Transformation Temperature Research Articles

Novel solar absorber from cement industry waste

Solar radiation harvesting is a global imperative that requires the development of effective solar absorbers. The current work focuses on the development and testing of solar absorbers using glass derived from industrial cement waste. Glass samples were prepared experimentally by combining 25 % cement plant waste with 75 % silica sand and additives. To increase absorptivity and reduce transmittance, cobalt (at 0.2 % and 0.4 % by weight) and basalt (at 10 %, 20 %, 30 %, and 40 % by weight) were added as additives to reduce transmissivity of the glass. The effects of various additives, as well as variations in surface roughness, on optical properties were examined. Adding basalt found to be more effective than cobalt in improving the optical characteristics and hardness of the glass. With 20 %–40 % basalt, absorptivity increased significantly to 98 %, while emissivity was around 4.4 % and transmittance was minimal at around 0.2 %. Furthermore, the polished glass had better optical qualities than the roughened glass. The samples were investigated and characterized using analytical techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential thermal analysis (DTA). The transformation temperatures from amorphous to crystalline structure of glass containing 30 and 40 % basalt were determined. Accordingly, the glass containing 40 % basalt was heat treated at 900 °C for 2h leading to crystallization of the glass. The absorptivity decreased to 97 % and the emissivity increased to 6 %. The results indicate that the glass with 40 % basalt addition is an excellent low-cost candidate for solar absorber manufacturing.

Microstructure and transformation temperatures of Si-added Ni–Ti–Cu and Ni–Ti–Zr shape memory alloys

Microstructure and transformation temperatures of Si-added Ni–Ti–Cu and Ni–Ti–Zr shape memory alloys

Elaboration and characterization of Cu–Zn–Al shape memory alloys

AbstractThe study examines Cu–Zn–Al shape memory alloys, vital in aeronautics and automotive sectors. It aims to characterize their thermo-mechanical transformations induced by composition and heat treatments, focusing on how these impact mechanical properties, especially grain size refinement. Analysis covers transformation temperatures, micro-hardness, induced transformations, and mechanical tests. Results show thermoplastic martensitic transformations, with micro-hardness aiding in identifying characteristic points. The study's novelty lies in understanding how grain size refinement affects these transformations and the role of micro-hardness in precise characterization.

Modeling martensitic transformation temperatures in Zirconia–Ceria solid solutions using machine learning interatomic potentials

Abstract Shape memory ceramics (SMCs), while exhibiting high strength, sizeable recoverable strain, and substantial energy damping, tend to shatter under load and have low reversibility. Recent developments in SMCs have shown significant promise in enhancing the reversibility of the shape memory phase transformation by tuning the lattice parameters and transformation temperatures through alloying. While first-principles methods, such as density functional theory (DFT), can predict the lattice parameters and enthalpy at zero Kelvin, calculating the transformation temperature from free energy at high temperatures is impractical. Empirical potentials can calculate transformation temperatures efficiently for large system sizes but lack compositional transferability. In this work, we develop a model to predict transformation temperatures and lattice parameters for the Zirconia–Ceria solid solutions. We construct a machine learning inter-atomic potential (MLIAP) using an initial dataset of DFT simulations, which is then iteratively expanded using active learning. We utilize reversible scaling to compute the free energy as a function of composition and temperature, from which the transformation temperatures are determined. These transformation temperatures match experimental trends and accurately predict the phase boundary. Finally, we compare other relevant design parameters (e.g. transformation volume change) to demonstrate the applicability of MLIAPs in designing SMCs.

