Powder metallurgy steels (PMSs) are the 21st century evolution of steel manufacture providing metal designed to withstand tremendous impact and high temperatures. In the 1960s, Americans began to actively introduce various additives into alloys to gain steels usable for most complicated industrial applications. Then, the powder steel, or particle steel, came as the solution to provide most reliable and durable alloys.
Powder steel features a very fine grain of tiny steel particles forming a consistent microstructure. The powder steel is also known as powdered high-speed tool steel, as it is used in producing industrial tools capable of cutting steel and endure similar extreme operation modes.
Powder steel causes a real stir in the world of knives today. If the custom knife is made of powder steel, then it usually costs more than usual. Manufacturers from the USA are pioneers, but not pioneers in this case. It was them who first began to use premium alloys of this type – hence this pricing policy. But, of course, it’s not just about it: powder steels have many features and differences from other types of steels. Let’s try to understand this issue and cover, in addition to powder steel, forged steel along with rolled steel.
The technology of its creation has become known since “ancient times”: in the 17th century BC, the Indians made an iron column in a similar way. The delight is that it is still intact to this day. However, powder steels gained wider coverage and fame in the 60s of the 20th century, when Americans began to actively introduce various alloying additives into alloys to make them more reliable and durable.
Powder steels are produced by way of a specific manufacturing process that results in an extremely fine-grained structure of the metal allowing outstanding metallurgical properties and richer chemical composition. The delicate method of producing powder steel requires being performed in a laboratory rather than in a steel plant.
The principle of producing powder steel requires sintering metal into a fine-grained structure bonded into a consistent micro-texture. Gas atomization is used to eject, through a narrow nozzle, a stream of super-hot liquefied steel through nitrogen sprays that rapidly cool and solidify the metal into a fine, perfectly uniform powder. This technique allows for an excellently uniform distribution – especially of carbides – at a particle level. Provided the alloy is properly mixed, there will be no weak spots and the structure of the mixture will be even throughout the ingot. The metal powder is then pressed, at high pressure and temperature, into workable bars of steel to be further processed as normal metal.
The powder metallurgy steel process is more expensive; however, it secures considerable advantages in terms of service properties of the metal. The specific micro-structure of the powder metallurgy steel (the uniform distribution of particles) provides a blade with an increased toughness, better wear resistance, cleaner finishes and improved grindability. The powder steel can also achieve higher alloy grades and can be heat treated to a higher temperature with less risks of failure. Part-to-part uniformity of texture yields better product quality, while shapes and mixes of the material can be very flexible. Moreover, there is actually no waste of metal with this technology: any leftovers can be recycled into powder again and the cycle can be repeated. Thus, the powder metallurgy steel process is a resource-conscious technique. The repeated use of metal powder can be versatile enough to create a variety of alloy components.
Powder steel is one of the latest innovations in steel making that is used in knife manufacturing. Powder steel makes knife blades perform at their peak levels with a much less risk of failure, which is especially important in knives.
Of course, the use of the cutting-edge technology can cost a bomb: knives made from powder steels are expensive and rare as they are difficult to produce. It takes the expertise and craftsmanship of a seasoned knifemaker to properly execute the difficult process of making and heat-treating these steels. However, the result is worth it: correctly produced powder steel knives are the toffs of knifemaking. They feature extremely high hardness (up to 67 on Rockwell C), great toughness, fair corrosion resistance, and the specific microstructure provides fine sharpness and great edge retention (the blade stays sharp much longer than other traditional steels).
The structure of finished powder steels includes martensite, carbides and various non-metallic inclusions. The martensitic base is harder and more brittle than the carbides – therefore, it is essentially the density and the uniformity of carbides distribution that determines the strength and reliability of the final product, the knife blade. During the powder steel production process, all components of the metal undergo crystallization to then become homogeneous steel. The speed and quality of crystallization can be increased to improve the distribution of components in powder steels. During the manufacturing process, a variety of components can be added to modify specific functional characteristics or appearance of a steel alloy.
Powder steels provide a material that is as durable and reliable as possible – therefore, army knives, hunting and fishing knives are often made of powder steels. Such knives are renowned for their outstanding sharpness – most of them can easily cut paper with just one movement. Professional processing and proper care keep such knives extremely sharp for an incredibly long time. Remember that it is better to sharpen knives made of powder steels in a workshop or with a special tool, because their extra-thin edges require careful handling.
The complicated technology and additional resources that are required for the powder steel process make final products more expensive. However, the costliness of the process is offset by the high quality of the products and the waste-free feature of the production.