Ironmaking & Steelmaking: Processes,Products and Applications

The production and development of the ironmaking process in China are crucial for energy saving, emission reduction and transformation and promotion processes of iron and steel industry. In order to fully understand the production and techniques of ironmaking blast furnace in China, the production and operation indexes of large blast furnaces were analysed in this paper. Then challenges of the ironmaking in China were discussed. On this basis, the future development of ironmaking in China was further analysed. The study will contribute to understanding the state of ironmaking process of China.

Phosphorus removal in basic oxygen steelmaking is a significant problem for integrated steelmakers. Phosphorus removal is required due to its deleterious effect on the mechanical properties of steel. However, this is progressively becoming more difficult due to the increasing phosphorus content of many iron ores. Many studies have investigated dephosphorisation and published empirical phosphorus partition (L_P) equations for a range of conditions. The structure of these equations has been used to develop a new partition relation that allows the effect of minor slag constituents such as TiO₂, Al₂O₃ and V₂O₅ on steel dephosphorisation to be tested. Al₂O₃ was found to have a weak negative effect on the measured L_P, except at the lower oxygen potential range tested, where a positive correlation was observed. Increasing TiO₂ and V₂O₅ contents were found to decrease the measured L_P; however, these correlations became less prevalent at the higher oxygen potential ranges tested.

Trumpet-shaped ladle shroud (TLS) has been widely employed in practical continuous casting processes. In this study, the fundamental flow pattern in an industrialised TLS is discussed using large eddy simulation. The effect of geometrical designs on fluid flow is investigated for two types of TLSs. The flow structure is found to be sensitive to the ratio (H/D) of the trumpet length (H) to outlet diameter (D). The H/D is suggested to be equal to or larger than four in the current cases to obtain a well-developed flow pattern and avoid reverse flow at the outlet of the TLS. Plant observations show that a relatively quiet molten bath and well covered tundish flux are achieved using the optimised TLS.

The evolution of macro inclusions during continuous casting was investigated by large-area inclusion characterization using ASPEX and analysis of nozzle blockage deposits. Six kinds of inclusions over 5 μm were observed in samples taken from the tundish and the slabs: single alumina particles, alumina dendrites, refractory-related alumina, alumina associated with bubbles, alumina clusters and Al–Ti complex oxides. By examining the morphology of the nozzle blockage deposit, it was concluded that the refractory-related alumina in the slabs came from the decarburization layer washed away by the steel stream. Some of the alumina clusters that came from the nozzle blockage deposit dislodged by the steel flow, were formed by the agglomeration and sintering of 5–20 μm inclusions that were carried over from the tundish. Two kinds of Al–Ti oxides were found in the tundish, and their evolution mechanisms during the casting process were proposed.

In the present study, the reduction of in-flight particles of iron ore concentrate by carbon monoxide has been investigated. A mathematical model was developed for simulating the motion of particles in a CO–Ar gaseous mixture within the reactor. Pre-designed experiments were carried out in a fabricated experimental set-up for validating the model. Excellent agreement between the model predictions and the experimental data approved the accuracy of the model. The nucleation and growth model and the fminsearch optimising method were used for investigating the reaction kinetics. The following equation was obtained relevant to CO reduction of the magnetite concentrate particles:

High-quality coking coals all over the world are gradually approaching extinction. These days, steel industries are trying to focus more on the utilisation of non-coking grades of coal. The present work involving high-ash, high-volatile lignite coal can be used indirectly in iron-making processes. Direct use is not possible due to low amount of carbon and high value of ash. High ash content leads to huge sulphur content, and this leads to high cost involvement in secondary processes. On the other hand, huge amount of iron ore fines are generated during mechanised mining, sizing, screening, transportation, beneficiation and sintering processes. Iron ore nuggets are formed from inferior quality iron ore fines using suitable binders with the applied pressure. Mechanical properties of iron ore nuggets are also assessed through shatter and abrasion test. A furnace was designed, to indirectly utilise high-ash, high-volatile lignite coal, for pre-reduction iron ore nuggets. Iron ore nuggets were partly reduced by CO, H₂ and fine carbon produced from volatilisation of coal. Optimized pre-reduced nuggets, having high mechanical stability was directly charge in the raising hearth furnace for pig iron production.

The influences of the strain rate on the tensile properties and fracture behaviour of DP600 and DP780 advanced high-strength sheet steels have been studied. The variation of their mechanical properties depending on the strain rate have been researched by applying uniaxial tensile tests at three different strain rates (0.001, 0.01, 0.06 s⁻¹). The influences of strain rate on fracture behaviour have been investigated by displaying the fracture surfaces of the material. Strain rate increase has been determined to increase the yield strength, tensile strength, total elongation and hardening rate. The strain hardening coefficient has been found not to be significantly affected by the strain rate. It has been determined that, the fracture has occurred faster during necking while load-carrying capacity has increased with strain rate increase.

This paper considers the equipment and technological characteristics of continuous annealing process (CAP) to solve the issue of strip buckling. It analyses the mechanism of hot buckling and transverse compressive stresses from internal and external forces. A basic description of strip buckling is given together with a new concept of a buckling index. The critical buckling condition is presented, and the model of strip buckling index in the CAP is proposed. The distribution of strip buckling index in different sections of the process is analysed quantitatively along with the influence of incoming strip shape, transverse temperature difference, roller profile, friction coefficient, set tension and strip processing speed on the strip hot buckling index in CAP. Results show that with the influence of thermal stress, the transverse compressive stress that affects the middle part of the strip is largest in the heating section, which is also where hot buckling occurs most easily; centripetal force is dominant in the soaking and slow cooling sections, and in these sections buckling occurs at the roller shoulder. In different sections, the strip buckling index distribution differs, whereas the influence of other parameters on buckling index remains similar.

Second stage dynamic strain aging is observed during cold drawing of low carbon steel wire rods with higher free nitrogen content. The effect is prominent in thinner wires which have experienced higher strain and are thereby heavily stressed. Consequently, these severely deformed wires with higher nitrogen content are prone to early environmental degradation.

Inclusions containing Mg existed in low carbon aluminium killed steel even though Mg is not added during LF treatment. To investigate the mass transfer mechanism of Mg in low carbon aluminium killed steel, both industrial practice and kinetic calculations were carried out in the present work. The results from industrial practice showed that Mg concentration in molten steel and inclusions increased with refining time during ladle furnace treatment. The inclusion size tended to become smaller with the increase of Mg concentration in the inclusions. The erosion rate of refractory with different composition was tallied. A refractory-slag-metal-inclusion multiphase reaction model was developed to investigate mass transfer mechanism underlying the variation of Mg among the steel, the slag, inclusions and the refractory. The calculated results exhibited a good predictability of the content of Mg in the molten steel, slag and inclusions. The results showed that Mg dissolved into molten steel in two ways: the first is in the way of slag/steel reaction, the second is in the way of refractory erosion which is the main way.