On the basis of the thermodynamic analysis of solute redistribution, a slab central segregation model was established, which is called “solute precipitation quantity” model, and the simulation result was analyzed. The results show that, the origin of solute precipitation during the solute redistribution process is the existence of chemical potential gradient; the carbon concentration of Q235B slab central line increases suddenly to maximum 0.76% at the end of solidification; once the casting speed changes from 1.2 m/min to 1.6 m/min, the maximum segregation degree will increase from 5.057 to 5.103.

It is briefly introduced the current intelligent manufacturing of domestic and foreign steel companies and the strategy of intelligent manufacturing of main suppliers abroad and Big River Plant. The development strategy of intelligent manufacturing of the domesticated steel companies for the future was provided.

NbC morphology of carbon round steel in niobium microalloying was studied and analyzed after rolling. According to the study, when the mass fraction of niobium in medium carbon steel is 0.03%, niobium carbide above 5 μm will be precipitated in the process of continuous casting solidification.When the heating temperature of billet rolling is about 1 250 ℃ and the holding time of high temperature section is more than 4 h, the solution of micron grade niobium carbide can be obtained.

Longitudinal cracks are typical surface defects of slabs, which seriously affect the quality of casting slabs and process progression. The identification and prediction of longitudinal cracks is of great significance to improve the quality of the cast slabs. According to the dynamic evolution and one-dimensional propagation characteristics of the mould thermocouple temperature in time series during the formation and propagation of longitudinal cracks, the typical variation trends of the thermocouple temperature in time series under longitudinal cracks and normal conditions were captured and extracted. Dynamic Time Warping (DTW) method is used to measure the similarity and difference of time series temperature under different working conditions, and k-Nearest Neighbor (kNN) classification algorithm is used to establish online identification and classification model for longitudinal crack of continuous casting billet.The results show that the model has a high accuracy rate for the identification of longitudinal crack and normal condition samples, which provides a reliable way for real-time detection and accurate prediction of slab longitudinal cracks.

Mould fluxes play an important role in production of defectless casting strands, ensuring the refinement of the constant speed and highly efficient continuous casting. Mould fluxes technologies have made great progress with the rapid development of steelmaking and continuous casting. Many studies have been done to deepen and systematic the function mechanism, performance control and the abilities of keeping the smooth running of continuous casting and improving the quality of casting strands. At present, the mould fluxes technology, on the whole, can satisfy the production requirements of continuous casting in China. However, there are still many works to do in increasing investment in research and development, and stabilizing the conditions of raw materials and production process, etc. The mould fluxes technologies, which include the match of the mould fluxes and the continuous casting process, basic researches, the development of kinds, production and market situation, selection of mould fluxes, etc, have been analyzed in this paper. Meanwhile, some thoughts about the further development of mould fluxes have been put forward.

In order to solve the problem that the continuous casting parameters of Q355B slab in a steel plant do not match with each other when the casting speed is increased, ProCAST software was employed to establish the solidification heat transfer model of the slab, and the solidification characteristics of the slab under different continuous casting parameters were studied. The results show that the casting speed has the greatest influence on the slab solidification, followed by the specific water flow rate, and the smallest is superheat in the calculated range. With the increase of casting speed or the decrease of specific water rate or the increase of superheat, the slab temperature, the solidification end and the length of two-phase zone increase to different degrees except the shell thickness. In the actual production process,it is found that changing the casting speed billet production without changing the specific water volume and the position under light pressure, the three failed to effectively cooperate with each other, resulting in serious intermediate cracks. Based on simulation results, when the casting speed is increased to 1.0 m/min, the specific water flow rate is increased from 0.38 L/kg to 0.55 L/kg, as a result, the generation ratio of intermediate crack is reduced from 70% to about 11%, and the center segregation of slab above the level of C1.5 increases by 24.5%.

