Search Results (17)

We investigated the protective properties of ultrathin laminated coatings, comprising three pairs of Al₂O₃ and TiO₂ sublayers with coating thicknesses < 150 nm, deposited on AISI 310 stainless steel (SS) and Si (100) substrates at 80–500 °C by atomic layer deposition. The coatings were chemically etched and subjected to corrosion, ultrasound, and thermal shock tests. The coating etching resistance efficiency (R_e) was determined by measuring via XRF the change in the coating sublayer mass thickness after etching in hot 80% H₂SO₄. The maximum R_e values of ≥98% for both alumina and titania sublayers were obtained for the laminates deposited at 250–400 °C on both substrates. In these coatings, the titania sublayers were crystalline. The lowest R_e values of 15% and 50% for the alumina and titania sublayers, respectively, were measured for laminate grown at 80 °C on silicon. The coatings deposited at 160–200 °C demonstrated a delay in the increase of R_e values, attributed to the changes in the titania sublayers before full crystallization. Coatings grown at higher temperatures were also more resistant to ultrasound and liquid nitrogen treatments. In contrast, coatings deposited at 125 °C on SS had better corrosion protection, as demonstrated via electrochemical impedance spectroscopy and a standard immersion test in FeCl₃ solution. Full article

In this study, the microstructure and corrosion behavior of gas tungsten arc (GTA) welds of borated stainless steel (BSS) with a boron content of 1.62 wt.% were investigated using various filler metals. The filler metals used in this study were 308L, 309L, and 310 without the B component. A small amount of the B component was observed in the weld metal (WM) of all specimens, even though none of the filler wires contained boron. This result was caused by the dilution of the B component from the BM into the WM by the welding heat. The segregation of boron in the WM resulted in Cr-depleted areas, which negatively affected the corrosion resistance of the welded specimens. The corrosion resistance of 308L WM with the highest fraction of B components was the most deteriorated, whereas 309L WM with the lowest boron content exhibited the best corrosion resistance. Using a filler metal without the B component is expected to effectively improve the weldability and corrosion resistance of BSS; however, it can also reduce the neutron absorption capacity. Therefore, for BSS to be used as a spent nuclear fuel storage container material, the boron content of the filler metal must be carefully considered. This study provides a foundation for research aimed at improving the development and applicability of filler metals in borated stainless steel and makes it competitive for application in fourth-generation nuclear power systems. Full article

In this paper, VGCF/304L stainless steel composite was prepared using spark plasma sintering (SPS) with 2 vol.% nanocarbon fiber. Then, phase content, grain size, and mechanical properties were evaluated. The results showed that the Vickers hardness of 304L sintered stainless steel and the composite prepared by SPS under the condition of 950 °C for 10 min were 244 HV and 310 HV, respectively, which is an increase of about 27.0%. The yield strength ascended from 587.1 MPa to 890.2 MPa, registering an increase of approximately 51.6%. Concurrently, the ultimate tensile strength rose from 821.5 MPa to 1064.7 MPa, with an approximate increase of 29.6%. This method for improving the mechanical properties of stainless steel is expected to be widely adopted for producing fiber-reinforced metal matrix composites with excellent overall performance. Full article

In order to enhance the resistance of superalloys to high-temperature molten chloride salt corrosion, Fe-Al coatings were prepared on 310S and 347H stainless-steel surfaces via pack aluminizing. Then, the coatings were annealed at different temperatures to explore the influence of temperature on their phase constitution, microstructure, microhardness, and corrosion resistance. The results showed that the annealing temperature had a considerable effect on the corrosion resistance of the Fe-Al coatings, which was related to the change in the phase composition of the coatings that occurred due to the annealing treatment. The growth rate of the coating on 347H steel was higher than that on 310S steel, and their thicknesses from aluminizing at 800 °C for 20 h were 209.6 and 153.5 µm, respectively. When annealing at 900 °C for 30 h, the phase composition of the coatings was completely transformed into (Fe, Cr, Ni) Al. The corrosion loss rate of the annealed coating was clearly reduced, the loss rate of the 310 coating was 6.0 and −0.25 mg/cm² before and after annealing at 900 °C and that of the 347 coating was 4.89 and −0.7 mg/cm² before and after annealing at 750 °C, respectively. The two coatings showed good corrosion resistance to molten chloride salts, as demonstrated by the oxide scale (Al₂O₃) that formed on the surface, which had a thickness of about 30~40 µm. Full article

