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.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
1 Introduction
Systematic study of weld wire consumable microstructures subjected to unique thermal cycles during welding is desirable for improved understanding of underlying mechanisms. The weld metal and heat-affected zone (HAZ) show large changes in microstructural composition after welding, even over small distances, due to region-specific thermal histories. Chemical variations between specific microstructural regions present challenges for mechanism identification.
High-strength steel filler wires are investigated here, aiming to achieve high toughness with improved understanding and advanced chemical concepts. Particular focus is given to quenched and tempered (Q+T) steels with yield strengths above 960 MPa where there are few appropriate filler materials. These grades of steel are applied in thicknesses greater than 8 mm, challenging thicknesses for single-pass laser keyhole welding. Advanced methods for welding 50-mm-thick high-strength low-alloy (HSLA) steel include double-sided gas metal arc welding (GMAW), studied by Chen et al. [1]; however, this is only applicable where access to both sides of the sheet are possible. When this is not possible, multi-layer techniques can be used, such as the multi-layer technique developed and optimized by Li et al. [2] for 30-mm-thick steel plates. However, each weld pass experiences multiple and varied thermal cycles with dissimilar cooling rates. Overlapping of pulsed laser exposure was studied in detail by Chatterjee et al. [3], with detailed analysis of microstructures in laser beam–welded dissimilar metals [4, 5].
Kurc-Lisiecka and Lisiecka [6] studied rapid cooling rates, generated by low thermal inputs, with t8/5 times ranging between 0.6 and 1.3 s. These cooling rates yielded microstructures of allotriomorphic ferrite (α), polygonal ferrite (αl), fine-grained upper and lower bainite (αb, αlb), and martensitic islands (α’). Acicular ferrite (αa) is associated with increased toughness, and was described by Loder et al. [7] to compete with bainite formation in the presence of non-metallic inclusions (NMI). Fattahi et al. [8] found NMIs with a minimum diameter of 0.2 μ m to be favorable, while Sarma et al. [9] found that 10–36% of inclusions at this size started αa-nucleation. Acceptable mechanical properties of welded R4 grade steel were reported by Jorge et al. [10], with tensile strengths of the weld metals obtaining up to 860 MPa. The influence of NMIs on the mechanical properties and workability of down-stream processes was evaluated by Gupta et al. [11]. The microstructure of a GMAW, for a heat input of 1.8 kJ/mm and a post weld heat treatment of 600∘C for 2 h, consisted of tempered α’ and α; the Mn and Cr content was higher than the here studied consumables, while the C and Si content was lower. The thermal cycles that result from multi-pass techniques affect the microstructure through two temperature-dependent mechanisms, recrystallization or grain growth. The final shape, size, and type of grains were found by Liu et al. [12] to be influenced by multiple thermal cycles.
Pipe-line steels grades (of at least grade X80) face similar challenges with microstructures and toughness behavior of weld metals in cold climate operations, below − 60∘C. GMAW of X80 at a traveling speed of 5 m/min was demonstrated by Midawi et al. [13] using two similar consumables chemistries to the here studied pipeline wire consumable. Their wire contained lower amounts of Mn and Ni. The weld diluted 30% with a primarily interlocking αa microstructure with NMIs detected. Grain boundary α was observed with a fraction of αI. When cooling rates of 20–30∘C/s occur, desirable acicular microstructures can be achieved, avoiding αI and α, with similar results found by Tang and Waldo [14]. Keehan et al. [15] found that cooling times of t8/5 = 3 − 13 s changed a mainly αlb and α’ mix with interspersed coalesced bainite to a relatively fine αb and αlb mixture. Tang and Waldo [14] enhanced αa formation with increased Mo concentrations, with dual parallel lath αa, while Madariaga et al. [16] showed increased volume fractions of αa using two-stage cooling with lower cooling rates.
Competitive formation of α, αl, and αW is repressed by Ti-based inclusions, which was determined by Blais et al. [17]. Lee et al. [18] found that Ti-oxide, Ti oxysulfide, and Ti-Ca-oxysulfide inclusions can influence austenite (γ) grain size, and inclusion density. Jung et al. [19] studied migration of boron to grain boundaries in relation to increasing NMI nucleation potential. Zhang et al. [20] found a lower degree of mismatching between the nucleants and the crystal structure, resulting in higher nucleation potential of Ti inclusions containing O and N. Kang et al. [21] observed a Mn depleted zone (a result from the short diffusion range of Mn) with increased amounts of Ti inclusions, which enhanced αa nucleation.
