| 1. |
- Akselsen, Odd M., et al.
(författare)
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A first assessment of laser hybrid welding of 420 mpa steel for offshore structure application
- 2013
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Ingår i: 14th NOLAMP Conference. - Luleå : Luleå tekniska universitet. - 9789174396881 - 9789174396898 ; , s. 171-182
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For many years, laser hybrid welding has been used in various industries to increaseproductivity and reduce costs. One example is the adaption of the hybrid process inshipbuilding. The next natural step is to further develop the process for the oil and gasindustry, where the welded joint properties requirements are more severe, and the ability tohandle tolerance deviations is more critical. As a first attempt to develop hybrid laser processfor the use in offshore structures, the present investigation addresses preliminary weldingtrails carried out with 15 kW fibre laser with appropriate gas metal arc welding equipment,using double Y joint geometry and 20 mm thick 420 MPa steel plates. The subsequent weldtesting included both Charpy V notch impact and CTOD fracture mechanical testing at -30°C.The results indicate that the heat affected zone (HAZ) of the examined steel appeared withsatisfactory Charpy and CTOD toughness (> 200 J, > 0.2 mm) while the weld metal hadinsufficient toughness (20-40 J, < 0.2 mm). With a better welding wire, designed for lowtemperature applications, it is reasonable to suggest that laser hybrid arc welding can be usedfor applications even below a temperature of -30°C.
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| 2. |
- Akselsen, Odd M., et al.
(författare)
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Effects of phase transformations on residual stresses in welding of stainless steels
- 2007
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Ingår i: International Journal of Offshore and Polar Engineering. - 1053-5381. ; 17:2, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, we investigate the effects of solid state phase transformation on residual stresses in welding super-martensitic stainless steels, using the Satoh experimental test approach. The results obtained clearly demonstrate that the austenite-to-martensite phase transformation has remarkable effects on the final tensile residual stress level, and stresses as low as 70 to 170 MPa were found, depending on the weld thermal program. These results may imply that unnecessary conservatism is often used when assuming residual stresses to be of the same order as the base metal yield strength.
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| 3. |
- Akselsen, Odd M., et al.
(författare)
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Weld metal mechanical properties in hyperbaric GTAW of X70 pipeline
- 2006
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Ingår i: International Journal of Offshore and Polar Engineering. - 1053-5381. ; 16:3, s. 233-240
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Tidskriftsartikel (refereegranskat)abstract
- In the present investigation, 2 different wires for hyperbaric (underwater) GTA (gas tungsten arc) welding of X70 pipelines have been tested with respect to their weld metal mechanical properties. Welding of full coupons at different pressures (seawater depths of 16, 75 and 200 msw) was done with subsequent weld metal chemical analyses, hardness measurements, tensile testing and Charpy V notch testing as well as microstructure characterization. It is shown that both wires satisfied strength requirements set to X70 grade, representing a weld metal overmatch situation. Both wires gave sufficient impact toughness, but the toughness of the Ni-Mo containing weld was reduced with increasing seawater depth. This observation was strongly linked to the positioning of the Charpy V notch, and crack growth in a brittle, partially transformed region as a consequence of reheating by subsequent stringer beads. The embrittling microstructure consisted of high carbon MA (martensite-austenite constituents islands) decorating prior austenite grain boundaries. This microstructure was less pronounced when welding with the high Ni wire, which may explain why no similar toughness drop was found.
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| 4. |
- Bunaziv, Ivan, et al.
(författare)
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Deep penetration fiber laser-arc hybrid welding of thick HSLA steel
- 2018
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 256, s. 216-228
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Tidskriftsartikel (refereegranskat)abstract
- The present investigation addresses laser-arc hybrid welding of 45 mm thick steel with variation in a wide range of process parameters. High volume fraction of acicular ferrite formed in the upper part of the weld metal regardless process parameters. Significantly lower fraction of acicular ferrite was found in the root due to substantially increased cooling rates and the inability to deliver filler wire to this region, resulting in bainite-martensite microstructures in the root. The delivery of filler wire to the root can be enhanced by increasing the air gap between the plates. Higher heat inputs reduce cooling rates in the root which create softer and ductile microstructures, at the expense of a much wider and coarser grained HAZ. The results obtained showed high fusion line and weld metal toughness at low temperature (−50 °C).
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| 5. |
- Bunaziv, Ivan, et al.
(författare)
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Filler metal distribution and processing stability in laser-arc hybrid welding of thick HSLA steel
- 2020
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Ingår i: Journal of Manufacturing Processes. - : Elsevier. - 1526-6125. ; 54, s. 228-239
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Tidskriftsartikel (refereegranskat)abstract
- Welds made by high power laser beam have deep and narrow geometry. Addition of filler wire by the arc source, forming the laser-arc hybrid welding (LAHW) process, is very important to obtain required mechanical properties. Distribution of molten wire throughout the entire weld depth is of concern since it tends to have low transportation ability to the root. Accurate identification of filler metal distribution is very challenging. Metal-cored wires can provide high density of non-metallic inclusions (NMIs) which are important for acicular ferrite nucleation. Accurate filler distribution can be recognized based on statistical characterization of NMIs in the weld. In the present study, it was found that the amount of filler metal decreased linearly towards the root. The filler metal tends to accumulate in the upper part of the weld and has a steep decrease at 45–55 % depth which also has wavy pattern based on longitudinal cuts. Substantial hardness variation in longitudinal direction was observed, where in the root values can reach > 300 HV. Excessive porosity was generated at 75 % depth due to unstable and turbulent melt flow based on morphology of prior austenite grains. The delicate balance of process parameters is important factor for both process stability and filler metal distribution.
