Steel Terminology Glossary

American Society for Testing Material, an organization founded in 1898 for issuing standard specifications on material, including metals and alloys.

Cooling of the heated metal, intermediate in rapidity between slow furnace cooling and quenching, in which the metal is permitted to stand in the open air.

A steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range.

Steels of the American Iron and Steel Institute. AISI is a North American trade association with 50 member companies and more than 100 associate members. These companies represent the United States, Canada, and Mexico in all aspects of the steel industry. Common and alloy steels are numbered in a system essentially the same as the SAE. The AISI system is more elaborate than the SAE in that all numbers are proceeded by letters: “A” represents basic open-hearth alloy steel, “B” acid Bessemer carbon steel, “C” basic open hearth carbon steels, “CB” either acid Bessemer or basic open-hearth carbon steel, “E” electric furnace alloy steel.

A material that is dissolved in another metal in a solid solution; a material that results when two or more elements combine in a solid solution.

A steel that has had small amounts of one or more alloying elements (other than carbon) such as such as manganese, silicon, nickel, titanium, copper, chromium and aluminum added.

Metallic or non-metallic elements such as aluminum, boron, chromium, cobalt, copper, manganese, nickel, silicon, titanium, tungsten, vanadium, zirconium, added in specified or standard amounts to a base-metal to make an alloy.

A generic term denoting a heat treatment consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften but also to simultaneously produce desired changes in other properties or microstructure.

A technique used to form pure bainite, a transitional microstructure found between pearlite and martensite. In normalizing, both upper and lower bainite are usually found mixed with pearlite. To avoid the formation of pearlite or martensite, the steel is quenched in a bath of molten metals or salts. This quickly cools the steel past the point where pearlite can form, and into the bainite-forming range. The steel is then held at the bainite-forming temperature, beyond the point where the temperature reaches an equilibrium, until the bainite fully forms. The steel is then removed from the bath and allowed to air-cool, without the formation of either pearlite or martensite.

The basic steel structure state in which an alloying is uniformly dissolved into iron.

Phase in certain steels, characterized as a solid solution, usually off carbon or iron carbide, in the gamma form of iron. Such steels are known as “austenitic.” Austenite is stable only above 1333°F in a plain carbon steel, but the presence of certain alloying elements, such as nickel and manganese, stabilizes the austenitic form, even at normal temperatures.

An alloy which, because of the presence of alloying elements such as manganese, nickel and chromium, shows stability of austenite at normal temperatures.

A plate-like crystalline microstructure that can be found in steel. Bainite forms when a steel is cooled slower than the rate required to form martensite but faster than the rate that would be required to form pearlite or other slower cooling rate crystalline microstructure.

Semi-finished or finished piece of metal in a straight length.

A steelmaking process in which air is blown through the molten iron so that the impurities are thus removed by oxidation. Sir Henry Bessemer (1813-1898) was an English inventor who patented the first inexpensive industrial process for the mass-production of steel from molten pig iron.

The second-stage product of steel production. An ingot or bloom that has been reduced by hot-rolling and are taken out directly during casting process of steel. They are highly ductile and soft and produced in a square cross-section of area less than 36 square Inches.

A vertical shaft-type smelting furnace in which an air blast is used, usually hot, for producing pig iron. The furnace is continuous in operation using iron ore, coke, and limestone as raw materials that are charged at the top while the molten iron and slag are collected at the bottom and are tapped out at intervals.

A semi-finished form of steel that will be further processed into mill products. A bloom generally has a cross section greater than 36 square inches.

A hot rolling mill that takes continuously cast slabs or ingots and processes them into blooms.

Usually added in trace amounts between .0005-.003% to significantly increase the hardenability, especially for low carbon alloys.

Brazing and soldering are techniques for joining metals in the solid state by means of a fusible filler metal with a melting point well below that of the base metal.

A process of annealing usually carried out in a controlled atmosphere so that the surface oxidation is reduced to a minimum and the surface remains relatively bright.

A common standard method of measuring the hardness of certain metals. The smooth surface of the metal is subjected to indentation by a hardened steel ball under pressure or load. The diameter of the resultant indentation in the metal surface is measured by a special microscope and the Brinell hardness value read from a chart or calculated formula.

Describes a material’s tendency to break before bending or deforming either elastically or plastically. Brittleness increases with decreased toughness, but is greatly affected by internal stresses as well.

