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Keywords = quenched and tempered

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15 pages, 4359 KiB  
Article
Phase Transformations During Heat Treatment of a CPM AISI M4 Steel
by Maribel L. Saucedo-Muñoz, Valeria Miranda-Lopez, Felipe Hernandez-Santiago, Carlos Ferreira-Palma and Victor M. Lopez-Hirata
Metals 2025, 15(7), 818; https://doi.org/10.3390/met15070818 - 21 Jul 2025
Viewed by 215
Abstract
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 [...] Read more.
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 article belongs to the Special Issue Advances in Steels: Heat Treatment, Microstructure and Properties)
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11 pages, 1703 KiB  
Article
Influence of Electrolytic Hydrogen Charging and Effusion Aging on the Rotating Bending Fatigue Resistance of SAE 52100 Steel
by Johannes Wild, Stefan Wagner, Astrid Pundt and Stefan Guth
Corros. Mater. Degrad. 2025, 6(3), 30; https://doi.org/10.3390/cmd6030030 - 9 Jul 2025
Viewed by 209
Abstract
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 [...] Read more.
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
(This article belongs to the Special Issue Hydrogen Embrittlement of Modern Alloys in Advanced Applications)
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21 pages, 15017 KiB  
Article
Effects of Pretreatment Processes on Grain Size and Wear Resistance of Laser-Induction Hybrid Phase Transformation Hardened Layer of 42CrMo Steel
by Qunli Zhang, Peng Shen, Zhijun Chen, Guolong Wu, Zhuguo Li, Wenjian Wang and Jianhua Yao
Materials 2025, 18(12), 2695; https://doi.org/10.3390/ma18122695 - 7 Jun 2025
Viewed by 531
Abstract
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 [...] Read more.
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 article belongs to the Section Metals and Alloys)
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20 pages, 10057 KiB  
Article
An Investigation of Heat Treatment Residual Stress of Type I, II, III for 8Cr4Mo4V Steel Bearing Ring Using FEA-CPFEM-GPA Method
by Tao Xia, Puchang Cui, Tianpeng Song, Xue Liu, Yong Liu and Jingchuan Zhu
Metals 2025, 15(5), 548; https://doi.org/10.3390/met15050548 - 15 May 2025
Cited by 1 | Viewed by 476
Abstract
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 [...] Read more.
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
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16 pages, 3392 KiB  
Article
DED Powder Modification for Single-Layer Coatings on High-Strength Steels
by Unai Garate, Enara Mardaras, Jon Arruabarrena, Garikoitz Artola, Aitzol Lamikiz and Luis Norberto López de Lacalle
J. Manuf. Mater. Process. 2025, 9(5), 152; https://doi.org/10.3390/jmmp9050152 - 6 May 2025
Cited by 1 | Viewed by 574
Abstract
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 [...] Read more.
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
(This article belongs to the Special Issue Advances in Directed Energy Deposition Additive Manufacturing)
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23 pages, 13109 KiB  
Article
Study of the Effect of Regulating Alloying Elements and Optimizing Heat Treatment Processes on the Microstructure Properties of 20MnCr5 Steel Gears
by Li Luo, Yong Chen, Fucheng Zhao, Weifeng Hua, Xu Song, Zhengyun Xu and Zhicheng Jia
Lubricants 2025, 13(5), 202; https://doi.org/10.3390/lubricants13050202 - 1 May 2025
Viewed by 680
Abstract
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 [...] Read more.
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
(This article belongs to the Special Issue Novel Tribology in Drivetrain Components)
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14 pages, 5879 KiB  
Article
Effect of Post-Weld Heat Treatment Cooling Strategies on Microstructure and Mechanical Properties of 0.3 C-Cr-Mo-V Steel Weld Joints Using GTAW Process
by Syed Quadir Moinuddin, Mohammad Faseeulla Khan, Khaled Alnamasi, Skander Jribi, K. Radhakrishnan, Syed Shaul Hameed, V. Muralidharan and Muralimohan Cheepu
Metals 2025, 15(5), 496; https://doi.org/10.3390/met15050496 - 29 Apr 2025
Viewed by 583
Abstract
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 [...] Read more.
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
(This article belongs to the Special Issue Welding and Joining of Advanced High-Strength Steels (2nd Edition))
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20 pages, 15551 KiB  
Article
Effect of Microstructure and Compressive Residual Stress on the Fatigue Performance of AISI 4140 Steel with QPQ Salt-Bath Nitro-Carburizing
by Hao Chen, Tai-Cheng Chen, Hsiao-Hung Hsu and Leu-Wen Tsay
Materials 2025, 18(9), 1995; https://doi.org/10.3390/ma18091995 - 28 Apr 2025
Viewed by 646
Abstract
Quench–polish–quench (QPQ) nitro-carburizing of AISI 4140 steel in a salt bath was performed in this study. Nitro-carburizing in a salt bath enhanced the formation of Fe-nitride on the outer surface layer. Moreover, the oxidizing treatment formed a thin oxide layer decorated on the [...] Read more.
