Medium Carbon Low Alloy Steel Research Articles

Preparation of bainite phase microstructure by laser-electromagnetic induction hybrid solid-state phase transformation

Increasing the proportion of bainite and martensite phases is one of the effective ways to enhance the toughness of medium-carbon low-alloy steel(42CrMo). In this paper, the surface heat treatment of 42CrMo steel is carried out by using a laser heat source to achieve complete austenitization, then with electromagnetic induction heating for several times to implement insulation, and eventually to promote bainite phase transformation. In conjunction with the temperature history curves, OM, SEM, and EBSD are used to characterize the bainite morphology and percentage of bainite via different parameters of the hybrid process. The results demonstrate that the hybrid process combined with twice electromagnetic induction heating can yield a considerable proportion of bainite phase in 42CrMo steel. The resulting duplex structure, consisting of bainite and a minor fraction of martensite, exhibits a significant increase (81.1%) in tensile strength, while maintaining similar impact toughness. The elongation after fracture only has a slight reduction of 5.5% compared to that of the substrate. This innovative process provides a practical alternative to traditional bainite isothermal treatment method which must perform in a heat treatment furnace. Therefore, it is presented as a promising solution for enhancing the mechanical properties of medium-carbon low-alloy high strength steels.

A Review of High-Speed Turning of AISI 4340 Steel with Minimum Quantity Lubrication (MQL)

AISI 4340 is a medium-carbon low-alloy steel that has gained distinctive attention due to its advanced properties including high strength, high toughness, and heat resistance. This has led to its commercial usage in a wide variety of industries such as construction, automotive, and aerospace. AISI 4340 is usually machined in a hardened state through a hard-turning process, which results in high heat generation, accelerated tool wear, low productivity, and poor surface quality. The application of high-speed machining helps improve the material removal rate and surface finish quality, yet the elevated temperature at the cutting zone still poses problems to the tool’s lifespan. Apart from using advanced cutting tool materials, which is costly, researchers have also explored various cooling methods to tackle the heat problem. This paper presents a review of a sustainable cooling method known as minimum quantity lubrication (MQL) for its application in the high-speed turning of AISI 4340 steel. This study is centered on high-speed turning and the application of MQL systems in machining AISI 4340 steel. It has been observed that the hard part turning of materials with a hardness exceeding 45 HRC offers advantages such as improved accuracy and tighter tolerances compared to traditional grinding methods. However, this process leads to increased temperatures, and MQL proves to be a viable alternative to dry conditions. Challenges in optimizing MQL performance include fluid penetration and lubrication effectiveness.

Determination of the gamma-percentage time to failure of ball studs of vehicle suspension and steering joints made of medium-carbon low-alloy steel

Determination of the gamma-percentage time to failure of ball studs of vehicle suspension and steering joints made of medium-carbon low-alloy steel

Mechanisms of strength–plasticity enhancement and stress-induced phase transition in a medium-carbon low-alloy steel

Mechanisms of strength–plasticity enhancement and stress-induced phase transition in a medium-carbon low-alloy steel

Unveiling Impact of Electron Beam Optics on Weld Attributes in EN30B Steel

The influence of electron optics in terms of beam oscillation (BO) has been studied on weld quality of several steels and reported to develop cosmetic weld with smooth surface and enhanced weld properties. However, effect of electron beam oscillation on the weld quality of medium carbon low alloy steel, especially EN30B, have not reported well and investigated in this study. By manipulating magnetic lens in-line with electron beam, the diameter of oscillating beam (OD) and its effect on weld quality has been studied. The OD was changed between 0.5 mm and 2 mm. Numerous tests, including XRD, SEM, EBSD, hardness, wear, and tensile, were used to characterize the weld quality. Welds with BO significantly lowered the heat input rate than welds without oscillation. In presence of beam oscillation, retained austenite (RA) in the weld increased and it became least in welds made without BO. Tensile residual stress was found in the fusion zone (FZ) and it was higher with beam oscillation, especially with higher OD. In contrast to columnar grains predominantly found in welds made without BO, significant equiaxed grains were identified in welds made with BO. Nonmetallic inclusions (NMIs) in the weld became finer and less by use of BO. Introducing BO enhanced the hardness and reduced wear rate of weld, particularly at greater beam OD. Although Weld strength was diminished in comparison to the base metal (BM), beam oscillation increased the weld's ductility and strength.

