Steel casing pipes used in the construction of deep oil wells usually require both high strength and corrosion-resistant behavior. Due to the exploration of deep H₂S-bearing oil reservoirs, sulfide stress cracking (SSC) is becoming an increasingly serious concern for casing steel. The nonmetallic inclusions in the steel are among the key reasons for its service failure. The rare earth element Ce can be used to modify the inclusions in casing steel and improve its SSC resistance. Here, taking C110 grade casing steel (the highest class currently in service) as the investigated object, the modification behavior of Ce inclusions in the steel and the effect of the addition of Ce in varying amounts (0.01, 0.024, and 0.042 wt.%) on the modified products were studied through high-temperature tube furnace experiments and thermodynamic calculations. The results showed that Ce had an obvious modification effect on the CaO·Al₂O₃ inclusions in casing steel, and the diffusion of dissolved Ce in the steel was the limiting step of the modification reaction. With the extension of reaction time, the sequence describing the modification of inclusions in the steel was determined as follows: CaO·Al₂O₃ → CeAlO₃ → Ce₂O₃/Ce₂O₂S. The final stable product after modification depended on the amount of Ce added. With 0.01 wt.% Ce, the stable phase in molten steel was Ce₂O₃; on the other hand, upon adding ≥0.024 wt.% Ce, the stable phase became Ce₂O₂S. In addition, the thermodynamic stability of Ce₂O₃ decreased, and it was transformed into CeAlO₃, Ce₂O₂S, Ce₂S₃, and CeS during solidification. On the basis of our results and the considerations for smooth casting, the addition of a proper amount of a rare earth element is suggested for industrial trials, following the achievement of a significant and surprising improvement in the qualified rate of SSC resistance for the final steel products. The relevant mechanism is also analyzed.

Tundish with channel-type induction heating is one of new technologies adopted widely in China by the steel industry in the recent years, which can supply a constant liquid steel temperature control for the sequenced continuous casting process. For a five-strand tundish with induction heating in service, a kind of novel bifurcated split channel has been designed to solve the poor consistency of temperature and fluid flow for each strand that occurs with the conventional straight channel-type. The temperature distribution and fluid flow behaviors under the two structure modes were compared numerically by an electromagnetic-heat-flow multi-physics field coupling model. The results show that the maximum temperature difference between each strand outlet of the tundish can drop to less than 4 °C upon using the bifurcated channel, as compared to 10 °C under the original straight channel mode. According to the simulated results, case FK-A0 has been chosen as the optimized structure for industrial application. It has been verified through temperature measurements during the casting operation that the novel bifurcated split channel can improve the consistency of steel temperature for every strand of the tundish. The average temperature difference between the edge strand and the middle strand is 4.25 °C lower than the original straight channel, resulting in an upgraded metallurgical effect for the induction heated tundish.

Compared to the conventional deoxidation process with Al or Si-Mn for 55SiCr spring steel production, the possibility of using a Si-Ca-Ba compounded deoxidizer to control the behavior of non-metallic inclusions in spring steel was explored in this study. The effect of the addition sequence of deoxidizer and alloys into molten steel on the morphology, size, and composition of the inclusions was emphatically studied at 1873 K (1600 °C) using a high-temperature electric resistance furnace. The results indicate that adding alloy first can form less harmful inclusions in steel, which are roughly spherical and smaller than 3 μm in diameter, and its inclusion evolution path is MnO-SiO₂-Al₂O₃→CaO-SiO₂-Al₂O₃ and CaO-Al₂O₃-MgO. While adding deoxidizer first, the inclusions in steel are harmful due to its mostly irregular geometry and relatively large size over 5 μm. The inclusion evolution path is Fe-O→CaO-Al₂O₃(-SiO₂) and CaO-Al₂O₃-MgO. The formation and evolution mechanism of inclusions under different addition sequences were discussed. In addition, the solubility limits of MgO from refractory into steel were studied to inhibit its corrosion by molten steel.

High-grade non-oriented silicon steel is a critical material for new energy vehicles and energy-efficient appliances due to its superior magnetic properties. However, these properties are significantly degraded by non-metallic inclusions, particularly Ti(C,N). This study employs integrated thermodynamic and kinetic calculations to systematically analyze the formation and growth mechanisms of Ti(C,N) inclusions in high-grade non-oriented silicon steel, trace the sources of [Ti], and propose targeted theoretical control strategies. Results indicate that Ti(C,N) inclusions do not precipitate above the liquidus temperature (1779 K). During solidification, microsegregation enriches Ti, C, and N; however, only TiN precipitates in the final stage as its ion product exceeds the solubility limit, whereas TiC remains undersaturated—findings valid within the present composition window and modeling framework. Inclusion size is governed by cooling rate and initial Ti/N content, where higher cooling rates yield finer inclusions and lower Ti/N content suppresses precipitation. Titanium originates from primary sources (raw materials and alloys) and secondary sources (decomposition or reduction of TiO₂ in slag/refractories). Therefore, mitigating [Ti] requires strictly limiting primary input and suppressing secondary formation through optimized process control, such as reducing BOF slag carryover, lowering refining temperature, and controlling [Al] content.