The fluid flow phenomena of the hot metal during KR mechanical stirring desulfurization process was investigated using water model. The effect of the rotation speed and the immersion depth of the impeller on the velocity and turbulent kinetic energy in the ladle was discussed using a particle image velocimetry (PIV). The flow pattern in the KR ladle was a typical doubleroll flow. When the rotation speed of the impeller increased from 110 r/min to 210 r/min, the spatial distribution of the velocity and turbulent kinetic energy changed little while the maximum velocity increased from 0.15 m/s to 0.3m/s, and the turbulent kinetic energy increased from 0.01 m²/s² to 0.035  m²/s². When the immersion depth of the impeller varied, the spatial distribution of the velocity and turbulent kinetic energy changed significantly while the magnititude varied little.

With the increasing supply of scrap and severe requirements for energy conservation and environmental protection, high efficiency low consumption high scrap ratio converter technology is demanded increasingly urgent in steel industry. At present, the technical scheme of high scrap ratio converter lacks systematization in our country, and the scrap ratio of converter is generally not exceed 35 %. Systematic high scrap ratio converter technology should be researched around how scrap is added and how heat gap in converter is compensated. Preheating scrap and good combustion in the converter are the key technologies to improve converter energy utilization efficiency and further increase the scrap ratio. Combining C-O reaction theory and existing trials, the result shows that post combustion ratio (PCR) and heat transfer efficiency (HTE) of C-O reaction to the molten steel can be significant improved. Compared to the common top-blowing, the current C-O reaction heat transferred to the molten steel can be raised by more than 88.3 %.

The dephosphorization rule of low temperature and low silicon molten iron was better studied in Masteel 70 t converter site, the limited dephosphorization reaction and low dephosphorization rate due to the slow slag formation in the early stage and the drying back in the medium stage. The FeO mass fraction in  slag was increased from 10.46 % to 24.70 % at the third minute by improving the feeding method and lance position control, the dephosphorization reaction was strengthened to achieve the purpose of slagging and dephosphorization.The dephosphorization rate at first turning down  increased from 72.1 % to 86.6 %，and tapping rate at first turning down  increased from 68.4 % to 74.3 % by the optimization, and the technical indicators such as steel consumption and oxygen lance age had been improved which provided support for fast-paced production and energy saving in the field.

The process of tapping without waiting sample based on sublance technique was introduced. Based on the thermodynamic analysis, combined with large data statistical analysis, the relationship between the parameters measured by sublance and the phosphorus content in molten steel was studied. The results showed that phosphorus content increased linearly with main-blow temperature.With the increasing of main-blow carbon content, phosphorus content increased and the increase amount was not obvious when main-blow carbon mass fraction was over 0.40 %.With the increasing of end-point temperature, phosphorus content increased. With the increasing of endpoint oxygen, phosphorus content decreased and the decrease amount was not obvious when end-point oxygen mass fraction was over 500×10^-6.When end-point temperature was higher than 1 685 ℃ or end-point oxygen mass fraction was lower than 300×10^-6, phosphorus content fluctuated greatly. The process practice showed that when the main-blow temperature or carbon was high, the auxiliary blowing should be adjusted properly to avoid the end-point oxygen too low or the end-point temperature too high, which could effectively reduce the occurrence of high phosphorus and meet the requirements of dephosphorization effect of converter. This process provided an important way to shorten the smelting cycle, reduce the energy consumption of steelmaking process and refractory consumption.

The sustainable development of environment was affected by high energy consumption, high pollution steel enterprises.The development of clean energy and the promotion of green economy were the road to the development of the metallurgical industry. Based on its own hot metal conditions, Nanjing Steel has developed manganese-based high-efficiency composite slagging materials to achieve clean production. It was found that when the ratio of manganese to silicon was 0.8-1.0, the dephosphorization rate of the converter reache over 90 %, and the dephosphorization stability was the best. When the Mn mass fraction in the slag reached 3.5 %, the slag had the best melting property and the lowest oxygen supply. When the final slag (FeO) mass fraction was 20 %-22 % and the final slag (MnO) mass fraction was 3.0 %-3.5 %, the slag dephosphorization efficiency was the best. The average mass fraction of residual manganese in the end point molten steel could be increased from 0.050 % to 0.092 % by using manganese-based high-efficiency composite slagging material. The use of high-efficiency composite metallurgical materials improves the stability of converter smelting, reduces soot emissions, reduces smelting production costs, and improves the overall competitiveness of enterprises.

