AISI 316L Research Articles

Surface segregation phenomena encountered during solid carbon active screen plasma nitrocarburizing of AISI 316L

Plasma nitrocarburizing of an austenitic stainless steel AISI 316L was performed in an N2-H2 atmosphere (50 % H2 and 50 % N2) with a carbon-fiber reinforced carbon (CFC) active screen. The experimental concept of a plasma-discharged CFC active screen in conjunction with a substrate holder at floating potential ensures that no charged particles are present on the sample surface and no sputtering occurs. As a result, carbon contaminations are formed on the surface which were studied in detail with a combination of scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). The results indicate that a layer of about 25–50 nm of carbon is formed. At the same time, a strong segregation of Mn, Ni and Cr is observed below the coating within the steel substrate. Both effects progress with treatment time and there exists a clear correlation between the formation of the carbon layer and the segregation effect.

Experimental Characterization and Phase-Field Damage Modeling of Ductile Fracture in AISI 316L

(1) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements. (4) The novel implementation offers the possibility for better control of the ductile behavior of metallic materials and damage initiation, evolution, and propagation.

Melt pool control-assisted additive manufacturing of thin-walled parts

Thin-walled aerospace components manufactured by laser directed energy deposition are susceptible to thermal accumulation effects owing to their deposition path and efficiency, further leading to the edge collapse. The melt pool width, as the carrier of thermal input, is an important geometric factor reflecting the state of the melt pool. Therefore, an in-situ melt pool control technique was proposed. The melt pool width as the control target was monitored using a coaxial camera, and the laser power was adjusted in real time based on the proportional-integral-derivative algorithm. A thermal accumulation model in conventional mode and a thermal suppression model in control mode were derived. The surface roughness, porosity, microstructure, and tensile properties of AISI 316 L stainless steel were compared between two modes. The results demonstrated that the roughness and porosity of thin-walled parts were respectively reduced by 45.3% and 82.7% after control. The periodic evolution of interlayer columnar and equiaxed crystals, and the increase in deformation twins contributed to a simultaneous increase in tensile strength and toughness, with a maximum increase of 35.7% in elongation.

Microstructural Evolution and Wear Resistance of Surface Alloyed AISI 316L Stainless Steel with Equi-atomic CoCrFeMnTi by Continuous Wave Diode Laser

In this investigation, a multicomponent alloyed surface was developed on AISI 316L stainless steel (AISI 316L SS) substrate by melting it with a fiber coupled diode laser having 3.6 mm beam diameter (using argon as shrouding gas) along with simultaneous melting of equiatomic pre-mixed elemental powders of cobalt (Co), chromium (Cr), iron (Fe), manganese (Mn) and titanium (Ti) (high entropy alloy). The process parameters used in the experiment were laser power (1800–2200 W) and scan speed (6 mm/sec to 8 mm/sec). Following laser surface alloying (LSA) a detailed microstructural characterization of the surface and evaluation of surface mechanical properties (micro/nano hardness, Young’s modulus and wear resistance) were undertaken. Due to LSA there is formation of near eutectic microstructure consisting of FCC and BCC phase mixtures along with the precipitates of Fe2Ti randomly distributed in the microstructure which was confirmed by X-ray diffraction (XRD) and electron back scattered diffraction (EBSD) analysis. There is an increase in microhardness in the processed zone from 180 VHN (of as received AISI 316L SS) to 309–650 VHN. In addition, there is an increase in Young’s modulus from 208 GPa for as received AISI 316L SS to 228–301 GPa for laser surface alloyed zone. The wear resistance (against WC ball in fretting wear mode) property of AISI 316L SS substrate after LSA was superior to the substrate. The wear mechanism was established.

Additive manufacturing of AISI 304L stainless steel: A review of processing parameters and mechanical performance

Additive manufacturing (AM) has become a favorable method for producing 304L stainless steel (SS) for various industrial applications, which is owing to its favorable characteristics including corrosion resistance, mechanical performance, and design flexibility. This review paper presents a comprehensive overview of the processing factors along with the mechanical performance of AM-fabricated 304L SS (AM304LSS). Firstly a discussion is provided for the fundamental principles of AM techniques that are common for processing SS304L. This includes selective laser melting (SLM), laser beam powder bed fusion (LB-PBF), direct metal laser sintering (DMLS), directed energy deposition (DED), wire-and-arc additive manufacturing (WAAM). Subsequently, the impact of key processing factors i.e. laser power, and powder characteristics on the microstructure and mechanical properties of AM304LSS is presented. In addition, this article examines recent progress in process optimization strategies and post-processing techniques for improving and enhancing the mechanical properties and surface finish of AM 304L stainless steel components. Finally, significant insights are provided for researchers, engineers, and practitioners involved in the advancement and application of AM304LSS components.

