Glossary of Steel Terms

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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 wires. 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.

The relative ease of machining a metal.

The capacity of a material to be machined easily.

Machinability Index
A relative measure of the machinability of an engineering material under specified standard conditions.

Etching of a metal surface for accentuation of gross structural details and defects for observation by the unaided eye or at magnifications not exceeding ten diameters.

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

Etching of a metal surface with the abjective of accentuating gross structural details, for observation by the unaided eye or at magnifications not exceeding ten diameters.

A graphic reproduction of a prepared surface of a specimen at a magnification not exceeding ten diameters. When photographed, the reproduction is known as a photomacrograph (not a macrophotograph).

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

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

The structure of a metal as revealed by examination of the etched surface at a magnification not exceeding ten diameters.

The structure of metal as revealed by macroscopic examination.

The structure of metals as revealed by examination of the etched surface of a polished specimen at a magnification not exceeding ten diameters.

Magnetic-Particle Inspection
A nondestructive method of inspection for determining the existence and extent of possible defects in ferromagnetic materials. Finely divided magnetic particles, applied to the magnetized part, anre attracted to and outline the pattern of any magnetic-leakage fields created by discontinuities.

The oxide or iron of intermediate valence which has a composition close to the stoichiometric composition Fe3O4.

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.

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 someinstances, part of the carbon is removed completely.

(Chemical symbol Mn.) Element No. 25 of the periodic system; atomic weight 54.93. Lustrous, reddish-white metal of hard brittle and, therfore, 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 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.

Manual Welding
Welding where in the entire welding operation is performed and controlled by hand.

Quenching an austenitized ferrous alloy in a medium at a temperature in the upper part of the martensite range, or slightly above that range, and holding it in the medium until the temperature throughout the alloy is substantially uniform. The alloy is then allowed to cool in air through the martensite range.

(1) A hardening procedure in which an austenitized ferrous material is quenched into an appropriate medium at a temperature just above the Ms temperature of the material, held in the medium until the temperature is uniform through-out -but not long enough for bainite to form - and then cooled in air. The treatment is frequently followed by tempering. (2) When the process is applied to carburized material, the controlling Ms temperature is that of the case. This variation of the process is frequently called marquenching.

In steel, a metalstable transition phase with a body-centered-tetragonal crystal structure formed by diffusionless transformation of austenite generally during cooling between the Ms and Mf temperatures.

A distinctive neddle 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.

(1) In an alloy, a metastable transitional structure intermediate between two allotropic modifications whose abilities to dissolve a given solute differ considerably, the high-temperature phase transformed to martensite depends to a large extent upon the temperature attained in cooling, there being a rather distinct beginning temperature. (2) A metastable phase of steel, formed by a transformation of austenite below the Ms (or Ar) temperature. It is an interstitial supersaturated solid solution of carbon in iron having a body-centered tetragonal lattice. Its microstructure is characterized by an acicular, or needle-like, pattern.

Martensite Range
The interval between the Ms and Mf temperatures.

(a) Element intermediate in lustre 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 has a specialized, even if erroneous, meaning; it covers elements commonly prosent in simple steel; carbon, manganese, phosphorus, silicon and sulfur.

The principal phase or aggregate in which another constituent is embedded.

The principal phase in which another constituent is embedded.

Matt or Matte Finish
(Steel) Not as smooth as normal mill finish. Produce by etched or mechanically roughened finishing rolls.

Mechanical Polishing
A method of producing a specularly reflecting surface by use of abrasives.

Mechanical Properties
The properties of a material that reveal its elastic and inelastic behavior where force is applied, thereby indicating its suitability for mechanical application; for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit.

Mechanical Properties
Those properties of a meterial 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.

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

Mechanical Twin
A twin formed in a metal during plastic deformation by simple shear of the structure.

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 Point
The temperature at which a pure metal, compound or eutectic changes form solid to liquid; the temperature at which the liquid and the solid are in equilibrium.

Melting Range
The range of temperature in which an alloy melt; that is the range between solidus and liquidus temperatures.

An opaque, lustrous, elemental substance that is a good conductor of heat and electricity and, when polished, a good reflector or light. Most metals are malleable and ductile and are, in general, denser than other substances.

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 proficted at high speed by gas pressure against the object being coated.

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

An optical instrument designed for both visual observation and photomicrography of prepared surfaces of opaque materials at magnifications ranging from about 25 to about 1500 diameters.

Possessing a state of pseudo-equilibrium that has a free energy higher than that of the true equilibrium state but from which a system does not change spontaneously.

Mf Temperature
The temperature at which martensitic transformation is essentially complete during cooling after austenitization.

Microbands (deformation)
Thin sheet like volumes of constant thickness in which cooperative slip occurs on a fone scale. They are an instability which carry exclusively the deformation at medium strains when normal homogeneous slip is precluded. The sheets are aligned at +/- 55(degrees) to the compression direction and are confined to individual grains, which usually contain two sets of bands. Compare shear bands.

A crack of microscopic size.

A graphic reproduction of the prepared surface of a specimen at a magnification greater than ten diameters. When photographed, the reproduction is known as a photomicrograph (not a microphotograph).

The structure of a prepared surface of a metal as revealed by a microscope at a magnification greater than ten diameters.

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

Mild Steel
Carbon steel containing a maximum of about 0.25% C.

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
A measure of the rigidity of metal. Ratio of stress, within proportional limit, to corresponding strain. Specifically, the modulus obtained in tension or compression is Young's modulus, stretch modulus or modulus of extensibility; the modulus obtained in torsion or shear is modulus of rigidity, shear modulus or modulus of torsion; the modulus covering the ratio of the mean normal stress to the change in volume per unit volume is the bulk modulus. The tangent modulus and secant modulus are not restricted within the proportional limit; the former is the slope of the stress-strain curve at a specified point; the latter is the slope of a line from the origin to a specified point on the stress-strain curve. Also called elastic modulus and coefficient of elasticity.

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 twist. The ratio of stress to strain within the perfectly elastic range.

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

(Chemical symbol Mo) Element No. 42 of the peridic 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 (degrees) F.; boiling point about 6600 (degrees) 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 in 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 temperbrittleness. (4) Raises hot and creep strength, red hardness. (5) Enhances corrosion resistance in stainless steel. (6) Forms abrasion-resisting particles.

Ms Temperature
The temperature at which a martensitic transformation starts during cooling after austenitization.

Muntz Metal (A refractory Alloy)
Alpha-beta brass, 60% copper and 40% zinc. Stronger than alpha-brass and used for castings and hot-worked (rolled, stamped, or extruded) products. High strength brasses are developed from this by adding other elements.

Music Wire
A polished high tensile strength cold drawn wire with higher tensile strength and higher torsional strength than any other material available. These high mechanical properties are obtained by a combination of the high carbon content, the patenting treatment and by many continuous passes through drawing dies. The high toughness characteristic of this material is obtained by the patenting. Such wire is purchased according to tensile strength, not hardness.

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