Search Results (377)

This study investigates H13 steel through Q-P-T (quenching–partitioning–tempering) heat treatment experiments, focusing on the effects of quenching and tempering temperatures on its microstructure and mechanical properties. Experimental results demonstrate that elevated heat treatment temperatures induce grain coarsening and increased hardness. Under the optimized thermal processing parameters of 1020 °C quenching followed by 530 °C tempering, H13 steel achieves an optimal balance between strength and toughness. This balanced performance effectively addresses the issue of insufficient toughness and susceptibility to fracturing when H13 steel is utilized as shank material. Full article

This study investigates the effect of tensile test temperatures, ranging from 300 °C to 600 °C, on the microstructure, mechanical properties, and fracture behavior of AISI H13 11 tool steel manufactured by laser powder bed fusion (LPBF) under three material conditions: As-Built (AB), Direct Double-Tempered (DTT), and 13 Quenched and Double-Tempered (QTT). Optical and SEM observations show that quenching before tempering leads to a more homogeneous microstructure. Full austenitization during quenching eliminates the laser track patterns and cellular structures characteristic of the AB and DTT conditions, resulting in a microstructure like that of conventionally processed material. Tensile test results reveal that, while all material conditions (AB, DTT, and QTT) perform similarly at lower temperatures (up to 300 °C), significant differences emerge at elevated temperatures. At 300 °C, AB, DTT, and QTT maintain 87.5%, 85.8%, and 83.1% of their room-temperature yield strength, respectively. However, beyond this point, the DTT condition clearly outperforms the others. QTT shows a sharp decline above 300 °C, retaining only ~24% of its yield strength, whereas AB and DTT maintain approximately 80%. The superior performance of DTT becomes more evident at higher temperatures: it retains 25% and 20% of its yield strength at 500 °C and 600 °C, respectively, higher than both AB and QTT. Full article

In this study, we utilized Thermo-Calc software (2023a) to optimize the heat treatment process of martensitic stainless steel 90Cr18MoV through phase diagram calculations. The microhardness of 90Cr18MoV was characterized using a nanoindentation instrument. The microstructural morphology of the samples was analyzed using scanning electron microscopy (SEM). The composition of the samples was characterized through scanning electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Additionally, laser confocal microscopy (FIB) and transmission electron microscopy (TEM) were employed to characterize the precipitate phase composition and size before and after heat treatment, while also observing the dislocation structure within the samples. The relationship between the quenching temperature and the percentage of residual austenite content in the material was established. The influence of the dislocation structure and precipitate size on the hardness of the samples was investigated. The research findings confirm that the observed secondary hardening phenomenon in tempered samples is attributed to the co-precipitation of two types of carbides, M₂₃C₆ and MC, within the matrix. The study investigated the effects of the tempering temperature and duration on the size of secondary precipitates, indicating that M₂₃C₆ and MC particles with sizes less than or equal to 20 nm contribute to enhancing the matrix, while particles larger than 30 nm lead to a reduction in hardness after tempering. Notably, during the tempering process, M₂₃C₆ precipitated from the matrix nucleates on MC. Full article

The study investigates the influence of post-weld heat treatment (PWHT) on the microstructure and hardness of hardfacing layers applied to hot forging tools. The research focuses on three tool steels (55NiCrMoV7, X37CrMoV5-1, and a modified X38CrMoV5-3) and uses robotized gas metal arc welding (GMAW) with DO015 filler material. It examines the structural and mechanical differences in the hardfaced layers before and after heat treatment involving quenching and tempering. The findings reveal that PWHT significantly improves microstructural homogeneity and hardness distribution, especially in the heat-affected zone (HAZ), mitigating the risk of crack initiation and tool failure. The study shows that untempered as-welded layers exhibit microstructural inhomogeneity and extreme hardness gradients, which negatively impact tool durability. PWHT leads to tempered martensite formation, grain refinement, and a more stable hardness profile across the joint. These improvements are critical for extending the service life of forging tools. The results underscore the importance of customizing PWHT parameters according to the specific material and application to optimize tool performance. Full article

