In this paper, it is introduced the online accelerated cooling process test of a type of hot rolled C-Mn seamless steel pipe in 460 production line of Baotou Steel Pipe Co., Ltd.. The test results showed that the effects of online accelerated cooling process on microstructure and properties of test steel were significant, generation of proeutectoid ferrite in two phase region could be restrained by online controlled cooling so that the matrix grains were refined as well as grain size was increased from level 6.5 under non controlled cooling conditions to level 8 and the banded structure of steel was improved. The mechanical properties and impact properties of steel pipe are significantly improved, the yield strength could reach 300~345 MPa, tensile strength could reach 485~545 MPa, average value of longitudinal impact energy at room temperature could reach 102 J, average value of longitudinal impact energy at 0 ℃ could reach 86 J and average value of longitudinal impact energy at -20 ℃ could reach 60 J.

The effects of flow control device on flow conditions of molten steel in tundish are studied with the method of physical simulation through establishing physical model of tundish for double-strand slab caster with geometric similarity ratio of 1∶4 based on the similarity principle. The results showed that the peak time and average retention time of molten steel in tundish were increased, volume of dead zone for molten steel in tundish was reduced due to the optimized flow control device was adopted by tundish of slab. The peak time of molten steel is increased by 240.98%, average retention time of molten steel is increased by 2.37% and volume of dead zone is reduced by 7.56%. As a result, the flow conditions of molten steel in tundish are optimized as well as collision, aggregation, floatation and removal of inclusions in tundish are promoted so that the cleanliness of molten steel is ensured.

The effects of MgO on rheological property of blast furnace slag of Baotou Steel are analyzed by preparing slag specimen with pure chemical reagent under N₂ atmosphere based on the 4^# blast furnace slag of Baotou Steel under laboratory conditions and crude fuel conditions of blast furnace ironmaking production of Baotou Steel. Moreover, the effects of MgO on melting property and enthalpy of blast furnace slag of Baotou Steel are also explored. The results showed that the MgO content of slag was increased from 8.00% to 13.00%, melting temperature of blast furnace slag of Baotou Steel was on the rise, viscosity and viscous flow activation energy showed a trend of first decreasing and then increasing, fluidity and thermal stability of slag became first good and then poor under experimental conditions. In addition, the characteristic temperature of melting property for blast furnace slag of Baotou Steel shows a trend of first decreasing and then increasing as well as enthalpy of slag shows a trend of increasing with the increase of MgO content of slags, which show that the heat storage capacity of slag in blast furnace hearth is enhanced. The MgO content of blast furnace slag of Baotou Steel is suggested to be controlled at 10.00% by comprehensively considering the experimental study results, relevant theoretical calculations and control level of MgO content of existing blast furnace slag of Baotou Steel.

In this paper, the microstructure and macrotexture of Hi-B steel at various stages of production are analyzed with such detection means as Zeiss microscope and X-ray diffractometer. The results showed that the microstructure of Hi-B steel was ferrite at all production stages. The microstructure is completely recrystallized after decarbonizing and nitriding annealing and average grain size is 28.92 μm as well as secondary recrystallization is completed after high temperature annealing and average grain size of finished product is about 2 cm. The texture types in sub-surface of hot rolled plate are mainly three types of typical shear textures. The texture of cold rolled plate is mainly composed of α line texture and rotating cube texture {001}<110>, the texture after decarburizing annealing is mainly α^* texture and γ line texture {111}<112> as well as the macrotexture after high temperature annealing is mainly Goss texture. The texture of Hi-B steel after stretching, leveling and annealing is single Goss texture with accurate orientation as well as its strength reaches peak.

The changes of microstructure for air quench steel slag are studied by observing the changes of various phases in air quench steel slag with time as well as calculating the numbers and area of particles for various phases with the softwares of Photoshop and Image J. The results showed that the phase types of air quench steel slag were not changed with time and diffraction peak intensity was slightly decreased. The number of particles for dicalcium silicate phase in slag is decreased significantly with time and total area of the phase is changed a little. Within 20 days,the average particle size is increased from 4.96 μm to 6.06 μm, while there are no significant changes for other phases. It can be seen that the increase of particle size for dicalcium silicate is due to its own recombination, not the change of other phases. The equation of phase change for dicalcium silicate in air quench steel slag is 1-(1-α)^1/3=0.039 T.

