Relation between roughness and processing conditions of AISI 316L stainless steel treated by ultrasonic shot peening

This article assessed the roughness induced by ultrasonic shot peening. Surface properties of AISI 316L steel specimens were modified through the variation of ultrasonic shot-peening parameters (shot material, shot diameter, sonotrode amplitude vibration and coverage). Each surface was characterized using fifty surface roughness parameters and two types of robust Gaussian filter (low pass and high pass) associated with twenty one cut-off lengths. For each type of processing parameter, the most relevant roughness parameter and its corresponding length scale and filter were found. A linear relationship was identified between the four ultrasonic shot-peening parameters and the mean density of furrows with a coefficient of determination equal to 0.97.     

Empirical modeling of shot peening parameters for welded austenitic stainless steel using grey relational analysis

The attempt of this paper is to present an effective approach for the optimization of the shot peening process of welded AISI 304 austenitic stainless steel with multi performance characteristics using Grey relational analysis (GRA) based on Taguchi orthogonal array. Twenty-seven experimental runs are performed to determine best process parameters level. An analysis of variance (ANOVA) is carried out to identify significant peening parameters. The response tables are obtained for analyzing the optimal levels of shot peening parameters and major factors that affect the quality function. The multiple performance characteristics including tensile strength, surface hardness and surface roughness are the quality functions considered for the optimization. Further mathematical models are developed using regression analysis for the tensile strength, surface hardness and surface roughness. It will be very helpful to the engineers in deciding the levels of the shot peening parameters for desired performance characteristics.     

Structural analysis and intergranular corrosion tests of AISI 316L steel

Pure AISI 316L steel is investigated after solution heat treatment (1050 °C/H₂O) and structural sensitization (650 °C). Two quite different intergranular corrosion tests are used to determine the degree of structural sensitization due to the precipitation of secondary phases along the grain boundaries (mainly the M₂₃C₆ and σ‐phase): the oxalic acid etch test and the electrochemical potentio‐kinetic reactivation test. Generally, the dissolution of chromium‐rich carbides (M₂₃C₆) is provoked by oxalic acid etch tests, whereas the chromium‐depleted zones, in the vicinity of chromium‐rich carbides (M₂₃C₆), are attacked by electrochemical potentio‐kinetic reactivation tests. Both intergranular corrosion tests are used to determine the maximum degree of structural sensitization. Thus structural analysis by carbon replicas reveals the Laves phase, and both the M₂₃C₆ and (Cr,Mo)_x(Fe,Ni)_y phases. The results of intergranular corrosion tests are related to the findings of the structural analysis.     

Studies on the influence of process parameters on the AISI 316L resistance spot-welded specimens

Energy saving and improving product performance are long-term concerns in extrusion process. Therefore, this paper proposes a novel extrusion process called alternate extrusion (AE). The proposed process uses split punches alternately instead of the overall structure to apply the downward load, but receives an unexpected load-saving and grain refinement effect. Experimental and finite element method (FEM) methods were used to investigate the effects of different extrusion ratios on microstructure and mechanical properties. Results indicate that load value is significantly reduced, grain size is considerably refined, and tensile strength and elongation of material are improved after AE processing. The fractography shows that the fracture mode of AZ31 magnesium alloy changes from brittle to ductile. Although the actual extrusion ratio decreases in AE process, additional shear forces produced by different punch-alternating loads at the interface improve microstructure and mechanical properties. Therefore, AE can achieve grain refinement and load saving and improve strength and plasticity of magnesium alloys.     

Investigations on surface integrity of AISI 1045 using LPB tool

Low plasticity burnishing (LPB) is relatively a new method of surface enhancement, which raises the burnishing to the next level of sophistication. LPB can provide deep stable surface compression for improved surface integrity characteristics. The present study focuses on the surface roughness, microhardness, surface integrity and fatigue life aspects of AISI 1045 work material, using full factorial design of experiments. The assessment of the surface integrity aspects on work material was done, in terms of evaluating the interaction effects of parameters, identifying the predominant factor amongst the selected parameters, their order of significance and setting the levels of the factors for minimizing surface roughness and/or maximizing surface hardness and fatigue life. Mathematical expressions were developed for surface characteristics of importance as response variables. Subsurface microhardness studies were also done to assess the depth of compression, altered material zone and correlate fatigue life with surface roughness and surface hardness. The process can be applied to critical components effectively, as the LPB process today has significant process cycle time advantages, and lower capital cost. Additional cost reduction will be realized by introducing proven high speed machining concepts into the LPB process.     

