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The effect of different types of cleaning solutions (neutral, acidic, and alkaline) on the corrosion of AISI 304 stainless steel were studied. The corrosion resistance was observed based on an accelerated immersion process simulating the pattern of steel corrosion over time at room temperature. A potentiodynamic polarization technique was conducted to estimate general corrosion rates. Various electrochemical parameters including potential corrosion (Ecorr), corrosion current density (icorr) and Tafel slopes were analyzed and discussed. The corrosion products after the immersion process were observed by using an optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The results indicated that there was different corrosion resistance for cleaning solutions with different pH value. The CS-E sample showed the best corrosion resistance due to its alkaline condition. The CS-I sample had the highest corrosion rate due to a decrease in the repassivation of the pit.

Cast austenitic stainless steel grade CF8C of ASTM A351 possesses varying degrees of suitability for services both at high temperatures and in corrosive environments. CF8C contain Nb of 1% max as per ASTM A351, i.e. 8 times the carbon content. Unlike CF8M and CF3M of ASTM A351, CF8C grade has option for stabilization treatment due to Nb present which forms carbides, between 870 and 900 °C after solution annealing in austenite matrix. This prevents depletion of chromium around grain boundary and prevents sensitization of steel. However, this stabilization treatment has been mentioned as supplementary requirement of ASTM A351 Clause 3.1 depending on the end property requirement. In this line, experimentation carried out on solution annealing and solution annealing + stabilization treatment of CF8C grade and testing carried out in order to evaluate properties after both treatments. For other stainless steels like CF8M, and CF3M of ASTM A351 similar experiment carried out.

This study evaluates the effects of temperature, H2S, and Cl− concentration on the onset of localized corrosion, in UNS S31603 stainless steel by evaluating the changes in the behavior of the passi...

Effect of active screen plasma nitriding (ASPN) on microstructure, hardness, and wear loss of 347H austenitic stainless steel (AuSS) was studied at various processing parameters. Scanning electron microscopy, x-ray diffraction (XRD), hardness, and wear tests were performed on samples. The XRD analysis showed the presence of S-phase (γN-expanded austenite) in samples nitrided at 350 °C and 400 °C. In contrast, samples nitrided at higher temperatures ranging from 450 to 550 °C showed the presence of various types of nitride phases in the nitrogen-enriched layer. The case depth and mass of nitrided samples increased with the increase in nitriding temperatures owing to the increase in diffusivity of nitrogen at a higher temperature. The wear loss of samples nitrided at higher temperatures was lower than those nitrided at lower temperatures due to the formation of a higher amount of hard nitride phase(s) in the nitrogen-enriched layer at temperature ≥ 450 °C.

In this study, room temperature tensile properties of type 304, a metastable austenitic stainless steel, prior rolled above Md temperature (200 °C and 300 °C) are compared with mill-annealed and material prior rolled at room temperature (25 °C). Strain-induced martensite that formed during the tensile tests, followed using in-situ using magnetic measurements, display kinetics that vary with prior deformation temperature and strain. Scanning Electron Microscopy and Electron Backscattered Diffraction studies provided direct evidence for shear band formation during prior deformation. Kinetics of strain-induced martensite is found to fit the Olson–Cohen equation modified to include the prior deformation strain and martensite formed during prior deformation. The systematic changes observed in the model parameters of the modified Olson–Cohen equation are explained. The strain hardening in the material is analyzed and correlated with changes in the rate of formation of strain-induced martensite with respect to strain.

To study and understand the solidification behavior of super austenitic stainless steel under different cooling rates and segregation laws of alloying elements is of great significance to optimize the subsequent diffusion annealing homogenization treatment process and improve product quality. According to Thermo-Calc thermodynamic simulation results and combined with high temperature laser confocal scanning electron microscope (HT-CSLM), the tissue morphology of 904L super austenitic stainless steel was observed in-situ during solidification. The solidification path of the test steel was determined via calculation with the Scheil-Gulliver model. Microscopy techniques, including true color microscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron probe microanalyzer (EPMA) were used to analyze the influence of different cooling rates (6 ℃/min, 50 ℃/min, and 100 ℃/min) on the solidification structure and determine the main distribution law of alloying elements. This analysis determined that the solute distribution coefficient (K) of Cr, Mn, Mo, Cu, and Si elements is less than 1 during the solidification process, which means that they will accumulate in the liquid phase. Among them, elemental Mo segregation is the most severe, while elemental Ni hardly segregates. As the cooling rate increases, the crystallization temperature of the test steel decreases, and the secondary dendrite arm spacing λ2 decreases, the concentration of Mo in the residual liquid phase increases.

