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首页> 外文会议>New developments on metallurgy and applications of high strength steels >FRACTAL MORPHOLOGY AND MECHANICAL PROPERTIES OF ACICULAR FERRITE MICROSTRUCTURES ON MEDIUM CARBON MICROALLOYED STEELS
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FRACTAL MORPHOLOGY AND MECHANICAL PROPERTIES OF ACICULAR FERRITE MICROSTRUCTURES ON MEDIUM CARBON MICROALLOYED STEELS

机译：中碳微合金钢上针状铁素体微结构的分形形态和力学性能

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The acicular ferrite is a highly sub-structured non-equiaxed ferrite often developed under continuous cooling conditions. Researches conducted on welds have shown that this austenite decomposition product is actually an intragranularly nucleated bainite. Like bainite, acicular ferrite partially grows by a displacive transformation mechanism. The main difference between both microstructures lies in the nucleation sites of lenticular plates. Acicular ferrite plates nucleate on non-metallic inclusions inside the austenite grains and develop autocatalytically in a chaotic interlocked arrangement. This misoriented disposition of plates produces an attractive strength-toughness combination. rnWhen characterizing acicular ferrite microstructures a major complexity arise which is linked to the geometry of plates. Indeed, acicular ferrite plates are not only randomly oriented in the space but they also developed in several generations which show extremely dissimilar sizes. This “roughness” of acicular ferrite microstructures can only be revealed by means of electron microscopy observations. Scanning and transmission electron microscopy (SEM TEM) observations have also revealed the self-similarity of acicular ferrite plates. rnFractal geometry is known to provide a useful framework to characterize irregular and selfsimilar metallic microstructures from both qualitative and quantitative point of view. In the present study, to better understand the particular morphology of acicular ferrite, a fractal analysis has been conducted on medium carbon microalloyed steels microstructures, using an imaged based box-counting methodology. This characterization has proved that acicular ferrite has a fractal nature in microstructures of steels with a given chemical composition under defined thermal conditions. rnIn the second part of the work, mechanical tests have been carried out and the influence of the fractal morphology of acicular ferrite on the mechanical properties of three medium carbon microalloyed steels has been studied. The results point out an exponential relationship between fractal dimension of acicular ferrite and properties like strength.
机译：针状铁素体是高度亚结构的非等轴铁素体，通常在连续冷却条件下产生。对焊缝的研究表明，该奥氏体分解产物实际上是晶内成核的贝氏体。像贝氏体一样，针状铁素体通过位移转变机制而部分生长。两种微观结构之间的主要区别在于双凸板的成核位置。针状铁素体板在奥氏体晶粒内的非金属夹杂物上成核，并以混沌的互锁结构自动催化发展。板的这种方向不正确的布置会产生有吸引力的强度-韧性组合。当表征针状铁素体的显微组织时，会出现很大的复杂性，这与板的几何形状有关。的确，针状铁素体板不仅在空间中随机定向，而且还发展了几代，其尺寸极为不同。针状铁素体微结构的这种“粗糙度”只能通过电子显微镜观察来揭示。扫描和透射电子显微镜（SEM TEM）的观察也揭示了针状铁素体板的自相似性。分形几何形状提供了一个有用的框架，可以从定性和定量的角度表征不规则和自相似的金属微观结构。在本研究中，为了更好地理解针状铁素体的特殊形态，已使用基于图像的盒计数方法对中碳微合金钢的显微组织进行了分形分析。此特征已证明，在给定的化学条件下，针状铁素体在具有给定化学成分的钢的显微组织中具有分形性质。在工作的第二部分中，进行了力学测试，并研究了针状铁素体的分形形态对三种中碳微合金钢的力学性能的影响。结果指出针状铁素体的分形维数与强度等性质之间呈指数关系。

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