Amount Of Niobium Research Articles

Жароміцні інтерметалідні сплави та особливості їх легування

The work considers the prerequisites for the development of creep-resistant and heat-resistant alloys, based on intermetallics, taking into account the optimal combination of their physical and mechanical properties, as well as structural characteristics. It is shown that there is a sufficient number of intermetallics, which have a density lower than iron-based alloys, which, in combination with high melting temperatures and heat resistance, makes them promising materials for aerospace application, in particular, for gas turbine engine parts manufacturing. The most suitable creep-resistant and heat-resistant intermetallics can be called aluminides and silicides of titanium, nickel and molybdenum. For these compounds, it is possible to combine high values of specific strength with alloying-favorable types of crystal lattice. One of the most important and common creep-resistant alloys based on intermetallics is Ni3Al with FCC lattice. For this material, complex optimized alloying is the main way to increase creep resistance. The heat resistance of such alloys is significantly increased by applying ceramic coatings. Titanium aluminides Ti3Al and TiAl mainly have only a low density among the advantages. Their fragility at room temperatures and tendency to superplasticity at high temperatures significantly limits their application. The impact of disadvantages may be reduced by applying thermomechanical processing of such materials, which aims to change their structure. Alloying titanium aluminides with a large amount of niobium was chosen as a solution that significantly reduced marked week sides of Ti-Al intermetallic alloys. As a result, this led to the creation of a new alloy based on intermetallic Ti2AlNb with a high set of operational characteristics. Mo-Si and Mo-Si-B can be considered as one of the most perfect systems for creating heat-resistant intermetallic alloys. They combine an acceptable density, high creep and heat resistance, which can be additionally increased by reinforcing with ceramic particles. Keywords: intermetallic-based alloys, creep resistance, alloying, Ni-Al, Ti-Al, Mo-Si, Mo-Si-B.

Ta/Nb doping motivating cubic phase stability and CO2 tolerance of Sr2Co1.6Fe0.4O6-δ double perovskite for high-performing SOFC cathode

Developing cathodes that are both phase-stable and tolerant to carbon dioxide (CO2) is a crucial and challenging task for solid-oxide fuel cells (SOFCs) operating at reduced temperatures. The activity of oxygen reduction reaction (ORR) in SOFC cathodes is typically influenced by factors such as geometric features and oxygen vacancies. In this study, new and robust cathodes for SOFCs, Sr2Co1.5Fe0.4Ta0.1O5+δ (SCFT) and Sr2Co1.5Fe0.4Nb0.1O5+δ (SCFN) are developed by doping a small amount of niobium (Nb) and tantalum (Ta) into Sr2Co1.6Fe0.4O5+δ (SCF) using a simple solid-state reaction technique. The effects of Nb/Ta doping on the crystal structure, oxygen vacancies, electrical conductivity, and electrochemical properties of SCFT and SCFN are investigated. The results reveal that these materials possess a fully cubic structure in the Fm-3m space group, with improved oxygen vacancy and electrical conductivity. They also exhibit good chemical compatibility with electrolytes at 1100 °C for 8 h and remain thermally stable when exposed to air and CO2 at 700 °C, without any additional phase formation. The area-specific resistance (ASR) of the SCFT cathode is found to be only 0.06 Ω cm2, whereas the SCFN cathode has an ASR of 0.10 Ω cm2. The superior performance of SCFT can be attributed to the higher oxygen vacancy, which enhances oxygen surface exchange kinetics and diffusivity compared to SCFN. When tested in a single cell using humidified H2 as the fuel and ambient air as the oxidant, the SCFT cathode achieves a power density of 656 mW cm−2 at 700 °C, while the SCFN cathode reaches 559 mW cm−2, indicating the potential of SCFT as a promising cathode material for SOFCs. The excellent performance of these materials can be attributed to their mixed electronic-ionic conduction properties, unique structural features, and high observed oxygen vacancy, which contribute to their remarkable electronic conductivity and significant ionic mobility.

