Heat Treatment Process Research Articles

Comprehensive Study of CoCrCuNi High-Entropy Alloys: Effects of Preparation, Heat Treatment, Computational Simulation, and Alloying Elements

High-entropy alloys have attracted widespread attention from researchers worldwide due to their unique microstructure and outstanding mechanical properties, making them a prominent focus in the field of metallurgy. Among the various high-entropy alloys, the CoCrCuNi system was among the first alloys discovered, and it has shown significant progress in development. By employing different preparation and heat treatment processes, researchers have obtained alloys with diverse performances. The addition of various alloying elements or other components can lead to pronounced variations in the properties of CoCrCuNi high-entropy alloys. This work provides a comprehensive review of recent research progress on CoCrCuNi high-entropy alloys. It covers the preparation methods, thermodynamic and kinetic simulation calculations, as well as discussions on heat treatment processes and the influence of alloying elements on the microstructure and mechanical properties of CoCrCuNi high-entropy alloys. Finally, the review concludes with a prospective analysis and predictions for the potential applications and future directions in developing novel high-entropy alloys.

Stiffness and hardness of thermally modified timber assessed with explainable machine learning

Thermal modification is an environmentally friendly practice to enhance the durability of wood. Despite the method's effectiveness in improving wood durability and dimensional stability, the mechanical properties of wood could be compromised following the heat treatment process. While most of the literature has focused on studying the impact of wood modification on stiffness or strength, less attention was given to characterization and nondestructive prediction of wood hardness following thermal treatment. Hardness, an important quality indicator of wood, has been a subject of limited research in the context of developing predictive models for assessing the hardness of thermally modified wood. The existing research in this area has either been scarce or unsuccessful, with poor predictive performance being a common issue. This research studies the impact of thermal modification on the longitudinal and transverse hardness of some common North American softwoods (Douglas-fir, Western hemlock, red cedar) and hardwoods (red alder, paper birch). It also aims to develop an explainable machine-learning (TreeNet gradient boosting machine) predictive model for hardness prediction using stress wave data combined with wood density and information about the type of wood species and heat treatment level. The impact of heat treatment on the stress wave velocity, density, and hardness was studied, and the dependency of the variables was assessed using correlation and clustering analysis. Machine learning modeling showed that the longitudinal and transverse hardness could be predicted by having a maximum R2 (test data) of 70.62 and 72.78, respectively, with a relative importance of the predictors in descending order as wood species > density > wave velocity >MOEdyn> heat treatment. Using the top 3 critical parameters yielded an R2 (test data) of ∼69 % for both models. The developed model could predict the hardness of various wood species treated at different temperatures, having only the type of wood species and its density followed by the stress wave velocity, which can be measured at an industrial scale.

Experimental study in steady-state for determining the coefficient of external heat transfer on the outer wall of rotating tubes during the quenching process by immersion in water tank

The quenching process by immersion is one of the steel tube industry's most commonly used heat treatment processes. For mathematical models to be reliably used as tools capable of simulating different geometries and cooling mechanisms, knowledge of the heat transfer coefficient between the surface of the tube and the water is essential. The present work's primary objective is the experimental determination of the heat transfer coefficient between the external surface of the tube and the water. For this purpose, an experimental apparatus capable of representing the conditions of a real process was built. The predominant heat transfer regime in the single-phase region was mixed convection for the conditions tested. Two correlations were proposed to represent the data obtained for this region. Based on existing correlations in the literature, the first one returned a mean absolute error of 13.97 %. The second one was proposed based on an optimization tool, returning a mean absolute error of 6.29 %. Concerning the two-phase region, the obtained data characterized a transition regime and the beginning of the nucleated boiling. In this region, it was possible to observe that the effect of increasing rotation on the external heat transfer coefficient decreases with increasing tube surface temperature, which follows studies in the literature. The repeatability test shows that the apparatus could replicate the heat transfer coefficient values for the free convection region, staying within the range of uncertainties. However, for the boiling region, the data showed more significant disagreement. This behavior is mainly due to the difficulty of keeping the surface under the same conditions, which have greatly influenced the formation of bubbles and heat transfer.

