The sintering atmosphere of powder metallurgy is an important factor affecting the properties of sintered products

Metal powder metallurgy is a kind of technology that uses metal powder as raw material to make metal or alloy parts through molding and sintering. The leading manufacturers in the MIM industry can directly produce porous, semi dense or fully dense materials and products by using this technology, so it is widely used.

In the sintering of metal powder metallurgy products, the sintering atmosphere is one of the important factors affecting the properties of sintered products. The sintering atmosphere of metal powder metallurgy can be divided into three types: protective atmosphere, controllable atmosphere and air atmosphere. The following is the relevant content of these three kinds of sintering atmosphere summarized by Zhongwei Precision in MIM technology experience.

1、 Protective atmosphere

The protective atmosphere is divided into reducing atmosphere and neutral atmosphere, and the reducing atmosphere is divided into hydrogen and decomposed ammonia. In the sintering process, the main role of the protective atmosphere is to protect the sintered products from oxidation.

Reducing atmosphere: hydrogen has strong permeability at a certain temperature and is a combustible gas with strong chemical activity. It is often used as a protective atmosphere in the sintering of refractory powder metallurgy products such as tungsten alloy, hard alloy, stainless steel, etc; Decomposition ammonia is a mixed gas composed of hydrogen and nitrogen obtained from the thermal decomposition of liquid ammonia. It can be used as a reducing agent and also as a sintering atmosphere in powder metallurgy. MIM experts found that most metals can be sintered in this atmosphere, except some products containing nitrogen can not be sintered in this atmosphere due to chemical reaction with this atmosphere.

Neutral atmosphere: neutral atmosphere mainly includes nitrogen, ammonia and vacuum. Vacuum atmosphere is widely used in precision and complex parts. Vacuum sintering can avoid the harmful components in the atmosphere from polluting small and complex metal parts.

2、 Controllable atmosphere

Zhongwei precision MIM experts divide this kind of atmosphere into exothermic and endothermic atmosphere, which are transformed from hydrocarbons.

Exothermic type can be used to control the carbon content in sintered P/M products, which can be divided into light type atmosphere and dense type atmosphere. The carbon potential of the light exothermic atmosphere is very low. When it is used for the sintering of low-carbon steel and copper products, it is only used for non oxidizing heating. The carbon potential of the concentrated exothermic atmosphere is higher, which can be used to prevent the oxidation of powder metallurgy iron based and copper based parts and reduce the decarburization of iron based parts.

Compared with exothermic atmosphere, endothermic atmosphere is a controllable atmosphere with stronger reducibility and higher carbon potential. In powder metallurgy, it is mainly used as a protective atmosphere when sintering iron based parts and copper based parts, and sometimes as a carburizing agent.

3、 Air atmosphere

This sintering atmosphere is mainly through a certain amount of air in the sintering furnace, which can also be regarded as sintering under normal pressure. Zhongwei Precision is generally used in the sintering products of small complex metal parts and MIM ceramic materials.