Influence of Indentation on the Fatigue Strength of Carbonitrided Plain Steel

Jiewei Gao,Lei Xu,Zhenyu Zhu,Guangze Dai,Junwen Zhao,Hengkui Li

doi:10.1155/2015/492693

Abstract

To study the influence of indentation on the fatigue strength of untreated and carbonitrided specimens of S38C steel, the fatigue limit of specimens with and without indentations was tested. Fracture surfaces were observed using scanning electron microscopy (SEM). The results show that the fatigue strength of the untreated specimen decreases with increasing dimension of indentation, without significant difference compared to the predicted results. Compared to the fatigue limit of the untreated specimen, those of the carbonitrided specimen and the carbonitrided specimen whose compound layer was polished were improved by 12% and 40%, respectively. The fatigue strength of the carbonitrided specimen decreased sharply with increasing indentation size because of the presence of microcracks in the compound layer. When the compound layer was removed, the fatigue limit was observed to be less sensitive to indentation than that of the carbonitrided specimen.

Highlights

A large number of surface treatment methods have been developed with the target of hardening a material’s surface and introducing compressive residual stress to enhance component service performance, such as corrosion resistance, fatigue resistance, wear resistance, or fretting resistance [1]
Artificial indentations were produced on untreated specimen (UCN), carbonitrided specimens (CN), and compound layer being polished (CNP) specimens of S38C plain steel
When the compound layer was removed, the fatigue strength was enhanced by up to 40% compared to that of the untreated specimen

Summary

Introduction

A large number of surface treatment methods have been developed with the target of hardening a material’s surface and introducing compressive residual stress to enhance component service performance, such as corrosion resistance, fatigue resistance, wear resistance, or fretting resistance [1]. The strength of the material surface is hardened by the precipitates, and compressive stress is introduced by the expansion of the diffusion layer [3]. Because of its high hardness and electrochemical stability, this layer plays an important role in enhancing the wear resistance and corrosion resistance of treated materials; the diffusion layer rather than the compound layer plays a dominant role in determining the fatigue strength [6]. In the contact fatigue test or wear test, the compound layer fails by delaminating and breaking into pieces, which deteriorates the test conditions [8]

Methods

Results

Conclusion