Metallurgical Terms
I
I
Chemical symbol for Iodine
Ihrigizing
A method of producing a high silicon (about 14%) case on iron and steel. The
metal parts, together with a suitable quantity of silicon carbide, are charged
into a rotating retort through which is passed a continuous stream of chlorine,
and the furnace is heated to about 1000˚C. A treatment of about 2 hours is
required to produce a case of 1mm. Ihrigized iron or steel is said to have an
increased resistance to corrosion, to scaling and to galling and seizing.
Image Analyzing Computer
An instrument which, by means of a television scanning system, measures the
area, size and number of inclusions, or other phases, in a metal sample. The
information is fed into a computer and then displayed or recorded. In this way
the cleanness of steel, for example, can be rapidly and accurately assessed.
Impact Test
A test to determine the resistance of a material to a suddenly applied
stress, i.e., shock. A notched test piece is normally employed and the testing
machines in general use are the Izod and Charpy. The resistance is usually
reported as the energy in ft.-lb. or kg.m. required to fracture or bend the test
piece, or as kg.m. per square centimeter of section behind the notch.
In
Chemical Symbol for Indium
Inclusion Count
A method of assessing the number and size of non-metallic inclusions.
Several methods are in use such as Fox, Jernkontoret and A.S.T.M. The methods
depend on
microscopical examination of selected areas and comparing with standard charts
or estimating areas. It is usual to take into account the type of inclusion as
well as its size.
Inclusions
Usually non-metallic particles contained in metal. In steel they consist of
sulphides such as manganese sulphide and oxides such as silicates or alumina. By
causing local stress concentrations inclusions can cause a reduction in
ductility and fatigue strength, or if large, a reduction in tensile strength.
Induction Hardening
A process of hardening steel by heating it, by means of an alternating
magnetic field, to a temperature within or above the transformation range,
followed immediately by quenching. This process may be applied to both surface
hardening and full hardening.
Ingot
A mass of metal cast into a mould. It differs from a casting in that it has
to be rolled or forged to be made usable.
Ingot Iron
Iron of comparatively high purity, produced in the same way as steel, in the
open hearth furnace, under conditions that keep down the carbon, manganese and
silicon content, e.g., Armco Iron.
Ingot Mould
Primarily, the function of an ingot mould is to provide a receptacle for the
molten steel, which shall, after freezing, be in a form suitable for subsequent
working.
Moulds are generally of cast iron.
Inhibitors
(See Pickling)
Intercrystalline Corrosion (Inter granular Corrosion) (Weld Decay)
This occurs in chromium-nickel austenitic steels submitted to chemical
attack after heating within the range 500˚-800˚C. At this temperature the carbon
is precipitated at the grain boundaries as chromium carbide thus reducing the
chromium content; of the austenite adjacent to the boundaries and rendering it
susceptible to corrosion. Under corrosive conditions ausienitic stainless steels
may suffer grain boundary attack if previously heated in this range of
temperature; examples are the heat affected tones of welds and steel which has
been slowly cooled from high temperatures. Susceptibility to intercrystalline
corrosion may be prevented by making the steel with a low carbon content, e.g.,
<0•03 %, or by adding a stabilizer such as niobium or titanium to combine with
the carbon and prevent the formation of chromium carbide.
Intercrystalline Corrosion Tests
Of various methods for determining susceptibility of stainless steels to
intercrystalline corrosion, the two most commonly used are the sulphuric
acid-copper sulphate test (Hatfield or Strauss test), and the boiling 65% nitric
acid test (Hue test)
Interrupted Quenching (Time Quenching)
Rapid cooling to a selected temperature by quenching in a suitable medium,
such as molten salt or lead, holding at the temperature for an appropriate time
and then allowing cooling to room temperature. (See also Austempering and
Martempering).
Inverse Annealing
A heat treatment, analogous to precipitation hardening, applied to cast
iron, usually to increase its hardness and strength.
Inverse Segregation (Negative Segregation)
A concentration of certain alloy constituents that have lower melting points
in the region corresponding to that first solidifying; caused by interdendritic
flow of enriched liquid through channels where the pressure drops with
contraction of dendrites. The internal evolution of hydrogen may also give a
positive pressure, aiding this flow and causing a liquated surface.
Investment Casting
(See Precision Casting)
Ir
Chemical symbol for Iridium
Isothermal Annealing
The steel after being converted to austenite by heating is cooled to a
predetermined temperature at which it is held until transformation to ferrite
and pearlite is complete.
Isothermal Transformation Curve
(See Time Temperature Transformation Curve)
Izod Impact Test
A test piece of 10mm square or 0•45in. diameter section is notched
transversely by a V-cutter, to a depth of 2mm and an angle of 45˚. The radius at
the bottom of the notch is ¼mm. The piece is fixed vertically in the vice of the
machine by the lower end with the notch at the level of the face of the vice.
When the pendulum of the machine is released a knife edge carried in the tup of
the machine strikes the piece at a distance of 22mm above the notch, on the same
side as the notch. The angle of swing of the pendulum beyond the vertical after
breaking the test piece is indicated by a pointer. From the amount by which the
angle falls short of the angle to which the pendulum would have swung if there
had been no test piece, the amount of energy absorbed in breaking the test piece
is known, and is indicated in ft.-lb. The height of fall of the centre of mass
of the pendulum is 2ft., and the capacity of the machine 150 ft.-lb., or 120
ft.-lb., the distance from the pivot to the striking edge being 4 feet. The
striking velocity, when using the full capacity of the machine, is 13.6ft
second.