Microstructure evolution and mechanical properties of martensitic stainless bearing steels with different carbon nitrogen ratios

This study investigates the effect of adjusting the carbon nitrogen ratio on the microstructure and mechanical properties of martensitic stainless bearing steels, keeping the equivalent total carbon and nitrogen content. The results demonstrate that the sample with nearly equal weight percentages of C and N exhibits optimal comprehensive performance, achieving impressive yield strength, ultimate tensile strength, and uniform elongation of up to 1806.5 MPa, 2279.3 MPa, and 4.5%, respectively. Distinct phase ratios and morphologies observed across the three C/N ratios after identical heat treatment process suggest varying intrinsic mechanisms due to differences in C and N solid solubility in the matrix. The specimen with almost balanced C and N shows the highest interstitial atom solubility in the austenite phase, stabilizing austenite and lowering stacking fault energy. Abundant fine twins in martensite and stacking faults in austenite contribute to increased elongation without compromising strength. In contrast, specimen with higher N/C ratio exhibits numerous nitrides, limiting N atom solid solution in austenite during austenization, resulting in martensite with twins and dislocations. Specimen with higher C/N ratio shows extensive carbide precipitation and mainly dislocation-type martensite. The study deepens the understanding of C and N interactions in advanced bearing steels and provides a foundation for improving mechanical properties of such steels.

Exploring residual stress analysis in the machining of hypoeutectic high chromium white cast iron alloys through the hole-drilling method

Abstract High chromium white cast irons (HCWCIs), ASTM A352, Type A and Class III, i.e., 25%Cr iron in as-cast condition consists of proeutectic austenite (γ-Fe), transformed martensite (α-Fe) and discontinuous Cr-rich, i.e., M7C3/ (Cr, Fe)7C3 type of carbides, which are hard and brittle in nature. Fully annealed thermal treatment was performed to improve iron’s machinability leading to fully pearlitic matrix with minor retained γ-Fe content. Eutectic (Cr, Fe)7C3 type of carbides are not affected by heat treatment processes. Resulting from corresponding manufacturing process, the magnitude and distribution of residual stresses (RSs) in as-cast and after machining were measured using hole-drilling method (HDM), as they are known to be harmful to corrosion and fatigue resistance. Furthermore, general metallurgical material characterisation was performed in as-cast and heat-treated conditions. As a result, this study revealed hardness variation, 547 and 555BHN in as-cast as compared to 327BHN in heat-treated condition. Furnace and actual cast component chemical analysis revealed a slight variation, especially between carbon (C) and chromium (Cr). Furthermore, eutectic type of carbides and precipitated secondary, i.e., (Cr, Fe)23C6 type of carbides within fully pearlitic matrix with minor amounts of retained γ-Fe were detected within the dominant matrix, i.e., pearlitic matrix in as-annealed condition. Detected magnitude and distributions of RSs on heat-treated sample resulted in higher tensile stresses in the surface and compressive in the interior as compared to sample in as-cast condition. Thus, this study was successfully in measuring RSs in as-cast and upon machining of hypoeutectic irons of HCWCI alloys using HDM.

Study on Grain Boundary Characteristic Distribution of Nickel Base 625 Alloy Controlled by Deformation Heat-Treatment Process

Study on Grain Boundary Characteristic Distribution of Nickel Base 625 Alloy Controlled by Deformation Heat-Treatment Process

