EFFECT OF GAS SHIELDING AND HEAT INPUT ON AUTOGENOUS WELDING OF DUPLEX STAINLESS STEEL Paper 1701

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1 EFFECT OF GAS SHIELDING AND HEAT INPUT ON AUTOGENOUS WELDING OF DUPLE STAINLESS STEEL Paper 1701 Antti Salminen 1,2, Elin Westin 3, Esa Lappalainen 1 and Anna Unt 1 1 Laboratory of Laser Materials Processing, Lappeenranta University of Technology, P.O. Box 20, FI Lappeenranta, Finland 2 Machine Technology Centre Turku Ltd, Lemminkäisenkatu 28, FI Turku, Finland 3 Böhler Schweißtechnik Austria GmbH, Böhler-Welding-Str. 1, A-8605 Kapfenberg, Austria Abstract Stainless steel is increasingly being used in various applications where the laser process may be the perfect tool for welding autogenously. Use of the keyhole welding mode typically assures high weld quality and productivity. Heat tint and discoloration on the surface may decrease the corrosion resistance and have to be removed or minimized. With laser welding, it is possible to limit the weld bead and root oxidization and thereby decrease the need for postweld cleaning. The main drawback of using a keyhole when welding duplex stainless steels is the high cooling rate, which can cause unfavorable phase balance in weld metal. Thus addition of over-alloyed filler metal or even post-weld annealing is required. Another solution is to use laser hybrid welding to increase the heat input and add filler metal. This is, however, not an attractive choice for welding thin materials and in continuous production. The excellent beam quality of modern high-brightness lasers can, together with high power provide a great opportunity to shorten the total welding time, but the difficulty in obtaining suitable phase balance remains or is even enhanced. This study concentrates on testing the effect of dynamic beam forming on the laser beam absorptivity and resulting weld microstructure in order to define the usability of this technique for welding of thin duplex stainless steel sheets. The differences between various focal spot configurations were analyzed together with the effect of gas shielding technique. The focal spot size and shape had a significant effect on the absorption and heat input and thus affected the weld metal microstructure. Introduction The investment in laser equipment for welding is typically justified by new opportunities to increase productivity and quality of a product at lower cost and in some cases with new design. When evaluating the total fabrication cost, the high initial cost of the modern lasers can often be motivated and laser welding is continuously expanding to new application areas. Laser manufacturers have constantly been developing new lasers to provide improved performance at lower cost. The development has further been driven by new laser vendors recently entering the market with excellent products. The newest contribution in the high power laser range is the high power fiber laser. This laser offers new opportunities with its high continuous wave power with good absorption, high beam quality, small product size, low maintenance requirement and suitability of using fiber optics in beam transportation. Despite there are major advantages, there exist applications where laser welding would not be the first option. In case of stainless steel, for instance, the welds often have to be free from spatter for optimum corrosion resistance as spatter may act as an initiation point of corrosion. In some cases the unfavorable microstructure may also result from the rapid cooling rate associated with laser welding. Much remains in understanding the modern high-brightness laser equipment and technique, and process development for such applications may be challenging encountering the extreme power intensity together with low total heat input. Welding with High Power Modern Lasers The new generation disk and fiber lasers are highly potential tools for different welding cases; especially for applications requiring deep and narrow penetration. The studies have shown that the better the beam quality and the smaller the spot size, the narrower weld and the higher productivity. Due to the short history of these lasers, there is only limited information available on the effect of parameter variations, resulting welding performance and potential of the process. There are some data available on welding of austenitic stainless steel types such as EN

