肥粒體基球墨鑄鐵400℃中溫脆性與熱循環誘發脆性破壞之依存性探討

Relationship between Intermediate Temperature Embrittlment at 400℃ and Thermal Cycling Induced Intergranular Embrittlment of Ferrite Spheroidal Graphite Cast Iron

林宏茂(Hung-Mao Lin) ； 呂傳盛(Truan-Sheng Lui) ； 陳立輝(Li-Hui Chen)

《鑄造工程學刊》 40卷2期 (2014/06) Pp. 1-16

摘要

由於在熱循環之冷卻過程時試片由高溫降至低溫，試片存在溫度差異而使試片承受拉伸應力作用，因此在400℃溫區之拉伸性質值得重視。肥粒體基球墨鑄鐵在各溫度時尚具有良好的延性，但是就高矽及高殘鎂量試料而言，在約400℃附近溫度範圍進行拉伸試驗時發生沿晶脆性破壞，且在破斷面上發現許多氧化鎂介在物聚集。提高殘鎂量對於400℃中溫脆性有促進作用，在拉伸破斷面上可觀察到許多含鎂的介在物聚集及金屬鎂殘留於晶界上，以及提高材料的凝固速率使微觀組織細化，因為含鎂的介在物的分散作用及晶界金屬鎂殘留的程度降低，均可抑制中溫脆性發生。本研究利用球墨鑄鐵400℃中溫脆性之發生與熱循環誘發沿晶脆性破壞間關係之檢討結果相互比較，可確認兩者之間具有密切關連性存在。而且經由針對肥粒體基球墨鑄鐵熱循環誘發沿晶脆性破壞的檢討，可理解本材料熱循環誘發沿晶脆性破壞發生原因以及防治方法，進而提高本材料於熱循環應用的信賴度。

關鍵字

肥粒體基球墨鑄鐵 ； 熱循環誘發脆性破壞 ； 中溫脆性

並列摘要

Since the specimens were subject to tensile stress when their temperatures changed from high to low during the cooling of thermal cycling, tensile properties at the temperature around 400℃ is important. Ferritic spheroidal graphite cast irons exhibited excellent ductility at all temperatures. In contrast, intergranular brittle fractures tended to occur and caused extensive clustering of magnesium oxide inclusions on fractured surfaces when the specimens with high silicon and high residual magnesium specimens were subject to tensile testing at the temperature around 400℃. Increasing the amount of residual magnesium promoted intermediate temperature embrittlment at 400℃. On the fractured surfaces, extensive clustering of inclusions containing magnesium oxide and metallic magnesium residues on grain boundaries were detected. Increasing the solidification rate of the material can refine microstructures and disperse the distribution of the inclusions containing magnesium, and the reduced amount of metallic magnesium residues suppressed the intermediate temperature embrittlment. This study was able to verify the relationship between the intermediate temperature embrittlment of spheroidal graphite cast iron at 400℃ and thermal cycling induced intergranular brittle fractures. This study provides insight on how thermal cycling induced intergranular embrittlment occurred in spheroidal graphite cast iron and ways to prevent it. As a result, the reliability of the application of this material in thermal cycling can be assured.

並列關鍵字

ferritic spheroidal graphite cast iron ； thermal cycling induced intergranular embrittlment ； intermediate temperature embrittlment