RESEARCH PROGRESS ON STRENGTHENING PROCESS OF H13 STEEL FOR SHIELD CUTTER RING

As China continues to advance the modernization process, a large number of infrastructure construction projects need to use shield machines to build tunnels. As a key component of the shield machine/TBM direct contact working environment, the hob is extremely complex and extremely harsh due to the extremely complex and extremely harsh working environment, resulting in hobs. It is very easy to damage when in service. The damage of the hob directly leads to many problems such as project delay and capital consumption. Therefore, improving the mechanical properties of the hob and prolonging the service life is an important engineering problem to be solved urgently. Based on the service performance of disc cutter, this paper analyzes its failure form and wear mechanism, and summarizes the strengthening process and improvement method of the H13 steel disc cutter ring. In this paper, the advantages and disadvantages of previous researchers and optimization methods are reviewed for H13 steel material composition, heat treatment process, surface coating strengthening process, and other processes. Finally, the performance strengthening of hob cutter ring is discussed and prospected, in order to provide a reference for hob strengthening technology path and industrialization realization.

Retained austenite in medium manganese steel with dissimilar morphology and composition

The microstructure and mechanical properties of medium manganese steel with a composition of 0.2C-5Mn-0.5Si-1.5Al (wt.%) were investigated, employing a two-stage heat treatment process. The microstructure following pretreatment comprised pearlite, martensite, and ferrite. Subsequent intercritical annealing resulted in the formation of retained austenite with varying morphology and composition. The filmy retained austenite transformed from pearlite exhibited a higher Mn content compared to the blocky retained austenite transformed from martensite, while also displaying a slower growth rate. Moreover, the filmy retained austenite exhibited superior thermal and mechanical stability. Tensile tests showed that the test steels not only obtained high strength (>1000 MPa) and high elongation (>30%), but the stress-strain curves also showed continuous yielding behaviour and a more reasonable ratio of tensile strength to yield strength.

Buckling behaviour of high-strength retrofitted steel sections manufactured through post heat-treatment processes

High-strength steel is increasingly popular in construction for its strength-to-weight ratio, which lowers the self-weight of structures and reduces transportation, erection, and foundation costs. Induction hardening (IH) process which involves rapid heating and cooling of the material leads to microstructural changes which enhance the hardness and strength of conventional steel, elevating it to the level of High Strength (HS) steel. This study reports an extensive investigation on the buckling response and design of IH post-treated structural steel Circular Hollow Sections (CHS). It includes tensile coupon tests, microstructural analyses, initial geometric imperfection measurements, and residual stress evaluations to determine the effects of IH treatment on CHS. Column buckling tests were conducted, and a numerical model was developed and validated against the experimental results which was utilised to study systematically the effect of imperfections. The findings suggest that the magnitude of the imperfections in IH steel sections doubled compared to the non-treated condition, whilst there was a minimal impact on the residual stresses. A comprehensive parametric study was performed using finite element models to study the structural response of IH steel CHS columns over a large range of global slendernesses and allow the assessment of the buckling curves specified in EN 1993–1–1. It was concluded that the buckling curve a (imperfection factor, α=0.21) specified in EN 1993–1–1 provides the best buckling load predictions for the IH steel CHS columns, the response of which is superior to that of their virgin counterparts, despite the increased imperfections caused by the heat-treating process.

Enhancing the life of forging dies by investigating different heat treatment methods

ABSTRACT The present study investigates the impact of a Conventional Heat Treatment (CHT) and a Modified Heat Treatment (MHT) method that incorporates a deep cryogenic treatment in the process, on the mechanical properties, the microstructure of samples, and the lifespan of forging dies. The samples treated with the modified heat treatment showed less variation in elongation at similar strengths. The addition of deep cryogenic treatment in the heat treatment process increased the volume of fine, uniformly distributed carbides, enhancing secondary hardening compared to conventional methods. This treatment, followed by tempering, improved the die's service life and resulted in moderately higher impact toughness. The average lath length and width were reduced with modified heat treatment when observed after the second tempering. The wear of the forging die was reduced with modified heat treatment, and the service life was increased.

Producing antifriction babbitt В83 layer by gas-dynamic cold spraying

The technological processing of antifriction layer from Babbitt by gas-dynamic cold spraying was carried out on the DIMET-403. The coating was sprayed on plain bearings for marine low- and medium-speed diesel engines, turbines, and shaft lines. Technical requirements for antifriction layer materials, standard technological processes of preparation, spraying, heat treatment, and quality control are also considered.

