Austenitic Stainless Steel Type Research Articles

Novel high nitrogen austenitic stainless steels: From high-throughput screening to experimental validation and properties relationship

The quest for affordable and price-stable alternatives for nickel as the main austenitizing alloying element is pushing the stainless steel industries to develop new types of Ni-lean austenitic stainless steels. This work focuses on the challenges of designing austenitic stainless steels with appreciable nitrogen content using computational methods, which can still be produced at 1 atm N2 pressure and thermomechanically processed without excessive cracking or N2 degassing. CALPHAD-based computational tools enabled the identification of promising alloys by high-throughput screening from more than 2000 candidates based on predefined criteria considering composition (Ni-poor, N-rich), phase stability (austenite), degassing (far from N2 loss from liquid or solid phase), cost (Ni-lean), and pitting resistance equivalent number (PREN > AISI 201 stainless steel). The resulting alloys exhibited an austenitic microstructure with dispersed micrometric and nanometric aluminum nitrides (AlN) precipitates. Even with the occurrence of appreciable AIN precipitates, hot rolling was performed without cracking, resulting in equiaxed austenitic grains. The mechanical properties of the developed alloys exceeded those of AISI 201 stainless steel in terms of hardness, yield strength, and ultimate tensile strength, with values of 304 HV, 534 MPa, and 953 MPa, respectively, yet with considerable ductility (∼40% elongation). Even in the presence of AlN that pick up some of the nitrogen from solid solution, the corrosion resistance of the developed alloy was superior to the AISI 201 stainless steel. This research provides valuable insights for developing and processing high-nitrogen austenitic stainless steels to compete with 201 and 304 stainless steels in terms of mechanical properties and corrosion resistance.

Micro-/Meso-Structure Control of Multi-Hostmetal Alloys by Massive Nitrogen Supersaturation.

The low-temperature plasma nitriding was utilized to describe the microscopic solid-phase separation in the austenitic stainless-steel type AISI316, induced by the nitrogen supersaturation. This nitrogen supersaturated layer with the thickness of 60 μm had a two-phase nanostructure where the nitrogen-poor and nitrogen-rich clusters separated from each other. Due to this microscopic solid-phase separation, iron and nickel atoms decomposed themselves from chromium atoms and nitrogen solutes in this nitrogen supersaturated AISI316 layer. These microscopic cluster separation and chemical decomposition among the constituent elements in AISI316 were induced in the multi-dimensional scale by the plastic straining along the slip lines in the (111)-orientation from the surface to the depth of matrix. The nitrogen solute diffused through the cluster boundaries into the depth. With the aid of masking technique, this nitrogen supersaturation and nanostructuring was controlled to take place only in the unmasked AISI316 matrix. The nanostructures with two separated clusters were mesoscopically embedded into AISI316 matrix after the masking micro-textures. This microscopic and mesoscopic structure control was available in surface treatment of multi-host metals such as superalloys and high entropy alloys.

Numerical study and design of S35657 stainless steel welded stub columns

As a new type of austenitic stainless steel with high nitrogen and low nickel, S35657 stainless steel has the characteristics of high strength and low price, and it has a good application prospect in the field of construction. To supplement the relevant research on S35657 stainless steel structures and to evaluate the applicability of existing specifications and design methods, a finite element model was established using ABAQUS software and calibrated using existing test results. Furthermore, a series of parametric analyses were carried out, focusing on the effects of width-to-thickness ratio, initial geometric imperfection, and welding residual stress on the local buckling of S35657 stainless steel welded section columns. On this basis, the critical width-to-thickness ratio limit of the compression plate was proposed. Finally, the test results and the simulation results were compared with the calculation results of load-carrying capacities for local buckling in the European code (EN1993-1-4), the American code (SEI/ASCE8–02), the Chinese specification (CECS410:2015), the direct strength method (DSM) and the continuous strength method (CSM). Based on the effective width method and DSM, two new approaches to calculate the load-carrying capacity for local buckling were proposed and demonstrated to obtain reasonable accuracy.