Recent developments in the 3D printing of austenitic stainless steels have led to the need for standardization of electrochemical techniques used to assess the corrosion performance of these alloys. Currently, ASTM standards for austenitic stainless focus on assessing their resistance to different modes of corrosion such as pitting, crevice, and intergranular corrosion. Due to the complexity of the additive process, selective corrosion occurs in microstructural features such as cellular structures and melt pool boundaries. Standardized corrosion testing needs to incorporate these microstructural features. This study characterizes the corrosion behavior of laser powder bed fusion stainless steel in a variety of ASTM standards with special attention to melt pool boundary dissolution, cellular structures, and intergranular corrosion.

The metastable austenitic stainless steel AISI 347 offers the possibility to induce a phase transformation from γ-austenite to ε- and α’-martensite when machining. This knowledge is well understood during cryogenic turning and was already applied to improve the surface morphology of metastable austenitic steel. However, the potential of this in-process hardening method is so far limited to rotationally symmetrical components. The aim of this study is to investigate deformation induced phase transformation during cryogenic milling, aiming at an improved surface morphology and at the resulting beneficial surface properties of the workpiece for parts with complex geometries.

The deposition of austenitic stainless steel coatings on high-strength low-alloy steel surfaces was a common method in engineering. However, excessive dilution of the substrate resulting in degradation of the coating properties is a constant challenge. In this paper, tungsten argon arc welding (TIG) technology was optimized based on the response surface method to produce a very low dilution (4%) stainless steel coating on the surface of Q355 steel. The intergranular corrosion sensitivity of the two coatings was tested by the double-loop electrochemical potentiodynamic reactivation technique. The DOS value of the coating made by the TIG technique (6.83%) is lower than that of the coating made by flux-cored arc welding (9.31%). The improved intergranular corrosion resistance is attributed to the dilution rate, grain size, grain boundary type, and inclusions. A technique of manufacturing low dilution coatings is provided, achieving a 50% savings in welding material.

Austenitic stainless steels (ASS) are among the most used structural materials because of their excellent mechanical and corrosive properties. In addition, 316L ASS has excellent weldability because of its low carbon content. This steel normally contains 5–10% residual delta ferrite to avoid hot cracking and micro-fissuring of the weld metal. Many studies show that selective dissolution of austenite or ferrite can occur in 316L steel. In a survey of the selective dissolution of phases in duplex stainless steel (DSS), Lo and coauthors studied the effect of electrolyte composition (H2SO4 + HCl solutions) on the active–passive transition. They showed that corrosion occurred only in the austenitic phase in solutions of 2M H2SO4 + 0.25–1.2M of HCl. Increasing the % of HCl, > 1.2%, austenite, and ferrite contributed to the corrosion process. The present authors did not find the effect of this electrolyte in the study of selective corrosion in 316L ASS welded in the literature. Therefore, this study aims to determine how the phases behave on 316L ASS by applying 2M H2SO4 + 1.5M HCl solution. In this work, we welded the steel by the autogenous TIG process using three heat inputs. The purpose of welding was to obtain different amounts and morphology of ferrite and determine whether this affected the selective dissolution of the phases. After the corrosion tests, the samples showed selective austenite corrosion irrespective of the volume fraction and morphology of the ferrite. In summary, the corrosive etches severely consumed the austenite because of the significant difference in the electrochemical potential between the phases. Therefore, with more nickel, austenite functioned as an anodic region, and the δ-ferrite, with more chromium, worked as a cathodic region.

