Laser welding of thick section ultra-high strength (>1000 MPa) steels often results in bad weld appearance, cracking and porosity. This investigation aims to understand phenomena of laser welding of 15 mm thick D6A ultra-high strength steel. Both 1G (flat or downhand, i.e. laser beam is directed downward to-wards the earth) and 2G (horizontal, i.e. laser beam is horizontal to the earth surface) position welding were carried using an IPG fibre laser at a maximum power of 13 kW. Weld bead geometry, microstructure, morphology, integrity and residual stresses were characterised. The results show that laser welding at 1G position always lead to serious defects including root sagging, while 2G position can overcome these problems and has a much wider operating parameters window, which is caused by the combination of the effect of force status of gravity and surface tension, and the gradual or sudden change of direction of metal plume overflow with the increase in power density. The longitudinal residual stresses of welded joint of D6A steel at 2G position show a nearly symmetric distribution not only in the weld centre but also across the weld thickness which indicates that the residual stresses using 2G position is more uniform than using 1G position.

1.
Webster
,
S.
,
J.K.
Kristensen
, and
D.
Petring
,
Joining of thick section steels using hybrid laser welding
.
Ironmaking & Steelmaking
,
2008
.
35
(
7
): p.
496
504
.
2.
Zhang
X.
,
Ashida
E
,
Tarasawa
S.
, et al,
Welding of thick stainless steel plates up to 50 mm with high brightness lasers
.
Journal of Laser Applications
,
2011
.
23
(
2
): p.
7
.
3.
Zhang
,
M.
, et al,
Optimization of deep penetration laser welding of thick stainless steel with a 10 kW fiber laser
.
Materials & Design
,
2014
.
53
: p.
568
576
.
4.
Kaplan
,
A.F.H.
and
G.
Wiklund
,
Advanced welding analysis methods applied to heavy section welding with a 15 kW fibre laser
.
Welding in the World
,
2009
.
53
: p.
295
.
5.
Sokolov
M.
,
Salminen
A.
,
Katayama
S.
, et al,
Re-duced pressure laser welding of thick section structural steel
.
Journal of Materials Processing Technology
,
2015
.
219
: p.
278
285
.
6.
Haug
P.
,
Rominger
V.
,
Speker
N.
, et al,
Influence of Laser Wavelength on Melt Bath Dynamics and Resulting Seam Quality at Welding of Thick Plates
.
Physics Procedia
,
2013
.
41
: p.
10
.
7.
Powell
,
J.
, et al,
Weld root instabilities in fiber laser welding
.
Journal of Laser Applications
,
2015
.
27
(
S2
).
8.
Avilov
V. V.
,
Gumenyuk
A.
,
Lammers
M.
, et al,
PA position full penetration high power laser beam welding of up to 30 mm thick AlMg3 plates using electromagnetic weld pool support
.
Science & Technology of Welding & Joining
,
2012
.
17
(
2
): p.
128
133
.
9.
Avilov
V.
,
Fritzsche
A.
,
Bachmann
M.
, et al,
Full Penetration Laser Beam Welding of Thick of Thick Duplex Steel Plates with Electromagnetic Weld Pool Support
, in
The 34rd International Congress on Applications of Lasers & Electro-Optics2015
,
Laser Institute of America
:
Atlanta, GA, USA
. p.
571
579
.
10.
Guo
W.
,
Liu
Q.
,
Francis
J. A.
, et al,
Comparison of laser welds in thick section S700 high-strength steel manufactured in flat (1G) and horizontal (2G) positions
.
CIRP Annals - Manufacturing Technology
,
2015
.
64
(
1
): p.
197
200
.
11.
Shen
X.
,
Li
L.
,
Guo
W.
, et al
Comparison of processing window and porosity distribution in laser welding of 10 mm thick 30CrMnSiA ultrahigh strength between flat (1G) and horizontal (2G) positions
.
Journal of Laser Applications
,
2016
,
28
(
2
):
022418
.
12.
Uspenskiy
,
S. A
,
Petrovskiy
,
V. N
,
Shcheglov
, et al,
Spectral diagnostics of a vapor-plasma plume produced during welding with a high-power yt-terbium fiber laser
.
Optics and Spectroscopy
,
2013
.
115
(
1
): p.
140
146
.
13.
Tsay
,
L.W.
,
C.S.
Chung
, and
C.
Chen
,
Fatigue crack propagation of D6AC laser welds
.
International Journal of Fatigue
,
1997
.
19
(
1
): p.
25
31
.
14.
Shyh-Chi
Wu
,
Kuang-Hung
Tseng
,
Hua-Chiang
Wen
, et al,
Tribological behavior of electron beam D6ac weldment
.
Applied Surface Science
,
2013
.
264
: p.
45
51
.
15.
Chang
,
T.
,
L.
Tsay
, and
C.
Chen
,
Influence of gaseous hydrogen on the notched tensile strength of D6ac steel
.
Materials Science and Engineering: A
,
2001
.
316
(
1
): p.
153
160
.
16.
Wu
S. C.
,
Wen
H. C.
,
Wu
M. J.
, et al,
Fracture re-sponses of microstructures of electron beam-welded D6AC
.
Vacuum
,
2012
.
86
(
12
): p.
1828
1833
.
17.
Kartal
,
M.E.
, et al,
Determination of the profile of the complete residual stress tensor in a VPPA weld using the multi-axial contour method
.
Acta Materialia
,
2008
.
56
(
16
): p.
4417
4428
.
18.
Elmesalamy
,
A.
,
J.A.
Francis
, and
L.
Li
,
A comparison of residual stresses in multi pass narrow gap laser welds and gas-tungsten arc welds in AISI 316L stainless steel
.
International Journal of Pressure Vessels and Piping
,
2014
.
113
(
0
): p.
49
59
.
19.
Kang
,
N.
,
J.
Singh
, and
A.K.
Kulkarni
,
Gravitational effects on the gas tungsten arc welds of 304 stainless steels
.
Materials and Manufacturing Processes
,
2003
.
18
(
4
): p.
549
561
.
20.
Miyazakia
,
Y.
and
S.
Katayama
,
Influence of la-ser-induced plume on penetration in laser welding
.
Welding International
,
2015
.
29
(
5
): p.
7
.
21.
Greses
,
J.
, et al,
Plume attenuation under high power Nd: yttritium–aluminum–garnet laser welding
.
Journal of laser applications
,
2004
.
16
: p.
9
.
22.
Moyer
,
J.
and
G.
Ansell
.
The volume expansion accompanying the martensite transformation in iron-carbon alloys
.
Metallurgical Transactions A
,
1975
.
6
(
9
): p.
1785
1791
.
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