Optimization of drilling parameters on surface roughness in drilling of AISI 1045 using response surface methodology and genetic algorithm

Modeling and optimization of cutting parameters are one of the most important elements in machining processes. The present study focused on the influence machining parameters on the surface roughness obtained in drilling of AISI 1045. The matrices of test conditions consisted of cutting speed, feed rate, and cutting environment. A mathematical prediction model of the surface roughness was developed using response surface methodology (RSM). The effects of drilling parameters on the surface roughness were evaluated and optimum machining conditions for minimizing the surface roughness were determined using RSM and genetic algorithm. As a result, the predicted and measured values were quite close, which indicates that the developed model can be effectively used to predict the surface roughness. The given model could be utilized to select the level of drilling parameters. A noticeable saving in machining time and product cost can be obtained by using this model.     

Surface roughness and cutting force prediction in MQL and wet turning process of AISI 1045 using design of experiments

This paper presents an investigation into the MQL (minimum quantity lubrication) and wet turning processes of AISI 1045 work material with the objective of suggesting the experimental model in order to predict the cutting force and surface roughness, to select the optimal cutting parameters, and to analyze the effects of cutting parameters on machinability. Fractional factorial design and central composite design were used for the experiment plan. Cutting force and surface roughness according to cutting parameters were measured through the external cylindrical turning based on the experiment plan. The measured data were analyzed by regression analysis and verification experiments were conducted to confirm the results. From the experimental results and regression analysis, this research project suggested the experimental equations, proposed the optimal cutting parameters, and analyzed the effects of cutting parameters on surface roughness and cutting force in the MQL and wet turning processes.     

喷丸与激光喷丸强化高强度钢对比试验

为了考察和对比喷丸(SP)和激光喷丸(LSP)2种表面强化技术对金属零件的强化效果,以30CrMnSiNi2A钢为试样,进行喷丸和激光喷丸强化处理试验。试验结果显示,2种强化试样的残余压应力和硬度都有较大的提高。分别测定了喷丸强化和激光喷丸强化试样在同一应力水平下的疲劳寿命,并运用扫描电镜分析了两者的疲劳断口。试验结果表明,激光喷丸强化试样中值疲劳寿命是喷丸强化试样的1.11~2.75倍,激光喷丸强化比喷丸强化在提高金属零件表面性能方面的效果更佳。     

Experimental investigation of shot peening: correlation of pressure and shot velocity to Almen intensity

The International Journal of Advanced Manufacturing Technology - Shot peening is a mechanical surface enhancement process that is extensively used in various industries to increase fatigue life of...     

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.     

Effect of burrs on the friction performance of hierarchical micro-dimple textured AISI 1045 steel

Journal of Mechanical Science and Technology - One of the common problems associated with surface texturing is the presence of burrs/bulges around a micro-dimple surface. This study experimentally...     

Effect of sigma phase on near-threshold fatigue crack growth behavior and ultrasonic evaluation in AISI 316L stainless steel

In this work, we examined the influence of microstructural changes, such as an intermetallic sigma (??) phase, on the fatigue behavior of high-temperature aged AISI 316L stainless steel. Nondestructive ultrasonic test and fatigue crack growth tests were performed to determine the threshold stress intensity factor of these artificially aged specimens. Ultrasonic test results characterizing the microstructural changes were compared with those of the fatigue tests to propose an empirical formula capable of predicting the threshold stress intensity factor by a nondestructive method. We observed a strong correlation between the increase in the volume fraction of the ?? phase and the decrease of ??K_th. Ultrasonic velocity increased in response to the coarsening behavior of the ?? phase in the vicinity of the grain boundaries.     

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.     