This paper investigates the machinability of AISI 316L stainless steel without and with NMI treatment, when machined with three different PcBN tool grades: low cBN content (50% vol.), medium (65% vol.) and high (90% vol.). The NMI treatment consisted of resulfurized and Ca-treated steels with two different Si/Al ratio. The tool materials were evaluated in terms of tool life, showing the best performance for the medium cBN content grade. Results showed that the crater wear has a more significant effect on the tool performance than the standard wear criteria of maximum flank wear. The worn tools were examined using scanning electron microscopy (SEM), focused ion beam (FIB) and transmission electron microscopy (TEM). In most cases, the crater exhibited three distinct regions from the edge to the end of the contact zone: the plateau, middle crater, and the upper region. Plateau and crater region displayed tool protective layer (TPL), consisting mostly of Al, Si, Mg and Ca-oxides; and some dimples in the tool from preferential wear of cBN grains. In the upper region of the best performing material, a ~1.5 μm thick TPL of mostly MnCr2O4 spinel was found, a result of the transfer of Mn- and Cr-rich oxide NMIs found in this material or oxidation of workpiece material, during the machining process. (Less)

The nickel-based Colmonoy-5 hardfacing alloy is used to hard-face 316LN austenitic stainless steel components in fast reactors. The nominal composition (in wt%) was listed as follows: 0.01 C, 0.49 Si, 0.87 Mn, 17.09 Cr, 14.04 Ni, 2.56 Mo, 0.14 N, and balance Fe. Hardfacing is a technique of applying hard and wear-resistant materials to substrates that need abrasion resistance. The thickness of hardfacing deposit varies between 0.8 mm and 2 mm based on parameter combinations. In this study, laser hardfacing process parameters including laser power, powder feed rate, travel speed, and defocusing distance were optimized to reduce weight loss of laser hard-faced Ni-based deposit. The tribological characteristics of reactor-grade NiCr-B hard-faced deposits were investigated. The RSM technique was used to identify the most important control variables resulting in the least weight loss of the nickel-based alloy placed on AISI 316LN austenitic stainless steel. Statistical techniques like DoE and ANOVA are utilized. Changing the laser settings may efficiently track the weight loss of laser hard-faced nickel alloy surfaces. These are created using the response surface technique. The deposit produced with a laser power of 1314 W, powder feed rate of 9 g/min, travel speed of 366 mm/min, and defocusing distance of 32 mm had the lowest weight loss of 16.4 mg. Based on the F value, the powder feed rate is the major influencing factor to predict the hardness followed by power, travel speed, and defocusing distance.

The ferrite content of austenitic stainless steel welds seriously affects to perform stainless steel welds. Keeping the ferrite content at the lower limit can reduce the thermal crack sensitivity o...

The use of post-processing heat treatments is often considered a necessary approach to relax high-magnitude residual stresses (RS) formed during the layerwise additive manufacturing laser powder bed fusion (LPBF). In this work, three heat treatment strategies using temperatures of 450 °C, 800 °C, and 900 °C are applied to austenitic stainless steel 316L samples manufactured by LPBF. These temperatures encompass the suggested lower and upper bounds of heat treatment temperatures of conventionally processed 316L. The relaxation of the RS is characterized by neutron diffraction (ND), and the associated changes of the microstructure are analyzed using electron backscattered diffraction (EBSD) and scanning electron microscopy (SEM). The lower bound heat treatment variant of 450 °C for 4 hours exhibited high tensile and compressive RS. When applying subsequent heat treatments, we show that stress gradients are still observed after applying 800 °C for 1 hour but almost completely vanish when applying 900 °C for 1 hour. The observed near complete relaxation of the RS appears to be closely related to the evolution of the characteristic subgrain solidification cellular microstructure.

Welding fumes have been found to be carcinogenic and stainless steel welders may be at higher risk due to increased formation of hexavalent chromium (Cr(VI)). The slag-shielded methods, identified to generate most airborne particles and Cr(VI), would potentially be most harmful. With ever-stricter limits set to protect workers, measures to minimize human exposure become crucial. Austenitic stainless steel flux-cored wires of 316L type have been developed with the aim to reduce the toxicity of the welding fume without compromised usability. Collected particles were compared with fumes formed using solid, metal-cored, and standard flux-cored wires. In part 1, the new wires were concluded to have improved weldability, to generate even less Cr(VI) in wt.-% than with solid wire and to be less acute toxic in cultured human bronchial epithelial cells as compared to standard flux-cored wires. In part 2, two additional institutes created fume emission datasheets for the same wires for correlation with the fume data obtained in part 1. The reported values showed large variations between the three laboratories, having a significant effect on the standard deviation. This is suggested to be the result of different welding parameters and various ways to collect and analyze the fume. More stringent specifications on parameter settings and fume collection would be required to increase the accuracy. This means that at present, it may not be possible to compare fume data on datasheets from two different wire producers and care should be taken in interpretation of values given in the available literature. Nevertheless, the laboratories confirmed the same trends for Cr(VI) as presented in part 1.

