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> What is heat treatment process ?

> What are it effects?

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> Why ? Toughness

Hardness

Ductility

Machineability

Refine Grain Structure

Residual Stresses

Wear Resistance

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Aircraft Industry

Automobile Manufacturing

Defense Sector Forging

Foundry

Heavy MachineryManufacturing

Powder Metal Industries

> Application

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Commonly Heat Treated Metals

> Ferrous Metals Steel Cast Iron Alloys Stainless Steel Tool Steel> Non-ferrous Metals Aluminum Copper

Brass Titanium

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Types of heat treatment processes

Austempering Martempering Ausforming

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Time-Temperature-Transformation(TTT)Curve

TTT diagram is a plot of temperatureversus the logarithmof time for a steel alloy of definite composition.

It is used to determine when transformations begin andend for an isothermal heat treatment of a previouslyaustenitizedalloy

TTT diagram indicates when a specific transformation starts and

ends and it also shows what percentage of transformation of

austeniteat a particular temperature is achieved.

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Time-Temperature-Transformation (TTT)Curve

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Continuous-cooling-tranformation(CCT)Curve

CCT diagram depends on composition of steel, nature ofcooling, austenite grain size, extent of austenitehomogenising, as well as austenitising temperature and time.

continuous cooling occurs through a series of isothermalsteps and the time spent at each of these steps depends onthe rate of cooling. The difference between successiveisothermal steps can be considered to approach zero.

The transformation at a temperature is not independent tocooling above it.

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CCT diagram depends on composition of steel, nature ofcooling, austenite grain size, extent of austenitehomogenising, as well as austenitising temperature andtime.

continuous cooling occurs through a series of isothermalsteps and the time spent at each of these steps depends onthe rate of cooling. The difference between successiveisothermal steps can be considered to approach zero.

The transformation at a temperature is not independent tocooling above it.

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Continuous-Cooling-Transformation(CCT)Curve

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Critical-Cooling-Rate-(CCR)Curve

When cooling curve is tangent to the nose of TTT- curve, it is

called as critical cooling rate. It can be defined as in twoways:1) Slowest cooling rate at which unstable austenite can beconverted into martensite. OR

2) fastest cooling rate at which unstable austenite can beconverted into pearlite. CCR is a dividing line between martensite and pearlite

transformation.

Factors affecting on CCR:1) carbon content2) Austenitic temperature

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Critical-Cooling-Rate-(CCR)Curve

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>Ausforming It is a hardeningprocess that produces very high strength

steel. This process converts metastable austensite to martensite

by quenching, and increase in strength upto 50% without anyloss in ductility. due to this fine structure will also changes.

Strengthening is directly proportional to deformation.1) Process:

Steel is heated to austenitic region.Temperature ismaintained so that uniform structure from surfece tocore.coolingis done between the temperature Ms Andnose.At this temperature- forging/rollingthen cooled at

room teperature.2) Properties:Gives better combination of tensile strength of 3000 N/m^2.

3)Application:Aircraft and automotive craft.

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> Ausforming

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> Austempering

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Austempering is an isothermal heat treatment that, when

applied to ferrous materials, produces a structure that is

stronger and tougher than comparable structures producedwith conventional heat treatments.

Conventional heat treaters heat the parts to "red heat" in acontrolled atmosphere and then quench them in a bath of oil

or water that is near room temperature. (Maybe even as highas a few hundred degrees Fahrenheit).

This produces a crystalline structure known as Martensite, a

hard, brittle phase. The parts are then tempered in anotherfurnace at 350F (177C) to 1100F (593C) to decrease the"brittleness.

During the process of quenching to Martensite, theMartensite reaction begins immediately.

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> Martempering

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Quenching from the austenitizing temperature into a hotfluid medium (hot oil, molten salt, molten metal, or afluidized particle bed) at a temperature usually above themartensite range (Ms point)

Holding in the quenching medium until the temperaturethroughout the steel is substantially uniform

Cooling (usually in air) at a moderate rate to prevent large

differences in temperature between the outside and thecenter of the section

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