Powder metallurgy offers many advantages for knife-making steels. 23 December 2019
Powder metallurgy : explanations and assets for knife making steels
Some of our steels are made from powder metallurgy, but what does that mean ?
What strange chemistry lies behind this complicated name?
In short, it is the latest technology for producing metal alloys by sintering, unlike traditional smelting.
Good, but what is "sintering"?
Sintering is an ancestral process for making everyday objects by heating a powder without bringing it to fusion, the most famous example being... pottery.
Powder metallurgy, therefore, is the technology of producing steel alloys by the sintering method.
As you will have realized, the most modern and efficient steels are obtained using a technique discovered, probably by chance, by the first humans.
But not everything is that simple....
Looking back on steel design history :
If the first humans were satisfied with a mixture of earth, clay, a bit of water and fire to create pottery and figurines, production of steel alloys isn’t really the same.
From early Iron Age to the Middle Ages, low furnaces were used to make iron by smelting ore. Then, starting from the Middle Ages, blast furnaces made it possible to obtain cast iron, which could be used in the manufacture of the iron alloys we know today.
Today, steel alloys are still produced by melting a basic metallic element mixed with one or more other metallic or chemical elements known as "alloying elements". The proportion of each of these elements determines the characteristics and properties of the resulting steel.
The beginning of steels made from powder metallurgy:
Since the early 1960s, the metallurgical industry has been interested in sintering technology to produce steel with improved capabilities (better machinability, forgeability, mechanical strength, etc.).
The use of this technology makes it the most recent process for steel production but also the most efficient, making it possible to obtain both steels with improved capacities and new alloys and special steels that would be impossible to produce with a conventional melting process.
Steps in the manufacture of steel made from powder metallurgy:
So, how does it work ?
As its name suggests, powder metallurgy technology is a perfectly controlled and automated process based on the use of metallic powders.
The raw materials are poured into a container, whose proportions are corresponding to the alloy we want to produce.
- The content of the tank is brought to its melting point by graphite electrodes and continuously stirred with electromagnets (1)
- When the mixture is perfectly homogeneous, the alloy, in its liquid phase, flows into a chamber where it is subjected to an atomization process (2) by a powerful spray of neutral gas (e. g. argon or nitrogen) which will transform the metal in its liquid state into rapidly cooled micro droplets. Obtained powders are perfectly homogeneous and free of any impurities (or inclusions). The ideal spherical shape and grain size (from 0.1 to 1,000 µm) are very precisely determined, according to the nature of the desired alloy.
- Once these powders have been obtained, they are collected in a capsule (3)
- After being hermetically sealed by welding (4), it is transferred to a Hot Isostatic Pressure (HIP) furnace. During this step, the powders will compress (5) and agglomerate to form a steel billet, free of any impurities or inclusions.
Assets of this technology for knife making steels:
Powder-engineered steels have an extremely fine and regular grain, allowing them to combine many advantages for the creation of knives blades:
- Excellent edge retention
- Easy sharpening
- Improved polishability
- Improved corrosion resistance
- Perfect homogeneity of steels = better carbide distribution
- The highest "Cleanliness" (no inclusions).
- High tenacity (resistance to crack propagation).
Many steels benefiting from this technology are available on eurotechni.com :
Difference in carbide distribution: powder metallurgy compared to conventional metallurgy