The paper studied and analyzed the using of calcium treatment technology in CSP production, the production scene is combined, the practical datas of change area scope of calcium and Ca/Als are counted and analyzed, the reasonable scope of technology target is put,

Electromagnetic stirring has great effect on the flow field in the mold and the behavior of steel/slag interface, a physical model of slab mold with similarity ratio of 1∶5 and a mathematical model were built to investigate the effect of electromagnetic stirring (EMS) current on the flow field, the freezing index (R_f) and slag entrapment index (R_e) were introduced to evaluate the probability of meniscus freezing and slag entrapment, respectively. The results indicate that the flow field measured by physical model can be using as the validation for mathematical simulation. When EMS is not applied, the flow field within the mold is a classical double-roll structure, the flow velocity at free surface is relatively small, the freezing index and slag entrapment index are 0.52 and 0, respectively. The flow field changes significantly for the case with EMS, a horizonal recirculation flow has generated in the upper part of mold, the flow velocity at free surface increases. With the increase of EMS current, the recirculation flow enhances, the freezing index decreases while the slag entrapment index increases, as the EMS current increases to 700 A, the freezing index and slag entrapment index change to 0.04 and 0.245, respectively. Therefore, considering the slag entrapment index and meniscus freezing index, the optimizing stirring current is 600 A.

The development history and field application of process control (level 2) system of continuous casting are discussed. Based on the characteristics of continuous casting process and the corresponding functional requirements, the status quo and shortcomings of the functional positioning, data generation and application of process control system in this process are discussed. The requirements for the continuous casting process control system are investigated in the light of the current digital and intelligent development requirement, and the structure, functions, development and data processing characteristics of the continuous casting process control system are discussed. On this basis, the future development direction of continuous casting process control system is further prospected, and the development suggestions of process control system are put forward.

Mainly introduced the problem about corner crack of low silicon boron steel in the production practice of plate manufacture department of Rizhao steel. It reduced slab corner cutting rate and production cost， improved the efficiency of enterprises in the practical production， through controlling the continuous casting machine equipment precision， nitrogen content in steel and using chamfering crystallizer.

According to the principle of similarity, a 1∶3 ladle physical model was established for the control of 100 t ladle casting in a steel mill. The hydraulics simulation method was used to study the lathe height and production process conditions. The relationship was compared with the judgment of the residual steel quantity predicted by the actual production of the steel mill. The results show that with the increase of the amount of steel, the starting and through height of the vortex first decrease and then increase. The residual steel quantity corresponding to the through-through height obtained by the simulation experiment is equivalent to the prediction and judgment value of slag in actual production. Casting process, blowing Ar flow only within a certain range, with the increase of blowing Ar flow, vortex height decreased, and the critical blow to wear height increases, there is proper blowing Ar flow, puckering blowing Ar appropriate flow rate of 18.0 L/min, the corresponding spin height is 42.6 mm, the residual amount of steel 4.9 t, double orifice blowing Ar appropriate single-hole flow of 17.4 L/min, the corresponding spin height is 40.3 mm, 4.6 t the residual amount of steel; Single-hole Ar blowing effect is slightly worse than double-hole Ar blowing effect.

In order to study the effect of rare earth （RE） on the composition and morphology of inclusions in HRB400E steel, the possible inclusions in the treated steel were calculated by thermodynamics, and the inclusions in HRB400E steel before and after rare earth treatment were characterized and analyzed by SEM and EDS. The result showed that Rare earth can be added in the smelting process of screw steel and the amount of added rare earth can reach 0.003 2%; the rare earth can purify the molten steel and reduce the S content of the steel from 0.018% to 0.004% by 77.78%; When the content of rare earth is 0.003 2%, the results of the thermodynamic show that order of the possible inclusion formation in the steel is REAlO₃>RE₂O₂S>Al₂O₃. The rare earth element plays a certain role in the modification of sulfur and oxygen inclusions. The inclusions are modified into RE₂O₂S and REAlO₃,the combination of rare earth elements and S reduces the precipitation of MnS inclusions in steel, which improves the properties of the steel．

