Search Results (397)

This study investigates the thermal response and surface modification of low-carbon manganese-alloyed 20GL steel during electrolytic plasma hardening. The objective was to evaluate the feasibility of surface hardening 20GL steel—traditionally considered difficult to quench—by combining high-rate surface heating with rapid cooling in an electrolyte medium. To achieve this, a transient two-dimensional heat conduction model was developed to simulate temperature evolution in the steel sample under three voltage regimes. The model accounted for dynamic thermal properties and non-linear boundary conditions, focusing on temperature gradients across the thickness. Experimental temperature measurements were obtained using a K-type thermocouple embedded at a depth of 2 mm, with corrections for sensor inertia based on exponential response behavior. A comparison between simulation and experiment was conducted, focusing on peak temperatures, heating and cooling rates, and the effective thermal penetration depth. Microhardness profiling and metallographic examination confirmed surface strengthening and structural refinement, which intensified with increasing voltage. Importantly, the study identified a critical cooling rate threshold of approximately 50 °C/s required to initiate martensitic transformation in 20GL steel. These findings provide a foundation for future optimization of quenching strategies for low-carbon steels by offering insight into the interplay between thermal fluxes, surface kinetics, and process parameters. Full article

The phase transformations of Crucible Particle Metallurgy (CPM) American Iron and Steel Institute (AISI) M4 steel were studied during heat treatments using a CALPHAD-based method. The calculated results were compared with experimental observations. The optimum austenitizing temperature was determined to be about 1120 °C using Thermo-Calc software (2024b). Air-cooling and quenching treatments led to the formation of martensite with a hardness of 63–65 Rockwell C (HRC). The annealing treatment promoted the formation of the equilibrium ferrite and carbide phases and resulted in a hardness of 24 HRC. These findings with regard to phases and microconstituents are in agreement with the predictions derived from a Thermo-Calc-calculated time–temperature–transformation diagram at 1120 °C. Additionally, the primary carbides, MC and M₆C, which formed prior to the heat treatment and had a minor influence on the quenched hardness. In contrast, the tempering process primarily led to the formation of fine secondary M₆C carbides, which hardened the tempered martensite to 57 HRC. The present work demonstrates the application of a CALPHAD-based methodology to the design and microstructural analysis of tool steels. Full article

Thermomechanical processing has a significant impact on the porosity and mechanical properties of AISI 316L stainless steel produced by laser powder bed fusion (L-PBF). This work evaluated the effect of three heat treatment conditions: as-built (HT0), annealed at 650 °C for 3 h with air cooling (HT1), and annealed at 1050 °C for 1 h followed by water quenching (HT2), combined with cold and hot rolling at different strain levels. The most pronounced improvement was observed after 20% hot rolling followed by water quenching (HR + WQ), which reduced porosity to 0.05% and yielded the most spherical pores, with a circularity factor ($f_{circle}$) of 0.90 and an aspect ratio (AsR) of 1.57. At elevated temperatures, the matrix becomes more pliable, which promotes pore closure and helps reduce stress concentrations. On the other hand, applying heat treatment without causing deformation resulted in the pores growing and increasing porosity in the build direction. The fractography supported these findings, showing a transition from brittle to more ductile fracture surfaces. Heat treatment combined with plastic deformation effectively reduced internal defects and improved both structural integrity and strength. Full article

The prediction of microstructure evolution during thermal processing plays a crucial role in tailoring the mechanical properties of metallic components. Therefore, this work presents a comprehensive, multiscale modelling approach to simulating phase transformations in large-diameter steel rings during cooling. A finite-element-based thermal model was first used to simulate transient temperature distributions in a large-diameter ring under different cooling conditions, including air and water quenching. These thermal histories were subsequently employed in two complementary phase transformation models of different levels of complexity. The Avrami model provides a first-order approximation of the evolution of phase volume fractions, while a complex full-field cellular automata approach explicitly simulates the nucleation and growth of ferrite grains at the microstructural level, incorporating local kinetics and microstructural heterogeneities. The results highlight the sensitivity of final grain morphology to local cooling rates within the ring and initial austenite grain sizes. Simulations demonstrated the formation of heterogeneous microstructures, particularly pronounced in the ring’s surface region, due to sharp thermal gradients. This approach offers valuable insights for optimising heat treatment conditions to obtain high-quality large-diameter ring products. Full article

