The interchange of filler metal and base metal during welding resulting in weld metal of composition borrowed from both. Limited admixture is necessary to complete metallurgical union across the joint.

The recrystallization that occurs over an extended period of time, resulting from austenite or other normally elevated-temperature structure being retained at a temperature and under conditions where it has not permanent stability. The result may be a change in properties or dimension. Under some circumstances, aging can be advantageous.

A material having metallic characteristics and made up of two or more elements, one of which is metal.

The process of softening a metal by heating it, usually above the upper critical temperature, and then cooling it at a slow rate.

The tendency of a material to fail suddenly by breaking, without any permanent deformation of the material before failure.

The contents of an alloy, in terms of what elements are present and in what amount (by percentage of weight).

Consumable electrode
A metal electrode that establishes the arc and gradually melts away, being carried across the arc (deposited) to provide filler metal into the joint.

Crack propagation
The development, growth, or progress of a crack through a solid.

Crater Cracks
Cracks across the weld bead crater, resulting from hot shrinkage.

Deposition rate
The speed with which filler metal is added to a weld joint, usually stated in terms of volume of metal deposited per minute.

The ability of a material to become permanently deformed without failure.

Fill welds
Welds in which a filler metal is deposited into the joint from an electrode or welding rod, fusing with the base metal on each side.

Filler metal
The metal that is deposited into the joint from an electrode or welding rod in order to achieve a weld of desired properties.

Melting of metal to the liquid state, permitting two contacting or neighboring surfaces to partially exchange their contents with the result that there is a thorough blending of the compositions after cooling.

The crystalline body that may be viewed under a microscope as having definable limits.

Inert Gas
A gas, such as helium or argon, which does not chemically combine with other elements. Such a gas serves as an effective shield of the welding arc and protects the molten weld metal against contamination from the atmosphere until it freezes.

Lower critical temperature
The temperature at which an alloy completes its transformation from one solid structure to another, as it cools.

The science and technology of extracting metals form their ores, refining them, and preparing them for use.

Cracks or fissures in a metallic structure which cannot be seen except with the aid of a microscope.

The detailed structure of a metal or alloy, as revealed by microscopic examination, showing the various continuous phases as well as any non-metallic inclusions.

Lacking iron in sufficient percentage to have any dominating influence on properties of the material.

The rock or earth in which we find metals in their natural forms.

Parent metal
The metal to be welded or otherwise worked upon; also called the base metal.


  1. The depth below the surface of the base metal to which welding heat is sufficient for the metal to melt and become liquid or semi-liquid. Also called the depth of fusion.
  2. The ability of arc or electrode to reach into the root of the groove between two members being welded.

Physical Metallurgy
That division of metallurgy applying to the changes in structure and properties of metals as a result of shaping, fabricating and treating.

The absorption of base metal by the weld metal as the result of admixture. Usually used specifically in reference to the migration of carbon or other critical alloying elements from the base metal into the weld metal. Depending upon the materials involved, this can be an asset and not a liability.

The scattered presence of gas pockets or inclusions in a metallic solid. Process Metallurgy-That division of metallurgy applying to the extracting, refining, and primary shaping of metals into a usable form.

Those features or characteristics of a metal that make it useful and distinctive from all others.

Reverse Polarity
An arrangement of the leads from a direct current power source whereby the electrode is the positive pole and the work piece is the negative pole of the arc.

Straight Polarity
An arrangement of the leads from a direct current power source whereby the work piece is the positive pole and the electrode is the negative pole of the arc.

The load, or amount of a force, applied to a material, tending to deform or break it.

Stringer bead
A weld bead deposited along a straight line, without weaving. Term is usually used only when there are a number of such beads deposited parallel to each other.

The tendency of segregated atoms of alloying elements or their compounds to attach to one another in thread-like chains.

Tensile strength
The resistance of a material to a force which is acting to pull it apart.

Ultimate tensile strength
The maximum pulling force to which the material can be subjected without failure.

Underbead crack
A crack in the hardened base metal just under the fusion line. It usually originates in the coarse-grained zone and is caused by hydrogen released from the austenite as it transforms during cooling. If cooling is rapid, the free hydrogen cannot escape to the surface and exerts tremendous pressure on the hard martensite crystals being formed. Underbead cracks occur parallel to the fusion line.

Upper critical temperature
The temperature at which an alloy begins to transform from one solid structure to another as it cools.

Weld Metal
A product of fusion, the metal that was fully melted by the heat of welding.

Yield Strength
The stress point at which permanent deformation results.