|Abstract: ||摘要:目前國內外核電廠使用之異質金屬銲接或銲補製程，多選用鎳基合金Inconel 152/52 作為接合低合金鋼管嘴與不銹鋼管件（或鎳基合金管件）等異質金屬銲件 之塡料。由於此兩種鋼材的熱膨脹係數差異相當大，銲件冷卻後易在界面處產生 殘留應力，使反應器壓力槽等組件經長時間高溫熱循環使用後，產生應力腐蝕破 裂及疲勞裂化等問題。 過去國內外核電廠的破損案例分析皆指出，鎳基合金之異質金屬銲件的應力 腐蝕發生位置，大多位於銲道及熱影響區等處，因此在該區域之晶界特性、碳化 物析出現象及填料成分差異造成的影響，皆為探討應力腐蝕發生機制的研究重 點。在鎳基合金填料的使用上，研究顯示最新開發的Inconel 152M/52M 與152/52 相較之下，由於成份上具有含量較多的Nb 及額外添加之少量B、Zr 等元素，不但 可有效降低銲件發生Ductility-dip cracking 的情況，亦能維持其優異的抗熱裂敏感 性，因此Inconel 152M/52M 之異質金屬銲件特性具有值得深入探討之價值。 本計畫為期三年，主要係針對 A508 低合金鋼與316L 不銹鋼進行異質金屬銲 接，探討銲件之顯微組織及機械性質、應力腐蝕及疲勞裂縫成長速率等研究，實 驗結果可供台電公司及核能研究所做為銲接及銲補製程之重要參考。第一年主要 進行異質金屬銲件之基本性質與顯微組織分析、探討Temper-bead 之回火效應，以 及評估不同填料之銲件性質差異；第二年進行異質金屬銲件之機械性質及應力腐 蝕特性研究，確定應力腐蝕之敏感區域；第三年則以模擬電廠環境對銲件特定區 域進行疲勞裂縫成長試驗為主。|
abstract:The welding of dissimilar metals is used extensively in various industries, which is more difficult than that of similar metals due to differences in physical, mechanical, and metallurgical properties of the involved materials. High residual stresses can be expected in the case of welding low alloy steels to stainless steels due to their differences in thermal expansion coefficients. Such welds may contain interfacial cracks as well as the formation of hard or soft zones adjacent to the weld interface due to carbon migration. The large difference in hardness / microstructure between the soft and hard zones, i.e., the sharp changes in compositions near the fusion boundary, often leads to failures in service. Further complication may arise if the influence of dilution and multi-pass welding are considered. Accordingly, the filler metal selection, welding process & procedure, post-weld heat treatment, mechanical tests, and the performance of dissimilar metal welds (DMWs) under various conditions should be evaluated thoroughly prior to the practical application. DMWs are used widely in nuclear power plants at locations where two different alloys, e.g. A508 and stainless steels (316L and 304L), are joined. Service failures of piping and nozzles in pressurized water reactors (PWR) occur frequently at the joints. Consequently, the cracking related problems such as hot and ductility-dip cracking, stress corrosion cracking, and fatigue cracking of DMWs have become the major concern of the nuclear industry. In general, sound joints can be obtained with nickel-base filler metals by common welding methods such as GTAW and SMAW. Recently, Alloys 52/152 are employed both in new constructions and repair welding due to the observed cracking in Alloys 82/182. For reduced susceptibilities to primary water IGSCC and ductility-dip cracking, the need for an improved DMW is obvious. Inconel 52M/152M filler metals containing 0.5~2.5% Nb and small additions of B and Zr are the new generation of filler metals, which are developed by International Nickel Company to meet such purposes. Numerous programs in the nuclear industry are undertaking to improved A508-316L (or 304L) DMWs with 52M/152M filler metals and to assess their performance. This is a three-year proposal and can be divided into three phases according the year of executions. The first-year program deals with the welding procedure, filler metal selection, microstructures, and characteristics of A508-316L DMWs. The application of temper-bead technique, which is used to eliminate the need for post-weld heat treatment after repair welding, is also included in the first year. The second-year program includes several mechanical tests and stress corrosion cracking tests of DMWs under various environments. Owing to the fact that most of premature failures in ferritic-austenitic DMWs in service occurred in the ferritic alloy, the emphasis will be placed on the heat-affected zone adjacent to the A508 side. The third-year program will concentrate on the fatigue crack growth behavior of distinct locations in DMWs under simulated PWR conditions. The detailed descriptions of the program are given in the following sections of this proposal.