Search Results (11)

This study investigates the influence of molten nitrate salt exposure on the intergranular corrosion (IGC) behavior of three grades of austenitic stainless steel (namely, AISI 304, AISI 304H, and AISI 321H). Two electrochemical techniques, double loop electrochemical potentiokinetic reactivation and potentiodynamic polarization methods, are applied after stainless steel is exposed to 600 °C molten nitrate salt, 60% NaNO₃, and 40% KNO₃ for varying immersion durations. Corrosion morphology is examined using optical microscopy and scanning electron microscopy images to assess susceptibility to IGC. IGC is prompted by the presence of chromium carbides at grain boundaries, which leads to chromium depletion around these carbides. The findings of the experiments reveal distinct IGC behavior among stainless steel grades. For AISI 304, the degree of sensitization (DOS) increases as exposure time progresses. However, AISI 304H and AISI 321H stainless steel exhibit diminishing DOS after 100 and 10 h of exposure, respectively. This trend is attributed to desensitization or the healing effect when stainless steel is exposed to molten salt for a prolonged time. The depletion and recovery of Cr near grain boundaries are confirmed by the inverse relationship to DOS of pitting potential. Full article

In this work, solution-annealed AISI 316H grade austenitic stainless steel was studied in terms of investigating the electrolytic hydrogen charging effects on the resulting Charpy impact toughness and dry sliding tribological behavior. Conventional Charpy impact bending tests were employed to study the mechanical response of the investigated material to dynamic loading conditions, whereas dry linear sliding tribological tests were used to study material friction and wear behavior. The obtained mechanical and tribological properties were correlated with corresponding fracture and tribological mechanisms, which were determined from morphological observations of fracture surfaces and tribological tracks. The applied testing procedures were individually carried out for the non-hydrogenated, hydrogen-charged, and dehydrogenated material conditions. The observed changes in individual properties due to applied hydrogen charging were rather small, which indicated the good resistance of solution-annealed AISI 316H steel against material degradation in currently used electrolytic hydrogenation conditions. Full article

Allowing for complex shape and low energy consumption, 3D printing, debinding, and sintering (PDS) is a promising and cost-effective additive manufacturing (AM) technology. Moreover, PDS is particularly suitable for producing bimetallic parts using two metal/polymer composite filaments in the same nozzle, known as co-extrusion, or in different nozzles, in a setup called bi-extrusion. The paper describes a first attempt to produce bimetallic parts using Inconel 718 and AISI 316L stainless steel via PDS. The primary goal is to assess the metallurgical characteristics, part shrinkage, relative density, and the interdiffusion phenomenon occurring at the interface of the two alloys. A first set of experiments was conducted to investigate the effect of deposition patterns on the above-mentioned features while keeping the same binding and sintering heat treatment. Different sintering temperatures (1260 °C, 1300 °C, and 1350 °C) and holding times (4 h and 8 h) were then investigated to improve the density of the printed parts. Co-extruded parts showed a better dimensional stability against the variations induced by the binding and sintering heat treatment, compared to bi-extruded samples. In co-extruded parts, shrinkage depends on scanning strategy; moreover, the higher the temperature and holding time of the sintering heat treatment, the higher the density reached. The work expands the knowledge of PDS for metallic multi-materials, opening new possibilities for designing and utilizing functionally graded materials in optimized components. With the ability to create intricate geometries and lightweight structures, PDS enables energy savings across industries, such as the aerospace and automotive industries, by reducing component weight and enhancing fuel efficiency. Furthermore, PDS offers substantial advantages in terms of resource efficiency, waste reduction, and energy consumption compared to other metal AM technologies, thereby reducing environmental impact. Full article

In contrast to austenitic and martensitic stainless steels, ferritic stainless steels have a lower hardness and wear resistance but exhibit excellent corrosion resistance. Due to this fact, their use in the aerospace, automobile, and house construction industries is restricted. Several methods have been utilized to enhance the tribological characteristics of ferritic stainless steels. In this work, titanium nitride coating has been carried out by using a cathodic cage of titanium material, and later on, the titanium cathodic cage is replaced by an AISI-304 cathodic cage in a CCPN chamber to form iron nitride coating on AISI-430 ferritic stainless steel coupons through a plasma nitriding process for 4 h at a fixed temperature of 400 °C. The microstructures and mechanical traits of all processed and control coupons were analyzed using scanning electron microscopy, X-ray diffraction, ball-on-disc wear tester, and microhardness tester techniques. The results showed that hardness increased up to 1489 HV with the titanium cage, which is much higher than the hardness of the base material (270 HV). The titanium cage-treated coupons have high layer thickness, smooth surface morphology, and a minimum crystallite size of 2.2 nm. The wear rate was reduced up to 50% over the base material after the titanium cage plasma treatment. The base coupon exhibited severe abrasive wear, whereas nitrided coupons exhibited dominant adhesive wear. In the iron nitride coatings, this effect is also important, owing to the more influential cleaning process in a glow discharge, and the better adhesion with enhanced interlayer thickness is attributed to the fact that the compliance of the interlayer minimizes shear stresses at the coating–substrate interface. The use of a graded interface improves adhesion compared with the case where no interlayer is used but a titanium interlayer of comparable thickness provides a significant increase in measured adhesion. For both titanium and iron nitride films, there is a reduction in wear volume which is a function of interlayer thickness; this will have a substantial effect on wear lifetime. Thus by careful control of the interlayer thickness and composition, it should be possible to improve coating performance in tribological applications. Full article