This study investigated the impact of temperature, time, and homogenisation on the transient liquid phase bonding of Inconel 617 to stainless steel 310, employing AWS BNI2 foil as an interlayer. Nine test series were conducted at temperatures of 1050 °C and 1100 °C, with bonding durations ranging from 10 to 60 min. The homogenisation process was carried out on specimens that underwent full isothermal solidification at a temperature of 1170 °C for 180 min. The microscopic analysis indicated that extending the time and raising the bonding temperature resulted in the extension of the isothermal solidified zone, accompanied by a reduction in the quantity of eutectic phases. Complete isothermal solidification was seen exclusively in samples bonded at temperatures of 1050 °C for 60 min and 1100 °C for a duration of 50 min. The size of the diffusion-affected zone expanded as the bonding temperature and duration rose, but the presence of brittle intermetallic phases diminished. The microstructure of the homogenised sample indicated that the diffusion-affected zone had been almost completely eliminated. Hardness variations indicated heightened hardness in the diffusion-affected zone (DAZ) and athermal solidified zone (ASZ). Shear strength is maximised in homogenised specimens with minimised ASZ. Full article

This work is focused on the development of creep and stress relaxation models on Inconel 625 and Stainless Steel 310 materials for additive manufacturing. At the end, the operational lifespan of an industrial-scale additive manufactured recuperator is evaluated. An industrial-scale recuperator for burners with a highly complex geometry is manufactured using Continuous Wave SLM and Pulsed Wave Selective Laser Melting techniques. The recuperator operates under steady but high thermal loads, reaching temperatures of up to 875 °C. Therefore, its service life is assessed, considering creep and stress relaxation phenomena. Two different materials are evaluated: Inconel 625 and Stainless Steel 310. Tensile testing has been conducted on samples at various temperatures to acquire material parameters, incorporating appropriately the anisotropic nature of the materials. Creep parameters were determined through creep experiments and data from the literature, and the recuperator response was simulated by FEA modelling. Analytical creep and stress relaxation models were proposed based on the simulation results for each material to predict their creep response. The service life was determined by applying a custom failure criterion based on the creep testing data. The Inconel 625 recuperator exhibits a service life that is significantly higher compared to any burner’s life, while the Stainless Steel 310 recuperator exhibits approximately 27 years of service life. Both materials are considered suitable; however, Inconel 625 offers higher resistance to creep according to creep tests, and due to its lower thermal expansion coefficient, the resulting thermal stresses are lower. Full article

This paper deals with a study of additively manufactured (by the Selective Laser Melting, SLM, method) and conventionally produced AISI 316L stainless steel and their comparison. With the intention to enhance the performance of the workpieces, each material was post-processed via hot rotary swaging under a temperature of 900 °C. The samples of each particular material were analysed regarding porosity, microhardness, high cycle fatigue, and microstructure. The obtained data has shown a significant reduction in the residual porosity and the microhardness increase to 310 HV in the sample after the hot rotary swaging. Based on the acquired data, the sample produced via SLM and post-processed by hot rotary swaging featured higher fatigue resistance compared to conventionally produced samples where the stress was set to 540 MPa. The structure of the printed samples changed from the characteristic melting pools to a structure with a lower average grain size accompanied by a decrease of a high fraction of high-angle grain boundaries and higher geometrically necessary dislocation density. Specifically, the grain size decreased from the average diameters of more than 20 µm to 3.9 µm and 4.1 µm for the SLM and conventionally prepared samples, respectively. In addition, the presented research has brought in the material constants of the Hensel-Spittel formula adapted to predict the hot flow stress evolution of the studied steel with respect to its 3D printed state. Full article

Tungsten Inert Gas (TIG) welding is a commonly used welding technique for ferritic stainless steel, due to its ability to produce high-quality, clean, and precise welds. This welding method provides excellent control over the heat input, making it suitable for thin-walled, high-alloy materials such as ferritic stainless steel. The purpose of this study was to investigate the effect of using two different filler materials, 310 (austenitic) and 410 (ferritic), on the microstructural and mechanical properties of Tungsten Inert Gas (TIG) weld butt joints of 430 ferritic stainless steel (FSS). The results showed that the choice of filler material significantly impacted the dilution percentage, the chromium-nickel equivalent ratio, microstructure, microhardness, and tensile characteristics of the welded joint. The use of 310 filler resulted in a columnar microstructure, whereas the use of 410 filler resulted in a ferritic (acicular ferrite) microstructure with the presence of martensite and austenite. The sample welded with 410 filler demonstrated superior mechanical properties compared to the sample welded with 310 filler. These findings emphasize the importance of selecting the appropriate filler material in order to achieve the desired microstructural and mechanical properties in 430 FSS welded joints. Full article

