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Causes of oxidation and Decarbonization in sintering process of MIM iron - based products

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-08-12 08:35:00
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In most cases, oxidation is often accompanied by decarbonization to varying degrees, which is also serious when oxidation is serious. It is often seen that surface of sintered iron-based products shows blue phenomenon, or hardness of sintered products is lower than standard, resulting in unqualified appearance and performance, affecting product quality, and wasting production costs due to scrap.

There are three kinds of oxidation in sintering of iron-based products: first is oxidation in early stage of sintering, second is oxidation in later stage of sintering, and third is mixed oxidation. Oxidation in early stage of sintering refers to oxidation of green part from room temperature to pre de-binding. The oxidation in later stage of sintering is oxidation in cooling area after high temperature sintering. Mixed oxidation is most serious oxidation phenomenon in whole sintering process.

1. Oxidation of green part from room temperature to pre-de-binding (pre-oxidation)

This kind of oxidation phenomenon usually does not see blue phenomenon. Product surface is relatively rough and does not have metal luster, hardness is usually lower than standard. Microstructure pearlite is few, presents serious decarburization phenomenon.

2. Oxidation in later stage of sintering

This kind of oxidation shows blue phenomemon in low temperature. Its oxidation is on surface, decarbonization is also on surface. Product performance almost not reduced. This type of oxidation mainly affects product appearance quality. When oxidation temperature is high or oxidation time is too long, product will also appear serious decarburization, desquamation. It will affect products performance seriously and eventually lead to scrapping.

3. Mixed oxidation

Mixed oxidation Products is not only low hardness, but also appears blue or yellow phenomemon on product surface. Most serious will occur epidermal desquamation phenomenon. Most products after this kind of oxidation can only be scrapped.

In short, no matter what kind of oxidation, when oxygen and iron have a chemical reaction, oxygen will also have a chemical reaction with carbon to decarbonize iron-based products. Due to unevenness of decarbonization, same product has different performance.

The reasons for decarbonization are as follows: (1) water in air and iron powder in free state of graphite compounds generated carbon dioxide volatilization; (2) Carbon dioxide reacts with carbon at a certain temperature to form carbon monoxide which is carried away by carrier. (3) During the reduction of oxides, some carbon is lost in the reaction.  Above show that H ? O and CO ? is main cause of iron-based products oxidation and decarburization.

Keywords in the article: sintering process of MIM
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