How to take correct measures to improve the quality level of mold steel during medium frequency electric furnace smelting, thereby eliminating mold steel defects.
Mainly include the following aspects:
① Select high-quality mold steel raw materials.
When smelting mold steel, we should try our best to use high-quality raw materials. Not only should the S and P content in scrap steel be low, but other harmful elements such as As, Sn, Pb and Cu should also be strictly controlled. Scrap steel should be made of good scrap steel (preferably the returned material of this group) or high-quality pig iron. When smelting by oxidation method, the amount of carbon removal during the oxidation period should be ensured as much as possible.
② Use high-quality refractory materials.
When smelting mold steel in an induction furnace, high-quality erosion-resistant refractory materials should be used. For example, high-quality magnesia-carbon bricks can be used for the furnace lining, and high-alumina or magnesia-carbon bricks are generally used for the ladle. Pay attention to the refractory materials used for pouring, etc.
③ Argon blowing and stirring used in smelting.
When mold steel is smelted, argon blowing is used for stirring, which can accelerate the floating speed of inclusions, and can make smaller inclusions form larger inclusions through collision and polymerization, which are easy to float. However, the amount of argon blowing must be controlled appropriately. If the argon blowing flow rate is too large or the argon blowing time is too long, the steel slag will be involved in molten steel, resulting in more slag inclusions or inclusions, and at the same time, the temperature of the molten steel will drop too much.
④ Use synthetic slag.
Adding specially configured slag to molten steel can strengthen the transformation process of harmful impurities into molten slag. There are many formulas for synthetic slag and there are many ways to add them. When it is necessary to remove non-metallic inclusions of a certain composition, Select the corresponding synthetic slag.
⑤ Use composite deoxidizer.
In recent years, composite deoxidants are generally used in the smelting of mold steel, which can make inclusions easier to separate from the metal. Such as Si-Mn alloy, AI-Mn-Si alloy, Ca-Si alloy, etc., which can be used as composite deoxidizers.
⑥ Use rare earth elements.
Rare earth metal elements are strong deoxidizers. You can choose alloys containing 30% to 50% rare earth (mass fraction). When added to molten steel, rare earth oxides and rare earth sulfides can become crystal nuclei during crystallization and are distributed within the crystal. Rather than being at the grain boundary, the harmful effects on steel properties can be minimized and the isotropy of the mold steel can be improved.