRD) combined with electro-polishing techniques were used to obtain the different residual stress profiles induced by shot peening in each steel. Moreover, the specimen roughness was also measured. Finally, fatigue tests were performed in a four-point loading rotating beam testing machine (R= -1) to determinate the fatigue life under a stress slightly higher than the fatigue limit of each steel. It was observed that every heat treated steel had an optimal Almen intensity in order to attain the best fatigue behavior, which is dependent on its mechanical properties. The optimal Almen intensity is larger for mid-strength steels than for weaker and stronger ones, due to the existing compromise between the extension of the induced compressive residual stress field and the surface damage produced by shot impacts.