PROCESSING of THERMOMECHANICAL ROLLED STEEL With Respect of Welding and Cutting - Presentation Jurgen Schutz

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12.01.2010 ADVANCED STEEL FOR THE FUTURE 1

Processing of thermomechanical rolled steel

Jürgen Schütz, EWEWelding Laboratory, Dillinger Hütte

with respect of welding and cutting

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Different delivery conditions of fine grained steel

Processing of thermo-mechanical rolled steel

Flame cutting

Forming

Welding

Flame straightening

Post weld heat treatment

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Flame cutting

Forming

Welding

Flame straightening


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Flame cutting

Forming

Welding

Flame straightening


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Oxygen cutting, plasmacutting, laser cutting

no preheat requiredno scale on thesurface

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flame cutting

material is combusted with oxygen and oxides are blown out

plasma-cutting

material is melted by ionized gas and blown outby gas jet (oxygen / nitrogen)

laser-cutting

material is vaporized (minor thickness) or combusted with oxygen

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material suiteable for gas cutting :

ignition temperature lower than melting temperature

melting temperature of oxides lower than melt temperature of base material

positive energy balance to keep material above ignition temperature

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liquidus-temperature

ignition-temperature

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Combustion of the plate ?

1. combustion of gas (acetylene, propane, 0.5 bar)

2. heating of subsurface to ignition temperature

3. combustion of iron within the oxygen (7 bar) jet, oxides are blown out inthe jet, (exothermic process ,autogenous)

1. nozzle

2. gas -oxygen (heating)

3. oxygen -jet (cutting)

4. plate to be cut

5. heating flame

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In brief

Oxy acetylene flame preheats the metal to the ignition point at the place to be cut. It also provides a protective shield between the cutting oxygen stream and the atmosphere.

Cutting oxygen combines with iron to form iron oxide.

Cutting oxygen jet blows away molten iron and iron oxide thereby cutting anarrow slit or kerf in the metal object.

Datum und Veranstaltung eintragen 12

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too fast o.k too slow

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Oxy-cutting

rapid heating and cooling at the flame cut edge

martensitique microstructure :

maximum hardness is only a function of carbon content

Hv = f(C) ; 800*C(%) +294

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90° section, 50 mm plate thickness 15° section, for hardness measurement

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Flame cutting

Forming

Welding

Flame straightening


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straining of outer surface :

ε = t / (2r + t)

r : mandrel (bending) radiust : plate thickness

approximate value : 2r >> t

ε = t/2r or….. ε = thickness / diameter

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0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

grinded edge

grinded edge

grinded edge

non grinded edge

non grinded edge

non grinded edge

Influence of edge preparation for technical bending specimen

bending (180°) without cracking crack initiation at subsurface crack initiation at edge

S460N0.18%C

S460N0.15%C

S460N0.13%C

S460M0.10%C

S460M0.11%C

r/t te

chni

cal b

endi

ng s

peci

men

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Hot forming

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Hot forming

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increase of yield strength

higher yield to tensile ratio

reduction of residual elongation

shift of transition from brittle - ductile

Effect of cold forming on steel properties

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12.01.2010 ADVANCED STEEL FOR THE FUTURE 28test temperaturetest temperature

impact impact energyenergy

initialinitial

after 5% after 5% strainstrain

ΔΔTTstrainstrain

staining staining + ageing+ ageing

ΔΔTTageingageing

Cold forming

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12.01.2010 ADVANCED STEEL FOR THE FUTURE 29test temperaturetest temperature

impact impact energyenergy

staining staining + ageing+ ageing

S + A +S + A +PWHTPWHTinitialinitial

Cold forming

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-100 -80 -60 -40 -20 00

25

50

75

100

125

150

S420M - 40mm (CMnNb)influence of straining, ageing and tempering on TT (1/4 thickness)

delivery condition 10 % strain 10 % strain + aged (250°/30min) 10 % strain + 580°C/30min

impa

ct e

nerg

y, a

vera

ge [j

oule

s]

test temperature [°C]

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Flame cutting

Forming

Welding

Flame straightening


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Consumables for welding TM-rolled steels :

Consunables have to be selected in a way that they fulfill the requiredmechanical properties ( i.e yield, tensile, toughness)

Welding position may be respected

Any subsequent PWHT has to be taken into account

But no difference to normalized steel

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DIN EN 499

electrode

460 MPa Reh

TT 47 J, -60°C

0.6-1.2 % Ni

E 24646 1Ni H5B

basic covered

DC –current, >105% efficiency

all welding positions

5 ml H2 /100g

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Welding

HAZ hardness

Hydrogen induced cracking - preheating

Toughness in the HAZ

Working range

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melt

A1-line

A3 -line

temperature

% C

CGWEZ

fine grained WEZ

partly aust. WEZ

0.15 %

temp. WEZ

1200

1600

1400

Base material

WEZ

Weld metal

200

400

fusion line

austenite

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S420M 100mm HAZ hardness as a function of distance from fusion line