Quench–polish–quench (QPQ) nitro-carburizing of AISI 4140 steel in a salt bath was performed in this study. Nitro-carburizing in a salt bath enhanced the formation of Fe-nitride on the outer surface layer. Moreover, the oxidizing treatment formed a thin oxide layer decorated on the outermost part of the QPQ-treated sample. The dense compound layer formed after nitro-carburizing in a salt bath consisted of refined granular Fe3N and transformed to Fe2N after post-oxidation treatment. Micro-shot peening (MSP) was adopted before QPQ treatment to increase the treated steel’s fatigue performance. The results indicated that MSP slightly increased the thickness of the compound layer and harden depth, but it had little effect on improving the fatigue strength/life of the QPQ-treated sample (SP-QPQ) compared to the non-peened one (NP-QPQ). A deep compressive residual stress (CRS) field (about 200 μm) and a hard nitrided layer showed a noticeable improvement in the fatigue performance of the QPQ-treated ones relative to the 4140 substrates tempered at 570 °C. The ease of slipping or deforming on the substrate surface was responsible for its poor resistance to fatigue failure. The cracking and spalling of the brittle surface layer were the causes for the fatigue crack initiation and growth of all of the QPQ-treated samples fatigue-loaded at/above 875 MPa. It was noticed that fatigue crack initiation at the subsurface inclusions was more likely to occur in the SP-QPQ sample fatigue-loading at 850 MPa or slightly above the fatigue limit. Full article
(This article belongs to the Special Issue Microstructure Engineering of Metals and Alloys, 3rd Edition)
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18 pages, 18331 KiB  
Article
The Effect of Cryogenic Treatment and Tempering Duration on the Microstructure and Mechanical Properties of Martensitic Stainless Steel 13Cr-2Ni-2Mo
by Muhammad R. R. Fatih, Hou-Jen Chen and Hsin-Chih Lin
Materials 2025, 18(8), 1784; https://doi.org/10.3390/ma18081784 - 14 Apr 2025
Viewed by 2460
Abstract
Martensitic stainless steel (MSS) is widely used in several parts of automobiles where high strength, hardness, and corrosion resistance are required. However, the metastability of retained austenite can transform into martensite under severe deformation, adversely affecting material properties. Cryogenic treatments (CTs) have been [...] Read more.
Martensitic stainless steel (MSS) is widely used in several parts of automobiles where high strength, hardness, and corrosion resistance are required. However, the metastability of retained austenite can transform into martensite under severe deformation, adversely affecting material properties. Cryogenic treatments (CTs) have been extensively employed in iron-based alloys for fastener application due to their advantageous effect. This study explores the heat treatment processes applied to 13Cr-2Ni-2Mo martensitic stainless steel (MSS), including austenitizing, cryogenic treatment, and tempering cycles. Cryogenic treatment at (−150 °C) for varying durations, followed by tempering at 200 °C for 2 h, and the impact of post-cryogenic tempering at 200 °C for different tempering duration on the microstructure and mechanical properties were evaluated. Experimental results indicate that the sample quenched at 1040 °C for 2 h (CHT) contains lath martensite, retained austenite, δ-ferrite, and undissolved carbide precipitation. Compared to as-quenched samples, hardness decreased by 5.04%, 7.24%, and 7.32% after tempering for 2 h, 5 h, and 10 h, respectively. Extending cryogenic durations to 2 h, 12 h, and 20 h promoted nucleation of a mixture of M3C and M23C6 small globular carbides (SGCs) and grain refinement but resulted in hardness reductions of 5.04%, 5.32%, and 8.36%, respectively. The reduction in hardness is primarily attributed to a decrease in solid solution strengthening and promoted carbide coarsening. Full article
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15 pages, 10499 KiB  
Article
Microstructure and Mechanical Characterization of AISI 4340 Steel Additively Manufactured by Laser Powder Bed Fusion
by Felix Aguilar, Thinh Huynh, Nemanja Kljestan, Marko Knezevic and Yongho Sohn
Metals 2025, 15(4), 412; https://doi.org/10.3390/met15040412 - 5 Apr 2025
Cited by 2 | Viewed by 932
Abstract
The effects of laser powder bed fusion (LPBF) parameters, such as power (200 to 350 W) and scan speeds (from 200 to 2000 mm/s), on the microstructure and mechanical properties of high-strength, low-alloy (HSLA) AISI 4340 steel were examined. A wide range of [...] Read more.
