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KISCC. Abbreviation for the critical value of the plane strain stress-intensity factor that will produce crack propagation by stress-corrosion cracking of a given material in a given environment.
knife-line attack. Intergranular corrosion of an alloy, usually stabilized stainless steel, along a line adjoining or in contact with a weld after heating into the sensitization temperature range.
kraft process. A wood-pulping process in which sodium sulfate is used in the caustic soda pulp-digestion liquor. Also called Kraft pulping or sulfate pulping.
lamellar corrosion. See exfoliation corrosion.
lamellar tearing. Occurs in the base metal adjacent to weldments due to high through-thickness strains introduced by weld metal shrinkage in highly restrained joints. Tearing occurs by decohesion and linking along the working direction of the base metal; cracks usually run roughly parallel to the fusion line and are steplike in appearance. Lamellar tearing can be minimized by designing joints to minimize weld shrinkage stresses and joint restraint. See also cold cracking, hot cracking, and stress-relief cracking.
Langelier saturation index. An index calculated from total dissolved solids, calcium concentration, total alkalinity, pH, and solution temperature that shows the tendency of a water solution to precipitate or dissolve calcium carbonate.
ledeburite. The eutectic of the iron-carbon system, the constituents of which are austenite and cementite. The austenite decomposes into ferrite and cementite on cooling below Ar1, the temperature at which transformation of austenite to ferrite or ferrite plus cementite is completed during cooling.
ligand. The molecule, ion, or group bound to the central atom in a chelate or a coordination compound.
limiting current density. The maximum current density that can be used to obtain a desired electrode reaction without undue interference such as from polarization.
linear elastic fracture mechanics. A method of fracture analysis that can determine the stress (or load) required to induce fracture instability in a structure containing a cracklike flaw of known size and shape. See also fracture mechanics and stress-intensity factor.
lipophilic. Having an affinity for oil. See also hydrophilic and hydrophobic.
liquid metal embrittlement. Catastrophic brittle failure of a normally ductile metal when in contact with a liquid metal and subsequently stressed in tension.
local action. Corrosion due to the action of "local cells,' that is, galvanic cells resulting from inhomogeneities between adjacent areas on a metal surface exposed to an electrolyte.
local cell. A galvanic cell resulting from inhomogeneities between areas on a metal surface in an electrolyte. The inhomogeneities may be of physical or chemical nature in either the metal or its environment.
localized corrosion. Corrosion at discrete sites, for example, crevice corrosion, pitting, and stress-corrosion cracking.
Iong-line current. Current that flows through the earth from an anodic to a cathodic area of a continuous metallic structure. Usually used only where the areas are separated by considerable distance and where the current results from concentration cell action.
luggin probe. A small tube or capillary filled with electrolyte, terminating close to the metal surface under study, and used to provide an ionically conducting path without diffusion between an electrode under study and a reference electrode.
macroscopic. Visible at magnifications to 25 x .
macrostructure. The structure of metals as revealed by macroscopic examination of the etched surface of a polished specimen.
magnetite. Naturally occurring magnetic oxide of iron (Fe3O4).
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 martensitic 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)
mechanical plating. Plating wherein fine metal powders are peened onto the work by tumbling or other means.
metal dusting. Accelerated deterioration of metals in carbonaceous gases at elevated temperatures to form a dustlike corrosion product.
metallic glass. An alloy having an amorphous or glassy structure. See also amorphous solid.
metallizing. (1) The application of an electrically conductive metallic layer to the surface of nonconductors. (2) The application of metallic coatings by nonelectrolytic procedures such as spraying of molten metal and deposition from the vapor phase.
microbial corrosion. See biological corrosion.
microscopic. Visible at magnifications above 25 x
microstructure. The structure of a prepared surface of a metal as revealed by a microscope at a magnification exceeding 25x.
mill scale. The heavy oxide layer formed during hot fabrication or heat treatment of metals.
mixed potential. The potential of a specimen (or specimens in a galvanic couple) when two or more electrochemical reactions are occurring. Also called galvanic couple potential.
