Production process of reduced iron powder
Iron powder is the most widely used metal powder in the powder metallurgy industry, and its consumption accounts for about 70% to 80% of the powder used in the entire powder metallurgy industry.
There are two main types of iron powder preparation processes for industrial powder metallurgy:
1: Reduced iron powder (including rolled iron scale reduced iron powder, iron concentrate reduced iron powder)
2: Water atomized iron powder.
Reduced iron powder
1.1 Rolled steel scale reduced iron powder
Rolled steel scales are also called iron oxide scales. During the heating and rolling process of steel, an iron oxide layer is formed due to the oxidation of the surface, and the scales are peeled off.
Using rolled steel scale as raw material, due to the difference of rolling batch and steel grade, impurities are easily mixed, which affects the quality and performance of reduced iron powder. Therefore, the selection and treatment of raw materials are very important, and there are high requirements for the control of impurities in iron scale, especially the control of SiO2 content mass fraction. SiO2)＜0.25%～0.35%
1.2 Iron concentrate reduced iron powder
The raw materials used in the preparation of reduced iron powder by using iron concentrate powder as a raw material are widely sourced and uniform in composition, and the prepared reduced iron powder has obviously excellent quality and quality stability. With the advancement of beneficiation technology, the purity of iron concentrate powder is getting higher and higher. The ultra-pure iron concentrate powder can reach the level of iron content greater than 71.5%, SiO2 content less than 0.2%, and Fe3O4 purity above 99%.
Si is the main impurity element in iron concentrate, mainly in the form of SiO2. The carbon reduction of iron concentrate is generally carried out at 1423K, but when it is higher than 1173K, SiO2 will combine with FeO to form ferrous silicate (Fe2SiO4), which is extremely difficult to reduce, making it difficult to increase the TFe content of reduced iron powder. Usually, after the content of SiO2 exceeds 0.2%, the content of TFe in the sponge iron decreases by 0.4% for every 0.1% increase in the content.
1.3 Preparation process of reduced iron powder
The production process of rolled iron scale reduced iron powder is similar to that of iron concentrate reduced iron powder. Rolled iron scale (or high-purity iron concentrate powder) is used as raw material, and solid carbon (coke powder or low-sulfur anthracite) is used as reducing agent. High temperature reduction produces sponge iron, which is then refined through the processes of coarse and fine crushing of sponge iron, reduction, powder cake crushing, screening and batching.
1.3.1 Hegnas method
The Hoganas process is a two-step reduction process for solid carbon-hydrogen developed by Sweden’s Hoganas Company. First, the iron ore concentrate powder and low-sulfur coke chips-limestone powder (for desulfurization) mixed with reducing agent are interlayered in the SiC reductant container, and heated to about 1200°C through the tunnel kiln to reduce the ore powder to sponge iron. . After the sponge iron is broken into smaller than 0.175mm (-80MESH) or smaller than 0.14mm (-100MESH), it is laid in a steel belt reduction furnace, and reduced and annealed with decomposed ammonia at 800-900°C. The annealed sintered powder is broken by hammer to obtain high-quality sponge iron powder.
1.3.2 Pylon method
After crushing the rolled steel scale of low carbon boiling steel to less than 0.147mm by Pylon method, it is placed in a multi hearth roaster and oxidized to Fe2O3 at 980°C. Then the Fe2O3 powder is fed into the belt furnace, and it is reduced to iron powder with hydrogen at a temperature not exceeding 1050°C.