High-nickel Steel Research Articles

Experimental and Numerical Analysis of Alkaline Exchange Membrane Water Electrolyzers

The operation of fuel cells and electrolyzers in alkaline conditions allows for the use of: i) less expensive electrocatalyst, such as nickel alloys and silver, ii) cheaper metals for porous layers and bipolar plates due to the less corrosive environment at high pH, e.g., nickel and stainless steel compared to titanium in PEMWE; and, iii) seawater for electrolysis [1]. However, it is only in the past decade that remarkable strides in polymer synthesis and stabilization techniques have enabled the fabrication of AEMs and ionomers that are stable at high pH and above 80oC, and have ionic conductivities as high as the standard PEM materials. Currently, several commercial AEMs and ionomers are available, e.g., Ionomr Aemion (hexamethyl-p-terphenyl poly(benzimidazolium)), Versogen and Sustanion. AEMWEs have demonstrated remarkable power and current densities, e.g., 2 A/cm2 at 1.8 V using 1 M KOH [2] and and 1 A/cm2 at 1.8 V using pure water and PGM-free catalysts [3]. Molero-Gonzalez et al. [4] also demonstrated AEMWE degradation rates of 13 μV/h over 8,900 h at a current density of 600 mA cm−2. Research however is still needed for the development of AEMWE with low-PGM and PGM-free electrodes that are able to operate over a wide range of operating conditions, e.g., alkalinity, temperature, pressure and low flow rate and with high durability. The development of these systems necessitates research and development in the areas of electrode fabrication, characterization, testing and numerical simulation to highlight the most critical limiting kinetic and transport processes in a wide range of available AEMs and catalysts.In this presentation, catalyst coated membranes (CCMs) fabricated in-house by inkjet printing using platinum and iridium as the cathode and anode catalysts onto reinforced Aemion+ membranes are assessed for their performance under a variety of feed methods. Three possible feed configurations are investigated: two-electrode feed, anode-only feed, and cathode-only feed, using a 1 M KOH solution as feedstock. These CCMs resulted in a performance of 0.9 A/cm2 at 2 V in two-electrode and anode-only feed configurations, but under cathode-only feed, the performance decreased to 0.55 A/cm2 at 2 V, as shown in the figure. Therefore, supplying electrolyte only to the anode does not lead to any performance penalties and eliminates the need for a gas separation unit. Short-term stability was also acceptable for anode-only and two-electrode feed but suffered under cathode-only feed. This performance disparity was not caused by an increase in membrane resistance, as the measured high frequency resistance did not change significantly. A reference electrode was integrated into the cell hardware to investigate the reasons for the difference in performance, finding that the poor cathode-only feed performance was largely caused by an increase in the anode overpotential. A two-dimensional AEMWE model was also developed to further analyze experimental results, and study ion and reaction distribution in each electrode, as well as the sensitivity of AEMWE performance on KOH concentration.Reference[1] Du et al. Chemical Reviews, 122 (13):11169-11896, 2022.[2] Fortin et al. Journal of Power Sources, 451:227814, 2020.[3] Li et al., Nature Energy, 5:378-385, 2020.[4] Molero-Gonzalez et al. Journal of Power Sources Advances 19:100109, 2023. Figure 1

Microstructural evolution of high-nickel steel during quenching, lamellarizing, and tempering heat treatment

To investigate the influence of Quenching, Lamellarizing and Tempering (QLT) heat treatment processes on the microstructural evolution of nickel alloyed steel, samples were subjected to quenching at 870 °C, followed by Lamellarizing from 720 °C to 780 °C, and tempering at 580 °C. The results indicate that the QLT treatment produces a multiphase microstructure consisting of tempered martensite and stabilized retained austenite. Lamellarizing at 770 °C produced a more uniform microstructure with reduced low-angle grain boundaries compared to 720 °C. Energy-dispersive spectroscopy (EDS) identified higher alloy element concentrations in retained austenite, contributing to its stability and enhancing low-temperature toughness. The results demonstrate that QLT heat treatment effectively modifies the microstructural characteristics and mechanical properties, offering a method to optimize material performance for specific applications.

