Search Results (88)

The induction quenching–tempering process typically enhances the surface strength and core toughness of alloy steels by utilizing the skin effect. However, the impact of parameters like quenching current and heating time on the microstructure and mechanical property of 34CrNiMo6 steel crankshafts remains unclear. In this work, the microstructure of 34CrNiMo6 steel after induction quenching exhibits three distinct zones: a martensite hardened layer; a transition zone of martensite and tempered sorbite; and a matrix of tempered sorbite. As the induction current (400, 500, and 600 mA) and heating time (3, 5, and 7 s) increase, the hardened layer thickness enhances (up to 3.21 mm). Under the 600 mA and 7 s, the hardened layer reaches peak hardness and residual stress values of 521.48 HV and −330.12 MPa, showing a decreasing trend from surface to core. After tempering at 330 °C for 2 h, the hardened layer mainly consists of tempered martensite, and the surface hardness and residual stress decrease to 417.94 HV and −12.33 MPa. The temperature gradient from quenching balances after tempering, with martensitic phase transformation and stress redistribution reducing hardness and residual stress. Furthermore, the induction quenching–tempering process enhances the toughness of 34CrNiMo6 steel when compared to the untreated specimen, boosting its tensile yield strength, elongation, and tensile strength by 15.3%, 14.9%, and 19.5%, respectively. This work deepens the understanding of induction quenching–tempering process and provides valuable insights for designing alloy steels with excellent mechanical properties. Full article

In this study, a duplex treatment combining carburizing, nitriding, and subsequent induction hardening (IH) was applied to JIS-SCM420 low-alloy steel. A comprehensive evaluation was conducted to assess surface characteristics, including microstructure, hardness, residual stress, and fatigue performance. The IH process successfully produced a high-nitrogen-content ε-Fe_2-3(N,C) compound layer (2–3 μm thick) and fine acicular martensite at the surface, significantly enhancing surface hardness (950 HV0.03) and inducing beneficial compressive residual stress (−477 MPa). The IH-treated material exhibited a plane-bending fatigue strength of approximately 775 MPa, notably higher than that of conventionally carbonitrided specimens (700 MPa). This improvement was primarily attributed to the formation of the hard ε-Fe_2-3(N,C) compound layer and refined martensitic structure resulting from induction hardening. Additionally, IH activated residual interstitial elements, promoting the precipitation of stable surface nitrides. These microstructural changes effectively suppressed fatigue crack initiation and propagation, thereby extending fatigue life under cyclic loading conditions. Full article

This study examines fatigue crack growth behavior in induction-hardened S38C axle steel with a gradient microstructure. High-frequency three-point bending fatigue tests were conducted to evaluate crack growth rates (da/dN) across three depth-defined regions: a hardened layer, a heterogeneous transition zone, and a normalized core. Depth-resolved da/dN–ΔK relationships were established, and Paris Law parameters were extracted. The surface-hardened layer exhibited the lowest crack growth rates and flattest Paris slope, while the transition zone showed notable scatter due to microstructural heterogeneity and residual stress effects. These findings provide experimental insight into the fatigue performance of gradient-structured axle steels and offer guidance for fatigue life prediction and inspection planning. Full article

Aluminum, boron, and titanium microalloyed into high-strength low-alloy boron steel exhibit a complex interplay, competing for nitrogen, with titanium demonstrating the highest affinity, followed by boron and aluminum. This competition affects the formation and distribution of nitrides, impacting the microstructure and mechanical properties of the steel. Titanium protects boron from forming BN and facilitates the nucleation of acicular ferrite, enhancing toughness. The segregation of boron to grain boundaries, rather than its precipitation as boron nitride, promotes the formation of martensite and thus the through-hardenability. Aluminum nitride is critical in controlling grain size through a pronounced pinning effect. In this study, we employ energy- and wavelength-dispersive X-ray spectroscopy and computer-aided particle analysis to analyze the phase content of 12 high-purity vacuum induction-melted samples. The primary objective of this study is to correctly describe the microstructural evolution in the Fe-Al-B-Ti-C-N system using the Calphad approach, with special emphasis on correctly predicting the dissolution temperatures of nitrides. A multicomponent database is constructed through the incorporation of available binary and ternary descriptions, employing the Calphad approach. The experimental findings regarding the solvus temperature of the involved nitrides are employed to validate the accuracy of the thermodynamic database. The findings offer a comprehensive understanding of the relative phase stabilities and the associated interplay among the involved elements Al, B, and Ti in the Fe-rich corner of the system. The type and size distribution of the stable nitrides in microalloyed steel have been demonstrated to exert a substantial influence on the properties of the material, thereby rendering accurate predictions of phase stabilities of considerable relevance. Full article

