To address the issue of low lime utilization efficiency in the KR desulfurization process at a steel plant, an innovative right-angled-hole cross impeller was developed. By integrating numerical simulation with water modeling experiments, the flow field characteristics of the novel impeller and its influence mechanisms on both the desulfurizer mixing time and the proportion of desulfurizer stably retained in the metal phase were systematically investigated. The results demonstrate that the right-angled-hole cross impeller enhances centrifugal effects to optimize flow field distribution, achieving efficient directional transport and homogeneous dispersion of desulfurizer. Within the rotational speed range of 156－201 r/min, the mixing time was substantially reduced by 23.4%－31.3%, indicating remarkable improvement in mixing efficiency. Under identical process conditions, the retention rate of desulfurizer in the metal phase increased from 26% to 44%, significantly improving the mixing effectiveness between desulfurizer and hot metal.

In response to the problems of deteriorating technical and economic indicators and rising production costs in the smelting process of electric furnace with direct reduced iron (DRI), the smelting process was systematically improved by optimizing the slag-making  system, power supply system,carbon powder and oxygen injection system, as well as the raw material feeding and steel retention and slag retention systems. The research results show that the optimized process by adding different ratios of DRI to the electric furnace can reduce steelmaking electricity consumption by about 10 kW·h/t, shorten the smelting cycle by 2 minutes, reduce steel material consumption by about 3 kg/t, effectively control the final slag composition, and reduce the average steelmaking cost by more than 10 yuan/t. With an annual steel production of  1.2 million tons, more than 12 million yuan in costs can be saved annually, providing practical experience and technical reference for the sustainable development of the electric furnace steelmaking industry.

The effects of traditional VD high-alumina process (high-aluminum molten steel inlet) and the VD aluminum-adjusting process (low aluminum molten steel inlet, adjusting aluminum after vacuum breaking) on the purity of Q355 wind power steel molten steel was compared. It was found that the VD aluminum-adjusting process significantly improved molten steel quality and reduced aluminum costs. The tests showed that the number density of inclusions decreased by 51.8% during the VD inlet stage under the VD aluminum-adjusting process, and the area fraction of inclusions decreased by 29.8% during the casting stage. Simultaneously, the proportion of Al₂O₃ in inclusions decreased substantially by 33.35%, while the CaO proportion increased, promoting the transformation of CA₂-C₁₂A₇ into C₁₂A₇. Consequently, the average B-type coarse inclusion rating on the steel plate decreased by 45%. The mass fraction of total oxygen decreased by 11.8%–24.8% across various stages in steel, while desulfurization efficiency decreased more moderately due to the lower aluminum content. In terms of cost, aluminum consumption decreased from 3.09 kg/t to 2.67 kg/t, saving 7.56 yuan/t. The results indicate that the VD aluminum-adjusting process delivers significant improvements in enhancing molten steel cleanliness and economic efficiency.

CaO-Al₂O₃-based mold fluxes have become a research focus due to their inhibition of steel-slag interface reactions. However, the formation of aluminate minerals tends to result in poor metallurgical properties of the mold flux. Na₂O decomposed from industrial raw material sodium carbonate can remedy such flaws, showing favorable application effects. CaO-Al₂O₃-based fluorine-free mold fluxes were prepared using calcium aluminate refining slag as the primary raw material. The soda ash mass fraction (3%-11%) was adjusted via single-factor method to investigate its effects on crystallization kinetics, thermodynamic behavior, and mineral phase evolution. Results showed that as soda ash mass fraction increased from 3% to 11%, the critical cooling rate for crystallization and slag film crystallinity first increased then decreased, while the incubation time exhibited an inverse trend. The initial crystallization temperature remained relatively unchanged. The primary crystalline phases were acicular Ca₃B₂O₆ and glassy microcrystalline Na₂CaAl₄O₈, both showing peak-then-decline trends in content. Optimal crystallization ability and refined mineral phase structure were achieved at 7% soda ash mass fraction.