Mechanical behaviour of low-, medium- and high-entropy Ti-Hf-Zr-Ni-Cu-Co shape memory alloys

The mechanical behaviour was studied in twelve senary Ti-HfXZrX-Ni-CuXCoX alloys with various configuration entropies, which were regulated by the X value - concentration of doping elements (Hf, Zr, Cu, and Co) that varied from 1 at% to 17 at% and the concentration of the Ni group (Ni+Cu+Co) that varied from 49 to 51 at%. The stress vs strain curves were obtained at three temperatures (-100 °C, 22 °C and 100 °C) at which the alloys were in different states (martensite, austenite, or a mixture of both). It was found that the senary Ti-Hf-Zr-Ni-Cu-Co alloys could undergo deformation via martensite reorientation, stress-induced martensitic transformation, and dislocation slip. The activation of the mechanisms depends on the deformation temperature compared to the temperatures of the martensitic transformations, as in the binary NiTi alloys. An increase in the X value from 1 to 10 at% increased the yield limit for dislocation slip in the austenite phase, while a further rise in the X value by 17 at% decreased this limit. An increase in the X value decreased the strain up to failure. The larger the [Ni] concentration or deformation temperature, the more pronounced the reduction in strain up to failure. An increase in X value from 1 to 5 at% significantly changed the fracture mechanisms from ductile to brittle due to the suppression of the dislocation movement.

A method for filling missing values in multivariate sequence bidirectional recurrent neural networks based on feature correlations

Multivariate real-life time series data often contain missing values. These missing values often affect subsequent prediction tasks. Traditional imputation methods generally consider only some of the characteristics of multivariate time series data. This can easily lead to inaccurate filling results. In this paper, a feature correlation-based bidirectional recurrent network (BRNN-FR) is proposed to solve the problem of missing values in multivariate sequence data. First, this method involves the design of a bidirectional prediction network based on time intervals and the use of forward and reverse time series information between data points to obtain the characteristics of data changes with time to the greatest extent. Second, considering the correlation between features, a combined feature selection strategy based on the Pearson correlation coefficient and mutual information was proposed. A multiple regression model was established to predict between features. Finally, a bidirectional network ensemble filling algorithm based on the relationships between features is established to predict missing values. Comprehensive experiments on four public datasets show that the mean absolute error (MAE), root mean square error (RMSE) and maximum R2 value (R2_score) of the BRNN-FR algorithm in the direct imputation test are better than those of the other comparison methods in most cases. BRNN-FR also achieved a better area under the curve (AUC) in the indirect comparison experiment of two classifications of in-hospital death after filling the medical dataset. Using the AIR air quality dataset and the power transformer temperature dataset from the ETTH1 interpolation regression to predict the next 3 hours and 6 hours of average numerical results, most of the optimal regression results are obtained.

Characterization of beta flecks and local solute segregation in Ti-17 alloy ingots produced by vacuum arc remelting

As a melt defect, beta flecks (β-flecks) may exist in many metastable β and α + β titanium alloys. In this work, the main characteristics of β-flecks, including detectability, macroscopic morphology, microstructural characteristics, and chemical composition, were investigated in an industrial-scale Ti-17 ingot produced by the vacuum arc remelting (VAR) process. The results show that β-flecks can be identified as dark areas in the ingot head through a specific heat treatment. Enrichment of Cr and Zr, along with deficiency of Mo, is found in the β-flecks, resulting in a lowered β transformation temperature (Tβ) and increased β phase stability in local areas. When soaked at temperatures from 45 to 15°C below Tβ, β-flecks can be distinctly visualized by adjusting the volume of α phase. Additionally, β-flecks exhibit continuous fluctuations in both chemical composition and microstructure, closely related to the size of the β-flecks. Based on the findings, it can be concluded that β-flecks may originate from residual segregated liquid during the final stage of solidification processes, forming as local defects in the final solidified microstructure. Analytical and numerical modeling provide insights into how solute elements segregate and evolve into β-fleck defects.

