STEEL

Which steel
High quality in steel is the basis for the maximum performance and endurance of a blade produced for cutting objects (knives, scissors, precision or medical bistouris etc.). Steel must be hard in order to keep a sharp cutting edge for long, being at the same flexible enough to bend without breaking. Moreover it must be stainless and performing a high resistance to corrosion. You obtain such qualities only by using rough materials of top quality and power.

The alloy "steel"
The materials normally used by the best blades manufacturers are high carbon content "AISI (Arerican Iron and Steel Institute) 440 e AISI 420", chrome hardenable steels . In other words they are stainless martensitic steels that contain at least 12 % chrome, which potential can be developed through an appropriate building and thermic treatment cycle. Martensitic steels are made of iron, carbon and chrome alloys, sometimes enriched with vanadium, molybden, nickel and tungsten in order to increase inoxidability, hardness and toughness. The best mix, distribution and fusion of this elements allows the production of top quality steel.

Hardening
The thermic tratment also called hardening is used to exploit martensitic stainless steel qualities at their best. When steel is mixed to other elements, it develops peculiar qualities; depending from the characteristics that need to be intensificated, use wise. A thermic treatment is what usually transforms an alloy steel into an optimum kniving steel. Any alloy steel has its own critical temperature, reaching which the steel crystal structure changes, causing the carbon solubility in the ferritic matrix to increase. Such temperature must be always kept constant in order to obtain steel austenitize, but not for too long because an increase in granulation dimension (which especially for knives blades should be kept preferrably low) must be avoided. The next step cools down the temperature (tempering) thanks to different means (water, oil, salt emulsions, ice, air etc.) in order to achieve the hardness level you want.

Tempering
After tempering, steel is hard and brittle at the same time. To achieve a suitable compromise between hardness (longer life of edges) and brittleness decrease (higher resistance in crash) a second thermic treatment is carried out. Scope of this treatment is to stretch the material subject to the internal cohesion state caused by tempering and to remove any left tension.

Hardness
You should always keep in mind that increasing the hardening point implies an increase also in permanent strain point (when material deformation changes from elastic to plastic and the tension breaking point increases) but diminishes ductility and resistance to crashes. On the contrary, an increase in toughness and elasticity brings a higher capacity in crash absorbing, higher ductility and ease of workability, but also a decrease in deformation point. From this examples it's clear that if the to be treated steel is aimed at the production of swords and machetes, the latter treatment will be preferred, seeing less strict tempering and stronger drawing so that breaks due to crashes can be avoided. On the other hand, by using steel for blades and knives blades production, you will use a strict tempering and a soft drawing, meant to stretch the material by keeping hardness at the maximun compatible level. A very satisfying way to check these aspects is the Rockwell test, which measures hardness.

Inoxidability
All metals, excluding precious ones like gold and platinum, tend to alter when coming in contact with atmosphere, water and with chemical industrial products. Resistance to corrosion of stainless steels is due to the formation of a passive superficial layer, called "passive film". In order to let this fine layer form, the chrome percentage in steel must be over 12%. This element generates an oxide upon the metal surface able to stop corrosion. Please keep always in consideration though that all steels (even stainless ones), having a strong ferrous matrix, are subject to oxidation and only a good maintenance preserves their integrity.

Alloy components
Carbon: increases duration of edge and elasticity point; increases hardness and fatigue to abrasion resistance.
Chrome: increases hardness, elasticity and tenacity; helps in fatigue resistance and corrosion.
Cobalt: increases resistance and hardness and allows high temperature endurance; multiplies the effects of other elements of the alloy.
Copper: increases resistance to corrosion and fatigue resistance. Manganese: improves capacity to hardness increase; deoxidates and degasses metals during bulk thermic treatments, increases hardness and dicreases brittleness.
Molybdenum: increases tenacity, capacity of hardening and fatigue resistance; increases workability and resistance to corrosion.
Nickel: increases resistance, hardness and resistance to corrosion. Phosphorus: dicreases brittleness when in high concentrations; increases resistance, workability and hardness.
Sylicium: increases workability, elasticity, deoxidates and degasses many metals.
Sulphur: increases workability when used in small amounts.
Tungsten: increases resistance, hardness and tenacity.
Vanadium: increases resistance, hardness and crash resistance; inhibits granulation.

N 690 STEEL
This kind of steel, selected for its exceptional features and used to produce all blades, comes from Austria and is manufactured by a small steel plant; highly specialized in high quality special steels. N 690 is a martensistic special steel with 17% chrome and it differentiates from AISI 440C steel thanks to a higher level of molybden (double). Not only molybden is a strong generator of carbides (improving cutting features) but increases resistance to corrosion in those steels highly connected to chrome. Moreover vanadium and cobalt alloys add ons increase the performances of this steel (vanadium is a also carbides generator with resulting increase in resistance to wear and therefore capacity of keeping edge sharpness for longer; cobalt prevents granulosity at high temperatures and improves drawing capacity and high temperatures resistance) . This steel features high resistance to corrosion and wear, keeps a sharpened edge for longer, can be easily polished and features also high levels in hardness, over 60 HRC (more than traditional steel AISI 440 C) that can be reached through the thermic treatment of tempering. These are the reasons why its employ is oriented towards blades and professional knives production. Thanks to the peculiar edge keeping quality and to oxidation resistance this steel is used in industrial kniving (food and fishing industries) and for butchering jobs. In the medical area, it's mainly used for surgical instruments production.