The Influence of Rapid Tempering on the Mechanical and Microstructural Characteristics of 51CrV4 Steel

The microstructure and mechanical properties of a low-alloy medium carbon steel (Fe-0.5C-0.9Mn-1Cr-0.16V, in wt.%) were investigated after rapid tempering and compared with a conventionally tempered counterpart. The conventional thermal cycle was performed in a laboratory-scale box furnace while rapid heat treatments were carried out using the Gleeble 3800 thermomechanical simulator machine. In the rapid heat treatments, the heating rate was 50 °C/s for austenitizing and 60 °C/s for the tempering process, with a cooling rate of 60 °C/s for both treatments. Austenitization was performed at 900 °C for 3 s and tempering was conducted at 300 °C and 500 °C for 2 s. For conventional routes, the heating rate for both austenitization and tempering was 5 °C/s. Likewise, the austenitization was carried out at 900 °C for 45 min and tempering was carried out at 300 °C and 500 °C for 30 min. The results revealed that rapid tempering resulted in a significantly increased impact toughness compared to conventional tempering, while maintaining a consistent high strength level. The quenched samples showed the highest hardness and tensile strength but obtained the lowest toughness values. The optimum combination of strength and toughness was achieved with the sample rapidly tempered at 300 °C, resulting in a tensile strength of 2050 MPa and impact energy of 14 J for sub-sized CVN samples. These desirable mechanical properties were achieved throughout the tempered martensitic microstructure with a minor fraction of pearlitic strings.

Effect of Nitrocarburizing and Post-oxidation Processes on the Microstructure and Surface Properties of AISI 4140 Steel

AISI 4140 çeliği, orta karbonlu düşük alaşımlı çelikler sınıfında yer almakta olup, yüksek sertleşebilirliğe sahip olması ve nispeten ekonomik bir çelik olması nedeniyle endüstride yaygın olarak kullanılmaktadır. AISI 4140 çeliği aynı zamanda nitrürlebilen çelikler arasında yer almaktadır. Nitrürleme işlemiyle, yüzeyde elde edilen sert nitrür tabakası sayesinde sadece aşınmaya dirençli bir yüzey değil aynı zamanda yorulma dayanımında da artış sağlanmaktadır. Bu çalışmada, düşük basınçlı gaz nitrokarbürleme işlemi ve farklı sürelerde son oksidasyon işlemi uygulanmış AISI 4140 çeliğinin mikroyapısal ve yüzey özellikleri araştırılmıştır. Bu amaçla, AISI 4140 çelik numuneler, 850 °C'de 60 dk östenitlenmiş 60 °C’de yağda soğutulmuştur. Soğutma sonrası numuneler 630 °C’de 60 dk temperlenmiştir. Gaz nitrokarbürleme işlem basamakları; 350 °C’de 45 dk ön oksidasyon, 550 °C’de 90 dk nitrürleme ve 550°C’de 480 dk nitrokarbürleme uygulanmış ve ardından numuneler 45-180 dakika aralığında su buharı kullanılarak son oksidasyon işlemine tabi tutulmuştur. Mikroyapısal karakterizasyon çalışmaları optik mikroskop, tarama elektron mikroskobu (SEM), enerji dağılımlı X ışını spektrum analizi (EDX), X ışını kırınımı (XRD) analizi, mikrosertlik ve yüzey pürüzlülüğü ölçümleriyle gerçekleştirildi. X ışını analiz sonuçlarından, numunelerin yüzey katmanının demir nitrür, ɛ-Fe2-3N ve ɣ’-Fe4N fazlarını ve demir oksit (Fe3O4) içerdiği tespit edilmiştir. Son oksidasyon süresi arttıkça, demir oksit (Fe3O4) tabaka kalınlığını arttığı belirlendi. Nitrokarbürlenmiş ve son oksidasyon işlemi uygulanmış AISI 4140 çelik numuneler içerisinde, en iyi sertlik derinliği, yüzey sertliği ve yüzey pürüzlülüğü birleşimi 150 dakikada son oksidasyon uygulanmış elde edilmiştir.

