Since iron powder began to be used in powder metallurgy industry in the early 1930s, there have been many production methods of iron powder. For various technical and economic reasons, many of these methods have never exceeded the stage of experiment or pilot test,

For example, the chemical metallurgy method of reducing ferrous chloride with hot hydrogen; other methods, such as the vortex mechanical grinding method (hametag process), the aqueous solution electrolysis method, the fluidized bed hydrogen reduction method, the rotating disk atomized liquid steel method (d.p.g.process), the air atomized liquid pig iron method (r.z.process) and the combined reduction method of transforming natural gas and solid carbon, have experienced relatively short time Industrial application, and then due to the emergence of other more competitive methods are no longer used in the industrial production of iron powder. As for the iron powder produced by carbonyl method (see carbonyl method), because of its fine particles and high price, it is not suitable for sintering mechanical parts and welding electrodes; however, it has high purity, special particle structure and excellent performance.

At present, the iron powder production process that dominates the iron powder market is: hegnas method and peyron method which belong to iron oxide reduction process, water atomization method which belongs to low carbon steel liquid, QMP method which belongs to high-purity pig iron shot peening and decarburization process and R) omfel% 26bull; method. Among them, the production of iron powder by hegnas method and water atomization method is overwhelming.

Hoganas process is a two-step reduction process of solid carbon and hydrogen developed by Hoganas company in Sweden. Firstly, the iron concentrate powder (total iron% 26ge; 71.5%, SiO2% 26lt; 0.5%) and low sulfur coke crumb limestone powder (used for desulfurization) mixed reductant are loaded in the SiC reduction container in a layer manner, and heated to about 1200 ℃ in the tunnel kiln to reduce the ore powder to sponge iron. Sponge iron is broken into smaller than 0.175mm (- 80 mesh) or smaller than 0.14mm (- 100 mesh), then it is spread in steel strip reduction furnace, and reduced annealing is carried out at 800-900 ℃ with decomposed ammonia. High quality sponge iron powder can be obtained by hammering the annealed sintered powder.

The scale of low carbon rimmed steel was broken to less than 0.147 mm by Pyron process, and then oxidized to Fe2O3 at 980 ℃ in a multi hearth roaster. Then the Fe2O3 powder is fed to the belt furnace and reduced to iron powder by hydrogen at a temperature of no more than 1050 ℃.

After removing or reducing phosphorus, silicon and other impurity elements by melting and slagging, the low carbon steel scrap by liquid-water atomization method flows into the atomizer through the leakage nozzle, and at the same time, it is sprayed into the high-pressure (about 8.3mpa) water flow to break the metal flow and form a droplet, which falls into the water tank below to cool and solidify into powder. After magnetic separation, dehydration and drying, the powder is sent to the belt furnace, and then it is reduced and annealed by decomposing ammonia gas at 800-1000 ℃, so as to obtain high-purity water atomized iron powder.

QMP method was developed by Quebec metal powder company in Canada. High purity molten hot iron (carbon content is about 3.3% - 3.8%) is injected into the leakage bag. The molten iron flowing from the leakage nozzle is smashed into particles (about 3.2mm) by the high-pressure water jet horizontally, and then falls into a water-cooled container that sucks in air, so that it is partially oxidized. The dried iron particles are crushed by ball milling, and then the powder screened to less than 0.147 mm is sent into the belt furnace protected by decomposed ammonia gas. The iron powder for powder metallurgy can be obtained by decarburization annealing with the oxygen contained in the iron particles at 800-1040 ℃ and reduction annealing with decomposed ammonia gas.