Key Welding Terminology and Definitions

Weld Metal

The portion of a weld that has been melted during welding.

Porosity

Cavity-type discontinuities formed by gas entrapment during solidification.

Fusion Zone

The area of base metal that has melted and fused with weld metal.

Undercut

A groove melted into the base metal adjacent to the weld toe that is not filled with weld metal.

Filler Metal

Metal added to the weld pool to form the weld joint.

Arc Length

The distance from the tip of the welding electrode to the surface of the weld pool.

Slag

A nonmetallic by-product formed during welding that covers the weld bead.

Heat-Affected Zone (HAZ)

Area of base metal not melted but whose microstructure was altered by welding heat.

Complete Joint Penetration

Fusion that has occurred through the entire joint thickness.

Backing

Material placed at the root of a joint to support molten weld metal.

Back Weld

A weld deposited after the root pass to ensure full penetration.

Weld Toe

The junction between the face of the weld and the base metal.

Weld Root

The point at which the back of a weld intersects the base metal surfaces.

Weld Face

The exposed surface of a weld on the side from which welding was done.

Groove Weld

Weld made in the groove between two members.

Fillet Weld

A weld of approximately triangular cross-section joining two surfaces at right angles.

Weld Reinforcement

Weld metal in excess of the metal necessary to fill the joint.

Interpass Temperature

The temperature between welding passes.

Preheat Temperature

The temperature of the base metal immediately before welding is started.

Postweld Heat Treatment

Heat treatment done after welding to improve properties.

Shielding Gas

Gas used to protect the weld area from atmospheric gases.

Tack Weld

Small welds made to hold parts in place temporarily.

Weave Bead

A weld bead made with oscillation motion during welding.

Stringer Bead

A weld bead made without weaving motion.

Arc Blow

The deflection of the welding arc from its intended path.

Electrode

A component that conducts current and can contribute filler metal.

Polarity

The electrical direction of current in welding (DCEN, DCEP, AC).

Crater

A depression at the end of a weld bead.

Overlap

Excess weld metal that extends beyond the weld toe or root and is not fused.

Spatter

Small particles of molten metal expelled during welding.