The effects of laser powder bed fusion (LPBF) parameters, such as power (200 to 350 W) and scan speeds (from 200 to 2000 mm/s), on the microstructure and mechanical properties of high-strength, low-alloy (HSLA) AISI 4340 steel were examined. A wide range of volumetric energy density (VED) between 93 and 162 J/mm3 produced samples with relative densities greater than 99.8%. The optimal parameter set was identified with laser power = 200 W, scan speed = 600 mm/s, hatch spacing = 0.12 mm, and slice thickness = 0.03, corresponding to VED = 92.6 J/mm3. Scanning electron microscopy revealed a predominantly martensitic microstructure for all processing parameters examined, although X-ray diffraction revealed the minor presence of retained austenite within the as-fabricated 4340 steel. Using the optimized LPBF parameters, the as-fabricated 4340 steel exhibited a yield strength of 1317 MPa ± 16 MPa, ultimate tensile strength of 1538 MPa ± 22 MPa, and 18.6 ± 1% strain at failure. These are similar to wrought 4340 steel quenched and tempered between 400 and 600 °C. Full article
(This article belongs to the Special Issue Additive Manufacturing of Metallic Materials)
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14 pages, 4115 KiB  
Article
Process Optimization Simulation of Residual Stress in Martensitic Steel Considering Phase Transformation
by Yuzheng Cui and Guang Yang
Crystals 2025, 15(4), 330; https://doi.org/10.3390/cryst15040330 - 30 Mar 2025
Viewed by 554
Abstract
The solid phase transformation of martensitic steel during heat treatment will affect the stress and temperature. Previous residual stress prediction models ignore the effect of phase transition on residual stress. In order to predict residual stress accurately, a residual stress calculation method considering [...] Read more.
The solid phase transformation of martensitic steel during heat treatment will affect the stress and temperature. Previous residual stress prediction models ignore the effect of phase transition on residual stress. In order to predict residual stress accurately, a residual stress calculation method considering solid phase transition was presented. The measures to reduce residual stress in quenching medium, cooling rate, and the starting temperature and tempering temperature of the martensitic transformation were studied. The experimental results show that residual stress decreases after air cooling. In a certain range, residual stress can be reduced during heat treatment by decreasing the cooling rate and the martensite start temperature. The recommended tempering temperature is 380 °C. Full article
(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)
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18 pages, 11000 KiB  
Article
A Novel Low-Cost Fibrous Tempered-Martensite/Ferrite Low-Alloy Dual-Phase Steel Exhibiting Balanced High Strength and Ductility
by Xianguang Zhang, Yiwu Pei, Haoran Han, Shouli Feng and Yongjie Zhang
Materials 2025, 18(6), 1292; https://doi.org/10.3390/ma18061292 - 14 Mar 2025
Viewed by 621
Abstract
Low-cost and low-alloy dual-phase (DP) steel with a tensile strength (TS) above 1000 MPa and high ductility is in great demand in the automobile industry. An approach to using a medium-carbon and fibrous DP structure for developing such new DP steel has been [...] Read more.
Low-cost and low-alloy dual-phase (DP) steel with a tensile strength (TS) above 1000 MPa and high ductility is in great demand in the automobile industry. An approach to using a medium-carbon and fibrous DP structure for developing such new DP steel has been proposed. The microstructure and mechanical performance of fibrous DP steel obtained via partial reversion from martensite in Fe-C-Mn-Si low-alloy steel have been investigated. The TS of the as-quenched DP steel is above 1300 MPa, while the total elongation is less than 6%. The total elongation was increased to above 13%, with an acceptable loss in TS by performing additional tempering. The fibrous tempered-martensite/ferrite DP steel exhibits an excellent balance of strength and ductility, surpassing the current low-alloy DP steels with the same strength grade. Plate-like or quasi-spherical fine carbides were precipitated, and the relatively high-density dislocations were maintained due to the delay of lath recovery by the enrichment of Mn and C in martensite (austenite before quenching), contributing to the tempering softening resistance. In addition, nanotwins and a very small amount of retained austenite were present due to the martensite chemistry. High-density dislocations, fine carbide precipitation, and partially twinned structures strengthened the tempered martensite while maintaining relatively high ductility. Quantitative strengthening models and calculations were not included in the present work, which is an interesting topic and will be studied in the future. Full article
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12 pages, 2245 KiB  
Article
Analysis of Fatigue Life After Application of Compressive Microstresses on the Surface of Components Manufactured by Metal Injection Molding
by Jorge Luis Braz Medeiros, Luciano Volcanoglo Biehl and Ismael Cristofer Baierle
Surfaces 2025, 8(1), 19; https://doi.org/10.3390/surfaces8010019 - 14 Mar 2025
Viewed by 734
Abstract
The metal injection molding (MIM) manufacturing process has made relevant advances for applications in components with complex geometries, small dimensions, and high production volumes. New technologies such as hot isostatic pressing (HIP), uniform polymer extraction, and sintering with reduced temperature variations improve metallurgical [...] Read more.
