The effect of fretting on the fatigue behaviour of plasma nitrided stainless steels

The plain fatigue and fretting fatigue behaviour of a plasma nitrided dual phase stainless steel known as 3CR12 and an AISI 316 austentic stainless steel have been studied in the present work, using a modified Wohler rotating-bending configuration. Test specimens were produced at two nitriding temperatures, namely 400 and 520 °C, representing low temperature and conventional nitriding temperature, respectively. The test results demonstrate that both nitriding processes can enhance the plain fatigue limit of these steels by approximately 10-25%, with the high temperature process being slightly more effective. Under fretting fatigue conditions, the beneficial effect of plasma nitriding is even more significant and the fretting fatigue limit is increased between 50 and 100% for 3CR12 and at least 50-150% for the AISI steel as the nitriding temperature is raised from 400 to 520 °C.     

Fretting fatigue properties of plasma nitrided AISI 316 L stainless steel: Experiments and finite element analysis

This study investigates the effects of thickness, hardness and composition of modified layer on the plain and fretting fatigue properties of the nitrided 316 L steel plasma nitrided under various processing conditions. Fretting fatigue behaviour of untreated and nitrided material is also analysed with the finite element method. Experimental and theoretical fatigue life results are compared. The result indicates that the nitriding process improved the fretting fatigue properties of 316 L stainless steel. The experimental test results are close to theoretical fretting fatigue life results, thus it yields that the established model in the numerical analysis is consistent in this regard.     

Fretting fatigue properties of plasma nitrided AISI 316 L stainless steel: Experiments and finite element analysis

This study investigates the effects of thickness, hardness and composition of modified layer on the plain and fretting fatigue properties of the nitrided 316 L steel plasma nitrided under various processing conditions. Fretting fatigue behaviour of untreated and nitrided material is also analysed with the finite element method. Experimental and theoretical fatigue life results are compared. The result indicates that the nitriding process improved the fretting fatigue properties of 316 L stainless steel. The experimental test results are close to theoretical fretting fatigue life results, thus it yields that the established model in the numerical analysis is consistent in this regard.     

Multi-pass scratch test behavior of modified layer formed during plasma nitriding

316L stainless steel and Ti6Al4V alloy were plasma nitrided at different treatment parameters, and the wear behaviors of the modified layers formed on the surface during nitriding were investigated by multi-pass scratch test. Phase structure and cross-sections of modified layers were also examined with XRD and SEM. While a single modified layer formed on surface of the 316L stainless steel, both modified and diffusion layers were observed on the surface of the Ti6Al4V alloy after nitriding. As a result, it was observed that phase structure and thickness for modified layers of 316L stainless steel and Ti6Al4V alloy, respectively, were the significant parameters for friction coefficient and wear rate. In addition, diffusion layer formed during the nitriding process caused on increase of wear resistance of Ti6Al4V alloy by supporting the modified layer on the surface.     

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.     

Behavior of medium carbon steel under combined fatigue and wear

The combined fatigue-wear life of medium carbon steel (AISI 1045) was investigated under various combinations of loads and sliding wear conditions using a rotating beam test. The direction of the maximum tensile stress due to bending was perpendicular to that due to wear [1]. Tests were also performed with specimens plated with a thin layer of cadmium or nickel-gold. All of the tests were conducted in the high cycle regime. The results show that the fatigue life of all the specimens at a stress level higher than the endurance limit of the specimen was within the experimental scatter of a typical fatigue test. The effect of sliding wear on fatigue life is manifested primarily by the stress field imposed by the slider on the specimen. In the case of plated specimens, the fatigue life was not significantly affected, although the wear rate was decreased by an order of magnitude.     

