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研究生:黃立全
研究生(外文):Huang Li Chuan
論文名稱:含硼ADI新製程及衝擊韌性之改進
論文名稱(外文):The Effects of Minute Addition of Boron on the Impact Properties of Austempered Ductile Iron
指導教授:張順太
指導教授(外文):Chang Shun Tai
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:材料科學與工程學研究所
學門:工程學門
學類:材料工程學類
論文種類:學術論文
論文出版年:2000
畢業學年度:88
語文別:中文
論文頁數:101
中文關鍵詞:沃斯回火延性鑄鐵衝擊強度
外文關鍵詞:ADIimpact strengthboron
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本研究在探討添加微量硼的球墨鑄鐵,經860℃沃斯田鐵化20分鐘及120分鐘,再經325℃及375℃沃斯回火後,硼含量及上述各熱處理變數對沃斯回火球墨鑄鐵(ADI)衝擊韌性的影響。
實驗結果顯示:經短時間及長時間沃斯田鐵化的球墨鑄鐵之急冷組織觀察及硬度測試,均顯示長時間沃斯田鐵化者,基地組織均勻,硬度變化幅度小,而可歸因於碳的擴散。
對於 325℃回火,加硼之ADI有較穩定的衝擊性質,對於硼含量 38ppm 的試棒,於沃斯回火 60 分鐘,可獲得最佳的衝擊強度。而未含硼的試棒,則在較短的沃斯回火時間,即有最好的衝擊強度。而且添加硼的試棒,其最佳衝擊值比相同熱處理製程的未含硼試棒,多了將近 30J。
對於 375℃ 沃斯回火的試樣添加硼亦可獲得較優異的衝擊性質,對於有硼或無硼試棒的衝擊強度,大體上有隨著沃斯回火時間的增長先上升而後略微下降的趨勢。其中添加微量硼,在高溫沃斯田鐵相之碳含量未完全平衡的組合,獲得最佳之衝擊強度。
就相同成分,但不同沃斯田鐵化時間的試樣來比較,在高溫時沃斯田鐵相內碳含量非完全平衡的試樣比完全平衡的試棒,其最大衝擊值較高,且出現較早。
對於添加硼的試棒,衝擊時的最大荷重,破斷所需之時間以及撓度,皆較大。而隨著沃斯回火時間的增加,上述三項性質皆會先上升後遞減,並與衝擊強度相呼應。然對於非完全平衡情況下的破斷時間及撓度會較完全平衡情況者為佳,但最大荷重則是完全平衡者較高。
而在相同組成,相同沃斯田鐵化溫度及時間,但進行沃斯回火熱處理溫度不同,時間相同的試棒來比較,可以發現,在 325℃ 進行沃斯回火熱處理者,其衝擊最大荷重較高;而在 375℃ 進行沃斯回火熱處理的試棒破斷所需時間以及撓度皆較優異,主要是因為上變韌鐵與下變韌鐵組織型態差異所致。
以加硼球墨鑄鐵為基材經沃斯回火所得之ADI,其衝擊性質較未含硼之同一基材優越,其原因應與硼與碳、氮相互結合形成之介在物有關。此介在物顆粒微細,僅0.5~1.0微米,遍佈基地。其定量關係,尚無法確立。
破壞面型態則隨 ADI 的延韌性優劣而有不同,延韌性佳者呈蜂巢孔延性破壞型態;反之,延韌性劣者則呈準劈裂破壞型態。
In this study, the effect of minute addition of boron (38ppm) on the impact properties of austempered ductile iron ( ADI ) has been investigated. The austenitizing schedule is set at 860℃ for 20mins or 120mins and then austempering at 325℃ or 375℃.
The optical micrographs and hardness profile of nodular cast iron without boron after austenitizing at 860℃ for 20mins or 120mins and then quenched show that a quenched nodular cast iron austenitizing for a longer time has a relatively uniformed matrix, and its hardness shows less scattering due to the sufficient diffusion of carbon at high temperature.
For samples austempered at 325℃, ADI with boron posses less scatted impact properties than that without boron. Maximum impact strength of ADI with 38ppm boron is obtained as austempered for 60mins. But maximum impact strength of ADI without boron is obtained for less austempering time. Maximum impact strength of ADI with boron, however, is better than that without boron by 30J for the same treatment.
