Nb Content Research Articles

High-Nb alkaline mafic dykes in the central Alps witness to the Triassic evolution of the Adria passive margin

The Edolo diabase dykes intruded the Variscan basement in the central Southalpine domain. Biotite 40Ar / 39Ar dating shows that the emplacement occurred during the final stage of Permian-Triassic lithospheric thinning. In this phase on the Adria passive margin, middle Triassic magmatism with disputed arc affinity is followed by a late Triassic alkaline event associated with continental rifting. The Edolo diabase dykes are Ti-rich and alkaline, with high Nb and Ta contents and ratios in igneous amphibole, biotite, and ilmenite. These features are typical of the late Triassic magmatism. In contrast, the early-crystallized clinopyroxene shows low Nb and Ta contents and ratios and an apparent arc affinity may be thus envisaged in the clinopyroxene parental melt. However, given the coexistence of both features in the same dykes, their composition cannot be interpreted in terms of transition between tectonic environments. Instead, it is likely attributed to the heterogeneity of the Adriatic lithosphere inherited from the Variscan to Permian evolution, which underwent asthenospheric upwelling due to Permian-Triassic extensional tectonics.

Enhancing electrochemical and passive behavior of Ti-based medium entropy alloys in proton exchange membrane water electrolysis anodic environment through Zr and Nb synergy

The synergistic effect of Zr and Nb on the passive behavior of non-equiatomic Zr-Ti-Nb as bipolar plates in proton exchange membrane water electrolysis (PEMWE) was investigated. The experiment revealed that the complementary change of Zr and Nb content resulted in the corrosion resistance sequence of Z40 > Z20 > Z26 > Z34. The primary constituents of the passive films predominantly comprised ZrO2, TiO2, and Nb2O5. The relative content of ZrO2 and Nb2O5 exceeded the atomic proportions of Zr and Nb in the substrate. Additionally, higher potentials had a significant impact on reducing the number of point defects in the passive films while increasing their thickness. The addition of Zr and Nb inhibited the formation of defects in the passive film. The study also investigated operation-induced passive behaviors. Accelerated stress tests were conducted using two square ripple potentials to simulate overload operating conditions. The findings indicated that the lower upper limit potential was insufficient to establish stable passivation.

Tribocorrosion behavior of Ti-Nb-5Mo alloys designed for biomedical applications

This study investigated the tribocorrosion behavior of three alloys of the Ti-xNb-5Mo system. OCP and COF values were monitored, and the alloys' repassivation rate was calculated after sliding. The wear volume of the alloys was calculated by analyzing the profilometry results obtained by confocal microscopy. The alloy with the highest hardness (Ti-20Nb-5Mo) had the lowest wear volume (0.06 ± 0.02 mm³). Furthermore, OCP results during sliding showed that increasing Nb content increased the corrosion resistance of the alloys.

Optical and electrical properties of niobium-doped indium oxide thin films prepared by co-sputtering technique

Indium oxide (In2O3) based thin films have attracted much attention due to their high transparency and low resistivity. In order to obtain good transmittance and high conductivity, niobium (Nb) element was chosen as dopant in In2O3 in this study. Nb-doped In2O3 thin films (InNbO) were deposited on substrate by co-sputtering technique. The influence of Nb content on the structural, optical and electrical properties of InNbO thin films was systematically investigated. These thin films are compact and uniform without obvious pores and cracks. And InNbO is cubic bixbyite structure similar to In2O3. When Nb content is 1.8 at%, the resistivity of InNbO is as low as 8.29 × 10−3 Ω·cm. The prepared thin films exhibit high optical transmittance from visible to near-infrared wavelength regions. The average transmittance of InNbO thin films can reach 80.74 % in visible light range (380 ∼ 750 nm), and 75.71 % in near-infrared region (750 ∼ 2400 nm).