Increases edge retention and raises tensile strength. Increases hardness and improves resistance to wear and abrasion.

Common or ordinary steel as contrasted with special or alloy steels, which contain other alloying metals in addition to the usual constituents of steel in their common percentages. There are 3 types of Carbon Steels, Low (.3% or less), Medium (.4-.7%) and High (.8% and up). High carbon is commonly used for knives.

The oldest method of case hardening in which carbon is added to the surface of iron-base alloys by absorption through heating the metal at a temperature below its melting point, in contact with carbonaceous solids, liquids or gases.

Hardening a ferrous alloy to make the outside (case) much harder than the inside (core). This can be done by carburizing, cyaniding, nitriding, carbon nitriding, induction hardening or flame hardening. Their application to stainless steel is limited wherever they decrease corrosion resistance.

Any object made by pouring molten steel into molds.

To shape molten metal by pouring into a mold to produce an ingot or a continuously cast slab.

A crystalline microstructure that can be found in steel consisting of iron and carbon compounds combined chemically, having the chemical symbol Fe3C. It is composed of 93% iron and 7% carbon. Cementite is also known as iron carbide. In some cases, cementite combines with ferrite, a byproduct of austenite, in order to build bainite and pearlite or lamellar structures.

The material that is loaded into an electric furnace that will melt into a composition that will produce a molten steel alloy. Normally recycled scrap, pure iron, and alloying elements.

Also known as the Charpy V-notch test, this test is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material’s notch toughness and acts as a tool to study the qualitative results of the impact test can be used to determine the ductility of a material.

A report of the chemical composition of the elements and their percentage that form a metal alloy.

Chromium (Cr) – Increases hardness, tensile strength, and toughness. Provides resistance to wear and corrosion. Essentially, it is the element that makes stainless steel stainless.

Increases strength and hardness, and permits quenching in higher temperatures. Intensifies the individual effects of other elements in more complex steels.

Cold forming is the process of forging metals at near room temperatures. In cold forming metal is formed at high speed and high pressure into tool steel or carbide dies. The cold working of the metal increases the hardness, yield, and tensile strengths.

A steel-forming process whereby molten metal is solidified into a semi-finished billet, bloom, or slab for subsequent rolling in the finishing mills.

Increases corrosion resistance. The main element used in brass, bronze, and nickel silver.

Gradual chemical or electrochemical attack on a metal by atmosphere, moisture or other agents.

The ability of a metal to resist deterioration as a result of a reaction to its environment. Provided by the elements Chromium (Cr), Copper (Cu), Molybdenum (Mo) and Nitrogen (N).

The proprietary process has been used for the commercial production of high speed steels and other high alloy tool steels since 1970 by Crucible Industries. The process lends itself not only to the production of superior quality tool steels, but to the production of higher alloyed grades which cannot be produced by conventional steelmaking. For most applications the CPM process offers many benefits over conventionally ingot-cast tool steels.

A temperature range in which an internal change takes place within a metal. Also referred to as transformation range.

The temperature at which steel changes its structure to austenite in preparation for hardening.

A ceramic pot or receptacle made of graphite and clay, or clay or other refractory material, and used in the melting of metal. The term is sometimes applied to pots made of cast iron, cast steel, or wrought steel.

Removal of carbon from the outer surface of iron or steel, usually by heating in an oxidizing or reducing atmosphere. Water vapor, oxygen and carbon dioxide are strong decarburizers. Reheating with adhering scale is also strongly decarburizing in action.

Created by Boye Knives, this blade material is a super-performing, investment cast non-rusting cobalt alloy. The process used to produce it transforms the original alloy into one infused with microscopic crystals which create tiny serrations along the blade edge. Not a steel, it cuts aggressively and keeps cutting, is completely impervious to seawater corrosion, and is non-magnetic. Named for the tree-like crystal patterns in the steel (from the Greek Dendron = tree, Greek Dendritēs = treelike).

A term first used by knifemaker David Boye to describe the cast 440C stainless steel he developed in 1981. The process used to produce it, investment casting, transforms the original steel into one infused with microscopic crystals which create tiny serrations along the blade edge. Named for the tree-like crystal patterns in the steel (from the Greek Dendron = tree; Greek Dendritēs = treelike).

A process that removes the oxide scale from the surface of the stainless steel, which develops from hot operations such as forging.