Enhanced Wear Behavior of a Stainless Steel Coating Deposited on a Medium-Carbon Low-Alloy Steel Using Ultrasonic Impact Treatment

This study aims to explore the effects of ultrasonic impact parameters on the surface modification of a stainless steel coating deposited on a medium-carbon low-alloy steel using argon arc surfacing welding. Ultrasonic impact treatment (UIT), at three different vibration strike numbers (40,000 times/(mm2), 57,600 times/(mm2), and 75,000 times/(mm2)) marked UIT–1, UIT–2, and UIT–3, respectively, was carried out to modify the surface structure and properties of the stainless steel coating. The surface morphological and structural features, phase compositions, grain size, topography, micro-mechanical properties, as well as the wear resistance of the coating before and after UIT with different impact parameters were experimentally investigated. The results of optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) analyses revealed that the grain refinement accompanied by the formation of the strain-induced α′–martensite occurred on the UIT-treated coating surface. With the increase in the vibration strike number, the surface grain size and roughness decreased, while the α′–martensite content increased. Micro-hardness after UIT was increased by about 19% (UIT–1), 39% (UIT–2), and 57% (UIT–3), and the corresponding wear rate obtained was decreased by 39%, 72%, and 85%, respectively. Significant improvements in wear resistance were achieved using UIT. However, an excessive vibration strike number on the per unit area (/mm2) might result in unwanted micro-cracks and delamination on the treated surface, deteriorating the performance of the coating. These findings validate that UIT parameters (such as the vibration strike number on per unit area) are of great importance to bringing about improvements in wear performance, and UIT is found to have a high potential in modifying the surface characteristics and optimizing the mechanical performances of the deposited coating for a wide range of potential applications.

Delamination Fracture in a Medium-Carbon Low-Alloy Steel Subjected to Tempforming

The effect of tempforming on strength and fracture toughness of a 0.4%C-2%Si-1%Cr- 1%Mo-VNb steel was examined. Tempering at a temperature of 600°C followed by plate rolling at the same temperature results in the formation of lamellar structure with a spacing of 72 nm between longitudinal boundaries and a lattice dislocation density of ~1015 m−2 that enhances fracture toughness in normal direction of tempformed plate. The increase in the absorbed impact energy is attributed to delamination, which occurs in plains intersecting the propagation path of main crack that blunts crack tip.

Non-isothermal tempering kinetics in a Cr–Mo–V medium-carbon low-alloy steel: a modeling proposal

Non-isothermal tempering kinetics in a Cr–Mo–V medium-carbon low-alloy steel: a modeling proposal

Water quenching cracking mechanism and prevention of steels

ABSTRACTQuenching is often an essential step in heat treatment of steels for enhancing strength. Water quenching which is low cost and free of pollution risk instead of oil quenching or polymer aqueous solution quenching which is high cost and has high pollution risk will be widely used in heat treatment enterprises. However, the problem of easy cracking of low alloy steels (especially medium carbon low alloy steels) quenched in water has long been a concern for many researchers. The finite element simulation (FES) is used to predict transient stress at cracking position during quenching of an AISI 4140 steel cylinder sample and found that the transient tangential tensile stress at cracking position was only 350 MPa which is smaller than half of the yield strength (775 MPa) of AISI 4140 steel. Such a low tensile stress causing quenching cracking is surprising. To ascertain the underline reasons, a phase-field finite element (PFFE) model is established to investigate the microscopic stress distribution produced by martensitic transformation. The results indicate that the microscopic stress at the junction of the lath martensitic variants in AISI 4140 steel exceeded 800 MPa, and thus such a high microscopic stress is considered as the origin of quenching cracking. By using two examples, our work further clarifies the basic principle of the water–air alternative timed quenching (ATQ) process invented by us as a process suitable for engineering applications with the ability to avoid water quenching cracking and ensure mechanical properties.

Tempering Behavior of a Si-Rich Low-Alloy Medium-Carbon Steel

Owing to the addition of Si, 0.33C-1.8Si-1.44Mn-0.58Cr steel exhibits a unique tempering behavior. The tempering takes place in two distinct sequential stages that are significantly different from those in steels containing 0.2–0.5 wt.% of Si. Stage I is associated with the precipitation of transition carbides in a paraequilibrium manner, can take place in temperatures ranging from ~200 to ~474 °C, and concurrently increases strength, ductility, and toughness. Stage II is associated with the decomposition of retained austenite to bainitic ferrite and transition carbides. As a result, no significant effect of overlapping of Stage I with Stage II takes place. Stage III does not occur at temperatures below ~474 °C, since the precipitation of cementite in a orthoequilibrium manner is suppressed by the addition of 1.8 wt.% of Si. It was shown that a major portion of carbon atoms redistributes to Cottrell atmospheres under quenching. During low-temperature tempering at 200–400 °C, the precipitation of transition carbides consumes a large portion of carbon atoms, thereby increasing the number of ductile fractures and improving the impact toughness without strength degradation. The formation of chains of cementite particles on boundaries takes place in Stage IV at a tempering temperature of 500 °C. This process results in the full depletion of excess carbon from a ferritic matrix that provides increased ductility and toughness but decreased strength.