MICROSTRUCTURE EVOLUTION AND PHASE TRANSFORMATIONS IN MICROALLOYED ARMOX 500T STEEL DURING A DILATATION PROCESS

With this work we successfully developed two modified Armox 500T alloys using microalloying with different amounts of niobium (Nb) and boron (B) to obtain a finer grain size, which in return enhances the remnant properties. Furthermore, different heat-treatment cycles were designed and performed using a quenching dilatometer to study the combined effect of thermal cycling and microalloying with Nb and B on the microstructure and transformation temperatures including the start and finish temperature of the austenite transformation (Ac1, Ac3) and the martensite start and finish temperature (Ms, Mf) of the investigated alloys. Dilatometry results show that increasing the content of Nb from 0.07 w/% to 0.13 w/% and B from 0.0035 to 0.0046 w/% increases the temperature range between Ac1 and Ac3 by 55 °C, indicating a broader range for changing heat-treatment temperatures. In addition, the Ms temperature is reduced by 13 °C due to austenite refinement caused by the microalloying of Nb and B. The effect of the annealing temperature at a constant heating rate showed a significant impact on the austenite grain size and hardness. Furthermore, the kinetics of phase transformations were theoretically studied using Thermo-Calc, and the numerical predictions were confirmed experimentally with dilatometry results. Metallography investigations using a scanning electron microscope (SEM) and an optical microscope (OM) were conducted to evaluate the microstructure evolution of the developed alloys. Hardness tests were performed to evaluate the effect of the grain refinement of martensite lathes caused by microalloying with Nb, B, and heat-treatment thermal cycling. It is found that the hardness of the modified Armox alloys in this research was improved by 14 % in comparison with the conventional Armox 500T.

The interplay between dopant and a surface structure of the photocatalyst – The case study of Nb-doped faceted TiO2

Anatase nanoparticles, exposing the majority of the {0 0 1}, {1 0 0} and {1 0 1} facets were synthesized and doped with different niobium amount to investigate the self-trapping of the excess electrons and resulting photocatalytic activity. Photocatalyst structure and presence of excess electrons inside the obtained Nb-doped anatase samples was confirmed by the combination of structural and spectroscopic analyses. Only for the {1 0 1} facets, introduced electrons were found to localize on the surface titanium sites, as long as the analysis was performed in the ambient environment. The photocatalytic activity data, studied in the reaction of 4-nitrophenol reduction and phenol oxidation, show that the dopant-introduced electrons might increase photocatalytic activity only for the anatase structures exposing {0 0 1} and {1 0 0} facets. Ultimately, the dopant effect on the photocatalytic activity depends on the exposed facet, which might be investigated for other systems to increase their applicability.

Surface Stabilization of Cobalt-Free LiNiO2 with Niobium for Lithium-Ion Batteries

Lithium nickel oxide (LiNiO2) is a promising next-generation cathode material for lithium-ion batteries (LIBs), offering exceptionally high specific capacity and reduced material cost. However, the poor structural, surface, and electrochemical stabilities of LiNiO2 result in rapid loss of capacity during prolonged cycling, making it unsuitable for application in commercial LIBs. Herein, we demonstrate that incorporation of a small amount of niobium effectively suppresses the structural and surface degradation of LiNiO2. The niobium-treated LiNiO2 retains 82% of its initial capacity after 500 cycles in full cells with a graphite anode compared to 73% for untreated LiNiO2. We utilize a facile method for incorporating niobium, which yields LixNbOy phase formation as a surface coating on the primary particles. Through a combination of X-ray diffraction, electron microscopy, and electrochemical analyses, we show that the resulting niobium coating reduces active material loss over long-term cycling and enhances lithium-ion diffusion kinetics. The enhanced structural integrity and electrochemical performance of the niobium-treated LiNiO2 are correlated to a reduction in the formation of nanopore defects during cycling compared to the untreated LiNiO2.

