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R. LADROUE 20051 R. LADROUE Rev1/2006.

HEAT TREATMENT




HEAT TREATMENT

Heat treatment can be defined as an operation or combination of operations involving the controlled heatingand cooling of a metal in the solid state for the purpose of obtaining specific properties.There are many types of heat-treating process available, fulfilling a wide variety of hardness and mechanicalproperties requirements.Quenching of steels involves the rapid cooling of austenite to transform it into the hard structure – martensite .

Annealing

Quenching

Tempering




HEAT TREATMENT

A

R

Ms

MF

M Martensitic transformation aera

A Austenite temperature transformation

R Reduction of residual austenitein martensite

Ms Martensitic startingtransformation

MF Martensitic finaltransformation

Annealing

Quenching

Tempering

Temperature

Time

3 different cycles for 3 different results




HEAT TREATMENT

Tempering is a process done subsequent to quench hardening.Quench-hardened parts are often too brittle.This brittleness is removed by tempering

Quenching is a process gives hardness and brittleness.Quench-hardened parts have special metallurgic properties.This brittleness is removed by tempering

Annealing removes quenching effects and gives to metalits initial properties

Initial structure

Hardness

Brittleness

-

+




HEAT TREATMENT

For a given steel composition and heat treatment condition, there is a critical cooling rate for full hardening atwhich all the high temperature austenite is transformed into martensite without the formation of either pearliteor bainite.

Quenching

The quenching speed affects hardness and mechanical properties

With a normal speed oil, hardness decreases rapidly below the surface due to the formation of pearlite andbainite.With a high speed oil, the critical cooling rate is exceeded to a much greater depth below the surface, resultingin an improved hardness profile.

The steel begins to transform at the Ms temperature and is fully hardened at the Mf temperature.The Ms temperature decreases with increasing carbon content of the steels .

In practice however, when a steel component is quenched, the surface cools more rapidly than the centre.This means that the surface could cool at the critical cooling rate and hence be fully hardened, whereas thecentre cools more slowly and forms soft pearlitic or bainitic structures.




HEAT TREATMENT

Transformation in function cooling rate


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HEAT TREATMENT

Cooling curve (drasticity)

as short as possibleVapour phase

Boiling phase

Convection phase under M F point

QuenchingPower

Cooling speed °C/s

Typical value :Theta 1 : 620°CTheta 2 : 320°C

Vapour phase

Boiling phase

Convectionphase

Time s

The cooling characteristics can either be shown as a graph of temperature againts time or as agraph of temperature against cooling rate for both normal speed and high speed quenching oils.



HEAT TREATMENT

Cooling power and quenching power

Cooling power :It ’s ability to evacuate calories from hot metal. It ’s characterised by drasticity.

Quenching power

It ’s ability for a fluid to confer mechanical characteristics to a metal and to obtain homogenous microstructures with minimum distortion:

At same 1 , quenching oil with lower 2 will have higher quenching power with riskto obtain more significant distortions.

At same 2, quenching oil with higher 1 will have higher quenching power.

If boiling aera increases, hardness in the centre will be higher and the risk to havedistortions will be bigger.



HEAT TREATMENT

A wide range of quenching characteristics can be obtained through careful formulation and blending.High quality quenching oils are formulated from refined base stocks of high thermal stability.Selected wetting agents and accelerators are added to achieve specific quenching characteristics.Complex anti-oxidant packages may be include to maintain performance for long periods of continued use,particularly at elevated temperatures. Emulsifiers may be added to enable simple wash-off in water afterquenching.

Quenching oils

Quenching oils can be divided into several categories, depending on the operational requirements.These include quenching speed, operating temperature and ease of removal.

Cold quenching oils

Half-warm quenching oil

Hot quenching oils

Super hot quenching oils

Vacuum quenching fluid

Normal speed

Medium speed High speed



HEAT TREATMENT

Quenching speed is important because it influences the hardness and depth of hardening that can be obtained.Quenching oils can be divided into normal, medium and high speed grades

Quenching speed

Normal speed quenching oilshave relatively low rates of cooling and are used in applications where the hardenability of the material is highenough to enable the required mechanical properties to be obtained, even with slow cooling.

High alloyed materials and tool steel are typical examples of where a normal speed quenching oil would be used.

Medium speed quenching oilsprovide intermediate quenching characteristics and are used widely for medium to high hadenability applicationswhere dependable, consistent metallurgical properties are required.

High speed quenching oilsare used for applications such as low hardenability alloys, carburised and carbo-nitrited components, or largecross-sections of medium hardenability steels where very high rates of cooling are required to ensure maximummechanical properties.