The Effect of Nitriding Temperature of AISI 316L Steel on Sub-Zero Corrosion Resistance in C2H5OH.

In this paper, glow nitriding processes at cathode potential are used at various temperatures to investigate how they affect the corrosion resistance of 316L steel in ethanol at temperatures of 22 °C and -30 °C. Lowering the test temperature reduces the corrosion rate of the nitrided layers. Conversely, glow nitriding at 450 °C improves the corrosion resistance of the tested steel. Increasing the nitriding temperature to 520 °C increases the corrosion rate. It should be noted that the ethyl alcohol solution, due to the lack of aggressive ions, does not cause significant changes in the corrosion rate of the steel. The value of the corrosion current varies in the range of 10-2-10-3 µA/cm2. Nitrided layers increase the contact angle measured for water and are entirely wettable for ethanol. The objective of this study is to evaluate the effect of the nitriding temperature of AISI 316L steel on its corrosion resistance in an ethanol solution at room temperature and at -30 °C.

Design, Manufacturing, Microstructure, and Surface Properties of Brazed Co-Based Composite Coatings Reinforced with Tungsten Carbide Particles

Brazing is a joining process that involves melting a filler metal and flowing it into the joint between two closely fitting parts. While brazing is primarily used for joining metals, it can also be adapted for certain coating deposition applications. The present study investigates the microstructure and corrosion behavior and sliding wear resistance of WC (Tungsten Carbide)-CoCr-Ni reinforced Co-based composite coatings deposited onto the surface of AISI 904L stainless steel using a vacuum brazing method. The primary objective of this experimental work was to evaluate the influence of WC-based particles added to the microstructure and the properties of the brazed Co composite coating. The focus was on enhancing the sliding wear resistance of the coatings while ensuring that their corrosion resistance in chloride media was not adversely affected. The morphology and microstructure of the composite coatings were investigated using scanning electron microscopy (SEM) and phase identification by X-ray diffraction (XRD). The SEM analysis revealed in the coating the presence of intermetallic compounds and carbides, which increase the hardness of the material. The sliding wear resistance was assessed using the pin-on-disk method, and the corrosion properties were determined using electrochemical measurements. The results obtained showed that as the WC particle ratio in the Co-based composite coating increased, the mechanical properties improved, the alloy became harder, and the tribological properties were improved. The evaluation of the electrochemical tests revealed no significant alterations of the manufactured composite in comparison with the Co-based alloys. In all cases, the corrosion behavior was better compared with that of the stainless-steel substrate.

On the Enhancement of Material Formability in Hybrid Wire Arc Additive Manufacturing

This paper is focused on improving material formability in hybrid wire-arc additive manufacturing comprising metal forming stages to produce small-to-medium batches of customized parts. The methodology involves fabricating wire arc additive manufactured AISI 316L stainless steel parts subjected to mechanical and thermal processing (MTP), followed by microhardness measurements, tensile testing with digital image correlation, as well as microstructure and microscopic observations. Results show that mechanical processing by pre-straining followed by thermal processing by annealing can reduce material hardness and strength, increase ductility, and eliminate anisotropy by recrystallizing the as-built dendritic-based columnar grain microstructure into an equiaxed grain microstructure.

Experimental investigation of fracture mechanism in organically modified silica-based coating applied on austenitic stainless steel AISI 904L under monotonic and very high cycle fatigue loading