Effects of Heat Treatment on Microstructure and Mechanical Properties of D-6A AISI Medium-Carbon Low-Alloy Steel

Effects of Heat Treatment on Microstructure and Mechanical Properties of D-6A AISI Medium-Carbon Low-Alloy Steel

Effect of Polymer Quenchants on the Toughness and Hardness of Different Medium Carbon Low Alloy Steels.

In the present study, medium carbon low alloy (MCLA) steels like AISI 5140 (EN18) and AISI 4140 (EN19) are treated in different quenching media under solutionizing temperature of 855°C. Quenched in SAE 250 oil, polyethylene glycol (PEG) (10% and 30%), and water. The quenched samples are step-tempered at 575°C and at 220°C sequentially with 60 minute soaking time. BHN, YS, UTS and tensile toughness are determined for the untreated and heat-treated samples. It is found that there is an excellent correlation, with correlation coefficients of 0.97. The standard generalized equation for these two steels are established. Tensile toughness = 19000 + 12 BHN- 215 El. The study revealed that the PEG is better in terms of cost, fire-resistant and biodegradable. 30% polymer quenched samples result in better tensile toughness properties as compared to 10% polymer quenched samples.

Strengthening a Medium-Carbon Low-Alloy Steel by Nanosized Grains: The Role of Asymmetrical Rolling.

A medium-carbon low-alloy steel was prepared via the asymmetric rolling process with different ratios of upper and down roll velocities. Subsequently, the microstructure and mechanical properties were explored by using SEM, EBSD, TEM, tensile tests and nanoindentation. The results show that asymmetrical rolling (ASR) can significantly improve strength while retaining good ductility compared with conventional symmetrical rolling. The yield strength and tensile strength of the ASR-steel are 1292 ± 10 MPa and 1357 ± 10 MPa, respectively, which are higher than the values of 1113 ± 10 MPa and 1185 ± 10 MPa for the SR-steel. The ASR-steel retains good ductility of 16.5 ± 0.5%. The significant increase in strength is related to the joint actions of the ultrafine grains, dense dislocations and a large number of nanosized precipitates. This is mainly because of the introduction of extra shear stress on the edge under asymmetric rolling, which induces gradient structural changes hence increasing the density of geometrically necessary dislocations.

Simultaneous enhancement of strength and ductility in a medium carbon low-alloy steel induced by secondary martensite and Cu-rich particles

This study aims to simultaneously improve the strength and ductility of a medium carbon low-alloy steel via Cu addition and the partitioning treatment. The obtained microstructure was heterogeneous that included temper martensite, retained austenite, M-A island/secondary martensite, bainitic ferrite, and nanosized Cu-rich particles. The partitioning temperature had significantly influence on the microstructure, leading to the distinct variations of mechanical properties. With the increase of partitioning temperature from 240 °C to 330 °C, yield strength decreased from 1470 MPa to 1110 MPa. However, it increased to 1210 MPa when the partitioning temperature further increased to 380 °C. In contrast, the ultimate tensile strength gradually decreased from 2300 MPa to 1440 MPa with the increase of partitioning temperature from 240 °C to 380 °C, while the ductility significantly increased from 9% to 26%. The concurrent increases of yield strength and ductility is attributed to the numerous nanosized Cu-rich particles formed in the temper martensite. In contrast, the increase of ultimate tensile strength was caused by the increasing secondary martensite which had high carbon concentration. By using the band contrast values obtained by EBSD mapping and Gaussian fitting, the distribution of temper martensite, secondary martensite, and bainitic ferrite were quantified. The results showed that the distribution of temper martensite and bainitic ferrite were correlated, which was apt to improve the coordinated deformation between the neighboring phases. In addition, the Cu-rich particles were found to preferentially nucleate at the edge of the strip carbide because the carbide edge acted as a channel for the rapid diffusion of Cu atoms. Surprisingly, the formation of numerous nanosized Cu-rich particles was always accompanied with the increasing ductility without the loss of strength, which provides a great potential for breaking through the trade-off between strength and ductility in steels.

Effect of Tempforming on Strength and Toughness of Medium-Carbon Low-Alloy Steel.

