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PROLAS 1
Project PROLAS - Final Report
Annex containing additional material by Alexander Kaplan, LTU,
June 2014
Content: 1. Selected slides from a survey presentation on PROLAS
(3 pages) 2. List of publications, and title pages of selected
publications (10 pages) 3. Guideline “Introduktion till
lasersvetsning” (Swedish version, 36 pages) 4. The final technical
report - from Oulu University (in English, 48 pages)
1. Selected slides from a survey presentation on PROLAS
Four EU regionally funded projects were recently carried out in
laser materials processing, complementary to each other. The
research carried out in PROLAS is of more fundamental and
generalized nature than in FATLAS and IndLas where industrial
applications were studied and spread, while FIF basically
identified the industrial SME needs for when and how to implement
advanced manufacturing technology.
The Workpackages (WP) in PROLAS have generated results of the
three types, as illustrated above: Developing cooperation,
exploring and publishing scientific and technical results, a final
guideline.
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PROLAS 2
A web-conferencing culture between the Finnish and Swedish
partners became established that enabled frequent distant meetings
and in turn close cooperation at all levels.
In WP2, the focused beams of two different types of modern high
power lasers were measured, analyzed and compared, namely the
Yb:fibre laser at LTU and the Yb:disc lasers at OU.
As part of the state-of-the-art studies, Alexander Kaplan
visited Japan in January 2014 and has seen welding by the today by
far strongest industrial high power laser, a 100 kW Yb:fibre laser.
In frame of an actual cooperation with the Japanese colleagues,
common publications are planned.
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PROLAS 3
A significant part of the project comprised laser welding
experiments, both at LTU and OU, to identify, understand and
suppress laser welding defects, which was published, reported and
entered in the developed guideline.
Knowledge published in literature and discovered in the project
was not only entered in State-of-the-Art-manuscripts and in the
guideline but for the first time also expanded in a new format of
documentation developed at LTU, by subway-system orientation and in
a visualizing systematic flow-chart.
Final seminar of the projects PROLAS and FIF in Tornio.
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PROLAS 4
2. List of publications and title pages of selected publications
International scientific journal publications fully or partially
accomplished (June 2014) in PROLAS, as acknowledged in most of the
papers. Marked yellow: joint publications between OU and LTU; Laser
beam (main topic) 1. Kaplan, A. F. H: Analysis and modeling of a
high power Yb:fibre laser beam, Optical Engineering,
v 50, n 5, p 054201 (2011). 2. Kaplan, A. F. H.: Comparison of
beam profiles for keyhole modelling of laser welding, Journal
of
Laser Applications, v 23, pp 042005 (9 p) (2011). High speed
imaging of the keyhole front 3. Eriksson, I., J. Powell, A. F. H.
Kaplan: Measurements of fluid flow inside laser welding
keyholes,
Sci. Techn. Weld. Join., v 16, n 7, pp 636-641 (2011). 4.
Eriksson, I., J. Powell, A. F. H. Kaplan: Melt behavior on the
keyhole front during high speed laser
welding, Optics and Lasers in Engineering, v 51, n 6, pp735-739
(2013). Absorption laser beam at keyhole front 5. Kaplan, A. F. H.:
Local absorptivity modulation of a 1 µm-laser beam through surface
waviness,
Applied Surface Science , v 258. n 8, pp 9732-9736 (2012). 6.
Kaplan, A. F. H.: Fresnel absorption of 1 µm- and 10 µm-laser beams
at the keyhole wall during
laser beam welding: Comparison between smooth and wavy surfaces,
Applied Surface Science (IF 1,73), v 258, n 8, 3354-3363
(2012).
7. Kaplan, A. F. H.: Absorptivity modulation on wavy molten
steel surfaces; the influence of laser wavelength and angle of
incidence, Applied Physics Letters (IF 3,77), v 101, pp 151605 (4
p) (2012). doi: 10.1063/1.4759126
8. Kaplan, A. F. H.: Laser absorptivity on wavy molten metal
surfaces: Categorization of different metals and wavelengths, J.
Laser Appl., v 26, pp 012007 (9 p) (2014).
9. Matti, R. S., T. Ilar and A. F. H. Kaplan: Analysis of laser
remote fusion cutting based on a mathematical model, J. Appl. Phys,
v 114, pp 233107-9 (2013).
Spatter 10. Kaplan, A. F. H and J. Powell: Spatter in laser
welding, J Laser Appl., v 32, n 3, 032005 (7 p)
(2011). doi:10.2351/1.3597830 Hot cracks 11. Wiklund, G, O.
