Glossary - H

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Hard Facing

A surface variation in which surfacing material is deposited to reduce wear.

Hardenability

A term used to describe the propensity of an alloy to harden when subjected to rapid cooling or quenching from elevated temperatures, for example, in the heat affected zone of a weld. Normally applied to steels, hardenability increases with increase in carbon and alloy content, by causing a lowering of the transformation temperature. In welding the effects are usually off-set by application of pre-heat to susceptible materials.

Hardness Testing

Hardness may be defined as 'resistance to indentation'. It is usually measured by pressing an indenter into a prepared, flat surface of the material under examination, using a known static load, and measuring the size of the impression produced. The hardness number is then obtained by reference to conversion tables for the specific test method being used. These numbers are based on a stress value obtained by dividing the load by the area of the impression.
The most common hardness test method is the Vickers, which uses a diamond pyramid indenter. Other tests include Rockwell (diamond cone indenter), and Brinell (hard steel ball indenter). The Shore Scleroscope is a dynamic test using a falling hammer to make the indent.

Heat Affected Zone (HAZ)

That portion of the base metal which has not been melted, but whose mechanical properties or microstructure have been altered by the heat of welding, brazing, soldering, or cutting.

Heat Capacity

Quantity of heat required to raise the temperature of a unit mass of material by 1oC.

Heat Input

Heat input is generally defined by the formula:
A x V
TS
Where A = Current (amps)
V = Voltage (volts)
TS = Travel Speed (mm/s)
The value is normally quoted in kJ/mm.
However, some of the energy generated by the arc fails to reach the weld pool because of radiation losses. To take these loses into account the heat input formula is multiplied by a
thermal efficiency factor related to the type of welding process used.
The thermal efficiency factors are:
Submerged arc 1.0
MIG, MMA and FCAW 0.8
TIG and plasma 0.6

Heat-Treatable Alloys

Alloys which can be strengthened or hardened by application of heat.

Helix

Is the amount of spring a welding wire exhibits. It is measured by throwing a length of wire onto a flat floor and then measuring how high the wire end is from the ground. Ideally the wire should have no helix at all. If the wire exhibits a helix then it may spiral as it leaves the torch contact tip.

Horizontal Welding Position

A weld made horizontally with the parent plate lying in the vertical plane. Designated as the 2G welding position.

Hose Check Valves

Non-return valves are fitted to the end of the gas hoses. They prevent the backfeeding of one gas into another. For example if the oxygen working pressure is much higher than that for the fuel gas and a hose check valve is not fitted, oxygen could backfeed into the fuel gas hose creating an explosive mixture.

Hot Cracking

Also known as solidification cracking, it is a discontinuity produced by tearing of the metal while it is at an elevated temperature.

Hydrocarbon Fuels

Compounds that are made up of mainly hydrogen and carbon that when combusted produce energy.

Hydrogen Cracking

A weld crack caused by the presence of hydrogen in the weld.