The common 300 series stainless steel smelting process under different raw material conditions was summarized. According to the different raw material structure, there are five kinds of 300 series stainless steel smelting processes widely used at present. The advantages and disadvantages of five kinds of 300 series stainless steel smelting processes were summarized, and the cost differences of five kinds of smelting processes based on production data were analyzed. The results show that the process of intermediate frequency furnace has cost advantage in the process with total cold raw materials. Compared with total cold raw materials, the process cost is better when the main raw material is nickel hot metal in small BF or RKEF (rotary klin electric furnace). Among all the raw materials, the most cost-competitive process is to use nickel hot metal of RKEF as the main raw material. The research results of this paper can provide reference for the selection of raw materials and process flow of 300 series stainless steel production.

Accurate prediction of endpoint phosphorus content can solve the problem that the composition of molten steel cannot be continuously detected during the converter blowing process, promote the rapid tapping of the converter and shorten the smelting cycle.Based on the actual production data of a 100 t converter in a steel mill in Hunan Province, a prediction model of molten steel phosphorus content at the end of the converter based on an ensemble learning algorithm was established. The main influencing factors were determined by analyzing the converter dephosphorization process, and the input variables of the model were determined based on the actual production of the steel mill. The interquartile range method, LOF algorithm and other methods were used for data preprocessing, and the best parameters of the model were determined by combining the 10-fold cross validation method and the grid search method.Four ensemble learning algorithms (RF, AdaBoost, MultiBoosting, and Stacking) were used to establish the models, and  the prediction results of the four models were compared, it was found that the Stacking model had the best prediction effect, with the highest hit rate, the lowest root mean square error and the average absolute percentage error, and the hit rates were 86.08% and 97.84% when the error of molten steel phosphorus mass fraction at the prediction end point was ±0.003% and ±0.005%, respectively.

Based on the oxygen supply parameters of a 100 t converter, a secondary combustion oxygen lance nozzle was designed and the turbulent jet characteristics of the fluid inside the converter were described through  k-ε  model calculation. A secondary combustion oxygen lance nozzle with a diameter of 13.3 mm, a tilt angle of  38°, and 8 secondary holes was design. The nozzle was applied in industrial production under the condition of oxygen flow rate of  24 500-26 000 m³/h and working oxygen pressure of 0.85 MPa. Industrial tests showed that the secondary combustion oxygen lance nozzle could meet the normal requirements for converter slagging. Compared to conventional oxygen lance nozzles, the secondary combustion oxygen lance nozzle had better smelting effect at the upper limit of oxygen flow rate of 26 000 m³/h, which was beneficial for controlling converter splashing and slag overflow. The secondary combustion oxygen lance nozzle could exert the secondary combustion effect of CO in the furnace, increase the temperature of molten steel by 23.80 ℃, increase the scrap ratio by 1.48%, and achieve good application results.

In order to further speed up the scrap heating rate and shorten the smelting cycle, a numerical simulation model of coherent oxygen-fuel mixed jet was established for the short process full scrap EAF steelmaking process. The effects of different oxygen-fuel ratio and different oxygen-fuel flow rate on the dynamic characteristics of mixed gas injection, the length of combustion zone and the position of combustion zone were analyzed. The results show that in the medium and high-grade burner modes, as the oxygen-fuel ratio increases, the outlet velocity and the length of the core section of the potential flow gradually increase, and the position of the beginning of the combustion reaction is delayed. When the oxygen-fuel ratio is 2.2, the length of the combustion reaction zone is the longest, which is conducive to the full mixing combustion of natural gas and oxygen. The gas-phase jet in the low-grade burner mode does not form a potential flow core, which means that the heat released by the combustion process may not be effectively concentrated on the scrap melting. Based on the numerical simulation results, the injection parameters and time of the oxygen-fuel lance were adjusted, the oxygen-fuel ratio was increased from 2.0 to 2.2, and the service time of the low-grade burner was shortened. The smelting data of a complete campaign was statistically analyzed, the power supply time was shortened by 0.7 min, and the natural gas consumption was reduced by 0.29 m³/t. 

To solve the problems of low oxygen supply intensity and long smelting cycle in the 210 t large converter, 10 oxygen lance nozzles were designed and water model test were performed. The results showed that the impact cavity formed by the 5-hole oxygen lance jet had better independence, and under the same oxygen flow rate, its impact depth was greater than that of the 6-hole oxygen lance. Among the ten oxygen lance nozzles, the nozzle 3 and nozzle 4 have the best impact depth. The impact area (radius) significantly increases with the increase of inclination angle, and the nozzle 3, 4, 9 and 10 have better impact areas compared with other nozzles. Therefore, the nozzle 3 was used as the new 5-hole oxygen lance for industrial testing, and the nozzle 9 was used as the new 6-hole oxygen lance for industrial testing. The experimental results were compared with the original 6-hole oxygen lance. The industrial test results show that in terms of phosphorus removal ability, the new 6-hole lance is the best, while the original 6-hole lance is the worst. Compared to the original 6-hole lance, the new 5-hole lance does not have the ability to shorten the oxygen supply time, while the average oxygen supply time of the new 6-hole lance is shortened by 22 s. In terms of lifespan, the new 5-hole lance is not as good as the original 6-hole lance, while the lifespan of the new 6-hole lance is equivalent to that of the original 6-hole lance.Compared to the original 6-hole lance, the new 6hole lance has a significant effect on reducing the total iron content in slag and steel material consumption.

