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8.
Technical Heat Treatment
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8. Technical Heat Treatment 95
When welding a workpiece, not only the weld
itself, but also the surrounding base material
(HAZ) is influenced by the supplied heat
quantity. The temperature-field, which ap-
pears around the weld when different welding
procedures are used, is shown in Figure 8.1.
Figure 8.2 shows the influence of the material
properties on the welding process. The de-
termining factors on the process presented in
this Figure, like melting temperature and -
interval, heat capacity, heat extension etc,
depend greatly on the chemical composition
of the material. Metallurgical properties are
here characterized by e.g. homogeneity,
structure and texture, physical properties like
heat extension, shear strength, ductility.
Structural changes, caused by the heat input
(process 1, 2, 7, and 8), influence directly the mechanical properties of the weld. In addition,
the chemical composition of the weld metal and adjacent base material are also influenced
by the processes 3 to 6.
Based on the binary system,
the formation of the different
structure zones is shown in
Figure 8.3. So the coarse
grain zone occurs in areas
of intensely elevated
austenitising temperature for
example. At the same time,
hardness peaks appear in
these areas because of
greatly reduced criticalcooling rate and the coarse
Temperature Distribution ofVarious Welding Methods
6
4
2
0
-2
-4
-6
-14 -12 -10 -8 -6 -4 -2 0 2 cm 6
cm cm6
4
2
0
-2
-4
-6
-8 -6 -4 -2 0 2cm
-60 -40 40 mmmm 60
250
500
750
C1750
oxy-acethylenewelding
manualmetalarcwelding
tempera
ture
723C
distancefromweldcentralline
heataffectedzoneduringoxy-acethylenewelding
heataffectedzoneduringmanualmetalarcwelding
300C
400C500C
600C 700C800C
900C300C
400C
500C 600C
700C
1250
1000
20-20 0
ISF2002br-er04-01.cdr
Figure 8.1
ClassificationofWeldingProcessInto
IndividualMechanisms
47
5
8 9 10
2
1
36
Heatingandmeltingtheweldingconsumable
1
Meltingpartsofbasematerial2
Reaction of passing weldingconsumablewitharcatmosphere
Reactionofpassedweldingconsumablewithmoltenbasematerial
Interactionbetweenweldpoolandsolidbasematerial(possiblyweldpasses)
3
4
5
Reactionofmetalandfluxwithatmosphere
6
Solidificationofweldpoolandslag7
Coolingofweldedjointinsolidcondition
8
Post-weldheattreatmentifnecessary
Sustainablealterationofmaterialproperties
Specificheat,meltingtemperatureandinterval,meltheat,boilingtemperature(metal,coating)
Specific heat, melt temperature and interval, heatconductivity,heatexpansioncoefficient,homogeneity,time
Compositionof atmosphere, affinity, pressure,temperature,dissotiation,ionisation,reactionspeed
Solubilityrelations,temperatureandpressureunderinf luence of heat source, specif ic weight,
weldpoolflux
Diffusionandpositionchangeprocesses,time,boundaryformation,ordered-unorderedstructure
Affinity,temperature,pressure,time
Meltheat,coolingconditions,densityandporosityofslag,solidificationinterval
Phasediagrams(timedependent),heatconductivity,heatcoefficient,shearstrength,ductility
Phasediagrams(timedependent), texturebywarmdeformation,ductility,moduleofelasticity
Phasediagrams,operatingtemperature,mechanicalandchemicalstrain,time
9
10
ISF2002br-eI-04-02.cdr
Figure 8.2
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8. Technical Heat Treatment 96
austenite grains. This zone of the weld is the area, where the worst toughness values are
found.
In Figure 8.4 you can see how much the forma-
tion of the individual structure zones and the
zones of unfavourable mechanical properties
can be influenced.
Applying an electroslag one pass weld of a 200
mm thick plate, a HAZ of approximately 30 mm
width is achieved. Using a three pass tech-
nique, the HAZ is reduced to only 8 mm.
With the use of different procedures, the differ-
ences in the formation of heat affected zones
become even clearer as shown in Figure 8.5.
These effects can actively be used to the ad-
vantage of the material, for example to adjust
calculated mechanical properties to one's
choice or to remove negative effects of a weld-
ing. Particularly with high-strength fine grained steels and high-alloyed materials, which are
specifically optimised to achieve special quality, e.g. corrosion resistance against a certain
attacking medium, this
post-weld heat treatment is
of great importance.