Microstructures can be tailored from the melt directly or through thermal post-heat treatments, altering an existing microstructure. The primary is exemplified by a furnace-melted homogeneous sample subjected to heat treatment, having the transient metallurgy during cooling being observed in situ (recording at 15 fps) by a laser scanning confocal microscope, demonstrated by Wan et al. [22], or by a ceramic-covered steel substrate dipping technique shown by Loder and Michelic [23]. Tempering post-processing heat treatments have been studied by Noureddine and Allaoui [24], showing improved mechanical properties in X70 HSLA weldaments. A post-welding heat treatment approach was studied with Gleeble systems, which are advanced thermal cycling equipment, utilized by Moeinifar et al. [25] to emulate multi-layer depositions thermally. Similarly, Fu et al. [26] investigated the changes of the microstructures for specific thermal treatments. The ability to isolate the thermal behavior is of significant importance to many fields, particularly in additive manufacturing that also is highly dependent on high quality parts. In additive manufacturing, Yan et al. [27] studied and identified the thermal signatures that lead to characteristic microstructures and deformations.
Applications using filler wire material cannot be directly modelled in the above manner. Microstructural alterations can be achieved with extended cooling cycles, special wire chemistries, or through multiple thermal cycling, which are hereby demonstrated using the “Snapshot” method. Filler wire characterization is typically done via multiple, wide GMAW tracks, for extraction that is then mechanically tested, e.g., via tensile and Charpy V-notch tests. The link from thermal cycles to microstructures is not provided by this method, and further, the sample is composed of heterogeneously mel- ted wire under multiple heating cycles. Lalam et al. [28, 29] created a neural network of weld metal properties in litera- ture to initiate linking of mechanical properties (understood on a qualitative basis) of ferritic steel welds to the condit- ions that they experience, described as dependencies of chemistry, thermal input, and post weld heat treatment.
Robertson et al. [30] recently developed a proficient tech- nique for investigating filler wire microstructures, designa- ted as the “Snapshot” method, by drilling a pocket into a me- tal plate, inserting cut wire lengths, and fusing a sample nug- get by laser beam exposure. The thermal cycle is expected to be representative of seam welding. This approach easily provides alternatives via temporal shaping of the laser pulse to achieve customized thermal cycles, even multiple cycles.
Thermocouples, pyrometers, or thermal imaging can measure the thermal history experienced at a specific position of the welded metal, with limitations as explored by Sundqvist et al. [31]. Here, for the Snapshot method, it was preferred to apply a technique known as Dualscope, based on high-speed imaging (HSI) where the camera image is split into two domains, each recording the process in a different spectral window, which enables the unknown emissivity to be cancelled out when deriving the temperature field. Similar methods are being developed, like those used by Devesse et al. [32], with progression of more accurate emissivity identification. Emission-based measurements are limited to surface temperature measurements, while Abderrazak et al. [33] employed computation fluid dynamics to predict volumetric temperature fields. During welding, complex melt pool convections can alter the temperature field, as was observed by Sundqvist et al. [31], depending on the driving forces like Marangoni convection accelerated by surface tension gradients or flow initiated by laser-induced ablation pressure. Chemical inhomogeneity of the weld metal arises from base metal diluting into the wire material. Investigations on the effect of pulse shape variants, and hence the thermal history, on the microstructure were examined for laser spot welding, employing combinations of ramping laser power, as demonstrated by Bertrand and Poulon-Quintin [34] in the use of dissimilar metals in dental applications.
Here, wire consumables for the high-strength structural steel S960QL of yield strength > 960 MPa and of pipeline grade X80 are studied. These steels are typically used with welding techniques like laser arc hybrid welding (LAHW) and narrow gap multi-layer welding (NGMLW) due to their lower cooling rates than GMAW. The recently developed efficient Snapshot technique is demonstrated here for the first time for systematic study of microstructure trends depending on different thermal cycles. To the knowledge of the authors, no method exists to mimic welding processes from granular components for metallographic studies at heating and cooling rates comparable with laser beam welding. Thermal cycles that are representative of many welding techniques (i.e., laser beam welding and narrow gap multi-layer welding) in a stationary manner were achieved with the use of long exposure to laser beam radiation. The modulation of the laser power was assumed to replicate the moving heat source in traditional welding, allowing for a more gradual cooling rate.
