Post-weld Tempered Microstructure and Mechanical Properties of Hybrid Laser-Arc Welded Cast Martensitic Stainless Steel

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TRODUCTION

HYDROPOWER is one of the most widely used renewable sources of energy for electricity generation. Considering the long-service life of hydropower systems that can operate for more than five decades, proper design and manufacturing are critical for achieving high performance with low operational and maintenance costs. The most important part of any hydraulic power system is the turbine that is an assembly of various sub-components, e.g., runner blades, crowns, and bands. These components are fabricated commonly from thick-walled stainless steel materials, such as CA6NM, which is a low-carbon martensitic grade that is manufactured in cast form and has high strength, FATEMEH MIRAKHORLI, Ph.D. Candidate, is with the Mechanical Engineering Department, E´cole de technologie supe´rieure, Montreal, QC H3C 1K3, Canada, and also with the National Research Council Canada-Aerospace, 5145 Decelles Avenue, Montreal, QC H3T 2B2, Canada. Contact e-mail: [email protected] XINJIN CAO, Senior Research Officer, is with the National Research Council Canada-Aerospace, and is also Adjunct Professor with the Mechanical Engineering Department, E´cole de technologie supe´rieure. XUAN-TAN PHAM and JEAN-LUC FIHEY, Professors, are with the Mechanical Engineering Department, E´cole de technologie supe´rieure. PRITI WANJARA, Senior Research Officer, is with the National Research Council Canada-Aerospace. Manuscript submitted September 2, 2015  Published with permission of the Crown in Right of Canada. Permission pertains to F. Mirakhorli, X. Cao, and P. Wanjara. METALLURGICAL AND MATERIALS TRANSACTIONS B

good toughness, and corrosion resistance.[1] However, assembly of large hydroelectric turbine components is a great challenge from the perspective of the highly complex blade geometry and sizeable overall dimensions. Thus, the manufacturing quality and cost of the turbine are highly dependent on the ability to join such low-carbon cast martensitic stainless steel components using methods that can provide high productivity, low material consumption, and good joint integrity with any imperfections and distortion remaining within acceptable levels. To date, due to the relatively low investment costs of manual and semi-automatic arc welding systems, such as GTAW, GMAW, and FCAW, arc welding with filler material has been widely used in industry to assemble the turbine. However, joints welded using arc-based manual welding processes exhibit a relatively large HAZ, high residual stresses, and distortion due to the considerable heat input and large thermal gradients from the multiple passes required for assembly. Also, compared to more advanced processes, the operational cost for assembly is high for arc welding due to its relatively slow speed (low production rate), high labor intensity, and cost of skilled welders, and considerable consumable costs; this latter is related to the small penetration depth that requires extensive grooving of the thick joint seam followed by multiple welds deposited with filler metal addition under sh

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