Thermomechanical properties of stainless steel and grade 91 welds with explosion cladding for Generation 3 concentrated solar power systems

Conventional fabrication methods, such as large-scale machining, forging and casting, for components designed for Generation 3 concentrating solar power systems (Gen3 CSP), are cost and time consuming, which become a barrier for achieving the target economic efficiency of Gen3 CSP. Another challenge is the cost of materials that can operate safely under the severe service conditions of temperature range 500 –750 ℃ in contact with molten salts. Ni-based superalloys are the most promising alloys for these conditions because of their superiority in corrosion resistance in molten salts and high temperature mechanical properties. However, their high cost imposes a challenge for Gen3 CSP capital cost control.

Explosion cladding was selected as a cost-effective technique for pipe production. C22 and Ni201 were selected as the candidate clad materials, operating in contact with the aggressive environment. SS 304H and Grade 91 were selected as candidate backer materials that will carry the load. To evaluate the interface compatibility and thermomechanical properties of the clad couples and their fusion weldments, metallurgical characterization and elevated temperature tensile testing with digital image correlation were carried out.

It was observed that the extremely fast explosion cladding process resulted in forming a defect free metallurgical bond with minimum interdiffusion between the cladder and backer at the interface. Metallurgical characterization of the 304H-Ni201 clad couple fusion welds showed more severe grain coarsening in CGHAZ in addition to formation of microcracks and secondary phases in HAZ/PMZ. The C22 clad led to a higher UTS in general than Ni201 clad. 304H-C22 clad couple outperformed the others in tensile tests at room and high temperature. Failure occurred along the fusion zone centerline in all 304H-C22 specimens.