- 學位論文
薄壁球墨鑄鐵鑄件厚度對球化效果之影響
Effects of Casting Thickness on Nodularity of Thin-walled Ductile Iron
摘要
本研究之主要目的在探討薄壁球墨鑄鐵之鑄件厚度與組成成分對顯微金相組織的影響。 實驗採用回爐料作為基礎鐵水，以消除有害微量元素的影響並交叉使用各種市售球化劑與接種劑；球化並接種處理後澆鑄分光試片、拉伸試棒用及階梯厚度鑄件。拉伸試棒與階梯厚度鑄件完全冷卻後開模，加工後量測化學組成成份、拉伸機械性質及顯微金相組織並觀察其相互關係。 由實驗結果可得知在高矽含量3 mm的薄壁球墨鑄鐵中只要少量的殘鎂量(0.02%)即可達到80%以上的球化率，符合球墨鑄鐵規範要求，代表生產薄壁球墨鑄鐵時正常球化處理下，可減少球化劑的使用量。使用含鉍之特殊接種劑處理，在厚度4 mm鑄件球墨數量最高，含鉍的接種處理後可達635 ea/mm2，較厚度3 mm鑄件球墨數量437 ea/mm2高出許多，使用特殊接種處理時冷速若過快則球墨數量不增反減，與一般接種時冷速越快球墨數量越多效果相異。厚度大於6 mm的鑄件，球墨數量影響肥粒鐵基地比例效果逐漸加大，因厚度較厚球墨數量減少使得肥粒鐵基地比例的增長有減緩或下滑之趨勢，鑄件厚度(為冷卻速率)薄壁球墨鑄鐵之肥粒鐵基地比例主要影響因素。 探討抗拉強度與伸長率關係時，比較ASTM A536 65-45-12等級之球墨鑄鐵，證實球化率需高於70%才可達到規範要求。
並列摘要
In this thesis, the microstructure will be studied what the different composition and casting thickness influence on. The base iron uses 100% recycle ductile iron to erase the effect of harmful elements which have micro content. Collect several kinds of commercial nodularitier and inoculants. Utilizing sandwich treatment method and inoculating before pouring. Follow the standard method to prepare the spectrometer, tensile test and microstructure specimen. Measure and study the chemical composition, tensile properties, Brinell hardness and microstructure [nodularity, nodule count, ferrite matrix content etc]. At least residual Mg have to be more than 0.02 % which the nodularity can be achieved 80% at 3 mm casting thickness in high silicon content ductile iron. Which means at high Si content thin-walled ductile iron can use less nodularitier in well Mg treatment. If we use the inoculants Bi alloy included, the nodule count can be achieved to 635 ea/mm2 at 4 mm thickness on thin-walled ductile iron; better than 437 ea/mm2 at 3 mm thickness. The results tell us the inoculants treatment is the most important factor to affect high nodule count than fast solidification rate (casting thickness). We can’t get higher nodule count when the solidification rate is too fast. But casting thickness is the most important factor to affect the matrix ferrite content when the thickness less than 6 mm. At the thickness exceed than 6 mm, the slow solidification rate will affect less nodule count which affect the less ferrite. This reason causes the matrix ferrite content will not raising continuous according thick casting. As ASTM A536 Ductile Iron grade, drawing the tensile strength and elongation relation, if we want to get the good quality ductile iron, the minimum nodularity is not less than 70%. We can get this result in this experiment.