The core process and key equipment of special steel bloom caster in a plant was discussed, the key equipment, technical points and process practice of controlling slab quality were expounded, emphatically described the important role of light and heavy reduction process in improving the internal quality of bloom, and introduced in detail the metallurgical effect of the caster in producing typical high carbon steel. The production practice shown that the central segregation of bearing steel can be significantly reduced, the central porosity can be improved and the central shrinkage can be eliminated by determining the reasonable soft and hard reduction interval and reduction process parameters under the condition of keeping the production drawing speed constant. The typical steel GCr15 produced by bloom caster was poured at a constant casting speed, the carbon segregation index of billet was between 0.97-1.06, the proportion of central porosity not greater than 1.0 is 100%, and there was no central shrinkage defect.

Taking the mold of 230 mm×1 600 mm slab continuous casting machine as the research object, the VOF model was established by CFD numerical simulation method, and the influence of continuous casting nozzle nodule on steel slag interface fluctuation and molten steel flow behavior was studied. The results show that the flow field in the mold is a typical double circulation morphology when there is no nodule at the nozzle.When there is nodule at the nozzle, there will be serious asymmetric flow on both sides of the nozzle in the mould, with a small range of nodule side stream and a large range of non-nodule side stream. The increase of kinetic energy on the non-nodular side of the nozzle leads to the decrease of the vortex center under the mold, which will increase the impact depth of the molten steel. In addition, due to the high vortex center on the nodule side of nozzle, the fluctuation of meniscus surface and steel slag surface is disordered. In the case of nodules, the steel fluid fluctuates greatly, with the maximum fluctuation difference of 4.03 mm. Without nodules, the fluctuation of molten steel is relatively stable, with the maximum fluctuation difference of 1.4 mm.

Chamfered mold has greater risk than the conventional mould in the process of on hot mold width adjustment,because of the temperature and thickness of the shell at the corner are quite different from the conventional mould. This problem can be solved by controlling the inclusions, the cooling and supporting of narrow slab and optimizing the width adjustment mode etc.

The slag crust not only deteriorates the effect of tundish metallurgy, but also hinders the development of smart continuous casting in the steel plant. In order to solve the solidified crusts of tundish fluxes, the effects of steel temperature, composition and melting point of tundish fluxes, and casting heats on the solidified crust at tundish stream zone were investigation in detail. The results show that fluxes thickness and thermal insulating property were the main factors for solidified crust at the tundish stream zone. For the poor fluxes thermal insulating property, the surface of tundish fluxes was melted during the ladle initial pouring stage. With the casting heats increasing, the thermal resistance of the tundish fluxes increasing, resulting in resolidating of the surface fluxes. In order to improving the insulating property of the upper tundish fluxes, the lower specific weight carbonized rice husks were chosen as heat preservation agent instead of carbonized rice ball, preventing the surface of tundish fluxes melt during the ladle initial pouring stage. After implementation, the solidified crust rate of the tundish fluxes in the No.1 continuous casting plant and No.2 continuous casting plant decreased from 47.3% and 35.3% to 15.0% and 10.7%, respectively.

Corner transverse cracks of HRB600 （E） steel slab with high strength threads produced by converter-refining-continuous casting （full water continuous casting machine） process are studied. The results show that the transverse corner cracks of HRB600 （E） billet are formed in the mould. It is concluded that the transverse corner cracks can be effectively solved by means of weak cooling, controlling casting speed, selecting reasonable flux and rational secondary cooling distribution ratio. After optimizing the process, the transverse corner cracks of the billet are basically eliminated, and there are no quality defects such as warping and scarring in the rolled products.

