Metallurgical Terms
B
B
Chemical symbol for Boron
B
(See magnetic flux density)
Bainite
An acicular aggregate of ferrite and carbide particles formed when austenite
is transformed at temperatures in the intermediate range, i.e., above the
martensite range and below the pearlite range. The structure of bainite varies
with the composition of the austenite from which it is formed and with the
temperature of its formation.
Balanced Steel
Steel in which the deoxidation is so controlled that the evolution of gas
during solidification approximately balances the shrinkage normally occurring.
Thus no pipe cavity is produced and a high yield of usable metal can be obtained
on rolling the ingot.
Banded Structures
Light and dark parallel bands revealed by etching and formed by the
elongation during rolling or forging of dendritic segregation in the ingot.
Base Metal
(a) A metal which becomes oxidized when heated in air, e.g., copper, lead,
zinc, and tin, as distinct from a noble metal such as Gold and platinum.
(b) In electro-metallurgy, a metal at the lower end of the electro-chemical
series.
(c) The preponderant metal in an alloy.
(d) The metal to be welded or cut.
Basic Oxygen Process
This method of steel making is becoming the major steel making process.
Furnaces of up to 350 tonnes capacity can produce steel in 40 minutes. The
charge consists essentially of molten pig iron but up to 30% of scrap may be
added. A water cooled lance directs a stream of oxygen on the surface of the
liquid bath oxidizing carbon and other unwanted elements. Lime is added to flux
the oxides and after refining the steel is tapped into a ladle.
Basic Slag
(See Slag)
Basic Steel
Steel produced in a furnace with a lining consisting of basic refractory
such as rammed magnesite or dolomite. A slag, rich in lime, is produced and the
sulphur and phosphorus pass into the slag during the working of the charge.
Batch Furnace
A furnace (as opposed to a continuous furnace) into which the work pieces
are charged singly or in batches, the furnace temperature then being controlled
to produce the desired temperature cycle.
Bauschinger Effect
The decrease in compressive yield strength and increase in tensile yield
strength obtained when a metal is plastically strained in tension beyond its
yield point.
Be
Chemical symbol for Beryllium
Becking
Increasing the diameter of a steel ring or drum by forging on a becking bar,
or mandrel, the forging being worked radially between the bar and the upper
tool.
Bend Test
A test in which a standard specimen is bent through a specified arc to
determine the degree of ductility and the soundness of internal structure.
Bessemer process
A method of producing steel in which air (which may be enriched by oxygen)
is blown through molten pig iron contained in a refractory-lined pear-shaped
cylindrical vessel, open at the upper end for the escape of gases, the vessel
being known as a Bessemer converter. The heat is produced by the oxidation of
impurities, silicon, manganese and carbon, by the oxygen of the blast. In the
acid Bessemer process, the lining is of ganister and the phosphorus content of
the pig iron remains unaltered. In the basic Bessemer process, the phosphorus is
oxidized, and passes into the slag. Magnesia or dolomite is substituted for the
acid ganister lining and lime is added to the charge before blowing begins. High
phosphorus pig irons are used, and much of the heat required to maintain the
fluidity of the iron is derived from the combustion of the phosphorus. The
highly phosphoric slag is a valuable by-product for use as a fertilizer. The
basic Bessemer process is known on the Continent as the Thomas Process. The
Bessemer process has been largely superseded by the Basic Oxygen Process.
B/H Loop (Magnetic hysteresis and hysteresis curve)
A closed figure formed by plotting magnetizing force against flux density
for a magnetic material when the magnetizing force is taken through a complete
cycle of increasing and decreasing values. The area of the figure is
proportional to the magnetic hysteresis loss.
Billet
(See Bloom)
Bi
(Chemical symbol for Bismuth)
Black Annealing
(a) A process of annealing without a protective medium.
(b) The first annealing process in the manufacture of tin plate. (See White
Annealing).
Black-Heart Process
A method of producing black-heart malleable cast iron which consists of heating
white cast iron, which is hard and brittle, to a temperature of about 850˚C for
a period of days. Oxidation is controlled by packing the iron in a suitable
mixture of burnt and new ore so that the carbon in the outer layers only is
oxidized. The iron carbide in the interior is broken down with the precipitation
of graphite, thus rendering the castings malleable and readily machinable. The
fracture shows a light grey outer layer, due to decarburization, and a dark grey
core.
Blast Furnace
A tall, cylindrical, refractory-lined furnace for the production of pig iron
or hot metal which can be used directly in a steel making process. The furnace
consists essentially of five main parts; bottom, hearth, bosh, stack and top.
