Most of the existing EAF end-point carbon prediction models ignore the influence of the remaining carbon mass in the EAF on the carbon content at the end of the next heat, and the thickness of the slag layer during EAF smelting is thick, and the molten steel splashes violently during smelting. If the composition of molten steel is not uniform, there will be a large deviation between the carbon content detected by the end point sampling of the electric arc furnace and the actual carbon content in the molten steel.If the carbon mass fraction sampled by the electric arc furnace is directly used as the analysis data, the predicted value of the model often deviates from the actual carbon content in molten steel. Aiming at the above problems, the multiple linear regression was used to calculate the yield of iron and steel materials, and the remaining amount of steel in each furnace was calculated. Then, a BP neural network was used to propose a predicition method for the carbon content at the end of the electric arc furnace. Experimental analysis showed that the error between the predicted value of the carbon mass fraction at the end of the model and the actual value was within ±0.02 %, and the hit rate reached 92 %, which had a high prediction accuracy.

Increasing the proportion of equiaxed grains and refining the microstructure are of great significance to improve the mechanical properties of steel. In this study, AISI4130 steel was treated with magnesium. SEM, macrostructure observation and microstructure analysis were used to analyze the internal mechanism of the influence of Mg on inclusions control, solidification structure and microstructure of steel. The results show that the proportion of equiaxed grains increases and the average grain size decreases after Mgtreatment. When the Mg mass fraction is between 0.002 %–0.006 %, the proportion of equiaxed crystal increases with the increase of magnesium content.After Mg-treatment, the Al₂O₃, MnS had changed to Al-O-Mg-Mn-S,When the content of Mg is high, the MgS-MnS becomes the most important inclusion in the steel. In the Mg-treatment steel, the density of inclusions of 1-2 μm increased significantly, and the proportion of inclusions of more than 5 μm decreased. The steel after Mg-treatment has acicular ferrite at Mg-O inclusions grow core. The microstructure of AISI4130 ingots with Mg mass fraction of 0.009 % and 0.023 % is staggered fine acicular ferrite, and its impact toughness are significantly improved, and the average impact energy is about three times that of non-Mg-treatment.

In order to analysis the formation of inclusions in 18Ni350 steel, based on the theory of minimum Gibbs free energy, the equilibrium solidification process and the precipitation behavior of the inclusion particles were investigated by using thermodynamics software FactSage under the specific composition. The effect of composition on precipitation process was studied. Meanwhile, ASPEX and SEM-EDS were used to detect the composition and size distribution of inclusions in the samples before and after magnesium treatment. The inclusions in the samples were mainly Al₂O₃-Ti₂O₃ series. The inclusions size was refined after magnesium treatment and the inclusions were with MgAl₂O₄ as core normally. It played a heteronucleation role in the formation of complex inclusions. The results provided important theoretical significance for the formation and control of inclusions in the molten pool of 18Ni350 steel.

Reducing the emulsification degree of the slag-steel interface in the continuous casting mold is very important to reduce the slag entrainment and improve the quality of the slab. In order to reveal the formation mechanism of the emulsification behavior and the fluid structure of emulsification, the emulsification behavior of the slag-steel interface in the argon blowing continuous casting mold was studied by water model experiments, the effects of mold section size, casting speed, argon flow rate and nozzle immerge depth on the emulsification behavior of the slag layer were analyzed. The results show that the retention of argon bubbles and droplets in the slag phase and the violent fluctuation of the slag-steel interface can promote the emulsification behavior. After the emulsification is complete, there will be three flow structures of smooth stratified flow, flocculated stratified flow and flocculated wave emulsification flow. By analyzing the thickness of the slag layer and the fluctuation of the liquid level, it is found that reducing the cross-sectional size of the mold, increasing the casting speed, increasing the argon flow rate and reducing the depth of the nozzle will aggravate the emulsification of the slag-steel interface. 

In order to optimize the flow pattern of molten steel in the continuous casting tundish to effectively remove nonmetallic inclusions，a multi-hole flow control device with different apertures was proposed in this study.A 1∶4 hydraulics model experiment was conducted to simulate a 70 t two-strand slab continuous casting tundish to measure RTD curves and a three-dimensional numerical model was established to analyze the flow field. The effects of the casting speed and the installation position of the flow control device on the flow characteristics of the molten steel in the tundish were studied，and the optimal combination of flow control devices was obtained. The results show that the flow rate is improved, the path of the fluid flow can be prolonged, the average resistance time is prolonged and the dead zone volume fraction is decreased. The flow control device of S_f=4 has the best effect on improving the flow field when the distance between the flow control device and the weir is 150 mm, and when the casting speed is 1.0，1.2，1.4 m/min，the dead zone volume fraction decreases 17.42 %, 15.55 %，28.72 %，the peak time is prolonged by 75, 41，56 s, the average residence time is prolonged by 78, 87, 126 s, respectively. 