09CrCuSb steel is widely used in the manufacturing industry of economizer, heat exchanger and other equipment due to its excellent sulfuric acid dew point corrosion resistance. However, 09CrCuSb steel is prone to surface cracks during continuous casting, which seriously affects the yield, so it becomes an urgent problem to be solved. Through the analysis of metallographic microscope and scanning electron microscope, it was clear that the cause of crack defects under the original process parameters was the precipitation of Cu and proeutectoid ferrite on the grain boundary of the billet surface. By increasing the mold water flow rate from 2 166.67 L/min to 2 666.67 L/min, the mold electromagnetic stirring current from 400 A to 450 A, the specific water volume of the secondary cooling system from 1.10 L/kg to 1.20 L/kg, the casting speed from 2.5 m/min to 3.2 m/min, and applying the thermal insulation device within the range of in and out tension leveler, the precipitation of Cu and proeutectoid ferrite on the grain boundary of the billet surface layer is effectively inhibited. As a result, the excellent surface quality of the billet is obtained, and the qualified rate of magnetic particle flaw detection of rolled round steel is increased from 19.19% to 99.07%. The idea and development practice of 09CrCuSb steel billet crack control provide a new idea for the billet crack control of the same series of low carbon steel containing Cu.

In order to control the transformation of non-metallic inclusions in Q195 steel during solidification and cooling, the transformation of inclusions in practical production process was studied by ASPEX automatic scanning electron microscope, and the thermodynamic principle of the transformation was calculated by FactSage software. The results show that inclusions in molten steel of Si-Mn-Al deoxidized Q195 hot rolled strip are mainly SiO₂-MnO-Al₂O₃. There is a sharp increase in sulfide inclusions in bloom after solidification and cooling. An increase of SiO₂ and an decrease of MnO in oxide inclusions can also be detected. The composition of inclusions in steel have obvious corresponding relationship with the size of inclusions, which is that the content of Al₂O₃ in inclusions increase with diameter of inclusion, while the content of SiO₂ decreases. As the size of the inclusion in bloom decreases, content of sulfides and SiO₂ in oxide inclusions have a dramatic increase. Thermodynamic calculation by FactSage indicates that SiO₂, Mn₂Al₄Si₅O₁₈ and MnS precipitate during solidification and cooling of steel, and the size of precipitated phase is generally small, which results in the increase of content of SiO₂ and MnS in small size inclusions. Thermodynamic theoretical calculation can explain the transformation of inclusion composition duiring solidification and cooling process.

Tundish is the last refractory container before the molten steel solidifies. It is the connection point from intermittent operation to continuous operation and the starting point of continuous casting. It plays a role in buffering, decompression, diversion, continuous casting, purification and protection of molten steel, improving the solidification structure, and promoting the uniformity of molten steel during continuous casting. With the improvement of the cleanliness and quality requirements of high-quality steel, the function of tundish metallurgy is becoming more and more important. The development of tundish metallurgical technology is centered on the continuous expansion and improvement of tundish metallurgical functions. Its core goal is to fully purify the molten steel before solidification, and to realize constant temperature and low superheat pouring of continuous casting. The technical approaches and development trends to realize tundish metallurgical functions are summarized.

Principle and fault diagnosis of DANIELI continuous casting machine fan segment hydraulic control were briefly introduced, which is of guiding significance to the daily maintenance and transformation of the hydraulic control system.Through the control of the roll gap at the entrance and exit of each sector, the control of the light pressure was realized.

The submerged start-up of ladle shroud inserted into tundish is an important means to eliminate the secondary oxidation of molten steel and improve the quality of molten steel in continuous casting process. However, the submerged start-up is easy to lead to the return of steel at the bowl of shroud. In view of the steel returning from the ladle shroud immersed open casting bowl, the specific causes were summarized from two aspects of equipment accuracy and process operation through on-site tracking analysis. The analysis results show that the ladle shroud immersed open cast steel return is related to the process operation method, the manipulator precision and the bead unseating precision. By improving the operation mode of wearing shroud, reforming the manipulator and detaching ring, standardizing immersion depth and other measures, steel return rate of ladle shroud is reduced from 0.2% to 0, and qualified rate of nitrogen increase of all steel grades is increased from 94% to 98%.

