Abrasion Resistant. A series of steel "grades" specifically engineered for high-wear applications. The abrasion resistant (AR) grade is determined by the nominal Brinell hardness; for example, AR200 would have a nominal hardness of (or an HBN range centered around) 200.
Alloy. A metallic substance composed of at least two elements.
Alloy Steel. An iron-based alloy that contains elements (other than carbon) added in notable amounts to improve certain properties.
Annealing. A general term for heating steel to alter the mircostructure - and thus alter the properties. A microstructure will always want to be in its lowest energy state, but we often prevent this by "locking" a microstructure into place with rapid cooling or by inducing stress through cold working. Imagine playing a game of Scrabble, and trying to get all of the pieces in a single layer in the box. The pre-annealed box would be like the random heap of pieces right after they're thrown in, and annealing would be like shaking the box to allow the pieces to slowly fall into place. The heat allows the atoms in metals to diffuse (move), so they are able to find their lowest-energy configuration.
Austenite. A microstructure of steel that forms around 1300F.
Bainite. A microstructure that forms in temperatures between those at which pearlite and martensite form.
Bend Test. A test in which a sample is bent around a radius to evaluate its ductility and yield properties.
Blanking. Cutting small pieces from what's usually a narrow (previously slit) coil.
Brinell Hardness. A measure of a material's resistance to indentation using the Brinell scale. A small ball made of steel or tungsten carbide is used to make an indentation, and the size of the indentation is measured to produce the Brinell number. The Brinell hardness is roughly double the tensile strength (in ksi) of the sample; for example, a material with a Brinell hardness of 400 will have a tensile strength of roughly 200 ksi.
Butt Welding. Joining two components in the same plane by welding their edges together.
Camber. The deviation of a strip edge from a straight line.
Carbide. A compound composed of carbon and one other element.
Carburizing. Using diffusion to increase the carbon content at the surface of a ferrous alloy (like steel). Increasing the concentration of carbon increases the steel's ability to be hardened through quenching, which improves wear and fatigue resistance. This process can also be referred to as Case Hardening, a more general term for hardening a steel component through carburizing or nitriding.
Casting. Pouring molten metal into a mold. Steel plates and coils are produced through continuous casting, where molten steel is poured into a bottomless vertical mold that continuously produces steel slab.
Charpy Test. See Impact Testing.
Chatter. Fixed-interval lines going across the width of the coil. Chatter is the result of vibrations in the mill (cold or hot).
Coke. A fuel used in the blast furnace where iron ore is converted to pig iron. Coke is made by heating coal, which burns off impurities. The carbon in coke reacts with the oxygen in the iron oxides to form carbon monoxide, leaving a reduced iron product in the form of pig iron.
Cold Reduction/Rolling. Passing a room-temperature steel strip through a set of rolls to reduce the thickness. Unlike hot rolling, dislocations created during cold reduction do not "heal," and the result is cold working. Cold rolling produces a bright, shiny finish.
Cold Working. Increasing dislocation density through plastic deformation. When the dislocation density is increased, dislocations that were previously mobile become locked in strain fields. This increases the strength of the material, but simultaneously reduces its ductility.
Corrosion. A phenomenon in which the environment destructively deteriorates a metal. Corrosion takes place through coupled half-cell reactions. Contact with water corrodes steel, and contact with salt water exponentially so.
CQ. ASTM's abbreviation for commercial quality. Other hot roll designations include Drawing Steel (DS), Structural Steel (SS), High-Strength Low-Alloy Steel (HSLAS), High-Strength Low-Alloy Steel with Improved Formability (HSLAS-F), and Ultra-High Strength Steel (UHSS). Cold roll designations additionally include Deep Drawing Steel (DDS), Extra Deep Drawing Steel (EDDS), and Special Forming Steel (SFS). Commercial quality and drawing quality are given chemistry requirements, but mechanical property limits are non-mandatory.
Crown. The parabolic bend of a roll or a strip of steel, usually measured in thousands of an inch. A parabolic profile is more easily guided through the stands at a hot strip mill than a flat profile, which can be harder to steer. The work rolls' crown on a temper pass line is made to match the crown of the incoming coil - this creates uniform elongation. Mismatched crown (either too small or too large) can create shape defects such as wavy edges and center buckle.