2 (AISI 304) with high power new generation lasers. The reports of e.g. Vollertsen et al. [1] and Kinoshita et al. [2] show some results with fiber laser whereas Brockmann et al. [3] have reported results achieved with disk lasers. It has been confirmed that the laser welds produced with these modern lasers are narrow with deep penetration; deviating from the shape typical for CO 2 and Nd:YAG laser welds. This means typically very efficient utilization of the laser energy into the welding process. It was also found that the welds became deeper and narrower with an increased power density. The smaller the focal spot diameter with certain beam quality and power, the deeper the penetration at higher speed [4]. Liu et al. [5] successfully welded 4 mm high strength steel with 2 kw fiber laser at a welding speed of 0.5 m/min. The welds with a fiber laser are typically narrow and as compared to the laser beam, narrowest in the middle of the thickness on average 2.2 times wider than the laser beam itself. The weld has typically the shape of an hourglass, with considerable widening in the lower part of the penetration. One phenomenon important for laser welding is naturally the absorption of the laser energy. It has been shown by Sokolov et al. [6] and Vänskä et al. [7] that the penetration depth is also depending on the joint configuration. With butt joint configuration the penetration is deeper than what can be achieved with the commonly used testing environment, bead on plate. The efficiency of absorption has also been shown by Kawahito et al [8] to increase with the speed. Welding of Duplex Stainless Steel with Laser Duplex stainless steels are gaining a more important role in metal industry and the sale of these alloys is constantly increasing. Duplex stainless steels offer highly economical combinations of strength and corrosion resistance due to favorable microstructure and chemical composition. The specific properties are obtained by a balanced two-phase microstructure consisting of ferrite and austenite of approximately equal proportions. The toughness and corrosion resistance of the weld metal and heat affected zone (HAZ) are consequently dependent on the phase balance [9]. The duplex grades generally solidify ferritically and the austenite is precipitated in solid-phase during subsequent cooling. The austenite formation is controlled by nitrogen diffusion and hence the cooling rate. Insufficient time for adequate austenite formation can result in considerable chromium nitride precipitation within the ferrite grains in the welds and HAZ, due to supersaturation of nitrogen during cooling, which in turn may have a detrimental effect on corrosion resistance and toughness. Laser welding of duplex grades has, due to the low heat input and rapid cooling rate, been associated with excessively high ferrite contents. For the duplex stainless steels 2205 (EN , UNS S31803) and 2304 (EN , UNS S32304), solidification structures close to one hundred percent ferrite have been reported [10-12]. In conventional welding, large deviations in phase balance between base metal and as-solidified weld metal can partly be avoided by adding nitrogen to the shielding gas, by using a nitrogen-based backing gas and/or by adding overalloyed filler metal. The influence of nitrogen addition to the shielding gas has been reported to be negligible when laser beam welding at the short wavelength of solid-state lasers, because of the small weld pool surface, short thermal cycles, lack of plasma inside the capillary and active evaporation [13-15]. The effect of adding matching filler wire during laser welding is small and addition of pure nickel in various forms has been reported to be necessary [16-20]. Autogenous fiber laser welding has, in addition, been found to cause the highest ferrite contents compared to other laser methods, having a negative effect on the pitting resistance [21]. The narrow welds and high intensity might increase the alloying element loss as Khan et al. [22] reported for Nd:YAG laser welding. The Challenge As previously explained there are challenges to achieve the right phase balance inside the narrow laser welds due to low heat input. Traditionally, increasing heat input in CO 2 laser welding has led into sagging of the weld metal. With lasers having a wavelength close to 1000 nm this has not been the case due to the smaller keyhole diameters. The positive effect of laser-gta hybrid welding used for 1-2 mm thick duplex steel has been reported by Westin et al. [23] to be gained via increased heat input, wider welds and better response to nitrogen additions to the shielding gas. Laser-GMA hybrid welding has been reported to significantly improve the austenite formation because of increased heat input rather than to the choice of filler metal alone [24]. The drawback is that laser-gma hybrid welding may give excessive weld metal reinforcement for butt welded thin sheet. For 8 mm and 13.5 mm thick material, studies have shown that the filler metal may not reach the weld root with single pass laser-gma hybrid welding [20,25]. It seems as if the filler material does not flow efficiently to reach the root even though this has been assumed traditionally. 525

