Hardenability

The relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surface where the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure.

Hardening

Increasing hardness by suitable treatment, usually involving heating and cooling. When applicable, the following more specific terms should be used: age hardening , flame hardening , induction hardening , laser hardening , precipitation hardening , and quench hardening .

Heat Treatment

Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.

Heat-Treating Film

A thin coating or film, usually an oxide, formed on the surface of metals during heat treatment.

Homogeneous Carburizing

Use of a carburizing process to convert a low-carbon ferrous alloy to one of uniform and higher carbon content throughout the section.

Hall Effect

A phenomenon observed in thin strips of metal and in some semiconductors. When a strip carrying current longitudinally is placed in a magnetic field that is perpendicular to the strip’s plane, a voltage appears between opposite edges of the strip that, although feeble, will force a current through an external circuit. The voltage is positive in some metals (such as zinc) and negative in others (such as gold). Also see ETTINGHAUSEN EFFECT, NERNST EFFECT, and RIGHT-LEDUC EFFECT.

Hairpin Pickup

A short, doubled length of wire that acts as a pickup coil at very-high and ultrahigh frequencies.