板式熱交換器用 316L不鏽鋼 與 IN-625接合製程之研究

Abstract

板式熱交換器因結構緊湊、熱傳效率高等優勢，在產業界被廣泛採用。隨著應用場合擴展至高溫高壓環境，對板片材料與接合部位的性能要求也隨之提高，銲後接點的組織與性質為影響整體產品可靠性的重要因素。 本研究分為兩部分進行：以碟片雷射對 IN-625 鎳基超合金進行同質銲接製程參數研究，並對 Alfa Nova HP52-20 板式熱交換器之 316L 不鏽鋼銲點進行破壞性分析。透過調控板材厚度配置與雷射功率等變因，搭配 EPMA/WDS 與 EBSD 分析，探討其對銲道顯微組織、析出相與接合品質之影響。 實驗結果顯示，雷射功率與穿透能力呈正相關，薄對薄 500 W 配置具有最小銲道間隙與最低變形，而厚板銲接則需提升至 2800 W 方可達成鎖孔模式，而在無氣氛保護的條件下，許多板材內都產生了TiN析出物，不利於整體結構之可靠性。而Alfa Nova HP52-20 之 316L 銲點則觀察到富鉻硼化物、與富鉻鉬硼化物兩類硼化物，其未構成連續性脆性相，推測與 Mo 元素之抑制硼化物粗化有關。研究成果可作為 IN-625 同質雷射銲接製程參數設計，以及板式熱交換器接合品質提供參考依據。

Plate heat exchangers have been widely adopted in industry owing to their advantages of compact structure and high heat transfer efficiency. As their applications extend to high-temperature and high-pressure environments, the performance requirements for plate materials and joints have correspondingly increased, making the microstructure and properties of joints a critical factor affecting the overall reliability of the product. This study is conducted in two parts: a process parameter study on homogeneous welding of IN-625 nickel-based superalloy using a disk laser, and a destructive analysis of the 316L stainless steel brazed joints in an Alfa Nova HP52-20 plate heat exchanger. By controlling variables such as plate thickness configuration and laser power, combined with EPMA/WDS and EBSD analyses, the effects on weld microstructure, precipitates, and joint quality were investigated. Experimental results show that laser power is positively correlated with penetration capability. The thin-to-thin 500 W configuration exhibited the smallest weld gap and lowest distortion, while thick-plate welding required power up to 2800 W to achieve keyhole-mode penetration; moreover, under the condition without shielding gas, TiN precipitates were generated within most weld specimens, which is detrimental to the overall structural reliability. In the 316L joints of Alfa Nova HP52-20, Cr-rich Boride and Cr/Mo-rich Boride were observed, which did not form continuous brittle phases, presumably related to the role of Mo in suppressing boride coarsening. The findings can serve as a reference for the process parameter design of IN-625 homogeneous laser welding, as well as for the joint quality assessment of plate heat exchangers.