3 The studies by Katayama et al. [26] show rather strong flow, but it may be that the molten volume around the keyhole is too small to enable sufficiently large volume of filler material to flow down. In addition, the cooling rate is also rapid and the root may be the first part to solidify. Keyhole can be made larger also with the optical scanner technology, which was demonstrated at least as principle as early as in the 1980 s, but has primarily been limited to certain application areas such as remote welding [27]. Use of scanners for changing the size of keyhole has not been popular due to lack of suitable lasers. When welding with a high quality beam, the scanner provides great potential for widening the weld and thus lowering the requirements on joint preparation. The scanners are programmable to adjust the frequency and amplitude separately to provide good control of the heat input. The scanner has been reported to enable use of lower welding speed than possible with normal autogenous welding which easily suffers from sagging in case of lower welding speed. These scanners are popularly also called dynamic beam forming tools. 100 mm size sheets. The samples were cleaned with acetone prior to welding. Welding Set-up The laser used in the experiments was an IPG Photonics YLR-5000 S fiber laser with a beam parameter product of 4.4 mm*mrad. The core diameter of the working fiber was 200 μm. The optical system used consisted of 150 mm collimation and 250 mm focusing lenses. The diameter of the focal spot was on surface of the workpiece mm. More details on the quality of the laser beam and the optical system can be found in Figure 1. Objective The objective was to study the effect of gas shielding and heat input on resulting weld quality, absorption and weld metal austenite content of two different duplex grades known to have limited laser weldability; 2304 (EN , UNS S32304) and 2205 (EN , UNS S32205) and two different ways of introducing the gas shielding. Experimental Procedure Materials and Workpiece Preparation The material welded were the duplex stainless steels 2304 and Both grades were 3 mm thick with a normal 2B surface quality. The duplex stainless steel 2205 is e.g. used in the chemical processing industry (pressure vessels, tanks, piping and heat exchangers), handling of oil and gas (piping, tubing, and heat exchangers) and in pulp and paper industry (bleaching equipment and stock handling systems). Duplex grade 2304 is generally found where 304L and 316L grades can be used and within the pulp and paper industry (chip storage tanks, white and black liquor tanks, digesters), caustic solutions, organic acids, food industry, pressure vessels (weight savings) and mining (abrasion/corrosion). The welding was performed bead-on-plate with parallel welds in horizontal position (PA) on 200 Figure 1. The laser beam quality with the optical setup. The beam quality was 4.4 mm mrad and the focal spot diameter 168 µm. The laser power was 4.5 kw on the surface of the workpiece in all experiments and the focal spot position was kept constant -2 mm, i.e. inside the material 2 mm from the top surface of the workpiece. Nitrogen shielding gas was introduced through an external side nozzle to the beam-material interaction spot at 10 l/min flow rate. The shielding gas was introduced with two different nozzle set-ups. The first arrangement had nozzle diameter of 4 mm and direction of almost vertical towards the welding process with distance of 30 mm. The other consisted of tube with inner diameter of 10 mm, which was directed to welding process from an 80 angle with a distance of 50 mm. Both feeding set-ups were carried out in leading position. The backing gas was pure nitrogen at 10 l/min flow in all cases. Scanner Utilization The scanner mirror was installed between the collimator and focusing lens. It was water cooled and oscillated along one axis such that the area formed by the laser beam was wider in one direction. The 526

4 scanning was performed both in the welding direction and perpendicular to it. The amplitude and the frequency were programmed with certain steps. The welding speed was set to compensate lower power density thus enabling full penetration. Variables Tables 1 and 2 show the parameters used for steel 2205 and 2304, respectively. In principle both materials were welded with same parameters, but there is slight variations e.g. in calorimetric testing which was carried out for both materials. Table 1. Parameters used for welding of The scanning frequency was 700 Hz except that in cases of other beam dimension is 0.30 mm the frequency is 400 Hz. Welding Gas shielding, Beam dimensions speed Nozzle W direction Transverse m/min 4 mm 10 mm d mm / F Hz d mm / F Hz 2,50 2,00 1,50 1,00 0,75 0,50 The absorption 0.3 0,3 The absorbed laser energy during welding was measured with a calorimeter designed for