Polypropylene (PP), with its good physical, thermal, and mechanical properties and excellent processing capabilities, has become one of the most used synthetic polymers. It is known that the overall properties of semicrystalline polymers, including PP, are governed by morphology, which is influenced by the crystallization behavior of the polymer under specific conditions. The most important industrial PP remains the isotactic one, and it has been studied extensively for its polymorphic characteristics and crystallization behavior for over half a century. Due to its regular chain structure, isotactic polypropylene (iPP) belongs to the group of polymers with a high tendency for crystallization. The rapid quenching of molten iPP fails to produce a completely amorphous polymer but leads to an intermediate crystalline order. On the other hand, slow cooling yields a material with high crystalline content. The processing conditions that occur in practice and industry are between these two extremes and, in some cases, are even very close. Therefore, the study of limits in processability and the impact of extreme preparation conditions on morphology, structure, thermal, and mechanical properties fills a gap in the current understanding of how the processing conditions of iPP can be used to design the desired properties for specific applications and is in the focus of this research. The first set of samples (Q samples) was obtained by rapid quenching, while the second was prepared by very slow cooling from the melt to room temperature (SC samples). Testing of samples was performed by optical microscopy (OM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic dielectric spectroscopy (DDS), and mechanical measurements. Characterization revealed that slowly cooled samples exhibited a significantly higher degree of crystallinity and larger crystallites (χ ≥ 55% and L₍₁₁₀₎ ≈ 20 nm), compared to quenched samples (χ < 30%, L₍₁₁₀₎ ≤ 3 nm). Mechanical testing showed a drastic contrast: quenched samples exhibited elongation at break > 500%, while slowly cooled samples broke below 15%, reflecting their brittle behavior. For the first time, DDS is applied to investigate molecular mobility differences between processing-dependent structural forms, specifically the mesomorphic (smectic) and α-monoclinic forms. In slowly cooled samples, α relaxation exhibited both enhanced intensity and an upward temperature shift, indicating stronger structural constraints due to a much higher crystalline phase content and significantly larger crystallite size, respectively. These findings provide novel insights into the structure–property–processing relationship, which is crucial for industrial applications. Full article

Based on end-quenching and step-quenching experiments combined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the quench sensitivity of a novel high-strength aluminum alloy was investigated and compared with that of GB/T 7075 and 7175 alloys; quench factor analysis (QFA) was employed to predict the hardness values of the alloy and investigate the effect of quenching rate on its mechanical properties. The experimental results indicate that when the cooling rate decreases from 402.5 °C/s to 3.6 °C/s, the hardness reduction rate of the novel high-strength aluminum alloy is 15%. Furthermore, the nose temperature of the time–temperature–property (TTP) curve for this alloy is 325 °C, with a critical transformation time of 0.4 s. The quench-sensitive temperature range is 219 °C to 427 °C, which is lower than the quenching sensitivity of 7075 and 7175 alloys. The new alloy reduces its quenching sensitivity by optimizing the composition of alloying elements. Furthermore, the QFA demonstrates high predictive accuracy, with a maximum error of 5%. The smaller the quenching factor τ, the greater the hardness of the alloy after aging. Combined with the TTP curve, the alloy properties are optimized by modulating the quenching rate. This study provides a theoretical basis for selecting hot forming–quenching integrated process parameters in automotive high-strength aluminum alloys. Full article

This work—mixing an original experimental approach, as well as numerical simulations—proposes to study film boiling modes around a small nickel sphere. While dealing with a simple looking phenomenon that is found in many industrial processes and has been solved for basic quenching regimes, we focus on describing precisely how vapor formation and film thicknesses, as well as vapor bubble evacuation, affect cooling kinetics. As instrumenting small spheres may lead to experimental inaccuracies, we optically captured, using a high-speed camera, the vapor film thickness at mid height, the vapor bubble volume, and the bubble detachment frequency, along with the heat flux. More precisely, an estimation of the instant sphere temperature, in different conditions, was obtained through cooling time measurement before the end of the film boiling mode, subsequently facilitating heat flux evaluation. We encountered a nearly linear decrease in both the vapor film thickness and vapor bubble volume as the sphere temperature decreased. Notably, the detachment frequency remained constant across the whole temperature range. The estimation of the heat fluxes confirmed the prevalence of conduction as the primary heat transfer mode; a major portion of the energy was spent increasing the liquid temperature. The results were then compared to finite element simulations using an in-house multiphysics solver, including thermic phase changes (liquid to vapor) and their hydrodynamics, and we also captured the interfaces. While presenting a challenge due to the contrast in densities and viscosities between phases, the importance of the small circulations along them, which improve the heat removal in the liquid phase, was highlighted; we also assessed the suitability of the model and the numerical code for the simulation of such quenching cases when subcooling in the vicinity of a saturation temperature. Full article