The Effect of Plasma Nitriding on the Tribology of Perfluoropolyether Grease-Lubricated 2Cr13 Steel Couples in Vacuum

A 2Cr13 steel was modified by plasma nitriding. The microstructure, phase composition and microhardness of the nitrided samples were examined. The friction and wear behaviour of the nitrided and unnitrided samples sliding against self-mating under PFPE grease-lubricated conditions in vacuum was investigated on a pin-on-disk type tribometer, with the interactions among the nitrided layer and grease to be focused on. The morphologies of the worn surfaces were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy. The chemical compositions of grease samples taken from the worn surfaces were analyzed by Fourier transform infrared spectroscopy (FTIR). Results show that the nitrided steel has better friction-reducing and anti-wear abilities than the unnitrided one under PFPE grease-lubricated conditions. In the former case, the wear of nitrided steel shows a transition from mild abrasive wear to fatigue one with increasing normal load. In the latter case, wear mechanism of unnitrided steel under all load applied is a combination of the severe abrasion and fatigue.     

Erosion–corrosion and corrosion properties of DLC coated low temperature gas-nitrided austenitic stainless steel

Low temperature nitriding of stainless steel leads to the formation of a surface zone of so-called expanded austenite, i.e. by dissolution of large amounts of nitrogen in solid solution. In the present work the possibility of using nitrogen expanded austenite “layers” obtained by gaseous nitriding of AISI 316 as substrate for DLC coatings are investigated. Corrosion and erosion–corrosion measurements were carried out on low temperature nitrided stainless steel AISI 316 and on low temperature nitrided stainless steel AISI 316 with a top layer of DLC. The combination of DLC and low temperature nitriding dramatically reduces the amount of erosion–corrosion of stainless steel under impingement of particles in a corrosive medium.     

Comparison of the fatigue life of F.F. shaft material according to various environmental temperatures

A rotary bending fatigue test was carried out with two kinds of materials, S43C and S50C, using the front engine and front driveshaft (F.F. shaft) of the vehicle. The specimens were heat-treated using the high frequency induction method (about 1 mm depth and HRC56∼60) and the test environment temperatures were -30 °C (-22 °F), +25 °C (+77 °F), and +80 °C (+176 °F) in order to determine the influence of the heat treatment and the temperatures. The fatigue life increased on the order of +80 °C, +25 °C, and -30 °C regardless of heat treatment. In comparison of the fatigue lives with the basis of the tested result at +25 °C, the fatigue lives of non-heated specimens decreased about 35%, but that of heat-treated specimens decreased by only about 5% at +80 °C, more than at +25 °C. And fatigue life of non-heated and heat-treated specimens were about 110% and 120% higher at -30 °C than that of +25 °C. The initiation of surface microcracks was observed at 0.2 fatigue life ratio in as-received S43C and S50C, but the average crack length in S50C was about 14% longer than that of S43C at the same fatigue life ratio.     

Experimental Study of Cyclic Rolling-Contact Fatigue of Silicon Nitride Balls

A newly developed pure-rolling fatigue test rig with three contact points for bearing balls was used to perform rolling-contact fatigue (RCF) tests. The fatigue properties of GCr ₁₅ steel balls and two kinds of Si ₃ N ₄ ceramic balls (GSN-200 and NBD-200) produced with different technologies were compared. Life test data, summarized in accordance with the Weibull theory, showed that the life of the GSN-200 balls was close to that of the GCr ₁₅ balls, whereas the life of the NBD-200 balls was much longer than those of GSN-200 and GCr ₁₅ . Under the same working condition, the temperature rise of all the ceramic balls was lower than that of the steel balls. Ball surfaces were examined after failure with optical microscopy and scanning electron microscopy. It was identified by test that the failure mode of ceramic balls was surface spall. The research shows that subsurface cracks play a dominant role in spalling failure. These cracks originated from volume defects of the material and propagate to form elliptical fatigue spalls.     