Steel of the mild-strength S355J2+N steel grade is the most often used steel for manufacturing carrying sections of constructions exposed to fatigue loads. The use of high-strength steels, such as S690QL, allows for the creation of structures that are light and simple to construct. However, increasing the yield strength of high-strength steels does not result in a corresponding increase in fatigue resistance. As a result, using high-strength steels for constructions subjected to fatigue loading can be a major design concern, raising the question of whether high-strength steels should be used at all. Most of the experimental investigations regarding the hot work tool steel X37CrMoV5-1 found in the literature are focused on its machining and wear resistance, with insufficient attention paid to the cyclic loads. This article evaluates the fatigue properties of mild-strength S355J2+N, high-strength S690QL, and X37CrMoV5-1 steel grades. A SHIMADZU servo-hydraulic testing machine is used to perform uniaxial tensile tests under uniaxial fatigue stress-controlled, fully reversed conditions (tensile–compression testing with R = −1 stress ratio) in accordance with EN ISO and ASTM standards. The aim of this paper is to highlight the fatigue characteristics of these three steels that are among the most used in their respective groups. Steel S355J2+N belongs to the group of hot-rolled normalized steels, S690QL belongs to the group of improved (quenched + tempered) steels with increased strength, and X37CrMoV5-1 belongs to the group of high-alloyed tool steels for hot work. This choice was made as the tested steels can be considered typical representatives of their groups. Based on the test results of these three steels, which are organized in S–N curves, the fatigue behavior of the entire mentioned groups of steels can be foreseen. Full article

End-milling operation of steel grade material is a challenging task as it is hard-to-cut material. Proper selection of cutting tools, cutting conditions, and cutting process parameters is important to improve productivity, surface quality, and tool life. Therefore, the present study investigated the end-milling operation of AISI 1522H steel grade under minimum-quantity lubrication (MQL) conditions using a novel blend of vegetable oils, namely canola and olive oil. Cutting process parameters considered were spindle speed (s), feed rate (f), depth of cut (d), width of cut (w), and cutting conditions (c), while responses were average surface roughness (Ra), cutting forces (Fc), tool wear (TW), and material removal rate (MRR). Experimental runs were designed based on the definitive screening design (DSD) method. Analysis of variance (ANOVA) results show that feed rate significantly affects all considered responses. Nonlinear prediction models were developed for each response variable, and their validity was also verified. Finally, multi-response optimization was performed using the combinative distance-based assessment (CODAS) method coupled with criteria importance through inter-criteria correlation (CRITIC). The optimized parameters found were: s = 1200 rpm, f = 320 mm/min, d = 0.6 mm, w = 8 mm, and c = 100 mL/h. Further, it was compared with other existing multi-response optimization methods and induced good results. Full article

Erosion–corrosion behavior of pipeline grade carbon steel alloy (AISI 1030) was investigated using a state-of-the-art jet impingement flow loop. Different impingement velocities (3 to 12 m/s) and angles (15°, 30°, 45°, 60°, and 90°) were employed (with/without sand particles) to study the degradation behavior of this pipeline grade steel in 0.2 M NaCl solution at room temperature. Experiments were conducted for a duration of 24 h at room temperature. The maximum erosion–corrosion (EC) rate was observed at an impingement angle of 45° at all velocities (3 to 12 m/s), as both the shear and normal impact stresses were of the same order of magnitude at this angle. At lower impingement angles, the effect of shear stress was more dominant and vice versa at higher impingement angles. The synergistic affect was found to be maximum at 45° due to enhancement of erosion by corrosion and/or corrosion by erosion. Ploughing, deep craters, raised lips, dimples, micro-forging/plastic deformation, and extrusion were the dominant erosion–corrosion mechanisms as observed by Field Emission Scanning Electron Microscopy (FE-SEM). The maximum corrosion wear scar depth was found to be 57 µm (average) at an impingement angle of 45°, as measured using an optical profilometer. The obtained results are very significant and can be used in process parameter optimizations to enhance infrastructure reliability. These results will also be the part of in-house database to develop a comprehensive erosion and erosion–corrosion model for erosion–corrosion prediction of different materials under various operational conditions. Full article