2 Methodology
The highly efficient Snapshot method is a technique that was originally demonstrated for observation of microstructural evolution originating from characteristic laser pulse–driven thermal cycles, see Fig. 1. Shaping the laser pulse, exhibited by Robertson et al. [30], alters the thermal cycle in a manner that is representative of welding methods that use filler wire. The wire and base metal can be processed together to observe material mixing, and microstructures for a unique thermal cycle, or the individual materials can be processed individually to determine their individual impacts for the processing cycle. The Snapshot method offers the opportunity to study weld metal microstructures in the solid phase, starting from austenization temperature. The application can, in principle, be applied for any welding technique and even other steel-processing techniques, e.g., additive manufacturing or heat treatment. The Snapshot method is particularly suitable for laser welding techniques because it achieves high cooling rates. Extended temporal pulsing was used previously to tailor the microstructure of the weld metal from the molten state, where it has been adapted further here to mimic multi-cyclic processes.
Here studied are two commercially available solid HSLA steel filler wires, provided by the wire manufacturing company Lincoln Electric. The wires are designated as LNM MoNiCr (EN ISO 16834-A: G Mn4Ni2CrMo), an under-matched wire for Q+T steel S960QL, and as LNM MoNiVa (EN ISO 16834-A: G M Mn3Ni1CrM), an over-matched wire for pipeline steel X80. In addition, a novel, developmental metal-cored wire was investigated, LNM MoNiCr-9X. This filler wire demonstrated a very high impact strength for its higher alloying content. All filler wires are designed to provide high toughness, with the investigation of improving mechanical properties by altering microstructural composition via thermal cycle tailoring. The chemical composition and mechanical properties of the base metals and associated filler wires are found in Tables 1 and 2, respectively.
Holes were drilled into 12-mm-thick sheets of S960QL steel with a diameter of 5.5 mm and a depth of 7 mm, as shown in Fig. 1(a). All of the wires had a diameter of 1.2 mm and were shortened to 8 mm lengths. Each hole contained 16 acetone cleaned wire pieces that were vertically inserted. The wires were arranged to tightly pack the cavity and reduce the voids between the wires. Excess wire above the cavity rim was ground flush to the base plate to provide a flat processing surface for the laser beam. A continuous wave (cw) IPG YLR-15000 Yb:fiber laser (1070 ± 10 nm wavelength) with a nominal output power of 15,000 W produced the laser beam. Optionally, the laser beam can be operated in pulsed mode with pulse lengths > 200 μ s. A 400-μ m-diameter processing fiber guided the beam into a Precitec YW52 optics by which it is focused (beam parameter product, BPP, 14.6 mm⋅mrad). The collimating and focusing lenses had focal lengths of 150 mm and 250 mm, respectively. Selected optical parameters of both the laser source and the optics are given in Table 3.
The laser beam was defocused by setting the focal plane 5 mm above the plate surface for the melting, square pulse (PS) and 45 mm for the subsequent reheating pulse (PRhI - PRhIV). The beam diameters, measured at the plate surface, were approximately 0.8 mm and 4.0 mm, respectively. The chosen beam diameters ensured melting of the loose wires in the first step and avoiding remelting in the subsequent steps. Argon was utilized as the protective gas, to reduce surface oxidation, with a flow rate of 18 l/min. The step-by-step outline of the process is given in Table 4.
The pulse PS is a square pulse of 2 kW for 8 s, see Fig. 1(b), which causes self-quenching conditions similar to those laser beam welding, yielding a solid nugget sample. These pulse parameters were chosen to promote melting of the wire material while avoiding fusion with the base metal. The Snapshot method can be altered in duration to allow for fusion and mixing the filler wire with the base metal. After reaching ambient conditions, a reheating pulse (PRh) was applied to sufficiently increase the nugget temperature, while remaining solid, to either recrystallize new γ-grains (if exceeding austenizing temperature A3) or to temper the microstructure. Linear decrease of the pulse power is antici- pated to linearly decrease the surface temperature. The above conditions are a part of a larger, systematic study of 88 combinations of pulse shapes, materials, and dilution rates.