Surface morphology significantly influences the fatigue life of the metallic materials. Therefore, improving surface performance is important for economic and safety applications. Silica-based coatings are anticipated to protect the metallic materials under synergistic operating conditions, such as fatigue and corrosion. However, pure inorganic silica-based coatings are brittle and fail to protect metallic materials. The properties of the sol–gel coatings can be determined by optimizing synthesis factors, such as synthesis steps, precursors, solvents, and catalysts. Organically modified silica-based sol–gel coatings were synthesized using 3-glycidoxypropyl trimethoxysilane and 3-aminopropyltriethoxysilane as precursors, with ethanol as the solvent. The resulting coating was named EtOH. This coating was applied on the surface of stable austenitic stainless steel AISI 904L with the dip coating method. The fracture behavior of the coating during monotonic loading has been studied by interrupted tensile tests at different load steps and examined closely with scanning electron microscopy. On the other hand, very high cycle fatigue experiments were conducted using an ultrasonic fatigue testing system at load frequency of 20 kHz on coated specimens to investigate the fracture behavior of the coating during cyclic loading. Three different kinds of fracture due to stress relaxation in the coating and at its interface with substrate were observed in monotonic loading. The same kinds of stress relaxation were observed in cyclic loading with the difference being that the range of experienced elongation in cyclic tests was significantly smaller. Therefore, the fracture in cyclic loading were concentrated in the vicinity of macro crack. The application of organically modified coatings could suppress the persistent slip bands and result in increased fatigue life for coated specimens.

The influence of low nitrogen doping on bacterial adhesion of sputtered a-C:H coatings

Heavily dependent on both surface and bacteria characteristics, multiple and complex parameters control bacterial adhesion to any biomaterial surface. That's why there are so many contradictory results regarding the antibacterial and adhesion inhibition properties of Diamond-Like Carbon (DLC) protective coatings, despite the well-established biocompatibility of this very broad group of materials. Aiming at Orthodontics, this study reports the modification of hydrogenated amorphous carbon coatings (a-C:H), by nitrogen incorporation upon reactive magnetron sputtering. The effect of low N content up to 10 at.% on the microstructure and bacterial adhesion was studied. Despite the progressive graphitization upon doping, the surface roughness was not significantly influenced and the water contact angles remained above 70°. The adhesion of three bacterial strains of Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa was evaluated. The median colony forming units was lower on the a-C:H and a-C:H:N coatings in comparison to the bare AISI 316L medical grade stainless steel surface, regardless the bacterial strain. The best bacterial adhesion inhibition capacity was achieved for N doping of 6 at.%, without using any antibacterial agents.

Quaternary nitrate and chloride molten salts for the next concentrating solar power plants: Corrosion considerations for the use of AISI 304L steel

The study addresses the advancement in concentrating solar power (CSP) plants by transitioning from binary nitrate salts to nitrate and chloride quaternary salts, focusing on the corrosivity of four salts as evaluated by immersion testing of AISI 304L stainless steel. Four compositions of salts were evaluated, from solar salt to equimolar NaNO3‐KNO3‐NaCl‐KCl, up to 21 days (500 h) at 500 °C in an open atmosphere, determining the corrosion kinetics using gravimetry. The morphology, chemical composition, and microstructure of the corrosion products were characterized using XRD, FESEM-EDS, and GD-OES. Exposure to the molten salt with 0 mol% Cl‐ (Solar Salt) resulted in negligible corrosion kinetics, consistent with previous studies. The salt with 14 mol% Cl‐ caused a stable corrosion product with a corrosion rate 30 times higher than without chloride. All quaternary salts exhibited a multilayer structure of the top surface with selective chromium (Cr) removal. Specimens exposed to salts with more than 29 mol% Cl‐ displayed a similar structure with Cr and iron (Fe) removal, resulting in more brittle layers and corrosion rates 90 to 250 times higher than the salt without chloride. GD-OES analysis confirmed Cl diffusion into the oxide layer, highlighting the role of pCl2(g) and pO2(g) in driving corrosivity. Based on the results, using in salts with 29 mol% Cl‐ at 500 °C is discouraged, while using 304L with 14 mol% Cl‐ in a cold tank may be considered.

Влияние режимов лазерной наплавки на геометрические размеры стального трека

Introduction. Laser surfacing is one of the leading trends in the field of additive technologies, which consists in layer-by-layer build of material using a laser as an energy source. To obtain a high-quality product, it is necessary to select the optimal building parameters correctly. The problem is that such optimization is necessary for all equipment, since minor differences in its characteristics can make significant changes in the parameters of layer-by-layer build. In order to determine the optimal build mode, it is enough to analyze the effect of various equipment parameters on the characteristics of single tracks. Therefore, the purpose of this work is to determine the most important parameters of laser radiation that affect the surfacing process and the optimal mode for building a single track of chromium-nickel steel. The work investigated single tracks obtained by laser surfacing of powder from austenitic chromium-nickel steel AISI 316L. The optimization factors included such characteristics as laser power, beam speed, flow rate of supplied powder and laser spot size. The wavelength of laser radiation was 1.07 μm. Research methods. To determine the quality and geometric dimensions of single tracks, the macrostructure of cross sections of specimens was studied using metallography and scanning electron microscopy methods. Results and discussion. It is established that the optimal mode for growing single tracks of steel AISI 316L is characterized by a laser radiation power of 1,250 W and a scanning speed of 25 mm/s. In this case, the optimal powder consumption rate is 12 g/min, and the laser spot size is 4.1 mm. The work shows that the powder consumption and laser spot size have the greatest influence on the coefficient of effective use of powder material. By changing it, the surfacing performance can be increased by 10–15 %.

