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Some steels, such as bearing steel, heat-resistant steel, ultra-high strength missile and aircraft steel, and rotor steel, all have higher quality requirements and strict composition control than general carbon steel and ordinary low alloy steel. Special steel

Production requires the ability of vacuum induction or electric remelting. Because the production of ultra pure steel requires longer continuous smelting and larger alloy addition, as well as the necessary facilities for secondary heating of steel in secondary smelting. These methods provide the following benefits:● The content of gases (such as hydrogen, nitrogen, and oxygen) is greatly reduced. The purity has been improved, that is, there are fewer non-metallic inclusions. Due to the sequential melting and solidification of steel, the looseness and segregation in the center of the steel ingot caused by casting are eliminated. The hot deformation workability of metals has been improved. Improved the mechanical properties of remelted steel at room and high temperatures, such as plasticity, impact resistance, fatigue resistance, and creep fracture strength.

1. Vacuum induction melting (VIM)

The steel industry applies two types of induction furnaces:oil core type and coreless type. In the remelting process, the chemical analysis composition of the loaded furnace material is basically the same as the final liquid metal. Apart from reducing residual substances and inclusions, no other important refining or smelting work will be carried out. When remelting alloy steel, certain alloy elements that are prone to vaporization or oxidation should be added under controlled conditions. Based on experience, alloy elements that need to be oxidized should be added as late as possible, while elements that are difficult to dissolve should be added earlier and during a strong stirring stage. The lining of the furnace is determined by the properties of the slag and the required temperature. Vacuum melting is often used as a remelting process on steel that requires very purity and becomes the first stage of the dual melting process. At this time, the steel liquid coming out of a vacuum induction furnace (such as VIM) enters a vacuum consumable electrode (vacuum arc remelting or VAR) furnace or an electric slag remelting (ESR) furnace for remelting. Oxygen, hydrogen, and a certain degree of nitrogen can all be removed in vacuum melting. Carbon can also be reduced to produce certain types of stainless steel. Use as low as 5 in these furnaces μ High pressure of mHg. By controlling pressure and gas composition, it is possible to use carbon or hydrogen to deoxygenate liquid metals, as they can produce gaseous deoxygenation products to prevent the formation of non-metallic inclusions. Low pressure can also remove nitrogen absorbed by steel. Some elements such as chromium, aluminum, and manganese have volatility that can lead to their loss. Therefore, during the addition process, they can be minimized by covering the liquid metal with an inert gas atmosphere instead of a vacuum. Improved vacuum induction equipment (such as the Thermal ⁃⁃⁃\Vac process) can be used as vacuum induction melting furnaces or metal flow degassing furnaces under low pressure. This system can be used for cold loading of induction furnaces and for melting, refining, and casting steel under low pressure. Steel can also be hot loaded into a vacuum furnace under low pressure, where the metal flow is degassed and reheated to compensate for the losses caused by degassing. The addition of alloy elements is adjusted to achieve chemical composition indicators and casting is carried out, all of which are carried out under low pressure. If what is being done isThe steel liquid does not require overheating during loading. Steel can be partially deoxidized before entering the vacuum induction furnace. This device is mostly used as a vacuum induction unit to melt cold furnace materials.