Metal Science and Heat Treatment最新文献

We propose a differential equation for the mathematical description of the kinetics of the isothermal transformation in supercooled austenite. This equation generalizes specific cases, including the Austin–Ricketts and Johnson–Mehl–Avrami–Kolmogorov (JMAK) equations. A series of computational experiments was conducted to evaluate the applicability of the derived equation in describing total transformation kinetics. The findings demonstrate that the generalized equation significantly improves the accuracy of mathematical descriptions for the experimental kinetics of isothermal bainitic transformation.

This article reviews the effects of dual-pulse spot welding (DSW) on the microstructure of welds, mechanical properties, and crack characteristics during the in-situ post-heating process, elucidating the mechanisms underlying these effects. The research findings indicate that dual-pulse welding change the microstructure of the fusion zone, modifies the grain size in the heat-affected zone, improves the fatigue resistance of weld points, and effectively reduces both the number and density of cracks. Additionally, it controls crack propagation, thereby decreasing crack length, minimizing welding defects, and enhancing the overall quality of the welded joints. These improvements are crucial for enhancing the safety and durability of welded structures.

The effect of temperature and duration of artificial aging on the strength and ductility characteristics of aluminum alloy 2219-T87 was investigated in static tensile tests of a 6 mmthick plate. It was found that the tensile strength of the alloy after aging decreases, and the yield strength increases significantly as a result of the precipitation hardening process. At the same time, an increase in the artificial aging temperature leads to more significant changes in the strength characteristics of the alloy, as well as to a decrease in its ductility. It is shown that in order to achieve the optimal ratio of mechanical characteristics of alloy 2219-T87 in each specific case, an individual approach to the assignment of the artificial aging mode is necessary.

We develop and implement a system for heat treatment of sucker rods based on the use of the algorithms of fuzzy logic and aimed at the automation of the process, reducing of human intervention in the process, and improving the accuracy of parameter control. The system makes it possible to dynamically adjust critical parameters, such as quenching temperature, feed speed, and the time of stay in the treatment zone. In the system, we use a Mamdani-type fuzzy logic controller combining the data of sensors and the rules specified by the operator in order to attain the optimal productivity.We tested a system on sucker rods of different lengths (7.5, 8.0, and 9.14 m) and diameters (16 – 22 mm) made of carbon, alloyed, and high-alloy steels. The application of the system makes it possible to realize consecutive control of the parameters of heat treatment, get a uniform distribution of hardness, and reduce the number of defects caused by manual works. Moreover, the use of automated loading and unloading mechanisms elevated the efficiency and decreased the time of production. As compared with traditional control methods, the proposed approach based on the use of fuzzy logic guarantees a significant improvement of the accuracy of heat treatment and the mechanical properties of rods.

The patterns of austenite grain growth in the structure of high-carbon Fe – C – Nb steels of various compositions and different states of precipitates containing Nb were studied. The morphology of primary austenite and distribution of precipitates at temperatures of 1050 – 1200°C are analyzed. It is found that in steel not containing Si and Mn, when the temperature increases above 1100°C, precipitates dissolve and become larger, resulting in growth of austenite grain. It is shown that an increase in the Nb content in steel and refinement of precipitates in its structure contribute to effective inhibition of austenite grain growth during reheating. In addition, steel containing Si and Mn is not prone to austenite grain growth.

The article examines the poorly studied effect of reducing the strength properties of artificially aged aluminum sheets made of Al – Mg – Si alloys preliminarily subjected to plastic deformation. Specimens of cold-rolled strip made of alloy 6022 obtained in industrial production were investigated. To assess the magnitude of deformations occurring during sheet stamping of car structural parts, the processes of forming the C- and D-pillars, the inner parts of the hood and the tray were modeled using the PAM-Stamp 2G software package. Quenching, stabilizing heat treatment, deformation, and artificial aging were performed under laboratory conditions. The mechanical properties of the alloy were determined during tensile testing of flat specimens. Transmission electron microscopy was used to investigate the microstructure of the alloy. Thermal hardening was found to slow down after stabilizing heat treatment and deformation. This effect is explained by the fact that the Mg – Si clusters formed in the course of stabilizing heat treatment are destroyed during deformation. As a result, artificial aging in the samples begins at an earlier stage of thermal hardening.

The article investigates the effect of the shape, distribution, and diameter of graphite inclusions as well as the content of ferrite, pearlite, and carbides in the structure of spheroidal graphite cast iron (SGCI) on its mechanical properties. Nine structural SGCI groups with ferritic, ferritic-pearlitic, and pearlite-ferritic matrices which differ in graphite parameters and the content of pearlite, ferrite, and carbides are analyzed. The cast iron microstructure was studied using optical microscopes and quantitative metallography methods. The mechanical properties were determined in static tensile strength tests. Regression equations were constructed to calculate the tensile strength and elongation values for cast irons with different structures.

The effect of the T6 heat treatment mode on the microstructure, mechanical properties and corrosion behaviour of the Al – 9.5Si – 1.5Cu – 0.45Mg (Al – Si – Cu – Mg) alloy was studied. It was found that the most effective T6 heat treatment mode for the Al – Si – Cu – Mg alloy is the following: heating to 490°C with a 5-hour hold, then heating to 530°C with a 4-hour hold and subsequent water quenching, followed by aging at 150°C for 12 hours. In the cast state, the alloy has a tensile strength of 225 MPa and a corrosion depth of 20 μm in a 3.5% NaCl solution. After T6 heat treatment according to the proposed mode, the tensile strength of the Al – Si – Cu – Mg alloy increases to 397 MPa, and the corrosion depth in a 3.5% NaCl solution decreases to 13 μm. The enhancement of strength and corrosion resistance of the alloy after aging is attributed to the spheroidization and refinement of the Si phase, fine 8-Al₂Cu and Q-Al₅Cu₂Mg₈Si₆ precipitates.

We study the regularities of formation of homogeneous lamellar structures in (α + β)-titanium alloys subjected to thermal treatment and gradient structures with fine lamellar α-phase in the surface layers in the course of thermal hydrogen treatment. We determine the structure of alloys in different states, their phase compositions, Rockwell hardness, and impact toughness. It is experimentally demonstrated that the decrease in the cooling rate from the β-region of the samples of VT23 alloy from 5 down to 0.01 K/sec leads to an increase in the mean thickness of the α-phase lamellae from 1.2 μm (initial state) up to 8 μm in the course of cooling with isothermal holdings in the (α + β)-region. In this case, the impact strength increases from 0.15 up to 0.68 MJ/m².We propose a scheme and modes of thermal hydrogen treatment of the rods of VT6 alloy guaranteeing the formation of a gradient structure with finely lamellar α-phase in the surface layer and a bimodal (α + β)-structure in the core. The hardness of the alloy in this structural state gradually changes from 39 HRC (rod surface) down to 32 HRC (core).

The article proposes a thermomechanical processing method based on rotary forging which ensures the production of long billets from Al – 2 wt.% Cu – 2 wt.% Mn alloys. Rotary forging of the alloy was performed at 200°C (after holding for 10 – 15 min) and subsequent annealing in the temperature range of 250 – 450°C. The study investigated the structure of the aluminum alloy in different states and measured its Vickers microhardness. Additionally, static tensile tests were conducted on the specimens. Long billets were obtained by rotary forging. They had high strength combined with significant plasticity (yield strength was above 300 MPa, elongation equaled 13%) as well as high thermal stability (up to 350°C) without additional introduction of zirconium into the alloy.