A TC4 titanium alloy plate was lap joined to a 304 austenitic stainless steel plate via friction stir welding. The microstructures at the lap joint interface were intensively examined by means of energy dispersive X-ray spectroscopy and transmission electron microscopy analysis, and the mechanical properties of the lap joint were evaluated by a microhardness and shear tensile test. The results show swirling-like stir zones of TC4 and 304 SS are formed along the interface, where an aprox. 200 nm interface layer composed of TiFe and TiFe2 intermetallic compound is dispersed at the high rotating speed of the tool. In addition, the high hardness value is discontinuous distribution at the interface, and the shear strength of the commercially TC4 plate and 304 SS FSW lap joint can reach 7507 N at a rotational speed of 600 rpm, a welding speed of 30 mm/min, and a press amount of 0.4 mm.

There are several possibilities for establishing a cohesion joint between dissimilar metals. In the case of thin sheets, the ultrasonic welding process is suitable. This process can establish a cohesion joint rapidly, with a low heat input between the thin sheets. The authors have tried to determine the optimal ultrasonic welding parameters for copper and austenite stainless steel joining by using an experimental method of joining. Suitable results were obtained by welding tests due dissimilarities in the chemical, physical and mechanical properties of the copper and stainless steel. A standard size sheet thickness and test sample was used for the welding by different parameters. The parameters were refined based on the theoretical and practical knowledge during the experiments. The experimental welding was made by a Branson L20 type welder machine. The joint made by the different parameters was inspected by shearing-tensile tests (maximal force level).

Steel (St) and aluminum (Al) have a high affinity to each other and form intermetallic compounds (IMCs) when bonded by friction stir welding (FSW). Understanding the effect of alloying elements of steel on the formation of IMCs will help to design joints in which the formation of IMCs is controlled. In this study, two kinds of steel, carbon steel (CS) and austenitic stainless steel (SS) with 3 mm thickness, were selected to be welded to aluminum by FSW under similar conditions. The effect of the rotation speed of the FSW tool was also examined in the range of 850–1300 RPM. The morphology, thickness, and composition of IMCs in the interfaces were studied by various characterization techniques. It was observed that the IMC layers in the SS/Al joints were much thinner than the ones in CS/Al joints (0.1–0.7 µm in SS/Al and 2–6 µm in CS/Al). Moreover, the thickness of IMC layer in CS/Al joints increased with increasing the rotation speed while in SS/Al joints it began to decline by exceeding a certain rotation speed. In order to explain these differences, diffusion-based equations were used to calculate the interdiffusion coefficients in both SS/Al and CS/Al couples. It was found that the interdiffusion coefficient in SS/Al was lower than CS/Al. This was attributed to the alloying elements of SS such as Ni and Cr which can diffuse to IMC layer and hinder the growth rate of IMCs. It was also observed that some form of liquation occurred in SS/Al joints at high rotation speed of FSW due to the formation of a low-melting multielement compound of Al–Fe–Cr–Ni. The decline of IMC thickness in SS/Al joints at high rotation speed was attributed to this multielement compound which was melted during FSW and reduced the nucleation rate of Al–Fe IMCs. Finally, the fracture of the specimens and the effect of IMC formation on the joint establishment were elaborated. It was concluded that the alloying elements of steel have a beneficial effect on controlling the growth of IMCs.

Purpose Effect of grain size on degree of sensitization (DOS) was been evaluated in Nickel free steel. Manganese and nitrogen contained alloy is a Ni-free austenitic stainless steels (ASS) having type 202 grade. The main purpose of this investigation is to find the effect of recrystallization on the DOS of stainless steel after the thermo-mechanical processing (cold work and thermal aging). Design/methodology/approach In the present investigation, the deformation of 202 grade analyzed using X-ray diffraction (XRD) and microstructural testing. Optical microstructure of Ni-free ASS has been done for cold worked samples with thermally aged at 900°C_6 h. Double loop electrochemical potentiodynamic reactivation test used for findings of degree of sensitization. Findings Ni-free ASS appears to be deformed more rapidly due to its higher stacking fault energy which gave results in rapid transformation from strain induced martensite to austenite in form of recrystallized grains, i.e. it concluded that as cold work percentage increases more rapidly recrystallization occurs. XRD results also indicate that more fraction of martensite formed as percentage of CW increases but as thermal aging reverted those all martensite to austenite. So investigation gives the conclusion which suggests that with high deformation at higher temperature and duration gives very less DOS. Originality/value Various literatures available for 300 series steel related to the effect of cold work on mechanical properties and sensitization mechanism. However, no one has investigated the effect of recrystallization through thermomechanical processing on the sensitization of nickel-free steel.