An immersion top blowing experimental device was designed to trace the movement of bubbles in water, hydraulic oil and glycerin. The bubble deformation, motion characteristics of the bubbles and the rising height of the liquid surface were studied under different gas flow rates (0.5，1.0，1.5，2.0 m³/h) and nozzle immersion depths (130，200，270，340 mm). The VOF model was used to analyze the deformation, movement and bulge height characteristics of bubbles in liquid. The numerical simulation results were in agreement with experiment. The results show that the fluctuation degree of liquid surface caused by different liquid viscosity is significantly different. With the increase of gas flow rate and immersion depth, the liquid surface bulge height increases, and the bulge height of water in the three kinds of liquid is the largest, and the immersion depth has greater influence than the gas flow rate. Under the same injection conditions, the liquid surface flow velocity of water ,hydraulic oil and glycerin decrease in turn, and the reference velocity of glycerin increases the most obviously, but the injection stability time increases the last.

In the current study, inclusions in the molten steel and the continuous casting slab of a ultra-low carbon Al-killed steel were analyzed using automatic scanning electron microscopy-energy dispersive spectrometer. The evolution of inclusions in the steel during continuous casting were analyzed and discussed by combining with thermodynamic calculation. The composition of each inclusion in the steel during continuous casting was mainly compounds of titanium and aluminum, with an average content of 98 %. Inclusions of the molten steel in the continuous casting tundish were mainly Al₂O₃ and Al₂O₃-TiO_x, and those in the continuous casting slab were mainly Al₂O₃, Al₂O₃-TiN and TiN. Inclusions of Al₂O₃ and Al₂O₃-TiO_x in the molten steel were significantly removed by attaching to the submerged entry nozzle and by removing to mold slag during continuous casting. As the temperature decreased, many TiN particles precipitated in the solid and mushy zone of the steel and became the dominant ones in the slab. A thermodynamic software was used to calculate the transformation of inclusions during cooling and solidification of the steel, showing a result agreeing with the measurement. According to the calculation results of Scheil equation, when the solid fraction was greater than 0.58, TiN can precipitate in the solid steel around the solidification front; when the solid fraction was greater than 0.83, TiN can precipitate in the molten steel around the solidification front. In the continuous casting slab, TiN inclusions accounted for 86 % of the total inclusions, and the TiN inclusions with Al₂O₃ cores accounted for 8 %.

In this paper, the effect of ladle nozzle on nitrogen addition of molten steel was introduced by the process of 110 t electric furnace→LF refining→VD refining→continuous casting in Jiangsu Yonggang Group Co.,Ltd. By optimizing the inner cavity structure of the long nozzle, the contact surface between the lower nozzle and the long nozzle was increased to improve the sealing performance, and the material was improved. Compared with the original long nozzle, under the same conditions, the nitrogen addition of molten steel decreased from 5.8×10^-6 to less than 1.2×10^-6, and the structure optimization of long nozzle achieved the expected results.

In this study, the metallurgical cause of battery shell pinhole defect during the cold stamping was analyzed and determined firstly. The pinhole defects were detected by ASPEX scanning electron microscopy. A lot of Al₂O₃ inclusion particles were found in the defect portion. It was considered that the large-size Al₂O₃ inclusions were broken and resulted in pinhole defects during the cold stamping process. Therefore, a systematic sampling analysis was performed on the smelting process and slab of battery shell steel. The results showed that the mass fraction of FeO in the ladle slag decreased to 11.12 % after slag modification during RH refining, and further decreased to 5.85 % at the end of the casting, which indicated that the oxidizing slag continuously transferred oxygen to the molten steel during the casting. The number density of inclusions in the molten steel was reduced from 28.1 pcs/mm² to 10.5 pcs/mm² by holding 10 minutes after RH treatment. The T.O and [N] mass fraction in the molten steel were reduced from 43.4×10^-6 and 32×10^-6 to 29.6×10^-6 and 28.5×10^-6. It was found that the number density of inclusions in the molten steel increased from 10.5 pcs/mm²  to 45.2 pcs/mm² at the beginning of casting, and the mass frction of T.O and [N] increased from 29.6×10^-6 and 28.5×10^-6 to 57.8×10^-6 and 56.1×10^-6 respectively, while the [Al_s] mass fraction in the molten steel reduced by 220×10^-6. It is necessary to improve the slag adjustment effect to reduce the incidence of pinhole defects in the battery shell, and the mass fraction of FeO in the slag should be reduced to less than 5 %.

