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Welding and Metallurgical terms finally explained.

The terms used in metallurgy can be very complex. Welding terms are usually very specific and a lot of the terms are also misunderstood, below you can find some of the most common used ones and what they actually mean.

Abrasive: Slag used for cleaning or surface roughening.

Active Flux: Submerged-arc welding flux from which the amount of elements deposited in the weld metal is dependent upon welding conditions, primarily arc voltage.

Adhesive Bonding: Surfaces, solidifies to produce an adhesive bond.

Air Carbon Arc Cutting: An arc cutting process in which metals to be cut are melted by the heat of carbon arc and the molten metal is removed by a blast of air.

Age hardening: Hardening by aging the material, for example: A material can become harder but more brittle over time.

Aging: A change of material properties that happens at ambient (or close to) temperatures after hot working, heat treating quenching or cold working.

Alloy: A metal composed of two or more chemical elements of which at least one is a metal.

Alloy steel: Steel containing a significant quantity of alloying elements (other than carbon and small amounts of manganese, silicon, sulphur and phosphorus added to produce changes in mechanical or physical properties.

Annealing: Heating metal to a suitable temperature followed by cooling to produce discrete changes in microstructure and properties.

Arc Blow: The deflection of an electric arc from its normal path because of magnetic forces.

Arc Cutting: A group of thermal cutting processes that severs or removes metal by melting with the heat of an arc between an electrode and the work piece.

Arc Force: The axial force developed by an arc plasma.

Arc Gouging: An arc cutting procedure used to form a bevel or groove.

Arc Length: The distance from the tip of the electrode or wire to the work piece.

Arc Time: The time during which an arc is maintained.

Arc Voltage: The voltage across the welding arc.

Arc Welding: A group of welding processes which produces coalescence of metals by heating them with an arc, with or without the application of pressure and with or without the use of filler metal.

Arc Welding Deposition Efficiency (%): The ratio of the weight of filler metal deposited to the weight of filler metal melted.

Arc Welding Electrode: A part of the welding system through which current is conducted that ends at the arc.

Austenite: A solid solution of one or more alloying elements in the fcc structure of iron.


Beach marks: Crack arrest ‘lines’ seen on fatigue fracture surfaces.

Billet: A solid piece of steel that has been hot worked by forging, rolling or extrusion, often used for machining.

Braze Welding: A method of welding by using a filler metal, having a liquidus above 840 °F (450 °C) and below the solidus of the base metals.

Brittle fracture: Fracture precedes by little or no plastic deformation.

Brittleness: The tendency of a material to fracture without first undergoing significant plastic deformation.

Butt Joint: A joint between two members lying in the same plane.


Carbide: a compound of carbon with metallic elements (f.d. tungsten, chromium).

Carbon equivalent (CE): A ‘weldability’ value that takes into account the effect of carbon and other alloying elements on a particular characteristic of steel.

Carbon steel: A steel containing only small quantities of elements other than carbon.

Cast iron: Iron containing more than 2 percent carbon.

Cast steel: Steel castings ,containing less than 2 percent carbon.

Cleavage: Fracture of a crystal by crack propagation.

Constitutional diagram: A graph showing the temperature and composition of limits of various phases in a metallic alloy.

Crack initiator: Physical fracture which encourages a crack to start.

Creep: Time dependent strain occurring under stress.

Critical cooling rate: The maximum rate at which austenite needs to be cooled to ensure that a particular type of structure is formed.

Crystalline: The general structure of many metals.

Crystalline fracture: A fracture of a metal showing a grainy appearance.


Decarburization: Loss of carbon from the surface of a ferrous alloy caused by heating.

Deformation: General term for strain or elongation of a metal’s lattice structure.

Deoxidation: Removal of oxygen from molten metals by use of chemical additives.

Diffusion: Movement of molecules through a solid solution.

Dislocation: A linear defect in the structure of a crystal.

Ductility: The capacity of a material to deform plastically without fracturing.


Elastic limit: The maximum stress to which a material may be subjected without any permanent strain occurring.

Etching: Subjecting the surface of a metal to an acid to reveal the microstructure.


Fatigue: A cycle or fluctuating stress conditions leading to a fracture.

Ferrite: A solid solution of alloying elements in bcc iron.

Fibrous fracture: A fracture whose surface is characterized by a dull or silky appearance.

Filler Material: The material to be added in making a welded, brazed, or soldered joint.

Fillet Weld: A weld of approximately triangular cross section that joins two surfaces approximately at right angles to each other in a lap joint, T-joint, or corner joint.

Filter Plate: A transparent plate tinted in varying darkness for use in goggles, helmets and hand shields to protect workers from harmful ultraviolet, infrared and visible radiation.

Flame Spraying: A thermal spraying process using an oxy-fuel gas flame as the source of heat for melting the coating material.

Flammable Range: The range over which a gas at normal temperature (NTP) forms a flammable mixture with air.

Flat Welding Position: A welding position where the weld axis is approximately horizontal and the weld face lies in an approximately horizontal plane.

Friction Stir Welding: A solid-state welding process, which produces coalescence of material by the heat obtained from a mechanically induced rotating motion between tightly butted surfaces. The work parts are held together under pressure.