Metallurgy Terms - Industrial Metallurgists

Metallurgy Terms

List of metallurgy terms, definitions, and courses we offer to learn more

A1 critical temperature: Applies to the iron-carbon alloy and phase diagram. The temperature at which transformations from austenite to ferrite + cementite during cooling and from cementite + ferrite to austenite occur under controlled, very slow cooling and heating (i.e., equilibrium) conditions. More rapid cooling and heating rates, like those encountered during normal steel processing, change this critical temperature downward and upward, respectively. Additions of other alloying elements also will shift the A1 critical temperature. To learn more see our Steel Metallurgy course.

A3 critical temperature: Applies to the iron-carbon alloy and phase diagram. The temperature at which steel with less than 0.78% carbon becomes 100% austenite during heating and at which austenite starts to transform to ferrite during cooling. This applies to controlled, very slow heating and cooling (i.e., equilibrium) conditions. More rapid heating and cooling rates, like those encountered during normal steel processing, change this critical temperature upward and downward, respectively. Additions of other alloying elements also will shift the A3 critical temperature. To learn more see our Steel Metallurgy course.

Acm critical temperature: Applies to the iron-carbon alloy and phase diagram. The temperature at which steel with more than 0.78% carbon becomes 100% austenite during heating and at which austenite starts to transform to cementite during cooling. This applies to controlled, very slow heating and cooling (i.e., equilibrium) conditions. More rapid heating and cooling rates, like those encountered during normal steel processing, change this critical temperature upward and downward, respectively. Additions of other alloying elements also will shift the Acm critical temperature. To learn more see our Steel Metallurgy course.

Activation polarization: To learn more see our Metal Corrosion course.

Active metal: A metal with a tendency to corrode when exposed to a corrosive environment. The electrode potential of a metal exposed to a specific aqueous solution can be measured to determine whether the metal is electrochemically active or noble. Learn more from our Metal Corrosion course.

Aging: A heat treatment process that results in the transformation of a supersaturated solid solution to precipitate particles that strengthen an alloy. Aging is used with certain aluminum alloys, PH stainless steels, copper-beryllium alloys, and other alloys. To learn more see our Principles of Metallurgy, Aluminum Metallurgy, and Precipitation Strengthening courses.

Anneal: heat treatment used to reduce metal strength and increase metal ductility. All metals can be annealed after cold working. Carbon, low-alloy, and tool steels can also be full-annealed and spheroidize annealed. To learn more see our Principles of Metallurgy and our Steel Metallurgy courses.

Anode: In a corrosion cell, the anode is the metal or site on a metal where oxidation (loss of electrons) occurs. The anode has a more negative electrode potential than the cathode. To learn more see our Metal Corrosion course.

Aqueous corrosion: Metal Corrosion

Artificial aging: Elevated temperature aging of aluminum alloys to form strengthening precipitate particles. See "aging" definition. To learn more see our Principles of Metallurgy, Aluminum Metallurgy, and Precipitation Strengthening courses.

Austenite: A metallic, non-magnetic solid solution of iron with carbon and other alloying elements. In plain-carbon steel, austenite exists above 727 °C. Other steel alloys have different eutectoid temperatures. Austenite exists at room temperature in some stainless steels due to the presence of nickel which stabilizes austenite at lower temperatures. To learn more see our Steel Metallurgy course Stainless Steel Metallurgy video.

Austenitize: The process of heating steel to form 100% austenite. Involves heating steel above the Acm or A3 critical temperature. To learn more see our Steel Metallurgy course.

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Bainite: Combination of ferrite and cementite in steel. The ferrite has a plate or needle shape and cementite is present as small particles. Bainite forms when carbon, low-alloy, and tool steels are cooled fast enough to avoid forming pearlite (plates of cementite and ferrite between the plates). To learn more about bainite see our Steel Metallurgy course.

Barrier coating: Physical barrier between a metal and its environment. The purpose of a barrier coating is to prevent a corrosive element from contacting the substrate. Barrier coatings include a wide variety of metals, polymers, and ceramics that are applied to a substrate using a wide variety of techniques. To learn more see our Corrosion of Metals course.

