Glossary

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

M B GRADE

A term applied to Open-Hearth steel wire in the .45/75 carbon range either hard drawn or oil tempered. Oil tempered wire of M B and W M B types are the most widely used of all spring wire. Oil tempered wire is more suitable to precision forming and casting operations than hard drawn wire because of close control of tensile strength and superior straightness.

NOTE – M B, H B and extra H B designate Basic Open Hearth steels, while W M B, W H B and extra W H B designate Acid Open Hearth Steels. The chemical composition and the mechanical properties are the same for both basic and acid steel.

MACROETCH TEST

Consists of immersing a carefully prepared section of the steel in hot acid and of examining the etching surface to evaluate the soundness and homogeneity of the product being tested.

MACROGRAPH

A photographic reproduction of any object that has not been magnified more than ten times.

MACROSCOPIC

Visible either with the naked eye or under low magnification (as great as about ten diameters).

MACROSTRUCTURE

The structure of metal as revealed by macroscopic examination.

MAGNESIUM

(Chemical symbol Mg.) – Element No. 12 of the periodic system; atomic weight 24.305. Specific gravity 1.77 with a melting point of approximately 1160°F. A silver-white light malleable, ductile metallic element that occurs abundantly in nature. The metal is used in metallurgical and chemical processes; in photography, in signaling, and in the manufacture of pyrotechnics because of the intense white light it produces on burning.

MALLEABILITY

The property that determines the ease of deforming a metal when the metal is subjected to rolling or hammering. The more malleable metals can be hammered or rolled into thin sheet more easily than others.

MALLEABILIZING

A process of annealing white cast iron in such a way that the combined carbon is wholly or partly transformed to graphitic or free carbon or in some instances, part of the carbon is removed ompletely.

MANGANESE

(Chemical symbol Mn.) – Element No. 25 of the periodic system; atomic weight 54.93. Lustrous, reddish-white metal of hard brittle and, therefore, non-malleable character. The metal is used in large quantities in the form of Spiegel and Ferromanganese for steel manufacture as well as in manganese and many copper-base alloys. Its principal function is as an alloy in steel making: (1) It is a ferrite-strengthening and carbide forming element. It increases hardenability inexpensively, with a tendency toward embrittlement when too high carbon and too high manganese accompany each other. (2) It counteracts brittleness from sulfur.

MARTENSITE

A distinctive needle like structure existing in steel as a transition stage in the transformation of austenite. It is the hardest constituent of steel of eutectoid composition. It is produced by rapid cooling from quenching temperature and is the chief constituent of hardened carbon tool steels. Martensite is magnetic.

MARTENSITIC STAINLESS STEEL

Has a body centered tetragonal (BCT) structure. These alloys are chromium stainless steels with medium to high carbon levels. They work harden slowly in the annealed (soft) condition but can be heat-treated to very high tensile strengths.

MATRIX

The principal phase in which another constituent is embedded.

MATT OR MATTE FINISH

(Steel) – Not as smooth as normal mill finish. Produced by etched or mechanically roughened finishing rolls.

MECHANICAL PROPERTIES

Those properties of a material that reveal the elastic and inelastic reaction when force is applied, or that involve the relationship between stress and strain; for example, the modulus of elasticity, tensile strength and fatigue limit. These properties have often been designated as “physical properties,” but the term “mechanical properties” is much to be preferred. The mechanical properties of steel are dependent on its microstructure. (See Physical Properties)

MECHANICAL SPRING

Any spring produced by cold forming from any material with or without subsequent heat treatment.

MECHANICAL WORKING

Plastic deformation or other physical change to which metal is subjected, by rolling, hammering, drawing, etc. to change its shape, properties or structure.

MEDIUM-CARBON STEEL

Contains from 0.30% to 0.60% carbon and less than 1.00% manganese. May be made by any of the standard processes.

MELTING RANGE

The range of temperature in which an alloy melts, that is the range between solidus and liquidus temperatures.

METALLOGRAPHY

The science concerning the constituents and structure of metals and alloys as revealed by the microscope.

METALLOID

(a) Element intermediate in luster and conductivity between the true metals and non-metals. Arsenic, antimony, boron, tellurium, and selenium, etc., are generally considered metalloids; frequently one allotropic modification of an element will be non-metallic, another metalloid in character. Obviously, no hard and fast line can be drawn. (b) In steel metallurgy, metalloid in has a specialized, even of erroneous, meaning; is covers elements commonly present in simple steel; carbon, manganese, phosphorus, silicon and sulfur.

METAL SPRAYING

A process for applying a coating of metal to an object. The metal, usually in the form of wire, is melted by an oxyhydrogen or oxyacetylene blast or by an electric arc and is projected at high speed by gas pressure against the object being coated.

MICROSTRUCTURE

The structure of polished and etched metal and alloy specimens as revealed by the microscope.

MILL EDGE

The edge of strip, sheet or plate in the as rolled state. Unsheared.

MILL FINISH

A surface finish produced on sheet and plate. Characteristic of the ground finish used on the rolls in fabrication.

MODULUS OF ELASTICITY

(Tension) – Force which would be required to stretch a substance to double its normal length, on the assumption that it would remain perfectly elastic, i.e., obey Hooke’s Law throughout the test. The ratio of stress to strain within the perfectly elastic range.

MODULUS OF RIGIDITY

Of a material suffering shear, the ratio of the intensity of the shear stress across the section to the shear strain, i.e., to the angle of distortion in radians; expressed on pounds or tons per square inch.

MOLD

A form of cavity onto which molten metal is poured to produce a desired shape.

MOLYBDENUM

(Chemical Symbol Mo) – Element No. 42 of the periodic system; atomic weight 95.95. Hard, tough metal of grayish-white color, becoming very ductile and malleable when properly treated at high temperatures; melting point 4748°F .; boiling point about 6600°F; specific gravity 10.2. Pure molybdenum can best be obtained as a black powder, by reduction of molybdenum trioxide or ammonium molybdate with hydrogen. From this powder, ductile sheet and wire are made by powder metallurgy techniques; these are used on radio and related work. Its principal functions as an alloy in steel making: (1) Raises grain-coarsening temperature of austenite. (2) Deepens hardening. (3) Counteracts tendency toward temper brittleness. (4) Raises hot and creep strength, red hardness. (5) Enhances corrosion resistance in stainless steel. (6) Forms abrasion-resisting particles.

MUSIC WIRE

A polished high tensile strength cold drawn wire with higher tensile strength and higher torsional strength than any other material available. The high toughness characteristic of this material is obtained by the patenting. Such wire is purchased according to tensile strength, not hardness.