Production of Low Temperature Synthetic Graphite

Synthetic graphite is a material consisting of graphitic carbon which has been obtained by graphitizing a non-graphitic carbon. The growth in demand, particularly in customizing properties for certain usage has brought about research on viable alternative, low-cost, and environmentally pleasant synthetic graphite production. Biomass wastes are amongst appealing carbon precursors which have been broadly checked out as replacement carbon for graphite production. This research aimed to synthesize synthetic graphite from oil palm trunks at low temperatures (500 °C, 400 °C and 300 °C) under controlled conditions to determine the physical properties and properties of the graphite obtained. After the heat treatment process, the obtained samples were then characterized by using XRD, SEM and RAMAN characterizations. Based on SEM and RAMAN characterization, it can be seen that graphite that undergoes a 500 °C pyrolysis process shows the best results compare to graphite that undergoes a pyrolysis process at the temperatures of 300 °C and 400 °C. The graphite flakes and the peaks obtained for 500 °C graphite are obviously present. For XRD characterization, the best samples at 500 °C were chosen to be characterized. From the results, the sample shows slight behavior imitating the commercialized graphite. Hence, from the characterizations of the samples, it can be concluded that the best synthetic graphite produced was from the oil palm trunks heated at 500 ° C.

Data-driven predictions of retained austenite content and yield strength and elucidation of the sliding wear performance of carbide-free bainitic steels

Carbide-free bainitic (CFB) steels have drawn much attention due to their high strength and toughness. The present work aims to build machine learning (ML) based surrogate models to predict retained austenite (RA) content and yield strength (YS) of isothermal transformed CFB steels and study the sliding wear performance. The input data for ML prediction were related to compositions, heat treatment process, and phases. The Random Forest regression and Gaussian process regression were respectively selected to build the predictive models for RA content and YS. Result shows that the predicted RA content agrees well with the experimentally determined ones in steel with high stability of untransformed austenite. For YS prediction, the present surrogate model can predict YS of CFB steels even without additional microstructural information such as dislocation and effective substructure size. Steels with different YS and RA content were designed to study the sliding wear performance. Result shows that the dominant wear mechanism of the tested steels is abrasive wear and the weight loss is inversely proportional to hardness when the load and wear distance are constant. Increasing YS and RA content can increase the initial hardness and work hardening ability at the worn surface, thereby enhancing wear resistance.

Fuel Cell Catalyst Layers with Platinum Nanoparticles Synthesized by Sputtering onto Liquid Substrates.

Platinum (Pt) nanoparticles are widely used as catalysts in proton exchange membrane fuel cells. In recent decades, sputter deposition onto liquid substrates has emerged as a potential alternative for nanoparticle synthesis, offering a synthesis process free of contaminant oxygen, capping agents, and chemical precursors. Here, we present a method for the synthesis of supported nanoparticles based on magnetron sputtering onto liquid poly(ethylene glycol) (PEG) combined with a heat-treatment step for attachment of nanoparticles to a carbon support. Transmission electron microscopy imaging reveals Pt nanoparticle growth during the heat-treatment process, facilitated by the carbon support and the reducing properties of PEG. Following the heat treatment, a bimodal size distribution of Pt nanoparticles is observed, with sizes of 2.5 ± 0.8 and 6.7 ± 1.8 nm, compared to 1.8 ± 0.4 nm after sputtering. Synthesized Pt nanoparticles display excellent specific and mass activities for the oxygen reduction reaction, with 1.75 mA/cm2 Pt and 0.27 A/mgPt respectively, measured at 0.9 V vs the reversible hydrogen electrode. The specific activities reported herein outperform literature values of commercial Pt/C catalysts with similar loading and are on par with values of bulk Pt and mass-selected nanoparticles of comparable size. Also, the mass activities agree well with the literature values. The results provide new insights into the growth processes of SoL-synthesized carbon-supported Pt catalyst nanoparticles, and most crucially, the high performance of the synthesized catalyst layers, along with the possibility of nanoparticle growth through a straightforward heat-treatment step at relatively low temperatures, offer a scalable new approach for producing fuel cell catalysts with more efficient material utilization and new material combinations.