The low nickel austenitic stainless steel (LNiASS) is more economical than the conventional 300-series austenitic stainless steels as 60% (approx.) of the Ni is replaced by manganese; it exhibits similar mechanical properties but inferior corrosion resistance. In this work, low nickel austenitic stainless steel samples were coated with Ni-based metallic powders using a thermal spray coating technique. The microstructures, phase composition and properties of coatings were examined using SEM, EDS, XRD and Vickers’s microhardness. The corrosion behavior was investigated by potentiodynamic polarization test in 0.5 M H2SO4 solution and 3.5 wt.% NaCl solution both for the uncoated and coated specimen. In both test solutions, the coatings that contained molybdenum and more chromium showed better corrosion resistance. The coated low nickel austenitic stainless steel can, therefore, be a cost-effective alternative to replace the widely used austenitic stainless steel in commercial as well as industrial applications.

Two different alloys were developed from the mixtures of pre-alloyed powders consisting of ferroalloys to get the required composition of austenitic stainless steel via the powder metallurgy techni...

Production of bulk high-nitrogen stainless steel components by the powder metallurgy route has gained significant attention lately. This requires the ability to alloy stainless steel powders with significant amounts of nitrogen. This work reports a novel powder nitriding approach to achieve the same. The response of 316 L stainless steel powders to low temperature(425–500 °C) nitriding treatments has been investigated. The nitrided powders have been characterized by Scanning Electron microscopy, X-ray diffraction and Vickers micro hardness measurements. The low temperature nitriding treatments resulted in the formation of a significant nitrided layer, consisting of a Cr-nitride free, expanded austenite phase with large quantities of dissolved nitrogen. The amounts of dissolved nitrogen introduced into the powders have been estimated from XRD based lattice parameter measurements. A maximum nitrogen uptake of 31 at. % could be achieved with an attended hardness of 1750VHN.

Wire plus arc additive manufacturing (WAAM) technology with higher deposition rate and efficient material utilization was employed to fabricate a stainless steel 321 (SS 321) wall for the first time. In this work, the microstructural characteristics, mechanical properties and corrosion performance of as-built SS 321 were evaluated. The micrographs confirmed the presence of columnar and equiaxed dendrites along the building direction, and recrystallization of grains was noticed due to the re-melting of former layers. The microstructure was dominantly austenite with a small fraction of ferrite within the austenitic matrix. Better tensile properties were noticed for as-printed SS 321 WAAM samples in-comparison to wrought counterpart. This is corroborated to the equiaxed and columnar dendritic microstructure with small fraction of ferrite (FN). The hardness decreased from bottom (247 HV) to top (196 HV) region in SS 321 WAAM plate and is attributed to the microstructural difference with varying amount of ferrite (6.3 to 3.7 FN). The impact strength of samples in the horizontal and vertical direction was 116 ± 2 J and 114 ± 2.5 J respectively, and is comparable with the wrought AISI 321 (123 ± 1.5 J). The reduction in impact toughness is attributed to the ferrite (

International audience; Ti-stabilized austenitic stainless steel was carburized in sodium containing a high carbon activity at three different temperatures, 500 °C, 600 °C, and 650 °C during 1000 hours and 5000 hours. The carbon profile, the carbide volume fraction, and the lattice parameter evolution as function of depth were determined using high-energy X-ray diffraction and electron probe microanalysis. At 650 °C and 600 °C, the carbon precipitated as M23C6 and M7C3 carbides in the sample. The volume fraction of M7C3 carbides was lower than predicted by thermodynamic equilibrium using Thermo-Calc software®. At 500 °C, carbides almost did not form in the steel. Instead, high carbon supersaturation of the austenitic matrix occurred. Both results demonstrate that the carburization profile was strongly influenced by the kinetics of carbide formation at temperatures lower than 650 °C. High-energy X-ray diffraction measurements demonstrated that the austenite and carbide lattice parameters evolved along the carbon profile. Both measured lattice parameter profiles of austenite and M23C6 carbide were compared to the ones predicted from chemical changes of austenite and carbides.

