Sangwoo Song

Type XM-19 stainless steel is a potential structural material for pressure vessel applications in small modular reactors (SMRs). In this study, the welding characteristics of XM-19 stainless steel were investigated using autogenous gas tungsten arc welding (GTAW) and fiber laser welding. The weld morphology, solidification behavior, and microstructure were evaluated using microscopy and solidification-mode prediction. Both GTAW and laser welds exhibited A-mode solidification under all investigated welding conditions; the dominant solidification morphology differed between the two welding processes. Additionally, Z-phase was observed in the interdendritic regions of both arc and laser welds.

This paper reviews SA-508 Grade 3 Class 2 low-alloy steel and Type XM-19 austenitic stainless steel as high-strength candidate materials for SMR pressure vessels, covering their material specifications and application status, with particular emphasis on filler metal development. For SA-508 Grade 3 Class 2, the key challenges include developing high-strength filler metals and evaluating the neutron irradiation embrittlement behavior of the base metal and weld metal for beltline applications. For Type XM-19, the establishment of manufacturing technologies for large forgings is needed for its application to nuclear pressure vessels. Although a dedicated filler metal is available, further verification of weld metal performance under reactor operating conditions is necessary, while optimization of the filler metal composition may be required.

^* CE_IIW = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

전 세계적으로 활발히 연구되고 있다. 핵융합로 블랑켓의 구조재료로 검토되는 저방사화강 (reduced-activation ferritic/martensitic steel, RAFM steel)은 화력발전용 소재로 사용되는 기존 9Cr 계열 내열강에서 고방사형 원소(Mo, Ni, Nb 등)를 W, V, Ta 등으로 대체하 여 설계된 합금이다. 저방사화강은 노멀라이징(normalizing) 과 템퍼링(tempering) 열처리를 통해 템퍼드 마르텐사이트

Wire arc-based metal additive manufacturing (AM) commonly results columnar grain structures aligned with the build direction, causing anisotropic mechanical properties and performance degradation. To mitigate the formation of columnar grain structures, ultrasonic vibration (UV) at 20 kHz was applied during the continuous heat input directed energy deposition (DED) process, targeting microstrucrual refinement in high-purity Ni alloy. The application of UV disrupted thermal gradients and facilitated dynamic recrystallization, transitioning columnar grains into equiaxed grains near the substrate. Electron backscatter diffraction (EBSD) analysis revealed a marked reduction in crystallographic texture, showing randomized grain orientations in UV-treated samples, contrasting with the strong anisotropy in untreated samples. High-speed imaging revealed localized vibrations at the interface between the metal bead and molten metal, forming band-like structures that progressively refined dendrites during solidification. These findings demonstrate the potential of UV to refine grain structures, enhance isotropy, and improve the mechanical properties of AM-produced materials.