合金化渗氮的组织性能与应用

针对合金化涌氮的组织性能进行了研究，研究结果表明，合金化渗氮可形成高硬度，低脆性和致密的渗层；４０Ｃｒ钢合金化参氮后的接触疲劳强度与常规气体氮碳共渗相比提高８３．３３％。     

氨合成塔冷管失效分析

采用金相、电子探针成分分析和显微硬度检测手段研究了断裂冷管段 ,同时进行现场硬度检测 ,说明断裂冷管形成了深度达 1mm的渗氮层 ,且由于渗氮致使氮化层严重脆化和开裂 ,同时氮化层在腐蚀氧化和冷热疲劳作用下 ,导致冷管表面形成了较深的冷热疲劳或氮化脆化裂纹 ,导致冷管的韧性降低 ,甚至断裂。建议严格控制合成塔的操作温度 ,定期检验塔内件承压元件的渗氮程度 ,以确保设备安全运行     

渗碳和碳氮共渗对16Mn钢疲劳性能的影响

实验研究了渗碳和碳氢共渗对１６Ｍｎ钢切口试件疲劳性能的影响规律。实验结果分析表明，碳氮共渗（含０．４％Ｃ－Ｎ）能显著地延长钢件的疲劳寿命．单一渗碳虽能延长钢件的疲劳寿命，但不如碳氮共渗者显著，而且表层中含碳量较低（０．４％Ｃ）时，延长疲劳寿命的效果不如含碳量高（０．８％Ｃ）时的效果好。     

Evaluation of gas nitriding process with in-process variation of nitriding potential for AISI H13 tool steel

Gas nitriding under controlled nitriding potential represents one of the important factors in enhancing the service life of dies used in the industry for hot aluminum extrusion. In the present study, AISI H13, a typical material used for hot extrusion dies, is gas nitrided using automated two-stage controlled nitriding process. Prior heat treatment on the material was carried out under the same controlled environment as used for hot extrusion dies to avoid any decarburization. The nitrided layer has been characterized using different techniques including optical microscopy, SEM, XRD, EDS, and microhardness analysis. It was found that controlled nitriding with in-process variation of nitriding potential can efficiently be used to control the morphology of compound layer and diffusion zone, effective case depth, case hardness, and quality of nitrided layer at sharp edges for better die performance. All the results were found in close agreement with established specifications required for improved die performance.     

A study on tensile and fatigue properties of aged NAS 254N stainless steel at elevated temperatures

The effects of aging on tensile properties and fatigue crack growth behaviors of NAS 254N stainless steel was studied. Yield strength and ultimate tensile strength of the aged specimens were almost the same as the as-received (as-rec.). The fracture strain, however, was decreased significantly by the aging, and the fracture surface of the aged at room temperature (RT) test was intergranular. As test temperature increased, yield strength, ultimate tensile strength and elongation decreased. And a type of serration was observed at 550-650°C As strain rate decreased, yield strength and ultimate tensile strength decreased, but elongation increased. It was observed that tensile strength and strain had a sudden change at one point. And this critical temperatureT _cr was 550°C. The effect of aging time on the tensile strength and strain was also investigated. Tensile strength and strain decreased significantly beyond 100hrs. Fatigue crack growth rate at RT was enhanced by the aging at high stress intensity factor range. This is due to the occurrence of the intergranular fracture in the aged specimen. At 650°C, the fatigue crack growth behavior was almost the same without intergranular fracture.     

钻杆接头材料35CrMo钢硫氮共渗层的摩擦学性能

为了提高钻杆接头的使用寿命,利用离子渗氮和硫氮共渗技术在钻杆接头材料35CrMo钢表面制备了氮化层和硫氮共渗层。在油润滑条件下采用自制的球-盘磨损试验机考察了表面渗层的摩擦磨损性能。利用了XRD研究了表面层的相结构,采用了带EDS的SEM对表面改性层和磨损表面进行了分析。结果表明:35CrMo钢硫氮共渗层的摩擦学性能明显优于原始渗氮层;具有优良润滑作用的FeS固体润滑膜在高硬度氮化层的支撑下,可以有效地改善钻杆接头的摩擦磨损性能。     

The effects of plasma nitriding process parameters on the wear characteristics of AISI M2 tool steel

The main aim of this work is to evaluate the effects of the plasma nitriding process on AISI M2 tool steel. In previous work, treatment time and temperature were varied to identify the treatment conditions for good wear behaviour. In the present work, the treatment time was fixed while temperature and gas pressure were varied. Samples were characterised by glow discharge optical spectroscopy, scanning electron microscopy, X‐ray diffraction, surface microhardness and wear test. The specimens nitrided at 400 and 900 Pa showed the best wear performance, which is possibly due to reduction of the friction coefficient and the low adhesive wear observed. Samples processed at 200 Pa showed spalling during the wear test, indicating a brittle surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low cycle fatigue of PPS polymer injection welds (I)-fatigue crack behavior-