HEAT TREATMENT

Temperature of operationCold quenching oilsare designed for general purpose use at temperature of up to 80°C for applications where distortion duringquenching is not a problem

Hot quenching oilsare designed for use at higher temperatures of up to 180°C for controlling distorsion during quenching, aprocess also know as marquenching.

Half warm quenching oilsare designed for use at medium temperatures between 60° and 120°C for martensitic quenching of mechanicalsteel parts with delicate geometry.

Super hot quenching oilsare designed for use at higher temperatures of up to 240°C for controlling distorsion during quenching,for scaled martensitic or bainitic thermic treatment of mechanical parts with complex geometry.

Vacuum quenching fluidis used for vacuum thermic and vacuum thermo-chemical treatments of steels



HEAT TREATMENT

THERMIC TO 10 Cold quenching oil, with a high flash point, used for heat treatment of good hardening capacity steel parts,with simple geometry (applications where distortion during quenching is not a problem)Application : Carbon steels, low alloyed steelsBolt, small mechanical parts, forged parts .

THERMIC TO 10 RSlightly accelerated cold quenching oil, with a high flash point used for heat treatment of alloyed andrelatively alloyed steel parts for engineering.

Application : Mid-hard carbon steels, Hard carbonic steels, Low alloyed steels, mid-alloyed steels,Stainless martensitic steelsTHERMIC TO 19 R

Accelerated cold quenching oil, with a high flash point used for thermic treatment of alloyed and relativelyalloyed steel parts with complex geometry.Application : Mid-hard carbon steels, Low alloyed steels, mid-alloyed steels

THERMIC TO 25 R

Very accelerated cold quenching oil, with a high flash point, used for heat treatment of steel parts for engineering.Application : Mid-hard carbonic steels, Low alloyed steels

THERMIC TO 18 LNeat mineral oil, used for cold quenching, accelerated, with a high flash point, allowing water washing of theparts after heat treatment.Application : Hard carbon steels, Low alloyed steels, Strongly alloyed steels

Cold quenching oils



HEAT TREATMENTHalf warm quenching oils

THERMIC TO 15Half-hot quenching oil, with a high flash point, used for martensitic quenching of mechanical steel partswith delicate geometry.Application : Hard steels, Mi-hard steels, Case-hardening steels

THERMIC TO 30 RExtremely drastic half-hot quenching oil. Only for steels with bad hardening capacityApplication : low alloyed steels, low hardening capacity steels, deeply cemented parts.

Hot quenching oils

THERMIC 100High flash point hot quenching oil, for scaled martensitic isotherm heat treatment and hot quenching.

THERMIC 150Identical to THERMIC 100 with highly reinforced oxidation resistance

THERMIC SPF 140Identical to THERMIC 100 with highly reinforced oxidation resistance and higher quenching power

THERMIC 200Identical to THERMIC 100 with highly reinforced oxidation resistance and different quenching power

Hot quenching oilsApplication : Carburizing Low and Medium alloyed steels, Carbonitriding Low alloyed steelsContinued hot quenching Hard carbon steels



HEAT TREATMENT

Super hot quenching oil

THERMIC SPH 250Super hot quenching oil for scaled martensitic or bainitic heat treatment of mechanical parts with complexgeometry.Application : same application than Hot quenching oilsSubstitute martensitic quenching into bath of nitrates, nitrite salts

Vacuum quenching oil

THERMIC SV6Vacuum quenching oil for scaled martensitic or bainitic heat treatment of mechanical parts with complexgeometry.Application : specific application (aeronautic, medical, automotive)Parts with problem of distortion



HEAT TREATMENT



HEAT TREATMENT

Factors modifying cooling curve

Composition of quenching oil

For a same quenching oil- Stirring of quenching oil- Temperature of fluid in use- Fluid oxidation- Fluid water content



HEAT TREATMENT



HEAT TREATMENT

StirringStirring has a very significant effect on quenching

speed.It reduces the duration and stability of the vapour phaseand increases the maximum cooling rate. Effectivestirring is essential to ensure that optimum propertiesare obtained, to maintain circulation of quenchantaround the parts, and to obtain uniform temperature inthe bath.



HEAT TREATMENT

Quenching oil temperature in useThe temperature of operation of a quenching

oil is important because it will have an influenceon the following factors :Quenching oil life timeThe quenching speedThe viscosity and hence the drag-outThe distortion of parts



HEAT TREATMENT

Oxidation

The formation of oxidised residues in abasic mineral oil decreases the stabilityof the vapour phase and increases themaximum cooling rate, thereby increasingthe risk of distortion and cracking.The use of specially formulated quenchingoils will reduce these problem types



HEAT TREATMENT

Water contentContamination of quenching oils with water

must be avoided at all costs. As little as 0.02%of water in quenching oil influences quenchingcharacteristics significantly and may cause softspots, distortion or cracking.