During wire and arc additive manufacturing (WAAM) of high nitrogen austenitic stainless steel (HNASS), the explosion of droplets with high-content nitrogen will induce grievous spatters, causing incomplete fusion, cracks and inclusions. In this study, the formation, characteristics and influence of spatters on cold metal transfer + pulse (CMT+P)-based WAAM of HNASS were investigated. The droplets exploded violently due to the sharp decrease of nitrogen solubility in liquid steel, which produced abundant spatters at the pulse stage. The spatter particles were a mixture of manganese oxides (MnO and Mn3O4) and molten metals of the wire. The overall particle size followed normal distribution. The majority of particles were spherically shaped in diameter of 20–150 µm, and over 80% of spatters were below 200 µm in diameter. Inclusion of manganese oxide spatter particles appeared in the deposition metals of single-pass single layer. The spatters at the root of the deposited metal can be hardly removed, which produced interpass defects in overlapping deposition. For multi-pass multilayer deposition, interlayer tearing occurred to reduce the mechanical properties of HNASS. The interlayer tearing was caused jointly by the incomplete fusion caused by spatter particles of manganese oxide and the large thermal stress. Hence, the spatters generated in the droplet transition for WAAM of HNASS must be controlled.

This paper describes an experimental corrosion study performed on austenitic stainless steel deposited mild steel substrate in 0.5 M sodium chloride medium. The study was performed with an aim to improve the corrosion resistance of mild steel substrate through surface deposition of a thin film of asutenitic stainless steel. The thin SS film was deposited by pulse laser deposition technique while using 316 L grade stainless steel foil as a target. Thin film deposition of 316 L stainless steel on mild steel brought about relative improvement in its resistance against corrosion. However, with respect to 316 L stainless steel foil, the specimen exhibited poor corrosion resitance in terms of corrosion rate (corrosion current density), lack of passivity and pitting potential. The reason for the inferior corrosion behaviour of deposited specimen is attributed to defective ferritic microstructure of the thin film and lack of nickel constituent which was associated with lower resistance and higher capacitance with respect to 316 L stainless steel foil. Similarly, with respect to mild steel, deposited mild steel showed better corrosion resistance due to passive role of chromium enriched film.

Micro hot embossing is a well-established technology to produce polymer microdevices and parts. This technology on metal powder/binder feedstocks is an innovator challenge that fits into the sustai...

This work is devoted to the study of the possibility of recycling bar scrap of stainless metals using radial-shear rolling. In the course of studies on the deformation of bar scrap in the form of pins made of 12X18N9T stainless austenitic steel on a radial-shear rolling mill, the resulting bar was obtained microstructure of two different types: on the periphery an equiaxed ultrafine-grained structure with a grain size of 0.4–0.6 microns was formed; in the axial zone anoriented, banded texture was obtained. This discrepancy in the structure of the peripheral and axial zones, together with the results of cross-section microhardness measurements of samples made of 12X18N9T austenitic stainless steel with a total degree of deformation of 44.4 %, indicates the gradient nature of the resulting microstructure.

The scarcity of oil and gas resources made High Pressure and High Temperature (HPHT) reservoir attractive to be developed. The sour service environment gives an additional factor in material selection for HPHT reservoir. Austenitic 28 Cr and super duplex stainless steel 2507 (SS 2507) are proposed to be a potential materials candidate for such conditions. C-ring tests were performed to investigate their corrosion behavior, specifically sulfide stress cracking (SSC) and sulfide stress cracking susceptibility. The C-ring tests were done under 2.55 % H2S (31.48 psia) and 50 % CO2 (617.25 psia). The testing was done in static environment conditions. Regardless of good SSC resistance for both materials, different pitting resistance is seen in both materials. The pitting resistance did not follow the general Pitting Resistance Equivalent Number (PREN), since SS 2507 super duplex (PREN > 40) has more pitting density than 28 Cr austenitic stainless steel (PREN < 40). SS 2507 super duplex pit shape tends to be larger but shallower than 28 Cr austenitic stainless steel. 28 Cr austenitic stainless steel has a smaller pit density, yet deeper and isolated.

