Metallurgy Glossary

Definitions for key metallurgy terms, properties, and material science concepts.

Mechanical Properties

Elastic Modulus

Also called Young's modulus, it is the ratio of stress to strain in the elastic (reversible) deformation region of a material, representing its stiffness. It is expressed in GPa.

Elongation

The percentage increase in gauge length of a tensile specimen at the point of fracture, used as a measure of ductility. Higher elongation indicates a more ductile material.

The progressive, localized structural damage that occurs when a material is subjected to repeated cyclic loading, often at stress levels well below the ultimate tensile strength. Fatigue failure can occur without warning.

Hardness

A measure of a material's resistance to localized plastic deformation, typically quantified by indentation testing. Common scales include Rockwell, Brinell, and Vickers.

Tensile Strength

The maximum stress a material can withstand while being stretched or pulled before breaking. It is expressed in units of force per unit area, such as MPa or psi.

Yield Strength

The stress at which a material begins to deform plastically, meaning it will no longer return to its original shape when the load is removed. It marks the boundary between elastic and plastic behavior.

Physical Properties

Coefficient of Thermal Expansion

The fractional change in length or volume of a material per degree change in temperature, expressed in µm/(m·K) or 10⁻⁶/°C. It describes how much a material expands or contracts with temperature.

Density

The mass per unit volume of a material, typically expressed in g/cm³ or kg/m³. Density is a fundamental intrinsic property that determines the weight of structural components.

Electrical Conductivity

A measure of how well a material conducts electric current, typically expressed as a percentage of the International Annealed Copper Standard (IACS) or in S/m. Higher conductivity means lower electrical resistance.

Magnetic Permeability

A measure of a material's ability to support the formation of a magnetic field within itself, indicating how strongly it responds to an applied magnetic field. Ferromagnetic metals like iron and nickel have high permeability.

Melting Point

The temperature at which a pure metal or alloy transitions from solid to liquid state at atmospheric pressure. Alloys often melt over a temperature range rather than at a single point.

Thermal Conductivity

The rate at which heat flows through a material per unit area per unit temperature gradient, expressed in W/(m·K). It determines how efficiently a metal transfers heat.

Composition & Alloying

Alloying Element

A chemical element intentionally added to a base metal to alter its mechanical, physical, or chemical properties. Common alloying elements include chromium, nickel, manganese, and molybdenum.

Carbon Equivalent

A single numerical value that combines the effects of carbon and other alloying elements to predict the hardenability and weldability of steel. It is widely used to assess the risk of cold cracking during welding.

Intermetallic Compound

A compound formed between two or more metallic elements with a fixed stoichiometric ratio and distinct crystal structure different from its constituent metals. Intermetallics are generally hard and brittle.

Precipitation Hardening

A heat treatment process that increases the strength of an alloy by forming a fine dispersion of second-phase particles (precipitates) within the metal matrix that impede dislocation movement.

Solid Solution

A single-phase microstructure in which atoms of one or more solute elements are dissolved within the crystal lattice of a solvent metal, either substitutionally or interstitially.

Weight Percent

A method of expressing alloy composition as the mass of a constituent element divided by the total mass of the alloy, multiplied by 100. It is the most common way to specify alloy chemistry in industry.

Heat Treatment

Annealing

A heat treatment process involving heating a metal to a specific temperature, holding it there for a set time, and then slowly cooling it, typically in a furnace. The goal is to reduce hardness, relieve internal stresses, and improve ductility.

Austenite

A face-centered cubic (FCC) phase of iron or iron alloy that exists at elevated temperatures in plain carbon steels and at room temperature in certain stainless steels. It is non-magnetic and dissolves up to 2.14 wt% carbon.

Case Hardening

A group of thermochemical processes that increase the hardness and wear resistance of the surface layer of a component while leaving the core tough and ductile. Common methods include carburizing, nitriding, and carbonitriding.

Martensite

A hard, brittle microstructure formed in steel when austenite is cooled rapidly enough to suppress diffusion, trapping carbon in a supersaturated body-centered tetragonal lattice. It is the hardest microstructural constituent in steel.

Normalizing

A heat treatment in which steel is heated to above its upper critical temperature (Ac3) and then cooled in still air, producing a finer and more uniform microstructure than full annealing.

Quenching

The rapid cooling of a metal from an elevated temperature, typically by immersion in water, oil, polymer solution, or forced air, to obtain a specific microstructure and improve hardness.

