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This paper presents the effect of magnesium on the morphology of carbides and on M 7 C 3 → M 23 C 6 (M = Cr and/or Fe) carbides transformation in the 21-4N heat-resistant steel. 21-4N heat-resistant steel was calculated by using the FactSage. The equilibrium carbide phase is M 23 C 6 and is stable up to 1492 K in Mg-added 21-4N heat-resistant steel. The studies involve a wide range of experimental techniques to characterize the investigated steels in the as-cast and hot-rolled state, including X-ray diffractometer, confocal scanning laser microscope (CSLM), scanning electron microscope, transmission electron microscopes (TEM) and microhardness testers. In the as-cast and hot-rolled samples with different magnesium contents, M 7 C 3 was detected due to nonequilibrium solidification, while the carbide types are M 23 C 6 in the prediction from equilibrium phase diagram. Lamellar structure in the as-cast sample is composed of FCC austenite and M 23 C 6 . And blocky shape carbide M 7 C 3 is wrapped by the lamellar structure M 23 C 6 .

This study examines the isothermal and non-isothermal reduction behaviors of iron ore compacts in a pure hydrogen atmosphere and compares the results obtained during the reduction process by CO. The different phases accompanying the reduction reactions were identified using X-ray diffraction (XRD) and its morphology was microscopically examined. In isothermal experiments, temperature plays a significant role in the reduction process. At any given temperature, the reduction rate during the initial stages is higher than that during the final stages. The reduction rate in H2 atmosphere was faster than in CO gas. The comparison of activation energy values suggested that reduction with H2 is more efficient than with CO. At the same temperature, the time required to achieve a certain degree of reduction was lower when using H2 gas than CO atmosphere. In non-isothermal tests, the heating rate has a significant effect on the reduction rate and reduction extent. At the same heating rate, the degree of reduction was higher in H2 atmosphere than in CO gas. Based on experimental data, the parameters of reaction kinetics were deduced by application of model-free and model-fitting methods. The reduction in H2 atmosphere was controlled by nucleation model (Avrami-Erofeev model), while the CO reduction reaction was controlled by gas diffusion.

The state of a blast furnace hearth, especially the liquid level of hot metal and slag during the tapping process, is of crucial importance with respect to a long campaign blast furnace. In practice, the state of the hearth is evaluated mainly by the experience of operators. In this paper, the electromotive force (EMF) is used to monitor the liquid level of a laboratory scale of blast furnace hearth and the effect of liquid level, EMF sensors position and the thickness of refractory on EMF signals are tested using a single layer of water and double layers of water and oil. After laboratory experiments, the electromotive force (EMF) is used to monitor the liquid level of torpedo ladle successfully. Laboratory experimental results show that the change in liquid level can be characterized by EMF signal. The state of liquid surface and local thermal state cause the EMF signal to vary in the circumferential direction of the vessel. Furthermore, the EMF signal magnitude decreases with the decrease of the thickness of the graphite crucible. Finally, the main conclusions of the laboratory experiment are supported by the torpedo ladle experiment.

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