Steel Heat Research Articles

Effect of Austempering Holding Time Variations of 30, 60, and 90 Minutes at 300 °C on The Microstructure and Toughness of Nodular Cast Iron

The phases of the nodular cast iron matrix are similar to those of steel. Therefore, heat treatment of steel can be applied to nodular cast iron. A potential heat treatment for nodular cast iron is austempering. This study aimed to determine the effect of austempering holding time at 300 °C on the microstructure and toughness of nodular cast iron. The austempering process begins with austenitizing at a temperature of 850 °C for 60 minutes, then the quenching process is carried out in a salt bath until a temperature of 300 °C is held with variations of 30, 60, and 90 minutes, then cooled to room temperature. Metallographic testing was conducted to determine the phase change before and after the austempering process using a Scanning Electron Microscope (SEM). Meanwhile, impact testing was carried out to determine changes in toughness before and after the austempering process. At a holding time of 30 minutes, metallographic testing on the raw material produced a gray coarse pearlite phase, black nodular graphite surrounded by white ferrite. After the austempering process, gray fine pearlite and black nodular graphite appeared. At the holding time of 60 and 90 minutes, the graphite sizes were bigger. Austempering withholding times of 30, 60, and 90 minutes resulted in impact energy of 4.2, 10, and 11 Joule. From the results of the study, it was concluded that an increase in holding time would increase the size of the graphite and the toughness of nodular cast iron.

Mechanical Properties and Microscopic Evaluation of Heat Treated D6A Ultra High-Strength Steel

This investigation aims to evaluate the influence of heat treatment on the hardness and microscopic characteristics of a specific grade of medium carbon steel, namely, the American standard D6A Ultra High-Strength Steel, which contains 0.47% carbon in its composition. After preparation, specimens were heated in a muffle furnace at a temperature of 830°C and held for 90 minutes, followed by quenching. Subsequently, the specimens underwent tempering at a temperature of 600°C for 60 minutes. The hardness and microscopic evaluation of the heat-treated steel were determined. The results also indicate a rapid increase in hardness with a decrease in thickness for the heat-treated material. For HRA (Rockwell Hardness A Scale) times of 5s and 10s, the hardness enhancement percentages were 29% and 103%, respectively, compared to specimens without heat treatment. Furthermore, a chamber pressure test assessed the suitability and optimal design of Ultra High-Strength Steel for a pressure vessel in a mortar gun. As the outer radius increases, there is a corresponding decrease in axial stress, hoop stress, and the maximum limit of ultimate stress for both internal pressures within the pressure vessel. For internal pressures of 100 MPa and 85 MPa, the optimal inner radius for the pressure vessel is determined to be 0.053m and 0.051m, respectively.

Implementation of optimal HF welding procedure of steel pipes for high-quality and energy-efficient welds

Electric currents of medium and high frequencies are used for inductive heating and welding of steel products. Furthermore, magnetic concentrators are used for the optimisation of transfer so that they direct the currents at a specific area of the heat-treated steel product. After years of study and detailed experimental research, we have found out that the material behaviour during inductive heat treatment also depends on the type of concentrator applied. The character of the electric current passing through the steel products changes through the application of different concentrators which directly alter the structure and quality of the final product. Ferritic and magneto-dielectric concentrators from different producers have been used in the research with HF inductive welding of steel pipes.

Multi-scale damage mechanism of hierarchically structured high-strength martensitic steels under shock loading

The multi-scale damage behaviors and underlying mechanisms of hierarchically structured high-strength martensitic steels are investigated via plate-impact recovery experiments, postmortem characterizations. Plate-impact experiments were conducted at compressive peak stresses ranging from approximately 5.5 to 11.0 GPa, and the tensile strain rates are ∼105 s −1. Significant improvement in the spall strength of the heat-treated martensitic steel is achieved (5.4 GPa), about 80% higher compared to the as-received bainite steel. The spall failure of the investigated martensitic steel exhibited a mixed-mode combination of brittle (micro-cracks) and ductile (voids) characteristics, known as quasi-cleavage spallation. As the impact velocity increased, voids nucleated successively at different types of boundaries as follows: boundaries between enriched and depleted zones, prior austenite grain boundaries, packet boundaries, block boundaries and lath boundaries. Shear cracking was found to be an important mechanism to accommodate the severe plastic deformation during spallation, giving the strict geometric constraints due to void nucleation tending to occur at grain boundaries. Additionally, molecular dynamics simulations considering realistic hierarchical structure of martensitic steel have been developed to validate the experimental results. These findings and simulation methods contribute a better understanding of the spall behavior of martensitic steels, as well as guidance for future design of high-strength martensitic steels with exceptional reliability and safety under extreme conditions.