Four pulsing cases designated by PRh (Fig. 1(b)) were studied with the parameters given in Table 5. The pulse shapes chosen here were assumed to have a similar thermal cycle to that of a moving heat source as seen in other welding methods. The use of a single or multiple pulses with various shapes offers many tailoring options for obtaining a particular thermal cycle strategy. The presented case utilizes a square pulse to generate an undiluted weld nugget that is convenient for further thermal processing. The square nature of the pulse yields a quenching cooling cycle that is representative to laser beam welding. The secondary pulse with decayed output power (ramped-pulse) simulates a reduced heat flux as in slower welding processes like arc welding or multi-layer processes. The gradient of the power decrease would then reflect on the speed at which the heat source would travel away from the measured point. The ramped-pulse also presents the opportunity to obtain austenization temperatures followed by linear cooling to a lower temperature, to enable controlled temperature conditions, like the thermal cycles that are used in furnaces to observe the formation of some microstructures.
For the demonstrated case, the initial square pulse fuses the only filler wire as in traditional wire-based processes with the option to fuse the filler material to the base metal (though it is not necessary). When only the wire material is processed, a case where the lack of fusion between the nugget and the substrate is the aim, it can be assumed that there is no change to the chemical composition of the wire material. This provides a controlled composition of material to be thermally processed. Additionally, if the material is not fused to the substrate, but is in contact with it, it is assumed to have representative heat conductive environment as a weld. In the presented case, the first pulse provides controlled chemical conditions by melting wire pieces to a nugget, and the second pulse provides controlled heat treatment. The second pulse (and additional pulses, mimicking multiple thermal cycles) does not melt the nugget but it exceeds the austenization temperature, assuming to restart and carry out controlled microstructure development, by a controlled cooling cycle, e.g., a linear decay.
A second reheating pulse was also investigated, PRh2, with the same parameters as PRhIV, after ambient conditions are obtained. For PRh2, the beam is transposed 2 mm off-axis from the original center, to spatially generate manifold thermal cycle combinations across a single nugget. This arrangement will alter the microstructure further through region-specific thermal treatment. Micrographs from nugget cross sections were obtained using optical microscopy methods in two locations, the center of the nugget and the top surface, for analysis of observed microstructure morphologies. A cold wire addition, laser-welded joint was made using a NGMLW technique. The sample was composed of 30-mm-thick S960QL (the same batch as used in the Snapshot method) with machined edges having a gap of 4 mm that was first butt-joint welded by autonomous laser beam welding at the 2-mm nose to prevent root humping (or root sagging). The same laser source was used, with comparable optics of the same focusing lengths (Table 3). Then, 1.2-mm-diameter LNM MoNiCr weld wire with a feed rate of 3.8 m/min was fed into the gap, using 6 kW continuous wave laser output power, traveling at a speed of 1.2 m/min to produce layer heights of approximately 1 mm. The laser beam was defocused to a spot diameter of 4.5 mm to ensure laser beam interaction with the sheet edges. The weld metal was then sampled and prepared using metallographic procedures for microstructural evaluation to then be compared with the Snapshot method.
The Dualscope method with HSI was utilized to record the thermal cycles. This device splits the image from the camera (RedLake Mono N4-S2, operated at 1000 fps, exposure time 30 μ s, resolution 260 μ/px) into a left hand and right hand image. Each side has a unique bandpass filter (width 40 nm), the left a 680 nm and the right a 769 nm. Based on Planck’s law and from a calibration curve via a sample in a furnace, the temperature is calculated. For the presented case, the temperature is calculated per pixel and time step, from the ratio of the grayscale values between the filtered right hand and left hand images. The Dualscope method has advantages compared with other measurement methods, like that it is contactless or that it reduces the uncertainty of the emissivity. The Dualscope, however, has limitations in the temperature range (for the most reliable range, 700–1200∘C was chosen, via exposure time) and is dependent on certain conditions, like saturation.
3 Results and discussion
The most significant microstructure trends of this first systematic Snapshot study are presented and discussed here, with respect to the aforementioned goals for enhancing the weld metal properties of high-strength steels. The results are provided in three sections: the microstructural analysis, the thermal analysis, and the comparison of Snapshot and NGMLW microstructures.
