Microstructure and Intergranular Corrosion Resistance Evaluation of Alloy 82 Weldments

Alloy 82銲道微結構與沿晶腐蝕阻抗之研究

李驊登(Hwa-Teng Lee) ； 劉得成(Te-Chen Liu)

《中國機械工程學刊》 39卷2期 (2018/04) Pp. 131-143

摘要

An investigation is performed into the grain boundary character distribution (GBCD), degree of sensitization (DOS), and intergranular corrosion (IGC) resistance of Alloy 82 overlay welds prepared using a manual gas tungsten arc welding (GTAW) process. Four different weldments are considered, namely as-welded (AW), sensitized (AW+SEN), solution-annealed (SS), and solution-annealed and then sensitized (SS+SEN). The results show that approximately 67.9% and 212.4 cm/cm^2 of the grain boundaries in the weldments were prepared by GTAW process found AW specimens are high-angle boundaries (＞15°). These boundaries prompt the precipitation of fine Cr-carbides during sensitization treatment, and therefore cause the formation of Cr-depletion zones close to the grain boundary. Consequently, the AW+SEN weldment has a high DOS. By contrast, AW+SEN welds are processed using a laser surface melting (LSM) technique with a continuous CO_2 laser beam and scanning speeds in the range of 0.8~1.2 m/min. It is shown that the LSM treatment could improve IGC and pitting corrosion resistance of the overlay weld mainly by reducing the amounts of fine precipitates along the subgrain boundaries of sensitized weld.

關鍵字

Alloy 82 weld ； laser surface melting (LSM) ； intergranular corrosion (IGC) ； pitting corrosion

並列摘要

本研究探討晶界特性和敏化程度對Alloy 82覆銲層沿晶腐蝕性質的影響。以傳統電弧銲接製備之銲道組織具有67.9% 和212.4 cm/cm^2高角度晶界(大於15度以上)，在銲後熱處理，使富鉻碳化物於晶界析出，鄰近基材形成缺鉻區。經電化學測試結果，敏化值達31%，腐蝕形貌為沿晶腐蝕及晶粒內孔蝕；使用雷射表面重熔技術，將富鉻碳化物重熔回基材並抑制其再度析出，明顯提升抗腐蝕能力。