Journal of Iron and Steel Research International最新文献

h-BN rods modified low-carbon alumina–carbon (Al₂O₃–C) refractories were prepared, and the effect of h-BN rod addition on the high-temperature properties was investigated and compared with commercial h-BN flake, carbon black, and carbon nanotubes additives. The results demonstrated that Al₂O₃–C refractories containing h-BN rods exhibited optimal high-temperature service performances, including 25% higher hot modulus of rupture, 21.3% higher thermal shock strength residual ratio, 20.9% lower in oxidation and 44.3% less in slag corrosion, compared to the counterpart specimens without additives. Moreover, benefiting from the synergistic enhancement of the rod-like h-BN and in-situ generated SiC whiskers, the high-temperature service performances of h-BN rods containing specimens outperformed counterpart specimens containing commercial h-BN flake, carbon black, and carbon nanotubes, respectively.

5052 Al and carbon fiber-reinforced polyamide 6 composite (CF-PA6) were jointed via ultrasonic welding with the assistance of temperature compensation device. The effects of the ultrasonic welding time and temperature compensation on the microstructure and mechanical properties of the joints were investigated. Through analysis of the wettability and fluidity of the molten carbon fiber-reinforced thermoplastic composites (CFRTP), the bonding mechanism and failure path of Al/CFRTP were clarified. The results show that under the conditions of temperature compensation of 220 °C and welding time of 1500 ms, the joint strength of the two components reaches 2480.4 N, which is 813.6% higher than that of Al/CFRTP components obtained at room temperature. Overall, temperature compensation prolonged the wetting time of molten CFRTP on the aluminum alloy surface. When the fluidity and wettability were coordinated with each other, a high-quality joint was formed. In addition, the ultrasonic welding process of Al/CFRTP mainly relies on “physical adsorption,” “diffusion effect,” and “mechanical locking effect” to achieve sufficient bonding, and the effect of hydrogen bonding is weak.

The micro-area characterization experiments like scanning Kelvin probe force microscope (SKPFM) and Kernel average misorientation have the defects of complex sample preparation and occasional errors in test results, which makes it impossible to accurately and quickly analyze the pitting behavior induced by inclusions in some cases, prompting attempts to turn to simulation calculation research. The method of calculating band structure and work function can be used to replace current-sensing atomic force microscopy and SKPFM to detect the potential and conductivity of the sample. The band structure results show that Al₂O₃ inclusion is an insulator and non-conductive, and it will not form galvanic corrosion with the matrix. Al₂O₃ inclusion does not dissolve because its work function is higher than that of the matrix. Moreover, the stress concentration of the matrix around the inclusion can be characterized by first-principles calculation coupled with finite element simulation. The results show that the stress concentration degree of the matrix around Al₂O₃ inclusion is serious, and the galvanic corrosion is formed between the high and the low stress concentration areas, which can be used to explain the reason of the pitting induced by Al₂O₃ inclusions.

The characterization techniques were employed like transmission electron microscope, X-ray diffraction and microstructural characterization to investigate microstructural evolution and impact of precipitate-phase precipitation on strength and toughness of a self-developed 32Si₂CrNi₂MoVNb steel during the quenching and tempering process. Research outputs indicated that the steel microstructure under the quenching state could be composed of martensite with a high dislocation density, a small amount of residual austenite, and many dispersed spherical MC carbides. In details, after tempering at 200 °C, fine needle-shaped ε-carbides would precipitate, which may improve yield strength and toughness of the steel. However, as compared to that after tempering at 200 °C, the average length of needle-shaped ε-carbides was found to increase to 144.1 ± 4 from 134.1 ± 3 nm after tempering at 340 °C. As a result, the yield strength may increase to 1505 ± 40 MPa, and the impact absorption energy (V-notch) may also decrease. Moreover, after tempering at 450 °C, those ε-carbides in the steel may transform into coarse rod-shaped cementite, and dislocation recoveries at such high tempering temperature may lead to decrease of strength and toughness of the steel. Finally, the following properties could be obtained: a yield strength of 1440 ± 35 MPa, an ultimate tensile strength of 1864 ± 50 MPa and an impact absorption energy of 45.9 ± 4 J, by means of rational composition design and microstructural control.

(Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x (x = 0, 0.1, 0.2, 0.3, 0.4 at.%) lightweight high-entropy alloys with different contents of Al were prepared via vacuum non-consumable arc melting method. Effects of adding varying Al contents on phase constitution, microstructure characteristics and mechanical properties of the lightweight alloys were studied. Results show that Ti₈Zr₆Nb₄V₅Cr₄ alloy is composed of body-centered cubic (BCC) phase and C15 Laves phase, while (Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x lightweight high-entropy alloys by addition of Al are composed of BCC phase and C14 Laves phase. Addition of Al into Ti₈Zr₆Nb₄V₅Cr₄ lightweight high-entropy alloy can transform C15 Laves phase to C14 Laves phase. With further addition of Al, BCC phase of alloys is significantly refined, and the volume fraction of C14 Laves phase is raised obviously. Meanwhile, the dimension of BCC phase in the alloy by addition of 0.3 at.% Al is the most refined and that of Laves phase is also obviously refined. Adding Al to Ti₈Zr₆Nb₄V₅Cr₄ alloy can not only reduce the density of (Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x alloy, but also improve strength of (Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x alloy. As Al content increased from 0 to 0.4 at.%, the density of the alloy decreased from 6.22 ± 0.875 to 5.79 ± 0.679 g cm⁻³. Moreover, compressive strength of the alloy by 0.3 at.% Al addition is the highest to 1996.9 MPa, while fracture strain of the alloy is 16.82%. Strength improvement of alloys mainly results from microstructure refinement and precipitation of C14 Laves by Al addition into Ti₈Zr₆Nb₄V₅Cr₄ lightweight high-entropy alloy.

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%.