Figure 8.6 shows areas in
the Fe-C diagram of differ-
ent heat treatment meth-
ods. It is clearly visible that
the carbon content (and
also the content of other
alloying elements) has a
distinct influence on thelevel of annealing tempera-
Microstructure Zones of a Weld -Relation to Binary System
heataffectedzone(visibleinmacrosection)
4
1 2 3 4 5 6
5
6
3
2
1
100
1500
1300
C
1200
1000
G
800
P
600
400
300
S
723
1147
1 2 3%
carboncontent
Tempera
ture
Hardness
age
ing
blue
bri
ttleness
weldbead
incompletemelt
coarsegrain
standardtransformation
incompletecrystallisation
recrystallisation
hardnesspeak
hardnesssink
0,8
2,0
6
0,2
ISF2002br-er04-03.cdr
Figure 8.3
Figure 8.4
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8. Technical Heat Treatment 97
tures like e.g. coarse-grain heat treatment or normalising.
It can also be seen that the start of martensite formation (MS-line) is shifted to continuously
decreasing temperatures with increasing C-content. This is important e.g. for hardening
processes (to be explained later).
As this diagram does not
cover the time influence,
only constant stop-tempera-
tures can be read, predic-
tions about heating-up and
cooling-down rates are not
possible. Thus the individual
heat treatment methods will
be explained by their tem-
perature-time-behaviour in
the following.
Development of Heat Affected Zone ofEB, Sub-Arc, and MIG-MAG Welding
gasmetalarcwelding
electronbeamwelding100
submergedarcweldingpass/cappedpass4
0
12
ISF2002br-er04-05.cdr
Figure 8.5
Metallurgical Survey ofHeat Treatment Methods
1600
C1536
metastablesystemiron-carbon(partially)
1392
1300
1200
1100
1000
911
800
700
600
500
400
300
200
100
20
C
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
20
1600
0 0,5 0,8 1 1,5 2
Carboncontentinweight%
302520151050
Fe
A
H B
1493C
d -solidsolution+austenite
d -solidsolution
cbcatomiclattice
melt
melt+austenite
diffusionheattreatment
coarsegrainheattreatment
E2,06
cfc
atomiclattice
A4heatcolors
yellowwhite
lightyellow
yellow
yellowred
lightred
cherry-red
darkred
brownred
darkbrown
1147
A3austenite
( -Mischkristalle)g
Acm
austenite+secondarycementite(Fe C)3
KS
austenite+ferriteA2 M
A1 P 723CO
recrystallisationheattreatment
recrystallisationheattreatmentQ
ferrite
( -solidsolution)a
softannealing
stressrelieving
cbcatomiclattice
hardening
tempering
MS
eutektoidic
steel
Cementitecontentinweight%ISF2002br-er04-06.cdr
melt+
-solidsolutiond
N
normalising+
hardening
G
769C
hypoeutectoidicsteel hypereutectoidicsteel
Figure 8.6
CoarseGrainHeat Treatment
Tempera
ture
Time
900
700
500
300
C austenite
A3
A1
austenite+ferrite
ferrite+perliteT
empera
ture
C-Content
longtimeseveralhours
intenseheating
0,4 0,8 %
ISF2002br-eI-04-07.cdr
Figure 8.7
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8. Technical Heat Treatment 98
Figure 8.7 shows in the detail to the right a T-t course of coarse grain heat treatment of an
alloy containing 0,4 % C. A coarse grain heat treatment is applied to create a grain size as
large as possible to improve machining properties. In the case of welding, a coarse grain is
unwelcome, although unavoidable as a consequence of the welding cycle. You can learn
from Figure 8.7 that there are two methods of coarse grain heat treatment. The first way is to
austenite at a temperature close above A3 for a couple of hours followed by a slow cooling
process. The second method is very important to the welding process. Here a coarse grain is
formed at a temperature far above A3 with relatively short periods.
Figure 8.8 shows schemati-
cally time-temperature be-
haviour in a TTT-diagram.
(Note: the curves explain
running structure mecha-
nisms, they must not be
used as reading off exam-
ples. To determine t8/5,
hardness values, or micro-
structure distribution, are
TTT-diagrams always read
continuously or isothermally.
Mixed types like curves 3 to
6 are not allowed for this purpose!).