An important class of short-fiber reinforced composites is the sheet molding compound, which is recently developed and currently used in many engineering applications. Fatigue failure of the composites is a subject of major concern in design and cyclic crack propagation is of particular significance in the fatigue life prediction of short fiber composites. However, research on the fatigue behavior of polymer injection weld, especially short glass fiber-filled polymer injection weld, has not been carried out. In this study the analyses of the fatigue crack growth behaviors at weld line and in the bulk are performed based on low cycle fatigue test.     

Effects of compressive stresses on torsional fatigue

Rolling contact fatigue (RCF) is the dominant failure mode in properly installed and maintained ball and roller element bearings. Lundberg and Palmgren in their seminal publication indicated that this failure is due to the alternating component of shear stress. Thus, torsional fatigue experiments have been used to predict the RCF behavior of bearing materials. In non-conformal contacts, due to Hertzian pressure the contact experiences large compressive stresses. Hence, it is critical to take into account the effect of these large compressive stresses in torsional fatigue to better simulate RCF conditions. This paper presents an investigation of torsional fatigue of bearing steels, while the effects of combined compressive stress and its relevance to material behavior in rolling contact fatigue is examined. An MTS test rig was used to investigate the fatigue life of several bearing steels and their failure mechanisms were evaluated through fractography. Then the effects of compressive stresses on torsional fatigue were investigated. A set of custom designed clamp fixtures were designed, developed and used to apply Hertzian pressures of up to 2.5 GPa on the torsion specimens. The experimental results indicate that at high cycle fatigue, a combination of shear and biaxial compression, by application of Hertzian contact, is more detrimental to fatigue life than shear alone; however, as expected it has little to negligible effects in the low cycle fatigue regime. Also the failure mode changes such that fracture planes form a cup and cone pair with multiple internal cracks as opposed to helical planes observed in pure torsion which are formed by a single crack. A 3D finite element model (using ABAQUS) was developed to investigate the fatigue damage accumulation, crack initiation, and propagation in the material. The topology of steel microstructure is modeled employing a randomly generated Voronoi tessellation wherein each Voronoi cell represents a material grain and the boundaries between the cells are assumed to represent the weak plane in the steel matrix. Continuum damage mechanics (CDM) was used to model material degradation during the fatigue process. A comprehensive damage evolution equation is developed to account for the effect of mean stress on fatigue. The model predicts the fatigue lives and crack patterns successfully both in presence and absence of compressive stresses.     

Heat aging effects on the material property and the fatigue life of vulcanized natural rubber, and fatigue life prediction equations

When natural rubber is used for a long period of time, it becomes aged; it usually becomes hardened and loses its damping capability. This aging process affects not only the material property but also the (fatigue) life of natural rubber. In this paper the aging effects on the material property and the fatigue life were experimentally investigated. In addition, several fatigue life prediction equations for natural rubber were proposed. In order to investigate the aging effects on the material property, the load-stretch ratio curves were plotted from the results of the tensile test, the compression test and the simple shear test for virgin and heat-aged rubber specimens. Rubber specimens were heat-aged in an oven at a temperature ranging from 50°C to 90°C for a period ranging from 2 days to 16 days. In order to investigate the aging effects on the fatigue life, fatigue tests were conducted for differently heat-aged hourglass-shaped and simple shear specimens. Moreover, finite element simulations were conducted for the specimens to calculate physical quantities occurring in the specimens such as the maximum value of the effective stress, the strain energy density, the first invariant of the Cauchy-Green deformation tensor and the maximum principal nominal strain. Then, four fatigue life prediction equations based on one of the physical quantities could be obtained by fitting the equations to the test data. Finally, the fatigue life of a rubber bush used in an automobile was predicted by using the prediction equations, and it was compared with the test data of the bush to evaluate the reliability of those equations.