冶金及製程參數對於縮墨鑄鐵生產之影響研究

Abstract

本研究擬探討：1. 縮化劑種類，2. 縮化劑添加量，3. 縮化處理後之熔液持溫時間，4. 縮化處理後之熔液持溫溫度，5. 進行二次接種與否，等冶金及製程參數對於縮狀石墨鑄鐵之顯微組織以及機械性質的影響，以期獲得生產縮墨鑄鐵之較佳製程條件。 研究結果顯示，在固定碳當量4.2%，接種劑添加量0.3%之處理條件下，對於25mm Y-block而言，Mg-RE系縮化劑在添加量0.6wt%，且未進行二次接種之處理條件下，可獲得縮化率約80~90%、無碳化物析出之縮墨鑄件；在相同處理條件下，進行二次接種處理則會使球化率提高、縮化率降低，而僅能得到縮化率約50~70%且無碳化物析出之縮墨鑄件。此外，在縮化接種處理後13~20分鐘Mg-RE系縮化劑會有明顯的退化現象，而導致片狀石墨的生成，但降低持溫度則有助於減緩此退化現象。另，對於已經退化並生成片狀石墨的鑄件而言，即使進行二次接種亦無法重新獲得縮狀/球狀石墨。 當採用RE系縮化劑時，在固定碳當量4.2%，接種劑添加量0.3%之處理條件下，對於25mm Y-block而言，在縮化劑添加量0.8~1.2wt%，且未進行二次接種之處理條件下，可獲得縮化率約40~70%之縮墨鑄件，但會有碳化物晶出；在相同處理條件下，實施二次接種處理雖然會使球化率提高，但可以完全消除碳化物，並得到縮化率約10~60%且無碳化物析出之縮墨鑄件。另，稀土元素由於不易揮發，因此在縮化接種處理後20~27分鐘才會發生明顯的退化。 對於最佳製程條件而言，Mg-RE系縮化劑在縮化劑添加量0.6%、接種劑添加量0.3%，且未進行二次接種之處理條件下，於縮化接種處理之後13分鐘可獲得縮化率達80~90%且無碳化物析出之縮墨鑄件。另一方面，RE系縮化劑則在縮化劑添加量0.8%或1.0%，接種劑添加量0.3%，且進行二次接種之處理條件下，於縮化接種處理後20分鐘可獲得縮化率約60%且無碳化物析出之縮墨鑄件。

The primary purpose of this research is to establish the optimal conditions for the production of compacted graphite cast iron by investigating the effects of metallurgical and processing parameters (types of compactizer, addition amounts of compactizer, holding time, holding temperature and late inoculation) on graphite morphology and mechanical properties of compacted graphite cast iron. The results show that, for a fixed C.E. value of 4.2% and addition amounts of 0.3% inoculant and 0.6% Mg-RE compactizer without late inculation, a carbide-free compacted graphite cast iron with 80~90% vermicularity can be obtained. For the same treatment condition, again a carbide-free compacted graphite cast iron but with lower vermicularity about 50~70% and was attained by conducting late inculation. In addition, flake graphite will generate when Mg-RE compactizer decayed at about 13~20 minutes after compactization and inoculation treatment, but lower holding temperature can slow down this phenomenon. Besides, compacted and spheroidal graphite cast iron can’t be reach by conducting late inculation after flake graphite generate. For using RE alloys as the compactizer, a fixed C.E. value of 4.2% and addition amounts of 0.3% inoculant and 0.6% RE compactizer without late inculation, compacted graphite cast iron with 40~70% vermicularity but with carbide can be obtained. For the same treatment condition, carbide can be eliminates by conducting late inculation and a carbide-free compacted graphite cast iron with lower vermicularity about 10~60% can be attained. RE alloys will decay at about 20~27 minutes after compactization and inoculation treatment due to less volatile. In terms of the optimal conditions for the production of compacted graphite cast iron, addition amounts of 0.3% inoculant and 0.6% Mg-RE compactizer without late inculation, a carbide-free compacted graphite cast iron with about 80~90% vermicularity can be obtained at about 13 minutes after compactization and inoculation treatment. In the other hand, addition amounts of 0.3% inoculant and 0.8%~1.0% RE compactizer with late inculation, a carbide-free compacted graphite cast iron with 60% vermicularity can be obtained at about 20 minutes after compactization and inoculation treatment.