High-Cu-content (Cu-content > 1.3 at.%) nanocrystalline alloys exhibit wide heat-treatment windows and favorable soft magnetic properties due to the presence of pre-existing α-Fe nanocrystals. By fabricating ribbons with varying thicknesses to tailor cooling rates, distinct structural characteristics were achieved in Fe₈₂B_16.5Cu_1.5 alloy ribbons. Notably, the face-centered cubic (fcc) γ-Fe phase was identified in Fe-based nanocrystalline alloys. The precipitation of the fcc γ-Fe phase originates from a phase-selection mechanism under specific cooling conditions, while its retention in the as-quenched ribbon with a thickness of 27 μm is attributed to kinetic suppression during rapid cooling and the nanoscale stabilization effect. The formation of the fcc γ-Fe phase significantly reduced the saturation flux density (B_s) and increased coercivity (H_c), concurrently destabilizing the residual amorphous matrix. By suppressing the precipitation of the γ-Fe and Fe₃B phases through precise control of ribbon thickness and annealing parameters, the alloy ribbon with a thickness of 16 μm achieved an optimal combination of B_s (1.82 T) and H_c (8.3 A/m). These findings on anomalous fcc γ-Fe phase precipitation provide novel insights into metastable phase engineering and offer structural design guidelines for alloys containing pre-existing α-Fe nanocrystals. Full article

Blast furnace slag, a high-temperature molten by-product generated during the ironmaking process in the metallurgical industry, has garnered significant attention for its resource utilization technologies. Compared to the traditional water-quenching method, dry granulation offers notable advantages. This paper systematically compares and analyzes the performance parameters of three typical dry treatment processes: mechanical crushing, air-quenching granulation, and centrifugal granulation. It reveals that the centrifugal granulation process demonstrates substantial technical superiority in key metrics, such as particle size distribution uniformity, particle morphology optimization, and heat recovery efficiency. Building on this, this study provides a comprehensive review of the current state of centrifugal granulation technology, from both experimental and simulation perspectives. Additionally, the combined processes of centrifugal granulation and air quenching can fully exploit the synergistic benefits of each technology, thereby enhancing overall efficiency. However, the wind’s cooling effect can lead to the premature solidification of molten slag when it splits into liquid filaments, resulting in slag wool. To address this, this paper proposes a centrifugal granulation device equipped with a windbreak board, which facilitates temperature zoning. This approach prevents premature solidification in the liquid filament region while ensuring the timely cooling and solidification of slag particles, offering a novel technical solution for optimizing centrifugal granulation in metallurgical solid waste resource utilization. Full article

Ultra-high strength steel (UHSS) contributes significantly to lightweight design, environmental compatibility and lower fuel consumption. However, it is essential to maintain excellent mechanical properties in terms of structural integrity, strength and ductility after the applied welding process. In this study, the effect of post-welding heat treatments on the welding of UHSS S1100MC was investigated in order to compensate for the deterioration in toughness that occurred as a result of joining by electron beam welding. Electron beam welding (EBW) provides high energy density and therefore relatively low heat input compared to arc welding. However, the narrow fusion zone (FZ) and heat-affected zone (HAZ) may have insufficient toughness values due to rapid cooling of the joint. In order to protect the relationship between strength and toughness, both the material and the joint were subjected to heat treatment at 500, 650 and 750 °C temperatures for 2 h and were cooled in the furnace. Microstructural characterization and mechanical testing, namely hardness, Charpy impact and tensile tests, were performed to correlate the influence of post-weld heat treatment on the microstructural formation and the corresponding mechanical properties. While the material and the joint maintained their hardness values at 500 °C of around 412 ± 15 HV_0.2, there was an approximately 8% decrease in hardness to 378 ± 18 HV_0.2 at 650 °C. At 750 °C, it dramatically lost its high hardness properties, resulting in a low 178 ± 9 HV_0.2. However, direct quenching from the austenitic temperature resulted in fresh martensite, which provided both the required strength and toughness values in the EBW joint. With a hardness of 437 HV_0.2, a tensile strength of 1345 MPa and a fracture elongation of more than 9%, superior mechanical properties could be achieved. Full article

