Case Histories


Term Definition
annealing A 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 marks Macroscopic (visible) progression marks on a fracture surface that indicate successive positions of the advancing crack front.
bend testing A test method for determining the relative ductility, soundness and toughness of a metal.
Brinell hardness test A 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.
brittle Permitting little or no plastic deformation prior to fracture.
carbonitrided A 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 hardening A 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 iron An 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 damage Wearing away of metal through the formation and collapse of cavities in a liquid.
Charpy impact testing A 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 markings A macroscopic pattern of ‘V’-shaped ridges. The apex of the ‘V’ points towards the region of fracture initiation
cleavage fracture A 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 work strain produced by an external force in a metal below its recrystallization temperature
corrosion The deterioration of a metal by chemical or electrochemical reaction with its environment
corrosion engineering The application of science and art to prevent or control corrosion damage economically and safely.
corrosion fatigue The effect of the application of repeated or fluctuating stresses in a corrosive environment
corrosion potential The potential of a corroding surface in an electrolyte, relative to a reference electrode.
creep A time dependent strain occurring under stress.
crevice corrosion A 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 Temperature The 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.
ductility The ability of a material to deform plastically without fracturing, being measured by elongation or reduction of area in a tensile test.
dye penetrant inspection A 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 analysis Used 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
elongation In 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 corrosion Destruction of metals by the simultaneous action of corrosion and abrasive wear of moving fluids
etching Subjecting the surface of a metal to preferential chemical or electrolytic attack in order to reveal microstructural details
fatigue The phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material.
fatigue strength The maximum stress that can be sustained for a specified number of cycles without failure.
fish mouth rupture The macroscale appearance of longitudinal fracture in an internally pressurized pipe, tube or pressure vessel.
forensic engineering The application of the art and science of engineering towards failure analysis and accident investigations.
fretting Wear that occurs between tight-fitting surfaces subjected to oscillation at very small amplitude.
fretting corrosion The deterioration at the interface between contacting surfaces as the result of corrosion and slight oscillatory slip between the two surfaces.
galling A 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.
Galvalume Trade name of an aluminum-zinc coating on sheet steel.
galvanic corrosion Accelerated corrosion of a metal because of an electrical contact with a more noble or nonmetallic conductor in a corrosive electrolyte.
graphite Free carbon in steel or cast iron
graphitic corrosion Deterioration of cast iron in which the metallic constituents are selectively leached or converted to corrosion products, leaving the graphite intact
hackle marks A line on a crack surface running parallel to local direction of cracking.
hardness A measure of the resistance of a material to surface indentation or abrasion.
heat checking A pattern of parallel surface cracks that are formed by alternate rapid heating and cooling of the extreme surface metal
heat treatment Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions and properties.
high carbon steel Carbon steels with carbon content in the range of 0.60 – 1.00 wt%
hot worked Deforming metal plastically at such a temperature and rate that strain hardening does not occur
hydrogen embrittlement A condition of low ductility in metals resulting from the absorption of metals
impact strength The amount of energy required to fracture a material by means of an impact test.
intergranular corrosion Corrosion occurring preferentially at grain boundaries
Knoop hardness Microhardness 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 steel Carbon steels with carbon content in the range of up to 0.30 wt%
magnetic particle inspection A non-destructive method of inspection for determining the existence and extent of possible defects in a ferromagnetic materials.
medium carbon steel Carbon steels with a carbon content in the range of 0.30 – 0.60 wt%
metallography The science dealing with the constitution and structure of metals and alloys as revealed by the unaided eye or by microscopic magnification
metallurgical failure analysis The analysis of failed metallic components through scientific methods, in an attempt to determine the cause of the failure.
metallurgy The 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
microstructure The structure of polished and etched metals as revealed by a microscope
nitriding Introducing 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 corrosion The formation of small hemispherical shaped cavities in a metal surface by non-uniform electrodeposition or by corrosion
polymeric failure analysis The analysis of failed plastic components through scientific methods, in an attempt to determine the cause of the failure.
powder metallurgy The art of producing metal powders and of utilizing metal powders for the production of massive materials and shaped objects.
residual stresses Stress present in a body that is free of external forces or thermal gradients
Rockwell hardness test A 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 fatigue Cracking and subsequent pitting of a surface subject to alternating contact stresses such as those produced under rolling contact or combined rolling and sliding.
selective leaching Corrosion 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 voids A void left in a cast metal as a result of solidification shrinkage
spalling The spontaneous chipping, fragmentation or separation of a surface or surface coating.
stainless steel Iron based alloys containing at least 10.5% chromium. Stainless steels are known for their excellent corrosion resistance.
steel Iron based alloy with carbon and manganese as the main alloying elements
strain A measure of the relative change in the size or shape of a body.
stress Force per unit area, often though of as force acting through a small area within a plane.
stress concentration The 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 cracking A cracking process that requires the simultaneous action of a corrosive environment and sustained stress acting on a sample often stainless steel.
stress relieving Heating to a suitable temperature, holding long enough to reduce residual stresses and then cooling slowly to minimize the development of residual stresses.
sulfide stress cracking Brittle failure by cracking under combined action of tensile stress and corrosion in the presence of water and hydrogen sulfide.
tempered Reheating hardened steel or hardened cast iron to a temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness
tension testing A 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.
toughness The ability of a metal to absorb energy and deform plastically before fracturing.
transgranular corrosion Corrosion within or across the grains of a metal
ultimate tensile strength The maximum tensile stress a material can withstand before fracturing
ultrasonic inspection A 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 hardness Macro or micro-hardness determined from the resistance of metal to indentation by a diamond pyramidal indenter.
wear Damage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and a contacting surface or substance.
yield strength The stress at which a material begins to exhibit plastic deformation (permanent deformation)

[1] American Society for Metals, Definition of Metallurgical Terms, 1977