TERRES et BECHOUEL Ben MOHAMED 2017 low cycle fatigue of nitrided layers (original) (raw)

Low Cycle Fatigue Behaviour of Nitrided Layer of 42CrMo4 Steel

International Journal of Materials Science and Applications

Steel 42CrMo4, used in the manufacturing of transmission systems (gears), poses problems in service under specific cyclic stress conditions of the operating mode of its bodies. The treatment of ion nitriding during 20 hours with 520°C applied to 42CrMo4 steel in an untreated state (quenched and tempered) led to the formation of a compound layer (mixture of nitrides γ' and carbonitrides ε with irregular thickness evaluated at 5µm and a diffusion layer of depth equal to 295µm). In the diffusion layer, the presence of inserted nitrogen leads to the increase in hardness (3 times that of basic material) and to the creation of a compressive residual stress field (-400MPa). This superficial hardening does not modify the tensile mechanical characteristics of 42CrMo4 steel but renders it more sensitive to overload in fatigue. As a result, a 0.7% total deformation imposed corresponding to a loading level of 850MPa, constitutes the limit of gain in fatigue obtained by the ion nitriding considered.

Service Behavior of Nitride Layers of Steels for Military Applications

Coatings, 2020

Steels which are utilized in the manufacturing of specific parts of military technology such as crankshafts of engines in heavy-duty vehicles or barrels of guns must be subsequently modified by heat treatment according to the requirements of customers. Despite the hard surface of martensitic structure obtained by hardening process, steels have a low wear resistance and high values of coefficient of friction. To improve these parameters and due to the fact that many of steels which are utilized for manufacturing of mentioned parts are also categorized as Nitralloy steels, in this paper, the improvement in these properties of chosen steels by the application of plasma nitriding has been studied. The steel equivalent 17Ni4CrMo (i.e., CSN 41 6720) and equivalent 42CrMo4 (i.e., CSN 41 5142) were chosen for the study. The chemical composition of chosen steels was verified by optical emission spectrometry. The microstructure and the diffusion layer were observed by optical microscopy due t...

Effect of nitriding on low-cycle fatigue properties

International Journal of Fatigue, 1997

Nitriding is a thermochemical surface treatment that is often utilized to improve the fatigue strength of mechanical elements. In fact it is well known that, after the treatment, owing to the formation, of zt nitrided external layer and a field of residual stresses that are compressive on the surface, the highcycle strength is strongly increased. Treatment characteristics include temperature and duration, whose values are generally decided by the operator. In this study, experimental axial tests were conducted on smooth specimen groups, which were each treated by using different durations. The results ,ow. the strong influence of treatment time on the elastic modulus values: in particular, if the duration increases, the elastic modulus increases too. A simple model allowed us to evaluate the distribution of the stresses in the case and in the core, and it was found that by increasing the treatment time the external layer is more stressed with respect to the core. Low-cycle fatigue was investigated, and the Ea-Nf curves obtained by means of the differently treated specimens were compared. The results show that increasing the duration decreases the fatigue behaviour for high applied strains, and only one overload may be sufficient to fracture the external layer.

Fatigue and fretting fatigue of ion-nitrided 34CrNiMo6 steel

Theoretical and Applied Fracture Mechanics, 2001

This work is concerned with the surface treatment (ion nitriding) of fretting fatigue and fatigue resistance of 34CrNiMo6. Tests are made on a servo-hydraulic machine under tension for both treated and non-treated specimens. The test parameters involve the applied displacements d AE 80±AE170 lm; fretting pressure r n 1000±1400 MPa; fatigue stress amplitude r a 380±680 MPa and stress ratio R À1. The ion nitriding process improves both fatigue and fretting fatigue lives. Subsurface crack initiation from internal discontinuities was found for ion-nitrided specimens.

Effect of the ion nitriding surface hardening process on fatigue behavior of AISI 4340 steel

Materials Characterization, 2008

Ion nitriding is a glow discharge surface modification technique, which is primarily used to increase the fatigue strength, wear, corrosion resistance and surface hardness of steels. Because of the formation of high compressive residual stresses in the case region, increasing surface hardness and case depth cause remarkable improvement in fatigue properties of steels. In this study, the ion nitrided properties of quenched and tempered AISI 4340 low alloy steel were investigated under different process parameters including time and temperature. It has been found that the ion nitriding surface treatment improves the fatigue strength and increases the fatigue limit depending on the case depth. Up to 91% improvement in fatigue strength of the steel has been attained by ion nitriding. It was determined that, the subsurface 'fish eye' type formation is the dominant fatigue crack initiation mechanism in ion nitrided AISI 4340 steel in high cycle region and its origin was nonmetallic inclusions.

Microstructural features controlling very high cycle fatigue of nitrided maraging steel

2014

On behalf of the Organizing Committee, we would like to welcome all participants to the sixth international conference on Very High Cycle fatigue (VHCF-6) event from Oct. 15-18, 2014, Chengdu, China. Most of the experimental studies on fatigue of structure materials are usually limited to testing period between 10 7 to 10 8 cycles, and unexpected fatigue failures have been recorded for some structural components which were assumed to have a fatigue limit. It was concluded that the fatigue life of numerous aeronautic, locomotive, automotive and biomedical structures may go beyond 10 8 cycles. A growing interest in the investigation of extreme high cycle fatigue behavior is basically from the expectation of reduction in environmental impact and enhanced economic efficiency of the components which drives the new design to reach very high fatigue lives. Long life fatigue behavior determination, damage evaluation and understanding of fracture mechanisms become extremely important for better selection of materials and improvement of design the components and structures. The VHCF conferences are international leading conference series on the ultra-long fatigue behavior of materials. It hosts scientists, engineers and engineering designers from all over the world and aims to provide a worldwide platform to exchange and present latest findings and ideas. VHCF-6 continues the trend of successful previous conferences started with VHCF-1 in 1998, organized by Prof. Claude Bathias in Paris, followed by VHCF-2 in 2001 organized by Prof. Stefanie Stanzle and Prof.

Tome XIII [2015]-Fascicule 4 [November] ION NITRIDING OF CONSTRUCTION STEELS

a free-access multidisciplinary publication of the Faculty of Engineering Hunedoara 1. Abstract: The present paper studies the influence of the parameters of ion nitriding (ammonia pressure in the chamber, the temperature of nitriding and the time for treatment) on the hardness of the nitride layer and the thickness of the nitride zone for construction steels 20MnCr5G and 100Cr6. To achieve the aim of this work a planned experiment has been used. A mathematical model has been derived for the two studied steels, reflecting the relationship between the parameters of control over the process of ion nitriding and the hardness of the formed layer, as well as the thickness of the combined zone. 1. INTRODUCTION Ensuring high quality of the products of mechanical engineering is directly related to increasing their reliability and durability, which, in turn, are defined by the wear-resistance of the materials. Ion nitriding and carbonitriding are used nowadays in machine building to improve ...