ТЕХНОЛОГІЧНІ ОСОБЛИВОСТІ ОДЕРЖАННЯ СПЛАВІВ ТА ЛІГАТУР СИСТЕМИ TI–ZR–NB–SN В УМОВАХ ЕЛЕКТРОННО-ПРОМЕНЕВОЇ ЛИВАРНОЇ ТЕХНОЛОГІЇ

Electron beam casting technology is a unique method for obtaining cast products and semi-finished products from a wide range of titanium alloys. This technology can be very promissing in production of biocompatible titanium alloys for endoprosthesis. A particularly difficult and important task in this context is preparation of Ti-Zr-Nb-Sn system alloys with high strength and low modulus of elasticity. As a result of experimental development of specified alloys melt preparation technological modes, possibility of obtaining complex titanium alloys with a high content of zirconium and niobium was shown. It is also determined, that when the niobium content in the charge is more than 30 % wt. there is a decrease in the concentration of titanium and zirconium in the melt due to their freezing on the walls of the skull. As a result, there is a change in the chemical composition of the melt, the amount of niobium in which can exceed 50 % wt. Maximum amount of tin that can be assimilated in titanium-based melts under EBCT conditions is 5 % wt., and niobium-based melts are twice less. It has been proven that obtaining melts of Ti-Zr-Nb-Sn system with a precise chemical composition, using the chosen method, is a difficult and still unsolved problem, but due to the possibility of melting alloys with a high content of niobium and zirconium in its conditions, this method is effective in the production of master alloys and ingots for the production of powders used as raw materials for additive tmanufacturing. Keywords: titanium alloys for endoprosthesis, foundry production, Ti-Zr-Nb-Sn, electron-beam casting technology.

Preparation of Nanocrystalline Nb-Doped SnO2 on Mesoporous Carbon for PEFC Electrocatalysts

Pt-based catalysts on carbon support (Pt/C) is widely used as polymer electrolyte fuel cell (PEFC) electrocatalyst. However, under high potential at the cathode, Pt detachment and aggregation due to carbon corrosion can occur. Therefore, conventional Pt/C electrocatalysts have a difficulty in durability[1]. SnO2 is known to be stable at high potentials in a PEFC cathode environment. Our research group has developed an electrocatalyst that uses carbon as a support framework, with SnO2 supported on it and Pt catalyst particles on SnO2 (Pt/SnO2/Carbon), achieving high durability [2-4]. However, the electronic conductivity of tin oxide is relativity low and the ORR activity with SnO2-based support tends to be inferior to that of Pt/C, the standard catalyst.Therefore, the objective of this study is to develop an alternative electrocatalyst that exhibits high ORR activity while maintaining high durability by using mesoporous carbon (MC) with nano-sized mesopores as a support framework and reducing the amount of SnO2 used by suppressing its grain growth.Tin oxide nanoparticles were supported on mesoporous carbon (CNovel\U0001f12c, TOYO TANSO) using ethoxide reagents. Tin oxide was doped with a small amount of niobium to improve the conductivity of SnO2 [5]. Electrocatalysts were prepared by loading of Pt particles of a few nm in diameter on the prepared supports using the Pt acetylacetonate method [6].Pt loading was examined by ICP Atomic Emission Spectroscopy. The crystallite size of SnO2 and Pt, and possible alloying of Pt and Sn were checked by XRD measurements. The electrochemical surface area (ECSA) of Pt was obtained by cyclic voltammetry (CV). The oxygen reduction reaction (ORR) activity was evaluated by determining the activation-dominant current value in the rotating disk electrode (RDE) measurement. The durability of the catalysts was evaluated by applying 60,000 of potential cycles between 1.0 and 1.5 VRHE simulating the start-up and shutdown of PEFC systems. The microstructure of electrocatalysts was observed using a field emission electron scanning microscope (SU9000, Hitachi High-Tech Corporation).Figure 1 shows (a) scanning and (b) transmission electron microscope images of the electrocatalysts before Pt loading (Sn0.98Nb0.02O2/MC). It was confirmed that tin oxide was loaded within the mesopores besides the MC surface. Furthermore, as shown in the transmission image in Fig. 1(b), the particle size of SnO2 on the surface is about 10 nm, while the particle size of SnO2 within the mesopores is about 5 nm, indicating that the presence of mesopores suppresses particle growth. Latest results of electrochemical properties of Pt-based electrocatalysts using Nb-doped SnO2 and MC after Pt catalyst decoration will be reported in this presentation. References T. Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 169, 044523 (2022).Y. Nakazato, D. Kawachino, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 165 (14), F1154 (2018).S. Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 165 (14), F1164 (2018).T. Yoshizumi, M. Nagamine, Z. Noda, J. Matsuda, A. Hayashi, and K. Sasaki, ECS Trans., 92 (8), 479 (2019).K. Sasaki, F. Takasaki, Z. Noda, S. Hayashi, Y. Shiratori, and K. Ito, ECS Trans., 33 (1), 473 (2010).A. Hayashi, H. Notsu, K. Kimijima, J. Miyamoto, and I. Yagi, Electrochim Acta., 53, 6117 (2008). Figure 1

