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HEAT TREATMENT LAB PRESENTATION

BOGIE HEARTH FURNACE

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PRESENTED BY

MUHAMMAD NAVEED ALAM

ABDUL RAHMAN

EHSAN UL HAQ

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CONTENTS OF PRESENTATIONFurnace classificationHeat treatment furnacesBogie hearth furnaceAtmosphere inside the furnaceApplications of bogie hearth furnaceHeat treatment processes performed in bogie

hearth furnaceTechnical data of bogie hearth furnaceConclusion

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CLASSIFIACTION OF FURNACES

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BOGIE HEARTH FURNACEBogie 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.

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INNER LINING OF THE FURNACE

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.

SUGGESTED REFRACTORY

Pre-fired, dense quality shapes containing

35-58 percent alumina (Al203)

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Figure 1. Bogie Hearth furnace

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Continuous Recirculating Bogie type Furnaces

• 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.

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Figure 2. Continuous Recirculating Bogie Type Furnace

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FURNACE ATMOSPHERES• 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 treatment.

• 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.

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• 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.

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Chemistry of Controlled Atmosphere Processes

Reactions taking place in the furnace may be grouped as

a) Reactions b/w metal and Oxygen

b) Reactions b/w metal and Carbon

c) Reaction b/w Gases

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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:

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• 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

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• 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 oxides.

• Those metals which have dissociation pressure lower than this point get oxidized in that atmosphere and vice versa.

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Critical Requirement of oxidation of some metals as a function of temperature containing water vapors and hydrogen

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Critical Requirement for oxidation of some selected metals in a atmosphere containing Carbon dioxide and carbon monoxide

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Effect of Alloying on critical atmosphere requirement of some metals at given temperature containing water vapors and

hydrogen

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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 methane.

• Gases responsible for decarburization are hydrogen and water vapours.

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• The following reactions are relevant in this context:

• For which the equilibrium constants are

• At a given temperature , the ratio

• Can be used for assessing the carbon potential

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• The total concentration is considered.• Methane Plays an important role in gas

carburizing in steel as it is the main source of carbon.

• It strongly Influences soot deposition.• The amounts usually presents are far in excess

of those are required for equilibrium with other gases.

• Accordingly, the carbon potential is very high.

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Effect of ratio of carbon monoxide to carbon dioxide in iron as a function of temperature

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• The following reactions also required due consideration:

• Water vapors are decarburization as:

• For non-ferrous metals following reaction is important:

• It is assumed when atmosphere is contaminated with sulpher.

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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 place:

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• 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.

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Commercially available Atmospheres

1. Town Gas

2. Ammonia

3. Charcoal

4. Liquid Organic Mixtures(Alcohol base for carburization)

5. Vacuum

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Process in Bogie Hearth Furnace

Pre heating for Forging• Press Hardening• Heating of sheet metals• Preheating of moulds

Processes related to Heat Treatment• Ageing• Hardening• Austempering• Stress releasing

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PRESS HARDENING

• This is a production process for hot forming of sheet metals

• It combines both heat treatment in single step.

• sheets are heated beyond the austenizing temperature and cool into cool forming tool in which they are quenched.

• This quenched hardening process produce martensitic structure which increase its properties.

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PREHEATING OF MOULDS

• This is mostly use in aluminum alloy industry.

• In which die are preheated before casting .

• This preheating increase production as well as performance of cast.

• Good quality of product is obtained from this.

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Process specifically related to Heat Treatment

• Ageing• Hardening• Austempering• Stress releasing

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AGEINGMetallurgical process in which metal

gets hardened with the passage of time,

there are two types:

i. Natural ageing

ii. Artificial ageing

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HARDENING

• Hardening is a metallurgical and metalworking process used to increase the hardness of a metal.

• Types – Age hardening– Case hardening/ Surface hardening– Flame hardening– Quench Hardening– Precipitate hardening– Induction hardening

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HARDENING PROCESS IN BOGIE HEARTH FURNACE

Hardening

Case hardening

Nitriding

Carburizing

Carbonitriding

Flame

hardening

Quenched hardening

Oil quench

Water quench

Precipitate hardening

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CASE HARDENING/ SURFACE HARDENING

• Thermochemical treatments to harden surface of part (carbon, nitrogen).

• Also called case hardening.• May or may not require quenching.• It involves– Carburizing– Nitriding– Carbunitriding

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In hardening carbon is deposited by diffusion process.Diffusion is material transport by atomic motion.

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CARBURIZING • 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.

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CARBON CONTENTS AND DISTANCE

• as we move from the surface to core the carbon decreases. And the strength of specimen also decreases.

• Carbon contents and distance are reciprocal to each other

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Case depth and carburizing time

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CARBURIZING METHODS • There are three different methods of

carburizing– 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

carburized.– Produce heterogeneous casing.

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GAS CARBURIZING • Components are heated in carburized atmosphere

by gas.• 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.

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NITRIDING

• 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

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FLAME HARDENING

• It does not change the chemical composition of specimen.

• For steel having 0.30 – 0.60% carbon contents.

• We mat apply oxyacetylene flame.

• Depth depends upon

– Time – Speed of travel – Adjustment of flame

intensity

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AUSTEMPERING

• 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.

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STRESS RELEASING

• 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 not change.

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CLASSIFICATION OF HEAT TREATMENT TECHNIQUES

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TEMPERING

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"

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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

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EFFECT OF TEMPERING ON HARDNESS

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ANNEALING

Annealing, in metallurgy and material science, is a heat treatment that alters a

material to increase its ductility and to make it more workable.

Annealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and

improve cold working properties.

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ANNEALING

It involves heating a material to above its critical temperature, maintaining a

suitable temperature, and then cooling.

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DIFFUSION ANNEALING

This process also known as homogenizing annealing is employed to remove any structural non-uniformity.

PROBLEM

Dendrites, columnar grains and non metallic inclusions in steel ingots, such defects may promote

brittleness and reduce ductility and toughness of steel.

SOLUTION

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.

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DIFFUSION ANNEALING

RESULT

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

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SALIENT FEATURES OF BOGIE HEARTH FURNACE

• Mechanized bogie drive• Excellent temperature uniformity by re-circulating hot

combustion products• Very close temperature control • Separate combustion section to avoid direct heating by

radiation• Very uniform properties of heat-treated parts• Ideal for long sections, coils and castings• alternative Lift and swing type doors to eliminate hot

air leakage• Sturdy bogie design to take care of the charge weight

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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.

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TECHNICAL DATA MODEL T max (˚C) INSIDE

DIMENSIONS (mm)

OUTSIDE DIMENSIONS (mm)

POWER RATING

(kW)

VOLUME WEIGHT (Kg)

WM 800/09

900 900x1500x600

2350x2500x2650

32 800 1300

WM 1500/09

900 1000x2500x600

2450x3500x2650

60 1500 2300

WM 2000/09

900 1000x2500x800

2450x3500x2900

80 2000 2800

WM 800/12

1280 900x1500x600

2350x2500x2650

40 800 1300

WM 5000/12

1280 1200x3000x1400

2700x4000x4500

180 5000 4300

WM 7000/12

1280 1200x4000x1400

2700x5050x4500

250 6700 5000

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CONCLUSIONThe 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 heat treatment

Maintaining constant temperature and raising the temperature at desired rate

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