molal solution. Concentration of a solution expressed in moles of solute divided by 1000 g of solvent .
molar solution. Aqueous solution that contains 1 mole (gram-molecular weight) of solute in 1 L of the solution.
mole. One mole is the mass numerically equal (in grams) to the relative molecular mass of a substance. It is the amount of substance of a system that contains as many elementary units (6.02 x 1023) as there are atoms of carbon in 0.012 kg of the pure nuclide 12C; the elementary unit must be specified and may be an atom, molecule, ion, electron, photon, or even a specified group of such units.
monomer. A molecule, usually an organic compound. having the ability to join with a number of identical molecules to form a polymer.
natural aging. Spontaneous aging of a supersaturated solid solution at room temperature. See also aging. Compare with artificial aging.
Nernst equation. An equation that expresses the exact electromotive force of a cell in terms of the activities of products and reactants of the cell.
Nernst layer, Nernst thickness. The diffusion layer or the hypothetical thickness of this layer as given by the theory of Nernst. It is defined by: id= nFD[(Co - C)/delta], where id is the diffusion limited current density. D is the diffusion coefficient, Co is the concentration at the electrode surface and delta is the Nernst thickness (0.5 mm in many cases of unstirred aqueous electrolytes)
neutron embrittlement. Embrittlement resulting from bombardment with neutrons, usually encountered in metals that have been exposed to a neutron flux in the core of a reactor. In steels, neutron embrittlement is evidenced by a rise in the ductile-to-brittle transition temperature.
nitriding. Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a suitable temperature (below Ac, for ferritic steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case.
nitrocarburizing. Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is performed primarily to provide an antiscuflfing surface layer and to improve fatigue resistance. Compare with carbonitriding.
noble. The positive direction of electrode potential. thus resembling noble metals such as gold and platinum.
noble metal. (1) A metal whose potential is highly positive relative to the hydrogen electrode. (2) A metal with marked resistance to chemical reaction. particularly to oxidation and to solution by inorganic acids. The term as often used is synonymous with precious metal.
noble potential. A potential more cathodic (positive) than the standard hydrogen potential.
normalizing. Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range.
normal solution. An aqueous solution containing one gram equivalent of the active reagent in I L of the solution.
normal stress. The stress component perpendicular to a plane on which forces act. Normal stress may be either tensile or compressive.
open circuit potential. The potential of an electrode measured with respect to a reference electrode or another electrode when no current flows to or from it.
organic. Being or composed of hydrocarbons or their derivatives, or matter of plant or animal origin. Contrast with inorganic.
organic add. A chemical compound with one or more carboxyl radicals (COOH) in its structure; examples are butyric acid, CH3(CH2)2COOH; maleic acid, HOOCCHCHCOOH; and benzoic acid. C6H5COOH.
organic zinc-rich paint. Coating containing zinc powder pigment and an organic resin.
overaging. Aging under conditions of time and temperature greater than those required to obtain maximum change in a certain property, so that the property is altered in the direction of the initial value.
overheating. Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working, or by a combination of working and heat treating, the overheating is known as burning.
overvoltage. The difference between the actual electrode potential when appreciable electrolysis begins and the reversible electrode potential.
oxidation. (1) A reaction in which there is an increase in valence resulting from a loss of electrons. Contrast with reduction. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.
oxidized surface (on steel). Surface having a thin, tightly adhering, oxidized skin (from straw to blue in color), extending in from the edge of a coil or sheet.
oxidizing agent. A compound that causes oxidation, thereby itself being reduced.
oxygen concentration cell. See differential aeration cell.
ozone. A powerfully oxidizing allotropic form of the element oxygen. The ozone molecule contains three atoms (O3). Ozone gas is decidedly blue, and both liquid and solid ozone are an opaque blue-black color, similar to that of ink.
partial annealing. An imprecise term used to denote a treatment given cold-worked material to reduce its strength to a controlled level or to effect stress relief. To be meaningful, the type of material, the degree of cold work, and the time-temperature schedule must be stated.
parting. See dealloying.
parts per billion. A measure of proportion by weight, equivalent to one unit weight of a material per billion (109) unit weights of compound. One part per billion is equivalent to 1mg/g.
parts per million. A measure of proportion by weight, equivalent to one unit weight of a material per million (106) unit weights of compound. One part per million is equivalent to 1 mg/g.
passivation. ( 1 ) A reduction of the anodic reaction rate of an electrode involved in corrosion. (2) The process in metal corrosion by which metals become passive. (3) The changing of a chemically active surface of a metal to a much less reactive state. Contrast with activation.
passivator. A type of inhibitor that appreciably changes the potential of a metal to a more noble (positive) value.
passive. (1) A metal corroding under the control of a surface reaction product. (2) The state of the metal surface characterized by low corrosion rates in a potential region that is strongly oxidizing for the metal.
passive-active cell. A corrosion cell in which the anode is a metal in the active state and the cathode is the same metal in the passive state.
passivity. A condition in which a piece of metal, because of an impervious covering of oxide or other compound, has a potential much more positive than that of the metal in the active state.
patina. The coating, usually green, that forms on the surface of metals such as copper and copper alloys exposed to the atmosphere. Also used to describe the appearance of a weathered surface of any metal.
pearlite. A metastable lamellar aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range.
phosphating. Forming an adherent phosphate coating on a metal by immersion in a suitable aqueous phosphate solution. Also called phosphatizing. See also conversion coating.
pH. The negative logarithm of the hydrogen ion activity; it denotes the degree of acidity or basicity of a solution. At 25oC (77oF), 7.0 is the neutral value. Decreasing values below 7.0 indicate increasing acidity; increasing values above 7.0, increasing basicity.
physical vapor deposition. A coating process whereby the cleaned and masked component to be coated is heated and rotated on a spindle above the streaming vapor generated by melting and evaporating a coating material source bar with a focused electron beam in an evacuated chamber.
physisorption. The binding of an adsorbate to the surface of a solid by forces whose energy levels approximate those of condensation. Contrast with chemisorption.
pickle. A solution or process used to loosen or remove corrosion products such as scale or tarnish .
pickling. Removing surface oxides from metals by chemical or electrochemical reaction.
pitting. Localized corrosion of a metal surface confined to a point or small area, that takes the form of cavities.
pitting factor. Ratio of the depth of the deepest pit resulting from corrosion divided by the average penetration as calculated from weight loss.
plane strain. The stress condition in linear elastic fracture mechanics in which there is zero strain in a direction normal to both the axis of applied tensile stress and the direction of crack growth (that is, parallel to the crack front); most nearly achieved in loading thick plates along a direction parallel to the plate surface. Under plane-strain conditions, the plane of fracture instability is normal to the axis of the principal tensile stress.
plane stress. The stress condition in linear elastic fracture mechanics in which the stress in the thickness direction is zero; most nearly achieved in loading very thin sheet along a direction parallel to the surface of the sheet. Under plane-stress conditions, the plane of fracture instability is inclined 45o to the axis of the principal tensile stress.
plasma spraying. A thermal spraying process in which the coating material is melted with heat from a plasma torch that generates a nontransferred arc; molten coating material is propelled against the base metal by the hot, ionized gas issuing from the torch.
plastic deformation. The permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit.
plasticity. The property that enables a material to undergo permanent deformation without rupture.
polarization. (1) The change from the open-circuit electrode potential as the result of the passage of current. (2) A change in the potential of an electrode during electrolysis, such that the potential of an anode becomes more noble, and that of a cathode more active, than their respective reversible potentials. Often accomplished by formation of a film on the electrode surface.
polarization admittance. The reciprocal of polarization resistance (dildE).
polarization curve. A plot of current density versus electrode potential for a specific electrode-electrolyte combination.
polarization resistance. The slope (dE/di) at the corrosion potential of a potential (E)/current density (i) curve. Also used to describe the method of measuring corrosion rates using this slope.
polyester. Resin formed by condensation of polybasic and monobasic acids with polyhydric alcohols .
polymer. A chain of organic molecules produced by the joining of primary units called monomers.
