Pellet swelling has been widely studied, being simultaneous with reduction reactions and common in the operation of blast furnaces. A tube furnace equipped with a camera recording system was used here to study the dynamic and isothermal reduction swelling behaviour of olivine and acid pellets under simulated BF shaft conditions. The olivine pellets were magnetically separated into three fractions, containing low, medium and high amounts of magnetite in the core. The divalent iron (FeO) content of these fractions was 0.1 wt-%, 0.2 wt-% and 2.9 wt-%, respectively. Pellets with a large magnetite nucleus were observed to encompass numerous cracks, which was reflected in a poor LTD test value, while SiO2-rich reference pellets with a different slag chemistry had more restrained swelling and cracking behaviour in dynamic reduction. Swelling in the olivine pellets was associated with cracking at the boundary between the original magnetite nucleus and the hematite shell.The dynamic reduction swelling test results showed lower reduction swelling indices (max 17% in volume) than under isothermal conditions (max 51% in volume), in which case the pellets were suddenly exposed to a strongly reducing atmosphere. It is thus suggested that the reduction swelling behaviour of iron ore pellets should preferably be studied dynamically under simulated blast furnace conditions in order to achieve a realistic understanding of their swelling behaviour in a blast furnace.

Sulphur and alkalis in the blast furnace gas have been associated affecting the reduction swelling behaviour of iron ore pellets. A tube furnace was used in this study to examine the dynamic reduction swelling behaviour of olivine and acid pellets in CO-CO2-N2 atmosphere with sulphur and potassium in gaseous phases up to 1 100°C simulating the conditions in the blast furnace shaft.No abnormal swelling was detected in sulphur or potassium containing CO-CO2-N2 atmospheres during dynamic reduction. Instead, sulphur in the reducing atmosphere was associated with pellet contraction and FeO-FeS melt formation which became more dominant with increasing sulphur partial pressures. In the extreme case, having a maximum of 1.0 vol-% S2 gas in the reducing atmosphere, the reduction reaction of wüstite to metallic iron was hindered. The formation of FeO-FeS liquid phase extends the cohesive zone towards the blast furnace top and lower temperatures and decreases the gas permeability. Furthermore, large amounts of potassium in the reducing atmosphere (max. 0.03 vol-%) led to swelling and cracking in the olivine pellets still remaining in the range of normal swelling.

The presence of non-metallic inclusions (NMI) such as sulphides and oxides may be detrimental to the control of the steel casting process and product quality. The need for their identification and characterization is, therefore, urgent. This study uses time-gated Raman spectroscopy for the characterization of synthetic duplex oxide-sulphide phases that contain CaS and the oxide phases of Al2O3, CA, C12A7, C3A, and MgO·Al2O3 (MA). Binary phase samples of CaS–MA, C3A–CaS, C12A7–CaS, Al2O3–CaS, and MA–CaS were prepared with varying phase contents. The relative intensities of the Raman peaks were used to estimate the samples’ phase content. For a quantitative estimation, linear regression calibration models were used to evaluate the change in phase content in the samples. The most suitable Raman peak ratios had mean absolute error (MAE) values ranging from 3 to 7 wt. % for the external validation error, and coefficients of determination (R2) values between 0.94 and 0.98. This study demonstrated the use of Raman spectroscopy for the characterization of the calcium sulphide, magnesium aluminate spinel, Al2O3, and calcium aluminate phases of CA, C3A, and C12A7 in a duplex oxide-sulphide system, and it offers potential for inclusion characterization in steel.

Calcium aluminate (CaO-Al 2 O 3) phases play a critical role in the study of non-metallic inclusions in aluminium killed, and calcium treated steels. In this study, the Raman spectroscopy technique, a versatile and non-destructive approach, was used to characterise binary calcium aluminate phases qualitatively and quantitatively. Calcium aluminate samples with varying CaO/Al 2 O 3 ratios were synthesised to produce a binary phase samples mixture of C12A7-C3A and C12A7-CA. Quantitative estimation was based on plotting a linear regression calibration model between the ratio of Raman band intensities and the phase fraction in the samples. With the linear regression, the phase fraction of C12A7-C3A and C12A7-CA was estimated with average absolute errors of 2.97 and 2.55 percentage points. This work demonstrates the potential suitability of using Raman spectroscopy technique for evaluating whether calcium aluminate phases in oxide inclusions fall within the liquidus region at steelmaking temperatures.