Solid‐Solid Phase Transformation Behavior of ϵ‐CL‐20 Induced by Typical Organic Solvents: A Theoretical and Experimental Study

AbstractThe solid‐solid phase transformation of ϵ‐CL‐20 induced by external conditions is one of the bottlenecks limiting the widespread applications of CL‐20‐based energetic materials. Herein, we report the investigation on the influence of solvent polarity on ϵ‐CL‐20 solid‐solid phase transformation behavior both theoretically and experimentally. Density functional theory (DFT) calculation was performed to evaluate the possibility of ϵ‐CL‐20 phase transformation induced by organic solvent molecules from the perspective of ϵ‐CL‐20 electronic structure and molecular structure variations. Additionally, experimental study of ϵ‐CL‐20 phase transformation induced by 1,2‐dichloroethane, ethanol, and methanol gas environment was conducted. Solvent with higher polarity was confirmed to significantly vary molecular surface electrostatic potential and molecular conformation of ϵ‐CL‐20 molecule. Furthermore, ϵ‐CL‐20 critical phase transformation temperature decreased when using inducing solvent with higher polarity. And the observed maximum phase transformation rate was the one induced by the highest polarity solvent. A four‐parameter model was established to describe the phase transformation process as a function of time based on the experimental results. Possible ϵ‐CL‐20 solid‐solid phase transformation mechanism was proposed. Hopefully, these results will be beneficial for the rational preparation and utilization of CL‐20‐based energetic materials.

Study on properties of pre-alloy powder of TiNiHf high temperature shape memory alloy for additive manufacturing by preheating treatment

In this work, pre-alloyed powder high-temperature shape memory alloy (Ti30Ni50Hf20) for additive manufacturing was preheated at 300–800 °C and thermoscycled at 650 °C to examine the influence of preheating temperature and thermal cycle number on the phase composition and phase transformation behavior. The results showed that the H phase precipitation occurred in the matrix with the rising preheating temperature within 300–600 °C, and the phase transformation temperature of the pre-alloyed powders also increased. When the preheating temperature exceeded 600 °C, the H phase dissolved back into the matrix, and the phase transformation temperature decreased. A total of 50 thermal cycles were conducted on the pre-alloyed powders at 650 °C, and the phase transformation temperature and phase composition remained stable after cycling. It can be concluded that the preheating temperature greatly affected the phase composition and phase transformation behavior of Ti30Ni50Hf20 high-temperature shape memory alloy pre-alloyed powders, while the number of thermal cycles delivered a minor effect.

Phase transformation and metallurgical characterization of heat-treated nickel-titanium rotary instruments using differential scanning calorimetry, X-ray diffraction, and energy dispersive spectrometry.

The present study aimed to evaluate the phase transformation behavior and elemental analysis of thermomechanical-treated nickel-titanium (NiTi) rotary instruments, TruNatomy (Dentsply Sirona), HyFlex CM (coltene, Whaledent), and Neoendo Flex (Orikam healthcare India), using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and energy dispersive X-ray spectrometry. A total of 18 NiTi rotary instruments, TruNatomy, Hyflex CM, Neoendo Flex, taper. 04, size 25 (except TruNatomy, size 26) were selected and were divided into three groups (n = 6). Three NiTi files from each group were investigated for the DSC test (n = 3). The two segments of each sample were cut carefully by slow-speed water-cooling carborundum disc at 3 mm from the tip and then 4 mm from the previous section. The mass of the samples was measured on the electronic balance and samples that weighed 10-15 mg were loaded into a 40 µL aluminum crucible. The samples are then subjected first to a heating cycle from 0°C to 100°C and subsequently a cooling cycle from 100°C to 0°C in the differential scanning calorimeter (Mettler-Toledo, NIT Srinagar) at a rate of 10°C min-1. XRD (Make. Rigaku Japan, smart lab 3kW, NIT Srinagar.) was performed to verify the DSC results. The remaining two samples from each group (n = 2) were subjected to XRD analysis. The sample preparation for XRD analyses was done precisely with slow speed water cooled carborundum disc and samples were sectioned into three segments. Each segment was 5 mm long and grounded to obtain a uniform smooth plane. The data obtained from DSC and XRD were subjected to origin 8.5 software and graphs were obtained that depict the transformation temperature and phase composition, respectively. Alloy distribution and trace elements of the NiTi rotary instruments were done using energy dispersive spectrometry microanalysis. The DSC results showed that the TruNatomy, Hyflex CM, and Neo Endo instruments had an Austenite finish (Af) temperature exceeding 37°C. The XRD graphs show the different intensity peaks that correspond to the various phases of NiTi rotary instruments. The TruNatomy is predominantly Austenite, Hyflex CM exists mainly in R-phase with a variable amount of austenite and martensite, while Neoendo flex endo mostly contains austenite phase. The elemental analysis revealed that all three file systems show Nickel and Titanium within their bulk structure in an equiatomic ratio. This study concluded that TruNatomy is predominantly martensite with a variable amount of austenite phase. There are differences in thermal transition temperature between the files.