Roles of hydrogen in shielding gas for compensate heat input on dissimilar joints of stainless steel series 200 between AISI 201LN and 214 by GTAW

Austenitic stainless steel type 200 series was developed for indoor work due to being inexpensive. It is useful for reducing production costs. In this present work, the roles of hydrogen in shielding gas for compensate heat input on dissimilar joints of stainless steel series 200 between AISI 201LN and 214 by GTAW process was investigated. The technique used in this study applied an hydrogen mixture in argon shielding gas to compensate for the depleted heat input when increasing welding speed at an acceptable maximum of 5% H + 95% Ar at a welding speed of 6 mm/sec. The results of this study are evaluated for the following aspects: weld bead shape completely melted together without filler metal and non-defect. Microstructure combine between the delta-ferrite and austenite matrix under FA solidification mode which delta-ferrite decreasing trend when increase welding speed paired with add hydrogen in argon. In addition, it was discovered that the chemical composition of base metal high move to low concentrated. While the micro-hardness has an upward according to the amount of increase hydrogen same as the tensile strength properties and percentage elongation. While the micro-hardness has an upward according to the amount of increase hydrogen same as the tensile strength properties and percentage elongation. The fracture of tensile occur adjacent to side 201LN. The pitting corrosion resistance depend on volume of delta-ferrite phase and initial pitted between delta-ferrite and austenite.

Failure analysis and electrochemical testing of ammonium chloride corrosion in a heat exchanger in a diesel hydrotreating unit of a petroleum refinery

Crude oil is a complex mixture of hydrocarbons and can contain various impurities, which vary depending on the source and geographical location from which it is extracted. These impurities include sulphur, nitrogen, some metals, asphaltenes, non-condensable gases and salts. Salts in oil are typically found in the form of ions, which means that they are dissolved in the water present in the crude oil, or in the form of solid salts that are later deposited in equipment, pipes, and ducts. These salts can be harmful because, when the oil is processed, the water present in the oil can separate from the hydrocarbons and cause corrosion of equipment in the oil refining plant. In addition, salts can form solid deposits that can obstruct equipment. It is therefore important to remove or reduce the presence of salts in oil during the refining process to avoid operational problems and problems with the quality of the refined product. Several occurrences are reported in the specialized literature of equipment failures in the oil refining industry involving corrosion by salts, especially ammonium chloride salts. Basically, ammonium chloride, whose chemical formula is NH4Cl, is an inorganic chemical compound consisting of ammonium ions (NH4+) and chloride ions (Cl−), It is known by several names, including “ammonium salt” or “ammonium salt” due to its composition. The aim of this paper is to investigate the failure of a shell-and-tube heat exchanger in the charge preheater system of the diesel hydrotreating unit of a Brazilian oil refinery, in which the root cause of the failure identified as responsible for the damage was ammonium chloride corrosion. A severe corrosive process was observed in the tubes of the tube bundle, including perforation in some tubes, as well as damage to the inside of the heat exchanger shell. The analysis methods employed involved the study of three different types of austenitic stainless steel in terms of corrosion resistance: 304, 316L and 317L, which were exposed to media containing sodium chloride and ammonium chloride at a concentration of 3.5 % (m/v). Two electrochemical corrosion tests were carried out in aqueous media, the first determining potentiodynamic polarization curves and the second electrochemical impedance spectroscopy. In addition to material characterization tests, such as determining the chemical composition, hardness and scanning electron microscopy of the corroded samples. The results of this paper indicate that the 317L steel samples have larger passivation regions, higher pitting potential values, lower passivation current density values, as well as lower corrosion rate values during the simulation of the equivalent electrochemical circuit, which implies greater resistance to corrosion in a medium containing ammonium chloride, compared to the others. The conclusions reached reveal the applicability of 317L austenitic stainless steel in environments containing ammonium chloride, such as in the diesel hydrotreating sections of oil refineries, in addition to the use of washing water in pipes and equipment to dissolve these salts. Due to the high corrosion resistance of 317L steel in media containing ammonium chloride, it could be extended to other refining sections, such as distillation, cracking and coking units in oil refineries. This research will enable potential gains in terms of increasing the operational life of equipment and installations, reducing corrective maintenance interventions and operational safety in the operation of the industrial plant.

