Journal of Iron and Steel Research International最新文献

The sulphate is an important factor restricting the efficient and stable operation of the activated coke (AC) flue gas purification system. The simulation experiments and in situ infrared tests of AC taken from desorption tower of the AC flue gas purification system were carried out to first calibrate the thermal desorption characteristics of adsorbed NH₃ and sulphate and explore the reaction behaviour of NH₃ with SO₂ and H₂SO₄. On this basis, some advice for optimising the sulphate generation was put forward to improve the purification efficiency of the AC system. The results show that the temperatures of the desorption of adsorbed NH₃, the decomposition of (NH₄)₂SO₄ and NH₄HSO₄ are 224, 276 and 319 °C, respectively, which lays the foundation for the quantitative analysis of sulphate on AC. Regardless of the NH₃ amount, only a small portion of H₂SO₄ is converted to sulphate, as the H₂SO₄ deposited in AC pores or agglomerated together could not come into contact with NH₃. The final reaction product of NH₃ and SO₂ is mainly (NH₄)₂SO₄ which is continuously generated because the newly generated H₂SO₄ is continually exposed to NH₃, if NH₃ is enough. The reaction of NH₃ with H₂SO₄ takes precedence over with NH₄HSO₄. In the initial stages in which H₂SO₄ is exposed to NH₃, the product is essentially all NH₄HSO₄ as intermediate. Then, it is further converted to (NH₄)₂SO₄ whose amount reaches equilibrium when the accessible H₂SO₄ is exhausted. All the NH₃ adsorbed on AC entering the desulphurisation tower generates NH₄HSO₄, but the amount is limited. The remaining SO₂ entering the denitrification tower mainly generates (NH₄)₂SO₄; thus, limiting the remaining SO₂ amount is necessary to guarantee denitrification efficiency. When the NH₃ injection is changed to the desulphurisation tower, the initial NH₃ injection rate can be increased to complete the conversion of accessible H₂SO₄ as soon as possible in order to obtain higher denitrification efficiency.

A prediction model leveraging machine learning was developed to forecast the tensile strength of wear-resistant steels, focusing on the relationship between composition, hot rolling process parameters and resulting properties. Multiple machine learning algorithms were compared, with the deep neural network (DNN) model outperforming others including random forests, gradient boosting regression, support vector regression, extreme gradient boosting, ridge regression, multi-layer perceptron, linear regression and decision tree. The DNN model was meticulously optimized, achieving a training set mean squared error (MSE) of 14.177 with a coefficient of determination (R²) of 0.973 and a test set MSE of 21.573 with an R² of 0.960, reflecting its strong predictive capabilities and generalization to unseen data. In order to further confirm the predictive ability of the model, an experimental validation was carried out, involving the preparation of five different steel samples. The tensile strength of each sample was predicted and then compared to actual measurements, with the error of the results consistently below 5%.

The microstructure, mechanical properties, and corrosion resistance of as-cast Zr–Sn–Co ternary alloys have been investigated in this experiment. The properties of as-cast Zr–1.5Sn–xCo (x = 0, 2.5, 5, 7.5, and 10 at.%) ternary alloys were investigated, and the alloy composition exhibiting the best comprehensive performance was identified. Subsequently, the chosen alloys were subjected to hot rolling treatment. The microstructure of the alloys in the rolled state was analyzed using the optical microscope, X-ray diffractometer, and scanning electron microscope. The mechanical properties of the alloys were analyzed using room temperature compression tests and microhardness tests, while the corrosion properties of the alloy were investigated through electrochemical testing. The results show that the strength of as-cast Zr–1.5Sn–Co ternary alloy increases significantly with the increase in Co content. The incorporation of Co element makes the corrosion resistance of as-cast Zr–1.5Sn–Co alloy increase significantly. The hot rolling treatment has minimal effect on enhancing the corrosion resistance of Zr–1.5Sn–2.5Co alloy. However, the mechanical properties of Zr–1.5Sn–2.5Co alloy after rolling treatment are significantly enhanced. The alloy exhibits the highest strength and hardness at a rolling temperature of 600 °C and exhibits the best plasticity at a rolling temperature of 800 °C.

