Effect of slag composition on the cleanliness of 28MnCr5 gear steel in the refining processes

The equilibrium reaction between CaO-Al2O3-SiO2-MgO slag and 28MnCr5 molten steel was calculated to obtain the suitable slag composition which is effective for decreasing the oxygen content in molten steel. The dissolved oxygen content [O] in molten steel un- der different top slag conditions was calculated using a thermodynamic model and was measured using an electromotive force method in slag-steel equilibrium experiments at 1873 K. The relations among [O], the total oxygen content （T.O）, and the composition of the slag were investigated. The experimental results show that both [O] and T.O decrease with decreasing SiO2 content of the slag and exhibit different trends with the changes in the CaO/Al2O3 mass ratio of the slag. Increasing the CaO/Al2O3 mass ratio results in a decrease in [O] and an in- crease in T.O. To ensure that T.O ≤ 20 ppm and [O] ≤ 10 ppm, the SiO2 content should be controlled to 〈5wt%, and the CaO/AI203 mass ratio should be in the range from 1.2 to 1.6.

Effect of slag composition and current density on ingot cleanliness during low-frequency/DC electroslag process

For in-depth investigation of the effect of low-frequency and DC remelting on the cleanliness of electroslag ingot,laboratory experiments were performed with different current densities and slag compositions to analyze the variation of oxygen content and inclusions in electroslag ingots.When 70%CaF_(2)+30% Al_(2)O_(3) binary slag is used for remelting,the current density has different effects on the cleanliness of electroslag ingots with different power supply modes.At the power frequency of 2 Hz,the oxygen content and the number of inclusions in the electroslag ingot increase significantly with the increase in remelting current density.By contrast,when consumable electrode connected to cathode(DCSP)or consumable electrode connected to anode(DCRP)is employed,the current density has little influence on ingot cleanliness.At the same current density,DCSP remelting has a more adverse effect on ingot cleanliness compared with DCRP remelting.Compared with the use of 70%CaF_(2)+30% Al_(2)O_(3) binary slag,using 60%CaF_(2)+20% Al_(2)O_(3) +20%CaO ternary slag significantly reduces the oxygen content and the number of inclusions in electroslag ingots,regardless of whether low-frequency or DC electroslag remelting occurs.The increase in oxygen and inclusions in electroslag ingot is caused by the electrolysis of Al_(2)O_(3) in the slag pool.The increased inclusions mainly involve Al_(2)O_(3) or Al-containing oxides with small size.As regards the power supply mode,low frequency,DCRP,and DCSP promote the electrolysis of Al_(2)O_(3) in the slag pool.From the perspective of remelting slag composition,the slag with lower Al2O3 content can reduce the pollution of electrolysis on electroslag ingot.

Effects of MgO and TiO_2 on the viscous behaviors and phase compositions of titanium-bearing slag

The effects of MgO and TiO_2 on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared（FTIR） spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO_2 content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO_2 contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia–alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO_2 content.

Effect of Al content on the reaction between Fe-10Mn-xAl(x=0.035wt%,0.5wt%,1wt%,and 2wt%)steel and CaO-SiO_(2)-Al_(2)O_(3)-MgO slag

The effect of Al content(0.035 wt%,0.5 wt%,1 wt%,and 2 wt%)on the composition change of steel and slag as well as inclusion transformation of high manganese steel after it has equilibrated with Ca O-Si O_(2)-Al_(2)O_(3)-Mg O slag was studied using the method of slag/steel reaction.The experimental results showed that as the initial content of Al increased from 0.035 wt%to 2 wt%,Al gradually replaced Mn to react with Si O_(2)in slag to avoid the loss of Mn due to the reaction;this process caused both Al_(2)O_(3)in slag and Si in steel to increase while Si O_(2)and Mn O in slag to reduce.In addition,the type of inclusions also evolved as the initial Al content increased.The evolution route of inclusions was Mn O→Mn O-Al_(2)O_(3)-Mg O→Mg O→Mn O-Ca O-Al_(2)O_(3)-Mg O and Mn O-Ca O-Mg O.The shape of inclusions evolved from spherical to irregular,became faceted,and finally transformed to spherical.The average size of inclusions presented a trend that was increasing first and then decreasing.The transformation mechanism of inclusions was explored.As the initial content of Al increased,Mg and Ca were reduced from top slag into molten steel in sequence,which consequently caused the transformation of inclusions.

Slag formation path during dephosphorization process in a converter

The slag formation path is important for efficient dephosphorization in steelmaking processes. The phosphorus capacity and the melting properties of the slag are critical parameters for optimizing the slag formation path. Regarding these two factors, the phosphorus partition ratio was calculated using the regular solution model （RSM）, whereas the liquidus diagrams of the slag systems were estimated using the FactSage thermodynamic package. A slag formation path that satisfies the different requirements of dephosphorization at different stages of dephosphorization in a converter was thus established through a combination of these two aspects. The composition of the initial slag was considered to be approximately 15wt%CaO-44wt% SiOz-41wt%FeO. During the dephosphorization process, a slag formation path that follows a high-iron route would facilitate efficient dephosphorization. The composition of the final dephosphorization slag should be approximately 53wt%CaO-25.Swt% SiO2-21.5wt%FeO. The composition of the final solid slag after dephosphorization is approximately 63.6wt%CaO-30.3wt%SiO2-6. 1wt%FeO.

Research on Composite Slag Dam Cast with Magnesia Castables and Alumina Magnesia Castables

To enhance the serdice life of magnesia based slag dam, composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone. Workability of the magnesia castables for the slag dam was improved and a suitable vibration shaping method was adopted to combine it with alumina magnesia castables. The result shows： （1） workability and setting performance of magtwsia castables can be improved to match with alumina magnesia castables by adjusting setting retarder and water reducing agent, and adding proper silica fume ; （2） composite slag dam cart be prepared with alumina m,agnesia castables and the improved magnesia castables, whether by up - down composite method or right - left composite method; in order to get full vibration arrd make interface .fluctuation have proper amplitude, the vibration time oJ the two methods after two different castables contact with each other is 3 and 2.5 minutes, respectively; （3）the result of the on-site test proves that the design aims for reducing pollution to hot metal and improving corrosion resistance have been achieved.

Development of Ultra-Low Oxygen Automobile Gear Steel

In view of process conditions of Vanadium Recovery and Steelmaking Plant, PanGang Group Panzhihua steel and Vanadium Co.,Ltd., and on the basis of making choice of a reasonable deoxidization process, some measures have been taken to the development of automobile gear steel (20CrMoH) such as the pre-refining technology during converter tapping, "white slag" refining in LF, RH Vacuum treatment, and even protective casting technology. Also different and suitable models of argon blowing from bottom of ladle were adopted in the platform after converter, LF refining and calcium treatment. Test results show that the high cleanness 20CrMoH gear steel slab with T[O] ≤15×10-6(The average T[O] is 11.8×10-6) could be obtained through all these measures.