Investigating helium ion irradiation resistance in additively manufactured austenitic stainless steels

Additive manufacturing (AM) enables the rapid fabrication of complex shapes using engineering materials such as austenitic stainless steels and can imbue them with high irradiation resistance for use in reactor components. This is attributed to their refined grain structure and high grain boundary area. In this study, austenitic stainless steels (type 304) fabricated via direct energy deposition (DED) and powder bed fusion (PBF) techniques were irradiated with 5 MeV He ions to an approximate dose of 0.6 dpa at 300°C; subsequently, they were characterized through electron microscopy and the micro tensile testing. The results revealed that austenitic stainless steels manufactured using AM methods exhibited outstanding mechanical performance. The high performance of austenitic stainless steels fabricated through the DED technique can be attributed to their high tensile strength and excellent ductility elongation. This excellent performance is believed to be caused by the low stacking fault energy and the corresponding martensite formation during deformation. In particular, it was found that better mechanical properties were maintained even after helium irradiation, which is an important result obtained from the micro-tensile test. Even a small variation in the chemical composition and sub-microstructure of AM materials could result in improved irradiation tolerances.

Estimation the Remaining Life for Reformer Unit Tubes Furnace Operated Beyond the Design Life

The aim of this work is to study and model creep damage accumulation for remaining safe working life estimation of tube material used in petroleum industry plants operated at a high temperature for long time beyond the design life. Material constants and other data required for life estimation were extracted from the output results of real accelerated creep rupture tests conducted at three test temperatures (700, 725, and 750(oC and at three constant stress applications (120, 130, and 140 MPa). Also, a time-temperature parameter method (Larson-Miller Method) was modified to be applied based on the results of the accelerated creep rupture tests to build life predicted master curve for austenitic stainless steel type 321H. It is found that creep rupture time for stainless steel alloy decreases as temperature or stress increase. Also, it distinguished from the creep curves for the serviced stainless steel alloy, that the onset of tertiary creep stage starts early (about 50% of creep curve), this reflects the reduction in creep strength of the alloy as a result of the degradation in alloy properties that take place during the service life. It is also found that the estimated remaining working life for the serviced tube samples made from austenitic stainless steel type 321H is about (54703 hr) based on the calculated stress level (40 MPa) and service temperature 570 oC. The difference between the estimated remaining life and the experimental creep test life is due to the differences between the applied stresses, where higher level of stresses in the experimental creep testes are used to accelerate failure of specimens. The application for the result of this work can be the petroleum industries that where heaters tubes serviced at such industry need to be estimated for the remaining life after the design life expire.

Semi-Continuous Functionally Graded Material Austenitic to Super Duplex Stainless Steel Obtained by Laser-Based Directed Energy Deposition

In this work, a semi-continuous functionally graded material (FGM) between an austenitic and a super duplex stainless steel was obtained. These materials are of great interest for the chemical, offshore, and oil and gas sectors since the austenitic stainless steel type 316L is common (and not so expensive) and super duplex stainless steels have better mechanical and corrosion resistance but are more expensive and complex in their microstructural phases formation and the obtention of the balance between their main phases. Using directed energy deposition, it was possible to efficiently combine two powders of different chemical compositions by automated mixing prior to their delivery into the nozzle, coaxially to the laser beam for melting. A dense material via additive manufacturing was obtained, with minimum defectology and with a semi-continuous and controlled chemical compositional gradient in the manufactured part. The evolution of ferrite formation has been verified and the phase fraction measured. The resulting microstructure, austenite/ferrite ratio, and hardness variations were evaluated, starting from 100% austenitic stainless-steel composition and with variants of 5% in wt.% until achieving 100% of super duplex steel at the end of the part. Finally, the correlation between the increase in hardness of the FGM with the increase in the ferrite phase area fraction was verified.