Body-centered cubic: An arrangement of atoms in a unit cell, where atoms occupy sites at the corner of a cube and at the center of the cube. Examples of body centered cubic metals include iron and chromium. To learn more see our Principles of Metallurgy course.

Cathode: In a corrosion cell, the cathode is the metal or site on the metal where reduction (gain of electrons) occurs. The cathode has a more positive or less negative electrode potential than the anode. To learn more see our Corrosion of Metals course.

Cathodic protection: Cathodic protection is used to control the corrosion of a metal by making it the cathode of an electrochemical cell. One method of protection connects the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode. The sacrificial metal then corrodes instead of the protected metal. An example is applying a zinc coating over a steel component, with the steel being cathodically protected by the zinc. For structures, such as pipelines and storage tanks, an external DC electrical power source is used to provide sufficient current between the anode and cathode to ensure protections of the structure. To learn more see our Corrosion of Metals course.

Cementite (iron carbide): A compound of iron and carbon with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It is a hard, brittle material and has an orthorhombic crystal structure. It is a metallurgical phase in steels and cast irons, and can be present as plates or particles, depending on how a steel or cast iron is processed. To learn more about cementite see our Principles of Metallurgy and Steel Metallurgy courses.

Chromium carbide precipitates: Chromium carbide precipitates form in austenitic stainless steels exposed to between about 425 and 870 C in some ferritic stainless steels exposed to over about 925 C. The precipitates form on the grain boundaries. Their formation enables corrosion by intergranular corrosion when an alloy is exposed to a corrosive environment, such as environments that contain chloride ions. To learn more see our Corrosion of Metals course and Stainless Steel Metallurgy video.

Coarsening: Precipitation Strengthening, Principles of Metallurgy

Cold rolling: A metal forming process in which metal plate or sheet, at room temperature, is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The temperature of the metal is below its recrystallization temperature. To learn more see our Principles of Metallurgy course.

Cold working: Any metalworking process in which metal is shaped below its recrystallization temperature, usually at the ambient temperature. This includes rolling, drawing, bending, and shearing processes. Cold working causes metal grains to distort in the direction of the flow of the metal and causes work hardening, making the metal stronger and harder while reducing its ductility. To learn more see our Principles of Metallurgy course.

Concentration cell: Water and other aqueous solutions in contact with a metal will normally contain dissolved oxygen. An oxygen cell can develop at any point where the oxygen in the air is not allowed to diffuse uniformly into the solution, thereby creating a difference in oxygen concentration between two points. Corrosion will occur at the area of low-oxygen concentration, which is anodic to the area of higher oxygen concentration. Crevice corrosion occurs due to the formation of a concentration cell.To learn more see our Corrosion of Metals course.

Concentration polarization: To learn more see our Corrosion of Metals course.

Corrosion cell: To learn more see our Corrosion of Metals course.

Corrosion reactions: To learn more see our Corrosion of Metals course.

Crevice corrosion: Crevice corrosion occurs in crevices between components and under surface debris, polymer coatings, adhesives. The driving force for the corrosion is the difference between the oxygen concentration inside the crevice and outside the crevice. To learn more see our Corrosion of Metals course.

Crystal structure: Describes the arrangement of atoms in a unit cell and the spacing between the atoms. Examples of arrangements of atoms include body-centered cubic (BCC) and face-centered cubic (FCC).  To learn more see our Principles of Metallurgy course.

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Dealloying: The selective leaching of the atoms of one element from an alloy. This results in the formation of a porous structure that is not strong enough to support the applied mechanical loads. One common example is dezincification of brass alloys used for plumbing, where the zinc is leached out of the alloy. To learn more see our Corrosion of Metals course.

Dezincification: A form of dealloying and occurs in brass alloys that contain more than 15% zinc. The zinc atoms leach out of the brass, resulting in the formation of a porous metal and reduction of the metal's strength. To learn more see our Corrosion of Metals course.