Spatially confined magnetic shape-memory Heuslers: Implications for nanoscale devices

Magnetic shape-memory (MSM) Heuslers are among the most promising materials for thermo-magneto-mechanical applications. However, the knowledge about the martensitic transformation (which is the basis of the multifunctionality in these materials) as a function of size reduction in the submicron scale is still very limited. Here, we aim to bridge this knowledge gap by investigating the behavior of these materials upon nanoscale confinement. We customize a top-down approach by patterning arrays of submicron epitaxial Ni-Mn-Ga structures with lateral sizes down to ∼70 nm, using a Cr hard mask on MgO(001) substrate. The structures include straight stripes, radial stripes, squares and triangles. The martensitic transformation temperature, sharpness, thermal hysteresis and magnetic characteristics of the material are investigated upon spatial confinement. Transmission electron microscopy techniques including Geometric Phase Analysis (GPA) algorithm, and quantitative theoretical analysis of stress help us to evaluate the martensitic transformation of Ni-Mn-Ga starting from continuous films and down to sub-micron patterns. We show that the size-dependent internal stress relaxation plays a primary role in broadening the martensitic transformation of the material, reducing thermal hysteresis, and pushing the transformation toward higher temperatures in the sub-micron structures. These findings highlight the importance of stress considerations upon incorporation of MSM Heusler materials into nanoscale functional devices.

OPTIMIZATION OF HEAT TREATMENT REGIME FOR A NEW BIODEGRADABLE Mg-Zr-Nd ALLOY WITH ENHANCED MECHANICAL PROPERTIES

Purpose. To develop a rational heat treatment regime for a new biodegradable magnesium alloy of the Mg-Zr-Nd system, to ensure enhanced mechanical properties throughout the entire treatment period. Research methods. Differential thermal analysis (DTA) was used to determine phase transformation temperatures. Microstructure analysis was conducted using optical microscopy (“Neophot 32” and “OLYMPUS IX 70”) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SELMI RЕМ-106I). Mechanical properties were determined using an INSTRON 2801 testing machine. The influence of cooling rate on microstructure and properties was studied using ProCAST simulation software. Heat treatment was carried out in a Bellevue type shaft furnace and a PAP-4M furnace. X-ray analysis was used to detect internal defects in samples. Results. A new heat treatment regime was developed for the biodegradable Mg-3.15Nd-1.25Zr-0.6Zn (wt%) alloy. Using differential thermal analysis and microstructure studies at various quenching temperatures, the optimal quenching temperature was established at 560 °C. Empirical relationships describing the influence of heat treatment parameters on the alloy's microstructure were calculated. The new heat treatment regime (quenching from 560 °C for 8 hours, air cooling + aging at 200 °C for 16 hours) resulted in improved mechanical properties (UTS = 276–282 MPa, δ = 5.2–5.8%) compared to the standard T6 regime. Scientific novelty. For the first time, a comprehensive study of the influence of heat treatment parameters on the structure and properties of a new Mg-3.15Nd-1.25Zr-0.6Zn (wt%) alloy with increased content of alloying elements was conducted. New dependencies describing the influence of quenching temperature on the alloy's grain size were established. Practical value. A new heat treatment regime for the biodegradable magnesium alloy was developed, which ensures complete dissolution of the pseudoeutectic phase and formation of strengthening phases, resulting in improved mechanical properties compared to the standard alloy Mg-2.5Nd-0.4Zn-0.5Zr (wt%) and the standard T6 regime.

