Search Results (68)

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

This study investigates the influence of plastic deformation and temperature on the formation of mechanically induced martensite and the associated changes in hardness in AISI 304 austenitic stainless steel. Cold rolling was performed at three temperatures (20 °C, 0 °C, and −196 °C) and various degrees of deformation (10–70%). Microstructural changes, including the formation of ε and α′ martensite, were characterized using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The results confirm that martensitic transformation proceeds via the γ → ε → α′ sequence, with transformation rates and martensite fractions increasing at lower temperatures and higher strains. The stacking fault energy of 25.9 mJ/m² favors this transformation pathway. Transformation rates of α′ martensite fractions significantly increased at lower temperatures and higher strains, 91.8% α′ martensite was observed at just 30% deformation at −196 °C. Hardness measurements revealed a strong correlation with martensite content: strain hardening dominated at lower deformations, while martensite formation became the primary hardening mechanism at higher deformations, especially at cryogenic temperatures. The highest hardness (551 HV) was observed in samples deformed to 70% at −196 °C. The findings provide insights into optimizing the mechanical properties of AISI 304 stainless steel through controlled deformation and temperature conditions. Full article

In this study, solid particle erosion tests were conducted to evaluate the resistance of AISI 4340 (EN24) and 8620 alloy steels against silicon carbide (SiC). These steels were selected due to their high hardness, yield strength (σ_y), ultimate tensile strength (σ_uts) and elongation (%), which are significant parameters, influencing wear resistance. An erosion rig based on the ASTM G76-95 standard was used to perform the testing. Tests were carried out using different impact angles, 30°, 45°, 60° and 90°, with a particle velocity of 24 ± 2 m/s. The abrasive flow rate was 0.7 ± 0.5 g/min and the temperature was between 35 °C and 40 °C. Characterization techniques such as SEM were employed to identify the chemical composition of AISI 4340 and AISI 8620 steels and optical microscopy to determine the morphology of SiC abrasive particles. In addition, the SiC particle size was between 350 and 450 µm; it was determined by the particle size distribution technique. SEM micrographs were obtained to classify the wear mechanisms, characterized by micro-cutting, micro-ploughing, grooves, pitting actions and embedded particles on the surface at 30° and 90°. The results showed that AISI 8620 steel exhibited higher erosion resistance than AISI 4340 steel. Finally, AFM was used to evaluate the roughness variations before and after erosion tests, specifically in the central zone of the wear scars at 30° and 90° for both materials. Full article

This study elucidates the dynamic tribo-mechanical response of laser-cladded FeNiCr-B₄C metal matrix composite (MMC) coatings on AISI 1040 steel substrate, unraveling the intricate interplay between microstructural features and phase transformations. A multi-faceted approach, employing high-resolution scanning electron microscopy (SEM) and advanced X-ray diffraction/Raman spectroscopy techniques, provided a comprehensive characterization of the coatings’ behavior under mechanical and scratch testing, shedding light on the mechanisms governing their wear resistance. Specifically, microstructural analysis revealed uniform coatings with a columnar structure and controlled defect density, showcasing an average thickness of 250 ± 20 μm and a transition zone of 80 ± 10 μm. X-ray diffraction and Raman spectroscopy confirmed the presence of α-Fe (Im-3m), γ-FeNiCr (Fm-3m), Fe₂B (I-42m), and B₄C (R-3m) phases, highlighting the successful incorporation of B₄C reinforcement. The addition of 5 and 7 wt.% B₄C significantly increased microhardness, showing enhancements up to 201% compared to the B₄C-free FeNiCr coating and up to 351% relative to the AISI 1040 steel substrate, respectively. Boron carbide addition promoted a synergistic strengthening effect between the in situ formed Fe₂B and the retained B₄C phases. Furthermore, scratch test analysis clarified improved wear resistance, excellent adhesion, and a tailored hardness gradient. These findings demonstrated that optimized short-pulsed laser cladding, combined with moderate B₄C reinforcement, is a promising route for creating robust, high-strength FeNiCr-B₄C MMC coatings suitable for demanding engineering applications. Full article

The study examined the influence of ion-plasma nitriding on the structure, mechanical, and tribological properties of high-speed steels AISI M2 and AISI M41. A comprehensive study was conducted on the changes in phase composition, microhardness, and wear resistance of the obtained modified layers. It was established that the optimal approach was the formation of high-nitrogen martensite without excessive nitrides, which ensured improved mechanical properties of the steels. The dependence of the nitrided layer depth and its microhardness on nitriding temperature and duration was investigated. It was found that at a temperature of 480–520 °C and a processing duration of up to 1 h, a hardened layer with a depth of 25–40 μm was formed, exhibiting increased wear resistance and microhardness of up to 10–12 GPa. The analysis of structural transformations confirmed the presence of ε and γ’ phases, which contributed to increased strength and reduced friction coefficient. The obtained results can be used to improve the technological processes of heat treatment for high-speed steels used in the production of cutting tools. The proposed nitriding parameters contribute to extending the service life of steel components, which is relevant for the mechanical engineering and metallurgical industries. Full article