Stainless-steel has become a widely preferred material type in the marine, aerospace, sanitary, industrial equipment, and construction industries due to its superior corrosion resistance, high mechanic properties, high strength, formability, and thermal and electrical conductivity. In this study, a multi-objective optimization method based on grey relational analysis was employed to optimize the fiber laser-cutting parameters of cutting speed, focal position, frequency, and duty cycle. Surface roughness and kerf width, which are the two most important parameters that determine laser-cutting quality, were simultaneously optimized. In order to assign the optimum level of each parameter individually, the Taguchi technique was applied. The cutting surface morphology was examined according to the grey relational grade with a 3D optical profilometer, and maps of the cutting surfaces were created. According to the results achieved using Analysis of Variance (ANOVA), it was seen that the parameters that affected surface roughness and kerf width the most were duty cycle, with a contribution rate of 49.01%, and frequency, with a contribution rate of 31.2%. Frequency was the most important parameter in terms of multiple responses, with a contribution rate of 18.55%. Duty cycle and focal position were the second and third most effective parameters, respectively. It was determined that the optimum parameter values for minimum surface roughness and minimum kerf width that could be obtained with the fiber laser cutting of 20 mm thick AISI 304L (DIN EN 1.4301) material were 310 mm/min cutting speed, −11 mm focal position, 105 Hz frequency, and 60% duty cycle. Full article

The paper’s aim is the assessment of corrosion behaviour of a CrN_x-coated 310 H stainless steel under simulated supercritical water conditions (550 °C and 25 MPa) for up to 2160 h. The CrN_x coating was obtained by the thermionic vacuum arc (TVA) method. The oxides grown on this coating were characterized using metallographic and gravimetric analysis, SEM with EDS, and grazing incidence X-ray diffraction (GIXRD). A diffusion mechanism drives oxidation kinetics because it follows a parabolic law. By XRD analysis, the presence of Cr₂O₃ and Fe₃O₄ on the surface of the autoclaved CrN_x-coated 310 H samples were highlighted. Corrosion susceptibility assessment was performed by electrochemical impedance spectroscopy (EIS) and linear potentiodynamic polarization. EIS impedance spectra show the presence of two capacitive semicircles in the Nyquist diagram, highlighting both the presence of the CrN_x coating and the oxide film formed during autoclaving on the 310 H stainless steel. Very low corrosion rates, with values up to 11 nm × year⁻¹, obtained in the case of autoclaved for 2160 h, CrN_x-coated samples indicated that the oxides formed on these samples are protective and provide better corrosion resistance. The determination of micro hardness Vickers completed the above investigation. Full article

As there is a strong pressure in the EU to reduce CO₂ emissions and overall fossil fuel consumption in the energy sector, many boilers are burning biomass instead of traditional fuels (coal, natural gas, oil, etc.). This is mainly due to the EU 2030 energy strategy, which commits Member States to reduce fossil fuel emissions by at least 40% (compared to the 1990 level) and to use at least 32% of renewable energy. The combustion of biomass containing aggressive elements such as chlorine or sulfur causes serious damage to various boiler components, with negative impacts such as reduced boiler lifetime, increased investments and maintenance costs, reduced availability, and others. These problems occur mainly in plants/boilers designed to burn coal and redesigned to burn biomass (straw, wood chips, wood pellets, etc.). In this paper, the corrosion resistance of heat coatings determined in long-term laboratory tests in an environment specifically corresponding to biomass flue gas is presented. These results can be used to design a suitable modification of existing coal boilers using conventional materials. The aim was to compare three completely different technologies currently available on local markets for the preparation of these coatings—thin wire arc spray (TWAS), high-velocity oxygen fuel (HVOF), and water-stabilized plasma. These coatings were compared with the base material of the boiler tubes—low alloyed steel 16Mo3 and high alloyed austenitic stainless steel AISI 310 as a more expensive option for retrofit. After 5000 h of exposure in an environment containing HCl and SO₂, no cracks or structural defects were observed in any of the coatings, and the substrate material showed no signs of oxidation. All the tested coatings had higher corrosion resistance than the 16Mo3 material, and some of them presented a corrosion behavior close to that of the high alloy AISI 310 steel. Structurally and corrosion-wise, the thermally sprayed coating prepared by HVOF technology was the best of all tested materials. Full article