In Situ Microstructural Evolution and Precipitate Analysis of High-Nickel Shipbuilding Steel Using High-Temperature Confocal Laser-Scanning Microscopy

This study investigates the microstructural evolution and mechanical properties of high-nickel shipbuilding steel during thermal processing using high-temperature confocal laser-scanning microscopy (HTCLSM). An in situ observation of the heating and holding processes reveals critical insights into phase transformations, grain-growth behavior, and the formation of precipitates. The experimental results demonstrate that austenitization begins at approximately 700 °C, with significant grain-boundary nucleation. At 900 °C, the formation of black precipitates was observed, and their persistence up to temperatures exceeding 1000 °C was confirmed. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses identified these precipitates as chromium carbides (Cr7C3), which significantly contribute to the material’s strength. A comprehensive analysis using transmission electron microscopy (TEM) confirmed the presence and distribution of Cr7C3 within the grains and along grain boundaries. These findings provide a deeper understanding of the microstructural dynamics in high-nickel steels, guiding the optimization of heat-treatment processes to enhance mechanical properties for maritime applications.

Optimizing Tempering Parameters to Enhance Precipitation Behavior and Impact Toughness in High-Nickel Steel

This study explores the effects of tempering on the precipitation behavior and impact toughness of high-nickel steel. The specimens underwent double quenching at 870 °C and 770 °C, followed by tempering at various temperatures. Advanced characterization techniques including optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to elucidate precipitation phenomena. Additionally, electron backscatter diffraction (EBSD) was employed to assess the misorientation distribution after tempering. Charpy impact tests were performed on specimens tempered at different temperatures to evaluate their toughness. The findings reveal that with increasing tempering temperature, the fraction of low-angle grain boundaries decreases, which correlates positively with enhanced impact toughness. The results demonstrate that tempering at 580 °C optimizes the material’s microstructure, achieving an impact toughness value of approximately 163 J.

Thermal resistance of steels with increased strength properties for pressure vessels of advanced VVER reactors of various designs

The paper considers the results of structural studies and mechanical tests after a long-term thermal exposure of laboratory heats of the metallurgically improved 15Kh2NMFA steel and steel with an increased content of nickel considered as materials for the pressure vessels of advanced VVER-type reactors of various designs. It has been shown that, both for the improved 15Kh2NMFA steel and the high-nickel steel, there are no signs of grain boundary embrittlement after an segregation provoking embrittlement heat treatment. This is explained by the extremely low grain boundary segregation of phosphorus in the initial state caused by a high degree of the structure dispersity as well as by rather a low content of impurities. Besides, no changes have been found in the yield strength value for the improved 15Kh2NMFA steel, which agrees with the structure investigation results. For the high-nickel steel, a tendency towards a minor yield strength decrease by 5 to 10% and a regular reduction of the critical brittleness temperature has been revealed. A decrease in the mechanical properties has been caused by a relatively low temperature of tempering for the high-nickel steel and, accordingly, by the potential occurrence of the structure recovery during long-term thermal exposure, as evidenced by the results of an X-ray diffraction analysis. Despite the structure recovery in the high-nickel steel under the long-term thermal exposure, the main strengthening carbide phases remain stable. Due to this, the yield strength value remains at a relatively high level that exceeds the values for the modern VVER-type vessel steels, even in the case of a thermal exposure much in excess of the expected operating conditions for advanced VVER reactors. The observed decrease of critical brittleness temperature during the long-term thermal exposure contributes to an increase in the steel resistance to brittle fracture.

Metallographic Evaluation of Increased Susceptibility to Intermediate Embrittlement of Engine Valve Forgings Made of NCF 3015 High Nickel and Chromium Steel.