To address the issue of surface grain coarsening in laser-induction hybrid phase transformation of 42CrMo steel, this study investigated the effects of four pretreatment processes (quenching–tempering (QT), laser-induction quenching (LIQ), laser-induction normalizing (LIN), and laser-induction annealing (LIA)) on the austenite grain size and wear resistance after laser-induction hybrid phase transformation. The results showed that QT resulted in a tempered sorbite structure, resulting in coarse austenite grains (139.8 μm) due to sparse nucleation sites. LIQ generated lath martensite, and its high dislocation density and large-angle grain boundaries led to even larger grains (145.5 μm). In contrast, LIN and LIA formed bainite and granular pearlite, respectively, which refined austenite grains (78.8 μm and 75.5 μm) through dense nucleation and grain boundary pinning. After laser-induction hybrid phase transformation, all specimens achieved hardened layer depths exceeding 6.9 mm. When the pretreatment was LIN or LIA, the specimens after laser-induction hybrid phase transformation exhibited surface microhardness values of 760.3 HV0.3 and 765.2 HV0.3, respectively, which were 12 to 15% higher than those of the QT- and LIQ-pretreated specimens, primarily due to fine-grain strengthening. The friction coefficient decreased from 0.52 in specimens pretreated by QT and LIQ to 0.45 in those pretreated by LIN and LIA, representing a reduction of approximately 20%. The results confirm that regulating the initial microstructure via pretreatment effectively inhibits austenite grain coarsening, thereby enhancing the microhardness and wear resistance after transformation. Full article

This review provides an overview of recent advancements in Cu-Ni-Co-Si alloys, focusing on their processing methods, microstructures, and properties. Due to their non-toxic composition, enhanced mechanical properties, and excellent electrical conductivity, Cu-Ni-Co-Si alloys have emerged as a promising alternative to traditional Cu-Be alloys in the electrical and electronics industry. This review discusses various synthesis techniques, including casting, vacuum induction melting, and additive manufacturing, and evaluates their effects on the formed microstructures. In addition, it explores the influence of different elements and thermal treatments on the alloys’ microstructures and properties, discussing strategies to enhance the properties of Cu-Ni-Co-Si alloys. Key strengthening mechanisms—including precipitation hardening, grain boundary strengthening, and solid solution hardening—are examined in detail, with particular emphasis on their synergistic effects in optimizing alloy performance. Furthermore, future research directions are highlighted, focusing on the optimization of alloying element concentrations and heat treatment protocols to achieve an enhanced balance between strength and electrical conductivity. These improvements are critical for meeting the demanding requirements of advanced applications in electronics and high-reliability components. Full article

In order to reduce the edge waves and defects of the strip in the forming process and obtain better properties of the strip, it is urgent to establish a better flexible cold forming process. In this paper, a finite element model of the production line was established to simulate the forming process, and the effective stress distribution at the corner of the strip was simulated. The effect of cold working hardening was basically consistent with that calculated by the analytical method and tensile test results. A mathematical model of the maximum normal strain along the tangent direction of the strip’s outer edge of each pass was established. With the constraint conditions that the maximum value of the normal strain value of each pass is less than the critical value and the upper and lower limit of the horizontal value of each test factor, and the maximum value of the normal strain of each pass as the goal, the number of cold forming passes, the bending angle of each pass and the working roll diameter of the roll have been determined. The optimized process parameters were used in the simulations. No edge wave at the strip edge and no “Bauschinger effect” in forming before high-frequency induction welding was found. The method proposed in this paper can optimize the key process parameters before the production line is put into operation, minimize the possible buckling of the strip edge during the forming process, and reduce the possible loss caused by design defects. Full article