potential. Any of various functions from which intensity or velocity at any point in a field may be calculated. The driving influence of an electrochemical reaction. See also active potential chemical potential, corrosion potential, critical pitting potential. decomposition potential. electrochemical potential, electrode potential. electrokinetic potential, equilibrium (reversible) potential, free corrosion potential, noble potential, open-circuit potential, protective potential, redox potential, and standard electrode potential.
potential-pH diagram. See Pourbaix (Potential-pH) diagram.
potentiodynamic (potentiokinetic). The technique for varying the potential of an electrode in a continuous manner at a preset rate.
potentiostat. An instrument for automatically maintaining an electrode in an electrolyte at a constant potential or controlled potentials with respect to a suitable reference electrode.
potentiostatic. The technique for maintaining a constant electrode potential.
poultice corrosion. A term used in the automotive industry to describe the corrosion of vehicle body parts due to the collection of road salts and debris on ledges and in pockets that are kept moist by weather and washing. Also called deposit corrosion or attack.
Pourbaix (potential-pH) diagram. A plot of the redox potential of a corroding system versus the pH of the system, compiled using thermodynamic data and the Nernst equation. The diagram shows regions within which the metal itself or some of its compounds are stable.
powder metallurgy. The art of producing metal powders and utilizing metal powders for production of massive materials and shaped objects.
precious metal. One of the relatively scarce and valuable metals: gold, silver, and the platinum-group metals. Also called noble metal(s).
precipitation hardening. Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening and aging.
precipitation heat treatment. Artificial aging in which a constituent precipitates from a supersaturated solid solution.
precracked specimen. A specimen that is notched and subjected to alternating stresses until a crack has developed at the root of the notch.
primary current distribution. The current distribution in an electrolytic cell that is free of polarization.
primary passive potential (passivation potential). The potential corresponding to the maximum active current density (critical anodic current density) of an electrode that exhibits active-passive corrosion behavior.
primer. The first coat of paint applied to a surface. Formulated to have good bonding and wetting characteristics; may or may not contain inhibiting pigments.
principal stress (normal). The maximum or minimum value of the normal stress at a point in a plane considered with respect to all possible orientations of the considered plane. On such principal planes the shear stress is zero. There are three principal stresses on three mutually perpendicular planes. The state of stress at a point may be (1) uniaxial, a state of stress in which two of the three principal stresses are zero, (2) biaxial, a state of stress in which only one of the three principal stresses is zero, and (3) triaxial, a state of stress in which none of the principal stresses is zero. Multiaxial stress refers to either biaxial or triaxial stress.
profile. Anchor pattern on a surface produced by abrasive blasting or acid treatment.
protective potential. The threshold value of the corrosion potential that has to be reached to enter a protective potential range.
protective potential range. A range of corrosion potential values in which an acceptable corrosion resistance is achieved for a particular purpose.
quench-age embrittlement. Embrittlement of low-carbon steels resulting from precipitation of solute carbon at existing dislocations and from precipitation hardening of the steel caused by differences in the solid solubility of carbon in ferrite at different temperatures. Quench-age embrittlement usually is caused by rapid cooling of the steel from temperatures slightly below Ac, (the temperature at which austenite begins to form). and can be minimized by quenching from lower temperatures.
quench aging. Aging induced by rapid cooling after solution heat treatment.
quench cracking. Fracture of a metal during quenching from elevated temperature. Most frequently observed in hardened carbon steel, alloy steel, or tool steel pans of high hardness and low toughness. Cracks often emanate from fillets, holes, corners, or other stress raisers and result from high stresses due to the volume changes accompanying transformation to martensite.
quench hardening. (1) Hardening suitable a,8 alloys (most often certain copper or titanium alloys) by solution treating and quenching to develop a martensite-like structure. (2) In ferrous alloys, hardening by austenitizing and then cooling at a rate such that a substantial amount of austenite transforms to martensite.
quenching. Rapid cooling of metals (often steels) from a suitable elevated temperature. This generally is accomplished by immersion in water, oil, polymer solution, or salt, although forced air is sometimes used.