Ductility is a physical property of a metal that defines the ability to withstand tensile stress and the plastic deformation that occurs—any force that pulls the two ends of a material away from each other. The term “ductile” literally means that a metal substance is capable of being stretched out into a thin wire, and it does not become weaker or become brittle in the process. The opposite of malleability. Provided by the element Manganese (Mn).

The ability of a material to resist abrasion and wear. Provided by the elements Carbon (C), Chromium (Cr), Manganese (Mn), Nitrogen (N) and Vanadium (V).

Also called flexibility, this is the ability to deform, bend, compress, or stretch and return to the original shape once the external stress is removed.

A loss of ductility of a material, making it brittle.

The body-centered cubic crystalline phase of iron-based alloys.

Related to iron (derived from the Latin ferrum). Ferrous alloys are, therefore, iron-base alloys.

A form of hot working whereby metal is heated and formed into a desirable shape by pressing or hammering.

Coating steel with zinc and tin (principally zinc) for rust proofing purposes.

The thickness of sheet metal is in the USA commonly specified by a traditional, non-linear measure known as its gauge. The larger the gauge number, the thinner the metal. Commonly used steel sheet metal ranges from 30 gauge to about 7 gauge.

The divisions within different types of steel based on carbon content or mechanical properties.

The individual crystal units in metals. A solid polyhedral (or many sided crystal) consisting of groups of atoms bound together in a regular geometric pattern.

The average grain diameter from a random cross-section of material.

The ability of a steel to be hardened by a heat treating process. Provided by the elements Manganese (Mn), Molybdenum (Mo) and Tungsten (W).

Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting.

Hardness testing consists of pressing an indenter into a flat surface under a perfectly controlled load, then measuring the dimension of the resulting indentation. The three methods most commonly used for stainless steel are the Rockwell B, Rockwell C and Vickers tests. The higher the number, the harder the material.

Steel consists of a microstructure of small crystals called grains or crystals. Heat treatment provides an efficient way to alter the crystalline structure and mechanical properties of a steel alloy, manipulating properties such as the hardness, strength, toughness, ductility, and elasticity.

The phenomenon by which metals such as steel become brittle and fracture due to the introduction and subsequent diffusion of hydrogen into the metal. This is often a result of accidental introduction of hydrogen during forming and finishing operations.

Usually synonymous with high-strength toughness, it is the ability resist shock-loading with minimal deformation.

The ability of a material to resist cracking due to a sudden force.

An initial cast form that results from a molten alloy being poured into an ingot mold. Remelted alloys also are called ingots.

A mineral that contains enough iron to be a factor in stainless steel production.

A similar property to ductility, it is a material’s ability to deform under compressive stress by hammering, rolling, or pressing.. Both of these mechanical properties (ductility and malleability) are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture.

Increases hardenability, wear resistance, and tensile strength. Deoxidizes and degasifies to remove oxygen from molten metal. In larger quantities, increases hardness and brittleness.

A body-centered tetragonal form of iron in which some carbon is dissolved. Martensite forms during quenching, when the face centered cubic lattice of austenite is distored into the body centered tetragonal structure without the loss of its contained carbon atoms into cementite and ferrite.

Sometimes called Powdered Injection Molding (PIM), is an advance metal forming technique that uses injection molding equipment for manufacturing both simple and complex metal parts to tight tolerances. The process involves combining metal with a binder that is injected as a liquid into a mold. The molded or “green part” is cooled and ejected from the mold. The molded part is then sintered (heated) to temperatures near the melting point in a protective atmosphere furnace to densify the particles using capillary forces in a process called Sintering. If performed in vacuum, it is common to reach 96-99% solid density. The end-product metal has comparable mechanical and physical properties with annealed parts made using classic metalworking methods. Post sintering heat treatments for MIM are the same as with other manufacturing processes.

Increases strength, hardness, hardenability, and toughness. Improves machinability and resistance to corrosion.

Adds strength and toughness.

Also known as Columbium. Improves strength and toughness. Provides corrosion resistance. Improves grain refinement and precipitation hardening.

Used in place of carbon for the steel matrix. The Nitrogen atom will function in a similar manner to the carbon atom, but offers unusual advantages in corrosion resistance.

Non-iron based metal, including copper, aluminum and their alloys (e.g., brass and bronze).