The most important heat treatment methods can be divided into sections of annealing, hard-
ening and tempering, and these single processes can be used individually or combined. The
normalising process is shown in Figure 8.9. It is used to achieve a homogeneous ferrite-
perlite structure. For this purpose, the steel is heat treated approximately 30C above Ac3
until homogeneous austenite evolves. This condition is the starting point for the following
hardening and/or quenching and tempering treatment. In the case of hypereutectoid steels,
austenisation takes place above the A1 temperature. Heating-up should be fast to keep the
austenite grain as fine as possible (see TTA-diagram, chapter 2). Then air cooling follows,
leading normally to a transformation in the ferrite condition (see Figure 8.8, line 1; formationof ferrite and perlite, normalised micro-structure).
1:Normalizing2:Simplehardening3:Brokenhardening4:Hotdiphardening5:Bainiticannealing6:Patenting(isothermal
annealing)
0,1
900
0
100
200
300
400
500
600
700
Caustenite
ferr
ite
lin
e
Tempera
ture
MS
2 3 4 6 5 1
1 10 10 10s
A3
A1
ferr
ite
perl
ite
ba
inite
martens
ite
Time
TTT-DiagramWithHeat TreatmentProcesses
ISF2002br-eI-04-08.cdr
Figure 8.8
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8. Technical Heat Treatment 99
To harden a material, aus-
tenisation and homogeni-
sation is carried out also at
30C above AC3. Also in
this case one must watch
that the austenite grains
remain as small as possi-
ble. To ensure a complete
transformation to marten-
site, a subsequent quench-
ing follows until the
temperature is far below
the Ms-temperature, Figure
8.10. The cooling rate dur-
ing quenching must be high enough to cool down from the austenite zone directly into the
martensite zone without any further phase transitions (curve 2 in Figure 8.8). Such quenching
processes build-up very high thermal stresses which may destroy the workpiece during hard-
ening. Thus there are variations of this process, where perlite formation is suppressed, but
due to a smaller temperature gradient thermal stresses remain on an uncritical level (curves
3 and 4 in Figure 8.8). This
can be achieved in practice
for example- through stop-
ping a water quenching
process at a certain tem-
perature and continuing the
cooling with a milder cooling
medium (oil). With longer
holding on at elevated tem-
perature level, transforma-
tions can also be carried
through in the bainite area
(curves 5 and 6).
Normalizing
Tempera
ture
Time
900
700
500
300
C austenite
A3
A1
austenite+ferrite
ferrite+perliteT
empera
ture
C-Content
0,4 0,8 %
transformationandhomogenizing
of -solidsolution(30-60min)
at30Cabove A
g
3
quickheating
aircooling
ISF2002br-eI-04-09.cdr
Figure 8.9
Hardening
Tempera
ture
Time
900
700
500
300
C austenite
A3
A1
austenite+ferrite
ferrite+perliteT
empe
rature
C-Content
0,4 0,8 %
startofmartensiteformation
quenchinginwater
about30Cabove A3
startofmartensiteformation
ISF2002br-eI-04-10.cdr
Figure 8.10
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8. Technical Heat Treatment 100
Figure 8.11 shows the quenching and tempering procedure. A hardening is followed by an-
other heat treatment below Ac1. During this tempering process, a break down of martensite
takes place. Ferrite and cementite are formed. As this change causes a very fine micro-
structure, this heat treat-
ment leads to very good
mechanical properties like
e.g. strength and tough-
ness.
Figure 8.12 shows the pro-
cedure of soft-annealing.
Here we aim to adjust a
soft and suitable micro-
structure for machining.
Such a structure is charac-
terised by mostly globular
formed cementite particles, while the lamellar structure of the perlite is resolved (in Figure
8.12 marked by the circles, to the left: before, to the right: after soft-annealing). For hypoeu-
tectic steels, this spheroidizing of cementite is achieved by a heat treatment close below A1.
With these steels, a part of the cementite bonded carbon dissolves during heat treating close
below A1, the remaining cementite lamellas transform with time into balls, and the bigger
ones grow at the expense of
the smaller ones (a transfor-
mation is carried out because
the surface area is strongly
reduced thermodynami-
cally more favourable condi-
tion). Hypereutectic steels
have in addition to the lamel-
lar structure of the perlite a
cementite network on the
grain boundaries.