Akselsen, A. J. Soegjerd and A. F. H. Kaplan: Geometrical aspects
of hot-cracks in
laser hybrid arc welding, Journal of Laser Applications, v 26,
pp 012003 (6 p) (2014).
Weld distortion 12. Eriksson, I., P. Haglund, J. Powell, M.
Sjödahl, A. F. H. Kaplan: Holographic measurement of
thermal distortion during laser spot welding, Optical
Engineering Letters, v 51, 030501 (3 p) (2012).
DOI:10.1117/1.OE.51.3.030501
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PROLAS 5
Weld surface shape 13. Karlsson, J., A. F. H. Kaplan: Analysis
of a fibre laser welding case study, utilising a matrix flow
chart, Applied Surface Science, v 257, n 9, pp 4113-4122
(2011).
Influence of joint edge preparation 14. Sokolov, M. S., A.
Salminen, A. F. H. Kaplan: Laser Welding of Structural Steels:
Influence of the
Edge Roughness Level, Optics & Laser Technology, v 44, pp
2064-2071 (2012). Measurement of fatigue crack growth through welds
15. Sundqvist, J., A. F. H. Kaplan1, J. Granström, K.-G. Sundin, M.
Keskitalo, K. Mäntyjärvi, X. Ren:
Identifying Residual Stresses in Laser Welds by Fatigue Crack
Growth Acceleration Measurement, submitted to Measurement Science
and Technology (2014).
New technique - donut welding 16. Eriksson, I., J. Powell, A. F.
H. Kaplan: Surface tension generated defects in full penetration
laser
keyhole welding, J. Laser Appl., v 26, pp 012006 (6 p) (2014).
Weld metallurgy 17. Keskitalo, M., K. Mäntyjärvi, J. Sundqvist, J.
Powell, A. F. H. Kaplan: The influence of shielding
gas on the properties of laser welded duplex stainless steel,
submitted to Journal of Materials Processing Technologies
(2014).
18. Keskitalo, M., J. Sundqvist, K. Mäntyjärvi, J. Powell, A. F.
H. Kaplan: The influence of shielding gas and heat input on the
properties of the EN 1.4521 type steel laser weld, under
preparation for journal submission (2014).
Guidelines for laser-arc hybrid welding 19. Eriksson, I., J.
Powell and A. F. H. Kaplan: Guidelines in the choice of parameters
for hybrid laser
arc welding with fiber lasers, Proc. LIM, Munich, Germany and
Physics Procedia, v 41, pp 119-127 (2013).
(further journal publications are under preparation, in
additional several conference papers exist) Joint publications
between OU and LTU at peer-reviewed conferences: 20. Keskitalo, M.,
K. Mäntyjärvi, J. Sundqvist, I. Eriksson, A. F. H. Kaplan: The
influence of shielding
gas on the properties of laser welded stainless steel, Proc.
NOLAMP 14, August 26-28, 2013, Gothenburg/Sweden (2013).
21. Sundqvist, J., I. Eriksson, A. F. H. Kaplan, M. Keskitalo,
K. Mäntyjärvi, J. Granström, K.-G. Sundin: Measuring the influence
of laser welding on fatigue crack propagation in high strength
steel, Proc. ICALEO, Miami (FL), Paper #2104 (2013).
22. Sundqvist, J., I. Eriksson, A. F. H. Kaplan, M. Keskitalo
and K. Mäntyjärvi: Influence of the metallurgy on fatigue crack
propagation in welded high strength steel joints, Proc. NOLAMP 14,
August 26-28, 2013, Gothenburg/Sweden (2013).
Below the title pages of selected publications
[13,16,7,15,21,22,17,20] are added:
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PROLAS 6
[13]:
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PROLAS 7
[16]
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PROLAS 8
[7]:
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PROLAS 9
[15]: Identifying Residual Stresses in Laser Welds by Fatigue
Crack Growth Acceleration Measurement Jesper Sundqvist1, Alexander
F. H. Kaplan1, Jan Granström1, Karl-Gustaf Sundin1, Markku
Keskitalo2, Kari Mäntyjärvi2, Xiaobo Ren3
1 Department of Engineering Sciences and Mathematics, Luleå
University of Technology, Luleå, 971 87 Sweden
2 Oulu Southern Institute, University of Oulu, Pajatie 5,
Nivala, FI-85500, Finland
3 SINTEF Materials and Chemistry, N-7465 Trondheim, Norway
Abstract The fatigue life of laser welds is often governed by
their surface topology which can act in a stress
raising manner and in turn influence the crack initiation time.