This research focuses on Fe-18Mn-10Al-1C-5Ni lightweight steel and deeply explores the influences of three different cooling methods, namely, water quenching (WQ), air cooling (AQ), and furnace cooling (FQ), on the precipitation behavior of the B2 phases and κ-carbides in the lightweight steel. The intrinsic relationship among the precipitated phases, mechanical properties, and fracture behavior is revealed. Compared with the WQ sample, the size of the intragranular B2 phase in the AQ sample did not change significantly (an increment of 9 nm), but nano-sized κ-carbides appeared at the grain boundaries and inside the grains. The yield strength and tensile strength of the AQ sample significantly increased to 1232 MPa and 1347 MPa, respectively, while an elongation of 17.4% was still maintained, which benefitted from the synergistic effect of the grain boundary B2, intragranular B2, and nano-sized κ-carbides. When the cooling rate of the heat treatment was further reduced, the size of the intragranular B2 phase in the FQ sample increased slightly (332 nm), and the κ-carbides at the grain boundaries became obviously coarsened (170 nm), resulting in a severe reduction in the elongation (2.3%) because, during the tensile deformation process, the coarsened κ-carbides at the grain boundaries promoted the nucleation of voids and microcracks. The present work provides new insights into the cooling heat treatment process of lightweight steel. Full article

In this paper, the crystal structure, microstructure, and deformation behavior in the Ti-33Nb alloy under furnace-cooling (FC) and water-quenching (WQ) conditions after holding at 950 °C for 0.5 h are reviewed. The stable and metastable phases obtained under FC and WQ heat treatments have significantly different influences on the mechanical properties of this alloy. The furnace-cooling specimens possess a β and α phase at room temperature, while water-quenched specimens are composed of a metastable β phase and martensite α″ phase. According to the results of the nanoindentation test, the hardness value of the FC specimens is 2.66 GPa, which is lower than that of the WQ specimens. It can be attributed to the presence of a large number of α phases. The indentation depth recovery ratio (η_h) and work recovery ratio (η_w) of the WQ specimens are 19.02% and 19.54%, respectively, indicating a better superelastic response than the FC specimens. In addition, the wear resistance (H/E_r) and yield pressure (${\mathrm{H}}^3/{\mathrm{E}}_{\mathrm{r}}^2$) of the WQ specimens are 0.0282 and 0.0030 GPa, respectively, suggesting a better wear resistance and resistance of plastic deformation. Full article

In the present work, the effect of quenching and partitioning cycles on the microstructure, hardness, and corrosion behavior of SAE 9254 spring steel was investigated. Initially, the critical phase transformation temperatures were analyzed by dilatometry. The samples were then treated by four routes of quenching and partitioning in a dilatometer with quenching stop temperatures of 250 and 220 °C. The partitioning temperatures were 300 and 400 °C. The partitioning time was 480 s. Quantitative characterization of austenite and martensite volume fractions was carried out by X-ray diffraction. Qualitative characterization was carried out by optical microscopy and scanning electron microscopy in addition to quantitative assessments of the chemical composition of segregations by EDS. The formation of martensite, retained austenite, and bainite was observed. The dilatometric curves displayed the occurrence of volumetric expansion in the partitioning step, indicating the formation of secondary martensite (fresh martensite) during the final cooling process (final quenching). The mechanical properties were evaluated by Vickers microhardness and nanoindentation tests. There was heterogeneity of hardness inside and outside the banding regions. The electrochemical properties were evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization tests in a 0.1 M H₂SO₄ solution. The best corrosion resistance was achieved for samples quenched at 250 °C and partitioned at 400 °C due to the higher volume fraction of retained austenite when compared to the other heat treatment conditions. Full article

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications. Full article

The development of high-strength cast irons with multiphase metal matrix structures is one of the new areas of modern materials science and mechanical engineering. This is so because of the high dissipative properties of such materials, which, in turn, ensure an improvement in their functional characteristics. It is known that one of the effective methods for obtaining alloys with a heterogeneous structure is a multi-stage heat treatment. Therefore, this study aimed to enhance the corrosion and friction properties of high-strength cast irons by combining different processing methods to create a bainite-martensitic matrix. High-strength cast irons with high ductility micro-alloyed with boron were chosen as the object for research. The experiments studied the effect of various types of multi-stage heat treatment on the structural features, tribological properties, hardness and corrosion resistance. The cast irons were quenched in water or liquid nitrogen after a controlled duration of isothermal exposure at different temperatures. It was established that cooling of isothermally hardened samples in liquid nitrogen makes it possible to effectively engineer the morphology and amount of the formed martensitic phase. It was observed that the high-strength cast irons with 10–15% lower bainite, residual austenite and martensite have the best frictional characteristics. This innovative method allowed the quenching of cast iron directly into liquid nitrogen without violent cracking. Full article