welding forming PWHT - · PDF fileif PWHT is applied, temperature has to be limited 50°C below tempering temperature during plate production. processing steel for hydropower plants

processing steel for hydropower plants 1

indroduction

high strength steelproductiondelivery condition

processing of DILLIMAX 690flame cuttingweldingformingPWHT


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


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


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


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


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


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]


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


too fast o.k too slow

influence of cutting speed



hot forming

hot formig (above tempering temperature) is not allowed for Q+T steel !



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


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


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


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


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)


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)


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.


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


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


test temperaturetest temperature

impact impact energyenergy

>200°C/h>200°C/h 75°C/h75°C/h 25°C /h 25°C /h

PWHTinfluence of cooling speed after PWHT on TT shift

Documents

welding forming PWHT - · PDF fileif PWHT is applied, temperature has to be limited 50°C below tempering temperature during plate production. processing steel for hydropower plants