An improved method for the quantification of microstructures via optical microscopy

Quantitative optical microscopy is a powerful tool for microstructural characterization of relatively large areas of multiphase materials, but accurate quantification often requires skillful sample preparation, imaging, and analysis techniques. Measuring phase fractions in a microstructure is done by segmenting images between features of interest and everything else and can be accomplished by a variety of techniques. With existing methods, in many cases, optimal contrast between the features of interest and the surrounding microstructural constituents is difficult to obtain and inconsistent across both individual images and a sample surface due to normal variations in materials and equipment, which can introduce measurement errors. A new machine-learning tool, the Labkit ImageJ plugin, provides a user-friendly method for training models for quantitative metallography and can be generally applied to study a wide variety of multiphase materials. Sørensen–Dice Indices were calculated to provide accuracy metric and show the improvement in image segmentation using Labkit to other common contrast-based thresholding methods versus manually-segmented representative images throughout the temperature range of this study. An example using intercritically heat treated HY-80 steel containing a duplex microstructure is presented using three different optical microscopy quantitative methods to show the improvement in reliability from the Labkit plugin. These quantitative measurements are augmented by differential scanning calorimetry and compared to CALculation of PHAse Diagram (CALPHAD) models to highlight the importance of experimental data for the design of heat treatments. A method for calibrating CALPHAD models to better predict industrial heat treatments is presented and shown to improve the accuracy of phase-fraction predictions, which is crucial for execution of intercritical heat treatments of steels.

STRUCTURE AND MECHANICAL PROPERTIES OF A SERIES OF STRUCTURAL STEEL AFTER HEAT TREATMENT WITH ENDURANCE IN THE INTERCRITICAL TEMPERATURE INTERVAL

Purpose. To show the effectiveness of various methods of heat treatment of the studied steels with heating in ITI, as a result of which their mechanical properties are increased, which is due to the acquisition of a multiphase structure, one of the components of which in some cases is metastable austenite.
 Research methods. Steels 14Г2, 20ГЛ, 20ГФЛ 45Г were investigated. Various types of heat treatment were carried out with heating in the intercritical temperature interval. In the studied steels, a multiphase structure dispersed in chemical composition was obtained. Durometric, metallographic and X-ray research methods were used. Mechanical properties under tension and impact toughness were determined. These properties were compared with those obtained from the studied steels after typical heat treatment.
 Obtained results. It is shown that in the investigated steels, when performing various methods of heat treatment, there is no need to obtain a single-phase austenite structure, which is homogeneous in terms of its chemical composition, during heating. The creation of a multiphase dispersed micro-inhomogeneous structure in the studied steels by heat treatment methods, which include regulated heating and holding in ITI, allows to obtain after normalization, hardening and high or low tempering, as well as isothermal tempering, a good combination of strength and plastic properties, the level of which exceeds that obtained after the usual process.
 Scientific novelty. The paper considers an alternative point of view, according to which to improve the mechanical and service properties of steels, it is necessary to obtain multiphase dispersed micro-inhomogeneous structures in them, consisting of martensite, bainite, ferrite, carbides, carbonitrides and metastable residual austenite, as well as their various combinations. In order to obtain such structures, it is advisable to use heating and holding in ITI during the heat treatment of pre-eutectoid steels, in which austenite is formed, along with ferrite and carbides. At the same time, austenite has chemical micro-heterogeneity, because the carbon concentration at its boundary with carbide is significantly higher than at the boundary with ferrite. This makes it possible to obtain a multiphase dispersed micro-inhomogeneous structure after heat treatment.
 Practical value. Increasing the mechanical properties of steels makes it possible to increase the operational stability of machine parts, which is an important task of materials science. One of the directions of its solution is to obtain a multiphase structure in steels, one of the components of which is metastable austenite, in which the dynamic deformation martensitic transformation (DSMT) and the effect of self-hardening under load (SHL) occur under load. Methods of heat treatment with heating at ITI are easily implemented in production conditions and allow for energy savings. Modes of their implementation should be chosen taking into account obtaining the necessary properties, the initial structure, its defects and the cross-section of the products.