Carbon macro-segregation of gear steel will aggravate the strip grade and affect the heat treatment deformation of gear. The most fundamental solution is to control the carbon segregation of continuous casting billet. Under the appropriate casting process speed, the technical means of optimizing the mold electromagnetic stirring parameters, dynamic end electromagnetic stirring, controlling the superheat of molten steel and optimizing the secondary cooling water distribution are adopted to improve the carbon segregation index and carbon range of continuous casting billet section. The results show that the selection of suitable continuous casting process parameters and dynamic end-stirring technology can substantially improve the internal quality of the cast billet and reduce the macroscopic carbon segregation of gear steel SAE8620H to the level of nine-point carbon polar difference no more than 0.025% and carbon segregation index 0.95-1.05, and effectively reduce the gear steel strip grade. At the same time, the heat treatment deformation of rolled round steel processed into gears is small and the deformation trend is good,The quality of products has been recognized by customers.

Round billets are widely used in the fields of wind power generation, petrochemical industry and machinery manufacturing. However, the problem of inclusions is the bottleneck of continuous casting of large round billets, which restricts the further improvement of the quality of large round billets. In order to improve the removal rate of inclusions, a three-hole swirl nozzle was proposed. Based on the large eddy simulation method, a three-dimensional transient mathematical model of the round billet mold was established, and the VOF method was used to describe the fluctuation of the slag-gold interface. The influence of the nozzle structure on the flow field of the crystallizer was studied. The research results show that when the swirl nozzle is used, there are many vortices of different scales in the upper part of the mold, the flow field distribution is relatively uniform, the fluctuation at the slag-gold interface is stable, and the speed is about 0.1 m/s. However, when the straight nozzle is used, the velocity of the flow field in the upper part of the mold is very small, and the fluctuation of the slag-gold interface is basically stagnant, which is not conducive to slag removal. In addition, due to the deep jet depth of the straight-through nozzle, the inclusions are not easy to float, and the inclusion removal rate is only 2.05%. The jet depth of the swirl nozzle is shallow, and the annular flow formed in the molten steel can effectively promote the inclusions to float up to the slag-gold interface, so the inclusion removal rate is high, reaching 10.52%. In summary, the three-hole swirl nozzle improves the flow state of molten steel, activates the slag-gold interface, and is beneficial to purifying molten steel, which has certain reference significance for the production of large round billets.

Production process of high efficiency continuous casting of general steel was studied and analyzed， and it is concluded that the main problems of high efficiency continuous casting are steel leakage，internal defects of slab and billet rhomboidity. By means of improving the spot-shaped high efficiency mould and high drawing speed protection slag， optimizing the water distribution of secondary cooling ratio， reducing the superheat of steel and the pressure of drawing straightener， the drawing speed of 160 mm×160 mm billet continuous casting was improved， and the maximum drawing speed was increased from 3.2 to 3.7 m/min. The billet steel leakage， internal quality and billet rhomboidity are also controlled at a better level.

Accurately predicting the defects such as cracks and center segregation of continuous casting strand and making a choice between offline cleaning and hot delivery are of great significance to stabilize the continuous casting production and improve the production quality. However, there are many factors affecting the quality of continuous casting strand in actual production. There are unpredictable disturbances in continuous casting production, and there is strong nonlinearity and coupling between production parameters, which makes the accurate prediction of the defects such as crack and central segregation of continuous casting strand very challenging. With the development of the continuous casting automation and computer technology, artificial intelligence has been paid more and more attention, among which machine learning has been gradually applied in the continuous casting production because of its strong nonlinear approximation ability. The research progress of the strand quality prediction at home and abroad are summarized from the aspects of the machine learning and expert system, and the advantages and disadvantages of various methods are analyzed and compared. Meanwhile, the quality prediction of continuous casting strand is prospected.