Aiming at the serious wear of the copper plate of the mould of the ultra-wide slab continuous casting machine, the reasons were analyzed in combination with the actual situation of the production site and the improvement measures were proposed. By controlling the runout of the foot roller to be no more than 0.5 mm, the accuracy of the zero section and the first section of the segment was increased to ±0.30 mm, which significantly reduced the wear of the wide surface of mould. The coating material of copper plate used a cobalt-nickel alloy, and the surface used thermal spraying surface modification technology and a heat treatment process, the hardness of the coating was increased from the highest 276 HV to 391 HV, an increase by 41.7 %, which enhanced the wear resistance of the coating. After adopting the above measures, the service life of the mould of the ultra-wide slab continuous casting machine can be stabilized to over 800 furnaces, and the improvement effect is obvious.

In view of the low self opening rate of 60 t ladle after VD process in a steel plant, the influencing factors such as hot repair operation, nozzle brick material, steel grade, ladle temperature, molten steel holding time and storage time of molten steel in ladle were analyzed. Due to the long storage time of molten steel in ladle after VD refining, the sintering layer of stuffing sand was thick and the self opening rate of ladle was low.Through the optimization and improvement of the material of the stuffing sand and the comparative test, the self opening rate of the ladle of the improved stuffing sand after VD process reached 99.38 %.

The clogs in SEN and inclusions in steelmaking process were analyzed by electron microscope, energy spectrum and phase analysis equipment. The results show that the large fluctuation range of mold level in W800 low aluminum non oriented silicon steel casting process is mainly caused by the accumulation of Al₂O₃ inclusions in the submerged nozzle. From RH ending to tundish, with the increase of slag oxidizability, the number density of Al₂O₃ inclusions increases gradually. Meanwhile, when w(CaO)/w(Al₂O₃) is less than 1.7 in slag, with the increase of w(CaO)/w(Al₂O₃), the activity of FeO decreases, and the number density of Al₂O₃ inclusions also decreases gradually. The addition of Al₂O₃ inclusions mainly come from the secondary oxidation of molten steel by top slag. The argon blowing flow of the stopper is small, and the inclusions will gather at the nozzle. Excessive argon blowing flow will cause large fluctuation range of mold liquid level. Proper stopper argon flow can effectively control the fluctuation range of mold liquid level. Through slag composition control and stopper argon flow adjustment, the cleanliness of molten steel is significantly improved, the number density of inclusions in tundish molten steel is reduced from 0.41/mm² to 0.35/mm², the compliance rate of mold liquid level fluctuation within ±1.5 mm is significantly increased, and the compliance rate is stable at more than 90 %.

 In order to study the change law of typical inclusions in the smelting process of quenching rails and further improve the control level of non-metallic inclusions in steel, the quenching rail produced by the "150 t converter steelmaking →150 t LF refining →VD degassing → 280 mm×380 mm billet continuous casting" process of a domestic steel mill was taken as the research object, and the smelting process system was sampled, combined with oxygen and nitrogen analysis, molten steel composition analysis and non-metallic inclusion analysis in steel, and its change law was studied from the aspects of inclusion composition, numerical density and size. The results show that the oxygen and nitrogen content and the density of inclusions in the quenching rail smelting process continue to decrease, and the effect of inclusion removal is obvious. The main component of the typical inclusions in LF inlet steel is SiO₂-MnO-Al₂O₃, which is mainly the deoxidation product produced by the converter using silicon manganese deoxidation alloying. The main component of the typical inclusions after LF alloying is CaO-SiO₂-Al₂O₃-MgO, the content of CaO and Al₂O₃ in the inclusions is significantly increased, and the content of SiO₂ and MnO is reduced, mainly due to the reaction of Ca and Al_s brought into the alloy accessories with dissolved oxygen or oxide inclusion in the steel, and the increase in MgO content is related to the erosion of the ladle refractory material. The main component of the typical inclusions in LF outbound steel is CaO-SiO₂-Al₂O₃-MgO, and the content of CaO and MgO in the inclusions is increased, and the content of  Al₂O₃ is decreased. It is mainly the result of the reaction of steel-slag and the transfer to molten steel after the reaction of molten steel and refractory. The typical inclusion core at inner arc 1/4 of the casting blank is Al₂O₃-MgO, and the outer layer is Al₂O_3-SiO₂-CaO. Affected by the addition of alloy accessories and the generation of inclusions and the aggregation and floating of inclusions, the size of inclusions fluctuates periodically over time within a certain range. In the LF and VD stages, due to the soft blowing, the inclusions are reduced in density and the size is increased. The size of the inclusions in the tundish is relatively stable, and the size of the inclusions in the casting blank is significantly increased due to the collision and aggregation of the inclusions in the continuous casting process. Some spinel-like inclusions during the rolling process are brittle, resulting in a decrease in the average size of the inclusions and a slight increase in the number. Therefore, strict controlling the content of Al_s in ferrosilicon and calcium barium silicon, as well as other impurities in accessories material, plays an important role in improving the cleanliness of the quenching rail.