The microstructure and mechanical properties of the compact strip production (CSP) processed quenching and partitioning (Q&P) steels were investigated through experimental methods to address the challenge of designing high-performance Q&P steels. Compared with the conventional process (CP) produced samples, with slightly reduced strength, the total elongation of the CSP produced samples was increased by nearly 7%. Microstructural analysis revealed that variations in austenite stability were not the primary cause for the differences in mechanical properties between the CSP and the CP. The CSP processed Q&P steel exhibited milder center segregation behavior in contrast to the CP processed Q&P steel. Consequently, in the CSP processed Q&P steel, a higher proportion of austenite and a lower proportion of martensite were observed at the center position, delaying the crack initiation in the central region and contributing to the enhanced ductility. The investigation into the CSP process reveals its effect on alleviation of segregation and enhancement of mechanical properties of the Q&P steel.

Different stress states have a significant influence on the magnitude of the microscopic plastic strain and result in the development of the microstructure evolution. As a result, a comprehensive understanding of the different scale variation on microstructure evolution during bending deformation is essential. The advanced high strength dual-phase (DP1180) steel was investigated using multiscale microstructure-based 3D representative volume element (RVE) modelling technology with emphasis on understanding the relationship between the microstructure, localised stress–strain evolution as well as the deformation characteristics in the bending process. It is demonstrated that the localised development in bending can be more accurately described by microscopic deformation when taking into account microstructural properties. Microstructure-based 3D RVEs from each chosen bending condition generally have comparable localisation properties, whilst the magnitudes and intensities differ. In addition, the most severe localised bands are predicted to occur close to the ferrite and martensite phase boundaries where the martensite grains are close together or have a somewhat sharp edge. The numerically predicted results for the microstructure evolution, shear bands development and stress and strain distribution after 3-point bending exhibit a good agreement with the relevant experimental observations.

A new flow control technology in continuous casting process named permanent magnet flow control-mold (PMFC-Mold) was proposed, in which the permanent magnets are arranged in Halbach array near the narrow region of the mold. The behavior of molten steel flow and the fluctuation of molten steel/slag interface in the PMFC-Mold under different continuous casting speeds were investigated. Firstly, a physical experiment of liquid Ga–In–Sn alloy circulating flow was carried out in Perspex mold with Halbach’s permanent magnets (HPMs) to investigate the magnetic field distribution of HPMs and its impactful electromagnetic braking effect. The numerical simulation of 1450 mm × 230 mm slab shows that a stronger magnetic field over 0.3–0.625 T is formed at the wide surface and the narrow surface of the mold, which provides an effective electromagnetic braking for controlling the impingement of molten steel jet and suppressing the fluctuation of molten steel/slag interface. The numerical simulation results show that in the PMFC-Mold, the region with the turbulent kinetic energy greater than 0.01 and 0.04 m² s⁻² on the upper backflow zone and near the narrow surface of the mold are significantly reduced. The maximum turbulent kinetic energy of the submerged entry nozzle (SEN) jet in front of the narrow surface is significantly reduced, and the SEN jet moves downward before impacting the narrow surface of the mold. In the PMFC-Mold, the region with the surface velocity greater than 0.2 m s⁻¹ on the steel/slag interface is eliminated, the flow pattern and fluctuation profiles on the molten steel/slag interface become regular on both sides of SEN, and the vortex near SEN disappears. The maximum fluctuation height of molten steel/slag interface is controlled below 2.59 and 5.40 mm corresponding to the casting speed of 1.6 and 2.0 m min⁻¹, respectively.

The variations in the mechanical and magnetic properties of cold-rolled 20Mn23AlV non-magnetic structural steel after annealing at different temperatures were investigated. The microstructure and precipitation changes during annealing were studied by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that recrystallization completed after annealing at 620 °C, resulting in grain sizes of approximately 800 nm and the best combination of strength and plasticity. The yield-to-tensile ratio of the non-magnetic structural steel after cold rolling continuously decreases from low to high temperatures after annealing, with the highest value being 0.89 and the lowest value being 0.43, indicating a wide range of yield-to-tensile ratio adjustment. The introduction of numerous dislocations during cold rolling provided favorable nucleation sites for precipitation, leading to abundant precipitation of the fine second-phase V(C, N). The phase composition of the samples remained unchanged as single-phase austenite after annealing, and the relative permeability values were calculated to be less than 1.002, meeting the requirements for non-magnetic steel in terms of magnetic properties.