The bottom is composed of refractory firebrick to a depth of about 5 meters and
stands on a concrete foundation; the hearth holds the accumulated molten iron
and slag; the bosh is the widest part of the furnace and is also the area having
the highest temperature; the stack extends from the bosh to the top and may be
over 30 meters in height; the top consists of a double bell and hopper. A large
pipe, known as the bustle pipe, encircles the furnace and distributes hot blast
to the tuyeres, through which hot air is blown and distributed through the
furnace; the tuyeres are situated below the bosh and vary in number according to
the size of the furnace. In operating the furnace, iron ore, coke and limestone
are fed in at the top through the bell and hopper; as they descend through the
furnace they are met by the ascending gas from the blast blown through the
tuyeres. This gas in contact with the coke forms carbon monoxide which in turn
reduces the iron oxide of the ore to metallic iron, the limestone forming a slag
with the earthy content of the ore. (In the beginning of the campaign of the
furnace, a fire is made in the hearth to provide the heat necessary to start
this reaction). The molten iron and slag thus formed trickle down the furnace
and collect in the hearth, the slag floating on the top of the iron. They are
tapped at intervals through the iron notch and the cinder notch respectively. A
modern blast furnace may have an output of as much as 5,000 tonnes of iron per
day.
Bloom
An intermediate product which has been rolled or forged down from an ingot
and is destined for further working into bars, sheet, tubes and forgings, etc.
It is usually square in section and more than inches square, smaller sizes being
known as billets.
Blooming Mill
A rolling mill used in reducing steel ingots to blooms, sometimes called a
cogging mill, and not always distinguished from a billet or slab mill.
Blowholes
(a) Round or elongated smooth walled gas-tilled cavities in solid metals
formed either by the trapping of gas evolved during solidification of the metal
or by steam or gas from the mould surface.
(b) (Gas Pocket) A cavity in a weld caused by the entrapment of gas.
Blue Annealing
A process of softening by heating hot-rolled sheet in the open furnace to a
temperature within the transformation range and cooling in air; the formation of
a bluish oxide on the surface is incidental.
Blue Brittleness
The loss of ductility found on testing steel in the blue heat range which
varies between about 200˚C and 400˚C according to the composition of the steel.
This embrittlement is shown by the increase in maximum strength and decrease in
the elongation, reduction of area and impact value. If steel is deformed at room
temperatures, heated in the blue heat range and then tested at normal
temperatures, the loss of ductility is revealed by the impact test rather than
by elongation. The term blue brittleness is derived from the fact that blue
oxide films are formed on polished steel within the range of temperature in
question.
Blueing
A treatment of the surface of iron-base alloys usually in the form of sheet
or strip, on which, by the action of air or steam at a suitable temperature, a
thin blue oxide film is formed on the initially scale-free surface. It is used
to improve the appearance and to increase resistance to corrosion.
Body Centred Cubic Lattice
The crystal lattice in which atoms are present at the corners of each cube
or rectangular prism, with one atom in the centre of such cube or prism. The
unit cell contains two atoms, because each corner atom is shared by seven other
cubes.
Boil
The period after melting in the production of steel, when as the carbon is
being oxidized; the liberated carbon monoxide gives the appearance of the metal
being on the boil.
Bonderizing
A chemical treatment similar to Parkerizing but shorter. The phosphate
coating is much thinner and smoother, giving a brighter finish for painting. It
is widely used as a pre-treatment in the manufacture of domestic articles.
Box Annealing, (Close, Coffin, Pack, or Pot Annealing)
This process consists of heating en masse a block of sheets resting on a
metal bed under a metal cover, sand being placed in the bottom to prevent the
entry of the furnace atmosphere.
Brazing
The process of joining two pieces of metal by fusing a layer of brass or
other non-ferrous metal between the adjoining surfaces.
Bright Annealing
A process of annealing which is carried out in a controlled furnace
atmosphere or vacuum so that surface oxidation is reduced to a minimum and the
surface remains relatively bright.
Brinell Hardness Test
The method consists of indenting the metal with a 10mm. diameter steel ball
subjected to a load of 3,000 kg. For non-ferrous metal, the load is reduced. The
load is applied for 10 to 15 seconds, after which it is removed; the diameter of
the recovered indentation is measured and the Brinell hardness number is
calculated by dividing the load applied (kilograms) by the superficial area of
the depression caused by the hard steel ball (in square millimeters).
Brittle Fracture
(See Fracture)
Burden
The ratio of the total weight of the ore and flux to the fuel charged into a
blast furnace. A heavy burden is one with a high ratio of ore to coke.
Burnt Steel
The term is usually applied to a condition in which visible oxide films ate
formed at the crystal boundaries of the steel. This denotes that the steel has
been heated almost to the solidus temperature and is, therefore, permanently
damaged. (See Overheating).