Residual stresses which are induced by
the fast heating and cooling cycle can have a strong impact on
the fatigue behaviour, often shortening
the fatigue lifetime of the welded component. This paper
describes how the standardized measurement
method for the fatigue crack growth rate can be expanded to
identify residual stress along the cracking
path. Here the method is studied for a three-point bending
fatigue testing of laser welds. The second
derivative of the measured crack opening and in turn crack
length over time, hence the acceleration
turns out to correspond well with the residual stress
distribution along the crack. Distinct acceleration
maxima and minima can be identified, correlating with tensile
and compressive stress, as was basically
proven by numerical simulation. The method is easy to apply and
provides valuable information, as
was demonstrated for different situations, like different high
strength steel and welding parameters and
cracking across two parallel welds or along the weld. The method
has potential for further extensions.
It was shown that the combination with additional analysis
methods can provide valuable
complementary information on the cracking behaviour.
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PROLAS 10
[21]:
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PROLAS 11
[22]:
INFLUENCE OF THE METALLURGY ON FATIGUE CRACK PROPAGATION IN
WELDED HIGH STRENGTH STEEL JOINTS J. SUNDQVIST1, I. ERIKSSON1, A.
F. H. KAPLAN1, M. KESKITALO2, K. MÄNTYJÄRVI2 1Luleå University of
Technology, Luleå, Sweden. 2 University of Oulu, Nivala,
Finland
Abstract
A literature study of high strength steels, fatigue and fatigue
assessment of welds has been conducted and is briefly presented in
this paper together with experiments on fatigue crack growth rates
of laser welded high strength steel. It is well-known that the
fatigue life of welded joints is heavily dependent upon the surface
geometry and welding defects because of crack initiation from the
high stress concentrations associated with these types of welding
flaws. However, the crack propagation through different weld zones
of laser-welded high strength steels and the corresponding impact
from the metallurgy is not fully understood. The experiments
comprise three-point bending fatigue tests on laser-welded high
strength steel with machined surfaces. Measurement of the fatigue
crack propagation rate transverse the weld and hence through the
different metallurgy and hardness of the heat affected zone and of
the weld can contain information on the impact of the metallurgy on
the crack propagation speed. The influence of different high
strength steel grades and of different welding parameters on the
crack propagation and fatigue life is discussed.
Keywords: fatigue crack propagation, weld, laser, high strength
steel, fatigue testing
1 Introduction
For many welded products fatigue is the main load situation to
be optimized. Many new high strength steel grades have been
developed that basically enable improved product design,
particularly weight reduction. However, welding usually lowers the
strength and fatigue life of steel which hinders the reduction of
plate thickness for dimensioning. For fatigue life assessment
mainly the geometrical aspects of a weld like the weld shape and
its stress raisers have been studied and considered, while the
impact of metallurgy on fatigue crack propagation is not well
understood yet. Therefore the present study aims at better
measurement and understanding of the influence of the metallurgy of
laser welded high strength steel on fatigue crack propagation. The
first part of this paper is a review of the mechanisms affecting
fatigue life of high strength steel after welding. A literature
study on the current research in high strength steel and fatigue of
laser welds was made and is presented in the beginning sections of
this paper. The second part of the paper describes a method for
measuring fatigue crack propagation through laser welds with
constant stress intensity factor. The method is discussed based on
first measurement results.
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PROLAS 12
[17]:
THE INFLUENCE OF SHIELDING GAS ON THE PROPERTIES OF LASER WELDED
DUPLEX STAINLESS STEEL M. Keskitalo1,* ,K. Mäntyjärvi1, J.
Sundqvist 2, J. Powell2, A. F. H. Kaplan2 1University of Oulu, Oulu
Southern Institute, Pajatie 5, FI-85500 Nivala, Finland 2Luleå
University of Technology, Department of Engineering Sciences and
Mathematics, SE-97 451 Luleå, Sweden
*18]Corresponding author Tel.: +358407750337
E-mail address: [email protected]
Abstract
Some grades of duplex stainless steel employ nitrogen as an
alloying ingredient which
promotes austenite formation in welds and improves toughness.
During laser welding with
argon as the shielding gas, nitrogen can be lost from the weld
pool and this can have a
deleterious effect on weld toughness. This paper investigates
whether or not this effect can be
remedied by using nitrogen as the shielding gas during laser
welding. Preliminary results are
very promising. Increased austenite levels in the weld metal and
improved toughness levels
have been noted if nitrogen rather than argon is employed as the
shielding gas.
Keywords: laser welding, duplex stainless steel, shielding gas.
Nitrogen. Argon.