Hardeningand Tempering
Tempera
ture
Time
900
700
500
300
C austenite
A3
A1
austenite+ferrite
ferrite+perliteT
empera
ture
C-Content
0,4 0,8 %
quenching
about30Cabove A3
hardeningandtempering
slowcooling
ISF2002br-eI-04-11.cdr
Figure 8.11
Soft Annealing
Tempera
ture
Time
900
700
500
300
C austenite
A3
A1
austenite+ferrite
ferrite+perliteT
empera
ture
C-Content
0,4 0,8 %
timedependentonworkpiece
10to20Cbelow A1
oscillationannealing+/-20degreesaround A1
or
cementite
ISF2002br-eI-04-12.cdr
Figure 8.12
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8. Technical Heat Treatment 101
Spheroidizing of cementite is achieved by making use of the transformation processes during
oscillating around A1. When exceeding A1 a transformation of ferrite to austenite takes place
with a simultaneous solution of a certain amount of carbon according to the binary system Fe
C. When the temperature drops below A1 again and is kept about 20C below until the trans-
formation is completed, a
re-precipitation of cemen-
tite on existing nuclei takes
place. The repetition of this
process leads to a step-
wise spheroidizing of ce-
mentite and the frequent
transformation avoids a
grain coarsening. A soft-
annealed microstructure
represents frequently the
delivery condition of a ma-
terial.
Figure 8.13 shows the principle of a stress-relieve heat treatment. This heat treatment is
used to eliminate dislocations which were caused by welding, deforming, transformation etc.
to improve the toughness of a workpiece. Stress-relieving works only if present dislocations
are able to move, i.e. plastic structure deformations must be executable in the micro-range. A
temperature increase is the
commonly used method to
make such deformations
possible because the yield
strength limit decreases with
increasing temperature. A
stress-relieve heat treatment
should not cause any other
change to properties, so that
tempering steels are heat
treated below temperingtemperature.
StressRelieving
Tempera
ture
Time
900
700
500
300
C austenite
A3
A1
austenite+ferrite
Tempera
ture
C-Content0,4 0,8 %
timedependentonworkpiece
between450and
650C
ferrite+perlite
ISF2002br-eI-04-13.cdr
Figure 8.13
Stress releaving
Heat treatment at a temperature below the lower transition point A 1, mostly
between 600 and 650C, with subsequent slow cooling for relief of internal
stresses; there is no substantial change of present properties.
Normalising
Heating to a temperature slightly above the upper transition point A3
(hypereutectoidic steels above the lower transition point A 1), followed by
cooling in tranquil atmosphere.
Hardening (quench
hardening)
Aco olin g fro m a tem pera ture abo ve the tra nsi tio n poi nt A3 or A1 with such a
speed that an clear increase of hardness oc curs at the surface or ac ross
the complete cross-section, normally due to martensite development.
Quenching and
tempering
Heat treatment to achieve a high ductility with defined tensile stress by
hardening and subsequent tempering (mostly at a higher temperature.
Solution or
quenching heat
treatment
Fast cooling of a workpiece. Also fast cooling of austenitic steels from high
temperature (mostly above 1000C) to develop an almost homogenuous
micro-structure with high ductility is called 'quenching heat treatment'.
Tempering
Heating after previous hardening, cold working or welding to a temperature
between room temperature and the lower transformation point A1; stopping
at this temperature and subsequent purposeful cooling.
TypeandPurposeofHeat Treatment
ISF2002br-eI-04-14.cdr
Figure 8.14
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8. Technical Heat Treatment 102
Figure 8.14 shows a survey of heat treatments which are important to welding as well as their
purposes.
Figure 8.15 shows princi-
pally the heat treatments in
connection with welding.
Heat treatment processes
are divided into: before,
during, and after welding.
Normally a stress-relieving
or normalizing heat treat-
ment is applied before
welding to adjust a proper
material condition which for
welding. After welding, al-
most any possible heat
treatment can be carried
out. This is only limited by workpiece dimen-
sions/shapes or arising costs. The most impor-
tant section of the diagram is the kind of heat
treatment which accom-panies the welding.
The most important processes are explained in
the following.
