As a deoxidizer for steelmaking, the most widely used ferroalloys are ferromanganese and ferrosilicon. Strong deoxidizers are aluminum (aluminum iron), calcium silicon, silicon zirconium, etc. (see deoxidation reaction of steel). Commonly used varieties used as alloy additives include: ferromanganese, ferrochromium, ferrosilicon, ferrotungsten, ferromolybdenum, ferrovanadium, ferrotitanium, ferronickel, niobium (tantalum) ferro, rare earth ferroalloys, ferroboron, ferrophosphorus, etc. According to the needs of steelmaking, various ferroalloys are specified in many grades according to the content of alloying elements or the carbon content, and the impurity content is strictly limited. Iron alloys containing two or more alloying elements are called composite iron alloys. Using this type of iron alloy, deoxidizing or alloying elements can be added at the same time, which is beneficial to the steelmaking process and can comprehensively utilize symbiotic ore resources more economically and rationally. Commonly used ones are: manganese silicon, calcium silicon, silicon zirconium, silicon manganese aluminum, silicon manganese calcium and rare earth ferrosilicon.
Ferroalloys are mainly used as deoxidants and alloying agents in steelmaking to eliminate excess oxygen and sulfur in molten steel and improve the quality and performance of steel.
1. It is used as a deoxidizer. During steelmaking, oxygen blowing and other methods are used to decarburize the molten iron and remove harmful impurities such as phosphorus and sulfur. This process will increase the oxygen content in the molten steel. Excessive oxygen content will reduce the mechanical properties of the steel. Add some elements that have a stronger binding force with oxygen than iron and whose oxides are easily discharged from the molten steel in the form of slag to remove oxygen from the molten steel. This process is called deoxidation. Silicon, manganese, and chromium alloys are used for this purpose.
2. It is used as alloy agent. Different alloying elements have different properties and uses.
Silicon can significantly improve the elasticity and magnetic permeability of steel. Therefore, silicon-based alloys are used when smelting structural steel, tool steel, spring steel and silicon steel for transformers; general steel contains 0.15%-0.35% silicon, and structural steel contains 0.15%-0.35% silicon. Silicon contains 0.40%-1.75%, tool steel contains silicon 0.30%-1.80%, spring steel contains silicon 0.40%-2.80%, stainless acid-resistant steel contains silicon 3.40%-4.00%, heat-resistant steel contains silicon 1.00 %-3.00%, silicon steel contains silicon 2%-3% or higher.
Manganese can reduce the brittleness of steel, improve the hot working properties of steel, and increase the strength, hardness and wear resistance of steel. The steel industry consumes more than 90% of its production of manganese. Manganese is an indispensable functional basic raw material for the production of high-quality steel. During the steel-making process, it can remove impurities such as oxygen and improve strength and hardness.
3. It is used as an inoculant for foundry crystal nuclei. One of the measures to improve the properties of cast iron and cast steel is to change the solidification conditions of the casting. In order to change the solidification conditions, certain iron alloys are usually added as crystal nuclei before pouring to form the center of the grains, so that the formed graphite becomes fine and dispersed and the grains are refined, thereby improving the performance of the casting.
4. It is used as reducing agent. Silicon alloys are respectively used as reducing agents in the production of ferromolybdenum, ferrovanadium and other ferroalloys; silicon-chromium alloys and manganese-silicon alloys are respectively used as reducing agents in the production of medium and low carbon ferromanganese.