steel research international最新文献

In this research work, finite element method (FEM)-based model is developed to investigate the influence of heat sink during tungsten inert gas (TIG) welding of 304L steel plate. The effect of copper backing plates is being discussed with heating and cooling by considering with and without backup plates in the FEM-based model in the SYSWELD software. The results reveal that the cooling rate is improved, and there is a drop to 200 °C temperature due to the heat sink. Numerical modeling discusses the significant variations in cooling rate during TIG welding with and without a heat sink. Two different experiments are conducted with and without a copper backup plate. Hardness, residual stress, and distortion in the weld plate are measured for each case. The residual stress and distortion using FEM-based calculation are predicted and validated with experimentally measured values. Maximum distortion is observed at the corner with a value of 3.48 mm in an upward direction. Comparison of with and without backup plate results shows that the copper plate is not so effective; only a 5% difference is observed for distortion in the weld plate, but it reduces the residual stress up to 25 MPa values.

Focusing on the deformation behavior of strip steel during laminar cooling in tandem hot rolling, a high-precision weighted integrated temperature prediction model is developed using machine learning techniques and validated through finite element analysis. Based on the strain theory of elastic-plastic mechanics and the phase transformation kinetics of continuous media, the coupled mechanism of temperature, phase transformation, and residual stress under varying initial conditions during laminar cooling was systematically analyzed. The results demonstrate that the proposed weighted integrated prediction model overcomes the limitations of single-model approaches. The predicted temperature range is 600–690 °C, with an root mean square error of 3.19, mean absolute error of 2.36, and R² of 0.985. During the cooling process, the final cooling temperature difference between the middle and edge of the strip changes with the initial cooling temperature difference. Notably, the phase transformation and residual stress variations at the edges are more pronounced than those in the central region. A 50.54% greater phase transition degree has been observed at the edge relative to the central region. The stress compensation of 60 IU flatness can reduce the stress difference between the middle and edge of the strip by 89.55% and improve the product quality of the strip.

Microstructure governs the mechanical properties of steel structures, and thus, predominantly influences their mechanical property. To gain an in-depth understanding of this mechanism and to provide theoretical guidance for the manufacturing and optimization of steel structures, this article systematically investigates the interaction among grain characteristics, stress distribution, dislocation density, slip system activation, and tensile properties in steel structures using a dislocation-based crystal plasticity finite element method. The results indicate that the tensile properties of a single crystal are governed by the peak internal stress, which is maximized at a grain orientation of ≈45° due to the activation of more slip systems. The mechanical performance of steels can be optimized through the synergistic effects of high-angle grain boundaries (HAGBs) and favorable textures, with HAGBs providing local strengthening and advantageous textures improving strength and ductility. Grain refinement and bimodal grain size distribution enables a balance of strength and toughness, while increased grain equiaxiality enhances local stress concentration, dislocation accumulation, and tensile strength. Additionally, reducing inclusion size intensifies local reinforcement and further improves tensile properties. These findings can provide new perspectives and a solid theoretical foundation for optimizing and controlling mechanical performance in steel manufacturing, welding, and additive manufacturing processes.

Stainless steel clad plates were prepared by a novel technique of horizontal continuous liquid–solid composite casting, following with hot rolling at different temperatures. The interfacial composition, microstructure, mechanical properties and uniaxial tension deformation behaviors were investigated, and the effects of rolling temperature on strengthening and toughening were analyzed. The stainless steel clad plates rolled at 1100 °C had the highest yield strength of 408 MPa, tensile strength of 547 MPa, elongation of 31% and interfacial shear strength of 499 MPa, which increased by 16.6%, 9.2%, 6.9% and 13.7%, respectively, compared with those of the plates rolled at 1200 °C. During uniaxial tensile deformation, local high strain regions with sharp strain gradient emerged first at the cladding interface zone, where geometrically necessary dislocations (GNDs) gradually accumulate and cracks form. Higher rolling temperature promoted diffusion of carbon at cladding interface and dynamic recrystallization. Therefore, the relative diffusion distances reached maximum of 2.18 and 1.4, and finer grains of 40.2 and 7.6 μm and higher GNDs density of 2.69 × 10¹⁴ and 2.55 × 10¹⁴ m⁻² formed in both stainless steel and carbon steel when rolled at 1100 °C, resulting in simultaneously improved interfacial shear strength, tensile strength and ductility.

Electric pulse, as a new environmentally friendly technology, can effectively improves the traditional solid solution aging heat treatment process, accelerate atomic diffusion, promotes the nucleation of second-phase precipitation, and shorten the precipitation time. Therefore, this study utilizes the electric pulse technique to prepare a Cu-rich phase. The mechanical properties are studied and found to peak at a relatively short pulse aging time. The Vickers hardness value stabilized around 125 HV, and the tensile strength reaches 561.5 MPa. The grains in the necking region are elongated during uniaxial tension, and the twin structures were severely disrupted. In addition, the degree of damage to the tensile samples is evaluated using digital image correlation technology. The hard-oriented copper texture {112}<111> and the S-type texture {123}<634> played a crucial role in stabilizing the plastic deformation of the structure. Cu-rich phases preferentially nucleated at planar defects such as dislocations and grain boundaries. With the extension of the pulse aging time, the average size of the Cu-rich phase gradually increases from 12.5 to 17.1 nm, but the density of the Cu-rich phase gradually decreases.