Thermal Cycling Behavior of Aged FeNiCoAlTiNb Cold-Rolled Shape Memory Alloys.

Fe-Ni-Co-Al-based systems have attracted a lot of interest due to their large recoverable strain. In this study, the microstructure and thermal cycling behaviors of Fe41Ni28Co17Al11.5Ti1.25Nb1.25 (at.%) 98.5% cold-rolled alloys after annealing treatment at 1277 °C for 1 h, followed by aging for 48 h at 600 °C, were investigated. From the electron backscatter diffraction results, we see that the texture intensity increased from 9.4 to 16.5 mud and the average grain size increased from 300 to 400 μm as the annealing time increased from 0.5 h to 1 h. The hardness results for different aging heat treatment conditions show the maximum value was reached for samples aged at 600 °C for 48 h (peak aging condition). The orientation distribution functions (ODFs) displayed by Goss, brass, and copper were the main textural features in the FeNiCoAlTiNb cold-rolled alloy. After annealing, strong Goss and brass textures were formed. The transmission electron microscopy (TEM) results show that the precipitate size was ~10 nm. The X-ray diffraction (XRD) results show a strong peak in the (111) and (200) planes of the austenite (⁠⁠γ, FCC) structure for the annealed sample. After aging, a new peak in the (111) plane of the precipitate (⁠⁠γ', L12) structure emerged, and the peak intensity of austenite (⁠⁠γ, FCC) decreased. The magnetization-temperature curves of the aged sample show that both the magnetization and transformation temperature increased with the increasing magnetic fields. The shape memory properties show a fully recoverable strain of up to 2% at 400 MPa stress produced in the three-point bending test. However, the experimental recoverable strain values were lower than the theoretical values, possibly due to the fact that the volume fraction of the low-angle grain boundary (LABs) was small compared to the reported values (60%), and it was insufficient to suppress the beta phases. The beta phases made the grain boundaries brittle and deteriorated the ductility. On the fracture surface of samples after the three-point bending test, the fracture spread along the grain boundary, and the cross-section microstructural results show that the faces of the grain boundary were smooth, indicating that the grain boundary was brittle with an intergranular fracture.

Calorimetric Studies of Phase Transformations in the La<sub>1 – x</sub>Y<sub>x</sub>Mn<sub>2</sub>Si<sub>2</sub> System

Differential scanning calorimetry (DSC) is used to determine the magnetic phase transformation temperatures of the La1 – xYxMn2Si2 (x = 0–1) alloys. For the compositions with х from 0 to 0.3, the temperature dependences of DSC signal exhibit λ-like endothermic effects observed near 300 K, which are related to the magnetic phase transition from the ferromagnetic to layered antiferromagnetic structure, and weak anomalies, which are observed in a temperature range of from 458 K for the composition with х = 0 to 323 К for the composition with х = 0.3 upon disordering of the layered antiferromagnetic structure. A clear endothermic peak corresponding to the disordering of interplane antiferromagnetic layered structure was found for the YMn2Si2. The data obtained are used to construct the magnetic phase diagram of the La1–xYxMn2Si2 system in a temperature range of 270–600 К. The differential scanning calorimetry is shown can be successfully used for the determination of temperatures of various magnetic phase transformations in rare-earth intermetallic compounds.