The promoter effect of Nb species on the catalytic performance of Ir-based catalysts for VOCs total oxidation

Ir/TiO2 catalysts promoted by niobium have been synthesized, characterized by different complementary techniques, and tested for the total oxidation of a set of alkanes and their mixtures. The addition of appropriate amounts of niobium to Ir/TiO2 catalysts resulted in a remarkable increase in the catalytic activity compared to the Nb-free Ir/TiO2 catalysts. The promotion caused by the presence of niobium has been related to the massive presence of isolated IrOx surface species which, interestingly, present remarkable reducibility and, consequently, excellent catalytic activity. Conversely, the IrOx species formed in the catalyst in the absence of niobium also include IrO2 clusters with lower intrinsic reactivity. Similarly, Nb-loadings exceeding the theoretical monolayer tends to the formation of bulk Nb2O5 species on the titania surface that provokes the formation of IrO2 nanoclusters. A positive influence on the reactivity of non-stoichiometric surface Ti3+ species that generates oxygen vacancies is also observed.

Metal-Ceramic Beads Based on Niobium and Alumina Produced by Alginate Gelation.

Full metal-ceramic composite beads containing different amounts of niobium and alumina, particularly 100 vol% alumina, 100 vol% niobium, and 95/5 vol% niobium/alumina, were produced by the alginate gelation process. The suspension for bead fabrication contained sodium alginate as gelling agent and was added dropwise into a calcium chloride solution to trigger the consolidation process. After debinding in air, sintering of the composite beads was performed under inert atmosphere. Samples in green and sintered state were analyzed by digital light microscopy and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Investigations by mercury intrusion porosimetry revealed that pure alumina beads featured smaller pores compared to composite beads, although the open porosities were comparable. The fracture strength was evaluated on single beads. Contrary to the pure alumina, the composite beads showed a clear plastic deformation. Pure niobium beads showed a ductile behavior with very large deformations. XRD analyses revealed the presence of calcium hexaluminate and beta-alumina as minor phases in the alumina beads, while the composite ones contained about 25 wt% of impurities. The impurities comprised NbO arising from the oxidation, and β-Nb2C, from the reaction with the residual sodium alginate.

NbCl5-Mg Reagent System in Regio- and Stereoselective Synthesis of (2Z)-Alkenylamines and (3Z)-Alkenylols from Substituted 2-Alkynylamines and 3-Alkynylols.