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

The effects of intercritical quenching on the microstructure evolution and mechanical performance of Cr–Ni–Mo–V steel with a banded structure are studied. It is found that the intercritical quenching temperature has a significant effect on the morphology, distribution, and relative amount of ferrite/martensite, as well as the carbide precipitates upon tempering treatment. It is indicated that owing to the initial banded structure of Cr-Ni-Mo-V steel, the ferrite formation in intercritical heat treatment also exhibits a banded distribution. With the increase in quenching temperature, the proportion of ferrite in the Cr-Ni-Mo-V steel decreases from 30 ± 3.2 vol.% to 18 ± 2.8 vol.%. Tempering treatment has no significant effect on the distribution characteristics of ferrite, but it promotes the recovery of martensite laths and the precipitation of carbides. The mechanical properties of Cr-Ni-Mo-V steel are determined by both the changes in ferrite content induced by intercritical quenching and the evolution of carbide types during tempering. Delamination cracks are observed on the fracture surface, which is attributed to the lamellar microstructure, improving the plasticity of Cr-Ni-Mo-V steel through stress dispersion and a multi-stage energy absorption mechanism. Full article

Taking a typical carburized alloy steel for heavy-duty gears as the research object, this work regulates carburizing–quenching and tempering processes to conduct a layer-by-layer analysis of gradient-distributed microstructures and mechanical properties in the carburized layer. The effects of tempering temperature on martensite evolution, mechanical properties, and wear resistance were specifically investigated. Results demonstrate that carburizing–quenching followed by cryogenic treatment generates high-carbon martensite at the surface, progressively transitioning to lath martensite towards the core. Low-temperature tempering promotes fine carbide precipitation, while elevated temperatures cause carbide coarsening. Specimens tempered at 175 °C achieve surface hardness of 800 HV and near-surface compressive yield strength of 2940 MPa. These samples exhibit 13% lower wear mass loss compared to 240 °C tempered counterparts, demonstrating superior wear resistance characterized by relatively flat wear surfaces, uniform contact stress distribution, and reduced cross-sectional plastic deformation zones. Key strengthening mechanisms at lower tempering temperatures involve solution strengthening, dislocation strengthening, and partial precipitation strengthening from carbides. Coherent carbides formed under these conditions impede fatigue dislocation motion via shearing mechanisms to suppress plastic deformation and fatigue crack initiation under contact fatigue stress, thereby enhancing wear performance. Full article

A set of bearing balls, fabricated with grade 100Cr6 bearing steel, was subjected either to ordinary quenching and tempering final heat treatment (leading to a mainly tempered martensitic microstructure) or to an alternative heat treatment (leading to a mainly bainitic microstructure). In order to compare their final properties and service performance, the balls were then subjected to rolling contact fatigue tests, as well as to other metallurgical and mechanical characterizations. Further mechanical tests, including tensile tests and rotating bending fatigue tests, were also performed on test specimens made with the same material and subjected to the same final heat treatments. The bainitic material, compared to the tempered martensitic one, exhibited a slightly better performance in the rotating bending fatigue tests, but not in the rolling contact fatigue tests. Full article

This study investigates the influence of key heat treatment parameters on the microstructure and mechanical properties of the powder metallurgy tool steel Vanadis 60. A fractional factorial design of experiments was applied to evaluate the effects of austenitising temperature, quenching medium, tempering temperature, and number of tempering cycles on hardness, flexural strength, and microstructure, using detailed phase characterisation by X-ray diffraction. The results reveal two distinct processing routes tailored to different performance objectives. Maximum hardness was achieved by combining austenitisation at 1180 °C, rapid oil quenching, and tempering at 560 °C. These conditions enhance the solubility of carbon and other alloying elements, promote secondary hardening, and reduce retained austenite. Conversely, higher toughness and ductility were obtained by austenitising at 1020 °C, air cooling, and tempering at 560 °C. These parameters favour the formation of a bainitic microstructure, together with lower martensite tetragonality and minimal retained austenite. A statistically significant interaction was identified between the austenitising temperature and the number of tempering cycles; three temperings were sufficient to compensate for the lower hardness associated with reduced austenitising temperatures. The results provide a robust guidance for optimising thermal processing in highly alloyed tool steels, enabling the precise tailoring of microstructure and properties in accordance with specific mechanical service requirements. 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

