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Steel And Metallurgic Terminology Glossary

   Considering that I have to use steel related terminology in steel sharts, in notes fot individual steels, reviews, articles, and consequently I get questions about those terms, I figure it's best if I put up a mini metallurgical glossary here.


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AISI
- American Iron and Steel Institute. An association of North American companies that mine iron ore and produce steel products. There are 50 member companies and more than 100 associate members, which include customers that distribute, process, or consume steel. The AISI has reorganized into a North American steel trade association, representing the interests of Canada, Mexico, and the United States.

Annealing
- A thermal treatment process, during which the grain structure of steel is recrystalized by allowing for new bonds to be formed at the higher temperature. Done by heating previously cold rolled steel sheet to a designated temperature, for a designated amount of time, and then cooled.

Alloy Steel
- By definition steels in which alloying elements exceed limits of the Carbon Steel, plus alloying elements not found in Carbon Steels such as Nickel, up to 3.99% (7.99% by another definition), Cobalt, etc.

ASTM
- American Society for Testing and Materials. A non-profit organization that provides a forum for producers, users, ultimate consumers, and those having a general interest (representatives of government and academia) to meet on common ground and write standards for materials, products, systems, and services.

Austenitic Stainless Steel
- Typically contains 18% chromium and 8% nickel and is widely known as 18-8. Nonmagnetic in annealed condition, this grade can only be hardened by cold working.

Carbides
- Simple explanation: Hard particles formed in steel when carbon forms with iron or transition metals.
In depth: Carbides control greatly the level of wear resistance and toughness in a steel. Because carbides are extremely hard, a great volume of them will make a steel very brittle, especially if the carbides are large and unevenly distributed. Steels vary from nearly 0% all the way to 30% carbide volume. (Auth. Larrin Thomas)

Carbon Steel
- By definition alloying elements do not exceed the following limits: 1% Carbon, 0.6% Copper, 1.65% Manganese, 0.4% Phosphorus, 0.5% Silicon, and 0.05% Sulfur.

Carbonitriding
- Case Hardening in which a suitable steel object is heated above Ac1 in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, to create a concentration gradient.

Case Hardening
- Generic term covering any of several processes applicable to steel that change the chemical composition or microstructure, or both, of the surface layer.

Cold Working
- Mechanical deformation of a metal at temperatures below its recrystallization temperature.

Cold Work Steel
- Steel used for cold working, i.e. blanking and forming of materials in cold condition, such as shearing, punching, cold forging, drawing, cold extrusion, rolling and powder pressing.

Edge Stability
- Simple explanation: Ability to hold a fine, acute, polished edge.
In depth: Edge stability is controlled most by carbide size and volume. The finer the carbide structure, the better a steel is at holding sharpness when sharpened very acutely and at a high polish. Evidences of a steel with low edge stability are losing initial sharpness quickly or chipping either while cutting or while sharpening with an acute bevel. The finer the edge and the finer the polish the more this will be apparent. Edge stability and toughness are often connected, but not always the same. Sometimes a steel can have high edge stability with fairly low toughness, or a steel with low edge stability can have moderate toughness. Blue Super has fairly high edge stability but low toughness; D2 has low edge stability but moderate toughness. Generally wear resistance and edge stability are opposed to each other since a greater volume of carbides means greater wear resistance but less toughness and edge stability, meaning one of the most important factors for selecting a steel are how much slicing it will be doing and how thick the edge will be. Usually edge stability is more important in kitchen knives.(Auth. Larrin Thomas)

Eutectic Mixture
- An eutectic mixture(also simply eutectic) is a mixture at such proportions that the melting point is a local temperature minimum, and all the components crystallize simultaneously at this temperature from molten liquid mixture. For steel(Iron and Carbon mix), it means crystallization of the Carbon. See also Eutectoid Point.

Eutectoid Point
- Temperature at which eutectic transformation occurs in molten steel. Speaking more metallurgical, this can be described as the austenite phase undergoing an eutectoid transformation to produce ferrite(solution with Iron as its main component) and cementite (iron carbide). For steel this point is at 727°C (1340.6°F), when Carbon content is about 0.83%. This is more accurate, metallurgical definition of High Carbon steel, C >= 0.83%, not more widespread marketing definition with 0.5% or more Carbon.

Ferretic Steel
- Contains very little nickel and either 17% chromium or 12% chromium with other elements such as aluminum or titanium. Always magnetic, this grade can only be hardened by cold working.

Grain size
- Simple explanation: Steel is made up of grains, smaller grains means greater toughness and strength. In depth: Smiths can vary heat treatment and forging processes to yield a finer grain size, though different steels are more easily heat treated for a finer grain size than others, this generally has to do with the alloy added, carbides "pin" the grain boundaries and prevent them from growing. The alloys with the highest melting point prevent grain growth the best. Vanadium and Niobium (Columbium) are often added to steels for finer grain. The reasons for grain size contributing to toughness and strength would require too much space to explain here. (Auth. Larrin Thomas)
ASTM definition of the Grain Size - The dimensions of the grains or crystals in a polycrystalline metal, exclusive of twinned regions and subgrains when present.

Hardening
- Increasing the hardness by suitable treatment, usually involving heating and cooling.

Heat Treatment
- Heating and cooling a steel object in such a way as to obtain desired conditions or properties.