In most steelmaking processes, huge amounts of waste heat at high temperature (700–800 °C) are thrown into the environment without any use. An alternative use for this waste heat is electricity generation through thermoelectric generators. However, these high temperatures, as well as their fluctuations over time, affect not only the conversion rate of the thermoelectric generator but also its useful lifetime. The incorporation of a latent thermal energy storage (TES) system could be a solution; nevertheless, the thermal stability and corrosive effect of the (PCM) phase change material are key aspects for the thermal storage system definition, in terms of durability. In this work, developed in the framework of the European project “PowGETEG” (RFSR-CT-2015-00028, funded by the Research Fund for Coal and Steel), a high-temperature analysis (700–800 °C) of the Li₂CO₃ thermal properties, thermal stability and corrosive effect on the AISI 304 and AISI 310 stainless steels is carried out. The results show that the eutectic salt Li₂CO₃ exhibits high thermal stability with neither change in its thermal properties nor material degradation. This work shows that lithium carbonate Li₂CO₃ and AISI 310 make a very good combination for the definition of a thermal storage system able to protect a high-temperature thermoelectric converter from temperature variations, making it more reliable. Full article

The aim of this work was to study the corrosion behavior of a Fe-Cr-Ni alloy (310 H stainless steel) in water at a supercritical temperature of 550 °C and a pressure of 250 atm for up to 2160 h. At supercritical temperature, water is a highly aggressive environment, and the corrosion of structural materials used in a supercritical water-cooled nuclear reactor (SCWR) is a critical problem. Selecting proper candidate materials is one key issue for the development of SCWRs. After exposure to deaerated supercritical water, the oxides formed on the 310 H SS surface were characterized using a gravimetric analysis, a metallographic analysis, and electrochemical methods. Gravimetric analysis showed that, due to oxidation, all the tested samples gained weight, and oxidation of 310H stainless steel at 550 °C follows parabolic rate, indicating that it is driven by a diffusion process. The data obtained by microscopic metallography concord with those obtained by gravimetric analysis and show that the oxides layer has a growing tendency in time. At the same time, the results obtained by electrochemical impedance spectroscopy (EIS) measurements indicate the best corrosion resistance of Cr, and (Fe, Mn) Cr₂O₄ oxides developed on the samples surface after 2160 h of oxidation. Based on the results obtained, a strong correlation between gravimetric analysis, metallographic analysis, and electrochemical methods was found. Full article

Microbial electrochemical technologies have revealed the opportunity of electrochemical enrichment for specific bacterial groups that are able to catalyze reactions of interest. However, there are unsolved challenges towards their application under aggressive environmental conditions, such as in the sea. This study demonstrates the impact of surface electrochemical potential on community composition and its corrosivity. Electrochemical bacterial enrichment was successfully carried out in natural seawater without nutrient amendments. Experiments were carried out for ten days of exposure in a closed-flow system over 316L stainless steel electrodes under three different poised potentials (−150 mV, +100 mV, and +310 mV vs. Ag/AgCl). Weight loss and atomic force microscopy showed a significant difference in corrosion when +310 mV (vs. Ag/AgCl) was applied in comparison to that produced under the other tested potentials (and an unpoised control). Bacterial community analysis conducted using 16S rRNA gene profiles showed that poised potentials are more positive as +310 mV (vs. Ag/AgCl) resulted in strong enrichment for Rhodobacteraceae and Sulfitobacter. Hence, even though significant enrichment of the known electrochemically active bacteria from the Rhodobacteraceae family was accomplished, the resultant bacterial community could accelerate pitting corrosion in 316 L stainless steel, thereby compromising the durability of the electrodes and the microbial electrochemical technologies. Full article

Different kinds of explosions are driven by the internal energy accumulated in compressed gas or superheated liquid. A well-known example of such an explosion is the burst of a vessel with pressure-liquefied substance, known as Boiling Liquid Expanding Vapor Explosion (BLEVE). Hot BLEVE accident is caused mainly by direct heating (pool fire or jet fire) of the steel casing at the vapor side of the tank to temperatures in excess of 400 °C. Thermal insulation around the tank can significantly reduce and retard the excessive heating of the tank casings in a fire. This will allow fire fighters enough time to reach the accident location and to cool the LPG (Liquid Petroleum Gas) tank to avoid the BLEVE, to extinguish the fire or to evacuate the people in the vicinity of the accident. The proposed algorithm addresses several aspects of the BLEVE accident and its mitigation: Computational Fluid Dynamic (CFD) Simulation of jet fire by using fire dynamics simulator (FDS) software by using large eddy simulation (LES); calculation of the convective and radiative heat fluxes by using the impinging jet fire theory; performing thermochemical and heat transfer analysis on the glass-woven vinyl ester coating of the vessel by using FDS software (version 5); and COMSOL Multiphysics (version 4.3b) during the heating phase of composite and calculation of the time period required to evaporate the liquefied propane by using the first and second laws of thermodynamics. Full article