Technical Data

Metallurgical Terms

Martensite.

A microconstituent of steel characterized by its acicular structure. Essentially a non-equilibrium condition of alpha iron formed directly from undercooled austenite. It is produced typically when steel is cooled from the hardening temperature at a speed greater than its critical cooling rate so that the transformation of austenite occurs at 400°C or below. It is the hardest of the decomposition products of austenite and is brittle but when tempered becomes softer and tough.

Mass Effect.

This term is commonly employed to signify the effect of size and shape during heat treatment, since it is the rate of cooling of a piece of steel which determines the properties resulting from a hardening or quenching process.

Matrix.

As used in metallography the term applies to the principal constituent in which the other constituents are embedded.

Maximum Stress.

(See Tensile Strength).

Meehanite.

A trade name applied to certain pearlite cast irons in which the molten metal has been treated with calcium silicide resulting, it is claimed, in increased tensile strength.

Melting Point.

(Fusion Point). The temperature at which a solid begins to liquefy. Pure metals, eutectics and some intermetallic constituents melt at a specific temperature. Alloys generally melt over a range.

Mercast process.

(See Precision Casting).

Mesnager Notch.

(See Charpy Test).

Mg.

Chemical symbol for magnesium.

Microhardness.

Hardness as measured with an indenter under the application of a low load, usually between 1 gram and 200 grams. Owing to the small size of the impression, the hardness of an individual phase in a microstructure can be determined.

Micron.

A unit of length equal to a millionth of a metre (0.001mm). It is used for expressing minute distances and is denoted by the Greek letter µ.

Mixer.

A large furnace used as a reservoir for molten pig-iron coming from the blast furnace. The product of several furnaces is thus mixed, and the composition can be regulated by making suitable additions. It is used in connection with the  Basic Oxygen Steelmaking process and direct casting of pig-iron.

Mn.

Chemical symbol for manganese.

Mo.

Chemical symbol for molybdenum.

Modulus of Elasticity.

(See Young’s Modulus).

Modulus of Rigidity.

In a torsion test, the ratio of the unit shear stress to the displacement caused by it per unit length in the elastic range. This modulus corresponds to the modulus of elasticity in the tension test. (Tensile Test).

Mohs’ Scale.

(See Hardness).

Mould.

(a) In the foundry, the cavity of desired shape, usually of sand, into which molten metal is poured.

(b) (See Ingot Mould).