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Welding InspectionHeat Treatments

Course Reference WIS 5

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Heat treatments

Heat treatments of steels are usually

intended for one of the following

purposes:-

•Remove stresses induced by cold working

•Refine the grain structure

•Decrease the hardness and increase ductility

•Increase hardness

•Improve machineability

•Improve mechanical properties as a whole

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Properties of steelMechanical properties :

Hardness a measure of the resistance to penetration!ensile strength a metal"s ability to withstand stress

in tension

#ompresive strength-a metal"s ability to withstand a

pressing or s$uee%ing together &hear strength - a metal"s ability to resist a sliding

past type of action

'atigue strength ability to take repeated loading

!oughness ability to resist shock

Ductility ability of a metal"s to stretches before it

breaks

(rittleness metal does not stretches before it

fractures

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Heat Treatment of SteelsHeat Treatment of Steels

)ll heat treatments are basically cycles of three elements

 Heating

 Holding *soaking+

 #ooling

 Post weld heat  treatments are used to change the properties of

the weld metal, controlling the formation of structures

 Pre heat  treatments are used basically to increase weldabilty,

control expansion and contraction forces during welding.

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Heat TreatmentsHeat Treatments

The heating rate

Temperature attained

The time at the attained temperature soa! time"

Cooling rate

!he relevant variables for heat treatment process,

which must be carefully controlled are as follows

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Heat Treatment of SteelsHeat Treatment of Steels

!he basic heat treatments are:

 )nnealing

 Hardening

 &tress relieving

 .ormalising

 !empering

 /re-heating

The method of applying the heat to the material may vary from

procedure to procedure. e.g flame, electrical resistance and

furnaces

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Heat Treatment of SteelsHeat Treatment of Steels

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Heat Treatment  #ormali$ing %in&ol&ed heating the material

  a'o&e the upper (riti(al

temperature and (ooling it

slo)ly in room temperature*

 +nnealing % Similar )ith #ormali$ing e,(ept

  that (ooling ta!es pla(e still more

  slo)ly in temperature (ontrolled

  o&en*

 

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Heat Treatment

 -uen(hing ./

 + (ontrolled (ooling pro(ess )hi(h (auses metals toharden*

 aterials must 'e heated at any ele&atedtemperature1'ut if hardness is important1the materialshould 'e heated a'o&e the upper (riti(al

temperature*

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