The control of end-point temperature and composition in converter steelmaking is an important operation in the later stage of blowing. The accurate temperature and carbon prediction is very important. In order to improve the end-point carbon and temperature hit rates of the converter blowing, main input variables were determined with characteristic correlation analysis method and the converter end-point prediction models based on the XGBoost algorithm were built up. The models were verified from the actual converter production data.In comparison with the results obtained from BP and optimized BP neural network models, it was found that the XGBoost algorithm model can achieve a high end-point hit rates under the premise of ensuring a fast convergence speed. In order to further improve the hit rates of end point temperature and carbon, the several important parameters in the XGBoost algorithm model were adjusted accordingly. Finally, when the temperature deviations were ±15 ℃ and ±10 ℃,the hit rates of end point with XGBoost algorithm model were 95.84 % and 91.69 %, respectively. When the deviations of carbon mass fraction in molten steel were ±0.015 % and ±0.01 %, the end point hit rates were 93.31 % and 87.84 %, respectively.

Aiming at the low dephosphorization rate caused by insufficient heat and slag-forming difficulty in low silicon molten iron steel-making of converter, through industrial trials, the relationships among the temperature at end point of different hot metal silicon content in the smelting process, the amount of thermal agent-ferrosilicon, the amount of scrap and ore were studied, and the KR silicon increasing technology and converter slagmaking technology of adding silica were combined. The results show that the chemical heat of hot metal is less when ferrosilicon is added into converter, and the furnace temperature rises slowly in the early stage. The addition amount of lime is less, and it is difficult to melt, which is bad for the formation of slag and dephosphorization process. However, ferrosilicon is well melted in KR device, and the absorption rate is close to 100 %. The dephosphorization rate of the hot metal with low Si mass fraction (≤0.3 %) increases from 82.3 % to 87.7 %. This can provide a theoretical guidance and technical reference for the dephosphorization process of hot metal with low Si content.

The control of dephosphorization slag is the key point in the dephosphorization stage of the new double-slag converter steelmaking process. In order to study the effect of basicity and total Fe content of the dephosphorization slag on the composition and proportion of slag phase, the industrial experiments of the new double-slag converter steelmaking process were carried out. Four dephosphorization slag samples with different basicities and total Fe contents were obtained by controlling the amount of the charged raw materials. The phase analysis and microscopic observation were carried out. The results show that the dephosphorization slag phase consists of P-rich phase and matrix phase. There is Fe-rich phase in the slag when the total Fe content is high. The P content in the P-rich phase is the highest, and the P content in the Fe-rich phase is the lowest. With the increase of basicity, the proportion of P-rich phase in the slag increases first and then decreases. The higher is the total Fe content in the slag, the higher is the proportion of the Fe_tO phase in the slag. When the P-rich phase accounts for about 40 %–50 %, the matrix phase accounts for about 13 %–35 %, and the Fe-rich phase accounts for about 23 %–35 %, it is favorable for dephosphorization in the new double-slag converter steelmaking process.

The Euler-Lagrange method was used for numerical modeling of the 150 t LF ladle, and the Kuo drag force model affected by the bubble shape was used. This method considered the influence of static pressure on bubble size. The argon inlet was at the bottom of the ladle and a rotating electromagnetic stirrer was at R/2 at the bottom of the ladle. The bubble behavior and the mixing time of the alloy were investigated. The results show that the electromagnetic stirrer placed eccentrically at the bottom can effectively change the bubble distribution state. In the range of 0-400 A, the greater the current intensity of the electromagnetic stirrer, the greater the degree of bubble deviation and the greater the degree of bubble dispersion. After applying the eccentric electromagnetic stirring at the bottom, the average residence time of 1 mm bubbles can be extended to 4.38 s, and the residence time of large bubbles such as 20 mm, 30 mm and 40 mm can also be extended by about 60 %. When the current intensity is 400 A, this electromagnetic stirrer can effectively improve the problem of lower temperature of molten steel at the bottom of the ladle and higher temperature around the center. When the current increases to 400 A, the alloy diffusion efficiency is increased by 60.4 %, and the mixing time of molten steel can be shortened by 145 s.

The physical and chemical properties of RH top slag for non-oriented electrical steel were studied by FactSage 7.2 thermodynamics software. The top slag optimization plan were proposed in combination with industrial production. Studies have shown that FeO and SiO₂ in RH top slag would cause secondary oxidation of steel. Combined with thermodynamic analysis, calculation of the absorption capacity of the top slag for Al₂O₃ and industrial tests, the ideal RH refining process top slag composition range is w(CaO)=50 %～60 %，w(SiO₂)≤5.01 %，w(CaO)/w(Al₂O₃)=1.5～2.0. At the end of refining, the slag system is close to the low melting point,w(CaO)/w(Al₂O₃)≈1.25. Industrial experiments showed that after the top slag compositions were optimized, T.O mass fraction of steel reached 14×10^-6 at the end of refining, the surface flaw rate of cold-rolled products decreased from 4.6 % to 0.3 %， and the smelting effect of RH top slag was excellent.

The development and research practice of CAS process for  tinplate in Shougang Jingtang were introduced. By reforming the bottom blowing pipeline, optimizing the argon flow control and inclusion modification treatment, the CAS refining process low nitrogen control technology, CAS bottom blowing nitrogen increasing technology and CAS ladle top slag upgrading technology were developed. The high-efficiency and low-cost CAS process for tinplate was successfully opened. The tinplate produced by CAS process fully meets the quality requirements, which not only ensures the quality of tinplate, but also relieves the pressure of RH process, and reduces the production process cost.

