Glossary

TermDefinition
AnnealingA generic term denoting a treatment consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate , used primarily to soften metallic materials, but also to simultaneously produce changes in properties or in microstructure.
Beach marksMacroscopic (visible) progression marks on a fracture surface that indicate successive positions of the advancing crack front.
Bend testingA test method for determining the relative ductility, soundness and toughness of a metal.
Brinell hardness testA test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter onto the surface of the metal.
BrittlePermitting little or no plastic deformation prior to fracture.
CarbonitridedA case hardening process in which a suitable ferrous material is heated above a lower transformation temperature in a gaseous atmosphere of such composition to cause simultaneous absorption of carbon and nitrogen by the metal surface.
Case hardeningA generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two by diffusion.
Cast ironAn iron containing carbon in excess of the solubility in the austenite that exists in the alloy at the eutectic temperature. The forms of cast iron are Gray Cast Iron, White Cast Iron, Malleable Cast Iron and Ductile Cast Iron
Cavitation damageWearing away of metal through the formation and collapse of cavities in a liquid.
Charpy impact testingA test method for determining the notch toughness or impact strength of a metal, in which a notched test specimen is struck and broken by a fallen pendulum. The energy absorbed is a measure of the impact strength or notch toughness of a metal.
Chevron markingsA macroscopic pattern of ‘V’-shaped ridges. The apex of the ‘V’ points towards the region of fracture initiation
Cleavage fractureA fracture, usually of a polycrystalline metal, in which most of the grains have failed by splitting, resulting in bright reflective facets – commonly associated with brittle fractures.
Cold workstrain produced by an external force in a metal below its recrystallization temperature
CorrosionThe deterioration of a metal by chemical or electrochemical reaction with its environment
Corrosion engineeringThe application of science and art to prevent or control corrosion damage economically and safely.
Corrosion fatigueThe effect of the application of repeated or fluctuating stresses in a corrosive environment
Corrosion potentialThe potential of a corroding surface in an electrolyte, relative to a reference electrode.
CreepA time dependent strain occurring under stress.
Crevice corrosionA type of concentrated localized corrosion of a metal that is caused by the concentration of dissolved salts, metal ions, oxygen or other gases, in crevices or pockets
Ductile-Brittle Transition TemperatureThe temperature at which the impact energy of a material drops below a specified threshold temperature for a Charpy Impact Test. Above this temperature, the material will have a tendency to bend and deform, absorbing energy before fracture. Below this temperature the material will have a tendency to shatter, failing catastrophically in a brittle manner.
DuctilityThe ability of a material to deform plastically without fracturing, being measured by elongation or reduction of area in a tensile test.
Dye penetrant inspectionA method of NDT used for finding discontinuities that are open to the surface of the component being examined. The testing involves the application of a liquid dye penetrant to the component. The wetting action of the dye will cause it to fill any cracks present. The part is then cleaned and a developer is applied to draw the dye out of the crack, thus making the crack visible.
EDX chemical analysisUsed in conjunction with the scanning electron microscope (SEM) the energy dispersive x-ray analysis test is a useful method for determining the bulk chemical composition of a sample as well as determining the microchemical composition of contaminants
ElongationIn tensile testing, elongation is the increase in gauge length measured after fracture of the specimen within the gauge length, usually expressed as a percentage of the original gauge length.
Erosion corrosionDestruction of metals by the simultaneous action of corrosion and abrasive wear of moving fluids
EtchingSubjecting the surface of a metal to preferential chemical or electrolytic attack in order to reveal microstructural details
FatigueThe phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material.
Fatigue strengthThe maximum stress that can be sustained for a specified number of cycles without failure.
Fish mouth ruptureThe macroscale appearance of longitudinal fracture in an internally pressurized pipe, tube or pressure vessel.
Forensic engineeringThe application of the art and science of engineering towards failure analysis and accident investigations.
FrettingWear that occurs between tight-fitting surfaces subjected to oscillation at very small amplitude.
Fretting corrosionThe deterioration at the interface between contacting surfaces as the result of corrosion and slight oscillatory slip between the two surfaces.
GallingA condition whereby excessive friction between high spots results in localized welding, with subsequent transfer of material and a further roughening of the rubbing surfaces of one or both of the two mating parts.
GalvalumeTrade name of an aluminum-zinc coating on sheet steel.
Galvanic corrosionAccelerated corrosion of a metal because of an electrical contact with a more noble or nonmetallic conductor in a corrosive electrolyte.
GraphiteFree carbon in steel or cast iron
Graphitic corrosionDeterioration of cast iron in which the metallic constituents are selectively leached or converted to corrosion products, leaving the graphite intact
Hackle marksA line on a crack surface running parallel to local direction of cracking.
