晶内铁素体形核与三维形态控制的研究

发布时间：2018-04-14 10:17

  本文选题：晶内铁素体 + 三维形貌　； 参考：《华北理工大学》2017年硕士论文

【摘要】：采用扫描电镜、拉曼光谱分析仪、高温淬火相变仪和高温共聚焦显微镜分别研究了夹杂物的尺寸和相组成成分、连续冷却的速度、奥氏体晶粒的尺寸在晶内铁素体形核过程中所起的作用。同时将聚焦离子束与电子背散射衍射结合,采用连续截面-计算机辅助三维重建的技术建立晶内铁素体的三维空间模型,揭示了其在三维空间层面上的形貌特征、联锁组织的形成原因并通过EBSD的分析手段分析了它的取向关系变化,进而对晶内铁素体的形核机理做了进一步的研究。主要研究结果如下:夹杂物诱导铁素体形核的能力因其尺寸的不同而有所差别,其尺寸增加时它的形核率是逐渐增加的,并存在一个峰值,3~4μm是最佳尺寸。典型的有效夹杂物的心部为Ti2O3和铝氧化物,MnS在其外部析出,从而形成贫锰区。在0.3~3℃/s这一范围内能获得针状铁素体,其中1℃/s最佳。奥氏体晶粒的平均尺寸正比于保温时间。晶内铁素体三维空间上的形貌多样,包括三棱柱状、板条状、等轴薄片状,甚至表现为不规则形状。较大尺寸的铁素体,它不是由某一个个体长大形成,而是由若干个小铁素体组合形成。铁素体融合长大的特点是长大后它的边界平直、光滑,表面也较为平整,没有铁素体之间的分界线;铁素体相互碰撞长大的特点是它们的边界并不平直、光滑,分界线清晰且表面凹凸不平。铁素体在生长时发生激发形核、碰撞、交叉现象,从而形成联锁组织。该组织内部取向差较小,绝大多数在2°以内而其边界的取向差较大,呈大角度晶界彼此分开。对于此实验钢,存在4种形核机制共同促进晶内铁素体的形成。夹杂物作为惰性介质的表面,提供适宜的形核地点和晶核形成的驱动力。MnS和铁素体间较小的错配度促进了晶内铁素体晶核的形成。MnS在Ti2O3表面沉淀析出形成贫锰区以及大量的激发形核都可加速晶内铁素体的形成。
[Abstract]:The size and phase composition of inclusions and the rate of continuous cooling were studied by scanning electron microscope, Raman spectrum analyzer, high temperature quenching phase transformation instrument and high temperature confocal microscope, respectively.The role of austenite grain size in the nucleation of intracrystalline ferrite.At the same time, by combining focused ion beam with electron backscattering diffraction, the three-dimensional spatial model of intragranular ferrite was established by using continuous cross-section and computer aided three-dimensional reconstruction technique, and its morphology characteristics at the three-dimensional level were revealed.The formation reason of interlocking structure and the change of orientation relationship of interlocking structure were analyzed by means of EBSD, and the nucleation mechanism of intracrystalline ferrite was further studied.The main results are as follows: the ability of inclusions to induce ferrite nucleation varies according to its size, and the nucleation rate increases gradually when the size increases, and there is a peak value of 3um 4 渭 m as the optimum size.The typical core of effective inclusions is Ti2O3 and aluminum oxide (MNS) precipitated from the outside of the inclusions, thus forming the manganese poor zone.Acicular ferrite can be obtained in the range of 0.3 鈩，

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