At concentration of 0.05% or more, foamingduring quenching is likely and this can giverise to fires and explosions.




HEAT TREATMENT

Quenchant selection

There are many factors to consider when selecting the most suitable quenchant for a particular application :

Material composition and component section sizeSpecification requirementsType of furnaceQuenching systemMethod of quenchingDistortion controlQuenchant removalQuenchant disposalEnvironmental requirements

It is important to understand : the mechanism of quenching

the factors that affect it

as these can have a significant influence on quenchantselection and the performance obtained from thequenching process.

Conclusion




HEAT TREATMENT

Cooling speed + -

meltedsalts

water +polymer

quenchant

very acceleratedcold

quenching oil

acceleratedcold

quenching oil

Coldquenching

oil

Half warmquenching

oil

hotquenching

oil water

super hotquenching

oil

E1394E MFGP

TO 25RTO 26R

TO 10TO 19 R

MT 22TO 10TO 18 L

1530 R

100SPF 140150200

SPH 250

* * Ours references are preceded by generic name THERMIC

Mineral base oil ½ SyntheticSynthetic

Cooling power in function composition




HEAT TREATMENT

MOTULTECH developed some polymer quenchant based

on PAG (Polyalkylene glycol) and PVP (Polyvinyl pyrrolidone).

The application of these polymer quenchant depends upon different factors :Type of furnace and quenching systemCharacteristic of steelSize, weight and geometry of partsPhysical properties required (hardness and thickness)

Advantages of MOTUL’S polymer quenchant : Environmental : polymer quenchant solutions are nonflammable,and no needs special protection as inert gas or fire extinguishing systems.

Cleaner, safer working environment : no smokes and fumes duringquenching or tempering.Improve cleanliness of area (no oily floors, cleaning by occasional washing with water).




HEAT TREATMENT

Technical advantages of MOTUL’S polymer quenchant :

Flexibility of quenching speed :We can change the rate of cooling by concentration, agitation, temperatureof bath separately or together.Reduction of stresses and distortion : a uniform polymer film reducesthermal gradient and stresses and distortion in fact.Tolerance with quenched parts : No presence of soft spot,

distortion and cracking associated with trace of water in mineral oil.

Production advantages with MOTUL’S polymer quenchant :

Reduction of costs : it depends type of polymer and concentration in use,but polymer in solution has lower viscosity than quenching oils and the

consumption by retention.Easiness cleaning :High temperature decomposition of componentswith formation vapor water and oxides of carbon.Low temperature residual film removed by simple washing in water.High cooling power : reduced time of quenchingOther advantages depend type of polymer and concentration in use.




HEAT TREATMENT

Typical applications for PAG

THERMIC E 1394 and THERMIC EM 20

Immersion quenching :for a wide range of steels (plain carbon steels, boron steels, spring steels,martensitic stainless steel, low and medium alloy carbunizing steels andhigher alloys steels of heavier section thickness.Immersion fore all parts (very small up to large shafts and forging, conventionalparts as bolts, bearing, crankshafts, steel bars, automotive parts…

Induction hardening and spray quenchingQuenching of gears, crankshafts, camshafts, drive shafts, tubes, bars… Heat treatment for aluminum alloysCastings and extrusion for aerospace industry, automotive industry(engine bloc, cylinder heads and wheels..




HEAT TREATMENT

Polyvinyl pyrrolidone :

THERMIC FGP

Characteristics :Quenching characteristics are a function of molecular weight of polymer, concentrationin use, bath temperature and agitation.

Effect of concentration : the maximum rate of cooling decreases with increasing

concentration. High concentration characteristics similar of standard quenching oilsEffect of temperature : the maximum rate of cooling decreases with increasingtemperature

Effect of agitation : the maximum rate of cooling increases with increasingconcentration



HEAT TREATMENT

Advantages MOTUL’S products :

high stability in use at different concentrationcompatible with hard, medium and soft watereconomical solutionlarge rate of dilutionexcellent anti-corrosion power

low consumption in uselow smokes and fumes during quenching

THERMIC E 1394 for Induction hardening and spray quenchingConcentration in use : 5 to 12 %

THERMIC EM 20 for immersion quenchingConcentration in use : 10 to 20 %

THERMIC FGP for immersion quenching Concentration in use : 15 to 30 %

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