this purpose. The temperature change of the water in the calorimeter and workpiece was measured and the absorption calculated accordingly. Visual Appearance Results and Discussion The experiments were started without scanning. The fiber laser welds were narrow and the weld metal ferrite content high; 87 ± 6% for 2304 and 95 ± 2% for The samples performed with the shielding gas arrangements using the smaller nozzle (4 mm) showed some oxidation on the cap and spatter on the root side, which may have a negative impact on the corrosion performance. In case of the wider (10 mm) gas nozzle the visual appearance of the welds was of much higher quality. There was almost no oxidation and weld surfaces were smooth throughout the experiments. The austenite content was low when welding with high speed, but was increased systematically as function of higher heat input. The variation in austenite content in the case of 10 mm gas nozzle was from 18.8% in case of 2.5 m/min to 34.9% in case of 0.75 m/min. When comparing the two gas shielding cases, increased austenite content was obtained by better gas shielding together with lower oxidation of the weld bead. Table 2. Parameters used for welding of The scanning frequency was 700 Hz except that in cases of other beam dimensions is 0.30 mm the frequency is 400 Hz. Welding Gas shielding, Beam dimensions speed Nozzle W direction Transverse m/min 4 mm 10 mm d mm / F Hz d mm / F Hz 2,50 2,00 1,50 1,00 0,75 0, ,3 527

5 In case of the 4 mm gas nozzle starting with 2.5 m/min welding speed, the welds were highly ferritic and spatter was found on both sides. The amount of spatter was highest when scanning transversely. There was also some undercut on the root side. The weld width increased with lower welding speed down to 0.75 m/min and the amount of spatter decreased, while the welds sank more and became increasingly oxidized. Figure 2 shows some typical cross-sections of welds performed with different heat input and gas nozzle of 10 mm in diameter. 2.5 m/min 2.0 m/min 1.5 m/min 1.0 m/min yielding clean weld surfaces directly after welding, Figure 3. Figure 3. Weld bead appearance with efficient gas shielding. 4.5 kw, 2.5 m/min, transverse scanning. When increasing the heat input and spot size, the weld became wider, but in some cases the weld showed less or more spatter, more oxide and sank more. Transverse scanning resulted in the widest welds and smoothest root surface appearance, while longitudinal scanning showed least spatter. Absorption The absorption measurements showed a clear change in absorption as function of the welding speed. The absorption decreased with decreased heat input or increased welding speed. This affects the the actual heat input. Figure 4 shows the absorption behavior of the process as a function of the welding speed. There difference in absorption between the two different alloys was small m/min 0.5 m/min Figure 2. Weld bead appearance of 2205 with different welding speeds. Even in case of 0.5 m/min the weld is acceptable for class B. In case of the 10 mm gas nozzle the quality was higher in all cases. Weld quality evaluation confirmed high quality (level B) in most specimens. As for the 4 mm nozzle, there was less spatter, but similar slight sagging of the welds performed with the lowest welding speeds. Addition of filler wire is a logical solution to prevent underfilled welds for optimum mechanical properties. Surface oxidation on both face and root may have a negative impact on the corrosion performance, unless subjected to thorough post-weld cleaning. With proper gas shielding arrangement the oxidation can be minimized and thus Figure 4. The absorption as a function of welding speed, with different parameter combinations. No noticeable difference between the scanning directions or non-scanning parameters was found. The effect of gas shielding on absorption was not studied in this work, but it has previously been seen that less oxidation leads to lower absorption. With 2.5 m/min welding speed, the heat input should be five times lower as compared to that of 0.75 m/min, 528

6 but the actual heat input will only be three fold as the absorption will be lower at lower welding speed. The absorption shows a fairly linear correlation with the welding speed. The base material, the use of scanning or the scanning direction did not have any large influence, which corresponds well with the results of Kawahito [8], but we as high absorption as described by Kawahito et al was not reached due to the fact that in this study the maximum penetration giving full penetration was not tested. negligible effect on the ferrite content, but longitudinal scanning had somewhat larger effect on the austenite formation. The difference between the two different shielding gas set-ups used here is probably rather small as with better gas