A high‐entropy (Er0.25Y0.25Ho0.25Yb0.25)2Si2O7 ceramic with good thermal properties and water‐vapor corrosion resistance

AbstractA high‐entropy rare‐earth disilicate (Er0.25Y0.25Ho0.25Yb0.25)2Si2O7 (hereinafter referred to as (EYHY)2Si2O7) ceramic was synthesized by a heat treatment process combined with spark plasma sintering. According to the experimental results, (EYHY)2Si2O7 presents good phase stability and low thermal conductivity ([1.48–2.35] W∙m−1∙K−1) from room temperature to 1200°C. Its coefficient of thermal expansion is (3.89–5.32) × 10−6 K−1 from 200 to 1400°C, similar to SiC‐based materials ([4.5–5.5] × 10−6 K−1). Due to the multiple doping effects, (EYHY)2Si2O7 exhibits outstanding corrosion resistance performance in water‐vapor corrosion tests. Its weight loss is 1.79 mg/cm2 after corrosion at 1600°C for 30 h in the presence of 50% H2O‐50% O2, which is lower than the corresponding four single components Re2Si2O7 (Er2Si2O7, Y2Si2O7, Ho2Si2O7, and Yb2Si2O7) under the same conditions. Therefore, high‐entropy (EYHY)2Si2O7 ceramics are regarded as potential environmental barrier coatings materials for SiC ceramic matrix composites.

Prediction of rotational bending fatigue life of bearing steel based on damage mechanics

Based on the theory of continuous damage mechanics, this paper proposes a fatigue damage evolution model and numerical calculation method considering the influence of vacuum chemical heat treatment process, and studies the rotational bending fatigue damage analysis and life prediction method of M50NiL bearing steel. Firstly, the constitutive model, fatigue damage evolution equation and material parameter calibration method in the theoretical model are given. Secondly, based on the ABAQUS platform, the damage mechanics-finite element numerical calculation method of fatigue damage analysis considering the influence of hardened layer is realized by writing the UMAT subroutine; then, the rotational bending fatigue test of M50NiL bearing steel treated by vacuum chemical heat treatment of quenching and tempering, carburizing and carbonitriding is carried out, and the influence of heat treatment process on fatigue performance is analyzed; finally, based on the proposed fatigue damage model and numerical calculation method, the rotational bending fatigue life of M50NiL bearing steel is predicted, and the results are compared with the experimental results to verify the correctness of the proposed method.

Influence of layer thickness and heat treatment on microstructure and properties of selective laser melted maraging stainless steel

As one of the main parameters of selective laser melting (SLM) process, layer thickness has a significant impact on the forming performance and efficiency of printed parts. Based on microstructure analysis and properties testing, the metallurgical mechanism, phase composition and mechanical behavior of SLM-formed Corrax stainless steel with different layer thicknesses were discussed. The influence of heat treatment process on the properties was comparatively investigated. The results indicated that at smaller or larger layer thicknesses, the increase in melt dynamic instability and spheroidisation feature easily induced the formation of unfused pore defects, which in turn led to lower relative density and mechanical properties. At the appropriate layer thickness, the suitable melt flow behaviour promoted the formation of good metallurgical bonding between adjacent melt channels. The maximum tensile strength, yield strength and hardness of the samples prepared at a layer thickness of 60 μm were 1224 MPa, 948 MPa and 39.2 HRC, respectively. The microstructure of the as-built samples was martensite and a small amount of austenite. With increasing layer thickness, the cooling rate of the molten pool decreased and the austenite content increased. After solution treatment, the alloying elements dissolved in the martensitic matrix resulted in lower mechanical properties. After aging and solution aging treatment, the mechanical properties were significantly improved due to precipitation strengthening of NiAl nanoparticles and dislocation strengthening. The corresponding tensile strengths were 1655 MPa and 1796 MPa, the yield strengths were 1328 MPa and 1573 MPa, and the hardnesses were 45.7 HRC and 50.2 HRC, respectively.