1. Introduction
This paper presents the results of an experimental program to
compare the hardness and
formability of Lean duplex stainless steel laser welds produced
with either Argon or Nitrogen
as the shielding gas. Duplex stainless steels are made up of a
combination of austenite and
ferrite and some grades of this material employ nitrogen as an
alloying ingredient which
promotes austenite formation in welds and improves toughness. In
standard laser welding,
using argon as a shield gas, nitrogen can be lost from the weld
pool and the austenite content
of the weld will be reduced. Kyröläinen and Lukkari (1999) and
the welding handbook of
Outokumpu Oyj (2010) has been noted that if the austenite
content of a weld is too low, this
can lead to nitride precipitation, which has a negative effect
on weld corrosion properties and
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PROLAS 13
[20]:
THE INFLUENCE OF SHIELDING GAS ON THE PROPERTIES OF LASER WELDED
STAINLESS STEEL
M. Keskitalo1, ,K. Mäntyjärvi1, J. Sundqvist 2, I. Eriksson 2,
A. F. H. Kaplan2 1University of Oulu, Oulu Southern Institute,
Pajatie 5, FI-85500 Nivala, Finland 2Luleå University of
Technology, Department of Engineering Sciences and Mathematics,
SE-97 451 Luleå, Sweden
Abstract
Argon is generally used as shielding gas for laser welding. As
Argon is an inert gas it does not have influence on the
microstructure of the weld material or on the heat input of the
weld, whereas nitrogen has solubility to austenite. Therefore
nitrogen as an interstitial atom increases the hardness of the
weld. This has been detected when comparing the hardness profiles
of nitrogen shielded welds of austenitic stainless steel with Argon
shielded welds. Nitrogen as the shielding gas can compensate the
softer structure of the weld in work-hardened and nitrogen-alloyed
steels. For the duplex stainless steel grades the nitrogen
additions promote formation of austenite in the weld, which
decreases the risk of lowered toughness. In this study the
influence of nitrogen shielding gas on the strength of the laser
weld has been examined. The strength of laser welds of nitrogen
alloyed work-hardened stainless steel seems to be slightly better
when using nitrogen shielding gas compared to welds for argon
shielding gas. It has also been verified that nitrogen as shielding
gas decreases the risk of weak toughness of laser welded duplex
stainless steel.
Keywords: laser welding, stainless steel, shielding gas
1 Introduction
Nitrogen alloying is used in order to increase the strength of
Austenitic stainless steel. The heat influence of welding can cause
a nitrogen loss of the weld. The study will determine the
influences of Nitrogen shielding gas on the hardness profiles of
the laser weld and also on the strength properties of Nitrogen
alloyed austenitic stainless steels. In addition the study will
compare the formability of Lean duplex stainless steel laser welds
which are welded with Argon and Nitrogen stainless steel. Low
austenite content of a weld can cause a nitride precipitation which
has a deleterious defect to the corrosion properties and toughness
[1]. The target of the study is to increase the austenite content
of the weld by using Nitrogen as shielding gas and backing gas [2].
The nitrogen as alloying element favours austenite according to
WRC-92 equations (1) and (2) [3]. Ni-ekv = %Ni+35*%C+20*%N+0,25*%Cu
(1) Cr-ekv = %Cr+%Mo+0,7*%Nb (2)
17. Keskitalo, M., K. Mäntyjärvi, J. Sundqvist, J. Powell, A. F.
H. Kaplan: The influence of shielding gas on the properties of
laser welded duplex stainless steel, submitted to Journal of
Materials Processing Technologies (2014).19. Eriksson, I., J.
Powell and A. F. H. Kaplan: Guidelines in the choice of parameters
for hybrid laser arc welding with fiber lasers, Proc. LIM, Munich,
Germany and Physics Procedia, v 41, pp 119-127 (2013).(further
journal publications are under preparation, in additional several
conference papers exist)21. Sundqvist, J., I. Eriksson, A. F. H.
Kaplan, M. Keskitalo, K. Mäntyjärvi, J. Granström, K.-G. Sundin:
Measuring the influence of laser welding on fatigue crack
propagation in high strength steel, Proc. ICALEO, Miami (FL), Paper
#2104 (2013).22. Sundqvist, J., I. Eriksson, A. F. H. Kaplan, M.
Keskitalo and K. Mäntyjärvi: Influence of the metallurgy on fatigue
crack propagation in welded high strength steel joints, Proc.
NOLAMP 14, August 26-28, 2013, Gothenburg/Sweden (2013).[17]:THE
INFLUENCE OF SHIELDING GAS ON THE PROPERTIES OF LASER WELDED DUPLEX
STAINLESS STEELAbstract1. IntroductionTHE INFLUENCE OF SHIELDING
GAS ON THE PROPERTIES OF LASER WELDED STAINLESS STEELAbstract1
Introduction