Study of Electroless Nickel Plating on Super Duplex Stainless Steel for Lithium-Ion Battery Cases: Electrochemical Behaviour and Effects of Plating Time

With increasing demand for Li-ion batteries, studies are focusing on enhancing battery performance and safety. However, studies on battery cases remain scarce. Herein, we propose the use of super duplex stainless steel SAF2507, which is a two-phase (austenite + ferrite) steel, for battery casings. Unlike conventional AISI304, SAF2507 maintains its corrosion resistance and strength at high temperatures and precipitates a secondary phase at approximately 975 °C. However, the effects of Ni plating on this secondary phase are not well documented. Therefore, the electroless Ni plating of SAF2507 after secondary-phase precipitation was studied. Briefly, heat treatment at 1000 °C was used to induce precipitation, and the electroless Ni plating behaviour over varying plating periods was analysed using open-circuit potential, potentiodynamic polarisation, and electrochemical impedance spectroscopy measurements. The plating state and corrosion behaviour were examined using scanning electron microscopy. Heat-treated SAF2507 steel with a secondary phase exhibited excellent electroless Ni plating behaviour, which enhances the safety and durability of Li-ion batteries. Furthermore, uniform plating and electrochemical behaviour were achieved after 180 s, suggesting that SAF2507 is superior to AISI304. These findings contribute to the development of safer and more efficient batteries and address the growing demand for Li-ion battery case materials.

Channel parameter optimization of one-strand slab induction heating tundish with double channels

Abstract A generalized three-dimensional mathematical model is built to study the influences of channel parameters (channel angle, channel section diameter, and channel distance) on the molten steel flow, heat transfer, and inclusion removal in the induction heating tundish. The results demonstrate that as the channel angle increases, the flow of molten steel in the discharging chamber gradually slows down. When the channel angle is 6°, the temperature of the discharging chamber is slightly lower than when the channel angles are 2° and 4°. When the channel angle is 2°, the inclusion removal rate is lower than when the channel angles are 4° and 6°, while the latter two have little difference. As the channel section diameter increases, the flow of molten steel in the discharging chamber gradually slows down. When the channel section diameter is 100 mm, the temperature distribution in the discharging chamber is uneven. While the temperature distributions of the discharging chamber are even and similar, when the channel section diameters are 150 and 200 mm. As the channel section diameter increases, the removal rate of inclusion gradually decreases. The variation of channel distance has little effect on the temperature distribution of the discharging chamber. When the channel distance is 600 mm, the removal rate of inclusion is lower than when the channel distances are 1,000 and 1,400 mm. Moreover, for the latter two, the removal rates of inclusions have little difference. For this model, the best channel angle is 4°, the best channel section diameter is 150 mm, and the best channel distance is 1,000 mm.

HEAT RESISTANCE OF CORROSION-RESISTANT STAINLESS STEEL CRNI65MWU AFTER VARIOUS TYPES OF FULL ANNEALING

The article discusses the influence of additional heat treatment of corrosion-resistant steel CrNi65MWU on increasing its heat resistance, as well as on changing the chemical composition of the protective oxide layer formed on the surface. The relationships between heat treatment modes and changes in the corrosion rate of selected steel under operating conditions in glass-forming production are shown. Research has also been carried out on the direct interaction of the melt of various types of glass with a heat-treated steel surface.

Mechanisms of Intragrain Plastic Deformation in Steel Heating Process

Mechanisms of Intragrain Plastic Deformation in Steel Heating Process

Content and Dispersion of Ferroalloys in the Coating During Microarc Alloying of Steel