This paper focused on determining the increased tendency of cracking after the die forging process of high nickel and chromium steel. The increase in carbon content in austenitic nickel-chromium steel promoted the tendency of valve forgings to forging intergranular crack on the valve head. Attention was paid to issues related to the chemical composition of the material to be considered when hot forming nickel-chromium steel components. Optical and scanning electron microscopies were used to examine the microstructure and fracture features of the samples removed from a fractured valve head. The embrittlement was due to microcavity formation at grain boundaries. Creep theory at grain boundaries was used to explain crack formation. The tensile behavior was interpreted from the evolution of the microstructure during deformation and referred to intermediate brittleness to explain the effect of carbon. It was found that the increased carbon content of the nickel-chromium steel and the strong undercooling observed at the edges of the valve head are factors that promote a reduction in grain boundary cohesion and enhance intermediate temperature embrittlement. Finally, it was found that the formation of a heterogeneous structure manifested by the presence of grain boundary M23C6-type carbides in the austenitic matrix was most likely related to the occurring brittleness.

(Invited) Aemion+® AEM Water Electrolysis with Excellent Iridium-Free Performance and Industrially Relevant Stability in Hot, Caustic Electrolyte

Hydrogen has a unique ability to maximize the utility of and enable new business models for intermittent renewable deployment. It can be stored cost-effectively in geological storage, transported between regions to suit geographic needs and bridge Dunkelflautes. Global electrolysis capacity must increase from the current <2 GW to 850 GW in 2030 (IEA Net Zero 2050) and in excess of 3500 GW in 2050 to enable this transition.Both traditional Alkaline (AWE) and proton-exchange membrane electrolyzers (PEMWE) are mature technologies that are anticipated to split the overall market share. However, each of these technologies face fundamental challenges:AWE operate at low current density, requiring large and difficult to transport systems, require high concentration electrolytes (e.g. 30 wt% KOH) to conduct hydroxides and ensure low gas solubilities for safety, which necessitates the use of expensive and difficult to machine high-nickel steels, especially in advanced, pressurized designs. Additionally, the porous nature of the electrode separator (e.g. Zirfon) compromises the desired dynamic load for pairing with intermittent renewables.PEMWE use a proton-conductive membrane to enable high current densities, dynamic loads, and differential hydrogen pressures, however, the most efficient operation requires iridium catalyst, which presents a near-term challenges with scalability, together with Ti and PGM structural elements that further impede cost-effectiveness.Alkaline anion-exchange water electrolyzers (AEMWE) address both of these challenges by operating with a cohesive, hydroxide-transporting membrane together with alkaline electrolyte to enable high efficiency, high current density operation, without iridium electrocatalysts or other scarce or expensive components. The realization of capital cost-effectiveness, dynamic load, and compact systems in one technology enables the most cost-effective green hydrogen and represents a step-change in the trajectory towards the DOE Hydrogen Shot target of $1/kg.The instability of alkaline anion exchange membrane chemistries based on quaternary amines or pendant imidazolium groups in relevant temperatures and alkalinities to industrial operations have historically resulted in untenable compromises and too-short lifetimes for industrial-scale deployment. Ionomr's Aemion+® AF2-AWP8-75-X and AF3-HWK9-75-X membranes are based on a sterically-protected imidazolium chemistries that are chemically robust (e.g. 6 months, 1 M, 80 °C without alteration to chemical or mechanical properties), and additionally exhibit low swelling to provide mechanical integrity to electrodes and enable operation in low concentration electrolytes. These membranes are an enabling technology for long-duration AEM water electrolysis.This talk highlights how Ionomr's Aemion+® membranes demonstrate target performances (e.g. >2 A/cm² at 2 V) with non-PGM OER catalysts with no apparent losses to 1000 hours operation across several configurations at ≥70 °C and 1 M KOH operation, and several longer lifetime demonstrations including 1 year durability using AWE electrodes and >6 months including hydrogen crossover measurement. This talk further highlights the potential for the three-dimensionality of electrodes in alkaline AEMWE and the necessary processing and operational requirements to create reproducible and stable GDEs with catalyst ink-based deposition techniques. Figure 1