High casting speed is the necessary condition for realizing low-cost and green production of deformed steel bars in billet caster, and it is the embodiment of the overall technological progress of continuous casting. After the billet caster of Fujian Sangang steelmaking plant has been transformed with high efficiency, casting speed with 160 mm×160 mm section deformed steel has the ability to reach 6.0 m/min. When screw thread steel with 160 mm×160 mm section billet is increased to 4.1 m/min in the production process, steel leakage and billet breaking accidents occur. Through comprehensive analysis of the mechanism and influencing factors of breakout accidents by means of investigation and tracing, it was found that mold vibration process, immersion nozzle insertion depth and mold powder performance parameters were the main factors causing breakout, and the qualitative and quantitative influence rules of three factors on breakout were studied from the perspective of mechanism and model. The results show that the lubrication state of the mold has a decisive influence on the stable production of high casting speed under the condition of uniform and strong cooling of the mold, and the appropriate vibration process is the limiting factor. After technical measures of the optimized mold vibration process(the average demoulding rate is greater than 20 mm/s), immersion insertion depth(120 mm) and mold powder are adopted(alkalinity 0.9, melting point 1 020 ℃, viscosity 0.23 Pa·s), casting speed of screw thread steel with 160 mm×160 mm section billet is finally increased from 4.1 m/min to 6 m/min, and no breakout occurred.

Based on the problems of center crack, triangle crack and product elongation deficiency of DL350 billet of titanium microalloy steel of Delong Company, the heat transfer model of billet was established by the optimization system of secondary cooling water distribution combined with the metallurgical limit criterion, and the optimization of secondary cooling water distribution was studied. ANSYS simulation was used to simulate the temperature of different specific water volume at 0.9-1.2 m/min. The results show that the simulation and experiment are in good agreement, and the quality of casting billet with specific water volume is improved after optimization. According to the drawing speed correlation water distribution method, the optimal specific water volume of 0.9, 1.0, 1.1, 1.2 m/min at different drawing speeds are 0.68, 0.73, 0.77, 0.80 L/kg. In production, the correctness of the simulation is also verified. From the morphology of the low magnification for billet produced after optimization, the defects of the billet great elimination, the surface and internal quality of the billet meet the needs of rolling technology, and finally the elongation of the product is improved and the production needs are met.

In order to fully consider the influence of filters and flow stabilizers on the internal flow field of high-pressure scale-removal nozzles, numerical modeling of full-size scale-removal nozzles and study of the internal flow field characteristics were carried out using CFD. The influence of nozzle structure and inlet pressure on the internal flow field characteristics of the nozzle was analyzed to reveal the characteristics of the flow field distribution in the central axis and to clarify the mathematical relationship between the exit velocity and inlet pressure. The results show that, compared with the simplified model, the internal pressure of the full-size model is lower, and there is a deviation of (2-4) × 10⁵ Pa between the two.For the full-size model, the internal pressure decay of the nozzle mainly occurs at the end of the shrinkage section and the nozzle outlet, where the pressure decay is about 0.6 MPa when the water flows through the filter and stabilizer. For different regions, the same conditions, the speed of the nozzle section. The change is much greater than the filter and shrinkage section. With the increase in the inlet pressure, the internal flow field pressure decay gradually increased, while the entire internal flow field speed also increased accordingly, and the greater the pressure, the more obvious the change in speed, that is, the nozzle inlet pressure and exit speed to meet the positive correlation.

Nodulation phenomenon of aluminium deoxidized sulphur-containing QC40 steel in a certain factory was analyzed.By scanning surface electron microscopy and energy spectrum analysis, it was found that the nodules were divided into two layers. The nodules near the inner layer of the nozzle were mainly MgO·Al₂O₃, high melting point CaO-Al₂O₃ and low melting point CaO-Al₂O₃. The nodules in the second layer are mainly MgO·Al₂O₃, CaO-Al₂O₃ with high melting point and CaS.The inclusions in the bar are mainly MgO·Al₂O₃, CaO-Al₂O₃ with high melting point and CaS inclusions.Analysis that appear this kind of phenomenon of nodular CaS belongs to high melting point is the cause of inclusion, but the liquid steel and wetting angle of 87° （less than 90°）, belongs to the wettability of molten steel and inclusion, Al₂O₃ and MgO style and high melting point CaO-Al₂O₃ and contact angle of liquid steel is greater than 90°, belongs to the high melting point and inclusion with poor wettability of molten steel, thus the CaS inclusions can only in the second the phenomena.The FactSage software was used to theoretically optimize the calcium treatment process of aluminum deoxidized sulfur-containing steel, and it was believed that by optimizing the calcium treatment process and reducing the secondary oxidation, the nodulation behavior of the immersed nozzle could be reduced or even eliminated.

