Fatigue Limit of Custom 465 with Surface Strengthening Treatment

Abstract

In order to study the effect of nitriding or shot peening on the surface modification and fatigue properties of martensitic stainless-steel Custom 465, the residual stress and micro-hardness of the strengthened layer are determined by X-ray and micro-hardness tester, respectively. The up-and-down method is used to measure the rotational bending fatigue strength at 1 × 107 cycles, and the fatigue fracture characteristic is observed by scanning electron microscopy. The relationship between surface residual stress and internal fatigue limit of surface strengthening treatment is discussed. Results show that nitriding or shot peening surface strengthening layer forms a certain depth of compressive residual stress, where in the surface compressive residual stress of the nitrided specimens is greater than the shot peened specimens. The micro-hardness of the nitrided or shot peened surface strengthening layer is significantly improved, where in the surface micro-hardness of nitriding specimens are higher than shot peening specimens. The nitriding or shot peening surface strengthening can significantly improve the fatigue limit of Custom 465, wherein the fatigue limits of nitrided and shot peened surface strengthened specimens are 50.09% and 50.66% higher than that of the un-surface strengthened specimens, respectively. That is, the effect of the two strengthening methods on fatigue limit is not very different. The fracture characteristics show that the fatigue crack of the un-surface strengthened specimens originates from the surface, while the fatigue crack of surface strengthened specimens originates from the subsurface layer under the strengthened layer. The relationship between the internal fatigue limit and the surface residual stress of the surface strengthened specimen can be used as a method for predicting the fatigue limit of the surface strengthened specimens.

Resistance to fracture due to cyclic fatigue of stainless steel manual files and its association to surface roughness

“…The presence of surface roughness on endodontic files has been reported to concentrate stress, giving rise to areas where cracks initiate during clinical use 1 , leading to fracture due to cyclic fatigue 2 . To date, mechanical, physical and heat surface treatments have been reported for stainless steel alloys -including sanding, grinding, abrading, electropolishing, nitriding, and combined plasma carburizing, among others-to alter surface texture and improve properties such as microhardness and resistance to fracture due to fatigue of the alloy [3][4][5] . However, in contrast to nickel-titanium files, stainless steel alloy files have not often been subjected to procedures to improve their properties, even though they are so frequently used in endodontic treatment.…”

Effect of Shot Peening on Redistribution of Residual Stress Field in Friction Stir Welding of 2219 Aluminum Alloy

“…To improve the fatigue life of industrial parts and components, various surface treatment technologies have been developed in recent decades [ 16 , 17 , 18 , 19 ]. Shot peening is a well-known surface strengthening technology, which can significantly enhance the fatigue strength and effectively prevent the failure of components.…”