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金属学报  2018, Vol. 54 Issue (3): 367-376    DOI: 10.11900/0412.1961.2017.00262
  本期目录 | 过刊浏览 |
Fe-1.5(3.0)%Si-0.4%C合金贝氏体不完全转变现象及伴随的渗碳体析出
武慧东1,2, 宫本吾郎3, 杨志刚1,2(), 张弛1,2, 陈浩1,2, 古原忠3
1 清华大学材料学院先进材料教育部重点实验室 北京 1000842 清华大学先进核能技术协同创新中心 北京 1000843 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Incomplete Bainite Transformation Accompanied with Cementite Precipitation in Fe-1.5(3.0)%Si-0.4%C Alloys
Huidong WU1,2, Goro MIYAMOTO3, Zhigang YANG1,2(), Chi ZHANG1,2, Hao CHEN1,2, Tadashi FURUHARA3
1 Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
2 Collaborative Innovation Center of Advanced Nuclear Energy Technology, Tsinghua University, Beijing 100084, China
3 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
引用本文:

武慧东, 宫本吾郎, 杨志刚, 张弛, 陈浩, 古原忠. Fe-1.5(3.0)%Si-0.4%C合金贝氏体不完全转变现象及伴随的渗碳体析出[J]. 金属学报, 2018, 54(3): 367-376.
Huidong WU, Goro MIYAMOTO, Zhigang YANG, Chi ZHANG, Hao CHEN, Tadashi FURUHARA. Incomplete Bainite Transformation Accompanied with Cementite Precipitation in Fe-1.5(3.0)%Si-0.4%C Alloys[J]. Acta Metall Sin, 2018, 54(3): 367-376.

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摘要: 

从热力学、动力学角度对Fe-1.5(3.0)%Si-0.4%C (质量分数)合金在400~500 ℃等温贝氏体相变过程中的贝氏体不完全转变阶段可以出现渗碳体析出的现象进行了深入分析。结果表明,贝氏体不完全转变阶段渗碳体的析出动力学非常缓慢。热力学分析表明,缓慢的渗碳体析出动力学与其很小的化学驱动力和/或渗碳体析出需要Si原子配分有关。证实了贝氏体不完全转变现象可以伴随有碳化物析出,但碳化物析出动力学在贝氏体不完全转变阶段需要非常缓慢。

关键词 含Si中碳钢贝氏体不完全转变渗碳体三维原子探针    
Abstract

Steels containing bainite microstructure are widely applied in various industrial areas. Incomplete bainite transformation is frequently used to control volume fraction of retained austenite as well as its stability and is also closely related to bainite growth mechanism. It is generally accepted that incomplete bainite transformation could occur when carbide precipitation is absent. On the other hand, some new studies revealed that carbide with very fine size were observed in “carbide-free” bainite in Si added steels. Our previous study on bainite isothermal transformation kinetics together with its microstructural evolution with Fe-1.5(3.0)%Si-0.4%C alloys (mass fraction) at 400~500 ℃ found incomplete bainite transformation phenomenon for the 3.0Si alloy at 450 ℃ and for two alloys at 400 ℃. In contrast with the generally accepted view, cementite precipitation with Si depletion was observed at the beginning of incomplete transformation stage. Further analysis on three dimension atom probe results revealed that the carbide volume fraction as well as amount of C atoms in carbide hardly changes during incomplete transformation stage. Thermodynamic analysis revealed that small chemical driving force for cementite precipitation and/or the necessity of Si partition are two factors accounting for the extremely slow cementite precipitation kinetics. It is thus proposed that incomplete bainite transformation and carbide precipitation could co-exist. Conditions for incomplete bainite transformation are modified as follows. Firstly, bainitic ferrite growth is stopped before reaching equilibrium fraction. In addition, carbide precipitation should be absent or its kinetics should be slow enough.

Key wordsSi added medium carbon steel    incomplete bainite transformation    cementite    threedimensional atom probe (3DAP)
收稿日期: 2017-07-03     
基金资助:资助项目 国家自然科学基金项目No.51471094
作者简介:

作者简介 武慧东,男,1991年生,博士生

图1  贝氏体不完全转变示意图
Alloy Mass fraction of element / % Temperature / ℃
C Si Fe Para-Ae3 NPLE/PLE T0 Ms
1.5Si 0.375 1.48 Bal. 835 823 674 380
3.0Si 0.379 3.09 Bal. 902 879 688 379
表1  Fe-1.5(3.0)%Si-0.4%C合金的名义成分及其部分特征温度
图2  3.0Si合金在450 ℃贝氏体等温转变30和120 s时显微组织的SEM像及贝氏体铁素体区域的TEM分析[17]
图3  1.5Si合金在400 ℃贝氏体等温转变30和120 s时显微组织的SEM像[17]及贝氏体铁素体区域的TEM分析
图4  3.0Si合金在450 ℃保温30和120 s时三维原子探针10%C、15%C和20%C等浓度界面的C原子分布图
Alloy Temperature Atomic fraction of C Ratio / %
30 s 120 s
3.0Si 450 >10% 1.23 1.06
>15% 0.57 0.51
>20% 0.37 0.32
3.0Si 400 >10% 1.65 1.64
>15% 0.60 0.63
>20% 0.17 0.17
1.5Si 400 >10% 2.45 1.82
>15% 1.51 1.21
>20% 0.69 0.44
表2  3.0Si合金在450和400 ℃,1.5Si合金在400 ℃保温时在贝氏体不完全转变阶段贝氏体铁素体中10%C、15%C和20%C等浓度界面包围的C原子富集区域置换型原子数量占铁素体置换型原子总数的比例
表3  3.0Si合金在450和400 ℃及1.5Si合金在400 ℃对应贝氏体不完全转变初期(30 s)和末期(120 s) 奥氏体和铁素体中C原子数量占比(rγ、rα)变化
Alloy Temperature / ℃ Transformation time / s rγ / % rα / % rγ+rα / %
3.0Si 450 30 82.3 6.7 89.0
120 85.8 5.0 90.8
3.0Si 400 30 80.5 7.0 87.5
120 74.1 7.0 81.1
1.5Si 400 30 45.3 5.1 50.4
120 47.7 4.9 52.6
  
图5  Fe-Si-C体系在450和400 ℃的等温截面相图
图6  Fe-Si-C体系在450和400 ℃的等温截面相图低C部分的局部放大
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