The substantial influences of Mo contents varying from 0 to 0.26 and 0.50 wt.% on the microstructural evolution and MX (M = Nb, V and Mo; X = C and N) precipitation characteristics of Nb–V–N microalloyed steels processed by hot deformation and continuous cooling were studied using a Gleeble 3800 thermomechanical simulator. Metallographic analysis showed that the ferrite microstructure transformed from polygonal ferrite (PF) in 0Mo steel to both acicular ferrite (AF) and PF in 0.26Mo and 0.50Mo steels, and AF content first increased and then decreased. The thermodynamic calculations and the experimental results proved that the quantity of solid solution of Mo in austenite obviously increased, which reduced the austenite (γ) to ferrite (α) transformation temperature, consequently promoting AF formation in 0.26Mo steel and bainite transformation in 0.50Mo steel. Moreover, the submicron Nb-rich MX particles that precipitated at the temperature of the austenite region further induced AF heterogeneous nucleation with an orientation relationship of ((011)_{{{text{MX}}}} //(100)_{{{text{Ferrite}}}}) and ([1overline{1}1]_{{{text{MX}}}} //[001]_{{{text{Ferrite}}}}). The interphase precipitation of the nanosized V-rich MX particles with Mo partitioning that precipitated during γ → α transformation exhibited a Baker–Nutting orientation relationship of (left( {100} right)_{{{text{MX}}}} //left( {100} right)_{{{text{Ferrite}}}}) and (left[ {001} right]_{{{text{MX}}}} //left[ {01overline{1}} right]_{{{text{Ferrite}}}}) with respect to the ferrite matrix. With increasing Mo content from 0 to 0.26 and 0.50 wt.%, the sheet spacing decreased from 46.9–49.0 to 34.6–38.6 and 25.7–28.0 nm, respectively, which evidently hindered dislocation movement and greatly enhanced precipitation strengthening. Furthermore, facilitating AF formation and interphase precipitation was beneficial to improving steel properties, and the optimal Mo content was 0.26 wt.%.

During the continuous casting process of low carbon steel, the solidified hook formed in the mold has great effects on the surface quality of the cast slab. Some factory experiments have been conducted to investigate the microscopic characteristics and reveal the influence of process parameters on solidified hooks. The depth of the hooks showed a positive correlation with the deflection angle, length, and oscillation mark (OM) depth, which indicates that the OM depth can serve as an approximate indicator for evaluating the depth of the solidified hooks. On the wide and narrow faces of the cast slab, the depth of the solidified hooks and the temperature distribution in the mold show opposite trends, with lower depths of solidified hooks at positions with higher temperatures. In addition, the influence of process parameters on solidified hooks was analyzed. With the increase in superheat, not only the depth of solidified hooks gradually decreases, but also the ratio of depression-typed marks increases. Increasing casting speed and decreasing immersion depth of the submerged entry nozzle will both lead to a decrease in the depth of the solidified hook.

The second phase dissolution and elements migration behavior of a nickel-based single crystal superalloy during solution heat treatment with direct current were investigated for simplifying and shortening the solution heat treatment of the Ni-based single crystal superalloy. The results showed that the electric current solution heat treatment improved microstructural homogenization as well as the distribution of alloying elements, especially for the refractory metal W and Mo. The microsegregation ratios for Mo and W after electric current solution heat treatment at 1230 °C for 4 h are near those without electric current at 1250 °C for 4 h. The electric current accelerated the γ′ phase dissolution process, and the γ′ phase could be completely dissolved at a lower treatment temperature or within a shorter treatment time under electric current solution heat treatment with direct current. A microcosmic current model was proposed to analyze the effect of the electric current on the solution heat treatment of the Ni-based single crystal superalloy.