銲接構造用鑄鋼SCW 450是澆鑄量相當大的鑄造用材質，因為經常需要以銲接方式與相關構件接合，因此其機械性質要求與SC 450相同外，額外要求其具低溫衝擊韌性，即0 ℃的沙丕衝擊值最小為27 J。
　　本研究旨在探討完全退火與正常化熱處理製程對於銲接構造用鑄鋼SCW 450低溫衝擊韌性的影響，並尋找最佳的熱處理條件。研究方法包括爐冷及空冷的熱處理，以OM及SEM觀察鑄鋼的顯微組織，0 ℃的沙丕衝擊試驗及破斷面型態觀察，並以ProCAST軟體模擬鑄鋼凝固過程，分析二次枝晶間距與局部凝固時間的關係。研究結果顯示熱處理後的波來鐵分佈型態、肥粒鐵晶粒尺寸及介在物顆粒皆是影響鑄鋼低溫韌性的重要因素。

　　Steel castings for welded structure SCW 450 enjoy a large tonnage in foundry production and it is usually welded into other parts to fabricate a complete construction. The quality requirements essentially same as that of SC 450 but with an extra toughness in low temperature, that is the Charpy impact value at 0 ℃must greater than 27 J.
　　The study has aimed to investigate the effect of full annealing and normalizing heat treating on the low temperature toughness of steel castings for welded structure SCW 450, and to find the optimal parameters of heat treating. The research methods included heat treating in furnace cooling and air cooling, OM and SEM observation on microstructure, low temperature Charpy impact testing and characterization of fracture morphology, the ProCAST package software was used to simulate solidification of casting to analyze the relationship between secondary dendrite arm spacing and local solidification time. The results show that after heat treating the presence of pearlite distribution, ferrite grain size and inclusion will all affect the low temperature toughness of this casting steel.

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