Increasing the equiaxed crystal ratio (ECR) is essential for the solidification quality of thin steel slabs during the high-speed continuous casting process. A three-phase solidification model was adapted to numerically predict the flow mode and ECR of a three-dimensional full-size thin slab continuous casting process. The effect of the switching period of strand electromagnetic stirring (SEMS) on ECR was analyzed. The results showed that the molten steel solidified rapidly in the funnel-shaped mold, and the solidification rate at the mold outlet reached 37%. Two recirculation zones formed in the molten pool when the electromagnetic stirring direction was fixed, which were separated by superheated molten steel. The liquid steel in the core of the upper recirculation was in a supercooled state. The flow pattern in the secondary cooling zone was composed of four or even five vortices after the stirring direction changed. ECR increased first and then decreased with the switching period of SEMS. ECR increased most significantly when the switching period was 16 s, which was increased by 17% compared with that of fixed stirring. And the distribution of the equiaxed phase became more uniform.

Aiming at the problems of complex system, expensive equipment and high maintenance cost of non-sinusoidal oscillation device for mold driven by hydraulic servo cylinder, a new type of mold non-sinusoidal oscillation technology with eccentric shaft linkage driven by servo motor was proposed. Firstly, the working principle to realize the non-sinusoidal oscillation technology was described. Secondly, the method for determining the rotation rule of servo motor was given. And for a non-sinusoidal oscillation waveform function, the servo motor rotation speed formula was given. Finally, on the prototype machine, the experiments were carried out. The results show that the servo motor-eccentric shaft-linkage system can realize the non-sinusoidal oscillation waveform precisely, and the equipment runs smoothly. The technology of non-sinusoidal oscillation driven by servo motor-eccentric shaft-linkage system has many advantages, such as lower equipment cost and maintenance cost, the long maintenance cycle, and equipment moving smoothly. This technology can be adapted to high casting speed and helps to promote the slab surface quality. It has the market prospect and the value of popularization.

As a novel macro-examination method, dendrite corrosion macro-examination demands higher requirements for the surface roughness and the preparation efficiency of steel billet specimens. The specimens were ground by an abrasive belt machine. The operation duration and the variation of surface roughness were investigated to determinate the optimum process for preparing steel billet specimens by abrasive belt grinding. The results show that for the specimens with a bumpy surface, the abrasive belt with mesh number 24 (700 μm) can be used to quickly remove the oxide layer and obtain a smooth and flat surface, which reaches the same effect as that by the milling machine. The abrasive belt with mesh number 120 (120 μm) can be used as the initial one to fine grind the flat surface. The grinding directions of the two successive abrasive belts remains vertical. With the mesh number increasing, the surface roughness gradually decreases. After completing grinding with the mesh number 2 000 (6.5 μm), both the horizontal and vertical surface roughness can reach less than 0.1 μm, which meets the requirements of the dendrite corrosion macro-examination. During the fine grinding, it is requisite to grind the specimens for a longer time when using the initial mesh number or the mesh number higher than 600 (23 μm), to ensure the fine grinding effect on the specimen surface. Thus, by abrasive belt grinding, the specimen preparation for the dendrite corrosion macro-examination can be efficiently completed.