On the Development of Smart Framework for Printability Maps in Additive Manufacturing of AISI 316L Stainless Steel.

In this work, we propose a methodology to develop printability maps for the laser powder bed fusion of AISI 316L stainless steel. Regions in the process space associated with different defect types, including lack of fusion, balling, and keyhole formation, have been considered as a melt pool geometry function, determined using a finite element method model containing temperature-dependent thermophysical properties. Experiments were performed to validate the printability maps, showing a reliable correlation between experiments and simulations. The validated simulation model was then applied to collect the data by varying laser scanning speed, laser power, powder layer thickness, and powder bed preheating temperature. Following this, the collected data were used to train and test the adaptive neuro-fuzzy interference system (ANFIS)-based machine learning model. The validated ANFIS model was used to develop printability maps by correlating the melt pool characteristics to the defect types. The smart printability maps produced by the proposed methodology can be used to identify the processing window to attain defects-free components, thus attaining dense parts.

Running-in Period During Sliding Wear of Austenitic Steels

The running-in period during dry sliding wear might determine the evolution to steady-state wear behaviour. To this end, the running-in period during sliding wear of austenitic stainless steel, AISI 316L stainless steel, and Hadfield steel were studied through the testing pin (flat-ended)-on-disk configuration. The effects of the normal load, sliding speed, and alloy type were assessed, and the specific wear rate and strain hardening characteristics were determined. The wear rate was correlated with wear mechanism, friction coefficient, hardening, and roughness to characterize the changes occurring during the running-in period. These changes could influence the responses of these materials to wear during the steady-state period. The stabilization of the specific wear rate and hardness was noted to align with the end of the running-in period.Graphical

NiCrBSi/WC Composite Claddings Processed on AISI 316L Steel Alloy by the Direct Laser Deposition Process: Studies on Dry Sliding Wear Behavior and Wear Mechanism Maps

Abstract This study presented the wear behavior of the NiCrBSi/WC composite claddings processed on an AISI 316L steel alloy substrate by laser cladding approach. The scanning electron microscope (SEM) morphology of the claddings has shown excellent substrate–cladding interface bonding, good WC particulate distribution, and no noticeable cracks and voids. The electron dispersion spectroscope (EDS) spectra have confirmed the presence of respective NiCrBSi alloy matrix and WC elements. The XRD spectra have identified various phases and compounds such as gamma-Ni, FeNi3, Ni3B, Cr23C6, Ni3Si, and W2C commonly in all the processed composite claddings. The microhardness of the claddings was measured between 791 and 1086 HV0.2 for increasing the reinforcement WC particulate percentage from 15 wt% to 60 wt%. It is about 470% surface hardness enhancement with the processed composite claddings compared with the substrate alloy. The reinforcement of WC from 15 wt% to 60 wt% with the composite claddings resulted in wear resistance enhancement from 21.85% to 60.64% and the coefficient of friction from 56.87% to 77.92% against the substrate. The wear-rate maps and their respective cladding's worn surface morphology have described the wear mechanisms typically as adhesive, abrasive, oxidation, and delamination. The wear mechanisms are mainly influenced by the WC particulate percentage. The increased WC particulate content has increased the dominance of the abrasive wear mechanism while reducing the window of the adhesive wear mechanism. The windows of various wear mechanisms and their ranges, such as adhesive 0.0033 to 0.028, abrasion 0.010 to 0.067, oxidation 0.012 to 0.093, and delamination 0.015 to 0.120 mm3/m, for NiCrBSi/WC composite claddings comprehensibly represented the wear behavior for the varied conditions of dry sliding wear parameters.

