4 Welding Metallurgy-3

7/25/2019 4 Welding Metallurgy-3

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WeldingWeldingMetallurgyMetallurgyNur Syahroni, ST., MT.

Welding Technology & Inspection (MO-091333)O

CEAN

ENGINE

ERING-

ITS


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PhasePhase

transor!ationtransor!ation

Welding Technology & Inspection (MO-091333) 2


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PhasePhase

transor!ationtransor!ationTime-Temperature Transformation

(TTT) Diagram

Pearlite

Bainite Spheroidite

Martensite

Continuous Cooling

Transformation Diagram (CCT)Mechanical Properties of Carbon

Steels



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PearlitePearlite



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Time-TemperatureTime-Temperature

Transformation (TTT) DiagramTransformation (TTT) Diagram

Consider eutectoidrea"tion#

Te!$erature $lays an i!$ortant role in therate o the austenite-to-$earlitetransor!ation

Plot $er"entage o transor!ation %s.logarith!i" o ti!e and temperature is

maintained constant

Welding Technology & Inspection (MO-091333) 5Pearlite


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Also &no'n asIsother!al

Transor!ation(iagra!

The diagra! assho'n )eside is%alid only or"ar)on steel 'ith

*.+'t C



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Welding Technology & Inspection (MO-091333) Pearlite

c!"#on steel $ith 0%6$t '


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Coarse pearlite (a)#

igh te!$erature /0ust)elo' eute"toidte!$erature

(i1usion rate o "ar)onato!s is high

Fine pearlite (b)

2o'er te!$erature

(i1usion rate o "ar)on

ato!s is lo'er igher strength 3

harder than "oarse$earlite

Welding Technology & Inspection (MO-091333) Pearlite


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(i1erent"o!$osition osteels ha%e

di1erent sha$eo TTT-diagra!

4or steel 'iththe"o!$osition#1,13%wt CtheTTT diagra! assho'n )eside A: Austenite

C: Pro-eutectoid Cementite

P: Pearlite


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BainiteBainite



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The !i"rostru"tureo bainite"onsistso ferriteandcementite$hases

(i1usional$ro"esses arein%ol%ed

5ainite )egin toor! at 67*oC/$oint N8 u$ to9:6oC.

Welding Technology & Inspection (MO-091333) 11Bainite



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5ainite or!s asneedles or$lates,de$ending on

the te!$eratureo thetransor!ation

Welding Technology & Inspection (MO-091333) 12Bainite


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SpheroiditeSpheroidite



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I a steel alloy ha%ing either$earliti" or )ainiti"!i"rostru"tures is heatedto, and let at, ate!$erature )elo' theeute"toid - or e;a!$le, at

a)out +**oC or asu


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MartensiteMartensite



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Transformation (TTT) DiagramTransformation (TTT) Diagram Martensiteis or!ed 'hen

austeniti?ed iron@"ar)on alloys arera$idly "ooled /or uen"hed8 to arelati%ely lo' te!$erature /in the%i"inity o the a!)ient8

Martensite is a non-euili)riu!single-$hase stru"ture that results

ro! a di1usionless transor!ationo austenite

Martensiti" transor!ation o""urs'hen the uen"hing rate is ra$idenough to $re%ent "ar)on di1usion

The hori?ontal and linear "hara"tero these lines indi"ates that the

!artensiti" transor!ation isinde$endent o ti!e

Welding Technology & Inspection (MO-091333) 16Martensite



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The 4CC austenitee;$erien"es a$oly!or$hi"transor!ation to a )ody-"entered tetragonal /5CT8!artensite

Martensite grains ta&e ona $late-li&e or needle-li&ea$$earan"e

The 'hite $hase in the!i"rogra$h is austenite

/retained austenite8 thatdid not transor! duringthe ra$id uen"h



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The $resen"e o alloyingele!ents other than"ar)on /e.g., Cr, Ni, Mo,and W8 !ay "ausesigniB"ant "hanges in

the $ositions andsha$es o the "ur%es inthe isother!al#

shiting to longer ti!es thenose o the austenite-to-$earlite transor!ation

the or!ation o a se$arate)ainite nose


+lloy steel +I,I 4340


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E;a!$le $ro)le!E;a!$le $ro)le!

sing the isother!al transor!ation diagra! or aniron@"ar)on alloy o eute"toid "o!$osition s$e"iy thenature o the Bnal !i"rostru"ture /in ter!s o!i"ro"onstituents $resent and a$$ro;i!ate$er"entages8 o a s!all s$e"i!en that has )een

su)0e"ted to the ollo'ing ti!e@te!$eraturetreat!ents. In ea"h "ase assu!e that the s$e"i!en)egins at +*oC and that it has )een held at thiste!$erature long enough to ha%e a"hie%ed a"o!$lete and ho!ogeneous austeniti" stru"ture

D Ra$idly "ool to >6*oC, hold or :*7s, and uen"h to roo!

te!$erature

D Ra$idly "ool to 96*oC, hold or :** s, and uen"h to roo!te!$erature

D Ra$idly "ool to 6*oC, hold or 9* s, ra$id "ool to 7**oC, holdor :*>s, and uen"h to roo! te!$erature



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SolutionSolution

a. :** )ainiteand no urthertransor!ationis $ossi)le

). :**!artensite

". 6* $earliteand 6* )ainite


4 Welding Metallurgy-3

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