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热电偶单丝法和双丝法是测量保护渣结晶性能很好的方法。对于各种类型的保护渣,采用Avrami方程对随时间变化的结晶率进行建模并与测试结果对比。大多数情况下,Avrami指数大约在1和2之间,两者之间数据吻合。不过在本文的研究中,利用Avrami方程建模时,不是简单地以违反假设条件为评价,而是同时考虑体积形核不仅在纯形核界面上发生,在较低的温度条件下也可能发生。提出一个数学模型并开展实验,各实验的步骤相同,但是需要对结晶区域周围可能发生的情况进行评价。测量的结果很理想,且表明:由于不同结构晶体的析出,结晶率的增长随着时间的推移不断减小。这些发现和现场使用后的保护渣渣膜的微观组织分析的结果一致。在形核发生并达到最大形核率时,晶体开始长大,沿传热方向,以这些晶体作为基底生长成为树枝晶。因此,在利用单丝法(SHTT)的实验里,铂丝和晶体基底的作用是一样的。文中的实验装置可以定量测量保护渣的生长速率,这些数据有助于评估现场使用的保护渣结晶性能。
The thermocouple monofilament method and the twin wire method are good ways to measure the crystallinity of the flux. For various types of mold fluxes, the Avrami equation was used to model the crystallization rate over time and to compare it with the test results. In most cases, the Avrami index is around 1 and 2, and the data match. However, in the study of this paper, when modeling with Avrami equation, it is not simply to evaluate the violation of the hypothesis, but also consider that the volumetric nucleation not only occurs at pure nucleation interface but also at lower temperature . Put forward a mathematical model and experiment, the experiment steps are the same, but need to evaluate the situation that may occur around the crystalline region. The measured results are very good, and show that the growth of the crystallization rate decreases with the passage of time due to the precipitation of different structural crystals. These findings are consistent with the results of the microstructure analysis of the protective slag film after in-service use. When nucleation occurs and reaches the maximum nucleation rate, the crystals begin to grow and grow in the direction of heat transfer, using these crystals as a base to grow into dendrites. Therefore, in the experiment using monofilament method (SHTT), the effect of platinum wire and crystal substrate is the same. The experimental setup in this paper quantifies the growth rate of mold flux and helps to evaluate the crystallinity of mold flux used in the field.