Journal of Iron and Steel Research(International)最新文献

Top gas recycling oxygen blast furnace (TGR-OBF) process is a promising ironmaking process. The biggest challenge of the TGR-OBF in operation is the dramatic decrease of top gas volume (per ton hot metal), which once led to hanging-up and shutdowns in practice of the Toulachermet. In order to avoid this weakness, the strategy of medium oxygen blast furnace was presented. The maneuverable zone of the TGR-OBF was determined by the top gas volume, which should not be far from the data of the traditional blast furnace. The deviation of ±12.5% was used, and then the maneuverable blast oxygen content is from 0.30 to 0.47 according to the calculation. The flame temperature and the top gas volume have no much difference compared to those of the traditional blast furnace. The minimum carbon consumption of 357 kg per ton hot metal in the maneuverable zone occurs at the oxygen content of 0.30 (fuel saving of 14%). In the unsteady evolution, the N₂ accumulation could approach nearly zero after the recycling reached 6 times. Thus far, some TGR-OBF industrial trials have been carried out in different countries, but the method of medium oxygen enriched TGR-OBF has not been implemented, because the accumulation of N₂ was worried about. The presented strategy of medium oxygen enriched TGR-OBF is applicable and the strategy with good operational performance is strongly suggested as a forerunner of the full oxygen blast furnace.

Fatigue crack growth as a function of a phase volume fraction in Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy was investigated using fatigue testing, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The α+β annealing treatments with different solid solution temperatures and cooling rates were conducted in order to tailor microstructure with different a phase features in the Ti-6242 alloy, and fatigue crack growth mechanism was discussed after detailed microstructure characterization. The results showed that fatigue crack growth rate of Ti-6242 alloy decreased with the decrease in volume fraction of the primary α phase (α_p). Samples with a large-sized a grain microstructure treated at high solid solution temperature and slow cooling rate have lower fatigue crack growth rate. The appearance of secondary a phase (α_s) with the increase of solid solution temperature led to crack deflection. Moreover, a fatigue crack growth transition phenomenon was observed in the Paris regime of Ti-6242 alloy with 29.8% α_p (typical bi-modal microstructure) and large-sized a grain microstructure, owing to the change of fatigue crack growth mechanism.

In order to expand the application of the electrodeposited Ni-Fe alloy foil, their mechanical and magnetic properties were studied after heat treatment. The development of grain growth during annealing was in-situ online investigated using a heating stage microscope, and the texture was analyzed via X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD). The results indicated that abnormal grain growth usually occurred during annealing at 1000–1050 °C. The {111} oriented grains preferentially grew as the annealing temperature and holding time increased. The plasticities of the electrodeposited Ni-Fe alloy foils after heat treatment were better than those of the original samples. The excellent ductility was obtained without a loss in magnetic properties after annealing at 1100 °C for 6 h.

The pre-reduced Bayan Obo ferroniobium (FeNb) ore concentrate block was taken as raw materials for studying the physical properties of niobium-enriched slag and changes in niobium recovery rate. In addition, the dephosphorization rate of the slag under different melting-separation conditions was investigated using the melting-separation test. The research results demonstrate that (i) the niobium recovery rate and dephosphorization rate of the slag decrease with the increase in melting-separation temperature; (ii) the niobium recovery rate of the slag initially increases and then decreases with increase in basicity and time; and (iii) the dephosphorization rate of the slag increases with the increase in basicity and time. When the test was performed under the conditions of basicity of 0. 6 – 0. 7, time of 7–10 min, and temperature of 1400–1450 °C, the niobium recovery rate and dephosphorization rate are over 96% and 95%, respectively. By scanning electron microscopy, it is observed that niobium mainly exists in the form of calcium and titanium silicate within the slag phase, with uneven distribution.

It is important to make full use of waste generated in the iron and steel manufacturing process for energy saving, emission reduction, low carbon production and a circular economy. Based on research on different kinds of industrial solid wastes from Shougang Jingtang, wastes have been optimized for use in sintering. At first, basic tests for all kinds of solid wastes that may be used in sintering were carried out, including chemical composition, calorific value of a fuel, holding time at high temperatures, the sintering pot test, etc. The results show that the appropriate solid waste ratios for current sintering conditions are: steel slag <5%, scale 2.0%, environmental ash 2.0%, and cyclone ash 1.0%; blast furnace dry ash, sintering electric field ash, and steelmaking ash should not be circulated in sintering. As for the fuel structure, both coking ash and nut coke should be below 15%. By optimizing the addition of solid wastes, the damage of harmful elements to sintering and blast furnaces has been significantly reduced, which satisfies the demands for blast furnace materials and earns benefits. The utilization of solid wastes has made a contribution to the circular economy and sustainable development.

