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RISS 인기검색어
- 검색키워드
- 저자 : Kazuyoshi Saida (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
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Chun, Eun−,Joon,Saida, Kazuyoshi Elsevier 2018 JOURNAL OF NUCLEAR MATERIALS Vol.505 No.-
<P><B>Abstract</B></P> <P>To clarify the influence of long-term σ phase embrittlement on repair weldability for type 316FR stainless steel weld metals (316FR-AF and 316FR-FA), the prediction of σ-phase embrittlement and a spot-Varestraint test were performed. The precipitation of σ and χ phases were characterized during accelerated aging treatments for both weld metals, and the precipitation behavior (σ+χ phases) could be expressed by a Johnson−Mehl-type kinetic equation. By using the variation of mechanical properties upon precipitation (σ+χ phases) and the determined kinetic equation, σ-phase embrittlement for 316FR-AF and 316FR-FA weld metals during service exposure in FBR plants could be successfully predicted. Specifically, a 30.7% decrement of the absorbed impact energy as compared with the as-welded specimens could be anticipated just after one year of service for 316FR−FA weld metal at 823 K. By using the simulated weld metal with σ-phase embrittlement, the possibility of weld cracking caused by σ-phase embrittlement during repair welding was confirmed, showing micro-crack formation within the σ phase after the spot-Varestraint test.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Prediction of σ-phase embrittlement in type 316FR stainless steel welds was performed. </LI> <LI> Precipitation of intermetallics could be expressed by Johnson−Mehl-type kinetic equation. </LI> <LI> 54% decrement of the absorbed impact energy as compared with the as-welded after one year of service at 823 K. </LI> <LI> Micro-cracks within the σ phase could be detected after spot-Varestraint test. </LI> </UL> </P>
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전은준,Hayato Baba,Kazutoshi Nishimoto,Kazuyoshi Saida 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.3
In order to quantitatively evaluate the solidification cracking susceptibility in laser welds of type 310S stainless steel, a transverse-Varestraint testing system using a laser beam welding apparatus was newly constructed. The timing-synchronization between the laser oscillator, welding robot and hydraulic pressure devices was established by employing high-speed camera observations together with electrical signal control among the three components. Moreover, the yoke-drop time measured by the camera was used to prevent underestimation of the crack length. The laser beam melt-run welding used a variable welding speed from 10.0 to 40.0 mm/s, while the gas tungsten arc welding varied the welding speed from 1.67 to 5.00 mm/s. As the welding speed increased from 1.67 to 40.0mm/s, the solidification brittle temperature range of type 310S stainless steel welds was reduced from 146 to 120 K. It follows that employing the laser beam welding process mitigates the solidification cracking susceptibility for type 310S stainless steel welds.
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Influence of Metallic Sodium on Repair Weldability for Type 316FR Stainless Steel
Eun-Joon Chun,Su-Jin Lee,Jeong Suh,Ju-Seung Lee,Namhyun Kang,Kazuyoshi Saida 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.1
The effect of residual metallic sodium on the solidification cracking susceptibility of type 316FR stainless steel was investigated via transverse-Varestraint tests. And a solidification brittle temperature range (BTR) of type 316FR stainless steel was 37 K. However, the BTR expanded from 37 to 67 K, as the amount of metallic sodium at the specimen surface increased from 0 to 7.99 mg/㎠. Microstructural observation of the weld metal suggested that metallic sodium existed in the weld metal, including in the cell boundaries, during welding solidification. Thermodynamic calculations suggested that sodium expanded the temperature range of solidliquid coexistence during welding solidification of the steel weld metal. Therefore, the increased solidification cracking susceptibility (i.e., expansion of the BTR) in the residual sodium environment was attributed to enhanced segregation of sodium during the welding solidification; this segregation, in turn, resulted in an expanded temperature range of solid-liquid coexistence.
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오스테나이트계 스테인리스강 레이저 용접부의 응고균열 거동 (Part 2)
천은준(Eun-Joon Chun),이수진(Su-Jin Lee),서정(Jeong Suh),강남현(Namhyun Kang),Kazuyoshi Saida 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.5
A numerical simulation of the solid/liquid coexistence temperature range, using solidification segregation model linked with the Kurz-Giovanola-Trivedi model, explained the mechanism of the BTR shrinkage (with an increase in welding speed) in type 310 stainless steel welds by reduction of the solid/liquid coexistence temperature range of the weld metal due to the inhibited solidification segregation of solute elements and promoted dendrite tip supercooling attributed to rapid solidification of laser beam welding. The reason why the BTR enlarged in type 316 series stainless welds could be clarified by the enhanced solidification segregation of impurity elements (S and P), corresponding to the decrement in δ-ferrite crystallization amount at the solidification completion stage in the laser welds. Furthermore, the greater increase in BTR with type 316-B steel was determined to be due to a larger decrease in δ-ferrite amount during welding solidification than with type 316-A steel. This, in turn, greatly increases the segregation of impurities, which is responsible for the greater temperature range of solid/liquid coexistence when using type 316-B steel.
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Influence of Metallic Sodium on Repair Weldability for Type 316FR Stainless Steel
Chun, Eun-Joon,Lee, Su-Jin,Suh, Jeong,Lee, Ju-Seung,Kang, Namhyun,Saida, Kazuyoshi The Korean Welding and Joining Society 2017 대한용접·접합학회지 Vol.35 No.1
The effect of residual metallic sodium on the solidification cracking susceptibility of type 316FR stainless steel was investigated via transverse-Varestraint tests. And a solidification brittle temperature range (BTR) of type 316FR stainless steel was 37 K. However, the BTR expanded from 37 to 67 K, as the amount of metallic sodium at the specimen surface increased from 0 to $7.99mg/cm^2$. Microstructural observation of the weld metal suggested that metallic sodium existed in the weld metal, including in the cell boundaries, during welding solidification. Thermodynamic calculations suggested that sodium expanded the temperature range of solidliquid coexistence during welding solidification of the steel weld metal. Therefore, the increased solidification cracking susceptibility (i.e., expansion of the BTR) in the residual sodium environment was attributed to enhanced segregation of sodium during the welding solidification; this segregation, in turn, resulted in an expanded temperature range of solid-liquid coexistence.
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