Principles of Sintering and Sinter Hardening

October 22, 2020

Sintering and sinter hardening are processes that can transform metal powder into useful components for different uses and industries. Typically, a press with a die that takes the shape of the final component is used to place and compact metal powder. Once the powder is compacted, it is subsequently subjected and placed under a high-temperature furnace to effectively bond and combine its particles.

At this point, the green component out of the heated metal powder will undergo the sintering process to produce metal products that are ready for sale or service. Alternatively, the sinter hardening process is carried out to cool the metal parts after sintering to produce a martensitic microstructure.

Understanding the Sintering Process

Sintering is the process of compacting and welding a solid mass of metal products through heat or pressure. Products out of this process do not have to be melted to the point of liquefaction. Most of the time, sintering is utilised in the steel manufacturing industry to create complex metal shapes, produce alloys, and work in metal with high melting points. Other uses of the sintering process include the initial or preliminary moulding of ceramic or glass powders.

The main purpose of the sintering process is to amplify the strength and structural integrity of the metal products. This amplification of the mentioned properties is possible as the process can reduce the porosity of the products. Other notable qualities of metal powder products that are enhanced by the sintering process include their electrical conductivity, thermal conductivity, and translucency.

Sintering is done in three phases. First, the metal powders are heated in the furnace at an appropriate temperature to create martensitic, crystalline structures. Then, the density of the metal powders’ particles will be increased to combine and merge them all. The merging process of these particles can be done through either transient liquid phase sintering or permanent liquid phase sintering. Lastly, the merged metal powders will now boast a solid form, which makes up the final product.

Alternative Metal Hardening Process

One notable alternative to the whole sintering process is known as sinter hardening. Sinter hardening effectively combines the features and benefits of the sintering and hardening processes into only one operation. With the sinter hardening process, the powder metal particles are sintered in a sintering furnace and then cooled slowly. Once they are cooled, they are transferred into a batch furnace so that the particles will be reheated and quenched, which are processes that make up conventional heat treatment.

The cooling rate of the sintering furnace is quite fast, allowing some parts of the powder metal product matrix to be transformed into martensite. As the transformation occurs, products out of this specific process will typically gain higher hardness. However, they may become brittle. Therefore, tempering them is done to lower their hardness and consequently increase their strength.

With sinter hardening, the need for secondary quench hardening treatment or oil removal is eliminated. Fewer steps during tempering are also seen with this alternative metal hardening process. Some drawbacks of this process, however, include the high cost of reheating and overall operations. A slight dip in the quality of the product is also expected with the sinter hardening process. Products out of sinter hardening are known to lose some performance and need thorough cleaning requirements.

For more information about these processes, just give us a call at PM Distributors.

 

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