The product quality of high-manganese and high-aluminum steels is closely related to the agglomeration behavior of inclusions. The study first establishes a 3D stability phase diagram of inclusions in high-manganese and high-aluminum steels. Based on that, laboratory-scale experiments with different Mn and Al contents are designed to prepare different inclusions. Furthermore, the change in interfacial properties including contact angle of inclusions and surface tension of molten steel with various Mn and Al contents is evaluated. On this basis, the effect of different steel compositions on the agglomeration characteristics of inclusions is investigated. As Mn content increases, the cavity bridge force between inclusions weakens. As Al content increases, the cavity bridge force of Al₂O₃ inclusions first increases and then decreases, and the cavity bridge force of AlN decreases. When the Al content is more than 1.58 wt% and <2.46 wt%, as the Mn content increases, the cavity bridge force of Al₂O₃ inclusions gradually decreases to less than that of AlN. The critical Mn and Al content relationship for changing the order of cavity bridge forces on inclusions is $��y_{�(�\text{Mn}�,�\text{wt}�\text{.}�\%�)�}�=�-�33.77�x_{�(�\text{Al}�,�\text{wt}�\text{.}�\%�)�}�+�82.94�$. The study can provide support for inclusion control in high-manganese and high-aluminum steel.

In this article, the effects of quenching + tempering (QT) and quenching + intercritical annealing followed by quenching + intercritical annealing followed by quenching + tempering (QLT) heat treatments on the microstructure and mechanical properties of 9Ni steel are systematically investigated. By integrating microstructure analysis with mechanical property testing, the mechanism by which heat treatment influences the strength and toughness of 9Ni steel is elucidated. The results indicate that after QLT heat treatment, the impact absorbed energy for V-notch (Akv) increases from 24.65 to 49.47 J, representing a 100% enhancement, while the tensile strength decreases by 6.8%. Microstructure analysis reveals that the significant improvement in toughness following QLT heat treatment is primarily attributed to the substantial refinement of the lath martensitic structure induced by intercritical annealing followed by quenching. Furthermore, electron back scattering diffraction analysis of the specimens demonstrates that high-angle grain boundaries effectively reduce the crack growth zone, markedly enhancing crack growth resistance, and thereby significantly increasing the impact energy of the test steel.

Dissimilar joints made of AISI 409L ferritic stainless steel and AISI 410 martensite stainless steel are joined by double pulse resistance spot welding process. Macrostructure, microstructure, microhardness, and tensile shear performance of joints are studied. The nugget size increases to 2.4 mm in diameter under the role of the second pulse and changes a little with the second pulse when 4 kA welding current is applied. The nugget is remelted and microstructure is coarsened during the second pulse. Hardness of nugget decreases to 330.7 to 386.5 HV. The combination of strengthening from bigger nugget and softening from coarsen microstructure contributes to the ignorable change in peak load and enhancement of ≈150% in failure energy. However, when 8 kA welding current is applied, the nugget used single pulse is 5.4 mm in diameter and the second pulse has a negligible effect on the nugget size. The microstructure in nuggets is tempered during the second pulse. Hardness of nugget and peak load of joints are similar among the samples. Martensite decomposition and carbides precipitation during tempering contribute to the 95% enhancement in failure energy. All the joints fail in button mode and significant deformation occurs on the propagation path of crack on samples used double pulse.

Hydrogen embrittlement (HE) occurs as a result of hydrogen atom ingress and causes a significant decrease in plasticity and strength, making it a crucial failure mode in high-strength low-alloy steels. The microstructure plays a vital role in HE fracture behavior because of the various hydrogen trappings. The welding thermal cycle and alloying elements determine the great difference of the microstructure of the welded joint. Thus, this article reviews the current studies investigating the role of the microstructure in determining the HE behavior of the welded joints, thereby aiming to reveal the fracture process and mechanism. Dislocations and inclusions in welded joints reduce HE resistance. Acicular ferrite with a fine interlocking structure can block the prolonging of hydrogen-induced cracking. The transformation of the retained austenite with a high concentration of hydrogen atoms into martensite accelerates HE fractures. The δ-ferrite in the welded joint promotes the HE resistance deterioration and hydrogen-induced cracking. Appropriate coating of the steel surface is an effective approach for preventing HE fractures.

Hydrogen direct reduced iron ore pellets (H-DRI) are an increasingly relevant raw material for electric-arc furnace steelmaking as steelmakers strives to reduce CO₂ emissions. Understanding the melting behavior of carbon-free H-DRI pellets in slag is needed to facilitate efficient industrial melting operations. The present study focuses on the role of slag during heating and subsequent melting of H-DRI pellets. Experiments where single H-DRI pellets are submerged in EAF slags with different FeO, Al₂O₃, and MgO contents have been done and evaluated. Results show that, within the experimental range, fastest melting progression is achieved with low FeO, high Al₂O₃ content slags. At the most favorable conditions, 80% apparent melting is reached after 15 s, in contrast to 50% under least favorable conditions. This is likely due to differences in thermal conductivity of the slag. In pilot-scale EAF trials where carbon-free H-DRI pellets is melted by continuous operation, melting performance improved with increasing FeO content. This can be explained by a decreasing viscosity which facilitated convective heat transfer. Therefore, the combination of experimental and pilot-scale results shows that convection is the dominating heat transfer mechanism in the industrial case why it should be the focus of future research and development efforts.