The reduction of N,N-disubstituted 2-alkynylamines and substituted 3-alkynylols using the NbCl5–Mg reagent system affords the corresponding dideuterated (2Z)-alkenylamine and (3Z)-alkenylol derivatives in high yields in a regio- and stereoselective manner through the deuterolysis (or hydrolysis). The reaction of substituted propargylamines and homopropargylic alcohols with the in situ generated low-valent niobium complex (based on the reaction of NbCl5 with magnesium metal) is an efficient tool for the synthesis of allylamines and homoallylic alcohols bearing a 1,2-disubstituted double bond. It was found that the well-known approach for the reduction of alkynes based on the use of the TaCl5-Mg reagent system does not work for 2-alkynylamines and 3-alkynylols. Thus, this article reveals a difference in the behavior of two reagent systems—NbCl5-Mg and TaCl5-Mg, in relation to oxygen- and nitrogen-containing alkynes. A regio- and stereoselective method was developed for the synthesis of nitrogen-containing E-β-chlorovinyl sulfides based on the reaction of 2-alkynylamines with three equivalents of methanesulfonyl chloride in the presence of stoichiometric amounts of niobium(V) chloride and magnesium metal in toluene.

Trace amount of niobium doped [formula omitted]-Ga[formula omitted]O[formula omitted] deep ultraviolet photodetector with enhanced photo-response

The growth of trace amount of niobium (Nb) doped β-Ga2O3 thin films have been demonstrated on (0001) sapphire substrates by radio frequency magnetron co-sputtering method. The crystallization, morphology and optical properties of Nb doped β-Ga2O3 films have been investigated. The deep ultraviolet (DUV) photodetector with a metal–semiconductor–metal structure based on trace amount of Nb doped β-Ga2O3 thin film was fabricated. The DUV photodetector exhibits high photo-to-dark-current ratio and fast photo-response speed, suggesting the performance of β-Ga2O3 photodetector can be improved by doping trace amount of Nb in β-Ga2O3 thin film.

Omega Phase Formation in Ti-3wt.%Nb Alloy Induced by High-Pressure Torsion.

It is well known that severe plastic deformation not only leads to strong grain refinement and material strengthening but also can drive phase transformations. A study of the fundamentals of α → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Before HPT, a Ti–3wt.%Nb alloy was annealed at two different temperatures in order to obtain the α-phase state with different amounts of niobium. X-ray diffraction analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for the characterisation of phase transitions and evolution of the microstructure. A small amount of the β-phase was found in the initial states, which completely transformed into the ω-phase during the HPT process. During HPT, strong grain refinement in the α-phase took place, as did partial transformation of the α- into the ω-phase. Therefore, two kinds of ω-phase, each with different chemical composition, were obtained after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one from the α-phase. It was also found that the transformation of the α-phase into the ω-phase depended on the Nb concentration in the α-Ti phase. The less Nb there was in the α-phase, the more of the α-phase was transformed into the ω-phase.

Investigation of CGHAZ Simulations of Low-Carbon Bainitic Steels

The effect of ten different combinations with various amounts of niobium (0-0.6 wt.%) and chromium (1-4 wt.%) on weldability and mechanical properties of thermomechanically rolled and direct-quenched low-carbon (0.035 wt.%) microalloyed bainitic steel were investigated. Two compositions were alloyed with boron to increase the hardenability, and two with titanium to improve the toughness properties in heat affected zone. The target of the study was to produce steel with 700 MPa yield strength combined with good impact toughness. Coarse grained heat affected zone (CGHAZ) simulations were performed using the Gleeble 3800 thermomechanical simulator to evaluate the weldability of the investigated steels using cooling time from 800 °C to 500 °C (t8/5) of 5 s and 15 s to simulate different heat inputs in actual welding procedure. Microstructures were characterized using light optical microscopy, and hardness profiles of simulated heat affected zones were determined as well as Charpy-V impact toughness at-40 °C and-60 °C. Shorter t8/5 time (5 s) produced generally better impact toughness properties compared to longer t8/5 -time (15 s). Steels with 4 % Cr had the highest impact energies. Generally, more softening occurred with longer t8/5-time (15 s). However, Cr and Nb alloying decreased the amount of softening in the CGHAZ region, especially with longer t8/5 -time. These results indicate that even with higher t8/5 -time, it is possible to achieve strength properties equivalent to the base material in the CGHAZ region by Cr and Nb alloying.