Metal oxidation takes place when an ionic chemical reaction occurs on a metal’s surface while oxygen is present. The chemical process involves the movement of electrons from the metal to the oxygen molecules. Then, negative oxygen ions generate and enter the metal. This leads to the creation of an oxide surface, i.e., rust. Oxidation is a form of metal corrosion.

When exposed in air, stainless steels passivate naturally (due to the presence of chromium). But the time required can vary. In order to ensure that the passive layer reforms rapidly after pickling, a passivation treatment is performed using a solution of nitric acid and water.

A characteristic condition of stainless steels which impedes normal corrosion tendencies to the point where the metal remains virtually un-attacked — hence passive to its environment.

A two-phased, lamellar (or layered) structure composed of alternating layers of ferrite and cementite that occurs in some steels formed by the cooling of austenite. Pearlite is a common microstructure occurring in many grades of steels. It is hard as well as strong because of the layered structure, and is used in a variety of applications. It is wear resistant because of a strong lamellar network of ferrite and cementite.

Improves strength, machinability, and hardness. Creates brittleness in high concentrations.

Localized corrosion (in the form of pits) of a metal surface that is confined to a small area.

The ability to mold, bend or deform in a manner that does not spontaneously return to its original shape. This is proportional to the ductility or malleability of the substance.

A term covering a wide range of ways in which materials or components are made from metal powders.

A process of hardening a ferrous alloy of suitable composition by heating within or above the transformation range and cooling at a rate sufficient to increase the hardness substantially. The process usually involves the formation of martensite.

In the heat treating of steel that has reached a high temperature (above the recrystallization phase), the step of cooling metals rapidly in order to obtain desired properties; most commonly accomplished by immersing air, liquid, oil, or water to rapidly cool it. This rapid quenching creates martensite.

A standard method for measuring the hardness of metals. The hardness is expressed as a number related to the depth of residual penetration of a steel ball or diamond cone (“brale”) after a minor load of 10 kilograms has been applied to hold the penetrator in position. This residual penetration is automatically registered on a dial when the major load is removed from the penetrator. Various dial readings combined with different major loads, give “scales” designated by letters varying from “A” to “H”; the “C” scale is most commonly in used for cutlery steels. The designated scale reading is notated as the scale number followed by HRC.

Increases strength. Deoxidizes and degasifies to remove oxygen from molten metal.

The process of bonding (fusing) of adjacent surfaces in a mass of particles by molecular or atomic attraction on heating at high temperatures below the melting temperature of any constituent in the material. Sintering strengthens a powder mass and normally produces densification and, in powdered metals, recrystallization.

An alloy of Iron with a minimum of 10.5% Chromium. Chromium produces a thin layer of oxide on the surface of the steel known as the ‘passive layer’. This prevents any further corrosion of the surface. Increasing the amount of Chromium gives an increased resistance to corrosion.

Improves machinability when added in minute quantities.

A process of heat treating, which is used to increase the toughness of iron-based alloys, by reducing hardness, precipitating carbides, relieving stress, and to improve elasticity and plasticity. Tempering is performed after hardening and involves heating the metal to a precise temperature below the critical point, and is often done in air, vacuum or inert atmospheres. Hardened, but un-tempered steel is too hard and brittle for most applications.

A non-ferrous metal that is lightweight, highly corrosion resistant, has a high degree of tensile strength, and superior strength-to-weight ratios. Approximately 40% lighter that steel.

Refers to a variety of carbon and alloy steels that are particularly well-suited to making tools. Tool steel is a particularly hard material that withstands heat and resists abrasion, and is available in a number of grades that are each suited to specific applications, such as punches, dies or cutting applications.

The ability of a material to resist fracturing when force is applied. Toughness requires strength as well as ductility, which allows a material to deform before fracturing. shock or impact.

An advanced material that is very hard and wear resistant, making it suitable for severe service applications such as cutting and grinding tools.

Adds strength, toughness, and improves hardenability.

A process in which raw materials are first melted within a vacuum using the heat from an induced magnetic field. The metal is often remelted again under a vacuum to produce very pure alloys. Together, these processes result in tighter control of a metal’s chemistry and greater consistency in structural properties such as toughness, ductility, and fatigue strength.

Increases strength, wear resistance, and increases toughness.

A testing method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated.

The ability of material to resist being abraded or eroded by contact with work material. Wear resistance is provided by both the hardness level and the chemistry of the alloy. Usually synonymous with hardness.

Increase in resistance to deformation (i.e., in hardness) produced by cold working.