processing steel for hydropower plants 1
indroduction
high strength steelproductiondelivery condition
processing of DILLIMAX 690flame cuttingweldingformingPWHT
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Processing of Dillimax 690 QT
high strength and elevated hardenabilityrequires special care during processing
Acting careless increases the risk to create defects
consequences are expensive repair work or evenrejection of the welded structural part
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Plate-Design of a DILLIMAX 690E (S690QL1) in 100 mmTensile Requirements (transversal)
ReH: ≥ 670 MPa / Rm: 770 - 940 MPa / A5: ≥ 14 %
Toughness Requirements (transversal)
at -60 °C ≥ 27 J
Chemical Composition
For the product analysis, the following limiting values are applicable:
Carbon Equivalent: CE(iiw) – 0.78 CET – 0.44 Pcm – 0.35
Stahlsorte Dicke C Si Mn P S Mo Ni Cr B mm max. max. max. max. max. max. max. max. max. DILLIMAX 690B DILLIMAX 690T DILLIMAX 690E
alle 0,20 0,56 1,70 0,025 0,012 0,64 1,90 1,60 0,005
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carbon equivalent :carbon equivalent :CEV =CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15PCM =PCM = C + Si/30 + (Mn+Cu+Cr)/20 + Mo/15 + Ni/60 + 5*BC + Si/30 + (Mn+Cu+Cr)/20 + Mo/15 + Ni/60 + 5*BCET =CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40
DILLIMAX
Dicke [mm] ≤ 20 > 20 ≤ 50 > 50 ≤ 100 > 100 ≤ 150 ≤ 20 > 20 ≤ 50 > 50 ≤ 80 > 80 ≤ 110 > 110 ≤ 150
C 0,16 0,16 0,16 0,16 0,16 0,16 0,16 0,16 0,16Si 0,30 0,30 0,30 0,30 0,30 0,30 0,30 0,30 0,30Mn 1,20 1,45 1,45 1,45 1,35 1,45 1,45 1,45 1,45Mo 0,12 0,27 0,37 0,47 0,22 0,37 0,37 0,42 0,52Ni 0,27 0,75 0,12 0,30 0,75 1,35Cr 0,60 0,80 0,90 0,55 0,55 0,80 0,90 0,90B 0,0020 0,0020 0,0020 0,0020 0,0020 0,0020 0,0020 0,0020 0,0020CEV 0,38 0,58 0,65 0,73 0,54 0,59 0,66 0,72 0,78PCM 0,25 0,30 0,32 0,34 0,29 0,31 0,32 0,34 0,35CET 0,29 0,36 0,39 0,42 0,34 0,37 0,39 0,41 0,44
690 B 690 T 1), E
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thermal cutting
rapid heating and cooling at the flame cut edge
martensitic microstructure :
maximum hardness is only a function of carbon content
Hv = 800*C(%) + 300
DILLIMAX 690 steels with 0.16 %C 430 HV
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0 2 4 6 8 10 12200
250
300
350
400
450
500
Dillimax 690V - 150 mm plate thickness hardness at flame cut edge
hard
ness
HV5
Bild no.4 distance from flame cut edge [mm]
3mm subsurface mid thickness
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thermal cutting
comparison between flame cut HAZ and weld HAZ
0 50 100 150 200 250 300 350 400 450 500 5500,25
0,50
0,75
1,00
1,25
1,50
1,75
2,00
2,25
1075
1127
1023
1063
1141
1070
1085
934
HAZ-width at mid thickness [mm]
100 mm 100 mm 50 mm 25 mm
cutting speed [mm/min]
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thermal cutting
preheating is necessary to avoid crackingtemperature shall not fall below the recommended preheating temperature during the entire cutting process
heat from the lower subsurface andcontrol the temperature on the upper subsurface
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hot forming
hot formig (above tempering temperature) is not allowed for Q+T steel !
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test temperaturetest temperature
impact impact energyenergy
initialinitialafter after 5% 5% strainstrain
ΔΔTTstrastra
inin
straining straining + ageing+ ageing
ΔΔTTageingageing
cold forminginfluence of strain and ageing on TT shift
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welding in cold deformed zones
0 200 400 600 800 1000 1200 14000
50
100
150
200
250
5% strained +aged 250°C / 30 min
cooling time t8/5 20 sec
DILLIMAX 690influence of temperature field on strained specimen
without strain 5 % strained
impa
ct e
nerg
y @
-20°
C
peak temperature weld thermal simulation
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welding of high strength steeltemperature control is mandatorytoo high heat input : reduction of strength / toughness in the HAZ and weld metaltoo low preheat / interpass : risk of cold cracking
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Hydrogen induced cracking is a particular concern for welding high strength steel
influenced by
chemical composition (CET)
thermal cycle / heat input ( Tp / Q)
hydrogen input (HD)
internal and external stress
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low hydrogen input
re-drying and proper storage of consumables !piping system for flux transportation free of condensed moisturearea be welded free from moist, rust, paint, oil, grease
hydrogen specimen within glycerin-bath
left : non re-dried electrode (HD 10 ml)right : electrode re-dried at 350°C / 120 min (HD 4ml)
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preheating and temperature control for welding :sufficiently area shall be preheated to avoid quick loss of heat, for plate thickness > 100 mm following Tp shall be applied
GSMAW (HD 2-3ml) 120 °CSMAW (HD 5ml) 150 °CSAW * (HD 7-9 ml) 175 °C
*) higher deposition rate and the residual moisture in fluxwill lead to higher hydrogen content
hydrogen effusion soakingimmediately after welding, before the weld area has cooled below 100°Cat 250-300 °C for 3-6 hrs (increasing time and temperature with increasing weld thickness)
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post weld heat treatment
possible aiming for :
• hydrogen effusion (250-350°C / 3-6 hrs)• hardness reduction in the HAZ (550°C / 15 min)• restore toughness after cold forming (S/D, 4°C shift per % strain)• stress relieving (cooling speed)
if PWHT is applied, temperature has to be limited 50°C belowtempering temperature during plate production.
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hardness survey across the joint, HV5 (average 5 indents)
location subsurface ¼ e (root)
as welded / PWHT as welded / PWHT
base metal 266 / 253 257 / 257
fine grained HAZ 333 / 270 320 / 298
coarse grained HAZ 393 / 338 330 / 315
weld metal 281 / 268 277 / 270
coarse grained HAZ 408 / 341 342 / 319
fine grained HAZ 363 / 311 324 / 319
base metal 264 / 250 257 / 260
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toughness in the heat affected zone90 mm DILLIMAX 690 , SMAW 1.8 kJ/mm
-60 -50 -40 -30 -200
50
100
150
200
250
base metal weld metal fusion line fusion line+2mm
impact energy [joules]
temperature [°C]-60 -50 -40 -30 -20
0
50
100
150
200
250
base metal weld metal fusion line fusion line+2mm
impact energy [joules]
temperature [°C]
as welded PWHT 580°C / 30 min