The metal injection molding (MIM) manufacturing process has made relevant advances for applications in components with complex geometries, small dimensions, and high production volumes. New technologies such as hot isostatic pressing (HIP), uniform polymer extraction, and sintering with reduced temperature variations improve metallurgical and mechanical properties. However, there are still knowledge gaps in understanding these technologies and the behavior of catalytic low-alloy steels obtained by the MIM process and cyclic applications. This study aims to analyze the behavior of Catamold 100Cr6 steel subjected to quenching and tempering heat treatment in different microhardness ranges and the effect of compressive stresses on the samples obtained by polishing using ceramic microchips. The samples were characterized using optical microscopy, scanning electron microscopy, an EDS microprobe, and X-ray diffraction and subjected to elastic return cycling and an experimental device developed to apply a 19° bending angle. The findings show a significant increase in fatigue life due to the compressive stresses (up to—430 MPa) generated by the reduction in retained austenite and surface plastic microdeformation, indicating the effectiveness of 100Cr6 Catamold steel in cyclic applications. Full article
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14 pages, 14815 KiB  
Article
Mechanisms of Hardness Variation in 14Cr12Ni3Mo2VN Martensitic Stainless Steel Under Different Tempering Temperatures Following High-Frequency Induction Quenching
by Jiashun Gao, Haoxin Lan, Qingshan Jiang, Shiqi Chen, Zhilong Xu, Yunchang Yu, Xiaolei Du and Lize Cai
Coatings 2025, 15(3), 306; https://doi.org/10.3390/coatings15030306 - 6 Mar 2025
Viewed by 837
Abstract
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 [...] Read more.
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 HV0.1. 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
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18 pages, 12435 KiB  
Article
Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents
by Jiangcheng Liu, Kai Guo, Haote Ma, Jiangli He, Junchao Wang, Chuanyou Zhang, Tiansheng Wang and Qingfeng Wang
Metals 2025, 15(3), 266; https://doi.org/10.3390/met15030266 - 28 Feb 2025
Cited by 2 | Viewed by 717
Abstract
With the rapid development of long-distance transmission pipelines for oil and natural gas, pipeline steel is continuously evolving towards higher pressure, larger diameter, and thicker wall thickness. Many extensive studies and research have been conducted on X70 pipeline steel produced through traditional processing [...] Read more.
With the rapid development of long-distance transmission pipelines for oil and natural gas, pipeline steel is continuously evolving towards higher pressure, larger diameter, and thicker wall thickness. Many extensive studies and research have been conducted on X70 pipeline steel produced through traditional processing routes. This study focuses on Nb-V-Ti-N microalloyed steel with different nitrogen contents, systematically investigating the variations in microstructure and tensile properties after quenching and tempering processes. The results indicate that after quenching treatment, when the nitrogen content of the tested steel is 0.0020 wt%, its primary microstructure consists of granular bainitic ferrite (GBF), acicular ferrite (AF), and residual M/A (martensite/austenite) components. As the nitrogen content increases, the contents of acicular ferrite and M/A constituents gradually rise, while granular bainitic ferrite correspondingly decreases. After tempering treatment, the microstructure of the tested steel transforms into granular bainitic ferrite, acicular ferrite, and carbonitrides. Notably, with the elevation of nitrogen content, the number of high-angle grain boundaries in the microstructure significantly increases. Meanwhile, the mean equivalent diameter (MED) defined by the misorientation angle (MTA) ranging from 2 to 15° and the dislocation density (ρ) exhibit an overall decreasing trend. Both of these factors contribute significantly to yield strength, resulting in a gradual increase in yield strength (YS) as the nitrogen content rises. Additionally, the study finds that as the nitrogen content increases, the size of precipitated particles continuously enlarges, and their proportion in the microstructure gradually increases. This discovery provides important theoretical basis and practical guidance for further optimizing the microstructure and mechanical properties of X70 pipeline steel. Full article
(This article belongs to the Special Issue Microalloying in Ferrous and Non-ferrous Alloys)
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