Impact of varying Nb content on conventional superconductivities in Nb-Si systems

Due to the superior properties of niobium silicon-based alloy materials, we systematically studied the structural stability, electronic properties and the relationship between Nb concentration and superconductivity of binary Nb-Si system under pressures below 40 GPa. We have identified three stable structures Nb5Si3, NbSi2 and Nb3Si, that have been experimentally confirmed under ambient pressure, as well as a new ground state stable structure Nb3Si2 above 37 GPa. Electronic structure calculations reveal that all the compounds are metallic. Furthermore we calculated the superconductivity transition temperatures of Nb3Si, γ-Nb5Si3, NbSi2, and Nb3Si2 at ambient pressure, finding that the critical temperature is closely related to the Nb-d states at the Fermi level and the vibration of Nb atoms. The calculated result of Nb3Si (TC=17.8 K) is in accordance with experimental observations, and the critical temperatures of γ-Nb5Si3 and Nb3Si2 are 7.7 K and 3.8 K respectively. In addition, we observed that the phase with a higher superconducting temperature tends to appear in compounds with higher Nb content. This may provide valuable insights into the influence of different structures and chemical compositions on superconducting performance, offering guidance for the design and synthesis of novel superconducting materials.

Effect of niobium content on microstructure and wear and corrosion resistance of laser-clad FeCo0.5CrNi1.5B0.5Nbx coatings on ductile iron

Ductile iron with a high carbon content is highly susceptible to the precipitation of brittle carbides during the cladding process, which makes it challenging to achieve the desired formability of the coating. In this study, FeCo0.5CrNi1.5B0.5Nbx (x = 0.1, 0.2, 0.3, and 0.4) high-entropy alloy coatings were designed using theoretical calculations and prepared on ductile iron through laser cladding. The effect of niobium (Nb) content on the microstructure evolution and phase composition of the coating was explored to determine the alloy component with the highest wear and corrosion resistance. All of the prepared coatings consisted of face-centered cubic (FCC) phases, along with Nb(C, B2) and Laves phases. With the increase in Nb content, the intensity of the diffraction peaks of NbC significantly increased compared to those of the other precipitates due to element diffusion. Nb0.3 coatings, which had the highest hardness, H/E, and H3/E2 values due to the most suitable percentage of FCC and hard phases, presented the lowest average friction coefficients of 0.48, 0.49, and 0.50, as well as the minimum wear volume of 0.64 × 108, 2.06 × 108, and 5.04 × 108 μm3 under loads of 10, 30, and 50 N, respectively. The wear mechanism of all the coatings was dominated by adhesive wear and oxidation wear under loads of 10 N and 30 N, while it changed to abrasive wear under a load of 50 N. Furthermore, Nb0.3 coatings also showed superior corrosion resistance due to the positive influence of the optimal Nb content on the oxide film. The Ecorr values were − 395 mV and − 337 mV, and the Icorr values were 0.21 × 10−6 A/cm2 and 1.10 × 10−6 A/cm2 in NaCl (3.5 wt%) and HCl (0.5 mol/L) solutions, respectively.

Some Considerations on Austenite Grain Growth Kinetics from High‐Temperature Laser Scanning Confocal Microscopy Observations

For more than 20 years, high‐temperature laser scanning confocal microscopy (HT‐LSCM) has become worldwide a proven technique for observing various metallurgical phenomena in situ. HT‐LSCM turns out to be a reliable and effective method for the observation of quantification austenite grain growth kinetics in steel, being highly relevant in casting and steel processing. In the present article, the measurement technique is briefly introduced followed by some basics on austenite grain growth. Finally, selected examples of recent research activities are discussed, including investigations into pure iron and the systems Fe–P, Fe–C, Fe–Al–N, and Fe–C–Nb–N. The influence of P on the grain growth kinetics is remarkable. At 1350 °C, the final grain size decreases from 255 μm in pure iron to 145 μm by adding 0.044 wt% P. In contrast, C enhances the grain growth in specific alloying ranges (0–0.30 wt%C), particularly at elevated temperatures. For a Al content of 0.025 wt% and only 50 wt ppm N, AlN loses the pinning effect above 1150 °C. In case of Nb(C,N), an elevated Nb content (0.085 wt%) provides stabilization of Nb(C,N) at 1150 °C, but at 1250 °C, no pinning of Nb(C,N) is visible anymore.

