Smelting new types of gear metal with large tonnage

Recovery of alloying elements for SCM822H steel during LF-VD refining. In the table, the “VD process”, that is, the alloy is added about 10 minutes before the VD, and the components are measured after the VD furnace. After "VD", the final alloy composition fine adjustment stage after the VD furnace. It can be seen that the recovery rate of silicon in the LF stage is relatively low, being 71.5, because the molten steel is highly oxidizing and the silicon is an easily oxidizable element. The recovery of silicon in the VD process is slightly improved.
The recovery of silicon after VD is significantly improved, reaching 96 or more. The recovery rates of manganese, molybdenum and chromium are higher in the whole LF-VD process, reaching 92 or more. Therefore, the yield of the alloying elements should be accurately grasped, and the alloy composition should be adjusted as close as possible to the target value before the VD furnace to minimize the fine adjustment of the components after the VD furnace.
The change of element concentration in the VD process is deoxidized and the molten steel after the initial adjustment of the composition reaches a certain value and then enters the VD furnace for vacuum treatment. The VD furnace of Beiman Special Steel Co., Ltd. has no feeding device. Before entering the VD furnace, the alloy and carbon content should be adjusted to be as close as possible to the target value. However, during the VD process, the alloy and carbon concentrations will change, so the law of change should be mastered.
The equation for the reaction of carbon and oxygen in molten steel to form carbon monoxide under vacuum conditions is as follows: [C] [O]=CO(G) This process enhances the deoxidation capacity of carbon by reducing the partial pressure of CO, but the molten steel tends to increase during this process. Carbon, carbon addition distribution.
It can be seen that the low carbon gear steel increases carbon in the process of about 90 in the VD process, and about 60 of the heat is increased by 0.02. Therefore, before the molten steel enters the VD furnace, the carbon added by the alloy is finely adjusted except for the VD. It is also necessary to set aside 0.02 to 0.03 of carbon to ensure constant carbon demand. After analysis, the carbon addition is caused by the ladle refractory magnesia carbon brick. Magnesia carbon bricks contain 14 to 16 carbon, and the smelting process is affected by the corrosion of steel slag to increase the magnesium oxide in the slag and increase the carbon in the steel.
In addition, the silicon content of the furnace at about 70 in the VD process is reduced, and the range is from 0.01 to 0.02. The slag sample before and after the VD is analyzed, and the silica content is significantly increased. The reason may be that the LF process is not completely deoxidized. In the early stage of the VD process, the degree of vacuum is not high, and when the carbon deoxidation ability does not exceed silicon, silicon reacts with oxygen in the steel to form silica.
Conclusion (1) The recovery rate of carbon in LF-VD process is low and unstable, and the recovery rate of carbon in 60 is only 40. (2) The heat of about 90 in the VD process, about 60 furnace Sub-carbon addition 0.02. Therefore, before the molten steel enters the VD furnace, in addition to the carbon added when fine-tuning the alloy after leaving the VD, it is necessary to leave 0.02-0.03 of carbon to ensure constant carbon demand. During the VD process, the silicon content of the furnace is reduced by about 60, and the range is 0.01 to 0.02. Other elements such as chromium, manganese, molybdenum and the like are not significantly changed.

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