shielding the absorption is lower and increase in heat input, decreasing also the cooling rate, thus showing smaller difference in lowest speeds in austenite ferrite fraction. Weld Geometry The measurements of the weld width and crosssection area were performed based on image analysis of the cross-section of the sample. Figure 6. The austenite fraction as a function of welding speed, with different parameter combinations. Conclusions Figure 5. The effect of welding speed on average weld width in weld cap, mid-section and root. The results the weld width decreased systematically with increased welding speed, Figure 5. New information was the ability of the process to tolerate the excessive heat input without considerable sagging phenomena even though the heat input was increased five times as compared to the fastest welding speed. Austenite content Figure 6 shows the effect of welding speed and gas shielding on the weld austenite content of With more efficient nitrogen shielding, the weld metal austenite content increased. The ferrite content increased with the welding speed (lower heat input and cooling rate). Most standards require at least 30% austenite. This level could be reached with a welding speed of m/min, giving reasonable productivity. A further increase of the heat input and spot size did not give any additional improvement of the ferrite content. Changes in amplitude and frequency had A spacer was used when fiber laser welding two duplex steel grades autogenously with two different shielding gas arrangements to investigate if it is possible to increase the heat input and enable better ferrite and austenite balance in the microstructure. The tests showed that linear scanning can be carried out in either direction, parallel or transverse, in respect to the welding direction. This enables use of higher heat input as compared to traditional laser welding with constant beam and spot size on the surface and having the maximum heat input with full penetration and acceptable weld quality. The scanning results in wider welds, which could be utilized to bridge joints with some air gap. Unfortunately it was found that the effect on the fraction of ferrite content is small. The scanning combined with suitable filler wire prone to for ferrite can be the suitable way to improve the fraction of ferrite content in weld metal. Acknowledgements This project was carried out as a part of the Finnish national research projects Pamowe funded by Academy of Finland and Innoliitos funded by the European Regional Development Program and the Finnish industry. The authors wish to present their gratuity to Mr. Pertti Kokko and Mr. Ilkka Poutiainen 529

7 for performing the welding tests and calorimetric measurements and Mr. Antti Heikkinen for metallography. References [1] Vollertsen, F. & Thomy, C. (2005) Welding with fiber lasers from 200 to W. In Proceedings of ICALEO 2005, Miami, FL, LIA, pp [2] Kinoshita, K., Mizutani, M., Kawahito, Y. & Katayama, S. (2006) Phenomena of welding with high-power fiber laser. In Proceedings of ICALEO 2006, Scottsdale, AZ, LIA, pp [3] Brockmann, R., Mann, K., Schlueter, H. & Havrilla, D. (2007) High performance industrial disk lasers for a broad range of applications. In Proceedings of ICALEO 2007, Orlando, FL, LIA, pp [4] Verhaeghe, G. & Hilton, P. (2005) The effect of spot size and laser beam quality on welding performance when using high-power continuous wave solid-state lasers. In Proceedings of ICALEO 2005, Miami, FL, LIA, pp [5] Liu, Z., Kutsuna, M. & u, G. (2006) Fiber laser welding of 780 MPa high strength steel. In Proceedings of ICALEO 2006, Scottsdale, AZ, LIA, pp [6] Sokolov, M., Salminen, A., Kuznetsov, M. and Tsibulskiy, I. (2011) Laser welding and weld hardness analysis of thick section S355 structural steel. Materials and Design, 32, 10, pp [7] Vänskä, M. Abt, F., Weber, R., Salminen, A. and Graf T. (2012) -ray Videography Investigation of Keyhole Form in Laser Welding of Different Joint Geometries. In Proceedings of ICALEO 2012, Anaheim, CA, LIA, 6 p. [8] Kawahito, Y., Matsumoto, N., Abe, Y. & Katayama, S. (2012) Laser absorption of aluminum alloy in high brightness and high power fiber laser welding. Weld. Int. 26, 4, pp [9] Liljas, M. (1994) The welding metallurgy of duplex stainless steels. In Proceedings of Duplex Stainless Steels 94, Glasgow, Scotland, 15 p. [10] McPherson, N.A., Samson, H., Baker, T.N. & Suarez-Fernandez, N. (2003) Steel microstructures in autogenous laser welds, J. Laser Appl. 15, pp [11] Hsieh, R.-I., Liou, H.-Y. & Pan, Y.