Glossary | L & M (The vocabulary of the coating and heat-treating industries—explained)

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L

Ladle

A metal receptacle, frequently lined with refractories. Used for transporting and pouring molten metal. The various types are hand bull, crane, bottom-pour, holding, teapot, shank, and lip-pour.

Laminar Flow

The flow regime which exists when the Reynolds Number is below 2000. The path lines of the particles are smooth and regular, and there is little interchange of fluid mass between adjacent layers.

Lap

A surface imperfection which appears as a seam. It is caused by the folding over of hot metal, fins, or sharp corners and then rolling or forging them into the surface but not welding them. Laps on tubes can form from seams on piercing mill billets.

Lapping

Rubbing two surfaces together, with or without abrasives, for the purpose of obtaining extreme dimensional accuracy or superior surface finish.

Laser Ablation

A deposition technique which uses a pulsed UV laser beam for vaporizing solid source materials. Much of the material ablates as macroparticles rather than vaporizing as atoms or molecules. A key advantage is that it can achieve congruent evaporation of complex materials, such as mixed oxides.

Laser Alloying

The application of a powder to a surface, followed by fusing and alloying into the surface via the heat from an impinging laser.

Laser Glazing

The melting and quenching of a surface to form a fine-grained structure, or ‘glaze’.

Laser Hardening

A surface-hardening process which uses a laser to quickly heat a surface above 900°C. Heat conduction into the interior of the part will quickly cool the surface, leaving a shallow layer of martensite.

Latent Heat

Thermal energy that is absorbed or released when a substance undergoes a phase change.

Lead (Pb)

An element that improves machinability. It does not dissolve in steel but stays instead as globules. As a result of environmental concerns, the use of lead in the steel industry has decreased.

Ledeburite

The eutectic of the iron-carbon system—the constituents being austenite and cementite. The austenite decomposes into ferrite and cementite upon cooling below the Ar1.

Leidenfrost Phenomenon

Slower-than-usual cooling rates, associated with a hot vapor blanket that surrounds a part being subjected to quenching in a liquid medium. The gaseous vapor envelope acts as an insulator, thus slowing the cooling rate.

Liquation Temperature

The lowest temperature at which partial melting can occur in an alloy, exhibiting the greatest possible degree of saturation.

Liquid Carburizing

The surface-hardening of steel via immersion in a molten bath consisting of cyanides and other salts.

Liquid Impingement Erosion

The progressive loss of material from a solid surface due to continued exposure to impact from liquid drops or jets.

Liquid Nitriding

A method of surface hardening in which molten-nitrogen-bearing, fused salt baths, containing both cyanides and cyanates, are exposed to parts at subcritical temperatures.

Liquid Nitrocarburizing

A nitrocarburizing process utilizing molten liquid salt baths below the lower critical temperature.

Liquid Spray Quench

Synonymous with spray quenching.

Localized Corrosion

Corrosion at discrete sites (e.g. pitting, crevice corrosion, and stress corrosion cracking).

Localized Precipitation

Precipitation from a supersaturated solid solution, similar to continuous precipitation, except that the precipitate particles form at preferred locations such as along slip planes, grain boundaries, or incoherent twin boundaries.

Low Activation Interior Coating

Any coating used on the interior of ships in order to minimize the activation of pigments on painted surfaces within a radiation environment.

Low Pressure Plasma Spraying (LPPS)

Plasma spraying carried out in a chamber which has been evacuated to a low partial pressure of oxygen. It is then usually partially backfilled with argon to avoid the possibility of forming a glow discharge.

Lubricant

Any substance interposed between two surfaces for the purpose of reducing the friction or wear between them.

M

Macrohardness

The hardness of a coating as measured on a macroscopic scale, which shows the coating's bulk properties.

Magnetic Storage Media

Whether magnetic materials are classified as “hard” or “soft” depends on how hard it is to reverse the polarity of, magnetize or demagnetize the magnetic field. Soft magnetic materials, such as the Permalloys (iron [Fe]:40–80% Ni) and Y2Fe5O12 (garnet), are used in memory storage devices where the data are changed often. Hard magnetic materials, such as Fe3O4, Co:Ni:tungsten [W], Co:rhenium [Re], gadolinium [Gd]:Co, and Gd:terbium [Tb]:Fe, are used in more permanent recording media, such as audio tapes. Various techniques are used to define the magnetic domains that act as the storage sites.