Physicochemical characteristics of new complex niobium-containing alloys

The authors studied the physicochemical characteristics of new complex alloys containing, %: 11 – 30 Nb, 23 – 28 Si, 3 – 10 Al and 3 – 4 Ti. It was shown that complex alloys have the most favorable values of density and crystallization temperatures compared to standard ferroniobium (60 wt. % Nb). Complex alloys with a low concentration of niobium have acceptable crystallization temperatures and optimal density values (5740 – 6560 kg/m3). This allows the pieces of ferroalloy to be completely in the liquid steel when it is released into the ladle, and to be constantly in motion, which increases absorption of the leading components. When the niobium concentration increases to 30 %, phase composition of the alloy changes: a decrease in the proportion of the low-temperature FeSi phase with low density values and an increase in the proportion of the high-density ternary compound NbFeSi2 with a crystallization temperature of ~1713 °C. An increase in Nb concentration from 11 to 17 % leads to a decrease in the crystallization temperature, and a further increase to 30 % Nb, on the contrary, is accompanied by an increase in the liquidus and solidus temperatures to 1700 and 1610 °C, respectively, which is consistent with liquidus line in phase diagram of the Fe – Nb system with a minimum in Nb concentration range ~18 %. The best characteristics, both from the point of view of obtaining ferroalloys and use for alloying steel, belong to an alloy containing, wt. %: 17.1 Nb, 24.6 Si, 7.6 Al and 3 Ti. This alloy is characterized by the temperature of crystallization onset (1550 °C) below the liquid steel bath temperature and belongs to the category of low-melting alloys. It has optimal density values – 6390 kg/m3, which has a positive effect on the performance characteristics of niobium ferroalloys.

Nb-content-dependent passivation behavior of Ti–Nb alloys for biomedical applications

Ti–Nb alloys have the advantages of non-toxicity, low elastic modulus, high strength, and good biocompatibility. However, the effect of Nb content on its passivation behavior in Hank's solution still needs to be investigated. This work investigated the microstructure, hardness, and corrosion behavior of Ti-xNb (x = 5, 15, 25 wt%) alloys. The β phase gradually increases associated with the increasing Nb content in Ti–Nb alloys, resulting in the dispersion strengthening of alloys. Moreover, with the increased Nb content, the samples show higher open circuit potential, lower passivation current density, and higher charge transfer resistance in Hank's solution at 37 °C. When the passive films of Ti–Nb alloys are formed under the high potentials of 1 V and 2 V, the passive films gradually dissolve after the withdrawal of applied potential, representing the decrease in the total impedance of the passive film. The reason for this phenomenon is the addition of Nb substantially decreases the oxygen vacancies in the passive film formed on the samples. Therefore, the impedance of the passive film is increased.

Geochemistry of Rocks at the Neskevara Rare-Metal Deposit of the Vuoriyarvi Alkaline–Ultramafic Complex, Kola Peninsula

The Vuoriyarvi Paleozoic alkaline–ultramafic complex with carbonatites is made up of a great diversity of rocks with various ore mineralization. The paper presents data on the geochemistry of pyroxenites, phoscorites, and carbonatites from the Neskevara deposit of rare metals. The pyroxenites of the rare-metal deposit are significantly enriched in Nb, Ta, and Th relative to the primitive mantle and the primary alkaline–ultramafic melt composition calculated for the Kola alkaline province and are characterized by high Nb/Ta, Zr/Hf, and Th/U ratios of 29, 35, and 14, respectively. HFSE are maximally enriched in the phoscorites and carbonatites of stages II and III, with the highest concentrations of Nb (16 000 ppm), Th (2800 ppm), and Zr (4000 ppm) found in the calcite–tetraferriphlogopite phoscorites, in which pyrochlore crystallization on the liquidus was identified. The rocks of the carbonatite series are strongly enriched in LREE relative to carbonaceous chondrite. The calcite–dolomite carbonatites of the late magmatic–carbothermal stage show REE enrichment up to 25 800 ppm. The chondrite-normalized REE patterns and (La/Yb)N ratio indicate that REE were systematically more strongly fractionated in the sequence pyroxenite (70)—phoscorite (90)—calcite (540) and dolomite (3790) carbonatites The crystallization sequence of minerals in the rare-metal phoscorites and carbonatites of intermediate stages indicates that magnetite and pyrochlore crystallized nearly simultaneously. The crystallization temperatures of such associations are, according to data of the magnetite–ilmenite thermometer, lower than 500–600°C, at ∆NNO = –0.3 and + 1.5 and corresponded to the temperature at which the rare-metal ore mineralization of the main stage was formed.