Figure 8.16 represents the influence of differ-
ent accompanying heat treatments during
welding, given within a TTT-diagram. The fast-
est cooling is achieved with welding without
preheating, with addition of a small share of
bainite, mainly martensite is formed (curve 1,
analogous to Figure 8.8, hardening). A simple
heating before welding without additional stop-
ping time lowers the cooling rate according to
curve 2. The proportion of martensite is re-duced in the forming structure, as well as the
Heat TreatmentinConnectionWithWelding
combinationpreheating
simplepreheating
increaseofworking
temperature
constantworking
temperature
local
preheating
preheatingofthe
completeworkpiece
isothermal
welding
postheating(postweldheat
treatment)
heattreatmentofthecomplete
workpiece
localheattreatment
annealing stressreleaving
stressreleaving
annealing hardening quenchingand
tempering
solutionheat
treatment
tempering
simplestep-hardening
welding
purestephardening
welding
modifiedstephardening
welding
Typesofheattreatmentsrelatedtowelding
heattreatment
beforewelding
combi-nation
accompanyingheattreatment
combi-nation
heattreatmentafterwelding
(post-weldheattreatment)
ISF2002br-eI-04-15.cdr
Figure 8.15
TTT-Diagram forDifferent Welding Conditions
800
700
600
500
400
300
200
100
0
0 1 10 102
103
104
105
s
C
Tempera
ture
T
Timet
MS
TA
(1) (2) (3)
tH
(1):Weldingwithoutpreheating,(2):Weldingwithpreheatingupto380C,withoutstoppagetime(3):Weldingwithpreheatingupto380Candabout10min.stoppagetime
T :Stoppagetemperature,t :DwelltimeA H
ISF2002br-er04-16.cdr
Figure 8.16
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8. Technical Heat Treatment 103
level of hardening. If the material is hold at a temperature above MS during welding (curve 3),
then the martensite formation will be completely suppressed (see Figure 8.8, curve 4 and 5).
To explain the temperature-time-behaviours
used in the following, Figure 8.17 shows a su-
perposition of all individual influences on the
materials as well as the resulting T-T-course in
the HAZ. As an example, welding with simple
preheating is selected.
The plate is preheated in a period tV. After re-
moval of the heat source, the cooling of the
workpiece starts. When tS is reached, welding
starts, and its temperature peak overlays the
cooling curve of the base material. When the
welding is completed, cooling period tA starts.
The full line represents the resulting tempera-
ture-time-behaviour of the HAZ.
The temperature time course during welding
with simple preheating is shown in Figure 8.18.
During a welding time tS a
drop of the working tem-
perature TA occurs. A fur-
ther air cooling is usually
carried out, however, thecooling rate can also be
reduced by covering with
heat insulating materials.
Another variant of welding
with preheating is welding
at constant workingtemperature. This is
Temperature-Time-DistributionDuring Welding With Preheating
tV tS tA
start endseam
transformationrange
Timet
TemperatureT
TS
A3
A1
TV
T :Preheattemperature,
T :Meltingtemperatureofmaterial,
t :Preheattime,
t :Weldingtime,
t :Coolingtime(roomtemperature),M :Martensitestarttemperature
A :Uppertransformationtemperature,
A :Lower
V
S
V
S
A
S
3
1 transformationtemperature
Courseofresultingtemperatureintheareaoftheheataffectedzoneofthebasematerial.
Temperaturedistributionbypreheating,Courseoftemperatureduringwelding.
ISF2002br-er04-17.cdr
Figure 8.17
WeldingWithSimplePreheating
A3
A1
Tempera
ture
T
Timet
tV tS tA
TA
TV
T :Preheattemperature,
T :Workingtemperature,
t :Preheattime,
t :Weldingtime,
t :Coolingtime(roomtemperature)
V
A
V
S
A
Temperatureofworkpiece,Temperatureofweldpoint
ISF2002br-eI-04-18.cdr
Figure 8.18
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8. Technical Heat Treatment 104
achieved through further
warming during welding to
avoid a drop of the working
temperature. In Figure 8.19
is this case (dashed line,
TA needs not to be above
MS) as well as the special
case of isothermal welding
illustrated. During isother-
mal welding, the workpiece
is heated up to a working
temperature above MS
(start of martensite forma-
tion) and is also held there
after welding until a transformation of the austenitised areas has been completed. The aim of
isothermal welding is to cool down in accordance with curve 3 in Figure 8.16 and in this way,
to suppress martensite formation.
Figure 8.20 shows the T-T course during
welding with post-warming (subsequent heat
treatment, see Figure 8.15). Such a treatment
can be carried out very easy, a gas welding
torch is normally used for a local preheating.