Web crippling resistances of cold-formed stainless steel sections: A proposal for EN 1993-1-4

The current EN 1993-1-4 does not have supplementary web crippling design provision for cold-formed stainless steel sections under local transverse forces. Therefore, designers are generally referring to the guidance in EN 1993-1-3 for cold-formed carbon steel sections. Over the past decades, quite a substantial number of tests have been carried out worldwide to study the behaviour of cold-formed stainless steel sections undergoing web crippling, among which the majority of the data were focused on C-sections as well as square and rectangular hollow sections (SHS and RHS). To this end, tailor-made design provisions for these stainless steel sections can be developed. In this study, up-to-date web crippling test data on cold-formed stainless steel C-sections and SHS/RHS were firstly collected. The applicability of the web crippling design provisions as per the new version of EN 1993-1-3 to stainless steel sections was assessed. New design provisions for cold-formed stainless steel unstiffened C-sections (unlipped channels), stiffened C-sections (lipped channels) as well as SHS and RHS under local transverse forces are proposed in this study. The newly developed web crippling design provisions for C-sections and SHS/RHS were derived based upon reliability requirements as regulated in EN 1990 using available experimental data reported on austenitic, ferritic and duplex stainless steel types of various grades. The proposed design provisions for stainless steel sections have been made in line with the development of the new version of EN 1993-1-3 provisions and therefore are recommended to EN 1993-1-4 for calculating web crippling resistances under local transverse forces.

Microstructure, properties and fracture failure mechanism of MAG welded joints of four types of stainless steels

In this study, four types of austenitic stainless steels (SUS 301L, SUS 304, SUS 316L and SUS 321) with different chemical compositions were butt welded by using MAG (metal active gas) welding. Unique information was gained by studying the solidification mode, microstructure and mechanical properties of the four welded joints under the same welding process, and their fracture mechanisms were analyzed from the perspective of crystallography. The results indicate that the microstructure of the four austenitic stainless steel base metals is uniformly sized equiaxed austenite with δ-ferrite distributed inside or at the boundary of austenite grains in 301L and 304 base metals. The welds of the four kinds of stainless steels are solidified in Austenitic-Ferrite (AF) solidification mode, and the final microstructures of the 301L, 304 and 316L weld are equiaxed grains while the 321 stainless steel weld grows into a dendritic structure due to its low temperature gradient. The microstructures of the fusion zone (FZ)/fine equiaxed zone (FQZ) and heat affected zone (HAZ) of the four types of stainless steels are closely related with the solidification mode of FZ, i.e. small FZ and HAZ regions result from Ferrite (F) solidification mode present in the 301L and 321 welded joints. However, larger FQZ regions generate in the 304 and 316L welded joints due to the Ferrite-Austenitic (FA) solidification mode. The 304 and 316L stainless steel tend to fracture at the HAZ positions due to the formation of FQZ; large angle grain boundary formed at the weld of 301L stainless steel is the reason for its fracture, and the good anisotropy of the weld and heat affected zone of 321 stainless steel also makes it easier to fracture in the base metal (BM). The section hardness distribution characteristics of the four stainless steels welded joints also verify their fracture tendency.

Finite element analysis and proposed design rules for 304D high-strength stainless steel I-shaped members in shear