Microstructure evolution and properties of laser cladding AlFeCrMoNbx refractory high entropy alloy coatings

Refractory high-entropy alloy (RHEA) has superior mechanical properties but low room-temperature ductility. However, eutectic heterostructure alloy has strength-ductility trade-off. In this study, the AlFeCrMoNbx (x = 1, 1.2, 1.4, 1.6, 1.8, and 2.0) RHEA coatings were successfully prepared on the surface of an M2 high-speed steel (HSS) by laser cladding. The increase of Nb content promoted the formation of eutectic microstructure, the coating changed from hypoeutectic structure to hypereutectic structure. When x = 1.8, the coating exhibited a near-eutectic structure consisting of BCC and Laves phases with high hardness and wear resistance. After annealed at 750 °C for 8 h, the phases and microstructure of Nb1.8 REHEA coating did not change, contributing to a high microhardness and wear resistance. With annealing temperature rising, the microhardness and wear resistance decreased. After annealing at 1050 °C, the hardness of the coating still remained 549 HV0.2, indicating a good high-temperature softening resistance of REHEA coating.

Effects of Nb addition on the microstructure and low-cycle fatigue properties of heat-resistant stainless steel

This study aims to improve the quality and durability of materials used in turbocharger housing, particularly to limit the degradation of automobile engine parts. As a result, niobium (Nb)-bearing heat-resistant cast austenitic stainless-steel samples have been explored. Two distinct steel samples, denoted as Alloy-A (with 0 wt.% Nb) and Alloy-B (with 1.5 wt.% Nb), were fabricated by centrifugal casting for investigating the effects of Nb content on the corresponding microstructure and low-cycle fatigue properties of these samples. The phases formed within these alloys were predicted by thermodynamic calculations using the Thermo-Calc software, with the results aligning well with the experimental results. The addition of Nb promoted the formation of niobium carbide, resulting in increased hardness and greater area fraction of the carbides present in the steel samples. Alloy-B displayed enhanced high-temperature strength over Alloy-A, while the low-cycle fatigue resistances of the two alloys were similar. Fatigue cracks predominantly initiated at the outer surface of the specimens, mainly in the carbide regions, due to the mismatch between the matrix and carbide hardness. This paper is the first to report the effect of Nb addition on the microstructure and low-cycle fatigue properties of heat-resistant cast austenitic stainless steel.

Enhanced thermoelectric figure-of-merit in ‘defective’ half-Heusler Nb0.8CoSb

The half Heusler alloys are potential mid-to-high temperature range thermoelectrics due to their high power factor, solid structural stability and high mechanical strength. However, the high lattice thermal conductivity inherent to these materials reduces the zT, rendering them less useful for practical applications. The ‘defective’ half-Heuslers provide an attractive alternative to mitigate these issues. In these materials, the intrinsic lattice defects present in the form of vacancies lower the lattice thermal conductivity substantially. Here, we study the effect of excess Nb and Sn doping in the defective half Heuslers Nb0.8+δCoSb1−xSnx. We show that Sn doping allows for: (i) optimizing the carrier concentration with a much finer control than if only δ is increased, and (ii) incorporation of a higher concentration of Nb in the structure. A combination of optimized carrier concentration and synergistic changes in the band structure, including the appearance of a new flat band near 50 meV above the Fermi energy due to excess Nb, suppresses the bipolarity and enhances the thermopower further at high temperatures as the average band effective mass of the carriers increases. We, therefore, obtain a high zT exceeding 1 at 1100 K for Nb0.85CoSb0.95Sn0.05. This value is ≈ 15% higher than the highest zT previously reported.