Tempering

A heat treatment applied after quenching in which hardened steel is reheated to a temperature below the lower critical temperature (Ac1) and then cooled, to reduce brittleness and internal stresses while retaining most of the hardness.

Corrosion & Protection

Cathodic Protection

An electrochemical technique that prevents corrosion of a metal structure by making it the cathode of an electrochemical cell, either by connecting it to a sacrificial anode or by applying an impressed direct current.

Galvanic Corrosion

An electrochemical process in which one metal corrodes preferentially when it is in electrical contact with a more noble (less active) metal in the presence of an electrolyte. The less noble metal acts as the anode and corrodes.

Intergranular Corrosion

Preferential corrosion attack along grain boundaries of a metal, often caused by compositional differences or the precipitation of detrimental phases at the grain boundaries compared to the grain interiors.

Passivation

The formation of a thin, stable, adherent oxide or hydroxide film on a metal surface that effectively reduces the rate of further corrosion by acting as a barrier between the metal and the environment.

Pitting Corrosion

A localized form of corrosion that produces small cavities or pits on the metal surface while most of the surrounding area remains unattacked. It is particularly common in passive metals exposed to chloride ions.

Stress Corrosion Cracking

A failure mechanism involving the simultaneous action of a corrosive environment and sustained tensile stress, leading to crack initiation and propagation at stress levels below the material's yield strength.

Manufacturing Processes

Casting

A manufacturing process in which molten metal is poured into a mold cavity of the desired shape and allowed to solidify, producing a near-net-shape component. Casting can produce complex geometries that are difficult to achieve by other processes.

Extrusion

A metal forming process in which a billet is forced through a die orifice under compressive pressure, producing a continuous product with a fixed cross-sectional profile. Aluminum, copper, and titanium are commonly extruded.

Forging

A manufacturing process that shapes metal by applying compressive forces through hammers, presses, or dies, either at high temperatures (hot forging) or near room temperature (cold forging). Forging refines the grain structure and improves mechanical properties.

Powder Metallurgy

A manufacturing technology in which metal powders are compacted into a desired shape and then sintered at elevated temperature to bond the particles into a solid component. It allows near-net-shape production with minimal material waste.

Rolling

A metal forming process in which stock is passed through one or more pairs of rolls to reduce thickness, achieve a specific cross-section, or improve mechanical properties. Hot rolling and cold rolling are the two primary variants.

Welding

A fabrication process that joins metals by causing coalescence through the application of heat, pressure, or both, with or without filler material. The result is a continuous metallurgical joint.

Testing & Standards

AISI/SAE Designation

A four-digit numbering system developed by the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE) to classify carbon and alloy steels by composition. The first two digits indicate the alloy family and the last two (or three) digits the nominal carbon content in hundredths of a percent.

Brinell Hardness

A hardness test in which a hardened steel or tungsten carbide ball is pressed into the metal surface under a specified load, and the hardness is calculated from the indentation diameter. Results are expressed in HBW (Brinell Hardness with tungsten carbide ball).

Charpy Impact Test

A standardized impact test in which a notched specimen is struck by a swinging pendulum hammer, measuring the energy absorbed during fracture in joules. It assesses the toughness and notch sensitivity of a material.

Nondestructive Testing

A group of inspection techniques used to evaluate the integrity, properties, and dimensions of materials and components without causing damage or impairing their future usefulness. Common methods include ultrasonic testing, radiography, magnetic particle testing, and dye penetrant testing.

Rockwell Hardness

A hardness test that measures the depth of penetration of an indenter under a major load relative to its position under a minor (preload) load. Results are reported on various scales (HRA, HRB, HRC, etc.) depending on the indenter and load used.

Tensile Test

A destructive mechanical test in which a standardized specimen is subjected to a controlled uniaxial tensile load until fracture, measuring properties such as yield strength, tensile strength, elongation, and reduction in area.

Metallurgy Fundamentals

Creep

The time-dependent, permanent deformation of a material under a constant load or stress at elevated temperatures, typically above 0.4 times the absolute melting temperature. Creep failure can occur at stresses well below the room-temperature yield strength.

Crystal Structure

The ordered, periodic three-dimensional arrangement of atoms in a solid metal, described by a unit cell that repeats throughout the lattice. The most common metallic crystal structures are face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP).