https://scholars.lib.ntu.edu.tw/handle/123456789/61994
標題: | D-6ac合金鋼之熱處理研究 | 作者: | 張世達 Chang, Shi-Da |
關鍵字: | 合金鋼;D-6ac | 公開日期: | 2004 | 摘要: | 本實驗之主要目的乃在於尋求D-6ac之最佳熱處理條件,其中包括了沃斯田鐵化溫度、回火溫度、回火速率等因素之配合。 經由機械性質(強度、延性、硬度、衝擊值)之測試及顯微組織(OM、TEM、SEM)的觀察來探討顯微組織與機械性質之關係,來瞭解回火組織之變態程度,進而掌握機械性質之變化,尤其是在回火組織中的碳化物析出的位置、種類、分佈與大小,其變化更嚴重左右著韌性值。 實驗結果顯示D-6ac經850℃ × 1hr 沃斯田鐵化後油淬火,再經200~250℃×2hrs回火可得到高強度並保有足夠韌性(1899∼2116Mpa, 1.17∼1.48kg-m);如經600~650℃×2hrs回火,則可得高韌性並保有足夠強度(1239∼1460Mpa, 4.58∼6.15kg-m)。回火於350℃左右會發生回火麻田散鐵脆性(TME),其原因為麻田散鐵板條界面的殘留沃斯田鐵變態析出雪明碳鐵所造成。回火於550℃以上時,若冷卻速度較慢則會有回火徐冷脆性發生,因此回火後須急冷以避免脆性發生。在沃斯田鐵化後進行深冷處理(subzero cooling),因為有效降低殘留沃斯田鐵含量,則回火後基地可完全地進行變態,析出分佈均勻之雪明碳鐵,便可以有效的提升衝擊韌性值,或者搭配良好的雙重回火條件,如:200℃回火後進行550℃的二次回火,則可以提高單次550℃回火的韌性,而此種回火處理方式,相信跟在第一道200℃低溫回火時,麻田散鐵變態析出大量之ε-carbide有關,其後再進行高溫回火時有促進雪明碳鐵析出並凝聚的效果。 The purpose of this work is to determine the best heat-treatment condition of D-6ac steel, which including the austenitizing temperature, tempering temperature, and cooling rate after tempering. The correlation between the microstructures and the mechanical properties will be discussed. The microstructures were observed by Optical Microscope(OM), Transmission Electron Microscope(TEM) and Scanning Electron Microscope(SEM). Furthermore, the toughness is seriously influenced by the position, type, distribution, and size of the carbide precipitating in the tempered structure. The results show that the specimens oil-quenched from 850℃ and then tempered in the range 200~250℃ would have high strength and sufficient toughness (1899~2116MPa, 1.17~1.48kg-m). If the specimens were oil-quenched from 850℃ and then tempered in the range 600~650℃, they would have high toughness and sufficient strength (1239~1460MPa, 4.58~6.15kg-m). Tempered martensite embrittlement (TME) will happen when D-6ac is tempered at 350℃. Since the retained austenite at lath boundary have transformed to discontinuous cementite along the lath boundary. When tempered at 550℃, slow cooling will cause the tempered embrittlement (TE). However, it can be prohibited by rapid cooling after tempering. Executing the subzero cooling after austenitizing can efficiently reduce the amount of retained austenite. Thus the tempered martensite may uniformly precipitates cementites and prompt it to raise its impact toughness. Two-stage tempering (200℃×1hr + 550℃×2hr) can improve the toughness due to a great deal of ε-carbides were precipitated during first-stage tempering and the ε-carbides will enhance the cementites to precipitate and aggregate during second-stage tempering. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/61333 | 其他識別: | zh-TW |
顯示於: | 機械工程學系 |
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ntu-93-R91522719-1.pdf | 23.53 kB | Adobe PDF | 檢視/開啟 |
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