Crystal Structure. For crystalline materials, or materials in which one particular formation of atoms is repeated throughout the material, the crystal structure is the general atomic arrangement.
Decarburization. Loss of carbon from the surface of a component.
Discontinuous Yielding. When the movement of dislocations is impeded by interstitial atoms the material exhibits a "upper yield point" and a "lower yield point." Dislocations are pinned by carbon and nitrogen atoms, and they become immobilized until a rise in stress allows them to be freed (upper yield point). During this rise in stress, unpinned dislocations multiply. The mobile dislocations decrease the stress level required to continue plastic deformation, and the stress reaches a lower yield point. This phenomenon can occur in ultra low carbon steels, and is the source of the surface defect known as coil breaks.
Discrete Plate. The product of a steel slab being rolled through a hot strip mill without coiling at the end.
Dislocation. An atomic-level defect around which some of the adjacent atoms are misaligned. Dislocations may present as an extra half-plane of atoms or a shift in one plane of atoms relative to another, or a combination of both. Dislocations can move - in fact, permanent deformation occurs by the motion of dislocations. If the dislocations can't move, a material can't plastically deform. Restricting the movement of dislocations makes a material harder and stronger. Dislocations can be "healed" through recrystallization (heat treatment).
DQ. See CQ.
Ductility. The amount of plastic deformation a material can withstand before fracturing. The ductility is usually measured as a percentage of elongation (below), and it's calculated by comparing the initial and final length of a specimen during tensile testing.
Elongation. Before performing a tensile test, the specimen gage length is marked and measured. After the tensile test has been performed, the gage length is remeasured using the same markings. The maximum gage length is divided by the original gage length to generate a percentage. This is the elongation.
Endurance Limit. In relation to fatigue, the endurance limit (or fatigue limit) is the maximum stress amplitude that a material can be subjected to, for infinite cycles, without failure.
Fatigue. The weakening of a material due to cyclic loading. Material failure due to fatigue has three stages: crack initiation, crack propagation, and fracture.
Full Hard. Steel that has been cold rolled and not subsequently annealed or heat treated for stress relief. Cold rolling increases the dislocation density, which increases the hardness of the steel.
Grain. A group of atoms with the same crystallographic orientation. At a grain boundary, two different crystallographic orientations meet. Grain size is one of the factors that determines the strength of a metal; smaller grains increase the strength.
Grain Growth. Temperature increases allow diffusion to occur more rapidly, allowing grains to merge and reorient.
Hardenability. The hardenability of a steel is a property that expresses how easily the steel can be hardened through thermal treatment. It is determined using the Jominy End Quench Test. Hardenability is influenced by chemical composition.
Heat-Affected Zone. Often referred to as HAZ, the heat-affected zone is a perimeter around a thermal cut or joint (laser cutting, welding) where the material was heated to the point that its microstructure changes from its original state.
Heat Treat. Increasing the temperature of steel to allow microstructural changes to take place.
Hot Rolling. Reducing the thickness of a steel slab in austenitic temperature ranges. At high temperatures, the microstructure is malleable and able to "heal" itself, and dislocations don't build up like they do during cold rolling.
Hydrogen Embrittlement. Because hydrogen atoms are so small, they can permeate the surface of steel and decrease toughness and ductility. Hydrogen can also be incorporated during the steelmaking process.
Impact Testing. A measure of a material's ability to absorb energy. Energy is absorbed through plastic deformation, so materials that are brittle can't absorb as much energy as ductile materials. An impact test is especially important for cold-environment applications, as some steels exhibit a "ductile-to-brittle" transition at low temperatures, and a certain steel's ability to absorb an impact (energy) may be compromised.
Inclusions. Nonmetallic phases introduced in the steelmaking process. Indigenous inclusions are the result of a chemical reaction that takes place in the steel, and are usually present in large quantities. For example, alumina inclusions are the result of deoxidizing with aluminum (see killed steel). Exogenous inclusions occur when an outside substance becomes entrapped in the steel (broken refractory brick, slag, etc.). Inclusions play a major role in reducing fracture resistance, which detrimentally affects impact strength and in some cases fatigue resistance.