Bearing steels are frequently used in highly loaded components, such as roller bearings, due to their excellent hardenability and wear resistance. Microstructure, hardness, and residual stress distribution of the bearings significantly affect the wear resistance of the parts. In the present study, experiments investigated the effects of austenitizing temperature (850, 900, and 950 °C), with or without cryogenic treatment, and induction hardening treatment (9 and 12 kW) on the microstructure, microhardness, the amount of retained austenite, surface residual stress, and wear behavior of JIS SUJ3 steel. The experimental results revealed that the austenitized specimens’ microstructure consisted of martensite, retained austenite, and dispersed granular alloy carbide exhibiting high hardness. After cryogenic or induction hardening treatment, the surface residual stress of austenitized specimens exhibited compressive stress rather than its original tensile stress state. The induction hardening treatment can significantly increase the microhardness of austenitized specimens, followed by quenching. Furthermore, the induction-hardened surface possessed less retained austenite. For practical industrial applications, a prior austenitizing heat treatment at 950 °C followed by hardening with an induction power of 12 kW was the optimal parameter for JIS SUJ3 bearing steel. The maximum microhardness and surface residual stress were 920 HV_0.3 and −1083 MPa, respectively, while the lowest weight loss was 0.5 mg after the 10,000-revolution wear test. Full article

The surface of a whole-roll flatness roll is in long-term contact with the steel strip, leading to slipping and wear and placing higher demands on the performance of the roll surface. This study establishes a finite element model for moving induction quenching and a phase transformation hardness numerical model by generating multi-field simulations and hardness predictions for the flatness roll during induction quenching. First, the thermal–physical properties of the roll material, MC3, are calculated using JMatPro V13.0. The dynamic domain and moving mesh techniques are applied in COMSOL Multiphysics to simulate time-varying boundary conditions, and the JMAK and K-M phase transformation models are used for electromagnetic–thermal–microstructure field simulations. Subsequently, the Taguchi method is used to optimize the induction quenching process of the flatness roll. After optimization, the martensitic hardened layer depth along the axial direction of the roll becomes uniformly distributed near the target value of 3 mm. Finally, through the modified Maynier hardness model, the corrected formula for the Vickers hardness of MC3 is obtained. The calculated hardness value of the roll surface in the simulation model reaches 950 HV, which agrees well with the experimental hardness results, validating the ability of the numerical model to guide specific processes. Full article

To investigate the effect of tempering temperature on the hardness and its underlying mechanisms in 14Cr12Ni3Mo2VN martensitic stainless steel after high-frequency induction quenching (HFIQ), the microstructure, energy-dispersive spectroscopy (EDS) of precipitated particles, residual austenite, residual stress, and microhardness of the material tempered at different temperatures were examined and analyzed. The results reveal that a secondary hardening phenomenon occurs during the tempering process in 14Cr12Ni3Mo2VN martensitic stainless steel. Overall, with increasing tempering temperature, the microhardness initially decreases slightly, then rises to a secondary hardening peak, and finally drops rapidly. The secondary hardening peak corresponds to a tempering temperature of approximately 440 °C, with a microhardness of about 483 HV_0.1. The secondary hardening phenomenon is likely attributed to the dispersion strengthening caused by the precipitation of alloy carbides during tempering. The precipitation and coarsening of carbides reduce lattice distortion and solid solution strengthening, while the release of residual stress diminishes stress-induced strengthening. Additionally, the decomposition of the martensitic structure leads to the formation of ferrite and carbides. The combined effects of these factors result in a decrease in hardness. Full article

JIS SCM440 steel is commonly used in precision parts after induction-hardening heat treatment. The fatigue behavior of induction-hardening parts largely depends on the combination of hardening depth and the magnitude and distribution of hardness and compressive residual stress. Therefore, it is necessary to determine the effects of different prior microstructures on the properties of JIS SCM440 steel after induction hardening. In the present study, the effects of prior microstructure (including spheroidized, annealed, normalized, and quenched and tempered) on the microhardness, hardening width, and residual stress of the induction-hardened specimens are investigated. The experimental results showed that the distribution behavior of residual stress in the hardened zone and heat-affected zone is due to the temperature gradient of the induction-hardening treatment. The hardened center appeared as compressive residual stress due to the martensitic transformation, which was accompanied by volume expansion. On the contrary, tensile residual stress will be generated in the heat-affected zone of incomplete phase transformation. The prior microstructure can affect the residual stress magnitude and distribution of microhardness and residual stresses due to the content of the cementite dissolved into the austenite at high temperatures. The difference in the carbon content of martensite after quenching will result in obvious differences in properties. The induction-hardened specimens with a normalized prior microstructure have the highest residual tensile stress in the heat-affected zone. The maximum residual tensile stress was 371 MPa in the heat-affected zone. The induction-hardened specimens with a quenched and tempered prior microstructure have the deepest hardening depth and widest residual compressive stress distribution range. The highest microhardness was 764 HV_0.3, while the maximum residual compressive stress was −752 MPa. Full article

