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標題: | 熱處理對 YOKE 8620MX鋼氫脆性質影響之研究 The influence of heat treatment on the hydrogen embrittlement of YOKE 8620MX steel |
作者: | Li-Jen Ho 何立仁 |
指導教授: | 林新智 |
關鍵字: | YOKE 8620MX鋼,麻田散鐵,氫脆,低溫拉伸,回火處理, YOKE 8620MX steel,martensit,hydrogen embrittlement,low temperature tensile test,tempering, |
出版年 : | 2019 |
學位: | 碩士 |
摘要: | YOKE 8620MX鋼為商用合金鋼,在工業上的應用包括防墜器的吊鉤、海洋船隻鋼板等等。淬火後在常溫下最大抗拉強度可達1635MPa,經 600℃鹽浴回火後最大抗拉強度仍超過1000 MPa以上,屬於超高強度鋼。然而材料強度越高越容易受到氫脆的影響,發生氫脆便會造成工程上無法預測的破壞。本實驗透過電化學方式對YOKE 8620MX鋼進行充氫,利用常溫拉伸和低溫拉伸試驗,評估在不同的熱處理條件和不同拉伸溫度下,氫脆對材料機械性質之影響。並使用SEM、TEM來觀察不同熱處理條件下鋼材的微結構和拉伸破斷面,藉此釐清在不同狀況下對材料氫脆性質之影響。
實驗發現,YOKE 8620MX鋼在水淬態下,為板條狀麻田散鐵組織,擁有高差排密度,並觀察到少許自回火的板片。經200℃回火後,開始有細小ε碳化物在麻田散鐵板條之內析出,且差排密度下降,充氫後的吸氫量最低,使之有本研究次佳的抗氫脆能力。經400℃回火後,細小ε碳化物轉變為針狀的雪明碳鐵在麻田散鐵板片內析出,雪明碳鐵與回火麻田散鐵基地組織之介面為可逆氫捕集位置,使其充氫後的吸氫量高於回火200℃的吸氫量,抗氫脆能力因此下降。經600℃回火時,針狀的雪明碳鐵球化,且回火過程中內應力消除,使其差排密度最低,在本實驗中有最佳抗氫脆能力。 在不同溫度下拉伸,YOKE 8620MX鋼的延伸率隨溫度降低而降低,但延伸率損失率隨溫度下降並沒有顯著改變,由實驗可知低溫及充氫都使材料傾向發生脆性破壞,但兩者之間並沒有明顯之加成作用。YOKE 8620MX鋼只有在水淬態下,材料在達降伏強度之前就已經發生破壞,經回火後抗氫脆能力有顯著提升。 YOKE 8620MX steel is a commercial alloy steel, and its industrial applications include hooks for fall arresters, marine steel plates, and so on. After quenching the ultimate tensile strength at room temperature can reach 1635Mpa, and the ultimate tensile strength after tempering in the salt bath at 600 °C is still more than 1000Mpa, which belongs to ultra-high strength steel. However, the higher the strength of the material, the more susceptible it is to hydrogen embrittlement , and the occurrence of hydrogen embrittlement can cause unpredictable damage to the project. In this experiment, YOKE 8620MX steel was charged hydrogen by electrochemical method. The effects of hydrogen embrittlement on the mechanical properties of the material under different heat treatment conditions and different tensile temperatures were evaluated by room temperature tensile tests and low temperature tensile tests. SEM and TEM were used to observe the microstructure and the fractured surface of the steel under different heat treatment conditions to clarifying the influence of the material on the hydrogen embrittlement properties under different conditions. The experiment found that YOKE 8620MX steel in the water quenched state, is lath martensite structure, has the highest dislocation density, and observed a little self-tempered plate. After tempering at 200 °C, fine ε carbides began to precipitate in martensite, and the dislocation density was reduced. The hydrogen absorption after charging was the lowest, therefore it has the better resistance to hydrogen embrittlement. After tempering at 400 °C, fine ε carbides are transformed into cementite precipitated in temper martensite matrix. The interface between cementite and the temper martensite matrix is a reversible hydrogen trapping site, which makes the hydrogen absorption capacity is higher than 200 ° C, and the hydrogen embrittlement resistance is thus lowered. When tempered at 600 ° C, cementite is spheroidized. At this time, due to the elimination of internal stress during the tempering process, dislocation density is the smallest, and the best hydrogen embrittlement resistance ability is obtained in this experiment. When doing tensile test at different temperatures, the elongation of YOKE 8620MX steel decreases with decreasing temperature, but the elongation loss rate does not change significantly with temperature. It is known from experiments that both low temperature and hydrogen charging tend to cause brittle failure, but there is no obvious additive effect between them. YOKE 8620MX steel only in the water quenched state, the material has been destroyed before the yield strength, after tempering, the ability to resist hydrogen embrittlement has been improved. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/21375 |
DOI: | 10.6342/NTU201902891 |
全文授權: | 未授權 |
顯示於系所單位: | 材料科學與工程學系 |
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