One of the typical components of oxide inclusions in steel is Al2O3-SiO2-MnO-MgO system. The equilibrium relations of Al2O3-SiO2-MnO-MgO slag with Fe-Ni alloy at 1 733 K was experimentally obtained, which is necessary for knowing the effects of MgO addition to the previously known Al2O3-SiO2-MnO system. The experiments were conducted under various slag compositions mainly focusing on the changes of Al2O3 saturation line and spinel formation line equilibrated with liquidus phase. SEM-EDS analysis was utilized to directly observe the phase image and to analyze the liquidus phase composition. Liquidus phase was then plotted on to the Al2O3-SiO2-MnO-MgO system from different angles.
This study investigated the boiling heat transfer characteristics of three upward circular water jets impinging on a hot moving steel sheet, with a specific focus on the interference effects between adjacent jets. Although run-out table (ROT) cooling is a key technology in thermomechanically controlled processing (TMCP), the quantitative understanding of multiple-jet cooling remains limited. Experiments were conducted using a heated stainless-steel sheet with an initial temperature ranging from 250 to 550 degrees C and a conveying velocity of 4.4 m/s. Three 7-mm diameter nozzles were arranged in the width direction of the sheet with nozzle spacings of 15 and 21 mm. The surface heat flux distribution was evaluated using an inverse heat conduction analysis based on temperature data measured using an infrared camera. High-speed imaging revealed that flow collisions between adjacent jets formed vertical water films, restricting the effective cooling area of the central jet. However, the relationship between the maximum heat flux and local surface temperature is consistent with existing correlations for single jets. These findings highlight that the experimental data for single jets can be used to approximately predict the heat removal for multiple jets.
The reduction rate of molten iron oxides containing CaO was measured at 1 723 K by injecting pure CO gas through an iron nozzle immersed in the molten oxide. Using the pressure pulse method, the size and generation cycle time of CO bubbles were identified during the reduction experiment. After the reduction experiment was held for 3 600 s, dense iron particles were observed beneath the iron nozzle, and oxide containing metallic iron was deposited on the inner surface of the nozzle. The reduction degree and the reduction rate decreased linearly with an increase in CaO content. Although the reduction rate at 100% FeO was not directly measured in this experiment, the value extrapolated from the current results was found to be lower than those reported in previous literature. The effect of CaO on the reduction rate was opposite to that investigated in previous studies using the top-blow CO gas method. While the top-blow method is the most likely to involve CO2 adsorption that controls the reduction rate, the CO gas injection method may be controlled by other factors, such as the activity of FeO.
The creep properties and microstructures of two types of Gr. 91 steel with different impurity (Sb, As, Sn) contents were investigated. The steel with higher impurity concentrations (Steel 1) ruptured in slightly shorter time than the steel with lower impurity concentrations (Steel 2). The reduction of area for Steel 1 was slightly lower than that for Steel 2 due to higher density of creep voids in Steel 1. However, no clear correlation was observed between impurity contents and either elongation or creep intolerance parameter (lambda). Microstructural observation revealed that the effect of impurities on the initial microstructure was considered negligible. During creep, the crystallographic relationship between common rotation axes and rotation angles at block/packet boundaries gradually disappeared. Among block boundaries, <011 >53 degrees and <011 >60 degrees were found to be more susceptible to creep deformation, whereas <111 >60 degrees was relatively less sensitive. This disappearance of crystallographic relationship was more pronounced in Steel 1 than in Steel 2, implying that the difference in creep strength between the two steels could be attributed to the ease of migration and merging of block/packet boundaries.
