Steel Processing Research Articles

A promising direction of development of out-of-furnace vacuuming processes of steel

Secondary furnace processing of steel is a key link in modern steelmaking production and will simultaneously solve the problems of improving steel quality and production efficiency. At the same time, there is a variant of secondary evacuation of steel with a simplified bottomless vacuum chamber, which has a number of technological and design advantages. The article discusses the main parameters of this process and proposals for its industrial application

Numerical Modelling and Experimental Validation of Selective Laser Melting Processes Using a Custom Argon Chamber Setup for 316L Stainless Steel and Ti6AI4V

Selective Laser Melting (SLM) is an advanced additive manufacturing technique that demands meticulous control over thermal dynamics to maintain the integrity and performance of manufactured parts. This study presents the development and validation of a thermal model designed to enhance the SLM process for 316L stainless steel (316L SS) and titanium alloy Ti6Al4V. A specially constructed Argon Chamber Setup, equipped with a 200 W continuous-wave (CW) fibre laser system, was used to create an SLM-representative environment for 316L SS, enabling precise experimental validation of the model. This validation serves as a robust baseline, facilitating the model’s extension to more complex materials like Ti6Al4V, thereby supporting a cost-efficient and safe approach to initial testing. The rigorously validated thermal model offers a comprehensive link between experimental data and numerical simulations in SLM. It supports process optimisation by accurately predicting thermal behaviours, contributing significantly to additive manufacturing advancements. By fine-tuning processing parameters, this model enhances material characteristics, thereby providing practical insights applicable to industrial production and improving the consistency and quality of SLM-manufactured parts.

Evolution of Microstructure and Hardness during Carburization Heat Treatment of Heavy-duty Gear Steels: Numerical Prediction and Experimental Study

Abstract In order to solve the problems of long process cycle, low efficiency and high cost in the carburization heat treatment process of 18Cr2Ni4WA heavy-duty gear steel. The carbon concentration distribution of 18Cr2Ni4WA steel under conventional carburizing process at 930℃ was studied by combining numerical simulation with experimental research. The results show that the carbon concentration distribution predicted by the simulation is in good agreement with the experimental results. The microstructure of the surface layer after low-temperature tempering consists mainly of fine acicular tempered martensite, while the core consists mainly of lath tempered martensite and bainite. The increase in hardness after carburization is mainly attributed to the solid solution strengthening of the carbon atoms. The increase in hardness after cryogenic treatment is mainly attributed to the precipitation strengthening of the carbides. In addition, compared to the conventional carburization at 930°C, the high temperature carburizations at 950°C and 970°C reduced the carburization time by 37.2% and 53.5%, respectively.

Numerical simulation on dehydrogenation behavior during argon blowing enhanced vacuum refining process of high-quality steel

Argon bubble blowing enhanced vacuum refining is a crucial process to remove hydrogen element in molten steel for high-quality steel manufacturing. However, the whole refining process is a black-box operation and the field information inside the reactor is not clear yet. In this work, an integrated mathematical model that coupling computational fluid dynamics and degassing chemical reaction is established to investigate dehydrogenation behavior under vacuum condition. The model accounts for three potential reaction sites to clarify the dehydrogenation mechanism of molten steel in detail. The simulation results indicate that the hydrogen removal by argon bubble surface contributes the most, followed by steel free surface, and little by bulk steel near the bath surface where the dehydrogenation occurs mainly at the initial treating stage. The total hydrogen removal ratio increases with reducing vacuum pressure and increasing the argon gas flow rate, but is independent of the initial hydrogen content.

Effect of nozzle clogging on vortexing during continuous casting processes: results of an experimental simulation

ABSTRACT Exogenous oxide inclusions in continuously cast steel primarily arise from the entrapment of slag during various stages of steelmaking, including in furnaces, ladles, and molds. To maintain steel cleanliness, operators often pause ladle and tundish processes before ‘slag vortexing’ begins, since this phenomenon (slag vortexing) can adversely affect product quality. Previous studies indicate that sub-entry nozzle clogging can lead to productivity issues and quality defects in cast products. Clogging can cause non-uniform reductions in nozzle diameter along the molten metal flow direction. This study examines the impact of drain port taper (a representation of nozzle clogging) on air core vortex formation during water drainage (simulating molten metal) using a parameter, ‘Characteristic Volume of Air Core.’ Results show that clogged drain ports are prone to vigorous vortexing, significantly affecting efflux velocity and static pressure at drain outlets. The current study also analyzes the dynamic behavior of air core vortexing due to nozzle clogging, revealing that clogging can induce fluctuations in liquid discharge, adversely affecting the casting process. These findings have practical implications for continuous casting processes in steel and other metals.

