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系統識別號 U0026-0812200915382733
論文名稱(中文) 低碳鋼在冷卻過程中相變態之 理論模型與實驗
論文名稱(英文) Theoretical modeling and experiments for phase transformation of low carbon steel during continuous cooling
校院名稱 成功大學
系所名稱(中) 材料科學及工程學系碩博士班
系所名稱(英) Department of Materials Science and Engineering
學年度 97
學期 2
出版年 98
研究生(中文) 雲建順
研究生(英文) Chien-Shun Yun
電子信箱 n5696147@mail.ncku.edu.tw
學號 N5696147
學位類別 碩士
語文別 中文
論文頁數 77頁
口試委員 口試委員-潘永村
口試委員-陳立輝
口試委員-敖仲寧
指導教授-郭瑞昭
中文關鍵字 熱力學數學模型  電子背向散射繞射分析  熱膨脹分析  相變態數學模型 
英文關鍵字 Thermodynamic mathematical model  EBSD analysis  thermal expansion analysis  phase transformation mathematical model 
學科別分類
中文摘要 本篇論文著墨於低碳鋼在連續冷卻中相變態以及微結構的演化過程之模型並以實驗予以佐證。在此模型中相變態的過程描述如下,首先當溫度降至Ar3溫度時沃斯田鐵會開始變態為肥粒鐵,在初期的階段肥粒鐵變態將會應循「成核及成長(nucleation and growth)」模型,接著當沃斯田鐵上能夠形成肥粒鐵核的位置皆被占滿時將會進入「據點飽和(site saturation)」的階段,此時將僅有唯成長階段(growth only)而沒有成核的行為,當溫度降至Ar1溫度時結束初析肥粒鐵之變態而開始了波來鐵組織變態。
在進行相變態比例預測前必須先計算在不同溫度下之成核速度、成長速度、擴散係數,這三者的計算必須先獲得在不同溫度下之平衡濃度以及相變態之自由能差這些熱力學數據,因此本論文必須先建立熱力學模型計算相變態方程式所需用到的平衡濃度以及相變態之自由能差這些熱力學數據。
為了得到在不同冷卻速度之Ar3以及Ar1溫度需先將試片以不同冷卻速度進行熱膨脹分析實驗找出分別的Ar3以及Ar1溫度,將其代入相變態數學模型計算初析肥粒鐵在此溫度範圍內增量累積之變態量。接著並以電子背向散射繞射分析最終微組織中各相的比例,其結果和以相變態數學模型結果相較下,在低冷卻速度時模擬預測值和實驗觀察值較為接近而在高冷卻速度下有較大的差異。
英文摘要 The thesis is focused on the establishment of a model, which predicted the phase transformation process of low carbon steel during continuous cooling, and utilized some experiments to prove the mathematic model. In this model, the progress of transformation is assumed as follows. The transformation from austenite to ferrite starts at the Ar3 temperature and ended at the Ar1 temperature followed by the transformation of pearlite .
The ferrite transformation follows ‘nucleation and growth’ model at the early stage and then follows ’site saturation’ model at the later stage. Owing to the phase transformation equation consisted of nucleation and growth mechanisms, so it’s necessary to calculate the diffusivity, nucleation rate and growth rate previously. However, these calculations were functions of some thermodynamic parameters, which included the equilibrium concentration and Gibbs free energy change of phase transformation. As a result, it’s a must to establish a thermodynamic model to calculate these thermodynamic parameters. The study also used the EBSD to analyze the final microstructure, including phase fraction and grain size distribution. Because the model required the Ar3 and Ar1 temperature of different cooling rate, we experimented the thermal expansion analysis of different cooling rate to derive the Ar3 and Ar1 temperature, and then calculated the transformation fraction of pre-eutectoid ferrite within the range.
Ultimately, we proceeded the EBSD analysis to observe the phase fraction of pre-eutectoid ferrite. In comparison with the experimental and simulated result, the value was much closer in the slow cooling rate than that in the quick cooling rate.
論文目次 中文摘要 ....................................................................................... I
ABSTRACT ............................................................................... III
致謝 ............................................................................................. IV
總目錄 ......................................................................................... V
表目錄 ..................................................................................... VIII
圖目錄 ........................................................................................ IX
第一章 前言 ................................................................................ 1
第二章 文獻回顧與基礎理論 .................................................... 4
2.1. 相變態熱力學理論 ........................................................... 4
2.1.1. 熱力學模型之比較 ...................................................... 4
2.1.2 相變態平衡條件及相變態之驅動力 ........................ 13
2.2 相變態動力學理論 ......................................................... 16
2.2.1 成核理論 .................................................................... 16
2.2.2 成長理論 .................................................................... 19
2.2.3 相變態比例 ................................................................ 22
第三章 實驗方法與模擬演算法 .............................................. 24
3.1 實驗方法 .......................................................................... 24
3.1.1 熱膨脹分析 ................................................................ 24
3.1.2 微觀組織分析 ............................................................ 25
3.2 模擬演算法 ..................................................................... 27
3.2.1 熱力學參數之計算 ....................................................... 27
3.2.2 動力學參數之計算 ....................................................... 30
第四章 模擬與實驗結果 .......................................................... 31
4.1 熱力學之數值模擬 ......................................................... 31
4.1.1 平衡濃度 .................................................................... 31
4.1.2 吉布士自由能 ............................................................ 32
4.2 動力學之數值模擬 ......................................................... 34
4.2.1 擴散係數 .................................................................... 34
4.2.2 成核速率 .................................................................... 37
4.2.3 成長速率 .................................................................... 40
4.2.4 相變態比例 ................................................................ 43
4.3 熱膨脹分析之實驗結果 ................................................. 47
4.4 相變態微觀組織分析 ..................................................... 54
第五章 討論 .............................................................................. 68
5.1 冷卻速度對初析肥粒鐵相比例的影響 ......................... 68
5.2 冷卻速度對初析肥粒鐵相之晶粒尺寸的影響 ............. 70
第六章 結論 .............................................................................. 72
參考文獻 .................................................................................... 74
附錄: 鐵-錳-碳系統之自由能及交互作用能量(單位:J) ........ 76
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