3.1 Microstructural analysis
Three wire types were used in this study: LNM MoNiCr, LNM MoNiVa, and LNM MoNiCr-9X. In Fig. 2(a, b), multi-layer GMAW microstructures (heat input 1.2 kJ/mm) are shown for LNM MoNiCr and LNM MoNiVa wire consumables as a reference to the microstructures produced by the Snapshot method. The cross-hatching microstructures indicate significant amount of αa, which is desirable for high toughness. Figure 2(c, d) shows a typical microstructure from the Snapshot method (at two magnifications, here for LNM MoNiCr-9X, by PRhI), tending to packages of parallel plates, oriented perpendicular to each other.
Figure 3 depicts natural quenching microstructures, PS, compared with reheating PRhI and PRhIV, for LNM MoNiCr, Fig. 3(a–c), and for LNM MoNiCr-9X, Fig. 3(d–f). Representative areas i–iii are highlighted.
Plate-like structures are seen in all micrographs, marked by area i, with conglomerates of plates into single packages in area ii. The plates occur either in a parallel arrangement, iii in Fig. 3(a), or in 60∘ orientations, iii in Fig. 3(d). For PRhI the plates become finer than for PS. In the case of PRhIV (Fig. 3(c, f) iii), the plates grew into each other (conglomeration) to join into a larger block, though in some regions it is still possible to see the secondary plates grow from a primary plate. The perpendicular cross-hatching of the secondary plates and primary plates is exemplified in iii of Fig. 3(e), an indicator of αa. Micro-alloying elements in the filler material allow for interlocked dendritic structures to form, even for grain refinement in prolonged cooling conditions. Both wires were designed for high toughness and as such tend to form a combination of \(\alpha ^{\prime }\), bainite, and in sufficient cooling times, αa. High toughness can be expected from the interlocking structures found in both the natural quenching and the reheated samples. The enveloped dark phase appears to be NMIs. Larger segregations of dark phases appear to be martensitic in nature and are likely α’ islands left from the transformation process, or αlb. The higher alloyed wire LNM MoNiCr-9X behaved similar to LNM MoNiCr, with a slight tendency to more interlocking, finer plates, and smaller packages.
Micrographs of the processed pipeline wire are shown in Fig. 4. For quenching, thick, short plates (typically 2–4 μ m wide, 5–15 μ m long) were formed, in iii in Fig. 4(a), mostly interlocking, accompanied by αgb, ii (up to 10 μ m thick) and by NMIs. PRhIV (Fig. 4(b)) leads to fine plates (less than 1 μ m thin, 15–20 μ m long), to a lesser extent interlocking (often as a singlet or doublet plate), i, and partially parallel, iii, with less αgb, ii (rather 3–5 μ m thin).
A weaker second reheating pulse (Fig. 4(c)) shows mainly parallel plates, ii, about 1 μ m thin but coagulating to larger structures, i, in distinct blocks, while hardly any more grain boundaries can be seen, indicating tempering without re-austenization. All samples show that a combination of pa- rallel and cross-hatched plates is formed, though to different extent. For all three wire materials, for the reheating cycles, the trend favors parallel (on cost of interlocking) plates that join to form conglomerates with extended heating.
Scanning electron microscopy (SEM) was used to further highlight some of the microstructural differences between pulse PRhI and pulse PRhII (Fig. 5) for the LNM MoNiVa filler wire. For the shorter pulse, PRhI Fig. 5(a), the bainitic plates are very parallel and narrow. Plate widths are approximately 1 μ m while several microns long. In the longer pulse, PRhII Fig. 5(b), the plates begin to coalesce into larger structures, with widths between 3 and 5 μ m. The large coalesced structures are nearly absent in higher magnification of Fig. 5(c) while a number of the coalesced structures are observed in Fig. 5(d). As was seen with optical microscopy, the longer pulse cycle lead to a coarser structure, with wider needles, coalesced grains, and more acicular structures.
3.2 Thermal analysis
The surface of a processed nugget is seen in Fig. 6(a). The temperature measurement during natural quenching typically led to surface temperature fields as seen in Fig. 6(b, c). Figure 6(d) shows a typical cooling cycle of the nugget surface after PS, slowing down. Figure 6(e) shows the thermal cycle during PRhI, showing an increase of the temperature (above A3, meaning recrystallization is realized), followed by an equilibrium/plateau and linear cooling.
Not measured but extrapolated is the subsequent quenching, towards martensite transition temperature, Ms. The measured linear cooling at (within limits) constant cooling rate is evidence of temperature control proportional to linear laser power ramp down, to generate a corresponding microstructure, systematically by the Snapshot method. More complex pulses could lead to a cooling cycle that is guided past the MS temperature, demonstrating complete control of the tailoring of the microstructure, even extension of a time spent at a given temperature.
3.3 Comparison of snapshot and NGMLW microstructures
The four chosen pulse cycles (the combination of the square pulse and the ramping pulse) were used to generate different conditions that are present in a NGMLW. The resulting microstructures from the Snapshot method are then compared with the microstructures that were generated in a NGMLW using materials from the same batch, both the base material and filler wires.
The here generated microstructures show different morphology aspects than αa-based microstructures in literature. The latter result from a vast amount of arc welding and Gleeble studies, mainly for lower strength wires and mostly for cooling rates in the range of 1–30∘C/s (for t8/5), exceptionally up to 50∘C/s. Here the metal experienced 50–300∘C/s, representative for fast laser-based techniques like laser arc hybrid welding, causing typically 60–700∘C/s.
Comparison of the microstructures found in the Snapshot method with a NGMLW shows similarities in the morphologies of the formed microstructures (Fig. 7). The composition of the NGMLW and the Snapshot is made up of bainites, ferrites, and martensite. The cross-hatching of microstructures has a tendency to increase toughness, while coalescenced and tempered microstructures often yield lower impact toughness. The first, unpublished, mechanical testing of the NGMLW confirms this trend. The highlighted regions in Fig. 7 show where the morphologies of selected microstructures are similar, though the size of the grains and packets is different. Characterization of the morphologies is discussed further by Kaplan et al. [35], in a co-current work of the Snapshot method. This can be contributed to different cooling rates of the sampled Snapshot method to the weld cap for this particular NGMLW sample. Using other pulse shapes to obtain different cooling rates would then be able to replicate different sections of a large weld for microstructural evaluations.
4 Conclusions
A new, highly efficient method for testing filler wire material under controlled thermal cycling was proposed in this paper. Temporal pulse shaping yielded linear cooling rates of the weld metal, further providing varied microstructural compositions. The major findings are summarized as follows:
-
1.
A recently developed testing method was demonstrated to enable an efficient, systematic study of the impact of tailored thermal cycles on the microstructure of welding consumables, to be replicated in the welding process.
-
2.
Linear ramp down of laser power enabled the decrease of surface temperature in a linear manner, at constant high cooling rate in the range 50–300∘C/s, hence much faster than furnace-based methods and even including the molten state.
-
3.
For the new highly alloyed consumable and the two commercial steel wires at their respective application strength limit, the main trends were similar; fast quenching of typically 200∘C/s has caused short, thicker plates of widely random orientation, which can be favorable for high toughness.
-
4.
Fast cooling at constant rate in the range 200–300∘C/s caused more parallel, thinner plates, indicating bainite, while four times slower cooling generated coarser packets in which plates coagulated, even more pronounced for a weaker third pulse.
-
5.
Systematic representative mapping and improved under- standing through the Snapshot method can facilitate optimization of the filler wire chemistry, welding processes, and hence the generated weld metal properties.
-
6.
Comparable microstructural components were obser- ved between the Snapshot method and a NGMLW ha- ving the same material composition.