Enhancing strength and toughness in a pearlitic rail steel via multi-alloying and accelerated cooling

The demand for higher speeds and heavier loads has emphasized the necessity to tackle the inherent trade-off between strength and toughness in pearlitic rail steels. Herein, the co-additions of Cr, Ni and Cu and accelerated cooling rate on the microstructure and mechanical properties of a medium carbon pearlitic steel were systematically investigated. In comparison with base alloy, the new steel exhibits smaller prior austenite grain size (PAGS) due to the drag effect of Cu and Ni solutes. The finer PAGS and lower C content increased the volume fraction of proeutectoid ferrite. The finer pearlitic nodule size (PNS) and pearlitic colony size (PCS) were attributed to the small PAGS and greater extent of undercooling due to the combined effect of multi-alloying and accelerated cooling. Additionally, the synergistic effects of multi-alloying and accelerated cooling rate decrease the pearlitic phase transformation temperature, accountable for the finer interlamellar spacing (IS). Compared with the base steel, the yield strength and ultimate tensile strength of the new steel increased from 587 MPa to 1069 MPa to 740 MPa and 1178 MPa, respectively, with a simultaneous increase of ductility from 12.4 % to 14.7 %. The strength increments are mainly attributed to the finer IS in the new steel. Meanwhile, the new steel possesses a higher impact toughness compared to the base steel due to the increased volume fraction of proeutectoid ferrite, and finer PNS and IS.

An investigation of rapid surface melting in nanowires

The investigation into virtual melting phenomena in nanowires holds significant relevance owing to its profound impact on material durability under extreme loading conditions. Thus, the exploration of this pivotal plastic deformation mechanism is undertaken utilizing the phase-field methodology. Employing a monolithic solver, we solve the coupled highly nonlinear time-dependent Ginzburg–Landau equation and dynamic elasticity equation. Our analysis encompasses the consideration of surface tension stress in conjunction with a coherent solid–liquid interface subjected to uniaxial transformation strain, thereby unveiling intriguing facets of melting phenomena. The investigation delves into the influence of transformation strain, kinetic coefficient, and temperature on the thickness of the solid–liquid interface and its corresponding velocity. This analysis is conducted through meticulous comparison with existing experimental data and molecular dynamics simulation. Moreover, employing the phase-field method yields precise descriptions of the system kinetics, capturing virtual melting phenomena in both pristine and flawed nanowire configurations.

Transformation of iron-minerals from natural aquifer media by sulfate-reducing bacteria: Behavior, mechanism, and Cr(VI) removal

Sulfate-reducing bacteria (SRB) and iron minerals are widespread in subsurface environments, where their mediated Fe and S transformations are crucial for contaminant immobilization. However, the mechanism mediated by SRB to transform natural iron minerals into reduced iron–sulfur compounds and the contaminant removal capacity of the transformation products remain unclear. Herein, the mechanism of native SRB-mediated transformation of iron-minerals from natural aquifer media into biogenic ferrous sulfide (FeS) was revealed and the Cr(VI) removal performance of the transformation product was evaluated. The results showed that Fe2+ production, sulfate reduction, and sulfide production occurred sequentially (rather than simultaneously) in the liquid phase. This suggests new processes and mechanisms for iron-mineral transformation: first, iron minerals dissolve to produce Fe2+ under enzymatic action rather than sulfide reduction; then, the generated Fe2+ accelerates sulfate reduction by SRB, producing sulfide in large amounts; finally, sulfide combines rapidly with Fe2+ to produce FeS. Elevated temperatures markedly shortened the required transformation time to start: maximum Fe production occurred at 18–24 days, 6–12 days, and 0–6 days at 10 °C, 20 °C, and 35 °C, respectively. Ambient temperature strongly affected SRB community composition, with Desulfosporosinus dominant at 10 °C and 20 °C and Desulfotomaculales prevalent at 35 °C. Sequential extraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analyses confirmed FeS as the main transformation product, which exhibited a highly efficient Cr(VI) removal capacity. Extending transformation time or increasing transformation temperature enhanced the Cr(VI) removal capacity of the transformation product. In column experiments, in-situ stimulation of SRB growth in aquifer media is able to form FeS, the Cr(VI) removal capacity of FeS reached up to 90.1 mg(Cr(VI))/kg(media). These findings suggest that biostimulation of SRB to mediate the in-situ transformation of iron-minerals to FeS has great potential for remediation of contaminated groundwater.