-4 -2 2 4150

175

200

225

250

275

S420M - 100mmSAW 5.0 kJ/mm

hardness HV 10

upper lower

distance from fusion line [mm]-4 -2 2 4

150

175

200

225

250

275

S420M - 100mmSAW 0,7 kJ/mm

hardness HV 10

upper lower

distance from fusion line [mm]

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1 10 205cooling time t8/5 s

HAZ hardness tests on bead on plate welds

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200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

Tmax (fusion line) 1350°C

40s

10s

tem

pera

ture

[°C]

time [sec]

20s

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50 100 150 200 2500

1

2

3

4

5

3-dimensional heat flow

40 s

30 s

10 s

20 s

heat input [kJ/mm]

interpass temperature [°C]

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1 10 100150

200

250

300

350

400

450WEZ-Härte

C,Si,Mn,Cr,Mo,Ni,Cu,B

C,Si,Mn,Cr,Mo,Ni,Cu,V,Nb

Ti

C,Si,Mn,Cr,Mo,Ni,B

C

t8/5 Zeit

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1 10

200

300

400

500

205

S 460 M

S 460 N

HAZ

har

dnes

s (H

V10)

cooling time t8/5 s

HAZ hardness tests on bead on plate welds

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Hydrogen induced crackparallel to fusione linein the CG-HAZ

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Hydrogen induced crackIn the HAZ of a multi-pass weld

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Calculation of minimum preheating temperature (EN 1011)

CET = C + (Mn + Mo)/10 + (Cr + Cu)/20 + Ni/40

To = 700 CET + 160 tanh (t/35) + 62 HD exp 0.35 + (53 CET - 32) Q - 330

t = Blechdicke (mm)HD = Wasserstoff-Eintrag (ml/100 g - DIN 8572)Q = Wärmeeinbringen ( kJ/cm)

Tekken Test :

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0255075

100125150175200

0 25 50 75 100plate thickness (mm)

Tp (°

C)

0255075

100125150175200

0 1 2 3 4 5welding heat input (kJ/mm)

Tp (°

C)

0255075

100125150175200

0,2 0,25 0,3 0,35 0,4 0,45 0,5CET = C + (Mn+Mo)/10 + (Cu+Cr)/20 + Ni/40 (%)

Tp (°

C) C Mn Mo Cr Cu Ni

0,07 1,55 0 0,03 0,2 0,20,12 1,55 0 0,03 0,2 0,250,18 1,45 0 0,03 0,05 0,05

CET 0,24 % 0,29 % 0,33 %Q 1,5 1,5 1,5d 50 50 50

HD 5 5 5

0255075

100125150175200

0 5 10 15hydrogen ml/100g deposit metal

Tp(°

C)

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0 20 40 60 80 100

25

50

75

100

125

150Heat input hydrogen

GSMAW 1.0 kJ/mm 2 ml/100g DMSMAW 2.2 kJ/mm 4 ml/100g DMSAW 3.3 kJ/mm 7 ml/100g DM

S460M

S460N

plate thickness

S500M

S355J2G3 (N)

S355G8+N Offshore

S355G8+M

S460 (N)heat input hydrogenGMAW 0.7 kJ/mm 2 ml/100gSMAW 2.0 kJ/mm 4 ml/100gSAW 3.3 kJ/mm 7 ml/100g

Preheating temperature EN1011

S420G2+M

plate thickness

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-80 -60 -40 -20 0 20 400

50

100

150

200

250

300

350 S355M (Nb) 0,08% C, 0,001% S S355N Offshore 0,12% C, 0.001% S S355N standard 0,20% C, 0,003% S S355N old 0,20% C, 0,028% S

impa

ct e

nerg

y [jo

ules

]

temperature [°C]

HAZ toughness of S355N and S355M

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TM High toughness / High safety

-120 -100 -80 -60 -40 -20 0 200

50

100

150

200

250

300

350 S355J2+N S460ML S690QL

Cha

rpy-

V [J

]

Temperature [°C]

Welding leads to

toughness

reduction

High toughnessin the base

material reducesthe risk of brittle

fracture and gives saftey!

Advantages of TM-steel - Processing

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Impact testing of thick welds for the approval of offshore steels

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0 1 2 3 4 50

50

100

150

200

250

300

GRD 450 TMCP plate thickness 60-100mm

FL FL+2mm FL+5mmmea

n im

pact

ene

rgy

at -4

0°C

[J]

heat input [kJ/mm]

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Temperature [°C]

max. interpass temp.

higher heat input

1 2 3 4 550

100

150

200

250

S355J2G370 mm

S355M - 100mm

min. preheat andinterpass temp.

Heat input [kJ/mm]

Working range

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Flame cutting

Forming

Welding

Flame straightening


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The flame straightening of a plate is based in principle on a local heating of the areato be shortened in combination with the hindrance of thermal expansion by the coldvicinity. This causes a bulging of the heated zone. When cooling down to ambient temperature the resulting tensile stresses willlead to the required deformation.

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The efficiency of the process depends on :

thermal fieldwall thicknessheating ratevery narrow located heatingrestraint and stiffness of the construction

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Lower limit of applicable temperature

At peak temperature the area to be straightened must undergo plastic deformation.During subsequent cooling the compressive stresses turn into tensile stresses.The final tensile stresses are producing the effect on geometry.Thus the temperature must be increased above the temperature wheresufficiently high compression stress are built up so that the yielding occurs

The yield strength at elevated temperature is lowered to such an extent that thecompressive stress will lead to sufficient bulging of the area to be straightened.

For S355 / 420M steel both conditions are fulfilled for temperaturesexceeding approximately 450°C.So any lower temperatures are ineffective for shaping.

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Upper limit of applicable temperature

The upper limit of the temperature range is shall not be exceededin order to regain the mechanical properties of the plate after subsequent cooling.

Two different flame straightening procedures have to be distinguishedbecause they require different temperature limits.

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In the first case the plate is only superficially heated. The heat input relatedto the plate thickness is small. Due to the steep temperature gradients in thethrough thickness direction cooling is very fast. Cooling speed is in the rangeof high heat input welding. Due to the fast transformation again a fine grainedmicrostructure is achieved which is very similar to the initial microstructure. Soare the mechanical properties.

Temperatures above 925°C shall not be permitted to avoid grain growth.(examples: line heating)

Surface heatingrapid coolingpeak temperaturemax. 900-950°C

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In the second case the entire cross section of the plate is heated. The heatinput related to the plate thickness is high. The heated area cools down slowerthan in the first case. The larger the heated area the slower the cooling. Aircooling represents the very extreme of such procedure.To avoid softening of the steel temperatures exceeding 600°C are notpermitted. For a short period 650°C may still be acceptable, but clearly below700°C so that a partial transformation to austenite can be excluded.

(examples: wedge heating, triangular heating)

Full section heatingrather slow coolingpeak temperaturemax. 600-650°C

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Zusammenstellung der Glühfarben beim Flammrichten

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Flame cutting

Forming

Welding

Flame straightening


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Response of tensile properties on PWHT (S420 M)

16,8 17,0 17,2 17,4 17,6 17,8 18,0 18,2 18,4 18,6 18,8380

400

420

440

20mm 25mm 50mm

yield strength MPa

Hollomon Parameter16,8 17,0 17,2 17,4 17,6 17,8 18,0 18,2 18,4 18,6 18,8

480

500

520

540

560

20mm 25mm 50mm

tensile strength MPa

Hollomon Parameter

Holdingtemperature

Holding time HP-Factor

600°C 60 min 17,00600°C 240 min 17,53600°C 480 min 18,05630°C 60 min 18,15630°C 240 min 18,25

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For post weld heat treatment

recommended parameters

530°C - 580°C

1-2 hours

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No hot forming allowedNo hot forming allowed

No heat treatment above ~600°CNo heat treatment above ~600°CProcessing temperatures up to ~600°C are acceptableProcessing temperatures up to ~600°C are acceptable“warm”“warm”--forming, PWHT,forming, PWHT,

Good initial toughness allows considerable cold deformationGood initial toughness allows considerable cold deformation

Excellent weldability as a result of the optimised chemical Excellent weldability as a result of the optimised chemical composition, benefits:composition, benefits:

the omission of preheating, the omission of preheating, the application of higher weld deposition ratesthe application of higher weld deposition ratesomission of post weld heat treatmentomission of post weld heat treatment

Weight reduction in the construction without a drawback for Weight reduction in the construction without a drawback for processingprocessing

Summary and conclusion

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• Distortion caused by residual stress :

• Yield strength will lower with increasing temperature

• Tensile stress occurs when material shrinks

• Transformation constituents (martensite/perlite) have higher volume thanaustenite, this creates compressive stress

• Expanding material will be plastically deformed due to colder vincinity(flame straightening)

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tensile

compressive

temperature900700500300

300

300

ferrite / bainiteformation

martensit formation

thermal shrinkage austenite

Yield point = f(T)

Entstehung von Schrumpf- und Umwandlungsspannungen

Documents

PROCESSING of THERMOMECHANICAL ROLLED STEEL With Respect of Welding and Cutting - Presentation Jurgen Schutz