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金屬模離心鑄造法研製梯度分佈TiC強化球墨鑄鐵基複合材料

A Study on Metal Mold Centrifugal Casting of Ductile Iron Based Composites with Graded Distribution of TiC

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[[abstract]]本實驗是利用改變Ti含量(0~0.91wt%)、接種劑添加量(0.6~1.0wt%)、球化劑添加量(1.2~1.4wt%)及澆鑄溫度(1327~1413℃)等實驗參數,再利用金屬模離心鑄造,研製內表層具TiC濃度梯度分佈之球墨鑄鐵基複合材料,探討Ti含量及離心鑄造製程參數,對TiC顆粒在球墨鑄鐵管中因離心力作用下之分佈情形,及其對球墨鑄鐵顯微組織和機械性質的影響。 本實驗採合金設計的方法,在鑄造時添加鈦鐵,以自生(In-Situ)的方式在球墨鑄鐵中析出TiC。而在金屬模離心鑄造下,因TiC之比重為4.94較鐵水(7.2)小,故在離心力的作用下,會分佈於球墨鑄管之內表面層,而形成TiC濃度梯度分佈之球墨鑄鐵基複合材料。試片取樣位置,以澆鑄端為原點,分別距澆鑄端30mm(以下稱為澆鑄端)、370mm(以下稱為中央處)和710mm(以下稱為非澆鑄端)處,擷取一扇形試片。分析距外管壁1mm、10mm和19mm處。利用WDS、XRD分析析出物化學組成與相組成,以OM、SEM觀察顯微組織。此外,利用影像分析儀(IA),對石墨與TiC量作定量計算,而以節點法(Point Counting)對肥粒鐵、雪明碳鐵作定量計算,波來鐵的含量則是以百分之百面積分率減去其它已算出的面積分率。在機械性質分析方面,取樣位置為鑄管中央處,測試拉伸及衝擊試驗;在硬度試驗方面,量測HRc及微硬度Hv(Microhardness)。 實驗結果顯示,利用金屬模離心鑄造,已可成功鑄造出內表層具有TiC顆粒分佈之球墨鑄鐵基複合材料。當Ti含量為0.22wt%時,內表層與外表層TiC顆粒的分佈量無明顯差異;當Ti含量大於0.22wt%時,隨TiC含量增加有上升的趨勢。TiC層的厚度為非澆鑄端>澆鑄端>中央處,而在距外管壁19mm處,TiC量為中央處>澆鑄端>非澆鑄端,而TiC量在整個扇形面積為非澆鑄端>澆鑄端>中央處。TiC顆粒大小平均為2~4μm。而在內管壁附近的鑄管軸向,TiC顆粒量的多寡依序為中央處、澆鑄端、非澆鑄端。此外,基地雪明碳鐵含量亦會隨Ti含量增加而上升;而就雪明碳鐵形成傾向而言,在軸向依次為非澆鑄端>澆鑄端>中央處,在徑向則為外管壁大於內管壁。對基地組織而言,隨Ti含量增加,肥粒鐵含量有下降趨勢,波來鐵含量有上升趨勢。在機械性質方面,強度會因Ti含量而小幅度升高,延、韌性則隨Ti含量增加而降低,即隨TiC量的改變,而有較明顯的變化。在硬度試驗中,HRC值隨Ti含量的增加而增加,而在相同Ti含量,內、外管壁的硬度值卻沒有明顯的變化,但在微硬度測試結果顯示,內管壁硬度值相較於外管壁則有明顯提昇。對石墨而言,當隨Ti含量增加,石墨會有退化的情形。球化劑在1.3wt%時,可使球墨退化情形獲得改善,球化率可達95%。接種劑有明顯抑制白口化的頃向,而達到減少雪明碳鐵量之目的。當澆鑄溫度提升到1413℃時,基地的雪明碳鐵、波來鐵量增加,而肥粒鐵量減少。

[[abstract]]The effect of process parameters, which include the amount of Ti(0~0.91wt%), the amounts of inoculant (0.6~1.0wt%), the amount of spheroidizer (1.2~1.4wt%) and the pouring temperature (1327~1413℃), on the distribution of TiC in ductile iron matrix, microstructures, and mechanical properties of ductile iron based composite were studied. The final purpose of this study is to manufacture ductile iron based composites with distribution of TiC reinforcing particles on the inner surface layer of the tube by using metal mold centrifugal casting. Owing to the fact that the specific gravity of TiC (4.94) is smaller than liquid iron(7.2). Therefore, the TiC particles are distributed to the inner surface layer of ductile iron tube under the action of centrifugal force. Specimens were section from pouring end (30mm away from the pouring end), central part (370 away from the pouring end), non-pouring end (710mm away from the pouring end). WDS and XRD were used to identify the TiC particles. Quantitative metallography of TiC, graphite and matrix structures were conducted using image analyzer and point counting method. The tensile property, impact toughness, and hardness were tested. The results showed that the ductile iron based composite with distribution of TiC particles on inner surface layer can be produced successfully. When the amount of Ti is lower than 0.22wt%, the fraction of TiC doesn’t change in interior region and outside region of ductiron tube. But if Ti content is large than 0.22wt%, the of TiC fraction increases with increasing Ti content in the inner layer of the tube. Thickness of TiC laminates follows the order of non-pouring end > pouring end > central part. The order of TiC fraction in the inner layer is central part > pouring end > non-pouring end. But the total amounts of TiC of the tube follows the order of non-pouring end > pouring end > central part. The average size of TiC particles is 2~4μm. The cementite fraction increases as the Ti content increases. The distribution of cementite is non-pouring end > pouring end > central part on the rotation axis of the tube and outside layer > inside layer along the wall thickness direction of the tube. Ferrite fraction decreases and pearlite fraction increases as Ti content increases. For the mechanical properties, the ductility and toughness decrease with increasing Ti content.

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