The Impact of Post-Furnace Steel Processing Equipment on Reducing Voltage Fluctuations Caused by Arc Furnaces

Arc devices are among the receivers with the highest power connected to power systems. Due to dynamic load changes, these receivers generate a number of disturbances that affect the quality of electric power. The most important disturbances include voltage fluctuations. It is also worth mentioning the asymmetry and deformation of the supply voltage curve. This article discusses the mutual interaction of receivers operating in parallel, operating stably, and devices with dynamic current consumption. Calculations based on model tests and the results of parameters characterizing the quality of energy, which were recorded in the line supplying the steelworks, are presented. The power supply conditions (power of the short-circuit network) were assessed to influence the degree of suppression of voltage fluctuations by loads with stable current consumption.

A Review of Welding Process for UNS S32750 Super Duplex Stainless Steel

Super duplex stainless steel UNS S32750 is widely used in marine industries, pulp and paper industries, and the offshore oil and gas industry. Welding manufacturing is one of the main manufacturing processes to make material into products in the above fields. It is of great importance to obtain high-quality welded UNS S32750 joints. The austenite content and ferrite content in UNS S32750 play an important role in determining UNS S32750 properties such as mechanical properties and corrosion resistance. However, the phase proportion between the ferrite phase and austenite phase in the welded joint will be changed during welding. Lots of research has been done on how to weld UNS S32750 and how to obtain welded joints with good quality. In this work, the recent studies on welding UNS S32750 are categorized based on the welding process. The welding process for UNS S32750 will be classified as gas tungsten arc welding, submerged arc welding, plasma arc welding, laser beam welding, electron beam welding, friction stir welding, and laser-MIG hybrid welding, and each will be reviewed in turn. The microstructure and properties of the joints welded using different welding processes will also be discussed. The critical challenge of balancing the two phases of austenite and ferrite in UNS S32750 welded joints will be discussed. This review about the welding process for UNS S32750 will provide people in the welding field with some advice on welding UNS S32750 super duplex stainless steel.

Selection of parameters of high-speed thermodeformation of Cr–Ni–Mo steel processing on the basis of imitation modeling

The temperature of the end of finishing stage, cooling rate and coil winding temperature are structure-sensitive parameters for bainite-grade steels in the production of plate less than 10 mm thick. Simulation modeling of high-speed thermo-deformation processing of Cr–Ni–Mo bainitic steel samples has been carried out in order to select the most rational technological modes in continuous hot rolling mills. The influence of strain rate and temperature as well as niobium and vanadium microalloying additives on phase transformations has been investigated.

Formation and strengthening mechanism of high entropy nugget for aluminum/steel resistance rivet welding

Resistance rivet welding (RRW) was a promising joining process for aluminum (Al) alloy and steel. The high entropy mixed nugget (HEMN) with the composition of Al0.8CoCrFe1.6Ni was obtained by introducing a high entropy alloy (HEA) rivet in RRW process. The high entropy played a significant role in facilitating the formation of solid solution. The HEMN microstructure exhibited a nanometer-sized weave-like structure caused by spinodal decomposition, comprising both BCC and B2 phases. The average hardness of the HEMN exceeded that of the Al/Steel mixed nugget, resulting in higher lap-shear strength and ductility. The analysis of strengthening mechanism demonstrated that the lattice misfit and order strengthening were the primary contributors. This study provided a novel strategy for joining dissimilar metal materials.

Al Alloy Melting Behavior and Interfacial Reactions with Steel Under Natural Convection

The Al alloy melting behavior and interfacial reactions during the steelmaking process of high-Al automotive steel were investigated in this study. The total dissolution time of Al bars (20 × 20 × 80 mm) in molten steel was quite short, decreasing from 21.4 s to 10.0 s with an increase in bath temperature from 1580 to 1620 °C. The Al alloy melting process at the molten steel temperature of 1600 °C included the formation of a solidified steel layer, the latter’s rapid melting, and Al alloy normal melting, while at 1600 °C, the process included a second increase in the thickness of the solidified layer. Because steel elements such as [Fe], [C], [O], and [N] could diffuse during the whole Al alloy melting process, an Fe (Al)-FeAl-FeAl2-Fe2Al5-Al diffusion layer along the direction of the Al-rich matrix could be found at the Fe–Al interface. Moreover, FexO, Al2O3, and unstable AlN inclusions could be observed in the FeAl layer. This study also investigated how to reduce the number of these easily formed inclusions. Decreasing the pre-heating process time and dissolved oxygen content could be useful in decreasing FexO and Al2O3 inclusion formation. Some small-sized AlN inclusions formed in the center of the Al bars where they could not come into contact with the molten steel directly during the melting process; even for the immersion time of only 1 second, these inclusions were not stable in molten steel at the refining temperature and disappeared during the melting process.