This work presents a novel, compact (six pieces), low-cost (<$500 USD), and easy-to-manufacture metallography mounting device. The device is designed to produce high-quality polymer encapsulated samples that rival those obtained from commercial equipment ($5000–$10,000 USD). Utilizing the House of Quality (HoQ) framework within Quality Function Deployment (QFD), the device prioritizes critical customer requirements, including safety (validated via finite element method, FEM), affordability, and compatibility with standard hydraulic presses. FEM analysis under 29 MPa pressure revealed a maximum Von Mises stress of 80 MPa, well below the AISI 304 stainless steel yield strength of 170 MPa, yielding a static safety factor of 2.1. Fatigue analysis under cyclic loading (mean stress ${\sigma }_m$ = 40 MPa, amplitude stress ${\sigma }_a$ = 40 MPa) using the Modified Goodman Criterion demonstrated a fatigue safety factor of 3.75, ensuring infinite cycle durability. The device was validated at 140 °C (413.15 K) with a 5-min dwell time, encapsulating samples in a cylindrical configuration (31.75 mm diameter) using a 200 W heating band. Benchmarking confirmed performance parity with commercial systems in edge retention and surface uniformity, while reducing manufacturing complexity (vs. conventional 100-piece systems). This solution democratizes access to metallography, particularly in resource-constrained settings, fostering education and industrial innovation. Full article

This study investigated the thermophysical properties of TWIP steel with respect to grain size. The coefficient of thermal expansion (β) of TWIP steel was approximately 22.4 × 10⁻⁶ °C⁻¹, and this value was hardly affected by the grain size. Therefore the density of TWIP steel was also unaffected by grain size within the tested range. The β in TWIP steel was higher than that of plain carbon steels (13–15 × 10⁻⁶ °C⁻¹) such as interstitial free (IF) steel and low-carbon steel, and stainless steels (18–21 × 10⁻⁶ °C⁻¹) such as X10NiCrMoTiB1515 steel and 18Cr-9Ni-2.95Cu-0.58Nb-0.1C steel. The specific heat capacity (c_p) increased with temperature because the major factor affecting c_p is the lattice vibrations. As the temperature increases, atomic vibrations become more active, allowing the material to store more thermal energy. Meanwhile, c_p slightly increased with increasing grain size since grain boundaries can suppress lattice vibrations and reduce the material’s ability to store thermal energy. The thermal conductivity (k) in TWIP steel gradually increased with temperature, consistent with the behavior observed in other high-alloy metals. k slightly increased with grain size, especially at lower temperatures, due to the increased grain boundary scattering of free electrons and phonons. This trend aligns with the Kapitza resistance model. While TWIP steel with refined grains exhibited higher yield and tensile strengths, this came with a decrease in total elongation and k. Thus, optimizing grain size to enhance both mechanical and thermal properties presents a challenge. The k in TWIP steel was substantially lower compared with that of plain carbon steels such as AISI 4340 steel, especially at low temperatures, due to its higher alloy content. At room temperature, the k of TWIP steels and plain carbon steels were approximately 13 W/m°C and 45 W/m°C, respectively. However, in higher temperature ranges where face centered cubic structures are predominant, the difference in k of the two steels became less pronounced. At 800 °C, for example, TWIP and plain carbon steels exhibited k values of approximately 24 W/m°C and 29 W/m°C, respectively. Full article

A well-designed complex microstructure containing both soft and hard micro-constituents can enhance the mechanical properties of steel. In this study, commercial AISI 9254 steel was annealed at 900 °C, rapidly cooled to 550 °C for 500 s to promote approximately 50% fine pearlitic transformation, quenched to 125 °C for partial martensitic transformation, and finally heated to 375 °C for 1800 s to complete the partitioning stage in a novel quench and partitioning (Q&P) process. Tensile testing revealed a yield strength (YS) of ≈1500 MPa, an ultimate tensile strength (UTS) of ≈1570 MPa, and a total elongation of ≈13.85%. This high yield strength indicates the ability of the material to support the development of lightweight, yet high-strength components for demanding applications. Additionally, the balanced total elongation helps mitigate the risk of brittle failure, enhancing fracture toughness and reducing the likelihood of premature failures in critical structural applications. These results indicate an increase of approximately 8.3% in strength and 34.5% in ductility compared to the as-received 9254 steel. X-ray analysis revealed that the complex microstructure had fewer crystallographic defect densities than the as-received sample. Secondary electron images showed ultrafine martensite laths and cementite lamellae within the body-centered cubic (BCC) matrix, with some proeutectoid ferrite found at prior austenite grains. Electron backscattered diffraction (EBSD) analysis estimated low internal distortion in martensite laths, with average crystal defect densities around 2.25 × 10¹⁴ m⁻². The BCC matrix contained ferrite and martensite, with carbide particles and a small amount of retained austenite detected by transmission electron microscopy (TEM). These findings confirm the enhanced mechanical properties of commercial 9254 steel through the novel Q&P processing. Full article