High-Temperature Oxidation Performance of Niobium-Containing Ferritic Stainless Steel for Exhaust Manifold

The high-temperature oxidation behavior of niobium-containing ferritic stainless steel suitable for exhaust manifolds was studied at 1000 °C for up to 50 h. The results showed that for the steels with the stable element Nb addition, the oxidation weight gain per unit area was reduced and the formation of spinel-like oxide MnCr2O4 was promoted. A small amount of niobium tended to segregate at the oxide/metal interface to form the Laves phase, which promoted the formation of the inner oxide layer of SiO2 and improved the oxidation resistance of the material. When the content of niobium increased to 0.7% (mass fraction), the formation of the SiO2 oxide layer was inhibited. Adding 0.5% Nb, the weight gain of the sample was 2.33 mg cm−2 and the oxide film thickness was only 8.1 μm, showing the best oxidation resistance.

Flotation-Calcination-Magnetic Separation Hybrid Process for Concentration of Rare Earth Minerals Contained in a Carbonatite Ore

A hybrid process consisting of flotation and magnetic separation has been developed to concentrate multi-phase rare earth minerals associated with a carbonatite ore that contains a significant amount of niobium. The deposit is known to contain at least 15 different rare earth minerals identified as silicocarbonatite, magnesiocarbonatite, ferrocarbonatites, calciocarbonatite, REE/Nb ferrocarbonatite, phosphates and niobates. Although no collector exists to float all the different rare earth minerals, the hydroxamic acid-based collectors have shown adequate efficiency in floating most of these minerals. 92% recovery of total rare earth oxide (TREO) and niobium in 45% mass was possible at d80 of <65 microns grind size. It was also possible to reduce the mass pull to 28%, but TREO and Nb’s recovery dropped to 85%. Calcination of the concentrate followed by quenching and fine grinding to <25 μm allowed upgrading the flotation concentrate by magnetic separation. It was demonstrated that at least 87% TREO and 85% Nb could be recovered in 16% of the feed mass. The paper discusses the overall concept of the flowsheet and the experimental strategies that led to this process.

Exploring the potential of biomass-templated Nb/ZnO nanocatalysts for the sustainable synthesis of N-heterocycles

Herein, we report a Nb/ZnO nanocatalyst for the efficient conversion of levulinic acid, a platform molecule easily obtained from lignocellulosic biomass, to N-heterocycles under mild reaction conditions and the absence of solvent. Nb/ZnO nanocatalysts were synthesized by a mechanochemical-assisted and sacrificial template method, involving orange peel valorization toward nanostructured materials. Two different synthetic approaches, either one-step or two-step, as well as the amount of niobium deposited onto the ZnO support were investigated in order to obtain the nanocatalyst with the optimal catalytic properties. Results revealed the critical role of the niobium for LA conversion. The nanocatalyst containing 10 wt% of niobium and prepared following a two-step approach (10 %Nb/ZnO_2) exhibited the best catalytic performance with a 94.5% of conversion and 97.4% of selectivity towards one specific N-heterocycle compound. This work exemplifies the possibility of sustainable production of value-added compounds, in particular N-heterocycles, from biomass-derived feedstocks by playing with the design of improved catalysts. Importantly, this research area provides sustainable alternatives to the current chemical industry that is heavily dependent on fossil fuels.

Investigation on strengthening and toughening mechanisms of Nb-Ti-ZrB2 metal matrix ceramic composites reinforced with in situ niobium and titanium boride

