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標題: | 含鈦、硼、鈮鋼板之大入熱量銲接銲道與熱影響區顯微組織研究 An Investigation on Microstructure of High Heat Input Welded Steel Plates with Ti、B、Nb |
作者: | Yu Chen 陳佑 |
指導教授: | 楊哲人 |
關鍵字: | 針狀肥粒鐵.晶粒內肥粒鐵.大入熱量銲接,熱影響區,鈦鈮複合型析出物, Acicular ferrite,Intragranular ferrite,High heat input welded,Heat affected zone,Complex carbonitrides (Ti,Nb)(C,N), |
出版年 : | 2009 |
學位: | 碩士 |
摘要: | 隨著工業的發展,大入熱量的銲接技術不斷進步,現今已經廣泛的在造船業、建築業、造橋工業等各方面應用。以往銲接熱影響區韌性不佳的問題目前已經可藉由合金設計的方式,控制沃斯田鐵晶粒大小以及產生理想的顯微結構來提升機械性質,但對於其詳細結構的發展機制仍然不甚了解,因此本研究對於銲道與熱影響區做了一系列顯微結構與機械性質的探討。
由顯微組織的觀察可發現銲道區域的典型針狀肥粒鐵以及熱影響區粗晶區的晶粒內肥粒鐵擁有相同的透鏡狀平板外型,但兩者尺寸相差約十倍。經由差排密度的量測可發現結構中均擁有高量的差排密度,這是由於兩者都是經由displacive相變態機制,為了維持不變平面應變而導入了高量的差排於其中。而透過鋼板設計鈦、鈮、硼合金元素的添加,使得熱影響區粗晶區晶粒大小控制在500μm左右,結構也以晶界上的高溫肥粒鐵以及晶粒內部的晶粒內肥粒鐵為主,性質不佳的費德曼肥粒鐵數量大幅減少,熱影響區的韌性甚至已經超越了銲道區域。 將實際焊接觀察結果與Gleeble熱模擬熱影響區粗晶區溫度曲線之結果對照,可發展出粗晶區晶粒內肥粒鐵之成核機制:當銲接完成從尖峰溫度緩慢冷卻時,(Ti,Nb)(N,C)複合型析出物會在先前沃斯田鐵內析出,此複合型析出物與沃斯田鐵之間有著cube-to-cube方位關係。由於擁有特定方位關係且晶格匹配性良好降低之間的介面能,同時在析出物周圍產生的Nb、C空乏區增加了相變態驅動力,晶粒內肥粒鐵會以此複合型析出物為成核位置成核生長,且兩者之間擁有Baker-Nutting方位關係,此為初生晶粒內肥粒鐵(Primary IGF);而從初生晶粒內肥粒鐵以及晶粒內部Idiomorphic Ferrite(IF)上經由sympathetic nucleation方式所生長出的次生晶粒內肥粒鐵(Secondary IGF)則會與先前沃斯田鐵之間擁有K-S方位關係。 To support the recent construction and transportation industries, a high strength steel plate associated with the high heat input welding technique has been developed. By alloy design, controlling austenite grain size and desired microstructure, the toughness in heat affected zone has been largely improved. The high heat input welded steel plate is produced by China Steel Corporation.In one aspect, the purpose of this study is to understand the relationship among microstructure of welded zone, microstructure of heat affected zone and the excellent mechanical properties after welding. In the other aspect, this study aims to elucidate the transformation mechanism of intragranular ferrite(IGF) in the heat affected zone. The microstructure of welded and heat affected zone have been investigated by optical microscope and transmission electron microscope. The acicular ferrite in welded zone and intragranular ferrite in heat affected zone both have high dislocation density. By addition of Ti, Nb, B, the prior austenite grain size can be refined to 500μm. Besides, the amount of widmenstatten ferrite can be reduced and further increase the amount of Intragranular ferrite by the present alloy design. Such a fine microstructure in the heated affected zone achieves excellent toughness superior to the toughness in welded zone. In order to study the transformation mechanism of intragranular ferrite, Gleeble machine was used to simulate the practical welding condition and the microstructure was studied by step quenching method using OM and TEM. During the cooling process, the complex carbonitrides (Ti,Nb)(C,N) precipitated from austenite grain with the cube-to-cube orientation relationship. These carbonitrides act as the nucleation sites for intragranular ferrite. The intragranular ferrite precipitating on the carbonitrides with the Baker-Nutting orientation relationship is called primary IGF. The following Intragranular ferrite called secondary IGF can transform by sympathetic nucleation and adopt K-S orientation relationship with the prior austenite grain. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/25970 |
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顯示於系所單位: | 材料科學與工程學系 |
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