The gradient high entropy alloy coating prepared in-situ by bidirectional diffusion of Mo/Nb and FeCoCrNi

Based on the influence of Mo and Nb content on the eutectic degree of FeCoCrNi high-entropy alloy (HEA), this study prepared in-situ HEA composite coatings with a gradient eutectic degree using the principle of element diffusion in the molten pool under a laser beam, namely Mo-CC and Nb-CC. Both of the two coatings were composed of the face-centered cubic (FCC) phase and Laves phase. Within the coating, there was a gradual decrease in the Laves phase and an increase in the FCC phase from top to bottom. The Laves phase in Mo-CC was rich in Mo (21.36 at.%) element and exhibited an orientation relationship with the FCC phase of [01¯1]Laves//[01¯1]FCC. The phase interface was a non-coherent crystal plane. The Laves phase in Nb-CC is enriched with Nb (36.15 at.%) element and demonstrated an orientation relationship with the FCC phase of [1¯2¯1]Laves//[001]FCC. The phase interface was a semi-coherent crystal plane. Furthermore, the process and mechanism of FCC phase transformation into FCC + Laves phase were elucidated by examining the mixing enthalpy, lattice distortion, and atomic radius difference. In terms of properties, the hardness of Mo-CC and Nb-CC from the top to the bottom section gradually decreased from the outer to inner section. Nb-CC possessed a higher surface average hardness (773.66 HV0.3) and superior tribological properties compared to Mo-CC. The gradient control method for HEA and the phase structure formation mechanism presented in this study provided valuable insights for the research and development of new HEA coatings.

Effects of Mo and Nb on the microstructure and high temperature oxidation behaviors of CoCrFeNi-based high entropy alloys

A series of CoCrFeNi(Mo, Nb) high entropy alloys (HEAs) were prepared using vacuum arc-melting. The effect of Nb and Mo on the microstructure and high temperature anti-oxidation properties of HEAs was investigated. The addition of only Mo was found to not cause formation of new phase, but did increase the lattice distortion. After the addition of Nb, as-prepared CoCrFeNiMo0.2Nb0.1 and CoCrFeNiMo0.2Nb0.2 alloys are characteristic of duplex-phase structures of FCC and Laves, in which the Laves phase is semi-coherent with FCC matrix. Our studies also revealed that the oxidation kinetics of the alloys followed parabolic rate law and the corresponding oxidation rate constants were calculated. Due to the synergistic effects of Mo and Nb, the anti-oxidation properties of HEAs improved significantly. It was also discovered that the new Laves phase containing Mo and Nb at the inner oxidation layer hindered the outward diffusion of active metal cations, ergo improving the oxidation resistance of HEAs. With increase of Nb content, it was further recognized that the layered structure of Laves phase was thinner and denser. Therefore, the oxygen ion diffusion process in the CoCrFeNiMo0.2Nb0.2 alloy can be inhibited effectively by the new formation of duplex-phase structures with undulated Laves phase and FCC matrix.

An inspection into the unexpected gamma precipitation in supersaturated U-13 at.% Nb subjected to aging

Phase separation of the U-Nb (13 at.%) alloy at an aging temperature of 723 K was investigated through transmission electron microscopy. Chemical redistribution initiated from a supersaturated state was identified after aging for half an hour before the discontinuous precipitation (DP) process. Such redistribution was accompanied by a fine two-phase structure and non-lamellar morphology. Among the decomposition products at this early stage, a lath-shaped Nb-rich phase was confirmed to be the bcc (γ) phase, with Nb content in the range of 35∼45 at.%. Meanwhile, discrete regions of much smaller size were detected to bare an Nb content approaching the equilibrium of the α phase. It is envisaged that the γ precipitation was a preceding event of the α. Thermodynamic estimation was carried out to reveal the decomposition mechanism responsible for this unexpected behavior. The results were in favor of a nucleation and growth mechanism over the spinodal decomposition. These results provide a deeper understanding and a new sight into the aging phenomenon of U-13Nb alloys, which are also worth consideration in other binary systems slightly outside the coherent spinodal regions such as Fe-20Cr.

