BOGIE HEARTH FURNACE
Bogie hearth falls in the category of Batch type
or continuous furnace and it is improved or
modified box type furnace.
This furnace is specifically suitable for bulky
and heavy components.
INNER LINING OF THE
Generally, heat treatment furnace should be lined
inside with low thermal mass type, that is, less
dense refractory and insulation material to
minimize heat storage by the inner lining.
Pre-fired, dense quality shapes
35-58 percent alumina (Al203)
Continuous Recirculating Bogie type
• These types of moving hearth type furnaces tend to be
used for compact stock of variable size and geometry.
• In bogie furnaces , the stock is placed on a bogie with a
refractory hearth, which travels through the furnace
with others in the form of a train.
• The entire furnace length is always occupied by bogies.
• Bogie furnaces tend to be long and narrow and to suffer
from problems arising from inadequate sealing of the
gap between the bogies and furnace shell, difficulties in
removing scale, and difficulties in firing across a
narrow hearth width.
Figure 2. Continuous Recirculating Bogie
• A controlled Atmosphere is defined as the
furnace atmosphere which protects the metal
from oxidation and maintain the desired
properties at the surface of metal during heat
• Broadly speaking controlled atmosphere is
either Protective or Chemically Active.
• Protective Atmosphere:
• The aim of Protective atmosphere to prevent
oxidation, decarburization and other unwanted
chemical changes on the surface of the metal.
• Bright annealing, normalizing of ferrous and
non-ferrous metals and alloys are the examples
of Protective atmosphere.
• Chemically Active Atmosphere:
• The aim of this atmosphere is to bring about
chemical changes on the surface of metal and
alloy through out its whole cross-section.
• Carburizing, carbonitriding, decarburization,
nitrididing, chromizing are the examples of
chemically active atmosphere.
Chemistry of Controlled Atmosphere
Reactions taking place in the furnace may be
a) Reactions b/w metal and Oxygen
b) Reactions b/w metal and Carbon
c) Reaction b/w Gases
A) Reaction b/w Metal and Oxygen
• These reactions are very important because
they for the basis on which techniques are
evolved for protecting the metals from oxygen.
• The reactions which control the oxidation in a
furnace can be written as:
• The composition of these Systems at equilibrium
is determined by:
• K1 & K2 are Equilibrium constants, and these are
related with KT as:
• The oxidation/reduction potential depends on the
ratio of the partial pressure of CO/CO2 and the
ratio of H2/H2O
• The actual required ratio is decided by the
oxide dissociation pressure of particular metal
at given temperature.
• The nature of different metals to oxidize can
be shown by graph.
• This shows the variation of oxygen
dissociation pressure of common metallic
• Those metals which have dissociation pressure
lower than this point get oxidized in that
atmosphere and vice versa.
Figure 3 , Oxygen Dissociation Pressure of some oxides with Temperature
Critical Requirement of oxidation of some metals as a function
of temperature containing water vapors and hydrogen
Critical Requirement for oxidation of some selected metals in a
atmosphere containing Carbon dioxide and carbon monoxide
Effect of Alloying on critical atmosphere requirement of some
metals at given temperature containing water vapors and
B) Reactions B/w Metal and Carbon
• In case of ferrous alloys many practical processes
involve lowering, maintaining or raising the
initial carbon level in material.
• In other words carburization, decarburization or
their prevention is involved.
• The common gases involve in carburizing the
ferrous material are carbon monoxide and
• Gases responsible for decarburization are
hydrogen and water vapours.
• The following reactions are relevant in this
• For which the equilibrium constants are
• At a given temperature , the ratio
• Can be used for assessing the carbon potential
• The total concentration is considered.
• Methane Plays an important role in gas
carburizing in steel as it is the main source of
• It strongly Influences soot deposition.
• The amounts usually presents are far in excess
of those are required for equilibrium with other
• Accordingly, the carbon potential is very high.
Effect of ratio of carbon monoxide to carbon dioxide in iron
as a function of temperature
• The following reactions also required due
• Water vapors are decarburization as:
• For non-ferrous metals following reaction is
• It is assumed when atmosphere is
contaminated with sulpher.
C) Reactions b/w Gases
• Atmosphere containing hydrogen, oxygen and
carbon are commonly used to bring about
changes in composition for obtaining
equilibrium at different temperatures.
• This changes the relative affinity of carbon
monoxide and hydrogen with oxygen.
• At 850 degree C following reaction takes
• Carbon bearing gases may deposit carbon
when temperature changes.
• If the water vapors are present the
concentration of carbon monoxide cab be
reduce because of the water gas reaction.
• Carbon deposition as a soot is also a practical
problem , particularly in the surfaces which act
as a catalytic site for the reactions.
Commercially available Atmospheres
Liquid Organic Mixtures(Alcohol base for
Process in Bogie Hearth Furnace
Pre heating for Forging
• Press Hardening
• Heating of sheet metals
• Preheating of moulds
Processes related to Heat
• Stress releasing
This is a production
process for hot forming
of sheet metals
It combines both heat
treatment in single step.
sheets are heated beyond
temperature and cool into
cool forming tool in
which they are quenched.
This quenched hardening
which increase its
PREHEATING OF MOULDS
• This is mostly use in aluminum alloy
• In which die are preheated before casting
• This preheating increase production as
well as performance of cast.
