薄壁石墨鑄鐵之高溫熱疲勞性質研究

Study on the Thermal Fatigue Property of Thin-Section Graphitic Cast Irons

范振佶(C. C. Fan) ； 張志宏(J. H. Jheng) ； 潘永寧(Y. N. Pan)

《鑄造工程學刊》 38卷3期 (2012/09) Pp. 9-20

https://doi.org/10.29809/JTFS.201209.0002

摘要

本研究係根據先前有關薄壁球墨鑄鐵所建立之耐高溫熱疲勞性質之最佳合金設計及造模條件，進一步針對薄壁石墨鑄鐵（厚度2～6mm），探討石墨形態對於熱疲勞性質之影響，以作為薄壁石墨鑄鐵在高溫熱循環下之最佳材料選用之依據。研究內容包含：（1）首先探討獲致薄壁縮墨鑄鐵之最適縮化及接種處理條件，並進一步探討顯微組織對於縮墨鑄鐵熱疲勞壽命之影響，（2）比較不同石墨形態鑄鐵之熱疲勞性質，（3）最後分析不同石墨形態鑄鐵之熱疲勞破壞機制。實驗結果顯示，對於球墨鑄鐵而言，即使在薄壁鑄件（2～6mm）仍能得到理想的球墨組織，然而對縮墨鑄鐵而言，僅當鑄件厚度達約6mm以上時，才能夠獲得理想之縮墨組織；在縮化劑0.4%及接種劑0.15%之處理條件下，於厚度6mm之鑄件可得到縮化率超過70%以及幾近肥粒鐵（95%以上）且無碳化物之縮墨鑄鐵。另，熱疲勞試驗（RT～800℃）結果顯示，在三種石墨鑄鐵中，球墨鑄鐵之熱疲勞壽命最高，接著為縮墨鑄鐵，而片墨鑄鐵最低，雖然片墨鑄鐵在阻檔高溫膨脹及變形之能力為三者最佳。此外，於縮墨鑄鐵中添加0.5%Mo可大幅提升熱疲勞壽命，甚至達2倍以上，顯示添加Mo對於熱疲勞壽命之提升效果遠大於石墨形態之影響。

關鍵字

薄壁石墨鑄鐵 ； 化學成分 ； 顯微組織 ； 熱疲勞性質

並列摘要

The optimal alloy design and microstructure for the high temperature (around 800℃) constrained cyclic thermal fatigue applications in thin-section ductile irons have been established previously by the authors. This study intends to investigate the effect of graphite morphology on the thermal fatigue property of thin-section (2mm~6mm) graphitic cast irons. The results show that it is feasible to produce carbide-free as-cast spheroidal graphite irons in relatively thin sections of 2-mm or 3-mm. However, for compacted graphite cast irons, graphite particles largely in nodular form always occurs in rather thin sections, and acceptable compacted graphite structure can only be obtained when the section thickness exceeds about 6-mm. Regarding the constrained cyclic thermal fatigue property (RT~800℃), cast irons with spheroidal graphite exhibit the best thermal fatigue life, which is followed by irons with compacted graphite, and then flake graphite cast irons, even though flake graphite cast irons show least swelling or distortion after cyclic thermal fatigue test. Furthermore, adding some 0.5%Mo to the irons significantly improves the thermal fatigue property, in some cases even by a factor of 2, implying that the role of Mo outweighs the influence of graphite structure in promoting thermal fatigue property.

並列關鍵字

Cast iron ； Thermal fatigue ； Thin-walled casting