Glossary of Metallurgical Terms
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I Chemical symbol for Iodine.
Impact Energy The amount of energy required to fracture a material, usually measured by means of an Izod test or Charpy test. The type of specimen and test conditions affect the values and therefore should be specified.
Impact Test A test designed to give information on how a specimen of a known material will respond to a suddenly applied stress, e.g. shock. The test ascertains whether the material is tough or brittle. A notched test piece is normally employed and the two methods in general use are either the Izod or Charpy test. The result is usually reported as the energy in ft.lbs. or KJ. required to fracture the test piece.
In Chemical symbol for Indium.
Inclusion Count A method of assessing the number and size of non-metallic inclusions present in metal.
Inclusions Particles of foreign material in a metallic matrix. The particles are usually compounds (such as oxides, sulfides or silicates), but may be of any substance that is foreign to (and essentially insoluble in) the matrix.  In general they are detrimental to mechanical properties but much depends on the number, their size, shape and distribution.
Induction Hardening A widely used process for the surface hardening of steel. The components are heated by means of an alternating magnetic field to a temperature within or above the transformation range followed by immediate quenching. The core of the component remains unaffected by the treatment and its physical properties are those of the bar from which it was machined, whilst the hardness of the case can be within the range 37/58 Rc. Carbon and alloy steels with a carbon content in the range 0.40/0.45% are most suitable for this process.
Induction Heating Heating by combined electrical resistance and hysteresis losses induced by subjecting a metal to the varying magnetic field surrounding a coil carrying alternating current.
Induction Tempering Tempering of steel using low-frequency electrical induction heating.
Ingot The mass of metal that results from casting molten steel into a mould. An ingot is usually rectangular in shape and is subsequently rolled into blooms and billets for rods, bars and sections and slabs for plates, sheet and strip. With the increasing use of the continuous casting process the ingot route is less used as the molten steel is now directly cast into a bloom or billet.
Ingot Mould The receptacle into which molten steel is poured to form an ingot. After solidification the steel is suitable for subsequent working, i.e. rolling or forging.
Intercrystalline Corrosion Chromium-nickel austenitic stainless steels are prone to this form of corrosion when they are welded and subsequently in contact with certain types of corrosive media. When heated within a temperature range of 450-800oC precipitation of the chromium carbides takes place at the grain boundaries in the area of the weld and these areas no longer have the protection of the chromium on the peripheries of the grains. This type of corrosion is also known as Weld Decay and Intergranular Corrosion. The most common way to avoid the problem is to select a grade of steel that is very low in carbon i.e. 0.03% or less, or one that is stabilised with niobium or titanium.
Intergranular Between crystals or grains. Also called intercrystalline.
Intergranular Cracking Cracking or fracturing that occurs between the grains or crystals in a polycrystalline aggregate.  Also called intercrystalline cracking.
Intergranular Fracture Brittle fracture of a metal in which the fracture is between the grains, or crystals, that form the metal. Also called intercrystalline fracture.
Intermediate Annealing Annealing wrought metals at one or more stages during manufacture and before final treatment.
Interrupted Aging Aging at two or more temperatures, by steps, and cooling to room temperature after each step. See aging, and compare with progressive aging and step aging.
Interrupted Quenching Rapid cooling to a selected temperature by quenching in a suitable medium, usually molten salt, holding at the temperature for an appropriate time and then cooling to room temperature. This process is used to minimize the risk of distortion.
Iron The term iron, as used in the chemical or scientific sense of the word, refers to the chemical element iron or pure iron and is the chief constituent of all commercial iron and steel.
Isothermal Annealing Heating to and holding at a temperature above the transformation range, then cooling to and holding at a suitable temperature until the austenite to pearlite change is complete.
Isothermal Transformation A change in phase that takes place at a constant temperature. The time required for transformation to be completed, and in some instances the time delay before transformation begins, depends on the amount of supercooling below (or superheating above) the equilibrium temperature for the same transformation.
Isothermal Transformation Curve Also known as the Time Temperature Transformation Curve. If a small piece of steel is heated sufficiently slowly for it to become austenitic and then plunged into a salt bath and held at a constant temperature below the upper critical point for a definite time followed by rapid quenching, it is possible by examination to determine the extent to which the transformation of the austenite has occurred. By taking a number of specimens of the same steel and treating them in the same way, but varying the holding temperature and time the behavior of the steel with time and temperature can be studied. The information obtained can be plotted as time- temperature transformation curves which is useful in heat treatment practice, particularly for martempering and austempering.
Isothermal Treatment A type of treatment in which a part is quenched rapidly down to a given temperature, then held at that temperature until all transformation is complete.
Izod Impact Test A test specimen, usually of square crossed section is notched and held between a pair of jaws, to be broken by a swinging or falling weight. When the pendulum of the Izod testing machine is released it swings with a downward movement and when it reaches the vertical the hammer makes contact with the specimen which is broken by the force of the blow. The hammer continues its upward motion but the energy absorbed in breaking the test piece reduces its momentum. A graduated scale enables a reading to be taken of the energy used to fracture the test piece. To obtain a representative result the average of three tests is used and to ensure that the results conform to those of the steel specification the test specimens should meet the standard dimensions laid down in BS 131. Contrast with Charpy test.
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