Effects of (α+β) heat treatment on the hydrogen embrittlement of zircaloy-4(α+β) 열처리가 지르칼로이-4의 수소 취성에 미치는 영향

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The influence of the characteristics of (α+β) heat-treated Zircaloy-4 on the hydrogen embrittlement was investigated. The (α+β) heat treatment was carried out at 890℃ and 950℃. After heat treatment the hydrogen was charged to about 150-200 ppm. The hydride morphology was observed with optical microscopy and related to the matrix texture and mechanical properties produced by the (α+β) heat treatment. Uniaxial tensile test after hydrogen charging was performed to evaluate the changes of mechanical properties. The ultimate tensile strength, uniform elongation, and total elongation were discussed with the hydride morphology and the characteristics produced by the (α+β) heat treatment. The fracture surface of tensile specimen was observed with scanning electron microscope. The (α+β) heat treatment and quenching resulted in a mixture of primary α and transformed β phases. During furnace cooling after hydrogen charging, the cooling rate was 1.5 ℃/min and this cooling rate was so slow that hydride precipitates mainly along grain boundaries than on the intragranular habit planes. The hydride was large with the length of about 50~150 μm and precipitated more or less parallel to the rolling - transverse plane. The difference in hydride morphology between the rolling and transverse specimen was not observed. The changes in crystallographic texture alone did not produce any difference in hydride traces because of the low variation of volume fraction of basal poles 0-30° from reference direction, $V_R$ with increasing volum e fraction of the transformed β, $f_α``$, the hydride precipitation along grain boundaries, and residual stress which were produced during quenching. Total elongation decreased markedly after the hydrogen charging due to the preferred precipitation of large hydride along grain boundaries and triaxial stress state in necked region after UTS. But the UTS and uniform elongation were not varied between the hydrogen uncharged and charged specimens, irrespecti...
Kim, In-Sup김인섭
한국과학기술원 : 원자력공학과,
Issue Date
60268/325007 / 000901551

학위논문(석사) - 한국과학기술원 : 원자력공학과, 1992.2, [ iii, 41 p. ]

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