Investigation on the desulphurisation process by powder injection during RH refining process of non-oriented silicon steel

In the present study, the desulphurisation process by powder injection during RH (Ruhrstahl-Heraeus) refining process was studied by establishing a kinetic model. The predicted results by the model were compared with experimental data obtained from industrial trials to verify its accuracy. The effects of the desulphuriser particle diameter, desulphuriser composition and powder injection rate on the desulphurisation process were analysed and discussed. Results show that the desulphuriser particle diameter and powder injection rate considerably affected the desulphurisation process. By decreasing the desulphuriser particle diameter and increasing the powder injection rate, the reaction area between desulphuriser particles and liquid steel considerably increased. Therefore, the desulphurisation rate and ratio increased. When the desulphuriser particle diameter decreased from 3.0 to 0.1 mm, the desulphurisation ratio increased from 44.6% to 88.4%. The ratio increased from 32.8% to 62.2% for 3.0 mm desulphuriser particles when the powder injection rate increased from 100 to 250 kg min−1. Furthermore, an increase in the desulphuriser basicity and CaO/Al2O3 ratio improved the sulphur capacity and accelerated the desulphurisation process. The desulphuriser used herein had a low sulphur partition ratio, and thus it yielded a lower desulphurisation ratio than the CaO-SiO2-Al2O3 desulphuriser.

Metallurgical characteristics and mechanical properties of dissimilar friction stir welded DH36 steel and UNS G10080 steel joints

The present study expanded the scientific comprehension of the friction stir welding process for dissimilar steels, namely high-strength shipbuilding grade DH36 steel and UNS G10080 steel. The effect of tool traverse speed and plunge depth on temperature history, microstructure characteristics, and mechanical properties is investigated experimentally. The metallographic characterizations were examined through an optical microscope and field emission scanning electron microscopy equipped with an energy-dispersive X-ray system. Microhardness, impact, and tensile tests were carried out on the friction-stir-welded specimens. Increasing the plunge depth and reducing the traversal speed resulted in an augmentation of the peak temperature, primarily attributable to higher heat generation. Within the range of process parameters used, the tool produced complex material movement, resulting in swirl-like and vortex-intercalated features, particularly adjacent to the stir zone/workpiece interface. These vortex-like features exhibited dynamically recrystallized fine-grained microstructures. The grain size in the stir zone and the thermo-mechanically affected zone is reduced by increasing the plunge depth and decreasing the traverse speed due to enhanced dynamic recrystallization, subsequently improving the hardness and toughness values. In the stir zone, the microstructure revealed the acicular-shaped bainite ferrite in the DH36 steel and the Widmanstatten ferrite in the UNS G10080 steel. The microhardness contours revealed the uneven hardness distribution across the weld cross-section due to the microstructural heterogeneity in the dissimilar steels. The maximum welding efficiency of 106 % and toughness of 46 J are obtained at 40 mm/min traverse speed with a plunge depth of 0.2 mm, which is attributed to sufficient heat generation and grain refinement.

Analysis of Metal Fused Filament Fabrication process chain for 316L stainless steel

Metal Fused Filament Fabrication (MFFF) has emerged as a prominent technology in Additive Manufacturing (AM), characterized by its cost-effectiveness, versatility in creating intricate geometries using diverse materials, and widespread availability of AM machines. However, the intricate processes of making filament, printing, debinding, and sintering in MFFF pose unique challenges, with a vast number of parameters influencing each stage. Specialized companies handle these stages for research purposes, yet detailed information on the processes remains limited. The objective of this research is to conduct a meticulous examination of the parameters governing the printing, debinding, and sintering of 316L stainless steel—a material widely employed in various industries. The goal is to provide researchers and manufacturers with a comprehensive understanding, enabling them to achieve high-density metal parts that rival those produced through Selective Laser Melting (SLM). This research employs a systematic approach in producing flawless metal parts through fine-tuning parameters such as printing speed, nozzle diameter, extruder and construction table temperatures, heating rate, nitric acid injection during debinding, and sintering atmosphere and temperature. Despite advancements in MFFF parameters in this study, a comparative analysis with SLM reveals superior mechanical properties and density in SLM-produced parts. Because, the robust bonding facilitated by a powerful energy source (laser) in SLM minimizes porosities, whereas MFFF relies solely on molten filament adherence, potentially leading to small gaps between layers. This research contributes valuable insights for achieving dense, defect-free metal parts through Metal Fused Filament Fabrication (MFFF). It sheds light on the persistent advantages of Selective Laser Melting (SLM) in terms of mechanical performance and density. The comprehensive understanding of parameters provided in this study empowers researchers and manufacturers to optimize MFFF processes for 316L stainless steel, narrowing the gap between the two technologies (MFFF and SLM) and enhancing the competitiveness of MFFF in producing high-quality metal parts.

