Nonmetal inclusion control has always been an important subject in clean steel production. In recent years，the focus of Mg application in steel has changed from the traditional modification of inclusions to the microalloying. This paper reviews the research status of Mg application in steel at home and abroad，represents the advantages of Mg from several aspects，such as cleanliness control，oxide metallurgy，solidification microstructure refinement，slab crack control，etc. The possible development fields and directions of magnesium clean steel are also analyzed and prospected.

In order to improve desulfurization equipment and technology of hot water pretreatment，and improve the desulfurization efficiency，a new type of agitator was formed through combining the advantages of agitator and spray gun with reference to the traditional KR desulfuration method. The flow field in the hot metal tank was analyzed by Fluent software and Eulerian model. The effects of different eccentricity，stirring speed and ventilation flow of the agitator on the desulfurization effect were studied from the aspects of flow velocity and gas distribution. The results showed that the new agitator could enhance the flow field，and the desulfurization gas ejected by the nozzle at the bottom of the agitator would make the desulfurization gas spread more widely and more evenly in the iron tank. When the new agitator had a stirring speed of 150 r/min，ventilation flow rate of 5.0 m³/h and eccentricity of 0.3，the distribution and intensity of gas was the best，and the flow field had a large average velocity，which was beneficial to the reaction of hot metal and desulfurization agent.

To solve the problem of low bottom blowing effect and fast erosion of bottom tuyeres caused by high oxidability of slag during semisteel steelmaking in Pangang Group Xichang Vanadium & Steel Co.，Ltd.，measures such as application of new bottom blowing tuyeres，optimization of bottom tuyeres arrangement and optimization of thermalreplacement scheme were adopted. Bottom blowing effect during the converter campaign was improved. Industrial application indicated that after the optimization of bottom blowing process，mean thermalreplacement time was shorten by 95 min，average phosphor distribution ratio（L_P）between steelslag during the whole converter campaign was improved from  78.0  to  92.5，mean TFe mass fraction in endpoint slag was reduced form 19.7 % to  18.6 %，and average carbonoxygen concentration product at endpoint was reduced from 0.002 8  to 0.002 3. Production efficiency of converter steelmaking was improved and cost of BOF blowing was reduced as well.

Due to the slump of steel scrap price in domestic，using steel scrap as the raw material for converter smelting can greatly reduce the production costs. Combined with its own process features，Tianjin Tiangang United Special Steel Co.，Ltd. fully used the arc heat source of LF furnace and the residual temperature of molten steel to melt steel scrap. According to the thorough research on the melting mechanism，melting and mixing time and inclusion analysis of steel scrap adding to LF refining furnace，the reasonable process of LF refining furnace with steel scrap as the addition was determined，thus the steel scrap ratio in steelmaking was improved，and the iron loss was reduced. Through production practice，when LF refining furnaces were fed with steel scraps reaching 1.54t per furnace in June，2019，iron loss could be reduced to 10.56kg/t. By means of benefit accounting，when a gap between the price of steep scraps used in LF refining and the sales price of actual steel billets reached more than 280yuan/t，distinct economic benefits could be produced. Furthermore，adding steel scraps during LF refining didn’t cause adverse effects to the quality of molten steel，The endpoint oxygen level met steel grade requirements，and showed remarkable effects.

The macro temperature field and microstructure in the twinroll strip casting are affected by the heat exchange of the cast roller and coating. In this paper，a physical model of the solidified shellcoatingcasting roller was established to study the effect of heat transfer coefficient (h1) between the solidified shell and the coating and the heat transfer coefficient (h2) between the coating and the casting roller on the solidification process. The results showed that the solidification of steel liquid conformed to the law of square root，the increase of h1 could effectively avoid the crack of the coating surface，accelerate the solidification of the steel liquid，and increase the mean grain area of the microstructure. The increase of h2 could prevent the coating from peeling，but it would increase the possibility of cracking in the coating surface，and at the same time，the average mean area of the microstructure would be increased.

In order to avoid the formation of brittle inclusions in tire cord steel, the measures that controlling the Al content of charge and alloy and making low basicity slag system in LF refining furnace were adopted，and the mass fraction of acid soluble aluminum (Al_s) in molten steel could be controlled at about 9×10^-6. By optimizing the type and content of antioxidants in ladle magnesia carbon lining brick, reducing the metal Al powder from 1.61% to 0.15%, and replacing the rest by the same amount of Si powder，w(Al_s) in molten steel reduced from 8.8×10^-6 to 6.1×10^-6, with a decrease of 30.7%. The average mass fraction of Al₂O₃ in typical composite inclusions in steel reduced to 8.6%, while the maximum was 23.8%. The inclusions could be controlled in the plastic zone of low melting point.

Remelting electroslag，continuous casting mold flux and secondary refining slag were taken as typical steelmaking slag systems. And the volatilization behaviors of each slag system were analyzed by thermogravimetric (TG) and mass spectrometry (MS). The results showed that the remelting electroslag volatilized violently above 1300℃，and the volatiles were mainly CaF₂，MgF₂ with a small amount of SiF₄ and AlF₃. The continuous casting mold flux volatilization was divided into two stages，in the first stage (750—1200℃) CaF₂ reacts with Na₂O and SiO₂ to form NaF and SiF₄, accompanied by the evaporation of a small amount of Na₂O. The second stage (>1300℃) was mainly the CaF₂ evaporation. For CaF₂-CaO based refining slag，the evaporation of CaF₂ was the most intense at the eutectic point (84%CaF₂-16%CaO). This research has guiding significance for the composition and performance control of fluorine-containing slag and metallurgical environmental protection in the steelmaking process.

The disintegration caused by f-CaO is one of the main obstacles to the utilization of steel slag. The f-CaO come from the incomplete dissolution of the quick lime and the decomposition of tricalcium silicate. In terms of the f-CaO derived from the undissolved lime，it is necessary to strengthen the dissolution behavior of lime in the converter process. The lime reactivity plays a key role on its dissolution, and is closely related to its microstructure. The evolution behaviors of the reactivity and microstructure of quick lime under high temperature were investigated in this work. The lime samples were prepared in the laboratory, the microstructure was detected and analyzed by SEM, XRD and a mercury-injection instrument, and the reactivity was test according to YB/T 105—2005 standard. The results showed that， when temperature increased, the reactivity and porosity of the quick lime decreased，and the average diameter of pores increased. The CaO crystals grew gradually under the action of the grain boundary migration. The change of microstructure was closely related to the change trend of lime activity. On basic of the growth of CaO crystal and the decrease of the porosity, the lime activity decreased，which would obstacle the dissolution of quick lime during the steelmaking process and increase the content of f-CaO in the slag.