Control strategy of reducing hydrogen enrichment in heat-affected zone during welding for ultra-high strength steels

The hydrogen diffusion behaviors in welded joints of ultra-high strength steel (UHSS), which are related to hydrogen-induced cracks (HIC) in welding, are not yet fully understood due to the lack of in-situ observation techniques for hydrogen during welding. An improved microphotography technique is proposed to visualize the hydrogen distribution within the as-welded joint. When UHSS is welded using traditional welding materials, the transformation temperature from γ to α phase (TF) of the weld metal (WM) is higher than that (TB) of the heat-affected zone (HAZ), resulting in the observed hydrogen enrichment in the HAZ. We developed a low transformation temperature (LTT) welding material. This material is designed so that the TF of WM is lower than the TB of HAZ, facilitating hydrogen back-diffusion from the HAZ to the WM. This back-diffusion effectively reduces the hydrogen concentration in the HAZ. Additionally, a thermo-mechanical hydrogen diffusion sequentially coupled finite element procedure was utilized to simulate hydrogen concentration evolution during welding, revealing the control process of phase transformation temperature differences (ΔT = TF - TB) on hydrogen diffusion behavior and the influence of residual stress on the accumulation of hydrogen. The microphotography technique has successfully validated these findings, which can help to mitigate the risk of HIC in the HAZ during welding of UHSS.

Influence of hot rolling on microstructure, mechanical properties, and martensitic transformation of TiNiCuNb shape memory alloy

TiNiCuNb shape memory alloys are a promising new class of materials with the potential to be applied as elastocaloric components. However, the mechanical processing of these alloys remains a challenge and new insights on this topic must enlighten the knowledge about this system. In this work, the effects of hot rolling on Ti46Ni38Cu10Nb6 alloy were investigated. The results showed that hot rolling leads to the increase of martensitic transformation temperatures and the formation of a matrix containing both B2 and B19 phases. The coarsening of the lamellar eutectic constituent was observed, and part of the β-Nb phase precipitated into the matrix after being dissolved due to hot work. Microstructural aspects and ultra-microhardness measurements suggest that dynamic recrystallization occurred during hot rolling.

Effect of nitrogen on the microstructure and strengthening mechanism of high performance tinplate

In order to meet the high strength and high formability requirements of the tinplate market, the nitrogen strengthening method was used for the chemical composition of the tinplate, and the action mechanism of nitrogen on the full-process tinplate substrate was explored. The present study designed tinplate with different nitrogen contents (named as 20 N steel and 150 N steel), and conducted phase transformation research and recrystallization temperature tests. SEM, XRD, EBSD, TEM, chemical dissolution analysis and tensile tests were carried out, and the influence of annealing process on the microstructure, mechanical properties and precipitation of annealed sheet was also explained. With the increase of nitrogen content, the phase transformation temperature decreases, the hardness increases and the recrystallization temperature increases. The microstructures of 20 N steel and 150 N steel annealed at different annealing temperatures are composed of ferrite and cementite distributed in chains. At the same annealing temperature, the recrystallization degree of 20 N steel is higher, the {111} texture accounts for a larger proportion, and the grain size is larger. With the increase of annealing temperature, the yield strength and tensile strength show a downward trend, while the elongation shows an upward trend. Compared with 20 N steel, the yield strength and tensile strength of the 150 N annealed sheet are significantly improved, and the elongation is slightly reduced. The calculation results show that the mechanism of nitrogen improving the strength of tinplate is mainly solid solution strengthening, and the improvement effect of fine grain strengthening and precipitation strengthening is weak.