The influence of heat treatment with different cooling rates on phase transition behaviors and magnetocaloric effect is systematically studied. Difference in atomic order is induced by changing cooling rates, where ordered phase is obtained in the furnace cooled (FC) sample while disordered phase is reserved in the water quenched (WQ) sample. The coupled magneto-structural transition is detected in both samples but the characteristic temperature significantly shifts to lower temperatures with increasing atomic order. Giant magnetic entropy change (ΔS_mag) derived from magnetic field induced martensitic transformation is confirmed for both samples, and can be remarkably enhanced by the atomic ordering. The largest ΔS_mag of 20. 9 J/(kg · K) is obtained at 307. 5 K under 5 T in the FC sample.

During high speed machining in the field of manufacture, chip formation is a severe plastic deformation process including large strain, high strain rate and high temperature. And the strain rate in high speed cutting process can be achieved to 10⁵ s^−1. 30CrMnSiNi2 A steel is a kind of important high-strength low-alloy structural steel with wide application range. Obtaining the dynamic mechanical properties of 30CrMnSiNi2 A under the conditions of high strain rate and high temperature is necessary to construct the constitutive relation model for high speed machining. The dynamic compressive mechanical properties of 30CrMnSiNi2 A steel were studied using split Hopkinson pressure bar (SHPB) tests at 30 – 700 °C and 3000 – 10000 s⁻¹. The stress-strain curves of 30CrMnSiNi2 A steel at different temperatures and strain rates were investigated, and the strain hardening effect and temperature effect were discussed. Experimental results show that 30CrMnSiNi2 A has obvious temperature sensitivity at 300 °C. Moreover, the flow stress decreased significantly with the increase of temperature. The strain hardening effect of the material at high strain rate is not significant with the increase of strain. The strain rate hardening effect is obvious with increasing the temperature. According to the experimental results, the established Johnson-Cook (J-C) constitutive model of 30CrMnSiNi2 A steel could be used at high strain rate and high temperature.

At the late stage of continuous casting (CC) ladle teeming, sink vortex can suck the liquid slag into tundish, and cause negative influences on the cleanliness of molten steel. To address this issue, a two-phase fluid mechanical modeling method for ladle teeming was proposed. Firstly, a dynamic model for vortex suction process was built, and the profiles of vortex flow field were acquired. Then, based on the level set method (LSM), a two-phase 3D interface coupling model for slag entrapment was built. Finally, in combination with high-order essentially non-oscillatory (ENO) and total variation diminishing (TVD) methods, a LSM-based numerical solution method was proposed to obtain the 3D coupling evolution regularities in vortex suction process. Numerical results show that the vortex with higher kinetic energy can form an expanded sandglass-shape region with larger slag fraction and lower rotating velocity; there is a pressure oscillation phenomenon at the vortex penetration state, which is caused by the energy shock of two-phase vortex penetration coupling.

The non-isothermal oxidation experiments of ilmenite concentrate were carried out at various heating rates under air atmosphere by thermogravimetry. The oxidation kinetic model function and kinetic parameters of apparent activation energy (E_a) were evaluated by Málek and Starink methods. The results show that under air atmosphere, the oxidation process of ilmenite concentrate is composed of three stages, and the chemical reaction (G(α) = 1—(1—α)², where α is the conversion degree) plays an important role in the whole oxidation process. At the first stage (α = 0. 05–0. 30), the oxidation process is controlled gradually by secondary chemical reaction with increasing conversion degree. At the second stage (α = 0.30–0.50), the oxidation process is completely controlled by the secondary chemical reaction (G(α) = 1 – (1 – α)²). At the third stage (α=0. 50 – 0.95), the secondary chemical reaction weakens gradually with increasing conversion degree, and the oxidation process is controlled gradually by a variety of functions; the kinetic equations are G(α)–(1–α)⁻¹ (ß=10 K · min⁻¹, where ß is heating rate), G(α) = (1 – α) ^−½ (ß= 15 – 20 K · min⁻¹), and G(α) = (1 – α)⁻²(ß=25 K · min⁻¹), respectively. For the whole oxidation process, the activation energies follow a parabolic law with increasing conversion degree, and the average activation energy is 160. 56 kJ · mol⁻¹.

Titanium nitride precipitation on a primary inclusion particle during solidification of bearing steel has been tracked by varying temperature in a confocal scanning violet laser microscope. Upon precipitation, an obvious growth of titanium nitride on a primary inclusion particle was observed due to the rapid solute diffusion in liquid steel. The onset of titanium nitride precipitation did not change with primary inclusion particle size, but the time of growth was greater for a smaller primary inclusion particle. Meanwhile, the particle size displayed little influence on the total precipitated amount of titanium nitride on it under the same conditions. At the later period of solidification, almost no change occurred in inclusion size, but the inclusion shape varied from circle to almost square in two-dimension, or cubic in three-dimension, to attain the equilibrium with steel.