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Home > Steel Types and Steel Properties Used in Knife Blades >
Steel is an alloy of iron and carbon. These two elements are combined in the molten state and form the new material when it solidifies. This is done by dissolving the alloying elements, adding them to molten iron and casting this into an ingot. The ingot is then rolled into shape while still hot and allowed to cool, producing so-called wrought steel.
Powder Metallurgy
Current state-of-the-art knife steels are formed using a complex process known as powder metallurgy. This involves instant cooling of the alloy using liquid nitrogen to form a powder which is then purified and re-shaped. This prevents formation of the large carbide particles which form when an alloy is allowed to cool slowly. Further heat treatment and quenching is performed to harden the final article. The resultant crystalline structure of the steel particles gives a honogenous, high quality steel.
CPM S30V steel produced by Crucible Materials Coporation, USA. , is formulated to promote the formation of vanadium carbides, which are harder and more effective than chromium carbides in providing wear resistance. CPM S30V is substantially tougher than other high hardness steels such as 440C and D2, and its corrosion resistance is equal to or better than 440C in various environments.
This steel is used in many Spyderco Knives for example; Spyderco Military Knife; Spyderco Mini-Manix Knife c101; Spyderco UK Penknife C94GP .
The standard blade steel used in Buck Knives is 420HC. This is a high carbon version of standard 420 martensitic stainless steels which is further hardened during Buck's exclusive heat treatment process. The finished blade steel has an optimum combination of wear resistance and corrosion withstanding properties.
Properties of Steels
Corrosion Resistance: The capability of the steel to resist damaging reactions with the environment. This is increased by addition of chromium, copper, molybdenum or nitrogen.
Edge Retention: The ability of the steel to withstand abrasion and wear. This is improved by adding carbon, chromium, manganese, nitrogen or vanadium.
Hardness: This is proportional to the strength of the steel, and measures resistance to deformation or penetration. Improved by carbon, chromium, cobalt, molybdenum, nitrogen or phosphorous.
Mohs Scale of mineral hardness:
This characterises the scratch resistance of various materials by comparing the ability of a harder material to scratch a softer material. For example, talc measures 1, pure gold measures 3, hardened steel measures 7 , diamond measures 10. Alumina Ceramic sharpening stones manufactured by Spyderco, measure 9 on this scale. These are manufactured in USA, in a process which combines a bonding agent with alumina particles. Alumina particeles are essentially synthetic saphires measuring 15 - 20 microns. The Spyderco sharpening stones are shaped and kiln-fired at 1649 degrees centigrade. Medium grit and fine grit stones are supplied with the Spyderco Tri-Angle Sharpmaker 204MF.
These have the advantage of lubricant-free sharpening, although after prolonged use will need cleaning to remove microscopic steel particles adhering to the stone. The sharpening effectiveness is gradually reduced as the stones become loaded with steel. They are easily cleaned by washing in fresh water and scrubbing with powdered abrasive and a scouring pad to remove steel residue from the open cell structure.
Hardenability: The ability of a steel to be harded by a heat tretment process. Improved by adding manganese, molybdenum or tungsten.
Heat Treating: A process which changes the physical properties of the metal by controlled heating and cooling to certain temperatures and limits.
Quenching: Rapid cooling of steel which has been heated to a high tempertaure, by soaking in air, oil or water. This process alters the crystalline structure, increasing hardness by forming martensite.
Austentitic Steel: The basic steel structure state being an alloy uniformly dissolved in iron
Martensitic Steel: A particular hard and brittle form of steel with a certain crystalline structure.
Tempering: A process of slightly softening and relieving stress in the steel by slow, steady heating to just below re-crystallisation temperature. This is followed by a slow, steady cooling phase.
Toughness: The ability of a material to withstand shock or impact, this is improved by addding chromium.
Classification of Steels. Steel is classified according to the elements used in the production which alter the physical properties of the steel.
Carbon Steels. These contain varying amounts of carbon, up to 1.65 % of manganese and 0.6 % of copper. There are 3 types of carbon steels. Low carbon steel contains 3 % or less carbon; medium carbon steel contains 4 - 8 % and high carbon steel (the type most commonly used in knives) contains more than 9 % carbon. The addition of carbon increases edge retention and raises tensile strength. It also increases hardness and improves resistance to wear and abrasion.
Alloy steels. May contain specific percentages of vanadium, molybdenum or other elements as well as larger amounts of manganese, silicon and copper than do conventional carbon steels. Vandium is used to increase wear resistance and toughness and limits the grain size of the crytalline particles. Molybdenum increases strength, hardenability and toughness of steel. It also improves machinability and resistance to corrosion , helps retain fine grain size and is often used in high speed tool steels in place of tungsten. Manganese increases hardenability, wear resistance and tensile strength. In molten metal it helps to de-oxidise and de-gas to remove oxygen, in larger quantities it increases hardness and brittleness. Silicon increases strength and also serves to de-oxidise and de-gas to remove oxygen in molten metal. The addition of copper helps to increase corrosion resistance.
High Strength Low Alloy Steels (HSLA Steels) These are low cost versions of regular alloy steels, containing only small amounts of the expensive alloying elements. Howvwer, they are specially processed to have greater strength than carbon steels of the same weight.
Stainless Steels These contain a minimum of 12 % chromium, which provides a much higher degree of rust resistance than carbon steels. The amount of chromium needed also depends on the other elements used in the steel. Chromium increases hardenability, tensile strength and toughness and provides wear and corrosion resistance.
Tool Steels These contain tungsten, molybdenum and other alloying elements that give them extra strength, hardness and resistance to wear.
Exotic Steels Although generally accepted as steel, these are not technically steels, for example, H1, ZDP-189, Telonite and Titanium
References:
Spyderco Product Guide 2008. Spyderco Knives, 820 Spyderco way, Golden, Colorado 80403, USA
Crucible-Data Sheet. Crucible Materials Corp. USA
Buck Knives. www.buckknives.com
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