• Good quality of product is obtained from
Process specifically related to Heat
Metallurgical process in which metal
gets hardened with the passage of time,
there are two types:
i. Natural ageing
ii. Artificial ageing
• Hardening is a metallurgical and metalworking
process used to increase the hardness of a metal.
– Age hardening
– Case hardening/ Surface hardening
– Flame hardening
– Quench Hardening
– Precipitate hardening
– Induction hardening
HARDENING PROCESS IN
BOGIE HEARTH FURNACE
CASE HARDENING/ SURFACE
• Thermochemical treatments to harden surface
of part (carbon, nitrogen).
• Also called case hardening.
• May or may not require quenching.
• It involves
In hardening carbon is deposited by diffusion
Diffusion is material transport by atomic motion.
• CARBURIZING is a case-hardening process in which
carbon is dissolved in the surface layers of a low-carbon
steel part at a temperature sufficient to render the steel
austenitic to form martensitic structure.
• There is a gradient of carbon, which show different phases.
CARBON CONTENTS AND
• as we move from the
surface to core the
carbon decreases. And
the strength of
• Carbon contents and
distance are reciprocal
to each other
• There are three different methods of
– Pack carburizing
– Gas carburizing
– Liquid carburizing
• Pack carburizing
– Components are covered with coarse particles of char
coal and sealed in container.
– For more than 0.030in. Case less than this can not
– Produce heterogeneous casing.
• Components are heated in carburized atmosphere
• Controlled carburizing atmospheres are produced
by blending a carrier gas with an enriching
gas, which serves as the source of carbon.
• In commercial practice carrier gas is used, which
is enriched with hydrocarbon.
• Chances of decarburizing of high carbon contents
steel are always present
• So it should be avoided.
• Heating the specimen in the atmosphere of mixture of
ammonia and dissociated ammonia.
• Effectiveness depends upon nitrides presence.
• Nitrides case consist of two zones.
– nitrides forming zone
– Alloy nitrides layer
• It does not change the
chemical composition of
• For steel having 0.30 –
0.60% carbon contents.
• We mat apply
• Depth depends upon
– Speed of travel
– Adjustment of flame
• AUSTEMPERING is the isothermal transformation of
a ferrous alloy at a temperature below that of pearlite
formation and above that of martensite formation.
• The specimen is left in the bath for the conversion of
austenite to bainite.
• Stress Relieving consists of heating the steel to
a temperature below the critical range to relieve
the stresses resulting from cold working,
shearing, or gas cutting.
• Through this microstructure of specimen does
CLASSIFICATION OF HEAT
Tempering is a heat treatment technique
applied to ferrous alloys, such as steel or cast
iron, to achieve greater toughness by
decreasing the hardness of the alloy. The
reduction in hardness is usually accompanied
by an increase in ductility, thereby
decreasing the brittleness of the metal.
HOW TEMPERING IS PERFORMED?
Tempering is usually performed after
quenching, which is rapid cooling of the
metal to put it in its hardest state. Tempering
is accomplished by controlled heating of the
quenched work-piece to a temperature below
its "lower critical temperature"
Photomicrograph of martensite, a very hard
microstructure formed when steel is
quenched. Tempering reduces the hardness
in the martensite by transforming it into
various forms of tempered martensite
Annealing, in metallurgy and material
science, is a heat treatment that alters a
material to increase its ductility and to make it
Annealing can induce ductility, soften
material, relieve internal stresses, refine the
structure by making it homogeneous, and
improve cold working properties.
It involves heating a material to above its
critical temperature, maintaining a
suitable temperature, and then cooling.
This process also known as homogenizing
annealing is employed to remove any structural
Dendrites, columnar grains and non metallic
inclusions in steel ingots, such defects may
promote brittleness and reduce ductility and
toughness of steel.
Steel is heated above the upper critical temperature
UCT (say 1000-1200˚C) and held at this
temperature for prolonged periods usually 10-20
hours followed by slow cooling.
Segregated zones are eliminated
A chemically homogeneous steel is obtained
as a result of diffusion.
Austenitic grains are coarsened hence
resuting coarse pearlite grains on cooling
SALIENT FEATURES OF BOGIE
• Mechanized bogie drive
• Excellent temperature uniformity by re-circulating hot
• Very close temperature control
• Separate combustion section to avoid direct heating by
• Very uniform properties of heat-treated parts
• Ideal for long sections, coils and castings
• alternative Lift and swing type doors to eliminate hot
• Sturdy bogie design to take care of the charge weight
SAFETY CONTROLS (in case of gas or
liquid fuel fired bogie hearth)
The objective of a combustion safety system is to stop
the flow of fuel. It is advisable to incorporate safety
controls to interrupt fuel supply in the event of:
• low atomizing air pressures and supply in case of
liquid fuel firing,
• low and high fuel pressure,
• low and high fuel temperature,
• power failure
• failure of any safety interlocks in safeguarding
the process parameters.
The success of heat treatment depends upon:
the proper choice of heat treating furnace and
the type of atmosphere maintained in it.
Providing protective atmosphere which is
necessary to ensure that surface deterioration
doesn’t take place in reactive metals during
Maintaining constant temperature and raising
the temperature at desired rate