-T. (1999) Weldability of 22% Cr duplex stainless steels. China Steel Technical Report 13, pp [12] Gooch, T.G. & Ginn, B.J. (1997) Properties of resistance and laser welds in UNS S32304 duplex stainless steel. In Proceedings of Duplex Stainless Steels '97, Maastricht, The Netherlands, pp [13] Sato, Y., Dong, W., Kokawa, H. & Kuwana, T. (2000) Nitrogen absorption by iron and stainless steels during YAG laser welding, ISIJ Int. 40, pp [14] Dong, W., Kokawa, H., Sato, Y.S. & Tsukamoto, S. (2003) Nitrogen absorption by iron and stainless steels during CO 2 laser welding, Metall. Trans. B 34B, pp [15] Roguin, P. (1998) Improved weld microstructure in welding austenitic-ferritic stainless steels, Weld. Int. 12, pp [16] Steffens, H.-D., Wilden, J. & Honekamp, E. (1997) Corrosion resistance and mechanical properties of laser beam welded duplex stainless steel. In Proceedings of JOM-8; Helsingor, Denmark, Ingenior-hojskolen Helsingor Teknikum, pp [17] Borggreen, K., Kristensen, J.K., Hansen, L.E., Kocak, M. & Dos Santos, J.F. (1999) Laser welding of heavy section duplex stainless steel grade 2205, in Proceedings of Stainless Steel World '99, The Hague, The Netherlands, Zutphen: KCI Publishing, pp [18] Baughn, K., Ahmed, N., Jarvis, L. & Viano, D. (2002) Tailoring the phase balance during laser and GTA keyhole welding of SAF 2205 duplex stainless steel. In Proceedings of 6th Trends in Welding Research, Pine Mountain, GA, USA, ASM Int. 2003, pp [19] Wu, H.C., Tsay, L.W. & Chen, C. (2004) Laser beam welding of 2205 duplex stainless steel with metal powder additions, ISIJ Int. 44, pp [20] Westin, E.M., Stelling, K. & Gumenyuk, A. (2011) Single-pass laser GMA hybrid welding of 13.5 mm thick duplex stainless steel. Welding in the World, 55, 12, pp [21] Westin, E.M. & Fellman, A. (2008) Laser hybrid welding of a lean duplex stainless steel. In Proceedings of ICALEO 2008, Temecula, CA, USA, LIA, pp

8 [22] Khan, P.A.A., DebRoy, T. & David, S.A. (1988) Laser beam welding of high-manganese stainless steels examination of alloying element loss and microstructural changes, Welding Journal 67, pp. 1s-7s. [23] Westin, E.M., Keehan, E., Ström, M. & von Brömssen, B. (2007) Laser welding of a lean duplex stainless steel. In Proceedings of ICALEO 2007, Orlando, FL, USA, LIA, pp [24] Westin, E.M. & Fellman, A. (2008) Laser hybrid welding of a lean duplex stainless steel. In Proceedings of ICALEO 2008, Temecula, CA, USA, LIA, pp [25] Fellman, A. & Westin, E.M. (2008) Fiber laser hybrid welding of stainless steel. In Proceedings of ICALEO 2008, Temecula, CA, USA, LIA, pp [26] Katayama, S., Kwahito, Y. & Mizutani, M. (2007) Plume behaviour and melt flows during laser and hybrid welding. In Proceedings of Lasers in Manufacturing 07, Munich, German Scientific Laser Society, pp engineer certificate from the Royal Institute of Technology (KTH) in Stockholm, Sweden in She worked until 2010 as a research engineer for Outokumpu Stainless at Avesta Research Centre and where she was responsible for weldability research on duplex stainless steels. In 2010 she finished her PhD on welding metallurgy at KTH and started working with market development of flux-cored wires for Böhler Welding Group in Austria. Mr. Esa Lappalainen, M.Sc. (Technology) received his M.Sc. from Lappeenranta University of Technology (LUT) in Currently he is currently working in the Laser Materials Processing Laboratory of LUT. Mainly he is concentrates on laser and laser arc hybrid welding. Ms. Anna Unt, M.Sc. (Technology) received her M.Sc. from Lappeenranta University of Technology (LUT) in She has been working in the Laser Materials Processing Laboratory of LUT since She also has M.Sc. degree in material science from Tallinn University of Technology (2009). Her main research interests are laser arc hybrid welding and welding metallurgy. [27] Grupp, M., Seefeld, T. & Vollertsen, F., (2003) Laser Beam Welding with Scanner. In Proceedings of the Second International WLT-Conference on Lasers in Manufacturing 2003, Munich, June 2003, 5 p. Meet the authors Professor Antti Salminen, D.Sc. (Laser Technology), IWE, has more than 25 years experience in various processes to process various materials with laser beam. He has been acting as researcher and project leader in several academic studies and working with industrial cases, in the field of process development, laser system development, product design for laser processing, consulting and technology transfer. He has published more than 300 papers of over than 200 scientific. Currently he is Professor of Laser Materials Processing and head of Laser Materials Processing Laboratory in Lappeenranta University of Technology. He is running projects for laser welding with high power, laser welding of polymers and glass, additive manufacturing, laser sintering of ceramics and in project for development of laser assisted manufacturing of micro/milli-scale devices for chemical processes. Dr. Elin Marianne Westin holds an M.Sc. degree in mechanical engineering with a major in materials and welding from Luleå University of Technology, Sweden and received her international welding 531