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CorrosionSource - Corrosion terms Category: Earth and Environment > Corrosion Date & country: 24/09/2008, USA Words: 336

ferrite
(1) A solid solution of one or more elements in body-centered cubic iron. Unless otherwise designated (for instance, as chromium ferrite), the solute is generally assumed to be carbon. On some equilibrium diagrams, there are two ferrite regions separated by an austenite area. The lower area is alpha ferrite; the upper, delta ferrite. If there is no..

filiform corrosion
Corrosion that occurs under some coatings in the form of randomly distributed threadlike filaments

film
A thin, not necessarily visible, layer of material

fish eyes
Areas on a steel fracture surface having a characteristic white crystalline appearance

flakes
Short, discontinuous internal fissures in wrought metals attributed to stresses produced by localized transformation and decreased solubility of hydrogen during cooling after hot working. In a fracture surface. flakes appear as bright silvery areas; on an etched surface, they appear as short, discontinuous cracks. Also called shatter cracks or snow..

flame spraying
Thermal spraying in which coating material is fed into an oxyfuel gas flame, where it is melted. Compressed gas may or may not be used to atomize the coating material and propel it onto the substrate

foreign structure
Any metallic structure that is not intended as part of a cathodic protection system of interest

fouling
An accumulation of deposits. This term includes accumulation and growth of marine organisms on a submerged metal surface and also includes the accumulation of deposits (usually inorganic) on heat exchanger tubing

fouling organism
Any aquatic organism with a sessile adult stage that attaches to and fouls underwater structures of ships

fractography
Descriptive treatment of fracture, especially in metals, with specific reference to photographs of the fracture surface. Macrofractography involves photographs at low magnification (< 25x); microfractography, photographs at high magnification (>25x)

fracture mechanics
A quantitative analysis for evaluating structural behavior in terms of applied stress, crack length, and specimen or machine component geometry. See also linear elastic fracture mechanics

fracture toughness
A generic term for measures of resistance to extension of a crack. The term is sometimes restricted to results of fracture mechanics tests, which are directly applicable in fracture control. However, the term commonly includes results from simple tests of notched or precracked specimens not based on fracture mechanics analysis. Results from test of..

free carbon
The part of the total carbon in steel or cast iron that is present in elemental form as graphite or temper carbon. Contrast with combined carbon

free corrosion potential
Corrosion potential in the absence of net electrical current flowing to or from the metal surface

free ferrite
Ferrire that is formed directly from the decomposition of hypoeutectoid austenite during cooling, without the simultaneous formation of cementite. Also called proeutectoid ferrite

free machining
Pertains to the machining characteristics of an alloy to which one or more ingredients have been introduced to give small broken chips, lower power consumption, better surface finish, and longer tool life; among such additions are sulfur or lead to steel, lead to brass, lead and bismuth to aluminum, and sulfur or selenium to stainless steel

fretting
A type of wear that occurs between tight-fitting surfaces subjected to cyclic relative motion of extremely small amplitude. Usually, fretting is accompanied by corrosion, especially of the very fine wear debris

fretting corrosion
The accelerated deterioration at the interface between contacting surfaces as the result of corrosion and slight oscillatory movement between the two surfaces; Deterioration at the interface between two contacting surfaces accelerated by relative motion between them of sufficient amplitude to produce slip

furan
Resin formed from reactions involving furfuryl alcohol alone or in combination with other constituents

galvanic anode
A metal which because of its relative position in the galvanic series, provides sacrificial protection to metals that are more noble in the series, when coupled in an electrolyte

galvanic cell
A cell in which chemical change is the source of electrical energy. It usually consists of two dissimilar conductors in contact with each other and with an electrolyte. or of two similar conductors in contact with each other and with dissimilar electrolytes

galvanic corrosion
Accelerated corrosion of a metal because of an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte

galvanic couple
A pair of dissimilar conductors, commonly metals, in electrical contact. See also galvanic corrosion

galvanic couple potential
See mixed potential

galvanic current
The electric current that flows between metals or conductive nonmetal in a galvanic couple

galvanic series
A list of metals and alloys arranged according to their relative corrosion potentials in a given environment. Compare with electromotive series

galvanize
To coat a metal surface with zinc using any of various processes

galvanneal
To produce a zinc-iron alloy coating on iron or steel by keeping the coating molten after hot dip galvanizing until the zinc alloys completely with the base metal

galvanometer
An instrument for indicating or measuring a small electric current by means of a mechanical motion derived from electromagnetic or electrodynamic forces produced by the current

galvanostatic
An experimental technique where by an electrode is maintained at a constant current in an electrolyte

gamma iron
The face-centered cubic form of pure iron, stable from 910 to l400 ºC (1670 to 2550 ºF

gaseous corrosion
Corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal. Also called dry corrosion