The torsion beam, integral to rear suspension systems in vehicles, is a critical component where strength and durability must be prioritized in specific regions. To enhance the strength of these regions, induction hardening, a localized heat treatment method, is employed. However, the application of this treatment introduces distortion, which compromises the precision of welding between components and raises significant concerns about product quality and safety. To address these challenges, the present study introduces a front-end analysis process for induction hardening aimed at predicting distortion following heat treatment. A three-dimensional model of the product was utilized to simulate the front-end process of induction hardening. A coupled analysis of electrical and thermal fields was conducted to replicate the heating effect induced by coils during the heat treatment process. Additionally, a thermo-structural coupled analysis was performed to predict the distortion occurring during the cooling phase. A comparative analysis with actual product measurements demonstrated that the proposed method achieved a distortion displacement prediction accuracy of 98%, thereby validating the efficacy of the proposed analysis process. Full article

Mechanical gears are essential in power transmission systems across various industrial applications. Their performance is critically influenced by residual stresses from manufacturing processes like induction hardening, case hardening, and shot peening. Surface compressive residual stresses enhance resistance to pitting fatigue, bending fatigue and crack propagation, improving overall hardness. In the present work, a Non-Destructive Thermographic method (Active thermography), based on measurement of the thermal diffusivity parameter, is presented to characterize the surface treatments applied to gears. Surface hardness was measured using a micro-hardness tester, and residual stresses were determined with an X-Ray diffractometer, showing variations due to surface treatments. The variation in the thermal diffusivity parameter, obtained using the Slope Method, was found to be an indicator of the surface treatments’ effectiveness. Full article

The laser-induced hybrid hardening process integrates laser quenching and electromagnetic induction heating to overcome traditional heat treatment limitations, enhancing the depth and properties of hardened layers for applications like wind turbine bearings. This study uses Box–Behnken design (BBD) experiments to analyze key process parameters and develops response surface methodology (RSM) and whale-optimization-algorithm-optimized back-propagation neural network (WOA-BPNN) models for prediction and optimization. The WOA-BPNN model outperforms the RSM model, achieving superior predictive accuracy with R² values exceeding 0.995 for both depth and hardness, with a root mean square error (RMSE) for depth of 0.099 mm and of 1.734 HV_0.3 for hardness, and with mean absolute percentage error (MAPE) of 0.697% and 0.7867%, respectively. The WOA-BPNN model provides an effective and reliable framework for optimizing laser-induced hybrid hardening, improving production efficiency and extending component life for industrial applications. Full article

Heat treatment technology changes all the mechanical properties of metallic materials. The influence of induction hardening, nitriding and boronising on the change in the microhardness, impact toughness, microstructure and coefficient of friction of conventional steels 42CrMo4 and 32CrMo12 has been examined and compared with results obtained in the sintered steels with an increased content of Cu, which were prepared using powder metallurgy technology. Widely used treatments for the examined materials include induction hardening and gas nitriding. This study focuses on comparing those technologies with alternative technologies of boronising. It was found that for powder metallurgy materials, boronising is a much more suitable process than nitriding because after the application of nitriding, the impact toughness dropped to one third of the impact toughness of the base material, while after boronising, the impact toughness remained unchanged. Through boronising, it was possible to achieve the unique possibility of improving the mechanical properties of sintered PM Fe-Cu-C steels and fully replacing the currently used nitriding process. Furthermore, compared to nitriding, it also increases the hardness of the surface layer many times to improve the friction properties and significantly increases the impact toughness. Full article