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The retained austenite content in TRIP590 steel was first measured by X-ray diffraction (XRD) method. Then, the effect of different test parameters (indexing rate, step size, field number, etc.) on the measured results of retained austenite content in TRIP590 steel by electron backscattered diffraction (EBSD) method was studied. By comparing the measured results between XRD and EBSD method, the optimal test parameters for the analysis of retained austenite content using EBSD were determined. Finally, the total content of retained austenite and the retained austenite contents with different aspect ratios in TRIP590 steel were analyzed, respectively. The results showed that the test parameters have a great influence on the measured results of retained austenite content in TRIP590 steel. In order to improve the test accuracy, high indexing rates, small step sizes and more field number are necessary for the analysis of retained austenite content in TRIP590 steel by EBSD method.

The hot deformation behavior of S460ML steel with different Nb contents was investigated by single-pass compression experiment on the Gleeble-1500 thermo-machine simulator at deformation temperatures ranging from 900 to 1200 °C and strain rates from 0.1 to 5.0 s−1. The critical strain of dynamic recrystallization (DRC) under different conditions was determined by using working hardening rate-strain curves. The relationship between critical strain and peak strain of DRC was discussed. By means of regression analysis method, the hot deformation activation energy of steels and the mathematical model for predicting DRC critical strain were calculated and established, respectively. The results showed that DRC occurred during hot deformation. As the deformation temperature increased and strain rate decreased, the critical strain of DRC decreased. The critical strain (εc) showed linear relationship with peak strain (εp). As Nb content increased, the needed deformation temperature for occurring DRC increased, while the needed strain rate for it decreased. The activation energy for hot deformation of S460ML steel increased with increasing Nb content.

The behaviors of typical iron ores at high temperature were observed by confocal scanning laser microscopy. Four critical temperature points and liquid flow velocity at high temperatures of iron ores were obtained and the temperature points contain temperature at which sample starts to shrink, temperature at which the initial liquid phase forms, temperature at which a lot of liquid forms and temperature at which liquid consolidation ends. Under the same CaO to Fe2O3ratio, the liquid phase fluidity of iron ore fines of Carajas (IOC) is good. However, under the same basicity, as the content of SiO2in IOC is low, the liquid phase fluidity of IOC is much smaller than that of Yandi fine. After analysis of the initial formation and development of the liquid phase and the final consolidation process, the high-temperature process evaluation system (HTPES for short) of iron ore was established. The idea of “dense ore matching fusible ore” instead of “relatively fusible ore” was proposed based on the results of HTPES and applied in ore matching of a sinter plant from Shougang Jingtang. The use of IOC (13–18%) instead of standard sintering fines (SSF) improved liquid phase fluidity and ensured the sinter quality. Furthermore, the use of IOC fine (18–23%) with Hainan fine (0–2%) instead of SSF, a mixture of hematite and Marra Mamba ore and concentrates guaranteed the quality of sinter ore through improving fluidity, in the meantime reducing ore matching costs. With the establishment and application of HTPES, the sinter plant has achieved good economic benefits under the premise of ensuring the quality of sinter ore.

The whole melting curve of iron ore during sintering process was obtained, and the melting characteristics of iron ore were defined and explained. The whole melting process of mixture, mixed by iron ore and CaO reagent at basicity of 2. 0 and 4. 0, respectively, was observed using a SiC heating furnace with camcorder unit, and the melting curves of mixture that were relative height vs temperature curves were obtained. Besides, the melting characteristics of iron ore during sintering were introduced through defining some points in the melting curves, such as liquid forming temperature, inflexion temperature and flowing temperature, and the meaning of different shapes of the melting curves was clarified.

The whole melting curve of iron ore during sintering process was obtained, and the melting characteristics of iron ore were defined and explained. The whole melting process of mixture, mixed by iron ore and CaO reagent at basicity of 2.0 and 4.0, respectively, was observed using a SiC heating furnace with camcorder unit, and the melting curves of mixture that were relative height vstemperature curves were obtained. Besides, the melting characteristics of iron ore during sintering were introduced through defining some points in the melting curves, such as liquid forming temperature, inflexion temperature and flowing temperature, and the meaning of different shapes of the melting curves was clarified.