Gibbs free energy
The thermodynamic function 3G = 5H - TSS, where H is enthalpy, T is absolute temperature. and S is entropy. Also called free energy, free enthalpy, or Gibbs function

glass electrode
A glass membrane electrode used to measure pH or hydrogen-ion activity

grain
An individual crystal in a polycrystalline metal or alloy; it may or may not contain twinned regions and subgrains; a portion of a solid metal (usually a fraction of an inch in size), in which the atoms are arranged in an orderly pattern

grain boundary
A narrow zone in a metal corresponding to the transition from one crystallographic orientation to another, thus separating one grain from another; the atoms in each grain are arranged in an orderly pattern; the irregular junction of two adjacent grains is known as a grain boundary

grain-boundary corrosion
Same as intergranular corrosion. See also interdendritic corrosion

graphitization
A metallurgical term describing the formation of graphite in iron or steel, usually from decomposition of iron carbide at elevated temperatures. Not recommended as a term to describe graphitic corrosion

green liquor
The liquor resulting from dissolving molten melt irom the kraft recovery furnace in water. See also kraft process and smelt

groundbed
A buried item, such as junk steel or graphite rods, that serves as the anode for the cathodic protection of pipelines or other buried structures. See also deep groundbed

half cell
An electrode immersed in a suitable electrolyte, designed for measurements of electrode potential; A pure metal in contact with a solution of known concentration of its own ion, at a specific temperature develops a potential which is characteristic and reproducible; when coupled with another half cell, an overall potential develops which is the sum..

halogen
Any of the elements of the halogen family, consisting of fluorine, chlorine, bromine, iodine, and astatine

hard chromium
Chromium plated for engineering rather than decorative applicactions

hard water
Water that contains certain salts, such as those of calcium or magnesium, which form insoluble deposits in boilers and form precipitates with soap

hardenability
The relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surfsce at which the metal exhibits a specific hardness (50 HRC, for example) or a specific percentange of martensite in the microstructure

hardfacing
Depositing filler metal on a surfsae by welding, spraying, or braze welding to increase resistance to abrasion, erosion, wear, galling. impact, or cavitation damage

heat check
A pattern of parallel surface cracks that are formed by alternate rapid heating and cooling of the extreme surface metal, sometimes found on forging dies and piercing punches. There may be two sets of parallel cracks one set perpendicular to the other

heat-affected zone
That portion of the base metal that was not melted during brazing, cutting, or welding, but whose microstructure and mechanical properties were altered by the heat; Refers to area adjacent to a weld where the thermal cycle has coused microstructural changes which generally affect corrosion behavior

hematite
(1) An iron mineral crystallizing in therhombohedral system; the most important oreof iron. (2) An iron oxide, Fe,O,, corrcsponding to an iron content of approximately 70%

high-temperature hydrogen attack
A loss ofstrength and ductility of .steel by high-temperature reaction of absorhcd hydrogen with carbides in the steel resulting in dec arbwri:.alien and internal fissuring

holidays
Discontinuities in ci coating (suchasporosity, cracks, gape. and similar Bawd) that allow areas of base metal to be exposed to any corrosive environment that contacts the coated surface

hot corrosion
An accelerated corrosion of' metal surfaces that results from the combined elTect of oxidation and reactions with sulfur compounds and other contaminunts, such us chlorides, to form a molten salt on a metal iurfuce that f1uxes, destroys, or disrupts the normal protective oxide. Seealso gaseous r erosion

hot cracking
Also called solidification crackinghot cracking of weldments is caused by the segregation at grain boundaries of low-melting constituents in the weld metal. This can resultin grain-boundary tearing under thermal contraction stresses. Hot cracking can be minimized bythe use of low-impurity welding materials and proper joint design. See also cold cra..

hot dip coating
A metallic coating obtained bydipping the base metal into a molten metal

hot shortness
A tendency for some alloys to separate along grain boundaries when stressed ordeformed at temperatures near the melting point.Hot shortness is caused by a low-melting constituent, often present only in minute amounts,that is segregated at grain boundaries

hot working
Deforming metal plastically at sucha temperature and strain rate that recrystallization takes place simultaneously with the deformation, thus avoiding any strain hardening.Contrast with c old ii orking

huey test
Corrosion testing in a boiling solution of nitric acid. This test is mainly used to detect the susceptibilty to intergranular corrosion of stainless steel

humidity test
A corrosion test involving exposureof specimens at controlled levels of humidity and temperature. Contrast with salt-fog test

hydrogen blistering
The formation of blisters on or below a metal surface from excessive internal hydrogen pressure; Formation of blister-like bulges on a ductile metal surface caused by internal hydrogen pressures. Hydrogen may beformed during cleaning, plating, corrosion, and so forth

hydrogen damage
A general term for the emhrittlement, cracking, blistering. and hydride formation that can occur when hydrogen is present in some metals

hydrogen embrittlement
A process resulting in adecrease of the toughness or ductility of a metal due to the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after ..