Phased Array Ultrasonic Testing for Inspection of LNG Storage Tank

Liquefied natural gas (LNG) is liquefied at -162°C at atmospheric pressure and stored in the inner shell. Due to the transport and storage characteristics of such low temperature conditions, 9% high nickel steel, which shows excellent strength and toughness even at low temperatures, is used for the inner wall. On the other hand, the base material of the inner wall has a tempered martensite structure, whereas the weld metal has an Inconel- based austenite structure with high damping properties in acoustics. Also, the weld metal is composed of an anisotropic structure completely different from the base material. These are considered obstacles in non-destructive testing. We applied automated phased array ultrasonic testing(PAUT) as a replacement of radiographic testing in inspection of LNG storage tank. To obtain the reference value data, a reference specimen for each thickness was prepared, and an automatic scanning device was designed and manufactured. Also, a customized phased array(PA) probe was developed and applied. All parts are integrated and operated as one system, and the data is analyzed and stored through an operating program developed in-house. The current system has proven its performance through field application to a much-improved level in the existing scanning device, probe and application method. In conclusion, it was proved that our technology can be commercialized by showing excellent detection ability.

Structural features ensuring the increase of service characteristics of high-nickel steels for pressure vessels of prospective energy-generation reactors

Complex structure studies and mechanical tests of low carbon Ni–Cr–Mo–V steels with low and high nickel content (low-Ni and high-Ni steels) were performed.Mechanical tests showed that high-Ni steels in initial state are characterized by higher strength properties and lower values of critical temperature of brittleness in comparison with low-Ni steels.Estimation of input of various structural elements in ensuring yield strength and brittle fracture stress (which is connected with critical temperature of brittleness) was performed. It was shown that increased strength characteristics of high-Ni steels are determined mostly by higher density of nanoscale carbide precipitations and dislocations. It was also shown that lower critical temperature of brittleness of high-Ni steels is associated with lower width of substructural blocks and, consequently, with higher number of barriers to brittle transcrystalline crack propagation.

Influence of thermally grown oxides on interfacial friction during hot deformation of large-size forging ingots

High-strength steels are pre-heated in gas-fired furnaces before undergoing the open-die forging process. This process increases thermal oxidation on steel surfaces, affecting the interfacial friction between ingot and anvils during deformation. Two medium carbon high-strength steels with different nickel contents were oxidized, and the mechanical characteristics of oxide layers were investigated by micro and nano-indentation methods. It was found that the formed layers on high nickel steel had lower Young modulus and hardness compared to the steel with lower nickel. Finite element modeling and ring tests were used to assess oxide layers' effect on interfacial friction during deformation. The results demonstrated that oxide layers' formation decreased the interfacial friction and deformation load, acting as lubricants at high temperatures.

Diffusionless α′ to γ transformation and its effect on hot ductility in a high-nickel steel

The role of diffusionless α′ to γ transformation on the microstructure evolution and hot ductility of high-nickel steel is investigated. In-situ Auger electron spectroscopy fracture test reveals the correlation of ductility loss and sulfur segregation at the grain boundary. The α′ to γ transformation start temperature is measured by heating the initial α′-martensite at various rates. The transformation temperature remains constant when the heating rate is higher than 15 °C/s. Despite the α′ to γ phase transformation, the diffusionlessly transformed specimen shows a similar γ grain size with the initial prior γ grain size. The γ grain size decreases dramatically after the continuous annealing of the transformed specimen. The temperature-dependent recrystallization behavior and corresponding hot-ductility are evaluated. The improved hot ductility is achieved by active recrystallization at 900–1100 °C. Due to the late recrystallization behavior, the improvement of hot ductility is limited after annealing at 800 °C. The origin of hot ductility loss and enhancement depending on the thermal cycles is discussed by sulfur segregation at the grain boundary and recrystallization behavior after diffusionless transformation.

