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Slag skin formed in electroslag remelting (ESR) is obviously deposited in layers in the thickness direction. In this pa-per, the specimens of slag skin in the production process were taken for experiment and analysis. The detailed microstructure and chemical composition were obtained at different positions. Based on the mechanism of quenching layer formation, it is suggested that the composition of the quenching layer can be used to reflect the composition of the slag pool in the corresponding time. The composi-tion change of the slag pool in ESR process can be speculated by checking the slag skin quenching layer near the mold at different posi-tions (different heights of an ingot).

M2 steel was melted by a 25 kg high-frequency vacuum induction furnace and was cast to ingots with a cross section of 100 mm×50 mm by the water-cooled copper mould and the sand mould.The effects of cooling rate on the ingot's secondary dendrite arm spacing(λ2),permeability,and size and distribution of grains and carbides were studied.The results show that fast cooling rate can effectively decrease the λ2,permeability and size of grains and network carbides,and improve the distribution and uniformity of network carbides and grains during solidification.The λ2 values of ingots cast with the sand mould and the water-cooled copper mould are 42.5 μm and 21.6 μm,the cooling rate is 1.06 K·s-1 and 12.5 K·s-1,and the permeability is 1.3×10-1 μm2 and 3.5×10-2 μm2,respectively.Fast cooling rate can effectively reduce the center carbon segregation degree.The area fraction of carbides is 0.46 and 0.30 respectively at the center of ingots cast with the sand mould and the water-cooled copper mould,and increases by 38.7%and 2.2% respectively compared with their average values.The average grain size of ingots cast with the water-cooled copper mould and the sand mould is 41.3 μm and 72.6 μm,respectively.Comparing with the sand mould ingot,the grain size at the center of the water-cooled copper mould ingot reduces by 43.2%,and the grain size of the water-cooled copper ingot is more uniform.The relationship between grain size and cooling rate was presented in this paper.

The mineralogical composition,microstructure and TiO2 distribution rule of low titanium-containing blast furnace slags after water cooling and air cooling were investigated by X-ray diffraction,polarization microscopy and scanning electron microscopy.The results show that main mineralogical compositions in these slags are all vitreous,gehlenite,perovskite and merwinite,but the contents of mineral components in the two kinds of slags have much larger differences. The average contents of gehlenite and perovskite in the air-cooled slag are 62.5% and 12.5%,which are 2.27 and 1.92 times as large as those in the water-cooled slag,respectively.The content of vitreous in the air-cooled slag is less than a third of that in the water-cooled slag. The mineralogical microstructure of the water-cooled slag is pretty different from that of the air-cooled slag. Gehlenite in the water-cooled slag is dentate,but in the watercooled slag it is feathery and needle-shaped,and its grain size is smaller. Perovskite forms as star points and dendritic in the watercooled slag and the air-cooled slag,respectively. Merwinite is spindle-shaped both in the water-cooled slag and the air-cooled slag. It could be concluded that TiO2 in the water-cooled slag mainly distributes in perovskite,vitreous glassy and gehlenite,but TiO2 in theair-cooled slag mainly distributes in perovskite and gehlenite,and the distribution ratio of TiO2 in the air-cooled slag is 8.41% higher than that in the water-cooled slag. Air cooling is more beneficial to increase TiO2 content in perovskite.

The microstructure and texture evolution of Hi-B steel produced by thin slab casting and rolling (TSCR) process in the laboratory was studied by metalloscopy and scanning electron microscopy. It was found that the microstructure and texture of the hot rolling slab of Hi-B steel, which was manufactured by simulated TSCR process in the laboratory, was inhomogeneous along the thickness direction. Ferrite grains in the surface decarbonization layer of the normalizing slab obviously coarsen; moreover, the texture of the normalizing slab inherited the texture type of the hot rolling slab, with only a difference in texture density. After cold roiling with big reduction rate, the coarse grains and grain boundaries were stretched to be fibrous bands in the rolling direction, and the α fiber texture and the γ fiber texture were the main texture style. With the deearburizing annealing carrying out, the recovery and reerystallization of the cold rolling slab occurred, primary recrystallization grains formed, and the texture was more centrally distributed. When the temperature increased to 1000℃, secondary recrystallization appeared; at 1010℃ the Goss grains grew up, and the Goss texture intensity reached to 61. 779. By testing, the products had a magnetic induction of 1. 915 T and an iron loss of 1. 0671 W.kg-1.

The effect of slag composition on the[C] content of ultra-low carbon steel at the end of smelting was investigated by the coexistence theory,dynamics analysis and experimental verification. A regression model of end-point[C] content was established with temperature and slag composition in a temperature range from 1853 K to 1973 K. The results show that the Fe O activity is little affected by temperature,while it is mainly affected by slag composition. However,the decarburization kinetics is mainly affected by slag composition and temperature. The end-point[C] content increases with increasing slag basicity,but it quickly decreases with increasing Fe O content in slag,so the end-point Fe O mass fraction in slag should be controlled in 12%-18%. In addition,the increment value of[C] is less than 0. 01% with the Mg O mass fraction in slag from 7% to 13%. The results also show that the end-point[C]mass fraction decreases with increasing temperature. Compared with industrial results,the average error rate of the regression model for the end-point[C] content in the ultra-low carbon steel is ±15. 25%,and the hit rate to[C] content predicted by the regression model reaches 69. 19% with a control precision of ±0. 01% for heats of the experiment.