hydrogen overvoltage
Overvoltage associated with the liberation of hydrogen gas

hydrogen stress cracking (HSC)
See hydrogen embrittlement

hydrogen-assisted cracking (HAC)
See hydrogenembriltlement

hydrogen-induced cracking (HIC)
Same as hydrogen embrittlement

hydrolysis
(1) Decomposition or alteration of a chemical substance by water. (2) In aqueous solutions of electrolytes, the reactions of cations with water to produce a weak base or of anions to produce a weak acid

hydrophilic
Having an affinity for water. Contrast with hydrophobic

hydrophobic
Lacking an affinity for, repelling, orfailing to absorb or adsorb water. Contrast with hydrophilic

hygroscopic
(1) Possessing a marked ability to accelerate the condensation of water vapor; applied to condensation nuclei composed of salts that yield aqueous solutions of a very low equilibrium vapor pressure compared with that of pure water at the same temperature. (2) Pertaining to a substance whose physical characteristics are appreciably altered by effect..

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 mi..

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 the temperature at which transformation of austenite to ferrite or ferrite plus cementite is completed

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 amenity 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, stress-corrosion cracking

long-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

sacrificial protection
Reduction of corrosion of a metal in an electrolyte by galvanically coupling it to a more anodic metal; a form of cathodic protection

salt fog test
An accelerated corrosion test in which specimens are exposed to a fine mist of a solution usually containing sodium chloride, but sometimes modified with other chemicals

salt spray test
See salt fog test

saturated calomel electrode
A reference electrode composed of mercury, mercurous chloride (calomel), and a saturated aqueous chloride solution

scaling
(1) The formation at high temperatures of thick corrosion product layers on a metal surface. (2) The deposition of water-insoluble constituents on a metal surface

season cracking
An obsolete historical term usually applied to stress-corrosion crackling of brass

selective leaching
Corrosion in which one element is preferentially removed from an alloy, leaving a residue (often porous) of the elements that are more resistant to the particular environment. Also called dealloying or parting. See also decarburization, decobbaltification, denickelification, dezincification, and graphitic corrosion

sensitization
In austenitic stainless steels the precipitation of chromium carbides, usually at grain boundaries, on exposure to temperatures of about 550 to 850 ºC (about 1000 to 1550 ºF), leaving the grain boundaries depleted of chromium and therefore susceptible to preferential attack by a corroding (oxidizing) medium

sensitizing heat treatment
A heat treatment, whether accidental, intentional, or incidental (as during welding), that causes precipitation of constituents at grain boundaries, often causing the alloy to become susceptible to intergranular corrosion or intergranular stress-corrosion cracking. See also sensitization

shear
That type of force that causes or tends to cause two contiguous parts of the same body to slide relative to each other in a direction parallel to their plane of contact

shear strength
The stress required to produce fracture in the plane of cross section, the conditions of loading being such that the directions of force and of resistance are parallel and opposite although their paths are offset a specified minimum amount. The maximum load divided by the original cross-sectional area of a section separated by shear

sigma phase
A hard, brittle, nonmagnetic intermediate phase with a tetragonal crystal structure, containing 30 atoms per unit cell, space group P4₂mnm, occurring in many binary and ternary alloys of the transition elements. The composition of this phase in the various systems is not the same and the phase usually exhibits a wide range in..

sigma-phase embrittlement
Embrittlement of iron-chromium alloys (most notably austenitic stainless steels) caused by precipitation at grain boundaries of the hard, brittle intermetallic sigma phase during long periods of exposure to temperatures between approximately 560 and 980 ºC ( 1050 and 1800 ºF). Sigma-phase embrittlement results in severe loss in toughness and ductil..

slip
Plastic deformation by the irreversible shear displacement (translation) of one part of a crystal relative to another in a definite crystallographic direction and usually on a specific crystallographic plane. Sometimes called glide

slow strain rate technique
An experimental technique for evaluating susceptibility to stress-corrosion cracking. It involves pulling the specimen to failure in uniaxial tension at a controlled slow strain rate while the specimen is in the test environment and examining the specimen for evidence of stress-corrosion cracking

slushing compound
An obsolete term describing oil or grease coatings used to provide temporary protection against atmospheric corrosion

smelt
Molten slag; in the pulp and paper industry, the cooking chemicals tapped from the recovery boiler as molten material and dissolved in the smelt tank as green liquor

soft water
Water that is free of magnesium or calcium salts