铸铁石墨形态的转变及生长动力学

用LMC定向凝固技术研究铸铁石墨形态的控制,探讨了凝固速度、变质、衰退对石墨形态的影响。在一定条件下获得了反映过共晶铸铁凝固速度和变质剂加入量与石墨形态关系的定量数据。对石墨形态连续衰变过程的观察研究,发现了蠕虫状石墨向过冷石墨转变的分界线。这表明石墨生长机制在分界线处发生了突变,在理论分析和实验探索的基础上,本文提出石墨生长模型,认为在一定条件下,石墨形态可以相互转变。在经历球状石墨(?)蠕虫状石墨(?)过冷石墨(?)A 型片状石墨的变迁中,石墨生长机制发生了渐变(?)突变(?)再渐变的过程。其中球状石墨(?)蠕虫状石墨的转变是渐变,蠕虫状石墨(?)过冷石墨的转变是突变,过冷石墨(?)A 型片状石墨的转变是再一次渐变。

Transition of Graphite Morphologies in Cast Iron and Its Growth Kinetics

The influence of solidification rate as well as modification and fading on thegraphite morphology was investigated by means of LMC directional solidification.The obtained quantitative data have revealed the effect of the solidification rateand the quantity of modifying agent on the graphite morphology.By observing thecontinuous fading process of the graphite morphology,the boundary of the transitionfrom vermicular to undercooled graphite is found.This phenomenon indicates that asudden growth of transition has occurred on the boundary.Based on theoreticalanalysis and the experimental results,a model of the graphite growth has beenproposed.Graphite morphologies are interchangeable under certain conditions.Inthe process of spheroidal(?)vermicular(?)undercooled type D flake(?)type A flakegraphite,the following changes in the graphite growth mechanism result:a gradualtransition,a sudden transition and then again a gradual transition.The transitionof SG(?)VG is a gradual one,VG(?)DFG is a sudden one and DFG(?)AFG is againa gradual one.