Differential aeration cell: A corrosion cell that arises due to differences of dissolved gas or ions in an electrolyte at adjacent areas on a piece of metal. A common form of a differential aeration cell is the oxygen concentration cell, which is caused by a difference in electrolyte oxygen concentration between two adjacent areas on a metal. When there is a difference in the concentration of dissolved oxygen at two points on a metal surface, the area in contact with electrolyte containing the higher concentration of dissolved oxygen will become cathodic to areas in contact with electrolyte with a lower concentration of dissolved oxygen. As a result, the anodic surface undergoes accelerated corrosion. Crevices between metal are susceptible to oxygen concentration cell formation. To learn more see our Corrosion of Metals course.

Diffusion: The motion of atoms through a metal. Diffusion is important for heat treating as the motion of atoms results in changes to a metal's microstructure, which results in changes to a metal's properties. To learn more see our Principles of Metallurgy course and Five Key Metallurgy Concepts video.

Diffusivity: The speed of atom motion through a metal during diffusion. Depends on the primary element in a metal, the element of the atom diffusing, and the metal's temperature. To learn more see our Principles of Metallurgy course.

Discontinuous yielding: Tensile Testing

Dislocation motion: To learn more see our Principles of Metallurgy course.

Dislocation: To learn more see our Principles of Metallurgy course.

Drawing: To learn more see our Principles of Metallurgy course.

Edge dislocation: To learn more see our Principles of Metallurgy course.

Elastic deformation: Tensile Testing

Elastic modulus: A material's resistance to non-permanent, or elastic, deformation. It is also known as Modulus of Elasticity. A metal's elastic modulus is measured based on the elastic portion of a stress-strain curve for a tensile specimen made of the metal of interest. To learn more see our Tensile Testing course.

Electric potential: Corrosion of Metals

Electrochemical cell: Corrosion of Metals

Electrochemical reaction: Corrosion of Metals

Electrode potential: Corrosion of Metals

Electrolyte: An electrolyte is a medium containing ions that are electrically conductive through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dissolving, the substance separates into cations and anions, which disperse uniformly throughout the solvent. Corrosion of a metal requires the metal be in contact with an electrolyte. To learn more see our Corrosion of Metals course.

Electromotive force: Corrosion of Metals

Elongation: Measure of the total amount of deformation of a tensile specimen during a tensile test. It is a calculated value, based on the fractional or percent change in the specimen length during a tensile test. Elongation is an indication of a metal's ductility - greater elongation indicates greater ductility. To learn more see our Tensile Testing course.

Energy dispersive x-ray spectroscopy (EDS): An analytical technique used for the elemental analysis or chemical characterization of a sample. When used with a scanning electron microscope, EDS is used to measure and analyze x-rays emitted from a sample due to the interaction between the electron beam and the atoms at the sample's surface. Its characterization capabilities are due to every element emitting a unique set of peaks on its electromagnetic emission spectrum. To learn more see our Metal Failure Analysis course.

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Face centered cubic: An arrangement of atoms in a unit cell, where atoms occupy sites at the corner of a cube and at the center of each face of the cube. Examples of face centered cubic metals include aluminum, copper, and gold. To learn more see our Principles of Metallurgy course.

Ferrite: Principles of Metallurgy, Steel Metallurgy

Filiform corrosion: Corrosion of Metals

Full anneal: Annealing

Galvanic corrosion: Galvanic corrosion occurs near the junction between two dissimilar metals.The driving force for the corrosion reaction is the difference in electrode potentials between the two metals. To learn more see our Corrosion of Metals course.

Galvanic series: To learn more see our Corrosion of Metals course.

General corrosion: General corrosion is also referred to as uniform corrosion. It is a form of corrosion that occurs over the entire exposed surface of a metal. Rust on a steel structure or the green patina on a copper roof are examples of uniform corrosion. The driving force for this type of corrosion is the electrochemical activity of the metal in the environment to which the metal is exposed. To learn more see our Corrosion of Metals course.

Grain boundary: Principles of Metallurgy

Grain growth: Principles of Metallurgy

Grains: Principles of Metallurgy

Impurity: Principles of Metallurgy

Intergranular corrosion: Interganular corrosion involves corrosion along the grain boundaries of the affected metal. The result is that the metal grains fall away and the metal is weakened. Austenitic stainless steels and precipitation strengthened aluminum alloys such as 2xxx alloys are examples of metals that can suffer from intergranular corrosion if the alloys are not properly processed and if they are exposed to corrosive environments. To learn more see our Corrosion of Metals course.