Effect of severe plastic deformation on aging kinetics of precipitation hardening 17–4 stainless steel

Precipitation hardening (PH) stainless steels are high chromium, high nickel and low carbon stainless steels which were mainly developed to provide high strength and fracture toughness while maintaining good corrosion resistance. Precipitation hardening treatment involves solution annealing treatment followed by aging treatment which is applied on these steel to impart high hardness, fracture toughness and strength. The PH stainless steels develop high strength and toughness through additions of copper, aluminum, titanium, niobium, vanadium, and/or nitrogen, which form precipitates during aging heat treatment. In this work effect of severe plastic deformation (SPD) on aging kinetics of pH 17–4 stainless steel was investigated. Severe plastic deformation was applied on the surface of pH stainless steel specimens by shot-peening process. For comparison, aging of specimens with shot-peening and without shot-peening were done. After aging specimens were characterized by microhardness testing, optical and electron microscopy. The results showed considerably high hardness in the range of 617–649 HV for pH 17–4 stainless steel after aging on severely deformed specimens which is nearly 29% higher than the specimens which were aged without SPD.

Stable high-nickel austenitic steel produced by electron beam additive manufacturing using dual wire-feed system

Phase composition, microstructure, tensile properties and fracture mechanism of the high-nickel austenitic steel produced by a dual wire-feed electron beam additive manufacturing were studied. The joint using of NiCr-alloy and 321-type stainless steel wires in additive manufacturing process assists the formation a fully austenitic structure in as-built billet. Its microstructure is stable against deformation-induced γ → α’ martensitic transformation due to the 5–7 wt.% increase of nickel concentration relative to the initial steel wire composition. The high-nickel steel possesses high ductility (δ ≈ 54%) and plastic flow behavior similar to the conventional cast 321-type steel subjected to a solid-solution treatment.

The Impact of the Lubricant Dose on the Reduction of Wear Dies Used in the Forging Process of the Valve Forging.

The paper presents the results of research on the influence of the settings of lubrication and cooling system parameters (solenoid valve opening time and lubricant feed pressure in terms of its quantity) in order to select the optimal lubricating conditions and thus reduce the wear of the dies used in the first forging operation of the valve forging made of high-nickel steel. Based on the observation of lubrication in the industrial process, it was found that a significant part of the lubricant fails to reach the die cavity, reaching the outside of it, which causes die wear due to seizure resulting from adhesion of the forging material to the tool surface as well as high lubricant consumption and dirt in the press chamber. The authors proposed their own mobile lubricating and cooling system, which allows for a wide range of adjustments and provided with automatic cleaning procedures of the entire system, unlike the fixed lubrication system used so far in the industrial process. First, tests were carried out in laboratory conditions to determine the highest wettability and the lubricant remaining inside the tool cavity. These tests determined the lubrication system parameter settings that ensured that the greatest amount of lubricant remains in the cold die cavity without the forging process. Then, to verify the obtained results, tests were carried out in the industrial process of hot die forging of valve forgings for short production runs of up to 500 forgings. The results were compared with the measurement of changes in the geometry of tools and forgings based on 3D scanning and surface topography analysis with the use of SEM (Scanning Electron Microscope). For the best results (the variant of the setting of the dose and the time of exposure to lubricant), the forging process was carried out with the use of a new tool up to the maximum service life.

A new type of gadolinium-rich precipitate in alloy steels

We designed three gadolinium-containing alloy steels (austenitic stainless, high nickel, and high manganese steels) as neutron-absorbing structural materials and analysed the gadolinium-rich precipitates of each alloy. The precipitates contained in each alloy were identified by scanning and transmission electron microscopy. Different types of precipitates were observed in each alloy. In particular, in the high manganese steel, a Fe-rich M12Gd phase was observed first. The melting temperature of Fe-rich M12Gd, which melts at a higher temperature than other precipitates, is ∼ 1270∘C. It can therefore be utilised to design an alloy with better hot workability and weldability.

