| 1. |
- Kaplan, Alexander F.H, et al.
(författare)
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Microstructure morphology characterization of welding consumables studied by pulse-shaped laser heating
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 36, s. 184-191
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Tidskriftsartikel (refereegranskat)abstract
- During welding, wire consumables can essentially contribute to the resulting microstructures and mechanical properties. In order to maintain high toughness even for high strength steel, certain microstructures are desirable, particularly acicular ferrite. An efficient, controllable test method was developed during which the wire is molten and experiences a thermal cycle by a shaped laser pulse, or a sequence of pulses, which shall resemble continuous laser-arc hybrid welding or narrow gap multi-layer laser welding. Different thermal cycles and wire chemistries have led to manifold microstructures. The morphology of the microstructures can become complex. Therefore, more detailed characterization of essential morphology aspects was carried out, to distinguish different results. The thermal cycles from quenching have led to shorter, thicker laths with more random orientation. The latter can be favourable for high toughness. Short reheating cycles by about 200 K/s caused finer, longer and more parallel laths, as for bainite, in varying size of blocks. Other aspects considered were grain boundary ferrite and non-metallic inclusions. Systematic variation of the thermal cycle by the testing method along with systematic description of microstructure morphology in more detail is a promising method to identify and optimize favoured routes for wire chemistry and welding techniques.
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| 2. |
- Kaplan, Alexander F. H., et al.
(författare)
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Microstructures from wire-fed laser welding of high strength steel grades
- 2020
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 32:2
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Tidskriftsartikel (refereegranskat)abstract
- In welding, wire-feeding enables alteration of the resulting microstructure and, in turn, the mechanical behavior of the welded joint. For pipeline steel grades, very few commercial wires are matching at high strength and simultaneously ensure sufficient toughness. New wire chemistries need to be investigated. Promising consumable chemistries can be studied through metal cored wires. One promising concept is alloys that promote acicular ferrite instead of bainite. Interlocking instead of parallel laths can lead to higher toughness. In the gouge range of 15–19 mm, laser-arc hybrid welding has been studied for pipeline steel grades X80 and X100. For efficient mapping of various weld metal conditions, a simplifying “snapshot” method was developed. A pulse shaped laser beam melts wire pieces in a controlled manner, reproducing thermal cycles in welding. The weld metal tends to form bainite, but under certain conditions, complex microstructures with interlocking laths can be generated. Slow thermal cycles can lead to coalescence of the laths to coarser structures, while fast cycles favored finer structures and occasionally lath interlocking. The formation of acicular ferrite was difficult to achieve. Advanced wire chemistries lowered the hardness of the weld metal, as did preheating.
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| 3. |
- Robertson, Stephanie, et al.
(författare)
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Microstructural Effects of Controlled Dilution of High Strength Steel Wire into S960QL
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 36, s. 146-153
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Tidskriftsartikel (refereegranskat)abstract
- Controlled dilution experiments were conducted in a novel manner that allowed for precise dilution of base material into the wire consumables, enabling for a prompt analysis of microstructural trends as dilution is altered. Different heat cycles and cooling rates of the wire material, without base metal additions, were shown to cause different microstructures, varying from parallel plates to random or interlocking[SR1] orientation, with varying size of packets. The proposed method enables more controlled conditions with a known dilution value from mass percentages. Chopped filler wire is weighed and added to the base metal crucible, base metal chips are also weighed and added to the filler wire in specific mass percentages. A pulsed laser irradiates the metal, melting the mixture into a sample nugget. Lack of fusion is a benefit in this method as contamination from the base plate is negligible. The cooling rate is influenced by the pulse shape, and can be used to reheat the nugget, demonstrating the microstructural evolution in a complex thermal cycle. This method is demonstrated for S960QL steel with under-matched wire consumable, generally used for laser-arc hybrid processes to obtain high toughness, where a representative thermal cycle is needed. The thermal cycle is measured via a remote process, Dualscope, to evaluate the spacial temperature of the surface. The microstructures found using the snapshot method are similar to those found in the narrow gap multi-layer weld, different only in the size of the grains and packets.
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| 4. |
- Robertson, Stephanie, et al.
(författare)
-
Microstructures of high strength steel welding consumables from directed thermal cycles by shaped laser pulses
- 2020
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 109:9-12, s. 2653-2662
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Tidskriftsartikel (refereegranskat)abstract
- Filler wire metallurgy was modified through temporally shaped laser pulses, controlling cooling cycles in a recently developed method. Trends were identified through efficient mapping while maintaining representative thermal cycles of welding processes. A primary pulse melted preplaced filler wires while a secondary, linearly ramped-down pulse elevated the nugget to re-austenization temperatures. Ramped-down pulses resulted in linear cooling rates comparable with and exceeding furnace-based methods, between 50 and 300∘C/s. The linear decay of laser output power guided the temperature through a regime to obtain desired microstructures. For three very high-strength steel filler wire chemistries, quenching resulted in smaller plates with cross-hatched microstructures, accompanied by grain boundary ferrite. Finer bainite microstructures started forming for fast linear temperature decay, about 250∘C/s. Slower decay or a weaker third cycle formed coarser microstructures with coalescent sheaves and less cross-hatching.
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| 5. |
- Volpp, Joerg, et al.
(författare)
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Toughness properties at multi-layer laser beam welding of high-strength steels
- 2021
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Ingår i: Welding in the World. - : Springer. - 0043-2288 .- 1878-6669. ; 65:1, s. 143-155
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Tidskriftsartikel (refereegranskat)abstract
- The material characteristics of high toughness and high strength in steel are usually not available at the same time. However, it would be an advantage if high-strength steels would show high impact toughness also at lower temperatures for applications in critical surroundings. In this paper, an approach of multi-layer welding of high-strength steel is presented in order to increase the weld-metal toughness using wire material in combination with thermal cycle modifications. Promising interlocking microstructures were found after multiple tempering of the previously applied structure at homogeneously distributed material in the weld seam. It was found that short thermal cycles during laser processing lead to insufficient time for carbon diffusion, which leads to remaining ferrite structures in contrast to the prediction of welding transformation diagrams. The additionally applied heating cycles during multi-layer laser welding induce the formation of interlocking microstructures that help to increase the weld seam toughness.
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