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The evolution of inclusions in molten steel in tundish before and after vacuum treatment during the production of GCr15 bearing steel in a steel plant is analyzed， the results showed that total oxygen content in molten steel increased greatly in tundish. Magnesium aluminum Spinel inclusions increased in RH soft blowing and tundish to varying degrees， and the number increased significantly in tundish. The MgO aggregate particles in the working layer of the tundish coating are greatly reduced， and some MgO particles are dissolved in the molten steel， resulting in the increase of oxygen content in the molten steel.The effect of different SiO2 content on the phase of tundish coating was discussed by thermodynamic simulation analysis. It was proposed that the control of SiO2 content at range 4%~6% and the strengthening of tundish masonry management can reduce the formation of high temperature low melting phase in tundish coating and effectively improve the flaw detection eligibility rate of bearing steel GCr15 head slab.

One of the important requirements for converter steelmaking is to accurately calculate the amount of lime added based on the conditions of hot metal and the requirements of molten steel， in order to avoid waste of flux. However， due to the fast pace of converter production and multiple influencing factors， it is difficult to accurately determine the amount of lime added. In order to accurately calculate the amount of converter lime， avoid lime waste and reduce unnecessary steelmaking cost， mechanism model， classification model and multiple linear regression model are established to calculate the amount of converter lime. Compared with the three models， the pure mechanism model has low calculation accuracy and is difficult to be directly applied to field production. According to the classification model optimized by mechanism model， only 60% of the furnace times difference is less than 500 kg/ furnace. A multiple linear regression model is established using SPSS， and the relationship between lime addition amount and other parameters is obtained WLime=4 147.24×wTSi+529.67×wTC+60.20×Wqf+0.405×VO-1 833.95. The verification results show that， 93% of the calculated difference of the furnace is less than 400 kg/ furnace， 77% of the calculated difference of the furnace is less than 300 kg/ furnace， which can basically meet the requirements of field use. After the model is applied in the field， the amount of lime added is effectively reduced.

In order to analyze the effect of cold joints on the interlayer bonding property of 3DPC and the formation mechanism of interlayer cold joints, the interlayer bonding property of a 3D printing cementitious material (3DPC) was evaluated by direct tensile test, and the process of interlayer cold joints extension of 3DPC was simulated by near field dynamic method. The results indicate that there is no cold joint between printed layers when the printing time of the upper layer is less than the starting time of the hydration induction period of cement, and the upper layer printing time and dosage of nano-clay have little effect on the interlayer bonding strength. After the upper layer printing time exceeds the starting time of cement hydration induction period, the number, continuity and length of interlayer cold joints increase with the prolongation of interlayer cycle time, and the interlayer bonding strength decreases, but the interlayer bonding strength can be significantly improved by adding nanoclay. The cold joint of 3DPC can be prevented and the interlayer bonding can be enhanced by controlling the upper layer printing time and by adding nano-clay to ensure proper relative humidity between 3DPC interlayer. [ABSTRACT FROM AUTHOR]