HardnessA measure of the resistance of a material to surface indentation or abrasion.
Heat checkingA pattern of parallel surface cracks that are formed by alternate rapid heating and cooling of the extreme surface metal
Heat treatmentHeating and cooling a solid metal or alloy in such a way as to obtain desired conditions and properties.
High carbon steelCarbon steels with carbon content in the range of 0.60 – 1.00 wt%
Hot workedDeforming metal plastically at such a temperature and rate that strain hardening does not occur
Hydrogen embrittlementA condition of low ductility in metals resulting from the absorption of metals
Impact strengthThe amount of energy required to fracture a material by means of an impact test.
Intergranular corrosionCorrosion occurring preferentially at grain boundaries
Knoop hardnessMicrohardness determined from the resistance of metal to indentation by a rhombic shaped pyramidal diamond indenter – ideal for measuring hardness of coatings and platings.
Low carbon steelCarbon steels with carbon content in the range of up to 0.30 wt%
Magnetic particle inspectionA non-destructive method of inspection for determining the existence and extent of possible defects in a ferromagnetic materials.
Medium carbon steelCarbon steels with a carbon content in the range of 0.30 – 0.60 wt%
MetallographyThe science dealing with the constitution and structure of metals and alloys as revealed by the unaided eye or by microscopic magnification
Metallurgical failure analysisThe analysis of failed metallic components through scientific methods, in an attempt to determine the cause of the failure.
MetallurgyThe science and technology of metals
Microbiologically influenced corrosion (MIC)The deterioration of metals as a result of the metabolic activity of microorganisms – also referred to as microbial corrosion or biological corrosion
MicrostructureThe structure of polished and etched metals as revealed by a microscope
NitridingIntroducing nitrogen into a solid ferrous alloy by holding at a suitable temperature in contact with a nitrogenous substance such as ammonia , in order to produce a hard case
Pitting corrosionThe formation of small hemispherical shaped cavities in a metal surface by non-uniform electrodeposition or by corrosion
Polymeric failure analysisThe analysis of failed plastic components through scientific methods, in an attempt to determine the cause of the failure.
Powder metallurgyThe art of producing metal powders and of utilizing metal powders for the production of massive materials and shaped objects.
Residual stressesStress present in a body that is free of external forces or thermal gradients
Rockwell hardness testA test for determining the hardness of a material based upon the depth of a specified penetrator under certain fixed conditions. Rockwell B and C scales are commonly used for the hardness testing of metallic components
Rolling contact fatigueCracking and subsequent pitting of a surface subject to alternating contact stresses such as those produced under rolling contact or combined rolling and sliding.
Selective leachingCorrosion in which one element is preferentially removed from an alloy, leaving a porous residue of the elements that are more resistant to the particular environment. Also called dealloying, ex. Graphitic corrosion
Shrinkage voidsA void left in a cast metal as a result of solidification shrinkage
SpallingThe spontaneous chipping, fragmentation or separation of a surface or surface coating.
Stainless steelIron based alloys containing at least 10.5% chromium. Stainless steels are known for their excellent corrosion resistance.
SteelIron based alloy with carbon and manganese as the main alloying elements
StrainA measure of the relative change in the size or shape of a body.
StressForce per unit area, often though of as force acting through a small area within a plane.
Stress concentrationThe elevation in local stress caused by a change in contour or a discontinuity. Typical stress concentration areas are sharp-cornered grooves or notches, threads, fillets, holes, etc,…
Stress corrosion crackingA cracking process that requires the simultaneous action of a corrosive environment and sustained stress acting on a sample often stainless steel.
Stress relievingHeating to a suitable temperature, holding long enough to reduce residual stresses and then cooling slowly to minimize the development of residual stresses.
Sulfide stress crackingBrittle failure by cracking under combined action of tensile stress and corrosion in the presence of water and hydrogen sulfide.
TemperedReheating hardened steel or hardened cast iron to a temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness
Tension testingA test where a uni-axial load is applied to a machined material specimen of predetermined size and shape to determine the tensile properties of the material.
ToughnessThe ability of a metal to absorb energy and deform plastically before fracturing.
Transgranular corrosionCorrosion within or across the grains of a metal
Ultimate tensile strengthThe maximum tensile stress a material can withstand before fracturing
Ultrasonic inspectionA non-destructive test applied to sound conductive materials having elastic properties for the purpose of locating non-homogeneities or structural discontinuities (e.g.. Cracks or voids) within a material by means of ultrasonic impulses
Vickers hardnessMacro or micro-hardness determined from the resistance of metal to indentation by a diamond pyramidal indenter.
WearDamage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and a contacting surface or substance.
Yield strengthThe stress at which a material begins to exhibit plastic deformation (permanent deformation)