The deposition of a thin (several tens of microns) protective coating in atmospheric conditions is a challenging task for surface engineering. The structural features and tribological properties of a particle-reinforced metal matrix composite coating synthesized on middle-carbon steel by air pulse-plasma treatments were studied in the present work. The 24–31 µm thick coating of “24 vol.% (TiC + WC)/Hardened steel matrix” was produced by 10 plasma pulses generated by an electro-thermal axial plasma accelerator equipped with a consumable cathode of novel design (low-carbon steel tube filled with “TiC/WC + Epoxy resin” mixture). The study included optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD, microhardness measurements, and dry “Ball-on-Plate” testing. The carbides were directly plasma-transferred to the substrate (steel of AISI 4145H grade) from the cathode without substantial melting. The hard (500–1044 HV) coating matrix consisted of 57 vol.% austenite (1.43 wt.% C) and 43 vol.% plate martensite was formed via carbon enrichment of steel from plasma flow. Additionally, a minor amount of oxide phases (TiO₂, WO₂, WO₃) were dispersed in the matrix. As compared to substrate, the coating had a lower coefficient of friction; its volumetric wear was decreased by 4.4 times when sliding against hardened steel ball and by 16 times when sliding against SiC ball. Full article

This work is aimed at the development and investigation of the oxidation behavior of ferritic stainless-steel grade AISI 441 and polymer-derived ceramic (PDC) protective coatings. Double-layer coatings of a PDC bond coat below a PDC top coat with glass and ceramic passive fillers’ oxidative resistance were studied at temperatures up to 1000 °C in a flow-through atmosphere of synthetic air and in air saturated with water vapor. Investigation of the oxide products formed at the surface of the samples in synthetic air and water vapor atmospheres, at different temperatures (900, 950, 1000 °C) and exposure times (24, 96 h) was carried out on both uncoated steel and steel coated with selected coatings by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The Fe, Cr₂O₃, TiO₂, and spinel (Mn,Cr)₃O₄ phases were identified by XRD on oxidized steel substrates in both atmospheres. In the cases of the coated samples, m- ZrO₂, c- ZrO₂, YAG, and crystalline phases (Ba(AlSiO₄)₂–hexacelsian, celsian) were identified. Scratch tests performed on both coating compositions revealed strong adhesion after pyrolysis as well as after oxidation tests in both atmospheres. After testing in the water vapor atmosphere, Cr ions diffused through the bond coat, but no delamination of the coatings was observed. Full article

Tooling in the die and mould industry is subjected to high-wear and high-temperature environments, which often leads to the premature failure of this high-added-value tooling. When severe damage occurs, an alternative to replacing the whole component consists of the repair by laser-directed energy deposition (L-DED). For that end, intermediate layers are commonly employed as buffer material, where introducing a functionally graded material (FGM) might be beneficial to avoid material incompatibilities and improve the overall performance of the tooling. In the present work, an FGM composed of gradient AISI 316L to AISI H13 has been manufactured, and its microstructure and hardness analysed. Firstly, cracking owing to the formation of brittle intermediate phases has been detected. Secondly, an increase of the hardness and a decrease of the corrosion resistance has been observed when transitioning from AISI 316L to AISI H13. Thirdly, despite the FGM composition evolving linearly, nonlinear material properties such as hardness and corrosion have been observed, which are conditioned by the microstructure formed during the L‑DED process and the nonlinear influence of the composition of steel on such properties. Consequently, nonlinear compositional gradients are recommended if linear mechanical properties are to be obtained in the case of steel FGMs. Full article

Now-a-days, the application of hard tuning with CBN tool has been massively increased because the hard turning is a good alternative to grinding process. However, there are some issues that need to be addressed related to the CBN grades and their particular applications in the area of hard turning process. This experimental study investigated the effects of three different grades of CBN insert on the cutting forces and surface roughness. The process of hard turning was made using the AISI H13 die tool steel at containing different hardness (45 HRC, 50 HRC and 55 HRC) levels. The work material were selected on the basis of its application in the die making industries in a range of hardness of 45–55 HRC. Optimization by the central composite design approach has been used for design and analysis. The present study reported that the cutting forces and surface roughness are influenced by the alloying elements and percentage of CBN in the cutting tool material. The work material hardness, feed rate and cutting speed are found to be statistically significant on the responses. Furthermore, a comparative performance between the three different grades of CBN inserts has been shown on the cutting forces and surface roughness at different workpiece hardness. To obtain the optimum parameters from multiple responses, desirability approach has been used. The novelty/robustness of the present study is represented by its great contribution to solve practical industrial application when is developed a new process using different CBN grades for hard turning and die makers of workpiece having the hardness between 45 and 55 HRC. Full article