Based on the solidification heat transfer model and the CAFE model, the solidification behavior and structure of 2311 die steel, with a cross-section dimension of 415 × 2270 mm at different casting speeds, specific water flow and superheat, is numerically simulated. Nail-shooting and acid-etching experiments are carried out on the slab to verify the model’s macroscopic size. With the increase in casting speed, the slab’s central equiaxed grain ratio (ECR) decreases and the average grain size increases. The increase in superheat promotes the growth of columnar grains and inhibits the growth of central equiaxed grains. When the superheat increases from 23 to 38 K, the ECR decreases from 43.2 to 29.64%, and the average radius of grains increases from 0.89 to 1.01 mm. With the increase in specific water flow, the ECR decreases, and the average grain radius is the smallest when the specific water content is 0.32 L kg⁻¹. Finally, the slab quality is improved by process optimization, and the central segregation index of carbon decreases from mean value of 1.15 to 1.05.

Inclusions are an important parameter affecting the fatigue life of materials. In this paper, the type, size, and quantity of inclusions in bearing steel were quantitatively analyzed using scanning electron microscopy and automatic scanning electron microscopy with an X-ray energy dispersive spectroscopy function. The effects of the inclusion parameters and positions on the rotating bending fatigue properties were analyzed using the rotating bending fatigue test. The results proved that for samples 1 and 2, the inclusions were mainly sulfides, Ti-containing inclusions, and their composite inclusions. For samples 3 and 4, the inclusions were mainly oxides or sulfide–oxide complexes. The number and maximum size of inclusions in sample 2 were relatively small. This was mainly due to the difference in the content of Al, S, and Ca elements in the different samples. The inclusion distance to the surface and the maximum inclusion size had a larger influence on the rotating bending fatigue life in comparison to the inclusion type. Moreover, nitride–oxides had a more detrimental effect on the rotating bending fatigue life as compared to the sulfide–oxide complex inclusions. A model was established on the basis of the inclusion size, depth, and stress by using the Python software. The simulation demonstrated that using five parameters fit well with the experiment results.

Few reports exist on the effect of the basicity of refining slag on inclusions in 15-5PH stainless steel and its removal efficiency. In this study, the effects of various basicities on the formation and removal efficiency of inclusions in molten steel were investigated. To investigate the effect of the chemical makeup of slag on the non-metallic inclusions in liquid steel, laboratory experiments and thermodynamic calculations were conducted on CaO-MgO-SiO₂-Al₂O₃-CaF₂ slag with various slag basicities and 15-5PH stainless steel. In the steel samples that had reacted with high-basicity slag samples, the magnesium content and aluminum yield were higher. Thermodynamic findings according to the ion and molecule coexistence theory showed that log ($a_{{\mathrm{SiO}}_2}^3/a_{{\mathrm{Al}}_2{\mathrm{O}}_3}^2$) decreases as slag basicity increases. This increases the Al concentration in liquid steel while decreasing the Si content. Log ($a_{\mathrm{MgO}}^3/a_{{\mathrm{Al}}_2{\mathrm{O}}_3}$) also increases, increasing the Mg content of the molten steel. With this, the transformation order of oxide inclusions is Al₂O₃ → MgAl₂O₄ → MgO. High-basicity slag increases the attachment of slag to inclusions and generates MgAl₂O₄ inclusions that are more easily adsorbed by inclusions in molten steel, thereby improving the cleanliness of molten steel.

The spatial distribution of equiaxed crystal zones during extra-thick slab solidification exerts a critical influence on the mechanical performance of the final product. This investigation establishes a dual-pathway control framework for solidification structure modulation, differentiating between intrinsic regulation through columnar-to-equiaxed transition (CET) positioning and extrinsic intervention via strand electromagnetic stirring (S-EMS) parameter adjustment. The aim is to improve the internal quality of extra-thick slabs, enabling further investigations into the material properties. To achieve this, a solidification heat transfer model along with a cellular automata–finite element model were developed to characterize the thermal conditions at CET initiation, with experimental validation conducted on a 475 mm extra-thick slab. The systematic analysis identified a significant correlation between continuous casting parameters, alloy concentrations, and CET positioning, while S-EMS experiments further elucidated the distribution patterns of the solidification structure and the formation mechanism of the white band in the mushy zone. This methodology bridges computational metallurgy with process engineering, offering systematic guidance for solidification structure control in extra-thick slabs.

Non-metallic inclusions have a great influence on the cleanliness and mechanical properties of steel

This study investigates the evolution of initial solidification during the continuous casting of 230 mm × 1255 mm slabs by establishing a heat transfer inverse calculation model and a slab solidification heat transfer model, with the results of the former used as boundary conditions for the latter. The results show that at the thermocouple measurement positions, the average heat flux in the outer arc direction is greater than that in the inner arc direction, which causes the flow field inside the slab to deflect. Meanwhile, with increasing distance, the transverse distributions of temperature and solidified shell thickness become uneven. The lowest temperature occurs within 100 mm of the slab center, and the maximum difference in solidified shell thickness is 4.47 mm. A “reheat” phenomenon occurs in the shell at the mold outlet. Increasing casting speed and decreasing superheat both alleviate the flow deflection, but they do not reduce the uneven distribution. Specifically, for every 0.1 m/min increase in average casting speed, the solidified shell thickness decreases by 0.74 mm, and for every 5 °C increase in superheat, the solidified shell thickness decreases by 0.07 mm. Superheat has almost no effect on the growth of the solidified shell. However, when the slab enters the secondary cooling section, the solidified shell growth rate accelerates.