Study on the effect of temperature on the microstructure and mechanical properties of as-cast CoCr2Ni3.5VAl1.5Ti high-entropy alloy

This study investigates the microstructure and mechanical properties of a CoCr2Ni3.5VAl1.5Ti high entropy alloy (HEA) annealed at 500 °C, 700 °C, 900 °C and 1100 °C for 6 h. The alloy was prepared using a vacuum induction melting furnace and annealed at the specified temperatures for 6 h. It was then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). The results indicate that with increasing annealing temperature, the alloy's phase structure transitions gradually from multiphase (fcc, bcc, hcp) to predominantly fcc phase, with relatively stable elemental distributions. Annealing at 500 °C–900 °C mainly strengthens the alloy through precipitates and dislocation strengthening, whereas at 1100 °C, strengthening occurs through grain boundary strengthening and precipitate growth, enhancing the material's strength and ductility. The alloy exhibits optimal comprehensive performance after annealing at 1100 °C. This study provides important insights for optimizing the heat treatment process of HEAs.

Influence of Annealing and Aging Parameters on the Microstructure and Properties of 1200 MPa Grade Cold-Rolled Dual-Phase Steel

With the rapid development of the automotive industry, the requirements for bodywork materials are not only focused on high strength but also on improved forming properties. To develop a new generation of automotive steels with higher strength–plasticity matching, a high elongation 1200 MPa grade V-Nb microalloyed cold-rolled reinforced formable dual-phase steel was developed in this experiment through rational compositional design and precise process machining. The properties of the test steel are improved by varying the over-aging temperature as well as the annealing temperature to achieve a good strength–plasticity balance. The results show that as the aging temperature increases, the tensile strength and yield strength of the test steel decrease, while the elongation continues to increase. At an aging temperature of 310 °C, the steel exhibits not only high strength but also better ductility. As the annealing temperature increases, the tensile strength and yield strength of the test steel initially increase and then decrease, while the elongation continues to increase. When the heat treatment process involves an annealing temperature of 860 °C and an over-aging temperature of 310 °C, the test steel achieves the best strength–plasticity balance.

Dependence of structures and performances of soft-magnetic FeCo-based metal glasses on cryogenic treatments

The amorphous structures, thermal stability, soft-magnetic properties and microhardness have been explored for quaternary quenched (Fe0.8Co0.2)75B21Ta4 (Fe0.8) and (Fe0.5Co0.5)75B21Ta4 (Fe0.5) metallic glasses (MGs) after deep (77 K), moderate (173 K) and shallow (253 K) cryogenic treatments (CTs). Compared to Fe0.5, the as-spun Fe0.8 exhibits significantly higher thermal stability and Curie temperature (686 K), which could be explained by the Mössbauer spectra results of higher A23 and lower hyperfine magnetic field as well as isomer shift. But the as-spun Fe0.5 shows a more prominent magnetic rejuvenation trend. Additionally, the observation of magneto-optic Kerr microscope displays that magnetic domains around surface defects exhibit a trend from being easy to magnetize to becoming difficult with increasing reverse magnetic field intensity.The cryo-treated Fe0.8 and Fe0.5 ribbons maintaining a completely amorphous structure reveal the improved soft-magnetic property and microhardness, and the performance optimization of Fe0.5 is more sensitive to CTs. Appropriate CTs distinctly decrease coercivity (Hc) of two tested MGs, and moderate CT reduces the Hc of Fe0.5 by 24.1%, achieving commendable magnetic softening. The Hc variation can be rationalized by the evolution of free volume in the amorphous matrix involving freezing, partial annihilation and imbalance under different CTs. Moreover, shallow CT significantly expands the heat-treatment processing window of MGs.