Hydrogen embrittlement (HE) can significantly degrade the mechanical properties of steels. This phenomenon is particularly relevant for high-strength steels where large elastic stresses lead to detrimental localized concentrations of hydrogen at defects. In this study, unnotched rotating bending specimens of the bearing steel SAE 52100 (100Cr6) quenched and tempered at 180 °C and 400 °C were electrochemically charged with hydrogen. Charged and non-charged specimens then underwent rotating bending fatigue testing, either immediately after charging or after aging at room temperature up to 72 h. The hydrogen-charged specimens annealed at 180 °C showed a sizeable drop in fatigue limit and fatigue lifetime compared to the non-charged specimens with cracks mainly originating from near-surface non-metallic inclusions. In comparison, the specimens annealed at 400 °C exhibited a moderate drop in fatigue limit and lifetime due to hydrogen charging with cracks originating mostly from the surface. Aging had only insignificant effects on the fatigue lifetime. Notably, annealing of charged samples for 2 h at 180 °C restored their lifetime to that of non-charged specimens. 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

The heat treatment residual stress of 8Cr4Mo4V steel bearings seriously affects the contact fatigue life. The micro stress concentration at the carbide interface leads to the initiation of micro cracks. Therefore, in this paper, the systematic analysis of heat treatment residual stress of 8Cr4Mo4V steel is conducted. FEA was used to analyze the residual stress of type I after heat treatment process. Based on numerical simulation and EBSD results, CPFEM was carried out to study the distribution of type II residual stress. Using high-resolution characterization results, GPA was performed to study type III residual stress caused by crystal defects. The FEA results indicate that thermal strain and phase transformation strain dominate the macroscopic stress change before and after martensitic transformation. During the first tempering process, the phase transformation leads to the release of quenching residual stress. The large stress concentration at the carbide interface is revealed by CPFEM. High-resolution characterization of coherent interface between carbide and matrix reveals that the micro residual strain at this interface is small. Through a systematic analysis of the residual stress of 8Cr4Mo4V steel, a basis is provided for modifying the macroscopic and microscopic residual stress of heat treatment to improve the bearing performance. Full article

In the design of L-DED (laser-directed energy deposition) cladding processes, the chemical composition of the metallic powders is typically assumed to match that of the intended coating. However, during the deposition of the first layer, dilution with the substrate alters the weld metal composition, deviating from the nominal powder chemistry. Although the application of multiple layers can gradually reduce this dilution effect, it introduces additional complexity and processing time. This study proposes an alternative strategy to counteract substrate dilution from the very first deposited layer, eliminating the need for multilayer coatings. Specifically, to achieve a corrosion-resistant monolayer of AISI 316L stainless steel on a high-strength, quenched-and-tempered AISI 4140 steel substrate, a dilution-compensating alloy powder is added to the standard AISI 316L feedstock. Single-layer coatings, both with and without compensation, were evaluated in terms of chemical composition, microstructure, and corrosion resistance. The results show that unmodified coatings suffered a chromium depletion of approximately 2 wt.%, leading to a reduced pitting potential of Ep = 725 ± 6 mV in synthetic seawater. In contrast, the use of the compensation alloy preserved chromium content and significantly improved corrosion resistance, achieving a pitting potential of Ep = 890 ± 9 mV. Full article

To optimize heat treatment of gears for high-end equipment and enhance their fatigue resistance, this paper studied the effects of Al, Mn and Cr content on surface microstructure, i.e., martensite, retained austenite, grain size, hardened layer depth and residual stress under different carburizing temperatures and low tempering of 20MnCr5 steel FZG gear. With numerical simulation combined with experimental verification, this paper establishes a simulation model for the carburizing process of 20MnCr5 steel FZG gear, analyzing the microstructure and retained austenite volume of the gear surface, after carburizing and quenching, by a scanning electronic microscope (SEM) and X-ray diffraction (XRD). In addition, the paper reveals the influence of the optimized heat treatment on the residual stress of the gear regulated with Al, Mn and Cr content in the meshing wear range of 200~280 µm. This study provides a guiding model theory and experimental verification for regulating proportions of alloying elements and optimizing the heat treatment process of low-carbon-alloy steel. Full article