High Carbon Steel
- More widespread definition and as mostly used in knives, defines high carbon steel as the steel with the Carbon content above 0.5%. However, correct metallurgical definition would be C above 0.83%, i.e. Eutectoid.

Heat
- Generic term denoting a specific lot of steel, based upon steelmaking and casting considerations.

Heat Number
- The alpha, numeric, or alphanumeric designator used to identify a specific heat of steel.

High Speed Steel
- Family of steels designed to hold an edge even when heated red hot by friction. While this is less likely to happen to your knife in everyday use, some of these steels have very high wear resistance. M2 tool steel or M4 tool steel for example. Though high speed tools at high hardness become rather brittle, thus not appropriate for large blades. However, when heat treatede properly M4 performs very well in large, heavy duty blades.

Hot-Cold Working
- mechanical deformation of austenitic and precipitation hardening steels at a temperature just below the recrystallization temperature to increase the yield strength and hardness by plastic deformation or precipitation hardening effects induced by plastic deformation, or both.

Hot Working
- Mechanical deformation of a metal at temperatures above its recrystallization temperature.

In Solution
- If alloy is "in solution" that means it is part of the steel and not currently tied up in carbides. This can also be called the matrix, e.g. there is 13% chromium in solution (the matrix).(Auth. Larrin Thomas)

Killed Steel
- Steel deoxidized to such a level that essentially no reaction occurred between carbon and oxygen during solidification.

Low Carbon Steel
- Steel with carbon content below 0.3%.

Lot
- Definite quantity of product manufactured under conditions that are considered uniform.

Martensitic Stainless Steel
- Typically contains 12% chromium and no nickel. This grade is magnetic and can be hardened by heat treatment.

Microalloyed Steel
- Low-Alloy steel that conforms to a specification that requires the presence of one or more carbide, nitride, or carbonitride-forming elements, generally in individual concentrations less than 0.15%, to enhance strength. The most common microalloying elements are Niobium (Columbium), Titanium and vanadium.
Matrix
- See In Solution.

Medium Carbon Steel
- Two definitions as with High Carbon Steel. In the knife marketing world it is a steel with C content between 0.3% and 0.5%. In metallurgy that would be the steel with C content below Eutectoid point - 0.83%.

Mild Steel
- generally refers to unhardenable steel, with very low Carbon content.

Nitriding
- Introducing nitrogen into a solid steel object by holding it at a suitable temperature in contact with a nitrogenous environment.

Quenching
- Rapid Cooling.

Recrystallization
- The formation of a new grain structure through a nucleation and growth process.

Recrystallization Temperature
- The approximate minimum temperature at which recrystallization of a cold-worked steel object occurs within a specified time.

Secondary Hardening
- The hardening phenomenon that occurs during high-temperature tempering of certain steels containing one or more carbide-forming alloying elements.

Stainless Steel
- By definition this type of alloys contain at least 10.50% chromium, with or without other elements. Based on the structures, stainless steels can be broken down into three groups: Austenitic, Ferritic, Martensitic. As per the Handbook of Comparative World Steel Standards book, stainless steel also has less than 1.20% Carbon.

Steel
- Common name for large family of Iron based alloys with Carbon content. Steel is easily malleable after molten stage. See also steel classifications.

Strength
- Simple description: To resist deformation or rolling.
In depth: Strength is most greatly controlled by the Rockwell hardness scale, abbreviated Rc, though different steels can have different yield or tensile strength even with the same Rockwell hardness. The things that factor into this are grain size and alloy in solution. According to Takefu steel (the makers of VG-10) Cobalt strengthens the matrix of steel, regardless of Rockwell hardness. Carpenter steel offers tensile and yield strength numbers of their steels at various hardnesses and the variety of strength numbers while at the same hardness for different steels can be observed. Generally strength and toughness are opposed to each other, raising the hardness lowers toughness. Only decreasing grain size increases both strength and toughness. Higher strength means the edge can be thinner, because the edge is less prone to rolling.(Auth. Larrin Thomas)

Tempering
- Reheating a quench hardened or normalized steel object to a temperature below Ac1, and then cooling it at any desired rate.

Toughness
- Simple explanation: Ability to resist chipping or breakage.
In depth: Toughness is controlled by amount of carbon in solution, the hardness the steel is heat treated to, the carbide size and volume, and the other alloy in solution. High amounts of chromium weaken grain boundaries (though generally carbide size and volume is the limiting factor as far as toughness in stainless steels). Nickel and silicon in moderate amounts increase toughness without effecting strength. Carbide size and volume are probably the greatest controlling factor for toughness. (Auth. Larrin Thomas)

Wear Resistance
- Simple explanation: The ability to resist abrasive wear.
In depth: Important when slicing, especially when slicing abrasive materials like rope and cardboard. Wear resistance is important for edge holding in many types of knives, but less important in general when it comes to kitchen knives, because edge stability, strength, and toughness are more important for holding an acute, polished edge. If a cook uses a slicing cut and the edge is thick (compared to Japanese and other thin kitchen knives), then wear resistance is beneficial. Generally greater wear resistance means it is more difficult to sharpen, so even with a knife that will benefit from a steel of greater wear resistance, less wear resistance may be preferred for easier resharpening.(Auth. Larrin Thomas)


Thanks and credits:

Special thanks Larrin Thomas of KF and Cotdt of BF for help with this page.



Last updated - 01/21/13