Magnetic Test

A method used to test the heat extraction rates of various quenchants. The test works by utilizing the change in magnetic properties of metals at their Curie point, or the temperature above which metals lose their magnetism.

Magnetron Sputtering

A synonym for sputtering.

Malleable Cast Iron

A cast iron made by the prolonged annealing of white cast iron (in which decarburization and/or graphitization eliminate some or all of the cementite). The graphite is in the form of temper carbon. If decarburization is the predominant reaction, the product will exhibit a light fracture surface—hence the name “whiteheart malleable”. Otherwise, the fracture surface will be dark (blackheart malleable). Ferritic malleable has a predominantly ferritic matrix. Pearlitic malleable may contain pearlitic, spherodite or tempered martensite, depending on heat treatment and the desired hardness.

Malleablizing

Annealing white cast iron in such a way that some or all of the combined carbon is transformed into graphite or, in some instances, part of the carbon is removed completely.

Manganese (Mn)

An element that deoxidizes the melt and facilitates the hot working of steel by reducing its susceptibility to hot shortness. It combines with sulfur to form MnS stringers, which aid machinability. Manganese contributes to the effectiveness of normalizing for strengthening and to the formation of fine pearlite. It also lowers the Ms Temperature, which increases the probability that some austenite will be retained.

Maraging

A precipitation-hardening treatment applied to a special group of iron-based alloys to precipitate one or more intermetallic compounds in a matrix of essentially carbon-free martensite.

Marine Coating

Any coating, excepting unsaturated polyester resin (fiberglass) coatings, that contains volatile organic materials. It is applied to ships, boats, and their appurtenances, buoys and oil drilling rigs intended for the marine environment.

Marquenching

See martempering below.

Martempering

(1) A hardening procedure in which an austenitized, ferrous work piece is quenched in an appropriate medium whose temperature is equal to the Ms of the work piece, held in the medium until its temperature is uniform throughout (but not long enough to permit the formation of bainite) 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.

Martensite

A generic term for microstructures formed by diffusionless phase transformation in which the parent and product phases have a specific crystallographic relationship. Martensite is characterized by an acicular pattern in the microstructure in both ferrous and nonferrous alloys. In alloys where the solute atoms occupy interstitial positions in the marensite lattice (such as carbon in iron), the structure is hard and highly strained; but where the solute atoms occupy substitutional positions (such as nickel in iron), the martensite is soft and ductile. The amount of high-temperature phase that transforms to martensite on cooling depends to a large extent on the lowest temperature attained, there being a rather distinct beginning temperature (Ms) and a temperature at which the transformation is essentially complete (Mf).

Martensite Range

The temperature interval between Ms and Mf.

Martensitic Stainless Steels

A corrosion-resistant, ferrous alloy with a predominant martensitic phase.

Martensitic Transformation

A reaction that takes place on cooling, in some metals, with the formation of an acicular structure called martensite.

Mass Effect

The effect that the mass of a component has on the properties of the material from which the part is made. In castings, such effects may arise due to the effect of mass on solidification and on the rate of temperature change heat treatment.

Matrix

The continuous phase of a material or coating in which separate particles of another constituent are embedded (like tungsten carbide particles in a cobalt matrix).

McQuaid-Ehn Test

A test to reveal grain size after heating into the austenitic temperature range. Eight standard McQuaid-Ehn grain sizes rate the structure; No. 8 being finest and No. 1 the coarsest.

MCrAlY

The variable M at the beginning can be Ni, Co or Fe. MCrAlY are high-temperature, corrosion-resistant alloys used to combat sulfidation and oxidation.

Mechanical Bonding

Usually represented by mechanical interlocking of the deposited particles with the rough heights on the substrate surface produced during grit blasting.

Mechanical Properties

The properties of a material that describe its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications. For example: modulus of elasticity, tensile strength, elongation, hardness, fatigue limit. Compare with physical properties.

Mechanical Testing

Any effort to determine a material's mechanical properties.

Mesh

The area made up of elements and nodes (or grid points) in a numerical simulation.