Killed Steel. The solubility of oxygen in molten steel is higher than the solubility of oxygen in cooled steel, so unless the oxygen is removed or tied up in a compound the oxygen can create bubbles and even blowholes as the steel cools. The term "killed" is used because deoxidized steel cools calmly. Silicon and aluminum are used to deoxidize steel, and aluminum also provides excellent austenitic grain size control.
Machinability. The ease with which a steel can be cut. Sulfide inclusions improve machinability by reducing fracture resistance, while silicate and other hard oxides inclusions are disadvantageous.
Microstructure. The structural features of a metal or alloy that are visible under a microscope. Grains and phases are part of the microstructure.
Normalizing. A heat treatment process that involves heating the steel to austenitic temperatures and then allowing it to cool in room temperature air. This increases ductility and toughness and gives the steel a uniform, fine-grained microstructure.
Orange Peel. A rough surface appearance similar to that of an orange peel. The rough surface is usually a result of forming a steel with large grains.
Pearlite. A two-phase microstructure composed of ferrite and cementite. It is one of three microstructures that result from cooling austenite, with the other two being martensite and bainite, which require faster cooling rates.
Phase. A distinctive and homogeneous form or portion of a system that has uniform characteristics.
Pickling. Passing steel through an acid bath to remove the outer surface layer. Pickling "cleans" the surface by removing scale, rust, and dirt.
Process Annealing. Heating cold-worked steel near but below austenitic temperatures to soften the microstructure.
Quenching. Quickly cooling a heated material in order to form a desired microstructure.
Reel Breaks. Raised lines across the width of the steel, usually confined to the head (OD) or tail (ID) of a coil depending on the processing. Reel breaks form at the head of the coil as it is wrapped around a down coiler; they're caused by the kink the very head of the coil creates when it is cinched by the mandrel. Reel breaks can be formed at any coil-to-coil process, but heavy gauges and soft steel are particularly susceptible.
Residual Stress. Stress that is present in the steel that is free of external loading or force. Temper mills and stretcher levelers are designed to realign residual stresses as the steel is uncoiled; any residual stress that remains may cause the steel to warp when it is processed further.
Rolling Direction. The alignment of the grains caused by rolling down to thickness at the hot strip mill. Grains are elongated parallel to the rolling direction. This leads to anisotropic properties, and it's the reason there are two testing directions: transverse ("against" the grains) and longitudinal ("with" the grains).
Scale. An iron oxide that forms when iron is in contact with air. It's formation is accelerated by heat, water, and especially salt water.
Segregation. As steel solidifies during casting, the first solid to form has a much lower alloy content than the liquid steel. As the solidification continues, the alloy content of the liquid continuously increases, until the last solid forms with a significantly higher concentration of alloys.
Slag. A by-product of the steelmaking process. Undesirable impurities undergo chemical reactions and float to the surface of the molten steel, forming slag. Slag also protects the steel from being exposed to oxygen at the surface.
Spheroidizing. Heating and cooling steel to produce spheroidal carbides. Heating the steel allows for diffusion to take place, and atoms will migrate to form structures with the lowest free energy - spheres.
Stress. Stress = Force / Area. It is a load applied to a cross-sectional area either in compression or tension.
Stress Relieving. Heat treating to remove residual stress.
Stretcher Leveling. Realigning residual stress (usually from a coil product) by gripping each end of a section and pulling the material flat.
Temper Pass. Realigning residual stress (usually from a coil product) by feeding the material through a set of rolls that squeeze the material. A small thickness reduction takes place.
Tempering. A heat treatment that softens hardened steel and improves toughness.
Tensile Strength. The maximum stress that can be sustained without fracturing. Synonymous with "ultimate" tensile strength.
Toughness. A material's resistance to fracture. Toughness can also be expressed as the ability of a material to absorb energy by plastically deforming - this is measured by a Charpy impact test.
Work Hardening. See Cold Working.
Yield Point Elongation. The elongation that occurs during discontinuous yielding.
Yield Strength. The stress required to produce a slight amount of plastic strain. The yield strength signifies the end of the elastic response and beginning of plastic deformation; it's the point where the material begins to yield. In some materials this transition is gradual, and the yield stress can be measured using a 0.2% strain offset.
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