Technical Issues in Fusion Welding of Reduced Activation Ferritic/Martensitic Steels for Nuclear Fusion Reactors

Abstract

Reduced activation ferritic/martensitic steels (RAFMs), which are the modified variants of 9Cr-1Mo heat resisting steels, have been recognized as candidate structural materials for the blanket module of nuclear fusion reactors. Since the blanket is exposed to a high flux of neutrons and complex periods of fluctuating mechanical and thermal stresses, evaluation of the high-temperature mechanical properties of both the RAFM steel and welds, and understanding of their degradation behaviors, are needed to provide feedback for the development of better RAFM steels and welding processes. In this review article, first, several welding processes used to fabricate the blanket modules are introduced. Microstructural evolution during fusion welding of the RAFM steel and its subsequent degradation during creep and/or irradiation are reviewed. The thermal stability of the RAFM steel originates from solid solution strengthening, sub-grain hardening and precipitation hardening. The degradation of the RAFM steel is discussed in terms of matrix recovery associated with lath widening and reduction of dislocation density, coarsening of precipitates and the formation of Laves and Z phases. This work helps provide insight on how to mitigate the microstructural degradation, and design optimal welding technology.

Effect of Laser Traverse Speed on the Metallurgical Properties of Fe-Cr-Si Clads for Austenitic Stainless Steel Using Directed Energy Deposition

“…Iron-chromium (Fe-Cr) alloys with excellent creep strength and heat resistance are in the spotlight as materials that can replace austenitic stainless steel [13,14]. To utilize Fe-Cr alloys as nuclear materials, many studies have been conducted on the addition and content control of alloying elements, such as Cr, Si, Al, and Mo [15,16], including evaluating their weldability [17,18].…”

Effect of Postweld Heat Treatments on Type IV Creep Failure in the Intercritical Heat-Affected Zone of 10% Cr Martensitic Steel Welded with Haynes 282 Filler

“…Thus, Type IV failure in the HAZ of 9-12% Cr martensitic steels should be clarified and remedied to ensure high safety and reliability of the component composed of the DMWs for use under USC or A-USC conditions. However, Type IV cracking in the DMWs is still not clearly understood, although it is reported to be associated with softening of the matrix, formation of Laves phase, coarsening of precipitates, and lack of sufficient precipitates pinning the grain boundaries [16][17][18][19][20].…”

Characterization of High-Temperature Tensile Properties and Thermal Stability in Gas Tungsten Arc Welds of Ti-added Reduced Activation Ferritic/Martensitic Steel

“…대표적인 저 방사화강으로는 유럽의 Eurofer97강, 일본의 F82H 강, 중국의 CLAM강 등이 있다 6,[9][10][11][12] . 핵융합로의 블랑켓은 약 400~500개의 박스 형태로 구성되어 있어 최종 부품을 제작하기 위한 용접 공정은 불가피하다 13,14) . 저방사화강의 용접 공정으로는 GTAW (gas tungsten arc welding), EBW (electron beam welding), Laser 용접 및 Laser-MIG (metal inert gas) hybrid 용접 등이 가장 많이 고려되고 있다 15) .…”

“…저방사화강의 용접 공정으로는 GTAW (gas tungsten arc welding), EBW (electron beam welding), Laser 용접 및 Laser-MIG (metal inert gas) hybrid 용접 등이 가장 많이 고려되고 있다 15) . 저방사화강은 Cr, W, Ta, V등의 합금원소들이 다량 포함되어 있어 용접균열 (재열, 저온균열) 발생 가능성이 높고, 용접금속 (weld metal)에서부터 열영향부 (heat affected zone, HAZ)를 거쳐 모재 (base metal)까 지 변형 불일치도가 높으며, 준안정 석출물들이 장기간 고온 노출로 인해 조대화 되거나, Z상과 같은 유해상으 로 변태될 가능성이 높다 14) . 템퍼드 마르텐사이트 조직 으로 이루어진 저방사화강은 용접시 단시간의 급격한 열사이클을 거치므로 용접부와 모재 간 상이한 미세조 직이 관찰된다.…”

“…조립역 (coarse grained HAZ, 16,17) 13,15,[18][19][20][21][22][23] . 그러나, 국내의 경우 모재 개발에만 집중되어 있으며, 부품 제작 기술 및 용 접부 특성에 관한 연구는 매우 부족한 실정이다 14)…”