Psoriasis is a multifactorial inflammatory disease. Methylglyoxal (MG) is a highly reactive dicarbonyl compound responsible for dicarbonyl stress in some inflammatory conditions, and it may play a role in the etiopathogenesis of psoriasis. Methods: A total of 50 patients with psoriasis and 35 healthy individuals participated in this study. The following indices were assessed in patients: Body Surface Area (BSA), Psoriasis Area and Severity Index (PASI), and Dermatology Life Quality Index (DLQI). MG concentration was evaluated in blood samples. The following inflammatory response indices were calculated: Systemic Inflammation Response Index (SIRI), Systemic Immuno-inflammation Index (SII), and Aggregate Index of Systemic Inflammation (AISI). Results: An analysis of the obtained data showed a statistically significant decrease in the mean serum MG concentration in patients with psoriasis when compared to the healthy individuals (1.19 ± 0.4 μg/mL vs. 1.75 ± 0.6 μg/mL; p = 0.000002). In the patients, MG concentration correlated negatively with psoriasis disease severity indicators (BSA and PASI), C-reactive protein (CRP) concentration, and inflammatory response indicators (SII and AISI). Conclusions: The decreased concentration of MG may be attributed to an increased accumulation of its derivatives (advanced glycation end-products) in the inflamed skin and/or scavenging by polyamines. Full article

The study describes experimental data on thermal tests during the condensation of HFE7100 refrigerant in a compact heat exchanger. The heat exchanger was manufactured using the additive 3D printing in metal. The material is AISI 316L steel. MPCM slurry was used as the heat exchanger coolant, and water was used as the reference medium. The refrigerant was condensed on a bundle of circular tubes made of steel with an internal/external diameter of d_i/d_e = 2/3 mm, while a mixture of water and phase change materials as the coolant flowed through the channels. Few studies consider the heat exchange in condensation using phase change materials; furthermore, there is also a lack of description of heat exchange in small-sized exchangers printed from metal. Most papers deal with computer research, including flow simulations of heat exchange. The study describes the process of heat exchange enhancement using the phase transition of coolant. Experimental data for the mPCM slurry coolant flow was compared to the data of pure water flow as a reference liquid. The tests were carried out under the following thermal and flow conditions: G = 10–450 [kg m−² s⁻¹], q = 2000–25,000 [W m⁻²], and t_s = 30–40 [°C]. The conducted research provided many quantities describing the heat exchange in compact heat exchangers, including heat exchanger heat power, heat exchange coefficient, and heat exchange coefficients for working media. Based on these factors, the thermal performance of the heat exchanger was described. External characteristics include the value of the thermal power and the heat exchange coefficient as a function of the mass flow density of the working medium and the average logarithmic temperature difference. The performance of the heat exchanger was presented as the dependencies of the heat exchange coefficients on the mass flux density and the heat flux density on the heat exchange surface. The thickness of the refrigerant’s condensate film was also determined. Furthermore, a model was proposed to determine the heat exchange coefficient value for the condensing HFE7100 refrigerant on the outer surface of a bundle of smooth tubes inside a compact heat exchanger. According to experimental data, the calculation results were in good agreement with each other, with a range of 25%. These data can be used to design mini condensers that are widely used in practice. Full article

AISI 431 martensitic stainless steels (MSS) with 2.5 wt% Cu were fabricated via laser-directed energy deposition additive manufacturing followed by single-step tempering treatment. The influences of different tempering times at 600 °C on microstructure and mechanical properties of the as-deposited 431-2.5Cu MSS have been explored and analyzed. The as-deposited MSS specimen primarily consisted of lath martensite, austenite and M₂₃C₆ carbide. After the single-step tempering treatment at 600 °C, Cu-enriched (ԑ-Cu) nano-precipitates and reverse austenite can be formed and promoted by extending the tempering treatment. The microhardness, strength and elongation can be improved with increasing the tempering time up to 1.0 h, and subsequently reduced with the tempering time prolonging to 2.0 h. Compared to 431 MSS that requires a multiple-step heat treatment for excellent performance, the 431-2.5Cu MSS specimen presented superior tensile properties after single-step tempering at 600 °C for 1.0 h in the present work. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of one-hour tempered MSS were 1611 MPa, 1334 MPa and 16.3%, respectively. This study provides a quantitative theoretical reference and experimental basis for realizing short-process fabrication of the Cu-bearing MSS with high strength and ductility. Full article