Unstabilized nitrogen-containing silicon steel 03Kh18N13S2AM2VFBR-Sh (EP 302M-Sh), intended for heat exchanger tubes operating in contact with heavy liquid-metal coolants and water at temperatures of 350 to 550°С, is prone to prolonged thermal aging and sensitization, initiating local metal corrosion in water at 350°С. Changes in the chemical composition of steel and the production of pilot batches of heat exchanger tubes did not lead to an increase in their thermal stability. One of the reasons for this is the factor of nitrogen solubility in austenite, which was neglected during the development of chemical compositions of metal. The principles of alloying and the conceptual chemical composition of unstabilized austenitic steel (EP 302M1-Sh), not prone to thermal aging and sensitization at a temperature of 350°С, have been developed, which excludes the possibility of local corrosion of the heat exchanger tubes during long-term operation in water. A 25% increase in yield point at 350°С compared to steel 08Kh18N10T and the absence of susceptibility to pitting, crevice, and hideout corrosion make thermally stable steel the preferred candidate material for producing heat exchanger tubes for innovative water-cooled power reactors. A possibility of creating economically alloyed austenitic steel, characterized by thermal stability at 350 to 550°С and corrosion resistance in liquid-metal coolants and supercritical steam-water medium, is shown.

In a core disruptive accident scenario, boron carbide, which is used as a control rod material, may melt below the melting temperature of stainless steel owing to the eutectic reaction with them. The eutectic mixture produced is assumed to extensively relocate in the degraded core, and this behavior plays an important role in significantly reducing the neutronic reactivity. However, these behaviors have never been simulated in previous severe accident analysis. To contribute to the improvement of the core disruptive accident analysis code to simulate these eutectic melting and relocation behavior, the thermophysical property database of the eutectic mixture implemented into the analysis code should be developed. As part of this database development, this study measured the thermophysical properties of the eutectic mixture in the solid state. In this study, pre-alloyed austenitic stainless steel containing boron carbide, which has the prescribed concentration of boron carbide and is homogeneous, is used as eutectic samples to reduce the uncertainty of samples and achieve accurate measurement. Based on these evaluation results, the effect of adding boron carbide on the thermophysical properties of austenitic stainless steel are discussed. Furthermore, regression equations that show the temperature (and boron carbide concentration) dependence are created for each thermophysical property.

High-nitrogen austenitic stainless steel (HNASS) has many excellent properties, such as high strength and toughness, high strain-hardening ability, strong corrosion resistance and low magnetization compared with the traditional widely used Ni–Cr austenitic stainless steel. The high nitrogen content in HNASS leads to the welded joint in the risk of many problems, such as nitrogen escape and loss, nitride precipitation, formation of pores and thermal cracks, resulting in the poor welding performance. The HNASS joints without obvious defects were obtained by metal inert gas (MIG) welding and laser-MIG hybrid welding, separately. The microstructures and properties of welded joints were compared. The nitrogen content in fusion zones of the two joints was tested by an oxygen, nitrogen and hydrogen analyzer. The tensile strength and the impact absorption energy of laser-MIG hybrid welded joint were about 27% and 20% higher than those of MIG welded joint, respectively. It could be attributed to the stronger solid solution strengthening effect resulted by the high nitrogen content of laser-MIG hybrid welded joint. The finer grains and the reduction of ferrite and precipitation phase in the microstructure of laser-MIG hybrid welded joint contributed to the improvement of toughness.

The erosion-corrosion behaviors of Z2CN19·10N austenitic stainless steel in a 3.5-wt% NaCl solution with various sediment contents (7 wt%, 10 wt%, 20 wt%) and flow rates (1 m/s, 3 m/s, 5 m/s) were studied using a rotary disk erosion-corrosion test device, scanning election microscopy (SEM), potentiodynamic polarization test and potentiostatic polarization test. The results showed that sediment concentration had a smaller influence on the electrochemical corrosion behavior of Z2CN19·10N stainless steel than the flow rate and that the flow rate mainly affected the pitting potential and passivation range, but it had little influence on the potential-constant polarization. When the erosion velocity was lower than 5 m/s, mechanical erosion was the main influencing factor, and no critical flow velocities appeared.