In order to study the formation and evolution of non-metallic inclusions in 27SiMn steel, the production status of a steel plant was systematically analyzed. The evolution behavior of inclusions in each stage of “LF inlet→before calcium treatment→after soft blowing→tundish→slab” was explored through industrial experiments. According to the current situation of calcium treatment of 27SiMn steel, the Al-Ca equilibrium reaction in the molten steel treated with calcium was calculated by thermodynamics. The results show that the inclusions before calcium treatment are mainly CaO-MgO-Al₂O₃ ternary inclusions, and the mass fraction of Al₂O₃ is about 67%. After soft blowing, in the ternary phase diagram of CaO-MgO-Al₂O₃ system, the mass fraction of Al₂O₃ was reduced by about 35%, and the inclusions moved to the side with high CaO mass fraction on average. In the ternary phase diagram of CaS-CaO-Al₂O₃ system, the inclusion composition does not enter the liquid phase region because of the high CaS mass fraction in the inclusion composition, which is about 21%. In the casting process, most of the inclusions were transformed into spherical CaO-MgO-Al₂O₃-SiO₂ composite inclusions, and a large number of CaS inclusions were observed. Through thermodynamic analysis, at 1 873 K, when w([Al])=0.022% in steel, w([Ca]) is controlled between 0.001 3% and 0.003 5%, which is in the region conducive to the formation of 12CaO·7Al₂O₃, which can improve the liquid modification effect of inclusions. At the same time, in order to prevent the precipitation of pure CaS inclusions in molten steel, w([S]) should be controlled below 0.004 8%.

Aiming at the problem that abnormal cooling intensity in unsteady continuous casting is easy to lead to defects in slab quality, an improved genetic algorithm was proposed to optimize the casting speed and cooling water from the perspective of system cooling. Based on the analysis of the industrial continuous casting data of a Chinese steel plant for three months, it was found that the unsteady continuous casting, such as the beginning casting, ending casting, change the nozzle, and change the tundish, due to the poor coordination between the casting speed and cooling water, leads to insufficient cooling intensity, which affects the quality of slab and continuous casting efficiency. The genetic algorithm was improved from the aspects of optimization objective and selection operator, so as to improve the convergence speed and optimization ability of the model while generating feasible solutions. The results show that the model optimization scheme met the industrial process rules, and the average heat release of the unsteady continuous casting system was increased from 45.87% to 49.05%, which is within a reasonable range, by appropriately increasing the secondary cooling water flow rate. This optimization method could guide the production control for the continuous casting system.

In view of the unstable quality of 20CrMnTiH gear steel large round bloom with diameter of ø650 mm, the effects of continuous casting process parameters on the macrostructure and carbon segregation of the round bloom were analyzed by comparing the electromagnetic stirring of the mold and the specific water flowrate of the secondary cooling. The results show that under the conditions of 200 A/1.5 Hz of electromagnetic stirring in the mold and 37/26 (0.101 L/kg) of specific water flowrate of the secondary cooling, the center equiaxed crystal ratio of the casting bloom is higher, and the carbon element distribution is more uniform, and the maximum carbon difference is 0.01%. Therefore, the adoption of this parameter can keep the center equiaxed crystal ratio of the round bloom for gear steel 20CrMnTiH and decrease the macro segregation fluctuation.

More high surface temperature is the necessary prerequisite to implement direct rolling process for billet. A feasible process design scheme and process parameters control has been put forward by discussing the influence of casting speed, cooling intensity, caster size,semi-production length, cutting type, heat cover and roller speed of direct hot charging.

The Ds inclusions containing ZrO₂ found in the products of a factory were systematically analyzed and studied, The results show that decarburization of Zr-containing immersion nozzles leads to the inclusion of ZrO₂-containing Ds inclusions. The CaO-Al₂O₃ （-MgO） phase is derived from the decarburization channel. The SiO₂ in the CaO-Al₂O₃-SiO₂ （-MgO） phase will be reduced by Al in the molten steel,ZrO₂ only acts like a tracer.

In order to study the influence of out of squareness and surface cracks on the quality of the slab, this paper adopts the methods of improving the matching of mold flux and steel grades, adjusting the distance between the water gaps of the mold and optimizing the secondary cooling process through theory and production practice. The effects of different Big R angle copper pipes on surface cracks were compared, and the mold was optimized to suppress cast-off and surface cracks. The results show that in the practice of optimizing the surface quality of 220 square billets with large R-angle copper tubes, rationally controlling the cause of out of squareness and effectively controlling the surface cracks of the billet can stably improve the quality of the billet.