The stainless steel I-shaped members are extensively used as plate girders due to their excellent performance. However, traditional stainless steel is often expensive and has a relatively low yield strength, limiting their application. In recent years, a new type of austenitic high-strength stainless steel named 304D (08Cr19Mn6Ni3Cu2N) was developed and extensively used. This new material has similar anti-corrosion properties as S30408 stainless steel, but has a lower cost and higher yield strength. However, no work has been undertaken on the shear resistance and design of such members. The material property and chemical property of such 304D members are quite different from those of traditional stainless steel, which may result in different performance in shear resistance. Hence, a total of six tensile coupon tests were performed to obtain the material properties of 304D high-strength stainless steel. Finite element (FE) models were established and validated against the corresponding test data reported by the authors and other researchers, although they are only traditional stainless steel. A comprehensive parametric analysis including 576 FE models was performed to examine the influences of the critical parameters on the shear resistance of such members. The results suggested that the shear resistance of 304D members increased by 61% on average, compared to S30408 members. The parametric analysis results were further used to assess the existing design methods in the GB 50017 (2017), EN 1993-1-4 + A1 (2015), ANSI/AISC 360–16 (2016), ANSI/AISC 370–21 (2021) and those proposed by Chen et al. (2018). Upon comparison, it was demonstrated that the existing design methods were generally over-conservative for predicting the shear resistance of such members. Design formulas were therefore proposed by modifying the original design eqs. A reliability analysis was then performed, indicating that the modified equations can closely predict the shear resistance of such members.

Analysis of fatigue performance of austenitic stainless steels with bimodal harmonic structures based on multiscale model simulations

Austenitic stainless steel with a bimodal harmonic structure (HS) is a recently developed material that consists of a periodic arrangement of coarse-grained (CG) structures surrounded by a network of ultra-fine grains (UFG). This material is characterised by high strength and good ductility. In this study, we analysed the fatigue performance of HS materials by modifying our previous multiscale model to extend its applicability from only homogeneous materials to HS materials. A novel method was proposed to characterise the microstructural features of HS materials considering the distributions of CG and UFG. A microstructure model was developed to reproduce grain maps using these characterised microstructures. The multiscale model was successfully validated by experimental results for two types of austenitic stainless steels. The model was used to elucidate the governing microstructural factors of fatigue performance in HS materials through systematic simulations. Consequently, a higher UFG area fraction was confirmed to improve fatigue life, and a UFG area fraction of approximately 40% is suggested for optimal microstructural design to balance fatigue performance and fabricating costs. This study presents the first step in the qualitative design of the fatigue performance of HS materials to replace the expensive and inefficient experimental analyses used in previous studies.

Effects of Plasma Nitriding Process on AISI 304 Stainless Steel

AISI 304 stainless steel is a type of austenitic stainless steel that contains a high percentage of chromium and nickel. It is one of the most widely used grades of stainless steel and is commonly used in a variety of applications, including kitchen equipment, food processing equipment, and chemical processing equipment. AISI 304 stainless steel is a versatile and widely used material due to its excellent corrosion resistance, durability, and non-magnetic properties. Low-temperature processes like ion implantation, plasma nitriding can prevent the corrosion resistance of stainless steels by diffusion of plasma into the surface of the material, forming precipitation of Chromium nitride. For this research work, plasma nitriding is carried out on AISI 304 at low-temperatures 550°C for the time duration of 8 hrs, 16 hrs and 32 hrs. The formation of nitrogen-enriched layers with high nitrogen content promoted to increase in surface hardness. Wear test were carried out with pin on disc machine and the samples were undergone with hardness tests. The microstructures of plasma treated samples were compared with untreated microstructures. It was noted that phase change occurred from austenite to expanded austenite forming a hard layer from the surface level improving the wear resistance of the material.

Effects of Salt Bath Nitriding Process on AISI 309 Stainless Steel

AISI309 stainless steel is a type of austenitic stainless steel that contains a high percentage of chromium and nickel, along with a small amount of manganese. It is designed to be used in high-temperature applications, such as in furnace parts and heat exchangers. Low temperature salt bath nitriding process was carried out on AISI 309 stainless steel at 550°C for time duration of 80, 160 and 240 minutes. The characteristics of the nitride surface were thoroughly assessed. The microstructure and phase components of the nitrided surface revealed a hardened layer of chromium nitride and iron nitride on the specimen surface. The case depth and the surface hardness were strongly influenced by the alloying components. To analyze the wear, a pin on disc machine was utilized and the wear test was carried out. From the wear test, wear loss were determined. Scanning electron microscopy revealed the variation between loss of material and the base material. A specimen which is untreated is kept aside and comparisons of results were done with nitrided samples.