Microstructure and Properties of Laser Surface Melted AISI 316L Stainless Steel

Microstructure and Properties of Laser Surface Melted AISI 316L Stainless Steel

Effect of alloy 625 buffer layer on corrosion resistance of nickel base hardfacing

Nickel base hardfacing alloys serve to mitigate corrosion losses at elevated temperatures. Efficacy of Nickel base hardfacing alloys can be compromised when applied onto Fe base substrates due to iron dilution in hardfacing. The degree of Fe dilution can be reduced by using advanced deposition methods and optimized deposition parameters. Gas Tungsten Arc Welding (GTAW) method is commonly employed for its cost-effectiveness and versatility, but it tends to induce higher Fe dilution due to increased heat input. This study aims to reduce the degree of Fe dilution and enhance corrosion resistance by introducing a nickel base buffer layer (alloy 625) between the nickel base hardfacing alloy and AISI 316L stainless steel substrate. For comparative purposes, Ni base hardfacing alloy was deposited on the substrate without any buffer layer. Hardfacing depositions were prepared using manual GTAW process. Process parameters namely, deposition current, voltage, travelling speed, pre-heating temperature, and cooling method were kept constant. Samples underwent aging at 1123 K for 4 h, followed by microstructural examination via optical and scanning electron microscopes. Iron (Fe) dilution quantification was performed using energy dispersive spectroscopy (EDS). The EDS analysis showed that the use of buffer layer between the hardfaced deposit and the substrate decreased the degree of Fe dilution in the hardfaced deposit. X-Ray diffraction (XRD) analysis was performed to identify various phases formed in the hardfaced deposit. Potentiodynamic polarization test was performed to assess the corrosion resistance of hardfaced deposit in 3.5 wt% NaCl solution. Results show significant improvement in corrosion resistance of hardfacings deposited sample with buffer layer as compared to those without buffer layer. Aging treatment further enhanced corrosion resistance. The corrosion resistance data is correlated with the microstructure and phases formed in various samples.

Parametric optimisation of laser welding of stainless steel 316L

This paper presents numerical and experimental studies focused on the optimisation of laser welding parameters for AISI 316L stainless steel. The focus of the numerical studies was to obtain the mathematical model with the least time complexity and the highest fidelity. Based on the comparison of different mathematical models, a combination of two models, double ellipsoidal and conical models, was found to be optimal for the numerical simulation of the laser welding process. The studies were also complemented by material characterization studies for validation purpose. A pulse duration of 8 milliseconds and a current of 400 amperes with an average power of 380W were found to be the optimum parameters for laser welding of standard gauge 12 sheet of stainless steel AISI 316L. In addition, the effect of duty factor of the pulsed laser beam on the weld profile was also investigated and was found to be a major contributor to the optimisation process. The properties of the sample welded with the optimised set of parameters were also compared with the base metal, and based on the mechanical characterisation studies, it was found that the yield strength and hardness of the welded sample were improved, but the overall ductility was slightly reduced as compared to the base metal. The average weld zone size was also reduced by increasing the power density due to multiple reflections of the beam.

An effective strategy for manufacturing ultra-high purity AISI 316L stainless steel by vacuum C deoxidization pretreatment plus Mg–Ca composite treatment

Aiming at the special ultra-high purity (UHP) requirements of AISI 316L stainless steel used in semiconductor equipment, a strategy of vacuum C deoxidization pretreatment plus Mg–Ca composite treatment was proposed in this work. The effects of this strategy on cleanness and inclusion modification were systematically investigated by experimental observations and thermodynamic calculations. The results demonstrated that this strategy significantly reduced the O and S contents to 0.0005 wt% and 0.0007 wt%, respectively. The main inclusions after vacuum C deoxidization were large-sized Al2O3·SiO2 and MnS. After Mg treatment, the oxide inclusions were gradually modified into MgO·Al2O3 and MgO, while the sulfide inclusion was still MnS. After additional Ca treatment, the inclusions were further modified into finer CaO, MgO, CaO·MgO, and CaS. Moreover, this strategy remarkably decreased the number and size of the inclusions. The best level was that all inclusions were smaller than 2 μm, and the proportion of inclusions smaller than 1 μm was as high as 75.47%. Meanwhile, the evolution mechanism of inclusions during different treatments was clarified in this work. Finally, the optimum process for preparing UHP AISI 316L stainless steel was proposed as vacuum C deoxidation plus 0.002 wt% Mg and 0.0016 wt% Ca composite treatment.

Investigation on the wear resistance of AISI 316L with micro dimples as a material for human implants’ structure

Investigation on the wear resistance of AISI 316L with micro dimples as a material for human implants’ structure