Excellent impact properties are also found in ADI with boron after austempered at 375℃. The impact strength of ADI increases and then decreases with increasing austempering time. ADI with and without boron both have this trend. Best impact strength of ADI is obtained at boron content of 38ppm and austenitizing for 20mins and then austempering at 375℃.
For the samples received at the same component but different austenitizing time, the maximum impact strength of the sample that carbon is unsaturated in austenite at high temperature is better than that of the sample that carbon is saturated in austenite at the same high temperature, and it appears at a shorter austempering time.
The maximum load, duration time, and deflection during impact test of the samples with 38ppm boron are more favorable than that without boron. Those properties increase and then decrease with increasing austempering time as does the impact strength. The duration time and deflection of the samples in which carbon is unsaturated in austenite are better appreciated than that carbon is saturated, while the maximum load of the samples in which carbon is saturated is higher.
For the samples at the same austenitizing temperature, austenitizing time, and austempering time but different austempering temperature show that a maximum load is higher at 325℃ austempered; on the other hand, the duration time and deflection are favorable at 375℃ austemered. The difference depends mainly on the microconstituents of upper bainite, lower bainite, and tempered martensite.
The impact properties of ADI with boron are better than that without boron, and the improvement is attributed to boron-contained inclusions. The tiny inclusions are around 0.5~1.0μm and spread all over the matrix. Its quantitative relation with property is not established yet in this study.
Fractomicrographs are different with the impact properties. The better impact properties is associated with dimple mold, but the fair impact strength is sometimes associated with a quasi-cleavage in nature.
中文摘要……………………………………………………………. Ⅰ
英文摘要……………………………………………………………. Ⅳ
論文目錄……………………………………………………………. Ⅵ
圖目錄………………………………………………………………………… Ⅷ
表目錄………………………………………………………………ⅩⅡ
第1章 前言………………………………………………………... 1
第2章 原理及文獻回顧…………………………………………... 3
2.1 球墨鑄鐵的沃斯回火熱處理……………………………….. 4
2.2 球墨鑄鐵的變韌反應……………………………………….. 5
2.3 變韌鐵的型態……………………………………………….. 6
2.4 影響ADI機械性質的因素…………………………………. 7
2.4.1 沃斯田鐵化溫度與時間的影響………………………… 7
2.4.2 沃斯回火溫度與時間的影響…………………………….. 7
2.5 合金添加的影響……………………………………………… 8
2.5.1 個別合金的影響…………………………………………. 9
2.5.2 合金偏析的改善………………………………………. 10
2.6 偏析情況下的變韌鐵變態………………………………… 11
2.7 沃斯田鐵基地碳含量的量測……………………………… 14
2.8 硼在鋼中及鑄鐵中的效應……………………………….… 15
2.9 含硼ADI之抗拉性質………………………………………. 18
2.10 ADI的斷面特徵與破裂傳播……………………………… 19
2.11 石墨對ADI破壞形式的影響……………………………... 20
第3章 實驗方法與步驟…………………………………………... 28
3.1 合金熔煉…………………………………………………… 28
3.1.1 原料及副原料…………………………………………. 28
3.1.2 熔煉及鑄造……………………………………………. 28
3.2 衝擊試樣之製備…………………………………………… 29
3.3 肥粒鐵化處理……………………………………………… 30
3.4 沃斯田鐵化碳含量與時間的選擇………………………… 30
3.5 沃斯田鐵化及沃斯回火處理……………………………… 32
3.6 衝擊強度及硬度測量……………………………………… 33
3.7 成分分析及金相觀察……………………………………… 33
第4章 結果與討論………………………………………………. 43
4.1 鑄態與肥粒鐵化的球墨鑄鐵組織比較………………….. 43
4.2 鑄態與肥粒鐵化處理後球墨鑄鐵的機械性質………….. 44
4.3 平衡與未平衡沃斯田鐵的急冷組織比較……………….. 46
4.4 ADI中合金元素的偏析…………………………………... 47
4.5 沃斯回火後的機械性質………………………………….. 49
4.5.1 沃斯回火時間對衝擊值的影響……………………... 49
4.5.2 沃斯回火時間對硬度的影響…………………………. 54
4.6 衝擊實驗瞬間荷重與時間的關係………………………….. 54
4.7 破斷面特性之分析……………………………………….. 60
第5章 結論…………………………………………………….….. 90
附錄……………………………………………………………….… 92
參考文獻…………………………………………………………... 96
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