The modification of MgO•Al 2 O 3 spinel inclusions into less detrimental mixture phases of CaO-MgO-Al 2 O 3 plays an essential role in refining calcium-treated aluminium killed steels. This study uses Raman spectroscopy for the characterisation of binary phase samples that contain MgO•Al 2 O 3 spinel and calcium aluminate (CaO) x -(Al 2 O 3 ) y phases. Samples were synthesised from MgO•Al 2 O 3 spinel (MA), Al 2 O 3 and calcium aluminate phases to achieve binary samples of CA-MA, C3A-MA, C12A7-MA and Al 2 O 3 -MA with varying phase fractions.The study also examined the possibility of a slight variation for non-stoichiometric spinel samples below the 1 600°C region in an MgO-Al 2 O 3 binary system. The relative intensities of the Raman band were used for the quantification of the phase fractions. For a quantitative prediction, linear regression calibration models were identified for each of the studied systems. This work demonstrates the use of Raman spectroscopy for the characterisation of calcium aluminate phases of CA, C3A, C12A7 and magnesium aluminate spinel phases along with Al 2 O 3 and its potential application in inclusion characterisation.

In order to reduce CO2 emissions in the iron and steel industry, the utilization of H2 gas as a reducing agent is a feasible option. The use of hydrogen bearing injectants in the lower blast furnace (BF) area increases H2O concentration in the upper part of the BF shaft and the charging of moist burden has a similar effect as well. For efficient BF operation, it is important to investigate the effect of high H2 and therefore high H2O concentrations in the reducing gas. This study focuses on the upper BF shaft area where hematite to magnetite reduction takes place and temperature is in the range of the forward water-gas shift reaction (WGSR). The effect of the WGSR on the composition of the reducing gas was estimated by experimental methods. A layer furnace (LF) was used to determine the temperature for the occurrence of the WGSR under simulated BF shaft conditions. The feed gas conversion was investigated in an olivine pellet layer. The WGSR was observed in an empty LF with CO-H2O-N2 gas at 500°C. With CO-CO2-H2O-N2 gas the WGSR was observed in an olivine pellet layer at 400-450°C and in a pre-reduced magnetite pellet layer at 300-400°C indicating the catalyzing effect of magnetite on the WGSR. The results offer additional information about the effect of high H2O concentration on the composition of the reducing gas through the WGSR. The occurrence of the WGSR in the actual BF and its effects were discussed.

Recent inclusion models are mainly focused on the compositional evolution of inclusion, steel and slag. Due to the importance of inclusion size distribution to steel properties, the evolution of inclusion size distributions should also be accounted for. As the first step to establish a model to predict the evolution of inclusion size distribution, the nucleation, growth and removal of alumina inclusions in molten steel were modeled by combining Kampmann and Wagner numerical model for nucleation, growth and coarsening with particle size grouping method. The model could simulate the time evolution of the size distribution of alumina inclusions after aluminum de-oxidation. The model was validated by using the experimental size distribution data of alumina inclusions available in the literature. The model calculation results were also compared with previous simulation results. The influences of interfacial tension between steel and inclusion and diffusion coefficient on the calculated inclusion size distribution were investigated. As interfacial tension between steel and alumina increases, the maximum number density decreases and the peak value of radius increases. As diffusion coefficient increases, the maximum number density decreases and the peak-value radius increases. The calculated size distribution curves showed a change from log normal to fractal, which is due to the change of dominating mechanisms for crystal growth and agglomeration.

The determination of alloying and impurity elements was performed from a stainless steel matrix and inclusions in process samples. An electrolytic extraction method was applied for the separation of inclusions using two different but commonly used electrolytes, 10% HCl and 10% acetylacetone in methanol. The elemental analyses were performed using atomic absorption spectrometry. The elements of interest were aluminum, arsenic, copper, vanadium, titanium and chromium. The aluminum containing inclusions were imaged using a field emission scanning electron microscope. The results for copper and chromium in both electrolytes, vanadium in 10% HCl electrolyte and arsenic in 10% acetylacetone electrolyte were in good agreement with industrial data. Titanium and aluminum were measured from the dissolved steel matrix but titanium was also detected in the inclusions. It was concluded that the analytical results for titanium and aluminum measured using an optical emission spectrometer is affected by the inclusions within the stainless steel.