In order to reduce the interface energy consumption during the casting-rolling process of high-quality low-carbon steel, the No.2 continuous casting machine at Meishan Steel implemented a transformation from a two-strand to a single-strand tundish. This modification increased the casting speed from 1.2 m/min to 2.4 m/min, enabling single-strand high-speed casting production. A combined approach of physical and numerical simulations was employed to investigate the flow characteristics and inclusion trajectories under different operating conditions. The results demonstrated that the original flow control devices of the tundish were no longer suitable for single-strand casting after modification, leading to significant dead zones (particularly on the blocked-strand side) and poor mixing homogeneity. By introducing a novel turbulence inhibitor and redesigned dam, the flow pattern on the blocked-strand side was notably improved. The dead zone volume decreased by 12.2%, the response time extended by 96.7%, the average residence time increased by 11.2%, and the peak concentration decreased by 45.3%, indicating superior flow field uniformity in the optimized tundish. The removal efficiency of inclusions was significantly enhanced in the modified tundish. The results of large sample electrolysis revealed that the average inclusion content decreased from 0.78 mg/kg (original configuration) to 0.29 mg/kg (optimized configuration). The implementation of new flow control devices effectively improved flow patterns in the tundish， enhanced the removal efficiency of inclusions and the cleanliness of molten steel, significantly increased the casting speed of the continuous casting machine, and assisted in energy-saving and carbon reduction in steelmaking.

Q345R steel is widely used in the manufacture of pressure vessels and boilers, which demand high mechanical properties and corrosion resistance because they are usually in service at high temperatures, high pressures or in environments with corrosive media. The presence of inclusions in steel could deteriorate the properties of the steel, seriously affecting the service safety and service life of the equipment. Understanding the formation mechanism and evolution of non-metallic inclusions in the refining and casting process of Q345R steel is a prerequisite for optimizing the inclusions control process. To this end, the evolution of inclusions in the refining and casting process of Q345R steel was investigated by industrial trials, and the influence of Ca treatment, reoxidation as well as cooling and solidification on the evolution of inclusions was discussed with FactSage 8.3 thermodynamic software. The trial results showed that at LF ending to VD breaking, the inclusions in steel were transformed from MgO-Al₂O₃, CaO-Al₂O₃-MgO(-CaS) and a small amount of CaO-CaS to liquid CaO-Al₂O₃-MgO, and the number density of inclusions was reduced from 53.58/mm² to 10.98/mm², and the removal rate of the inclusions was as high as 79.51%. After Ca treatment, the inclusions into CaO-Al₂O₃-MgO(-CaS) and a small amount of CaO-CaS, the mass fraction of Al₂O₃ in inclusions decreased to 35.10%, while mass fraction of CaS increased to 20.61%. During soft blowing to the ladle casting 5 min, the liquid steel occurred a serious reoxidation, the inclusions from CaO-Al₂O₃-MgO(-CaS) and a small amount of CaO-CaS transformed into CaO-Al₂O₃-MgO and MgO-Al₂O₃, the number density increased from 22.59/mm² to 53.77/mm², and the average size decreased from 1.95 μm to 1.56 μm. In the as-cast slab, due to the large amount of CaS precipitation, the inclusions were mainly MgO-Al₂O₃, CaO-Al₂O₃-MgO(-CaS), CaO-CaS and a small amount of MgO. In addition, based on thermodynamic calculations, a new target for inclusions modification during Ca treatment was proposed, i.e., Window 3 (w(T.Ca)=0.001 8%～0.002 8%), and the effects of  T.O, T.S, and Al_t in the steel on this window of inclusions modification were analyzed in detail and compared with the previous window of inclusions modification, and it was found that the content of T.O in the steel should be reduced as much as possible before the Ca treatment, the while ensuring the effect of Ca treatment, it can also effectively reduce the cost.