In order to improve the cleanliness of molten steel, control the morphology of inclusions and find a suitable calcium treatment process technology, the thermodynamic calculation of calcium treatment of aluminum-killed steel Q690 was carried out by using FactSage software. The effects of composition and temperature of molten steel on calcium treatment were analyzed. The calcium treatment model of Q690 steel was established, and the minimum calcium feeding amount required for complete liquid modification of inclusions in Q690 steel was obtained. The influencing factors of calcium yield were analyzed, and the calcium yield increased with the decrease of T.O content in steel before calcium treatment. The calcium yield was inversely proportional to the amount of wire feeding, meaning that the lower the feeding amount, the higher the calcium yield. Considering the castability and inclusion removal efficiency of Q690 steel, in order to reduce the risk of nozzle clogging during the casting process and avoid the complete liquidization of inclusions, the appropriate calcium addition amount of Q690 steel was determined to be 25.85-26.92 g/t. The results of industrial test show that after RH calcium treatment, the mass fraction of T.O can be reduced to less than 5×10^-6, and in billet it can be reduced to below 6×10^-6. After calcium treatment, the number density and area fraction of inclusions in the steel remained unchanged, and a large amount of inclusions with high CaS content precipitated in the steel during casting, as a result, the number density and area fraction of inclusions in continuous casting billet increase sharply, the number density of inclusions is about 6-8 per mm², the area fraction is about (150-230)×10^-6, the maximum size of inclusions detected in continuous casting billet is between 10-20 μm, and the cleanliness meets the quality requirements of high quality steel grades.

Ladle bottom blowing is an important component of steelmaking production and plays a positive role in improving the quality of molten steel. A ladle bottom blowing online intelligent control system based on thermal imaging temperature measurement technology and a multi parameter bottom blowing flow prediction and control model was designed and developed to address the significant fluctuations in flow rate during on-site bottom blowing control, combined with the practical experience of on-site operators. Based on the multi parameter ladle bottom blowing flow rate model, the current bottom blowing flow rate can be accurately determined. During the strong blowing stage, the calculated value of the model is slightly lower than the actual value by 20-100 L/min, which can still meet the on-site bottom blowing needs. The use of an online thermal imaging monitoring model to monitor and analyze the stirring of molten steel in the ladle can achieve real-time monitoring of the bottom blowing of the ladle, and calculate the ratio of the exposed area of the molten steel to the measured area. When the area ratio P_s is 0, 15%-20%, or greater than 60%, it can ensure the effect of stopping blowing, weak blowing, and strong blowing. A multi parameter prediction and control model for ladle bottom blowing flow rate was used and combined with an online thermal imaging monitoring model to calculate the ratio of bare leakage area of molten steel, the system has achieved precise control of on-site ladle bottom blowing flow rate. After the system was put into operation, the outlet-temperature fluctuation of the ladle was relatively uniform, and the proportion of furnaces below 1 550 ℃ decreased from 69% to 27.5%, the number of inclusions in the steel billet has been significantly reduced, accounting for about 80% of the amount before the system was put into operation. The occurrence of submerged nozzle clogging has also reduced, the bottom blowing effect was significantly improved, and at the same time, it assisted in efficiently completing the ladle bottom blowing stirring work on site, reducing personnel labor intensity.

Inclusions are one of the main factors that deteriorate the soft magnetic properties of high-grade non-oriented silicon steels. Reducing the number of inclusions and coarsening the size of inclusions through rare earth treatment can help alleviate the harm of inclusions to the soft magnetic properties. The current study conducted LaCe misch metal treatment on a high-grade non oriented silicon steel, and sampled from refining, casting, continuous casting slabs, hot-rolled plates, and final products. The steel composition and inclusion characteristics were detected, and the formation process of inclusions was analyzed based on thermodynamic calculation. The following conclusions were drawn: after adding misch metal for 3 minutes, the total mass fraction of rare earth in the steel was 64×10^-6, which gradually decreased during the subsequent refining process until the tundish molten steel was 25×10^-6. The decrease in sulfur content and increase in magnesium content in the refining process were mainly due to the desulfurization effect of CaO-CaF₂ desulfurizer and its erosion effect on refractory materials. Rare earth treatment slightly reduced sulfur content and increased magnesium content, but its effect was smaller than that of desulfurizer. After the addition of misch metal, MgO·Al₂O₃ in non-oriented electrical steel was modified into rare earth oxide sulfides and rare earth sulfides. The proportion of lanthanum and cerium in rare earth inclusions was related to their size. The atomic proportion of lanthanum and cerium in inclusions larger than 3 μm was almost equal, and these inclusions extended into a string like morphology after cold rolling; Inclusions smaller than 3 μm, possessed more cerium element and hardly deformed after rolling. Thermodynamic calculations showed that rare earth lanthanum had a stronger ability to modify inclusions than cerium. When using misch metal to modify inclusions in non-oriented electrical steel, rare earth elements tended to preferentially modify MgO·Al₂O₃ in the steel, and then reacted directly with dissolved oxygen, sulfur, and other elements in the steel to form rare earth inclusions.

