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題名 | 不同斷面沃斯回火球墨鑄鐵之高週疲勞性質=Effect of Cast Section Size on the High-Cycle Fatigue Strength of Austempered Ductile Irons |
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作者 | 魏景元; 林志光; | 書刊名 | 鑄工 |
卷期 | 23:4=95 1997.12[民86.12] |
頁次 | 頁1-20 |
分類號 | 472.2 |
關鍵詞 | 沃斯回火球墨鑄鐵; 高週疲勞; 厚斷面; 衝擊韌性值; 球墨直徑; Austempered ductile iron; High-cycle fatigue; Heavy-section casting; Impact toughness; Nodule diameter; |
語文 | 中文(Chinese) |
中文摘要 | 本研究的目的是探討不同斷面尺寸對沃回火球墨鑄鐵高週疲勞性質的影響。實驗材料分為 兩批,第二批材料多加上合金元素鉍(Bi),以了解鉍對改善厚斷面鑄件機械與疲勞性質的影響。熱 處理條件分為最佳韌性與理想強度、硬度兩種,進行疲勞試棒的沃斯回火處理。實驗結果顯示,當 斷面尺寸增加時,鑄件澆鑄凝固的速度降低,凝固時間增加,導致疲勞強度降低。這是因為鑄件尺 寸增加,球墨尺寸增加,球墨形狀劣化,發生縮孔及可能在晶界產生偏析的關係。在厚斷面鑄件取 樣位置不同時,由於澆鑄凝固時間不同,疲勞強度也不同。這與球墨變數和縮孔及可能發生偏析有 關。疲勞限與平均球墨直徑大小及衝擊韌性值有密切的關係,在對數刻度時,當球墨直徑增加,衝 擊韌性值下降時,疲勞限成線性下降,本文提出一個可預測疲勞限的關係式。 |
英文摘要 | This study investigated the relationship between high-cycle fatigue strength of austempered ductile iron (ADI) and cast section size. Two types of ADIs were prepared. The difference between these two materials is that the alloy element Bi was added in the second material. Two austempering heat treatments were applied to generate optimum toughness and optimum strength and heardness. Results showed that as the cast section size increased, the fatigue strength decreased. The decrease in high-cycle fatigue strength is attributed to the increase in graphite nodule size and numbers of microshrinkage pores, the deterioration in nodule shape and possibly the increase in the extent of cell boundary microsegregation as the cast section size is increased. Microstructure analysis showed significantly consistent change in nodule counts and the numbers of microshrinkage pores from the bottom to the top of heavysection casting. This change was attributed primarily to the large change in local solidification time. Fatigue strengths of specimens cut from the bottom of heavy-section casting were superior to those from the top. The nodule counts and nodularity were improved, when alloy element of Bi was added in heavy-section casting so as the fatigue stength. The fatigue limit of ADI depended mainly on graphite nodule size and impact toughness. On the logarithmic scales, the fatigue limit decreased linearly with increasing mean nodule diameter and decreasing impact toughness value. A prediction equation for the fatigue limit of ADI was introduced in terms of the nodule size and impact toughness. |
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