The evolution characteristics of the steel cleanliness and inclusions in a low-carbon aluminum killed steel produced by the the route of VD→ LF→calcium treatment→continuous casting and rolling under the converter process was investigated. It was found that the T.O mass fraction significantly decreased from 129×10^-6 at the LF start to 34×10^-6 before calcium treatment. But, there was still a problem that the w(CaO)/w(Al₂O₃) in the refining slag was too small. A significant increase on the contents of T.O and T.N in the steel after calcium treatment, indicating that the significant reoxidation occurred. It was necessary to strengthen the stabilization control of the calcium treatment process. During the refining process after deoxidation, the inclusions transformed from clustered Al₂O₃ to irregular Al₂O₃-MgO, and then to spherical CaO·2Al₂O₃ after the calcium treatment with a feeding amount of 0.64 kg/t steel. Due to the generation of a large number of small-sized inclusions during the calcium treatment process, the average size of inclusions decreased from 2.8 μm before calcium treatment to 2.3 μm after calcium treatment according to the detection of automatic SEM. However, at the same time, factors such as the entrainment of refining slag particles during calcium treatment increased the maximum size of inclusions to 28 μm after calcium treatment. Due to the reoxidation of the molten steel during the casting process, the number density of inclusions in the molten steel in tundish significantly increased to 45/mm², and the area fraction of inclusions also reached 268×10^-6 based on the detection results of automatic SEM. Therefore, it was necessary to further strengthen the protective casting of the molten steel during the continuous casting process.

Metallurgical defects initiate rejections in ultra sonic inspection were carefully characterized in present study, with emphasis on the origins of macro-sized calcium magnesia aluminates. It was found that large calcium magnesia aluminates could be categorized into two types. The first type was featured by huge sizes of several millimeters, as a layer of scatter oxide particles of calcium magnesia aluminates, spinel, calcium aluminates with certain amounts of SiO₂, and some CaS particles, resulting in steel plate delamination. The second kind of calcium magnesia aluminates were with sizes about several hundred microns, and appeared in rolling direction as string shaped B-type inclusions. Based on the correlated information of rolled plates and as-cast slabs, it was found that rolled plates contained the first kind of calcium magnesia aluminates were casted during the transition of ladles. As a result, it could be reasonably inferred that the first type of calcium magnesia aluminates were exogenous inclusions originated from entrapped teeming ladle slag, which agglomerated with endogenous spinel, CaS and calcium magnesia aluminate inclusions to form a huge inclusion cluster. During hot rolling, the agglomerated huge inclusion clusters were crushed into a layer of densely scatter oxide inclusion particles with sizes of millimeter scale. The first type of inclusions can be reduced and avoided by strictly controlling the ladle residue during casting and accurately marking non steady state slabs.The second type of inclusions should be endogenous ones formed during refining process, which was with estimated maximum sizes about 200-300 μm in as-cast slab and elongated into B-type inclusions in rolled plates because of chemical compositions locating in low melting point region in the ternary system of CaO-MgO-Al₂O₃. Hence, the latter type of inclusions can be decreased or avoided by refining process optimization. 

The addition of a certain amount of Zr element to marine engineering steel promoted the formation of specific non-metallic inclusions to induce the nucleation of acicular ferrite, thereby refining the grain structure and enhancing the impact toughness of the welding heat-affected zone under high-heat-input welding conditions. Scanning electron microscopy, high-temperature confocal microscopy, and optical microscopy were utilized to observe the transformation of inclusions  the nucleation of acicular ferrite on inclusion surfaces, the temperature variation during acicular ferrite nucleation, and the changes in the proportion of various microstructures after cooling in different samples under varying Zr content treatments. The electron backscatter diffraction (EBSD) system was employed to statistically analyze the distribution of grain boundary angles in each sample. Experimental results indicated that with an increase in Zr content, the predominant inclusion types in the steel shifted from Al₂O₃-TiO_x-MnO-MnS to Al₂O₃-TiO_x-ZrO₂-MnS-(TiN). When the Zr mass fraction reached 120 ×10-6, the steel exhibited a higher presence of monomeric ZrO₂. In situ observations revealed that as the Zr content in the steel increased, the onset temperature for the transformation of acicular ferrite decreased from 509 ℃ to 484 ℃, the nucleation temperature range increased from 57 ℃ to 71 ℃, and the area fraction of acicular ferrite initially increased from 26% to 36% before showing a decreasing trend. EBSD results suggested that adding of 0.002% mass fraction of Zr element could achieve a higher proportion of large-angle grain boundaries, indicating that a certain amount of Zr element can promote the formation of Zr-containing composite non-metallic inclusions to induce the nucleation of acicular ferrite and increase the temperature range for acicular ferrite nucleation.