Hydrogen effect on the high-nickel surface steel properties during machining and wear with lubricants

Purpose: The aim of the proposed research is to investigate the hydrogen effect on the high-nickel steel surface properties changing during machining and wear with participation of lubricant-cooling environments. Design/methodology/approach: The approach of the fracture mechanics and physicalchemical methods surface properties investigation was used to formulate the conclusions. Applying of lubricant-cooling (liquid, solid, gaseous) technological environments (LCTE) has change the morphology of chips and roughness of contact 23Ni1Mo3Ti steel surfaces depending on the experimentally fixed hydrogen concentrations (4.62…12.0 ppm). It correlates with both the roughness of the treated surface and the nature of the cutting products fragmentation: the maximum concentration of hydrogen - in the chips coincides with the minimum size of its defragmentation and reduction of the surface roughness. For nitrogen and oxygen, a similar relationship is traced poorly. Findings: On the basis of the fracture mechanics approaches it is confirmed, that in the conditions of the application of hydrogen containing (as chemical composition) (up to 12 ppm) and hydrogen accumulated (in nano container) (up to 600 ppm) LCTE, hydrogen enters the near crack initiation contact zone before fracture and taking part in changing structural material fracture mechanisms, improves its mashinning processes. Research limitations/implications: The results obtained on laboratory specimens should be tested during machining of real details made from high-nickel steel. Practical implications: The created technological approaches can be used in practice evaluation of mechanical properties and residual of modern gas turbine parts. Originality/value: It was shown, that hydrogen containing (in chemical composition) and hydrogen accumulated (in nano container) LCTE permits the hydrogen to enter in the near crack initiation contact zone before fracture and taking part in changing structural material fracture mechanisms.

Wear Mechanisms Analysis of Dies Used in the Process of Hot Forging a Valve Made of High Nickel Steel

Wear Mechanisms Analysis of Dies Used in the Process of Hot Forging a Valve Made of High Nickel Steel

Metallurgical characteristics of armour steel welded joints used for combat vehicle construction

Abstract Austenitic stainless steel (ASS) and High nickel steel (HNS) welding consumables are being used for welding Q&T steels, as they have higher solubility for hydrogen in austenitic phase, to avoid hydrogen induced cracking (HIC) but they are very expensive. In recent years, the developments of low hydrogen ferritic steel (LHF) consumables that contain no hygroscopic compounds are utilized for welding Q&T steels. Heat affected zone (HAZ) softening is another critical issue during welding of armour grade Q&T steels and it depends on the welding process employed and the weld thermal cycle. In this investigation an attempt has been made to study the influence of welding consumables and welding processes on metallurgical characteristics of armour grade Q&T steel joints by various metallurgical characterization procedures. Shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes were used for making welds using ASS, LHF and HNS welding consumables. The joints fabricated by using LHF consumables offered lower degree of HAZ softening and there is no evidence of HIC in the joints fabricated using LHF consumables.

Failure analysis of high nickel alloy steel seal ring used in turbomachinery

Abstract The purpose of this study is to identify the failure cause of the steel seal ring used in nuclear steam turbines. New high nickel steel alloy seal ring was compared with the failed seal ring. Metallographic analysis, scanning electron microscopy, nanoindentation and in-situ tensile testing were used to analyze the reasons of the seal ring failure at both macroscopic and microscopic scales. The main reason of the seal ring failure is a combination of stress and elevated temperature during turbine operation. Complex work environment caused recrystallization and recovery, resulting in grain refinement and secondary phases precipitation. Many secondary phase precipitates appeared at grain boundaries during use, causing formation of microvoids and cracks, ultimately leading to ring failure.

Advanced reactor vessel steels for reactors with supercritical coolant parameters

A set of studies, tests, and technological works is performed to design promising high-strength vessel steels for reactors with supercritical coolant parameters. Compositions and technological parameters are proposed for the production of reference steel (within the limits of the grade composition of 15Kh2NMFA-A steel) and high-nickel steel. These steels are characterized by high properties, including metallurgical quality and service and technological parameters. Steel of the reference composition has high (higher by 15%) strength properties, improved viscoplastic properties, and ductile–brittle transition temperature tc of at most–125°C. The strength properties of the high-nickel steel are higher than those of the existing steels by 40–50% and higher than those of advanced foreign steels by 15–20% at ductile–brittle transition temperature tc of at most–165°C. Moreover, the designed steels are characterized by a low content of harmful impurity elements and nonmetallic inclusions, a fine-grained structure, and a low susceptibility to thermal embrittlement.