用於核電廠結構與管路系統覆銲的鎳基Alloy 52銲材，在高入熱量的GTAW覆銲製程中可能存在著再熱裂紋(Reheat Cracking, RC)之問題。本研究目的主要評估Alloy 52鎳基銲材產生再熱裂的情形，尋找影響裂紋形成之條件，並以改變溫度及應變條件為基礎，試圖釐清Alloy 52銲材在不同溫度及應變下產生再熱裂紋的情況並建立Alloy 52銲材形成再熱裂之失效窗口(Failure Map)。
首先由裂紋形貌討論其特徵，發現裂紋形貌相當細小，但並無再熱裂的沿晶裂紋趨勢，且有穿晶的傾向，因此本試驗認為「預應變」的均勻程度決定了材料裂紋形成的重要因子，Alloy 52於高溫狀態時縱使晶粒內部強度大於晶界，但假設應力釋放後變形過大，晶粒還是有機會受到破壞而產生穿晶開裂的特徵；而失效窗口的部分，由於裂紋樣貌並未在沿晶破壞的標準之內，因此認為夾具無法給予試片理想的拘束狀態，使試驗結果帶有了不確定性，故無法明確定義失效窗口中的材料破壞應變門檻，未來的實驗設計應對此加以改善，以釐清在各溫度下Alloy 52形成再熱裂紋的敏感程度。

Reheat Crack (RC) may exist in the nickel base alloy weldment during the high heat input cladding process, ex：GTAW. To analysis the problem, this study was mainly focused on the formation of Reheat Crack in filler metal Alloy 52. To Alloy 52, Reheat Crack may be easy to form at the Ductility-Dip Temperature Range (DTR) with the sufficient stress condition. The Failure Map of Alloy 52 was constructed by changing the temperature and strain parameter. For the experimental procedure, Reheat Crack test specimen of Alloy 52 weld was restrained by the Bent Beam fixture, heated to the Ductility-Dip temperature, and held the specified temperature for 30 seconds, then the growth characteristics of Reheat Crack and Failure Map would be discussed.

The experimental results showed that the test method in this study was feasible to find the crack in Alloy 52 weld. By the optical microscope, the morphology of the crack was able to be observed. The crack possessed the tiny fissure dimension but it hadn’t the intergranular crack tendency. It couldn’t discuss the failure strain of Alloy 52 in this test, beause of the cracking result wasn’t according to the reheat cracking theorem. In the future work, if the test methods of the stress supplement have more stable, it could overcome the experimental error and evaluate the cracking phenomenon.

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