Electrochemical corrosion behavior of tantalum coated 316L stainless steel by D.C. Magnetron sputtering for orthopedic applications

The austenitic stainless steel type 316L was engineered with a thin multilayer of tantalum with a thickness of 1.504µm, 3.893 µm and 6.083µm and a duration of 15, 30 and 60 minutes, respectively, by the DC Magnetron Sputtering. Electrochemical behaviors of all three samples were investigated by potentiodynamic and electrochemical impedance spectroscopy techniques. Simulated body fluid was used as the corrosive medium for the electrochemical measurement. The highest corrosion resistance was obtained for the sample subjected to 60 minutes of Ta deposited on 316L S.S. according to EIS measurements, and the lowest corrosion rate of 0.0047 mm/year was obtained for the same sample according to the PD measurements. All the measurements were carried out after the determination of open circuit potential (OCP) at 37˚C with 1 ±°C. All the samples were then characterized by scanning electron microscopy (SEM) to observe the morphology of coating after corrosion. The number of corrosion pits observed from the SEM micrograph was much less on the three coated samples compared to the bare sample. X-ray Photoelectron Spectroscopy (XPS) was used to identify the chemical states of coated and bare 316L SS. Ta4f is present as oxidation states in Ta coated stainless steel 316L, whereas Ta4f is the main species examined along with other elements (C1s, N1s, O1s, Cr2p, Fe2p, Ni2p, and Mo3d). It was also observed that there was strong adhesion between substrate and Ta-coating. After the potentiodynamic studies, results show a significant improvement in corrosion resistance attributed to the strong, stable oxide layer formation.

Effect of Some Environmental and Stainless Steel Metallurgical Variables on the Values of Degree of Sensitization Measured by the Double Loop-Electrochemical Potentiokinetic Reactivation Test

The double loop-electrochemical potentiokinetic reactivation (DL-EPR) method estimates the degree of sensitization in stainless steels with ir/ia, the ratio of peak current densities during reactivation (reverse) and activation (forward) scans. Beyond sensitization level, other metallurgical variables, like inclusion content and cold work, or testing environment variables, like solution deaeration and solution aging, could potentially affect ir/ia. Austenitic stainless steel Types AISI 304 (UNS S30400) and AISI 303 (UNS S30300) were tested to assess the effect of those secondary variables on ir/ia. AISI 303 stainless steel had similar chromium and nickel contents to AISI 304, but higher contents of sulfur, resulting in a higher volume fraction of inclusions. ir/ia increased with inclusion content and decreased with cold work in AISI 304 stainless steel. In all cases, the DL-EPR test could discriminate solubilized from thermally aged specimens because confidence intervals of respective samples never overlapped. The testing solution was 0.5 mol/L H2SO4 + 0.01 mol/L KSCN, (sulfuric acid and potassium thiocyanate solution) and a common practice is to freshly prepare it just before the test. Measurements are usually performed under deaerated conditions. However, deployment of the technique, especially in the field, could be facilitated if naturally aerated solutions prepared in advance in a laboratory can be used. The oxygen content in solution and solution aging did not have a statistically significant effect on ir/ia.

High Density RF-DC Plasma Nitriding under Optimized Conditions by Plasma-Diagnosis

This paper is concerned with plasma diagnosis on a N2-H2 gas mixture to determine the optimum parameters for the nitriding process. Plasma parameters such as pressure, RF-voltage, and DC-bias were varied for optimization. The active species such as N2+ and NH were identified in plasma diagnosis. In the N2-H2 gas mixture, hydrogen imposed a great influence on plasma generation. The small addition of a hydrogen molecule into the gas mixture resulted in the highest yield of N2+ ions and NH radicals; the optimum hydrogen content was 20% in the mixture. The austenitic stainless-steel type AISI304 was nitrided at 673 K and 623 K to experimentally demonstrate that hydrogen gas content optimization is necessary to improve the surface hardness and to describe low temperature nitriding under high nitrogen flux at the surface.