References
Chen Y, Yang C, Chen H, Zhang H, Chen S (2015) Microstructure and mechanical properties of HSLA thick plates welded by novel double-sided gas metal arc welding. Int J Adv Manuf Technol 78:457. https://doi.org/10.1007/s00170-014-6477-0
Li R, Wang T, Wang C, Yan F, Shao X, Hu X, Li J (2014) A study of narrow gap laser welding for thick plates using the multi-layer and multi-pass method. Opt Laser Technol 64:172. https://doi.org/10.1016/J.OPTLASTEC.2014.04.015
Chatterjee S, Mahapatra SS, Bharadwaj V, Upadhyay BN, Bindra KS, Thomas J (2019) Parametric appraisal of mechanical and metallurgical behavior of butt welded joints using pulsed nd:YAG laser on thin sheets of AISI 316. Opt Laser Technol 117:186. https://doi.org/10.1016/j.optlastec.2019.04.004
Chatterjee S, Sahoo SK, Swain B, Mahapatra SS, Roy T (2020) Quality characterization of dissimilar laser welded joints of Ti6Al4V with AISI 304 by using copper deposition technique. Int J Adv Manuf Technol 106(9-10):4577. https://doi.org/10.1007/s00170-020-04935-5
Chatterjee S, Kumar Pandey A, Sankar Mahapatra S, Singh Arora K, Behera A (2020) Microstructural variation at interface during fiber laser joining of NiTi/Ti6Al4V and effect of mechanical strength. J Mater Process Technol 282:116661. https://doi.org/10.1016/j.jmatprotec.2020.116661
Kurc-Lisiecka A, Lisiecki A (2017) Laser welding of the new grade of advanced high-strength steel Domex 960. Mater Technol 51(2):199. https://doi.org/10.17222/mit.2015.158
Loder D, Michelic SK (2017) Systematic investigation of acicular ferrite formation on laboratory scale. Mater Sci Technol 33(2):162. https://doi.org/10.1080/02670836.2016.1165902
Fattahi M, Nabhani N, Hosseini M, Arabian N, Rahimi E (2013) Effect of Ti-containing inclusions on the nucleation of acicular ferrite and mechanical properties of multipass weld metals. Micron 45:107. https://doi.org/10.1016/j.micron.2012.11.004
Sarma D, Karasev A, Jönsson PG (2009) On the role of non-metallic inclusions in the nucleation of acicular ferrite in steels. ISIJ Int 49(7):1063. https://doi.org/10.2355/isijinternational.49.1063
Jorge JCF, Faragasso SM, Guimarães de Souza LF, de Souza Bott I (2015) Effect of post-welding heat treatment on the mechanical and microstructural properties of extra high-strength steel weld metals, for application on mooring equipment. Weld Int 29(7):521. https://doi.org/10.1080/09507116.2014.932984
Gupta A, Goyal S, Padmanabhan KA, Singh AK (2015) Inclusions in steel: micro-macro modelling approach to analyse the effects of inclusions on the properties of steel. Int J Adv Manuf Technol 77:565. https://doi.org/10.1007/s00170-014-6464-5
Liu Y, Zhang J, Pang Z (2018) Numerical and experimental investigation into the subsequent thermal cycling during selective laser melting of multi-layer 316L stainless steel. Opt Laser Technol 98:23. https://doi.org/10.1016/j.optlastec.2017.07.034
Midawi AR, Santos EB, Huda N, Sinha AK, Lazor R, Gerlich AP (2015) Microstructures and mechanical properties in two x80 weld metals produced using similar heat input. J Mater Process Technol 226:272. https://doi.org/10.1016/j.jmatprotec.2015.07.019
Tang Z, Stumpf W (2008) The role of molybdenum additions and prior deformation on acicular ferrite formation in microalloyed Nb-Ti low-carbon line-pipe steels. Mater Charact 59:717. https://doi.org/10.1016/j.matchar.2007.06.001
Keehan E, Zachrisson J, Karlsson L (2010) Influence of cooling rate on microstructure and properties of high strength steel weld metal. Sci Technol Weld Join 15(3):233. https://doi.org/10.1179/136217110x12665048207692
Madariaga I, Gutiérrez I, García-De Andrés C, Capdevila C (1999) Acicular ferrite formation in a medium carbon steel with a two stage continuous cooling. Scr Mater 41:229. https://doi.org/10.1016/S1359-6462(99)00149-9
Blais C, L’Espérance G, Evans G (1999) Characterisation of inclusions found in C-Mn steel welds containing titanium. Sci Technol Weld Join 4(3):143. https://doi.org/10.1179/136217199101537680
Lee J, Pan Y (1995) The formation of intragranular acicular ferrite in simulated heat-affected zone. ISIJ Int 35(8):1027. https://doi.org/10.2355/isijinternational.35.1027
Jung JG, Kim J, Noh KM, Park KK, Lee YK (2012) Effects of B on microstructure and hardenability of resistance seam welded HSLA linepipe steel. Sci Technol Weld Join 17(1):77. https://doi.org/10.1179/1362171811Y.0000000082
