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Laser Welding of Thick Structural Steels

Hans Engström, Jan Flinkfeldt, Klas Nilsson Luleå University of Technology

Tony Nilsson, SSAB Tunnplåt AB Anders Skirfors, SSAB Oxelösund AB

Marcus Miller, Volvo Articulated Haulers AB

(2)

Presentation

• Introduction

• Experimental

• Results

– Properties of welded material – Weld defects

– Process windows – Fatigue testing

• Conclusion

(3)

Introduction

Benefits of Laser Welding

• High Welding Speeds

• Low distortion

• New design opportunities

(4)

Laser equipment used

Laser I II

Power [kW] 12 17

Focal length [mm] 270 300

Beam diameter in focus [mm] 0,5 0,8 Double focusing optics 0,6 mm between focal spots

Shielding gas He He

Shielding gas arrangement ”Ring nozzle”

1

Coaxial nozzle + plasma gas Workstation Moving laser beam, fixed work

table

Fixed laser beam, x/y-table

(5)

Experimental set-up

(6)

Materials

High Strength Cold Forming Steel - DOMEX

High Strength Structural Steel - WELDOX

Wear Resistant Steel - HARDOX

(7)

Steel grade R

p0,2

MPa

R

m

MPa

A

5

(A

80

)

%

Charpy-V J/cm

2

/C Domex 355 XP 10 mm 376 462 38 (41) 344 / -20

Domex 460 MC 8 mm 523 616 19 (19) 223 / -20 220 / -40 Domex 600 MC 8 mm 674 749 22 (23) 103 / -20 80 / -40 Domex 390 XP 12 mm 410 507 28 (32) 363 / -20 295 / -40

Materials

Steel grade T mm

Rp 0,2 MPa

Rm MPa

A5

%

Charpy V J/ °C

Hardness HB

CE

IIW3

WELDOX 960 10 1027 1073 13 35 / -40

1

- 0,55

HARDOX 400 10 -- -- -- -- 408 0,37

HARDOX 400 15 989

4

1250

4

12

4

80 / -40

2, 4

400

4

0,38

(8)

Joint types and preparation

•I-joint, (butt weld) autogenous, laser cut or milled edges

•I-joint (butt weld) filler material 1 , laser cut or milled edges

•V-joint filler material 1

•Edge joint 90°

•Edge joint 45º

DOMEX 390XP 12 mm DOMEX 355XP 10 mm

Cutting machine 1 above; 2 below

1.

Esab OK Autrod 12.51, 12.64

(9)

Results DOMEX steels

Domex 355XP 10 mm

0 100 200 300 400

0 2 4 6 8 10 12 14 16

Distance (mm)

Vickers

Hv5

Domex 600 MC 8,0 mm

0 100 200 300 400

0 2 4 6 8 10 12 14 16

Distance (mm)

Vickers

Hv5

(10)

Results DOMEX

Strength OK Fracture in base material

Elongation OK Guaranteed values for base material achieved V-bending OK (Punch diameter=4xt)

Toughness OK Demand normally 50J/cm 2 at -20 º (base material)

Weld metal 355XP 390XP 460MC 600MC

8 mm -60º (-40º ?) -60º

10 mm -60º

12 mm -60º

(11)

Results WELDOX and HARDOX

200 250 300 350 400 450

0 2 4 6 8 10 12 14 16 18

Distance (mm)

Hardness (HV5)

WELDOX 960 10 mm HARDOX 400 10 mm

(12)

Results WELDOX and HARDOX

Material T [mm] ∆t8/5

[s]

RP 0,2

[Mpa] Rm

[MPa] A50

[%] Fracture

position Charpy V toughness

5

–40°C [J]

WM

3

/HAZ

4

WELDOX 960 10 6 1036 1088 24 BM

2

18/18

10 2 1032 1086 23 BM 15/15 HARDOX 400 10 5 1032 1058 4 HAZ 20/22

10 2 1108 1213 6 HAZ 30/15

10 1 1114 1230 7 HAZ 23/20

15 5 1011 1108 8 HAZ 30/27

(13)

Welding defects

2000x 400x

40x

1 mm

(14)

Process Windows

Power

[kW] Welding speed

[mm/min]

11 500 700 900 1100 1300 1400 1500 1600 14 800 1000 1200 1400 1600 1800 2000 2200 17 1000 1200 1500 1800 2000 2200 2400 2600

DOMEX 390 XP, 12 mm bead-on-plate

(15)

Process windows

11 14 17 kW

1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 m/min DOMEX 390 XP, 10 mm, lasercut

Autogenous

Not approved Approved Approved He/4% O2

1,2 1,4 1,6 1,8 2,0 2,2 2,4 11

14 17 kW

DOMEX 390 XP, 10 mm, milled Autogen

not approved approved

approved, He/4%O2

DOMEX 390 XP 10 mm

Laser cut

Milled

Autogenous

(16)

Process Windows

not approved

11 14 17 kW

1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 m/min DOMEX 390 XP, 10 mm, lasercut

Filler material

DOMEX 390XP 10 mm Filler material

Laser cut

Milled

1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 11

14 17 kW

m/min DOMEX 355 MC, 10 mm, milled,

Filler material

not approved approved

(17)

Process windows

11 14 17 kW

0,8 1,0 1,2 1,4 1,6 1,8 2,0 m/min DOMEX 390 XP, 12 mm, lasercut

Autogenous

= not approved

= not approved He/4%O2

= approved

= approved He/4%O2

11 14 17 kW

0,8 1,0 1,2 1,4 1,6 1,8 2,0 m/min DOMEX 390 XP,12 mm, milled

Autogenous

not approved not approved He/4%O2

approved approved He/4%O2

DOMEX 390XP, 12 mm

11 14 17 kW

0,8 1,0 1,2 1, 1,6 1,8 2,0 m/min DOMEX 390 XP, 12 mm, lasercut

Filler material

not approved, welding speed/wire speed=1:1 not approved, welding speed/wire speed=1:2 approved, welding speed/wire speed=1:1

approved, welding speed/wire speed=1:2

Autogenous

Laser cut

Milled Filler material

Bead-on-plate

(18)

Process windows

m/min Hardox 400, 10 mm laser cut

Autogenous

not approved approved

1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 11

14 17 kW

Weld speed/wire speed 1:1

11 14 17 kW

m/min Hardox 400, 10 mm, laser cut

Filler material

not approved approved

1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6

HARDOX 400, 10 mm

Autogenous Filler material

Laser cut

(19)

Weld Geometry

Thickness

[mm] Focal point position

[mm] Weld

geomertry Welding Speed [m/min]

Weld quality

10 +5 1,5 Approved

1,8 Approved

-5 1,2 Approved

± 0

12 -5 1,5 Approved

± 0 1,5 Not approved

+5 Not full penetration

(20)

Torsion Fatigue

150 120

Laser- stråle

10 1000

100000 1000000 10000000

No of cycles to failure, Nf

Stress range Mpa

MAG

Laser

Laser 2

(21)

Conclusions

• Weld quality laser dependent

• Process windows

- Fairly large for 10 mm material

- Reduced for 12 mm, use milled edges or filler material if laser cut edges will be used

• Torsion fatigue strength of box beam increased >50% by laser

welding compared to traditionally designed and MAG-welded

beams

(22)

More information……

Order the report

”Utveckling av lasersvetsteknik för detaljer i tjockt konstruktionsstål”

Luleå tekniska universitet 2000:20

RACER programme: www.mb.luth.se (Only in Swedish)

References

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