Sinter hardening in MIM

What is Sinter Hardening?

Sinter hardening is a process that produces martensite transformation during the cooling phase of the sintering cycle.

That is the sintering and heat treatment of powder metallurgy materials are combined into one process, so that the material production process is more effective and economic benefits are improved.

Characteristics of sinter hardening:

1) Metal plasticity is greatly improved. In the past, nickel-based alloys that could only be formed by casting but cannot be formed by forging can also be formed by sinter hardening die forging, thus expanding the types of forgeable metals.

2) The deformation resistance of metal is very small. Generally, the total pressure of sinter-hardening die forging is only one fraction to one tenth of that of ordinary die forging. Therefore, larger die forging can be made on equipment with small tonnage. 

3) High processing accuracy Sintering hardening forming processing can obtain thin-walled parts with precise size, complex shape, uniform grain structure, uniform mechanical properties, small machining allowance, and can be used even without cutting. Therefore, sinter-hardening forming is a new way to achieve less or no cutting and precision forming.

The influencing factors of sinter hardening mainly include: Alloying elements, cooling rate, density, carbon content.

The cooling rate of sinter hardening is 2~5℃/s, and the cooling rate is quite fast enough to cause the martensite phase transformation in the material. Therefore, the use of the sinter hardening process can save the subsequent carburizing process.

Material Selection:
Sinter hardening requires special powder. Generally, there are two types of iron-based powder metallurgy materials, namely:

1) Elemental powder mixed powder, that is, mixed powder composed of elemental powder mixed with pure iron powder. The most commonly used alloying element powders are graphite powder, copper powder and nickel powder. Partial diffusion or adhesive treatment can be used to bond copper powder and nickel powder on iron powder particles.

2) It is the most widely used low alloy steel powder in sinter hardening. In the preparation of these low-alloy steel powders, the alloying elements manganese, molybdenum, nickel and chromium are added. In view of the fact that the alloying elements are all dissolved in iron, the hardenability of the material is increased, and the microstructure of the material after sintering is uniform.