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Advantages of steam treatment technology for iron - based powder metallurgy parts

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-08-23 08:44:00
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Powder metallurgy technology can be used to manufacture parts of various materials, and iron based parts are the main products used in automobile, agricultural machinery, instrument, household appliances and other industries. Iron based parts can be used as friction reduction parts, such as oil bearing, but also as structural parts, such as gear, rotor, etc. Powder metallurgy production process usually includes powder manufacturing, mixing, pressing and sintering. In addition, high temperature steam treatment, steam treatment for short, is a post heat treatment for powder metallurgy part, which can improve product performance, such as hardness, air tightness, wear resistance and corrosion resistance, etc. The advantages of steam treatment process are:

In development of powder metallurgy iron based parts, product general density is around 7.0 g/cm3 by traditional pressing-sintering process, relative density at about 90%. The relative density of parts manufactured by repressing and re-sintering process and warm pressing process is generally between 92% and 94%. That is, there are inevitable gaps in powder metallurgy parts. A very important purpose of steam treatment is hole sealing.

For powder metallurgy parts used in refrigeration compressor, steam treatment has become the best and most economical technology for sealing holes and increasing air tightness. For example, the piston in connecting rod compressor is required to withstand 1.5 ~ 3.0MPa of gas pressure without leakage. Sealing by steam treatment is only 15% of copper permeation and 30% of fluoroplastics. Steam treatment, that is, place iron base parts into furnace, a certain amount of supersaturated steam is injected into the furnace under a certain temperature. There is a large amount of water vapor around the parts. When iron atoms touch the surface vapor, including outer surface and inner surface connecting the gap, oxidation reaction will take place, forming an oxide film. The main component of this oxide film is Fe3O4 with a density of 5.16g/cm3. Therefore, the volume ratio of Fe3O4 is larger than that of iron, so that the internal connection of parts is closed, achieved sealing hole purpose and increased air tightness. As the oxide film covers part’s substrate surface, it is very compact and firm to adhere to, resulting in the environment of water vapor and corrosive medium is difficult to enter parts, to achieve good rust prevention function. Since hardness of Fe3O4 is very high, the rockwell hardness of pure Fe3O4 is about 50HRC, and the apparent hardness of treated parts reaches more than 60HRB, which is beneficial to improve surface hardness, wear resistance and wear resistance, and the tensile strength can also be improved. After steam treatment, the tensile strength of iron-based materials can be increased by 40-50%.

Superior result for steam treatment is that product color presents a very smooth and beautiful blue-black metallic luster. This color is more comfortable for human eyes, and it is not easy to produce visual fatigue when sorting and packaging products. Oxide layer depth may be 0.51 ~ 1.27mm, and size generally increases by 0.005 ~ 0.01mm. There are no harsh requirements on technology and equipment, and the enterprise can easily meet treatment conditions. The treatment has no pollution to environment, low energy consumption, and economic and environmental protection.

Keywords in the article: powder metallurgy parts
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