Understanding the role of alloying elements Cr, Ni in erosion–corrosion process of nuclear grade austenitic stainless steel 304 L by total reflection X-ray fluorescence

Stainless steel (SS) has gained an indispensable position as one of the most widely used industrial material. In nuclear industry, it is one of the technologically most important structural materials used in pressure tube, containment vessel and reprocessing-related applications. In fact, SS 304 L is the workhorse material of the reprocessing plant which faces the hostile conditions of acid, temperature as well as high radiation dose. These conditions can affect the erosion-corrosion behavior of the material and can lead to poor mechanical properties. This also affects the life of the reactor components. In the present study, a systematic work has been carried out to develop an in-depth understanding of the Corrosion Rates (CRs) with respect to the loss of major and minor elements from SS into the corrosive nitric acid medium using Total reflection X-Ray Fluorescence (TXRF). The effect of acid molarity as well as temperature, on the erosion-corrosion behavior of SS304L was studied. The TXRF studies have revealed that the CR was maximum in 2 M HNO3 and minimum in 8 M, showing that as the nitric acid molarity has an important role to play in the corrosion and as the molarity increases, the passivation of SS 304 L also increases. This observation was further corroborated with the concentrations of Fe, Cr and Ni, which had leached into the nitric acid medium. The role of alloying elements, Cr and Ni, in the passivation of SS was also studied. The effect of temperature showed that at 45 °C, the rate of corrosion was minimum, as compared to at 25 °C and 90 °C which reveals that the formation of chromium oxide passive layer was thermodynamically most favorable at this temperature.

Comparative studies of Taguchi dynamic analysis, statistical, and artificial neural networks for low-carbon steel corrosion inhibition in acidic media

The aim of the present work is to optimize the corrosion inhibition process of low-carbon steel in 2.5 M phosphoric acid at different temperatures and inhibitor concentrations. The weight loss method is used to evaluate the corrosion rate in the absence or presence of a corrosion inhibitor. Taguchi dynamic (L16), mathematical regression, and artificial neural networks (ANN) are used during the data processing. The outcomes showed that the %IE increased with inhibitor concentration and temperature up to 50 oC. The Taguchi method showed that the optimum conditions for the corrosion inhibition temperature were found to be 50 oC and a 0.05 M KI concentration. Two mathematical models are proposed to construct a relationship between %IE and independent variables: the exponent model (EM) and the polynomial model (PM). PM was more accurate than EM, with a significant correlation coefficient approaching 0.9851. Temperature had a greater effect on the %IE than inhibitor concentration, which was consistent with Taguchi's findings. In ANN analyses, five networks were suggested: linear, a generalized regression neural network (GRNN), radial basis functions (RBF), and two multi-layer perceptron (MLP) networks. The highest correlation coefficient (0.996) and lower absolute error (0.126) were achieved by MLP 2:2-9-4-1:1.

РЕНТГЕНОСТРУКТУРНЫЕ ИССЛЕДОВАНИЯ СВАРЕННОГО ВЗРЫВОМ МЕДНО-СТАЛЬНОГО БИМЕТАЛЛА ПОСЛЕ ТЕРМИЧЕСКИХ ВОЗДЕЙСТВИЙ

The article presents the results of studies of diffusion processes in the joint zone of the bimetallic copper M3 + steel 30CrMnSiA after explosion welding and subsequent thermal effects at 880 °C with a holding time of up to 10 hours, 1000 °C with holding times of 24, 50, 100 hours and 1050 °C with a holding time of 1 hour. It is shown that the intensification of diffusion processes of steel into copper and copper into steel near the joint boundary with the formation of solid solutions causes a significant development of the thin structure characteristics: an increase in the level of relative lattice deformation and a refinement of mosaic blocks.