As the last refining equipment before the solidification of the molten steel, the tundish plays an important role in improving the cleanliness of the molten steel. In order to solve the problem of poor effect of the tundish to remove inclusions, a 50 t tundish of a certain plant was taken as the target.And a 1∶4 physical model was established to study the effects of different immersion depth of long nozzle, relative distance between the weir and the dam, distance between the weir and the center of the long nozzle, and height of dam and weir on the flow fluid of the tundish. And the optimized scheme of tundish flow field was obtained by analyzing the tundish flow field and RTD curves.The results showed when the immersion depth of long nozzle was 50 mm, the relative distances between the weir and the dam was 50 mm, the distance from the weir to the center of the long nozzle was 400 mm, the height of the weir was 282 mm, and the height of the dam was 64 mm, the effect of the metallurgical effect of the tundish was the best.With the optimized scheme, the proportion of the dead zone in the tundsih was decreased and the average residence time was extended.The results of industrial application showed that the total oxygen mass fraction decreased by 16.3% and the number density of inclusions decreased by 17.1% in the slab.

The movement and removal of inclusions inside the mold are mainly influenced by the flow pattern of the molten steel, and the flow pattern also directly determines phenomena such as the heat transfer and solidification during the continuous casting process. In the current study, systematically industrial trials on the macroscopic flow pattern, meniscus speed, and surface level inside a 1 300 mm×230 mm section mold were performed using nail board measurements. The effect of key continuous casting process parameters such as the casting speed, argon flow rate, and immersion depth of the submerged entry nozzle (SEN) on the flow pattern was proposed. Results indicate that the argon flow rate under low casting speeds (≤1.0 m/min) was the primary factor determining the flow pattern inside the mold. Under high casting speeds (≥1.3 m/min), the flow pattern remained as a double roll flow even with the argon flow rate increased to 6-10 L/min. The meniscus speed decreased as the SEN immersion depth increased, but the SEN immersion depth had little effect on the flow pattern. The level fluctuation increased with the increase of the casting speed and argon flow rate. After the argon flow rate increased from 6 L/min to 8 L/min, the proportions of level fluctuations greater than 3 mm at casting speeds of 1.2 m/min and 1.6 m/min increased from 0 to 6.7% and 15.0%, respectively. The critical transition relationship between the different gas volume fraction β_Ar and the steel throughput Q_steel was obtained. The relationship between the critical argon volume fraction and the steel throughput was β_Ar=-4.2+7.8Q_steel when the double roll flow changed to complex flow, and the relationship between the critical argon volume fraction and the steel throughput was β_Ar=-5.6+9.8Q_steel when the complex flow changed to single roll flow.

In order to improve the surface quality of continuous casting bloom in a factory, the surface cracks and porosity defects of bloom were analyzed and the use of mold flux was tracked. The results show that obvious decarburization occurs around the defect, the original austenite grain size is larger than the normal position, and the thickness of the liquid slag layer of the mold flux is relatively thin. By adjusting the height of mold flux, the melting rate of mold flux is optimized to increase the thickness of liquid slag layer. After optimization, the thickness of liquid slag layer was higher than before, and the incidence of cracks was obviously reduced. Magnetic flux leakage testing was carried out on the rolled products, and the qualified ratio of the studied steel grades increased from 51.6% in the previous period to 94.0%.

In order to reduce the oxygen content in heavy duty carburized gear steel and improve the fatigue life of gear materials, the oxygen content of finished forging was analyzed, and it was found that the ordinary production process couldn’t meet the requirements of customers. Therefore, the LF refining slag changing plus double VD vacuum refining operation process was developed, and the experimental results before and after optimization were compared by using on-line oxygen meter,Aspexautomatic inclusion scanninganalyzer,oxygen nitrogen hydrogen analyzer and XRF fluorescence analyzer. The research shows that the optimized process can reduce the oxygen mass fraction of the forging to 6×10^-6, and reduce the test value of the maximum inclusion size in the steel from 137.5 μm to 51.2 μm, successfully meet the needs of customers, and provide technical guidance for EBT+LF+VD+IC production process to produce ultra-low oxygen heavy duty carburized gear steel.