In the denitrification process, flue gas needs to be heated due to the temperature requirements of denitration reaction are high, more blast furnace gas is consumed so that a large amount of CO₂ is generated. In order to achieve the energy conservation and carbon reduction, energy saving type built-in direct fired furnace is used instead of traditional heating furnace. The flue gas is heated with the heat released by igniting the CO in flue gas with energy saving type built-in direct fired furnace so that the consumption of blast furnace gas and carbon emission are reduced as well as temperature requirements of denitrification could be met. The consumption of blast furnace gas is reduced by 17.9% with energy saving type built-in direct fired furnace, annual CO₂ emission reduction of over 35 000 t is achieved and annual cost saving could reach over RMB 4 million yuan through applications and comparisons, which could meet the requirements of energy conservation and carbon reduction for steel enterprises on the premise of meeting requirements of denitrification reactions.

The blast furnace hearth is the key part that restricts blast furnace campaign to over 15 years and the key factor determining blast furnace campaign. The direct causes for temperature rise on side wall of hearth are determined to be aggravated circulation of molten iron and severe erosion of carbon brick through studying erosion mechanism of hearth aiming at the rise of side wall temperature of 5^# blast furnace hearth. The temperature at iron notch of elevation of 8.663 m for side wall of hearth is decreased and basically stabilized at 350~450 ℃ before blowing out, which is within controllable range through taking such preventing measures as setting the early warning standards, strengthening daily management, optimizing standards of depth of iron notch and strengthening maintenance as well as adjusting production and operation parameters based on three-grade early warning.

The effects of riser brick for casting ingot mould used in the smelting equipment of laboratory, vacuum induction furnace on quality of steel ingot are greater. The molten steel in vacuum melting furnace is poured into ingot mould through riser brick and steel ingot is formed after cooling. The flow velocity and angle of the molten steel flowing through riser brick, inclusions in molten steel and inner wall of ingot mould all affect quality of steel ingot. In the paper, the optimization design for structure of riser brick is introduced, which is to add a diversion platform. On the one hand, the scouring force of molten steel to inner wall of ingot mould is reduced so that the service life of ingot mould and surface quality of steel ingot are improved; on the other hand, the retention time of molten steel in riser brick is increased so that the inclusions in molten steel float to be removed and internal quality of steel ingot is improved. The practices prove that the design of riser brick with optimization and transformation is reasonable as well as application effects are good.

The effects of refining slag on cleanliness of liquid steel are very important. Its main functions are improving the deoxidizing capacity of deoxidizing elements, absorbing nonmetallic inclusions in steel and preventing secondary oxidation of liquid steel to generate FeO, MnO and SiO₂. In the process of refining liquid steel, the reasonable composition of refining slag plays a role of adsorbing and removing inclusions in steel. In the process of smelting rare earth steel, rare earth oxides and rare earth sulfides are formed due to rare earth is easy to react with oxygen and sulfur elements in steel as well as rare earth elements could enter refining slag because of the function of potential energy of high oxygen and sulfur for refining slag. In the production process of steelmaking, the contents of each component in ternary refining slag CaO-SiO₂-Al₂O₃ are different and the effects of rare earth on physical properties of refining slag are different because of different deoxidation systems. In the paper, such physical properties of rare earth refining slag when smelting rare earth steel as melting point, viscosity and alkalinity are analyzed by means of testing to predict the physical properties of refining slag, which could provide theoretical basis for improving the level of slag formation, cleanliness of smelting steel grade and yield of rare earth.

The optimized coal blending system for coal injection is independently developed based on considering the physicochemical characteristics, safety performance and processing property of coal injection aiming at the problems in process of optimizing coal blending for coal injection of blast furnace. The coal blending scheme with cost optimization satisfied the constraint conditions of production demands is calculated by adopting the hybrid programming technology of VB+EXCELVBA, invoking such algorithms as plan solution and multiple linear regression as well as taking ACCESS as background database. The production applications show that the system model plays an important role in reducing costs and stabilizing quality for coal injection of blast furnace.