Zhang D, Terasaki H, Komizo Y (2010) In situ observation of the formation of intragranular acicular ferrite at non-metallic inclusions in C-Mn steel. Acta Mater 58:1369. https://doi.org/10.1016/j.actamat.2009.10.043
Kang Y, Jang J, Park JH, Lee C (2014) Influence of Ti on non-metallic inclusion formation and acicular ferrite nucleation in high-strength low-alloy steel weld metals. Met Mater Int 20(1):119. https://doi.org/10.1007/s12540-014-1013-1
Wan XL, Wu KM, Nune KC, Li Y, Cheng L (2015) In situ observation of acicular ferrite formation and grain refinement in simulated heat affected zone of high strength low alloy steel. Sci Technol Weld Join 20 (3):254. https://doi.org/10.1179/1362171815Y.0000000008
Loder D, Michelic SK, Bernhard C (2017) Acicular ferrite formation and its influencing factors - a review. J Mater Sci Res 6(1):24. https://doi.org/10.5539/jmsr.v6n1p24
Noureddine M, Allaoui O (2020) Effect of tempering on mechanical proprieties and corrosion behavior of x70 HSLA steel weldments. Int J Adv Manuf Technol 106:2689. https://doi.org/10.1007/s00170-019-04810-y
Moeinifar S, Kokabi AH, Hosseini HRM (2011) Effect of tandem submerged arc welding process and parameters of Gleeble simulator thermal cycles on properties of the intercritically reheated heat affected zone. Mater Des 32:869. https://doi.org/10.1016/j.matdes.2010.07.005
Fu Y, Zhang H, Wang G, Wang H (2017) Investigation of mechanical properties for hybrid deposition and micro-rolling of bainite steel. J Mater Process Technol 250:220. https://doi.org/10.1016/j.jmatprotec.2017.07.023
Yan Z, Liu W, Tang Z, Liu X, Zhang N, Li M, Zhang H (2018) Review on thermal analysis in laser-based additive manufacturing. Opt Laser Technol 106:427. https://doi.org/10.1016/j.optlastec.2018.04.034
Lalam S, Bhadeshia H, MacKay D (2004) Estimation of mechanical properties of ferritic steel welds. Part 2: elongation and Charpy toughness. Sci Technol Weld Join 5(3):149. https://doi.org/10.1179/136217100101538146
Lalam S, Bhadeshia H, MacKay D (2004) Estimation of mechanical properties of ferritic steel welds. Part 1: yield and tensile strength. Sci Technol Weld Join 5(3):135. https://doi.org/10.1179/136217100101538137
Robertson SM, Frostevarg J, Kaplan AFH, Hong SM, Kim JH, Bang HS (2019) Tailored laser pulse method to manipulate filler wire melt metallurgy from thermal cycles. Journal of Laser Applications 31(2):1. https://doi.org/10.2351/1.5096145
Sundqvist J, Kaplan AF, Shachaf L, Kong C (2017) Analytical heat conduction modelling for shaped laser beams. J Mater Process Technol 247:48. https://doi.org/10.1016/j.jmatprotec.2017.04.011
Devesse W, De Baere D, Guillaume P (2017) High resolution temperature measurement of liquid stainless steel using hyperspectral imaging. Sensors (Switzerland) 17(91):1. https://doi.org/10.3390/s17010091
Abderrazak K, Kriaa W, Ben Salem W, Mhiri H, Lepalec G, Autric M (2009) Numerical and experimental studies of molten pool formation during an interaction of a pulse laser (nd:YAG) with a magnesium alloy. Opt Laser Technol 41:470. https://doi.org/10.1016/j.optlastec.2008.07.012
Bertrand C, Poulon-Quintin A (2015) Temporal pulse shaping: a key parameter for the laser welding of dental alloys. Lasers Med Sci 30(5):1457. https://doi.org/10.1007/s10103-014-1606-4
Kaplan AF, Robertson SM, Frostevarg J, Volpp J, Ramasamy A, Kalfsbeek B (2019) Microstructure morphology characterization of welding consumables studied by pulse-shaped laser heating. Procedia Manufacturing 36:184. https://doi.org/10.1016/j.promfg.2019.08.024
Acknowledgments
The authors thank Jacob Fagerström for his aid in temperature data collection.
Funding
Open access funding provided by Lulea University of Technology. This study was financially supported by the EC Research Fund for Coal and Steel, RFCS, for the project OptoSteel, no. 709954 and by the program Interreg Nord 2014–2020, EU ERDF, for the project NorFaST-HT, no. 304-15588-2015.
Author information
Authors and Affiliations
Corresponding author
Additional information
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Robertson, S.M., Frostevarg, J., Ramasamy, A. et al. Microstructures of high-strength steel welding consumables from directed thermal cycles by shaped laser pulses. Int J Adv Manuf Technol 109, 2653–2662 (2020). https://doi.org/10.1007/s00170-020-05749-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00170-020-05749-1