The application possibilities of austenitic stainless steels in high friction, abrasion, and sliding wear conditions are limited by their inadequate hardness and tribological characteristics. In order to improve these properties, the thermochemical treatment of their surface by plasma nitriding is suitable. This article is focused on the corrosion resistance of conventionally plasma-nitrided AISI 304 stainless steel (530 °C, 24 h) in 0.05 M and 0.5 M sodium chloride solutions at room temperature (20 ± 3 °C), tested by potentiodynamic polarization and electrochemical impedance spectroscopy. Optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy are used for nitrided layer characterization. The experiment results confirmed the plasma-nitrided layer formation of increased micro-hardness related to the presence of Cr₂N chromium nitrides and higher surface roughness compared to the as-received state. Both of the performed independent electrochemical corrosion tests point to a significant reduction in corrosion resistance after the performed plasma nitriding, even in a solution with a very low chloride concentration (0.05 mol/L). Full article

In this work emphasis was given to determine the evolution of the retained austenite phase fraction via X-ray diffractometry technique in the as-hardened AISI 440C martensitic stainless steel surface subjected to cavitation for increasing test times. Scanning electron microscopy results confirmed the preferential carbide phase removal along the prior/parent austenite grain boundaries for the first cavitation test times on the polished sample surface during the incubation period. Results suggest that the strain-induced martensitic transformation of the retained austenite would be assisted by the elastic deformation and intermittent relaxation action of the harder martensitic matrix on the austenite crystals through the interfaces between both phases. In addition, an estimation of the stacking fault energy value on the order of 15 mJ m⁻² for the retained austenite phase made it possible to infer that mechanical twinning and strain-induced martensite formation mechanisms could be effectively presented in the studied case. Finally, incubation period, maximum erosion rate, and erosion resistance on the order of 7.0 h, 0.30 mg h⁻¹, and 4.8 h μm⁻¹, respectively, were determined for the as-hardened AISI 440C MSS samples investigated here. Full article

Monolayers of Ti and TiN coatings, as well as a Ti/TiN bilayer coating, were deposited on AISI M2 steel substrates using the PVD cathodic arc technique. The coatings had a thickness close to 5 μm and an average roughness between 98.6 and 110.1 μm due to the presence of microdroplets on the surface. The crystalline structure of the materials was analyzed using Grazing Incidence X-ray Diffraction (GIXRD) with an increase in temperature to study the dynamics of oxide formation. A phase composition study was conducted using the Rietveld refinement method. At the temperatures where critical growth of titanium oxides, both anatase and rutile, was observed, pin-on-disk tests were performed to study the tribological properties of the materials at high temperatures. It was determined that the oxidation temperature of Ti is around 450 °C, promoting the formation of a combination of anatase and rutile. However, the formation of rutile inhibits the formation of anatase, which is stable above 600 °C. In contrast, TiN showed an oxidation temperature of 550 °C, with an exclusive growth of the rutile phase. The Ti/TiN bilayer exhibited mixed behavior, with the initial growth of anatase promoted by Ti, followed by the formation of rutile. Oxidation and tribo-oxidation dominated the wear behavior of the surfaces, showing a transition from mechanisms related to abrasion at low and medium temperatures to a combination of abrasion and adhesion mechanisms at high temperatures (800 °C). Full article

While binder jetting (BJ) additive manufacturing (AM) holds considerable promise for industrial applications, defects often compromise part quality. This study addresses these challenges by investigating binding mechanisms and analyzing common defects, proposing tailored solutions to mitigate them. Emphasizing defect identification for effective quality control in BJ-AM, this research offers strategies for in-process rectification and post-process evaluation to elevate part quality. It shows how to successfully process metallic parts with complex geometries while maintaining consistent material properties. Furthermore, the paper explores the microstructure of AISI M2 tool steel, utilizing advanced image processing techniques like digital image analysis and SEM images to evaluate carbide distribution. The results show that M2 tool steel has a high proportion of M₆C carbides, with furnace-cooled samples ranging from ~2.4% to 7.1% and MC carbides from ~0.4% to 9.4%. M₆C carbides ranged from ~2.6% to 3.8% in air-cooled samples, while water-cooled samples peaked at ~8.52%. Sintering conditions also affected shrinkage, with furnace-cooled samples showing the lowest rates (1.7 ± 0.4% to 5 ± 0.4%) and water-cooled samples showing the highest (2 ± 0.4% to 14.1 ± 0.4%). The study recommends real-time defect detection systems with autonomous corrective capabilities to improve the quality and performance of BJ-AM components. Full article