The effect of tempforming on the strength and fracture toughness of 0.4%C-2%Si-1%Cr-1%Mo-VNb steel was examined. Plate rolling followed by tempering at the same temperature of 600 °C increases yield stress by 25% and the Charpy V-notch impact energy by a factor of ~10. Increasing rolling reduction leads to the reorientation and elongation of grains toward the rolling direction (RD) and the development of a strong {001} <110> (rotated cube) texture component that highly enhances fracture toughness. A lamellar structure with a spacing of 72 nm between boundaries and a lattice dislocation density of ~1015 m-2 evolves after tempforming at 600 °C with a total strain of 1.4. Two types of delamination were found, attributed to crack branching and the propagation of secondary cracks along the rolling plane perpendicular to the propagation direction of the primary crack. Delamination toughness is associated with the nucleation of secondary cracks in RD and their propagation over a large distance. The critical condition for delamination toughness is the propagation of primary cracks by the ductile fracture mechanism and the propagation of secondary cracks by the brittle quasi-cleavage mechanism.

High-pressure quenching effect on martensitic transformation characteristics and mechanical properties of low-alloy medium-carbon steel

In this study, the effect of high-pressure quenching at 2, 3 GPa on the martensitic transformation characteristics and mechanical properties of 40Cr steel was examined using EBSD, Mössbaue, and TEM. The results reveal that the microstructure following high-pressure quenching is a mixture of lath martensite and plate martensite, with plate martensite content increasing steadily as pressure is increased. Plate martensite exhibits distinct characteristics in the 2 GPa-sample, either crossing the prior austenite grain (PAG) or growing from the grain boundary into the interior. In 3 GPa-sample, the lath and plate martensite are distributed in clusters, with the majority of adjacent laths exhibiting {112} <111> twinning orientation relationship (OR). The number of variants was decreased from 24 for conventional quenching to 15 and the PAG size was refined to 15 μm. The percentage of M2 martensite increased from 67.71% at atmospheric pressure to 72.59% at 3 GPa, resulting in a decrease in the solid solution C content, which appears to incorporate with Cr to form fine, dispersed Cr23C6 particles. The hardness of the 3 GPa sample (807 HV) enhanced by 40%, and the compressive yield strength reached 3.5 GPa, which was three times that of conventional quenching.

Improving the impact wear properties of medium carbon steel by adjusting microstructure under alternating quenching in water and air

The microstructure and mechanical properties of steel play important roles in its wear resistance. In this study, low alloy medium carbon steel was prepared by alternating quenching in water and air for up to 3 cycles, followed by air cooling (AC) to room temperature (RQ), to obtain different microstructures. The mechanical and impact abrasive wear properties of the steel were tested under different alternating cycles, and the influence of the microstructure on the wear properties and mechanism was analyzed. The microstructure of the steel gradually changed from pearlite and ferrite to fine bainite, martensite, and retained austenite during the quenching process with an increase in the water-air alternation cycles. Compared with no alternation quenching cycle, the steel after alternating 3 cycles had the best combination of hardness, toughness, and wear resistance; that is, the hardness and impact toughness increased from 245 to 464 HV, and 28–50 J/cm2, respectively, and the impact wear resistance increased from 4.99 g-1 to 12.31 g-1. This was mainly owing to the multiphase microstructure, such as bainite/martensite, increasing the dislocation density of the sample and improving the mechanical properties of the steel, and the work-hardening of the retained austenite in the wear surface under the impact deformation, which improved the wear resistance of the steel.

Hydrogen permeation in a Cr–Mo–V medium-carbon steel: Effect of the quenching medium and tempering temperature

Hydrogen permeation tests are carried out to evaluate the effect of the quenching medium and tempering temperature on the permeation parameters and density of hydrogen traps, of a Cr–Mo–V low-alloy medium-carbon steel. Three types of steel membranes are tested: 1) in the as-quenched condition, 2) tempered at 235 °C and 3) tempered at 530 °C; each one quenched in two different media: oil or brine. From the as-quenched condition, the apparent concentration of hydrogen and hydrogen flux, tend to decrease as the tempering temperature increases. The membranes in the as-quenched condition and tempered at 530 °C, show lower hydrogen diffusivity and higher density of hydrogen traps than membranes tempered at 235 °C. It is concluded that tempering at 235 °C, promotes hydrogen induced cracking, which is contrary to what has been previously determined. The cracking is related to a higher hydrogen diffusivity and lower density of hydrogen traps.