FATIGUE FAILURE IN A LONGITUDINAL WELDED ELBOW OF A PROCESSING VESSEL

A longitudinal welded elbow made of austenitic stainless steel type 316 and used as a drain line on a processing vessel had suffered damage (leakage) after it had only been in operation for a few years. Process fluid that was drained out of the vessel consists of fatty acid containing hydrogen gas at a temperature of 150°C and a pressure of 60 bar(g). Initially, the drain process was carried out only once a year, but recently due to frequent changes in the types of product being made, the frequency of drain process has increased to several times a month. This study aims to determine the type and factors that have caused leakage in the elbow. Metallurgical assessment was carried out by preparing a number of specimens from the leaking elbow. A number of laboratory examinations were performed including visual and macroscopic tests, chemical composition analysis, metallographic examination, hardness tests and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) analysis. The results obtained indicate that the leaking elbow has experienced fatigue failure due to cyclic loadings caused by the increasing frequency of the number of drain processes carried out through the elbow. The factor causing fatigue failure at the elbow is likely due to welding defect of imperfect shape that formed on the inner wall of the elbow around the HAZ (heat-affected zone)/fusion boundary, and causing high stress concentrations in that area.

Austenitic Stainless Steel as a Catalyst Material for Photo-Fenton Degradation of Organic Dyes

In this paper, a typical austenitic stainless steel was used as a catalyst in the visible photo-Fenton degradation process of two model dyes, methylene blue and methylorange, in the presence of hydrogen peroxide and potassium persulfate as free radical-generating species. The concentration intervals for both peroxide and persulfate were in the range of 333–1667 μg/L. Very high photodecoloration efficiencies have been achieved using peroxide (>93%), while moderate ones have been achieved using persulfate (>75%) at a pH value of 6.5. For methylene blue, the maximum mineralization yield of 74.5% was achieved using 1665 μg/L of hydrogen peroxide, while methylorange was better mineralized using 999 μg/L of persulfate. The photodegradation of the dye occurred in two distinct steps, which were successfully modeled by the Langmuir–Hinshelwood pseudo-first-order kinetic model. Reaction rate constants k between 0.1 and 4.05 h−1 were observed, comparable to those presented in the reference literature at lower pH values and higher concentrations of total iron from the aqueous media.

Research regarding strip cladding of heat-resistant SA 387 Gr.11Cl.2 steel type

The continuous development of industrial processes in the petrochemical field requires the use of materials with anticorrosive properties, able to withstand working conditions at high temperatures but also in highly corrosive environments. The basic materials with anticorrosive properties have a high cost price which leads to the need to find alternative manufacturing solutions. In such situations, the use of bimetal plates or the option of welding cladding with an anticorrosive layer of the base material is used. The paper analyses the possibility of strip cladding using the submerged arc welding process of a reactor made of SA 387Gr11Cl.2 basic material, a heat-resistant alloy steel. To achieve the deposition of the appropriate anticorrosive layer (stainless steel type AISI 347) it was necessary to use a buffer layer made of austenitic stainless-steel type 309L. In order to eliminate the internal tensions appeared after the cladding process, the sample was subjected to a stress relieving heat treatment. After the heat treatment, the sample was subjected to non-destructive examinations (visual and penetrant testing) but also to destructive examinations specific to the approval tests of cladding technology (Metallographic tests, Vickers hardness test, bend test, ferrite number, chemical composition). Metallographic tests of cross-sectional phase structures were carried out in macroscopic and microscopic terms. In the area of the deposited material can be observed a typical austenitic casting structure resulting from the use of a high linear energy, specific to the automatic submerged arc welding. Following the performance of hardness measurements made in the characteristic areas of the deposition, it can be seen that there was a slight increase in the values obtained in the heat affected zone, without exceeding the prescribed values for the materials used. Following the analysis of the results obtained from the specific examinations and tests to the plated samples, it can be seen that they are within the limits prescribed by the standards in force regarding the approval of the cladding technology used.