Mechanisms leading to exceptional niobium concentration during lateritic weathering: The key role of secondary oxides

Niobium (Nb) is considered as one of the most immobile elements during supergene weathering due to its low solubility and the expected resistance of the pyrochlore mineral group (A2B2X6Y) in which Nb occupies the B site. Although the resistance of pyrochlore is challenged by direct evidence of alteration in lateritic profiles, the geochemical and mineralogical processes controlling its behavior in the critical zone remains elusive. This study uses a multiscale geochemical, mineralogical and spectroscopic approach to monitor Nb solid speciation in a thick weathering profile. The weathering of the pyrochlore-bearing core carbonatite facies from Morro dos Seis Lagos has resulted in a Fe-enriched laterite with exceptional Nb concentrations (2.91 wt% Nb2O5 on average). The preservation of the successive secondary phases (Ti-, Fe-, Ce-oxides) resulting from weathering processes along the horizons offers the opportunity to track Nb during pyrochlore alteration from the fresh parent rock to the final stages of weathering. Intense lateritization processes have led to an enrichment in Fe and Ti in the pyrochlore B-sites, resulting in the weakening of the structure and its ultimate destabilization due to weaker B-O bonds. After the release of Nb from pyrochlore, the fate of Nb is dependent on the secondary phases formed during weathering. In the lower horizons dominated by Fe oxides, goethite is the main host for Nb (1 wt% Nb2O5) due to its capacity to substitute Fe3+ for Nb5+, in contrast to hematite. In the upper horizons, where Ti oxides have formed during the reworking of the laterite, Nb5+ is preferentially incorporated into brookite and rutile (20 wt% Nb2O5), which may have formed owing to slightly acidic pH and high Nb activity during their growth. The presence of Nb in hollandite and cerianite in a vein from the manganiferous horizon involves the transport of Nb with mobile elements at the scale of the laterite. With this study, we describe a new model accounting for the formation of Nb-enriched laterites. The latter is based on the ability of Nb5+ to substitute for Fe3+, Ti4+, Ce4+ in minerals formed by lateritization processes after its release from pyrochlore. The nature of the secondary Nb-bearing oxides is dependent on the chemistry of the parent rock and the conditions of formation of the laterite. This work, evidencing the mobilization of Nb both at the scale of the mineralogical assemblage and of the entire profile questions the pervasive use of Nb as a geochemical invariant in the critical zone.

Phase equilibria in Zn–Nb–Ti ternary system at 600 and 450 °C

In order to determine the isothermal sections of Zn–Nb–Ti ternary phase diagram at 600 and 450 °C, the equilibrated alloy method was adopted by using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The experimental results show that there are seven and ten three-phase regions at the 600 and 450 °C isothermal sections, respectively. Besides, a continuous homogeneous solid solution (Nb,Ti)Zn3 phase was further identified, of which the lattice parameters increase with the increasing of Nb content in these two isothermal sections. Compared with the 450 °C isothermal section, the homogeneity range of (Nb,Ti)Zn3 phase increases slightly at 600 °C. No ternary compounds were detected at both 600 and 450 °C isothermal sections.

Room temperature nanoindentation creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings prepared by HVAF

The present study aimed to explore the creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings at room temperature using nanoindentation creep experiments. The coatings were subjected to different loading rates to assess their performance. The findings indicate that the high entropy effect of the (Co0.33Ni0.33Cr0.23Mo0.1)80-xNbx(B0.7Si0.3)20 (x = 0, 2 and 4 at. %) high entropy amorphous alloy coatings has a notable impact on the creep resistance and facilitates a uniform plastic deformation during creep. The shear transition zone (STZ) size and the free volume content during creep deformation exhibit an increase in response to the concentration of Nb. This phenomenon can be attributed to the elevated atomic packing density and the hindered movement of atoms resulting from the incorporation of Nb. Nb content has a favorable impact on the creep stress index, increasing creep stress. Also, the high concentration of Nb is found to mitigate the propensity of the stress exponent to drop with increasing loading rates. The high entropy effect of the as-sprayed coatings promotes high creep resistance and homogenous creep deformation.

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.