Introduction. The main disadvantage of traditional processes of diffusion surface hardening of steel products is its long duration. Therefore, the problem of intensification of such processes is relevant. To solve it, the use of high-energy effects on the material is proposed, which allows us to obtain a hardened surface layer from a coating composed of ferroalloy powders containing alloying elements. There is no data in the literature on the required content and dispersion of such powders in the composition of the coating. The aim of this study was to select the particle size of ferroalloys and their concentration in the coating to achieve the most effective hardening of the processed product.Materials and Methods. For experimental studies, cylindrical samples made of steel 20 with a diameter of 12 mm and a length of 35 mm were used. On the surface of these samples, an alloying coating containing ferroalloy powders and an electrically conductive gel as a binder was applied. After that, the samples were immersed vertically for half their length into a metal container, which was then filled with carbon powder with a particle size of 0.4–0.6 mm. Then an electric current of 2.5 to 3.0 A was passed in the circuit power source — container — carbon powder — sample. The duration of the process was 2–8 minutes.Results. The calculated estimation of the electrical conductivity of coal powder was performed, and the thermophysical parameters of microarc heating of steel were calculated. These include the power released by electric current on the surface of the steel product, the density of the heat flux, and the energy of a single microarc discharge. The expressions for calculating the particle size of ferroalloy powder were obtained, as well as the experimental dependencies of the diffusion layer thickness on the particle size of ferroalloys and their content in the coating.Discussion and Conclusion. The results of this study have allowed us to determine the size range of ferroalloys and their content in the coating. This information is essential for optimizing the alloying process and ensuring the most efficient surface hardening treatment for steel products. The data collected will be used to develop improved technological processes for the surface hardening process, leading to improved product quality and performance.

The Effect of Cetyl Trimethylammonium Bromide Addition as Surfactant in Multiwalled Carbon Nanotube-Based Nanofluid for Quench Medium in Steel Heat Treatment Application

Nanoparticle addition into a fluid can increase the thermal conductivity. Such fluid is commonly called a nanofluid. Due to its improved heat transfer characteristic, nanofluid is widely used as coolant in engine or electronic equipment. In the steel heat treatment industry, nanofluid can be utilized as a quench medium. By controlling the amount of nanoparticle added in the nanofluid quench medium, the cooling rate can be adjusted. To preserve the heat transfer effectivity, the stability of the nanoparticle become very important. Hence, surfactant is quite essential to improve the particle stability and avoid particle agglomeration and sedimentation. In this study, a multiwalled carbon nanotube (MWCNT) was used as the nanoparticle in the distilled water. The concentration of the MWCNT was varied at 0.1, 0.3, and 0.5 % w/v. For the surfactant, Cetyl Trimethylammonium Bromide (CTAB) was chosen to disperse the particle better. In each of the three MWCNT variations, CTAB was added from 3 – 30% w/v. The maximum thermal conductivity obtained was in the nanofluid with 0.3% MWCNT and 5% CTAB at 0.72 W/mK. For the steel hardness, the value was roughly stable at 33 – 35 HRC in the nanofluid with no CTAB and 3 – 5% CTAB addition. Excessive surfactant addition at 30% CTAB decrease the hardness significantly up to 17 HRC.

Microstructure refinement and enhanced mechanical properties of wire arc additively manufactured RAFM steel via post heat treatments

Reduced activation ferritic/martensitic (RAFM) steel with high strength and neutron radiation damage resistance is deemed one of the promising structural materials for fusion blankets. In this study, RAFM steel tube was prepared through wire arc additive manufacturing, and the evolution of phase composition, microstructural features and mechanical properties during the as-built and heat treatment processes were investigated. The results show that the as-built state is predominantly composed of α-Fe, and the microstructure's morphology from bottom to top consists of alternating columnar grain regions, equiaxed coarse grain regions, and fine grain regions. Normalizing and tempering treatment eliminates the heterogeneous microstructure, resulting in the presence of M23C6 carbides enriched with Cr and W, as well as MX phases enriched with Ta and V. Partitioning heat treatment results in the formation of ultrafine martensitic, quenched martensite and bainitic microstructures. The mechanical properties of wire arc additively manufactured RAFM steel are influenced by variations in microstructure. The coarse-grained region formed in the as-built state represent weak links. Normalizing and tempering treatment reduces the strength while improving ductility. Partitioning heat-treated RAFM steel exhibited a high strength of 1.1 GPa and an elongation of approximately 10.9%. This study provides a method of combining additive manufacturing with heat treatment to enhance the strength and ductility of RAFM steel simultaneously.