Experimental study and modelling of tool temperature distribution in orthogonal cutting of AISI 316L and AISI 3115 steels

Cutting tool temperature distribution was mapped using the IR-CCD technique during machining of carbon steel AISI 3115 and stainless steel AISI 316L under orthogonal cutting conditions using flat-face geometry inserts. The effect of work material treatment on tool temperature was investigated, and the results showed that AISI 3115 in heat-treated state displayed higher tool temperature than the as-rolled state. Stainless steel 316L with high sulphur content (0.027?wt.%) and calcium treatment displayed lower cutting tool temperature than the variant with low sulphur (0.009?wt.%). The experimental results were compared with theoretical tool temperature distributions based on a modified version of Komanduri and Hou??s analytical model. In particular, variable frictional heat source and secondary shear were introduced and modelling of the tool stress distribution on rake surface was also considered.     

Effect of electro discharge machining (EDM) on the AISI316L SS white layer microstructure and corrosion resistance

The localised corrosion resistance of austenitic stainless steels is strongly influenced by the quality of finished surface. EDM machining induces substantial changes by the high thermal gradients generated by electric sparks. Experimental techniques such as roughness measurement, scanning electron microscopy (SEM), energy dispersive microanalysis (EDX) and X-ray diffraction technique, reveal micro-geometrical, microstructural, chemical and mechanical changes. These changes lead to white and heat-affected layers with a depth less than 100 μm. The white layer is a melted material characterised by dendritic structure and constituted by austenite, chromium carbide and ε-carbide. The heat-affected layer is characterised by very large grain size comparatively to the bulk material. Electrochemical test coupled with metallographic examinations using SEM reveals a weakening of the resistance to pitting and intergranular corrosion comparatively to diamond polished surface. This weakening is correlated to differences in structure and chemical composition of white layer. Susceptibility to stress corrosion cracking has been attributed to the field of tensile residual stresses resulting from thermal effects. The removal of the white layer material by polishing or wire brushing restores the corrosion resistance of the AISI316L SS.     

Effect of shot peening coverage on fatigue limit in round bar of annealed medium carbon steel

Shot peening is an effective and economical technique for improving the fatigue strength of metallic components by inducing compressive residual stress and hardening the layer near the surface. The effect is generally evaluated by main two parameters: coverage and peening intensity. However, the valuable coverage for improving the fatigue strength depends on the shape of the target material. In this study, the effect of coverage on fatigue limit in round bar of annealed medium carbon steel was experimentally studied. The fatigue limits for shot peened round bar specimens with 140–2300% coverage increased 14–25% by comparing those for non-peened round bar specimens. The valuable range of coverage was 280–60% in the used material and shot peening condition for improving the fatigue limit in short time. The result indicates that the valuable coverage of the round bar material is higher than full coverage to improve the fatigue limit of the material due to the effect of incident angle on round bar, even though the degree depends on the materials and shot peening conditions.     

The effects of laser peening and shot peening on fretting fatigue in Ti-6Al-4V coupons

This paper describes testing of Ti-6Al-4V coupons in fretting fatigue and compares the effects of mechanical surface treatments on performance. Fretting fatigue tests were performed using a proving ring for fretting load, bridge-type fretting pads, and applied tension-tension cyclic fatigue stress. As-machined (AM), shot peened (SP), and laser peened (LP) coupons were evaluated, and data generated to compare residual stress, surface condition, lifetime, and fractographic detail encountered for each. Near-surface residual stress in SP and LP coupons was similar. The layer of compressive residual stress was far deeper in LP coupons than in SP coupons and, consequently, subsurface tensile residual stress was significantly greater in LP coupons than in SP coupons. SP coupons exhibited a rough surface and had the greatest volume of fretting-induced wear. LP coupons exhibited a wavy surface and had a small volume of wear localized at wave peaks. SP coupons had the greatest fretting fatigue lifetime, with significant improvement over AM coupons. Lifetimes of LP coupons were similar to those for SP coupons at high fatigue stress, but fell between AM and SP coupons at lower fatigue stress. Fractographic evaluation showed that fractures of AM samples were preceded by initiation of fretting-induced cracks, transition of a lead fretting crack to mode-I fatigue crack growth, and crack growth to failure. SP and LP samples exhibited behavior similar to AM samples at high fatigue stress, but in coupons tested at low stress the lead crack initiated subsurface, near the measured depth of maximum tensile residual stress, despite the presence of fretting-induced cracks. The level of fatigue stress above which lead cracks were initiated by fretting was higher for LP than for SP, and was predicted with good accuracy using an analysis based on linear elastic fracture mechanics, the fatigue crack growth threshold stress intensity factor range, and superposition of measured residual stress and applied fatigue stress.