Metal

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

Metallic Coating

Coating containing more than 5 grams of metal particles per liter of coating, as applied.

Metallographic Structure

The natures, distributions and amounts of the metallographic constituents in a metal.

Metallurgical Bonding

Produced either by chemical bonding between areas of the coating and substrate that are in intimate contact or by diffusional interaction between the coating and substrate. Metallurgical bonding can be enhanced by post-diffusion heat treatments.

Metallurgy

The science and technology of metals and alloys. Process metallurgy is concerned with the extraction of metals from their ores and with refining of metals; physical metallurgy with the physical and mechanical properties of metals as affected by composition, processing and environmental conditions; and mechanical metallurgy with the responses of metals to applied forces.

Mf Temperature

For any alloy system, the temperature at which martensite formation on cooling is essentially finished. See transformation temperature for the definition applicable to ferrous alloys.

Micrograph

A micrograph is produced when a section of the coating is taken, polished to show the particulate layers, and then photographed through a microscope.

Microhardness

The hardness of a material as determined by forcing an indenter, such as a Vickers or Knoop indenter, into the surface of a material under very light load; usually, the indentations are so small that they must be measured with a microscope. Capable of determining hardness of different microconstituents within a structure, or a measuring steep hardness gradients such as those encountered in case hardening.

Microinch

One millionth of an inch; 0.000001”.

Micrometer (┬Ám)

One millionth of a meter; 0.001 mm.

Microscopic Stresses

Residual stresses that vary from tension to compression in a distance (presumably approximating the grain size) that is small compared with the gage length in ordinary strain measurements. They are not detectable by dissection methods, but can sometimes be measured from the line shift or line broadening in an x-ray diffraction pattern.

Microsegregation

Segregation within a grain, crystal, or small particle.

Microstructure

The structure of a metal as revealed at high magnification, usually at 100× and higher.

Microtrack

A device for measuring powder particle size distributions.

Mil

One thousandth of an inch; 0.001”.

Mill Scale

The heavy oxide layer that forms during the hot fabrication or heat treatment of metals.

Minus Sieve

The portion of a powder sample that passes through a standard sieve of a specified number. Contrast with plus sieve.

Modulus Of Elasticity (E)

In tension, it is the ratio of stress to the corresponding strain within the limit of elasticity (Yield Point) of a material. For carbon and low alloy steels of any composition and treatment, the value is approximately 200 GPa or 30,000,000 psi.

Modulus of Resilience (Ur)

The amount of strain energy per unit volume required to stress a material from zero to the yield stress limit. The modulus of resilience is proportional to the area under the elastic portion of the stress-strain diagram. Units are Pa or psi.

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.

Modulus of Rupture

Used in both bending and torsion testing. In bending, the modulus of rupture is the bending moment at fracture divided by the section modulus. In torsion, modulus of rupture is the torque at fracture divided by the polar section modulus.

Modulus of Toughness (Ut)

The amount of work per unit volume of a material required to carry that material to failure under static loading. Equal to the area under the entire stress-strain curve. Units are Pa or psi.

Mold Coating (Mold Facing, Dressing)

(1) Coating to prevent surface defects on permanent mold castings and die castings.
(2) Coating on sand molds to prevent metal penetration and improve metal finish.

Molybdenum (Mo)

An element with atomic number 42. It increases the hardenability of steels, helps maintain a specified hardenability, and increases high temperature tensile strength and creep strength. Molybdenum hardened steels require higher tempering temperatures for softening. It is used as an alloying element for other metals and as a hardening element for steels and diecasting dies. Its melting point is 2620°C (4748°F).

Molybdenum Disulphide (MoS2)

A black, lamella structured solid with low sliding friction. Often applied as a powder filler to lubricants or dispersed in a polymer coating.

Monotropism

The ability of a solid to exist in two or more forms (crystal structures), one of which is the stable modification at all temperatures and pressures. For example, ferrite and martensite are a monotropic pair below Ac1in steels. Its alternate spelling is monotrophism.

Ms Temperature

For an alloy system, the temperature at which martensite starts to form on cooling. See transformation temperature for the definition as applicable to ferrous alloys.

Multiport Nozzle (Plasma)

A constricted nozzle with two or more internal bores. This distinction's purpose is to provide more control over the shape and stability of a plasma arc.


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