The formation mechanism and evolution of inclusions in SAE8620RH gear steel produced by EAF→LF→VD→CC process in a domestic steel mill were studied by SEM-EDS and thermodynamic calculation. The results show that the oxygen-sulfur composite inclusions in steel mainly exist in the composite form of  MgO·Al₂O₃ as the core and CaS wrapped outside. The experimental results show that the inclusions in liquid steel at the early stage of LF refining are mainly MgO·Al₂O₃, with a small amount of CaS wrapped around the outside. After Ca treatment, part of MgO·Al₂O₃ is modified into liquid calcium aluminate. After VD vacuum treatment, the CaS proportion of MgO·Al₂O₃ coating increased obviously. MgO·Al₂O₃ in the billet precipitates MnS again, forms a composite form of MgO·Al₂O_3-(Ca,Mn)S. Thermodynamic calculation results show that MgO·Al₂O₃ can be generated when the mass fraction of Al in liquid steel is 0.03 % and the mass fraction of Mg is 1.85×10^-6. In the early stage of LF refining, CaS is mainly generated by the direct reaction of [S] and [Ca], while in VD vacuum process, [S] and [Ca] in liquid steel will further reacted to form CaS, and calcium aluminate outside MgO·Al₂O₃ will also reacted with [S] to form CaS.

Tin free-cutting steel is a new environmentally friendly free-cutting steel that is expected to replace lead free-cutting steel. The existing form of tin in steel is an important factor affecting the cutting performance of steel. In this paper，metallographic microscopy (OM)，scanning electron microscopy (SEM)，electron microprobe (EPMA) and other characterization methods were used to analyze the state of tin in high sulfur free-cutting steel and the effect of tin content on the cutting performance. It was found that no significant tin precipitation phase was observed in the tin-containing steel. Tin was soluted in the solid steel matrix，and mainly tended to be soluted in the ferrite. Tin distorted the lattice of the ferrite. The cutting tests showed that when the mass fraction of tin changed from 0 to 1 600×10^-6，the C-type chip ratio increased from 60.19 % to 90.29 % at the cutting speed of 560 r/min. Tin content had a significant enhancement effect on the formation of C-type chip. In cutting the same sample，the proportion of C-type chip was also the largest at cutting speed 560 r/min compared to that at other two speeds，which indicated that the cutting performance was better at this speed. In addition，the addition of tin led to a reduction in surface roughness and better surface quality of the machined sample. The Vickers hardness also increased from 118.2 HV to 143.1 HV with the addition of tin mass fraction from 0 to 1 800×10^-6 by microhardness test. The solid solution of Sn in the steel increased the hardness of the soft steel matrix，which led to a significant improvement of the cutting performance of the steel.

X70MS pipeline steel is mainly used to transport oil and natural gas containing H₂S and other acidic media. Due to its special service environment, pipeline steel is required to have very good HIC resistance. In order to reduce the HIC sensitivity of X70MS pipeline steel and improve its service safety, the HIC resistance performance of X70MS pipeline steel was studied using NACE TM 02842016 hydrogen-induced cracking standard experimental method. The results show that the microstructure of X70MS pipeline steel is ferrite, bainite and M/A island. In the HIC test, each index parameter of cracks meets the requirements of the domestic evaluation standard of X70 pipeline steel for West-East Gas Pipeline Project，and has good resistance to HIC. HIC cracks are caused by the segregation of Al₂O₃ inclusions and C elements in the slab into the steel plate to form a large M/A island carbon-rich structure, the coupling effect between Al₂O₃ inclusions and M/A island structure will aggravate the deterioration of HIC resistance of X70MS pipeline steel, and the number, distribution and size of M/A islands are important factors affecting the HIC resistance of X70MS pipeline steel.

With the accelerated development of China’s stainless steel industry，the stock of stainless steel slag pile increases year by year and is difficult to use. Using stainless steel slag to prepare cement filler is an effective way to absorb a large amount of it. In this paper，the composition of AOD slag was modified by adding fly ash，and the cementitious properties of cement filler prepared by fly ash modified AOD slag were studied. The results showed that after high temperature modification of AOD slag with fly ash，it could form glassy matter after water quenching and quenching. With the increase of fly ash content，the content of glassy matter in modified AOD slag increased. When the mixing ratio of fly ash reached 35 %，the modified AOD slag was glassy matter. The analysis of mechanical properties and Cr leaching concentration of cementitious material showed that when the content of modified AOD slag was 20 %, the 28 day compressive strength of composite cement cementitious material was 54.4 MPa, which met the standard of P.C 52.5 cement. The Cr leaching concentration decreased with the decrease of modified AOD slag content, which was lower than 0.15 mg/L. The modified AOD slag could be safely applied to the field of building materials to realize the resource utilization of waste.