Nb-Ti-ZrB2 metal matrix ceramic composites with a fixed atomic ratio Nb/Ti = 2/1 and ZrB2 volume fraction changing from 0, 11 vol%, 23 vol% to 36 vol% were hot pressed at 1600 °C under 30 MPa. The influence of ZrB2 content and Ti addition on the phase constitution, microstructure evolution, toughening mechanisms and strengthening mechanisms were investigated. It was shown that the formation of in situ Nb-rich (Ti,Nb)B and Ti-rich (Nb,Ti)B was attributed to a high mutual solubility of monoborides and the amount of niobium and titanium borides increased with increasing ZrB2 content. The needle-shaped (Ti,Nb)B phase weakened the damage to fracture toughness caused by ZrB2 particle fracture due to crack bridging, crack defection and the pull-out toughening mechanisms. The highest fracture toughness of the Nb-Ti-ZrB2 composites was 12.0 MPa·m1/2. The stiff (Nb,Ti)B phase acted as a strong obstacle to the dislocation motion, leading to dislocation pile-up and enhancing the strength of the Nb-Ti-ZrB2 composites during compression tests. However, stress concentration around the needle-shaped (Ti,Nb)B phase easily leads to crack initiation and extension, resulting in decreased strength. The yield strength of Nb-Ti-ZrB2 composites ranged from 657.3 MPa to 1783.0 MPa owing to the combined influence of the strenghening mechanism caused by (Nb,Ti)B and the weakening mechanism caused by (Ti,Nb)B. The compressive deformation and failure process were also discussed in detail in this study.

Influence of niobium microalloying on the kinetics of static and dynamic recrystallization during hot rolling of medium-carbon high-strength steels

The temperature-strain conditions of dynamic and static recrystallization during hot deformation were determined at a rate of 1 sec–1 for medium-carbon steel microalloyed with titanium, boron, and vanadium containing different amounts of niobium. It was found that under hot rolling conditions niobium prevents the completion of dynamic recrystallization, and at temperatures below 970°C it drastically slows down static recrystallization in the pauses between successive reductions.

Welding of Cold-Resistant Micro-Alloed Steels 10HSNDA and 15HSNDA in the Atmosphere of Carbon Monoxide (II)

Micro-alloyed steels are widely used in the manufacture of critical welded structures operating under extreme conditions of the North. Microalloying of V, Nb and B is a simple and effective method of transferring known grades of structural steel and alloys to the category of increased and high strength, cold resistance, etc. The possibility of arc welding of steels grade 10CrSiNiAl and 15CrSiNiAl (10, 15ХСНДА in Russian), initially alloyed with trace amounts of niobium and vanadium to increase their cold resistance in carbon monoxide is considered. It is established that the use of the specified reducing atmosphere prevents the oxidation of the weld metal. The thermodynamic substantiation of the chemical reactions of microalloying elements proceeding in the weld pool, leading to the preservation of the steel composition, is presented. The chemical and metallographic analysis of welds was performed. The efficiency of using low-cost CO, or its mixtures with CO2, as substitutes for expensive argon and helium, when welding micro alloyed steels is shown.

Effect of MC carbide formation on weld solidification cracking susceptibility of austenitic stainless steel

The effect of secondary phase formation such as MC carbide during welding on solidification cracking susceptibility of fully austenitic stainless steels with various amounts of alloying elements and carbon was investigated. The solidification cracking susceptibility of Fe-24mass%Cr-26mass%Ni stainless steels with various amounts of niobium, titanium, zirconium, and carbon was evaluated by the Trans-Varestraint test.The addition of alloying elements such as niobium, titanium, and zirconium increased the brittle temperature range (BTR). The BTRs depend on the type and combination of the alloying elements and carbon content. Titanium was the most influential element on the increase in BTR compared to the other elements. The increase in carbon content tended to decrease the BTR, especially for the specimen containing titanium. The alloying elements formed phases such as the film-like MC-type carbide (MC) phase and granular Laves phase in the specimens containing 0.05% C, and a lot of the acicular MC phases in the specimens containing 0.20% C. The start temperature of the secondary phase formation differed depending on the type of the alloying element, and the temperature tended to increase with increasing carbon content. When the additions of niobium and titanium were compared, the amount of titanium segregation during solidification was smaller due to the formation of MC phases. Solidification simulation revealed that a higher amount and faster formation of the MC phase during solidification in 2Ti–20C contributed to reducing the BTR by increasing the carbon content. Thus, it is considered that the weld solidification cracking susceptibility depended on the type and amount of formation morphology, as well as start temperature during solidification corresponding to the composition of alloying elements and carbon.