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| 6. |
- Bunaziv, Ivan, et al.
(författare)
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Hybrid Welding of 45 mm High Strength Steel Sections
- 2017
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Ingår i: Physics Procedia. - : Elsevier. - 1875-3892. ; 89, s. 11-22
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Tidskriftsartikel (refereegranskat)abstract
- Thick section welding has significant importance for oil and gas industry in low temperature regions. Arc welding is usually employed providing suitable quality joints with acceptable toughness at low temperatures with very limited productivity compared to modern high power laser systems. Laser-arc hybrid welding (LAHW) can enhance the productivity by several times due to higher penetration depth from laser beam and combined advantages of both heat sources. LAHW was applied to join 45 mm high strength steel with double-sided technique and application of metal cored wire. The process was captured by high speed camera, allowing process observation in order to identify the relation of the process stability on weld imperfections and efficiency. Among the results, it was found that both arc power and presence of a gap increased penetration depth, and that higher welding speeds cause unstable processing and limits penetration depth. Over a wide range of heat inputs, the welds where found to consist of large amounts of fine-grained acicular ferrite in the upper 60-75% part of welds. At the root filler wire mixing was less and cooling faster, and thus found to have bainitic transformation. Toughness of deposited welds provided acceptable toughness at -50 °C with some scattering.
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| 7. |
- Bunaziv, Ivan, et al.
(författare)
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Laser-arc hybrid welding of thick HSLA steel
- 2018
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 259, s. 75-87
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Tidskriftsartikel (refereegranskat)abstract
- A standard laser-arc hybrid welding (S-LAHW) and LAHW with preplaced cut wire inside the groove before welding were studied and compared. The S-LAHW setup revealed problems with filler wire delivery to the root, resulting in substantial hardness increase due to bainitic-martensitic transformation. The applied finite element modelling confirmed significant cooling rate increase in the root area for deep penetration welds. Preplacement of cut wire prior to welding reduced hardness providing improved welds with higher homogeneity. This method was subsequently applied for multi-pass welding that revealed insufficient nucleation of acicular ferrite on non-metallic inclusions (NMIs). It is implied that a critical cooling rate has been exceeded where the NMIs become inactive, resulting in a microstructure consisting of a martensite and bainite mixture. This kind of microstructure is clearly harmful for the weld metal toughness.
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| 8. |
- Bunaziv, Ivan, et al.
(författare)
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Porosity and solidification cracking in welded 45 mm thick steel by fiber laser-MAG process
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 36, s. 101-111
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Tidskriftsartikel (refereegranskat)abstract
- Porosity and solidification cracking in joining of thick sections are very common issues in deep penetration keyhole laser-arc hybrid welding (LAHW). In the present work, 45 mm thick high strength steel was joined by a double-sided technique. With combined use of fast welding speeds and larger air gap between plates, higher amount of porosity was found because of the dynamic behavior of the keyhole walls. Solidification cracking formed at the centerline in the bottom of the weld due to high-depth-to-width geometrical ratio. Numerical simulations have been performed and showed very high cooling rate and stresses occurred in the root of the deep welds, which corresponds with higher cracking tendency.
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| 9. |
- Bunaziv, Ivan, et al.
(författare)
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Process stability during fiber laser-arc hybrid welding of thick steel plates
- 2018
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Ingår i: Optics and lasers in engineering. - : Elsevier. - 0143-8166 .- 1873-0302. ; 102, s. 34-44
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Tidskriftsartikel (refereegranskat)abstract
- TThick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources.
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| 10. |
- Bunaziv, Ivan, et al.
(författare)
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The penetration efficiency of thick plate laser-arc hybrid welding
- 2018
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 97:5-8, s. 2907-2919
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Tidskriftsartikel (refereegranskat)abstract
- Double-sided fiber laser-arc hybrid welding was used to join 45 mm thick high strength steel over a wide range of parameters in order to investigate the efficiency of the process. Air gap size, I- and Y-groove type preparation, pulsed and cold metal transfer pulsed arc modes, arc-laser setup, and travel speeds were compared, and in all cases, sufficient filler material was provided to fully fill the gap. The welds were investigated using high speed imaging and cross-sectional analysis to identify penetration depths, morphology, and imperfections. Larger joint air gaps were found to contribute most to weld penetration depth. Surprisingly, increased line energy decreased penetration efficiency in most cases. The laser-arc interdistance was also investigated, revealing an arc size and melt flow dependency for achieving higher penetration depth for a leading arc. It was found that, although penetration can be optimized, solidification cracking can be a limiting factor in the application of deep penetration hybrid welding for thick steel section joining.
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