Interstitial diffusion: Principles of Metallurgy

Interstitial site: Principles of Metallurgy

Interstitial: Principles of Metallurgy

Iron-Carbon Phase Diagram: Steel Metallurgy

Lattice site: Principles of Metallurgy

Localized corrosion: To learn more see our Corrosion of Metals course.

Low-alloy carbon steel: Steel Metallurgy

Martensite finish temperature: Steel Metallurgy

Martensite start temperature: Steel Metallurgy

Martensite: Principles of Metallurgy, Steel Metallurgy

Microstructure: Metal properties, Principles of Metallurgy

Mixed microstructure: Steel Through Hardening

Natural aging: Precipitation Strengthening, Principles of Metallurgy

Noble metal: To learn more see our Corrosion of Metals course.

Overage: Precipitation Strengthening, Principles of Metallurgy

Oxidation: To learn more see our Corrosion of Metals course.

Passivation: To learn more see our Corrosion of Metals course.

Passive: To learn more see our Corrosion of Metals course.

Passivity: To learn more see our Corrosion of Metals course.

Pearlite: Steel Metallurgy

Phase field boundary: Steel Metallurgy

Phase Transformations: Principles of Metallurgy

Phases:  Principles of Metallurgy

Pitting corrosion: To learn more see our Corrosion of Metals course.

Plain carbon steel: Steel Metallurgy

Plastic deformation: Tensile Testing

Plug corrosion: To learn more see our Corrosion of Metals course.

Polarization: To learn more see our Corrosion of Metals course.

Polycrystalline: Principles of Metallurgy

Potential difference: To learn more see our Corrosion of Metals course.

Precipitate: Precipitation Strengthening, Principles of Metallurgy

Precipitation strengthening: Precipitation Strengthening, Principles of Metallurgy

Process anneal: Annealing

Quench: Steel Metallurgy

Recrystallization anneal: Annealing, Principles of Metallurgy

Recrystallization: Principles of Metallurgy

Reduction: To learn more see our Corrosion of Metals course.

Rephosphorized steel: Steel Metallurgy

Resulfurized steel: Steel Metallurgy

Rockwell hardness: Failure Analysis of Metal Fractures

Sacrificial anode: To learn more see our Corrosion of Metals course.

Sacrificial coating: To learn more see our Corrosion of Metals course.

Scanning electron microscope: Failure Analysis of Metal Fractures

SEM: Failure Analysis of Metal Fractures

Sensitization: Intergranular Corrosion

Sensitized: Intergranular Corrosion

Single crystal: Principles of Metallurgy

Solid solution strengthening: Principles of Metallurgy

Solid solution: Principles of Metallurgy

Solution heat treatment: Precipitation Strengthening, Principles of Metallurgy

Spheroidize anneal: Annealing

Spheroidized cementite: Annealing

Strain: Tensile Testing

Stress corrosion cracking (SCC): The formation and growth of cracks due to the simultaneous action of a stress and a corrosive environment on a metal. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when exposed to a small number of chemical environments. To learn more see our Corrosion of Metals course.

Stress: Tensile Testing

Substitution: Principles of Metallurgy

Super-saturated solid solution: Precipitation Strengthening, Principles of Metallurgy

Temper: Steel Metallurgy

Tensile strength: This is the maximum stress that a tensile test specimen sustains during the test. See our Tensile Testing course to learn more.

Tensile test: A mechanical test during which a force is applied to a material specimen in order to measure the material's response to tensile stress. This test provides insight into the mechanical properties of a material including yield strength, tensile strength, and elongation. To learn more see our Tensile Testing course and this page.

Threshold stress: Stress Corrosion Cracking

Time-temperature-transformation diagram: Steel Metallurgy

Underage: Precipitation Strengthening, Principles of Metallurgy

Uniform corrosion: To learn more see our Corrosion of Metals course.

Unit cell: Principles of Metallurgy

Upper yield strength: Tensile Testing

Vacancy diffusion: Principles of Metallurgy

Vacancy: Principles of Metallurgy

Yield strength: Tensile Testing, Principles of Metallurgy

Yield stress: Principles of Metallurgy

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