The cleanliness problem of SCX400 wheel steel plates was checked by SEM and the results showed that the dot-line macro-inclusions inside the steel plates shaped from the big CaO-MgO-Al₂O₃ inclusions during rolling process, and those inclusions oriented form refining and casting process, not floating up into slag, consequently kept inside of slabs. Base on this study, actions were implemented to change inclusion into solid classes before RH process as Al₂O₃, MgO-Al₂O₃ or high melting point CaO-MgO-Al₂O₃ who have better tendency to float upon, and then global Al₂O₃-MgO-CaS inclusions, with high melting point. After that, inclusions were tested as Al₂O₃ or Al₂O₃-CaO cores coated by CaS inside the plate. The single-test qualified rate increased from previous 90 % to current 95.4 %, whilst cracking defect rate in production decreased to 0.5 %-1.0 % and the fatigue lifetime of wheels stabilized beyound million times.

In order to solve the problem of high order defect rate of network cementite structure on the surface of 70 steel wire rod, it was found that network cementite originated from the overflow area of solidification hook with abnormal oscillation marks on the surface of billet by means of analyzing metallographic structure of wire rod.The main reasons that caused abnormal oscillation marks on the surface layer of high carbon steel billet were the poor lubrication and excessive frictional resistance between the billet and the mold. The practice indicated that the proportion of abnormal oscillation marks on the surface of 70 steel billet was reduced from 22.09 % to 6.54 % and the defect rate of superficial network cementite on the surface of wire rod was reduced from 3.47 % to less than 0.50 % by adjusting the stroke M value of mold from 2.7 mm·min/m to 2.9 mm·min/m, the oscillation frequency of mold from 200 times/min to 180 times/min, the air-fuel ratio of heating furnace from 0.60－0.65 to 0.68－0.70, and the temperature of heating furnace from 1 040－1 080 ℃ to 1 050－1 090 ℃. Finally, the decarburization layer 
didn’t exceeded the standard, and the quality and performance of finished product meted the requirements. 

In order to improve the qualification rate of postweld detection of wind power steel plates, the unqualified and qualified steel plates of heat-affected zone after welding of 18 mm thick wind power steel were taken as the research object. Metallographic microscopes and scanning electron microscopes were used to analyze the metallographic structure and inclusions. The difference between qualified and unqualified parts of flaw detection was investigated, and the cause of unqualified of flaw detection in heat affected zone after welding was studied. The results showed that, the presence of large size aluminum oxide or calcium aluminate inclusions in the steel plate was the cause of failure in post-weld heat affected zone. Combined with actual production, the whole process was controlled from the beginning of tapping process to continuous casting process，and the proportion of type B inclusions below class 1.5 in the steel plate from 85 % to more than 98 %.The quality objection of flaw detection unqualified in the heat affected zone after welding was eliminated.

The shipbuilding steel with Mg treatment has excellent performance for large heat input welding, and the stable pinning effect of the particles is the key for the preventing of the grains coarsening. For conforming the behavior of pinned particles for Mg treated DH36 shipbuilding steel under high temperature, the high temperature confocal experiments and the welding thermal simulation experiments had been designed and performed. The results showed that, when the temperature was lower than 1 170 ℃，the pinned particles in steel were mainly the Ti & Nb composite particles like stars with small size and TiN particles. For higher temperature and longer high temperature duration, the Ti & Nb composite particles lost the pinning effect for solving in the steel, and the austinite grain size had grown from 5 μm to nearly 50～60 μm. The new steady pinned particles were mainly the Mg & Ti composite particles, and the stability was decided by the [Mg] content in the steel.

In this paper, the advantages and disadvantages of two kinds of 80 t steel ladle were compared from the aspects of refractory consumption, steel structure weight, equipment investment, ladle heat dissipation, operation cost and metallurgical effect. When the ratio of diameter to height of liquid steel bath in the 80 t steel ladle is close to 1，it has the advantages，1）Ladle has a lower weight and equipment investment is saved by ￥520 000~624 000；2）The refractory are consumed less and cost is saved by  ￥68 000 every year；3）Operation cost is lower and saved by ￥250 000 every year； 4）Ladle heat dissipation is less and cost is saved by ￥421 000 every year；5）Blind spots are reduced and is better for inclusion floating；6）The slag drawn into by vortex is reduced and the purity of liquid steel is heightened .