Effect of Multi-walled Carbon Nanotube and Polyethylene Glycol Addition in Nanofluid Quench Medium for Steel Heat Treatment Application

Effect of Multi-walled Carbon Nanotube and Polyethylene Glycol Addition in Nanofluid Quench Medium for Steel Heat Treatment Application

Heat Treatment of Steel 1.3520: Influence of Temperature and Austenitization Time

Heat Treatment of Steel 1.3520: Influence of Temperature and Austenitization Time

Microstructure and Mechanical Properties of Heat-Treated High-Nitrogen Martensitic Stainless Steel

Microstructure and Mechanical Properties of Heat-Treated High-Nitrogen Martensitic Stainless Steel

The beneficial effect of yttrium microalloying in the solid solution treatment of AISI 321 stainless steel：Grain refinement and inclusions modification

Solid solution treatment is an important means of regulating the microstructure and mechanical properties of austenitic stainless steel, and a suitable solid solution process window is critical for austenitic stainless-steel service. In this paper, the effect of (RE) yttrium and solid solution temperatures on the microstructure and mechanical properties of austenitic stainless steel was investigated by adding trace amounts of RE yttrium to AISI 321 stainless steel with different solid solution temperature treatments. The results show that the austenite grains gradually coarsen with the increase of solid solution temperature, and the addition of RE yttrium effectively inhibits the coarsening of grains and keeps an excellent the comprehensive mechanical properties of AISI 321 stainless steel at 1150 °C for 30 min, this indicates that the addition of RE yttrium broad solid solution process window for AISI 321 stainless steel. In addition, the RE yttrium microalloying has a positive modification effect on the carbonitrides with refinement and spherization, which has a good contribution to the strength and plasticity retention of the material. This research is expected to provide more options for the heat treatment of austenitic stainless steels.

Rotating gliding arc plasma: Innovative treatment for adhesion improvement between stainless steel heating elements and thermoplastics in resistance welding of composites

Rotating gliding arc plasma treatment was conducted on a stainless-steel heating element (HE) for the resistance welding of carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composites. The lap shear strength of 51.7 MPa, corresponding to an improvement of 14.63 % compared to that of joints welded using untreated HE, was successfully achieved after the plasma treatment. The results of the surface characterization tests revealed that owing to the cleaning and oxidation effects, the wettability as well as the surface bonding of the HEs were remarkably improved after plasma treatment. Moreover, the reduction of void defects within the welded joints was disclosed via nondestructive inspection of cross-sections, indicating that the enhancement of HE wettability resulted in the improved resin impregnation and void elimination. Besides, according to the fractographic analysis, the main failure mode changed from the HE/PEEK interfacial damage to a CF/matrix interfacial failure, indicating that the HE/matrix interfacial adhesion was highly strengthened after plasma treatment.

Surface Treatment Effects of Nitriding Parameters on 2344 Tool Steel

In this study; The effects of different processes applied to heat-treated tool steels on the hardness and wear resistance of the steel were examined. In line with this study, the effects of steels subjected to different times and processes on diffusion depth, white layer thickness and hardness were investigated. The molds were tested with the extrusion process in the determined parameters and their wear resistance was determined. After examining the results, the most suitable parameters for mold steels were determined.

Preparation of highly dewetted porous steel for shallow water AUV based on laser ablation method

Over the past two decades, autonomous underwater vehicles (AUVs) have been developed for various marine, commercial, and military applications. Porous metals, known for their lightweight high performance, suit AUV hulls, especially in shallow waters. However, because of their inherent hydrophilicity and porous structure, high humidity causes corrosion. In this study, a novel solution involving laser ablation and subsequent heat treatment of porous steel is proposed to improve the waterproofing performance both above and below water. By analyzing the surface structures, wetting attributes, and droplet behavior, the optimal laser and heat treatment parameters for superior performance are revealed. The porous nested structures created by laser ablation effectively reduce fog accumulation and, enhance the anti-fogging capabilities. Furthermore, the underwater stability ofsuperhydrophobic porous steels at different depths is systematically investigated. A method involving air injection into porous steel is proposed to address the limited air-pocket lifespan and instability of dehumidified surfaces. Experimental results confirm rapid and complete restoration of superhydrophobicity at a 0.9-meter depth. Thus, this study presents a practical corrosion-resistant surface material for AUVs in shallow-water environments and a new approach for achieving corrosion resistance in porous metals exposed to long-term aquatic conditions.