Based on the similarity theory, a 1∶3 water model experiment system was established to study the influence of different submerged nozzle (SEN) structures on slag entrapment behavior in a continuous casting mold with argon blowing. The variation of liquid level fluctuation and argon bubble distribution under different nozzle structures were investigated. The results showed that the main ways of slag entrapment in the mold were bubble impacting slag entrapment, shearing slag entrapment and emulsion pumping slag entrapment. When the concave bottom nozzle was used, it was easy to produce bubble impacting slag entrapment and emulsion pumping slag entrapment. When the convex bottom nozzle was used, it was easy to produce shearing slag entrapment and bubble impacting slag entrapment. When the concave bottom, rectangle, 20° inclined nozzle was used, the minimum number of slag entrapment was observed, that was 4 times/min. The liquid level fluctuation of convex bottom nozzle was more severe, and the rectangular nozzle was not conducive to reduce the liquid level fluctuation. The maximum wave height could reach 2.5 mm at the quarter position of the width of the mold at the 20°inclination angle convex bottom nozzle. The bubble distribution was more dispersed and the impact depth was greater in the large angle nozzle. The movement distance of argon bubble with liquid steel was longer with convex bottom nozzle.

The surface layer of narrow edge of ultra-low carbon steel slab was planed layer by layer, and the morphology, quantity, size, composition and space distribution characteristics of bubble defects carried in the 20 mm zone of surface layer with size more than 50 μm were analyzed by optical microscope, scanning electron microscope and energy spectrum. The results show that the bubble defects are caused by bubbles and alumina associated bubbles. Bubbles exist in the form of single and aggregation. A total of 122 bubble defects are found, and the number of bubble defects with the particle size between 50-100 μm is the largest, accounting for 60.66 % of the total. The bubble defects are unevenly distributed on the surface layer of the slab, more at both ends of narrow surface, and less at 40-60 mm away from narrow face on the inner arc of wide face. The average number density of bubble defects on the narrow face is greater than that on the wide face, and there are more bubble defects near 3 mm subcutaneously on the slab surface. After 11 mm subcutaneously, the size of bubble defects decreases with the increasing of subcutaneous distance.

At present，the phenomenon of uneven cooling in the width direction of slab was ignored in the dynamic secondary cooling control model and dynamic soft reduction model of slab continuous casting. The nozzle had the problems of poor atomization effect，serious nozzle blockage，small nozzle adjustment ability and unstable spray angle. The hinge point type sector segment had poor roll gap accuracy and difficult to assemble and disassemble，which cannot meet the requirements of modern continuous casting technology for high roll gap accuracy and reducing maintenance cost. To solve the above problems，an online simulation model of three-dimensional temperature field，a new type of high-efficiency nozzle，and a new type of gapless roll gap adjustment segment were developed and applied in many engineering fields. After upgraded，the detection pass rate of cast slabs was increased to 99.5 %，and the incidence of transverse cracks，longitudinal cracks，and corner cracks on the surface of cast slabs was reduced by 53.96 %，56.3 %，and 29.19 % respectively. The offline calibration of the segment and the online control of the roll gap accuracy were increased by more than 2 times，and the installation and disassembly time of the segment was reduced by 66 %.

In order to improve the inclusion control process and improve the quality and performance of cold-drawn steel tubes, the inclusions in the refining process of B18 cold-drawn steel tubes were systematically analyzed. The evolution of the purity of molten steel and the composition, morphology, particle size distribution and quantity of the microscopic inclusions during the refining process were studied. The results showed that the content of T.O and N in molten steel decreased significantly from LF to VD process, but the molten steel increased a little after entering tundish. The size of micro inclusions in LF to VD process was concentrated in 0-5 μm, and the total number of inclusions decreased with the refining process. In LF refining process, the main inclusions were Si-Mn-Al and Si-Ca-Al-Mg type inclusions and a small amount of CaS and MnS. In the process of 
VD refining, the Si-Mn-Al inclusions were transformed to Si-Ca-Al-Mg and CaS inclusions. The main inclusions in tundish steel were MgO-Al₂O₃-CaS and CaS、MnS inclusions.The large inclusions were SiO2-Al₂O₃, CaO-MgO-Al₂O₃, MgO-Al₂O₃-SiO₂ and other composite inclusions. The main sources of the large inclusions in tundish were deoxidation reaction products, slag involved and reaction products of molten steel and furnace lining.

The edge shear delamination of A709M-50F-2ZT steel plate seriously affects the product quality. In order to prevent such edge layer defects from recurring, the 30 mm thick A709M-50F-2ZT edge shear layered steel plate was taken as the research object. With the help of metallographic microscope, scanning electron microscope, etc., the metallographic structure and inclusions were analyzed. The results show that the internal cracks in the area of 1/3 to 1/4 of the thickness of the steel plate are the main cause of shear cracking. The shear delamination of the edge of the steel plate was eliminated in actual production by improving the purity of molten steel, reducing pouring overheating, strengthening the maintenance of continuous casting equipment.

In order to understand the cooling mechanism of steel slag treatment and realize the clean utilization of steel slag, the high temperature cooling test of molten steel slag was carried out. And the effect of cooling rate on the physical phase structure, phase transformation law, microstructure and stability of steel slag were studied by four different cooling treatment methods, viz., furnace cooling, air cooling, water mist cooling, and water quenching. The results of thermodynamic equilibrium calculations show that some of calcium crystallizes in the form of calcium silicate and calcium ferrite, and some exist in the form of metal oxide solid solution. The higher the basicity of the steel slag, the higher the content of free calcium oxide. The results of high temperature slag cooling experiments show that as the cooling rate increases, the content of silicate and solid solution oxides in the slag increases, while the content of free calcium oxide decreases significantly, the stability of the slag can be significantly improved.