In this way, the toughness properties of some
steels can be greatly improved. The lower
sketch shows a combination of pre- and post-
heat treatment. Such a treatment is applied to
steels which have such a strong tendency to
hardening that a cracking in spite of a simple
preheating before welding cannot be avoided,
if they cool down directly from working tem-
perature. Such materials are heat treated
immediately after welding at a temperaturebetween 600 and 700C, so that a formation
WeldingWithPreheatingand
StoppageatWorking Temperature
Tem
pera
ture
T
Timet
tS
tV tH tA
A3
A1
MS
TV
TA
:t =0H T :Preheattemperature,T :Workingtemperature,
t :Preheattime,
V
A
V
t :Weldingtime,t :Coolingtime(roomtemperature),
t :Dwelltime
S
A
H
ISF2002br-eI-04-19.cdr
Figure 8.19
Welding WithPre- and Post-Heating
TemperatureT
Timet
TN
tS
tN tA
A3
A1
A3
A1
TemperatureT
TN
TV TA
Timet
tV tS tNtR tA
2.Pre-andpost-heating
1.Post-heating
T :Preheattemperature,
T :Workingtemperature,
T :Postheattemperature,
t :Preheatingtime,
V
A
N
V
t :Weldingtime,
t :Coolingtime(roomtemperature),
t :Postheattime
t :Stoppagetime
S
A
N
R
ISF2002br-er04-20.cdr
Figure 8.20
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8. Technical Heat Treatment 105
of martensite is avoided and welding residual stresses are eliminated simultaneously.
Aims of the modified step-
hardening welding should
not be discussed here, Fig-
ure 8.21. Such treatments
are used for transformation-
inert materials. The aim of
the figure is to show how
complicated a heat treatment
can become for a material in
combination with welding.
Figure 8.22 shows tempera-
ture distribution during multi-
pass welding. The solid line
represents the T-T course of a point in the HAZ
in the first pass. The root pass was welded
without preheating. Subsequent passes were
welded without cooling down to a certain tem-
perature. As a result, working temperature in-
creases with the number of passes. The
second pass is welded under a preheat tem-
perature which is already above martensite
start temperature. The heat which remains in
the workpiece preheats the upper layers of the
weld, the root pass is post-heat treated through
the same effect. During welding of the last
pass, the preheat temperature has reached
such a high level that the critical cooling rate
will not be surpassed. A favourable effect of
multi-pass welding is the warming of the HAZ
of each previous pass above recrystallisationtemperature with the corresponding crystallisa-
ModifiedStepWeldHardening
A3
A1
MS
TA
THa
TSt
TAnl
TAnl
tAtAnltAb
tHa
tS
tHtAtH
Timet
TemperatureT
T :Workingtemperature,
T : Temperingtemperature,T :Hardeningtemperature,
A
Anl
H
T :Steptemperature,
t :Coolingtime,t :Quenchingtime,
St
A
Ab
t : Temperingtime,
t :Dwelltime,t :Weldingtime
Anl
H
S
Temperatureofworkpiece,
Temperatureofweldpoint
ISF2002br-eI-04-21.cdr
Figure 8.21
Temperature-Time DistributionDuring Multi-Pass Welding
T :Preheattemperature,
T :Meltingtemperatureofmaterial,t :Preheattime,
t :Weldingtime
t :Coolingtime(roomtemperature),
A :Uppertransformationtemperature,
M :Martensitestarttemperature
V
S
V
S
A
3
S
heataffected zone
1
432 } weldpassobservedpoint
1 2 3 4 weldpass
Tempera
ture
TA3
MS
TS
TV
Timet
tStV tA
ISF2004br-er04-22.cdr
Figure 8.22
7/30/2019 Chapter 8 - Technical Heat Treatment
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8. Technical Heat Treatment 106
tion effects in the HAZ. The coarse grain zone with its unfavourable mechanical properties is
only present in the HAZ of the last layer. To achieve optimum mechanical values, welding is
not carried out to Figure 8.22. As a rule, the same welding conditions should be applied for all
passes and prescribed t8/5 times must be kept, welding of the next pass will not be carried
out before the previous pass has cooled down to a certain temperature (keeping the inter-
pass temperature). In addition, the workpiece will not heat up to excessively high tempera-
tures.
Figure 8.23 shows a nomogram where working temperature and minimum and maximum
heat input for some steels can be interpreted, depending on carbon equivalent and wall thick-
ness.
If e.g. the water quenched and tempered fine grain structural steel S690QL of 40 mm wall
thickness is welded, the following data can be found:
- minimum heat input between 5.5 and 6 kJ/cm
- maximum heat input about 22 kJ/cm
- preheating to about 160C
- after welding, residual stress relieving between 530 and 600C.
Steels which are placed in
the hatched area called
soaking area, must be
treated with a hydrogen
relieve annealing. Above
this area, a stress relieve
annealing must be carried
out. Below this area, a
post-weld heat treatment is
not required.
Figure 8.23