Technological support of workpiece surface quality based on local cryogenic impact during processing of austenitic steels

Technological support of workpiece surface quality based on local cryogenic impact during processing of austenitic steels

A Surface Defect Detection Method for Cold-rolled Strip Steel Based on Improved YOLOv8

Cold-rolled strip steel has excellent mechanical properties, and it is widely used in the fields such as automotive manufacturing, construction industry, aircraft manufacturing and electronic product manufacturing. However, many different processing defects occur in the manufacturing process of cold-rolled strip steel, and this article proposes a visual detection method based on YOLOv8 to identify the surface defects on cold-rolled strip steel more accurately. Firstly, several common types of defects in cold-rolled strip steel were analyzed. Then, in order to enrich the dataset for subsequent detection, wavelet transform was used for filtering, denoising, and canny edge detection in the image processing stage for obtaining the clearer input model image with the more prominent graphics. Lastly, the CA attention mechanism was added into the YOLOv8 which is useful to improve the features recognition ability of the model, at the same time, the original standard convolution was replaced by DCS convolution and the loss function was optimized which is useful to get the lightweight models. The improved YOLOv8 model was validated on the NEU-DET dataset, the overall detection performance of the model such as the recall, the accuracy, and the average precision has significantly improved.

Phase transformation process and toughening mechanism of 12Cr1MoV heat-resistant steel for high-pressure boilers by external shower and internal spray heat treatment

To optimize the heat treatment process for 12Cr1MoV heat-resistant steel, this study designed a novel process of external shower and internal spray (ESIS), followed by air cooling. This new approach was simulated in the laboratory. The study focused on the variation in impact energy and the microstructural changes in the experimental steel subjected to different processes, specifically the T890 and T740 processes (where the numbers represent the termination temperature of ESIS). The phase transformation processes and toughening mechanisms of the steel after these treatments were thoroughly investigated. The theoretical analysis revealed that the microstructures of T890 and T740 steels consist of quasi-polygonal ferrite (QPF), granular bainite (GB), and pearlite. The QPF in T890 steel forms at a higher temperature compared to T740 steel, leading to a lower dislocation density and carbon content in QPF during the subsequent cooling phase. This results in the QPF in T890 steel having a hardness of 1.02 GPa lower than that of the QPF in T740 steel. The higher hardness of QPF in T740 steel correlates with reduced toughness and resistance to crack propagation. Under impact loading, the QPF in T740 steel exhibits insufficient crack propagation resistance to counteract the effects of microscopic defects within the tensile stress region of the fracture. Consequently, cracks preferentially propagate within the QPF, creating a relatively flat propagation path. In comparison, the fracture of T740 steel demonstrates a straighter propagation path in the tensile stress region than T890 steel, resulting in significantly lower impact energy for T740 steel.

PECULIARITIES OF CRACK FORMATION IN HETEROPHASE INCLUSIONS OF THE “EUTECTICS OF INCLUSION − MATRIX” TYPE

Purpose. The goal of the work was to study the peculiarities of crack nucleation in heterophase inclusions of the “eutectic inclusion − matrix” type during steel deformation. Methods. The research was carried out after deformation of samples from steels 08Yu, 12GS, 08kp, 09G2S, NB-57, 08GSYUTF in the temperature range of 20…1 200 °C with the speed of movement of grips 1 680 mm/min. The research methods were used − petrography, micro-X-ray spectral analysis (Cameca MS-4, Nanolab-7), optical microscopy (Neophot-21). Results. It is established that the variety of phases that make up heterophase inclusions of the type “eutectic of inclusion − matrix” leads to their different behavior under conditions of plastic deformation. It is shown that the nucleation of brittle or viscous microcracks occurs along the internal interfacial boundaries between the metal matrix and the second phase of the eutectic. It is determined that the nature of cracks is determined by the level of plasticity of the inclusion phases and the deformation temperature. It is shown that the critical degrees of deformation of the samples, at the achievement of which there were noticeable microcracks along the internal interfacial boundaries, depend on the temperature and nature of the phases of inclusions “eutectic of inclusion − matrix”. It is established that the values of critical degrees of deformation determine the level of cohesive strength of the internal interfacial boundaries in heterophase inclusions “inclusion − matrix eutectic”. Scientific novelty. Peculiarities of microcracking nucleation in heterophase inclusions of the “inclusion − matrix eutectic” type have been established. It is shown that the nature of microcracks formed along the interfacial boundaries depends on the temperature, level of plasticity and conditions of combination of brittle and plastic phases in inclusions of the “eutectic of inclusion − matrix” type, as well as on the deformation temperature. It is shown that the critical degrees of deformation of steels, when microcracks occurred along the inner interfacial boundaries, determine the cohesive strength of these boundaries and depend on the temperature and nature of the phases of inclusions such as “inclusion − matrix eutectic”. Practical significance. The use of the results obtained will make it possible to develop technologies for producing steels with regulated types of heterophase nonmetallic inclusions, which will significantly increase their technological and operational characteristics, as well as prevent the formation of various kinds of defects during the processing of steels by pressure and the operation of products.