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Modeling the austenite decomposition into ferrite and bainite.

机译：模拟奥氏体分解为铁素体和贝氏体。

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摘要

Novel advanced high-strength steels such as dual-phase (DP) and transformation induced plasticity (TRIP) steels, are considered as promising materials for new generation of lightweight vehicles. The superior mechanical properties of these steels, compared to classical high strength steels, are associated with their complex microstructures. The desired phase configuration and morphology can only be achieved through well-controlled processing paths with rather tight processing windows. To implement such challenging processing stages into the current industrial facilities a significant amount of development efforts, in terms of mill trials, have to be performed. Alternatively, process models as predictive tools can be employed to aid the process development' and also to design new steel grades. Knowledge-based process models are developed by virtue of the underlying physical phenomena occurring during the industrial processing and are validated with experimental data.; The goal of the present work is to develop an integrated microstructure model to adequately describe the kinetics of austenite decomposition into polygonal ferrite and bainite, such that for complex thermal paths simulating those of industrial practice, the final microstructure in advanced high strength steels can reasonably be predicted. This is in particular relevant to hot-rolled DP and TRIP steels, where the intercritical ferrite evolution due to its crucial influence on the onset and kinetics of the subsequent bainite formation, has to be quantified precisely. The calculated fraction, size and spatial carbon distribution of the intercritical austenite are employed as input to characterize adequately the kinetic of the bainite reaction. Pertinent to ferrite formation, a phenomenological, physically-based model was developed on the ground of the mixed-mode approach. The model deals with the growth stage since nucleation site saturation at prior austenite grain boundaries is likely to be attained during the industrial treatments. The thermodynamic boundary conditions for the kinetic model were assessed with respect to paraequilibrium. The potential interaction between the alloying atoms and the moving ferrite-austenite interface, referred to as solute drag effect, was accounted for rigorously in the model. To quantify the solute drag pressure the Purdy-Brechet approach was modified prior to its implementation into the model. (Abstract shortened by UMI.)
机译：新型先进的高强度钢，例如双相（DP）钢和相变诱发塑性（TRIP）钢，被认为是新一代轻型车辆的有前途的材料。与传统的高强度钢相比，这些钢的优越机械性能与其复杂的微观结构有关。所需的相构型和形态只能通过具有相当紧凑的加工窗口的良好控制的加工路径来实现。为了将这种具有挑战性的处理阶段实施到当前的工业设施中，必须进行大量的开发试验，例如工厂试验。或者，可以使用过程模型作为预测工具来辅助过程开发并设计新的钢种。基于知识的过程模型是根据工业加工过程中发生的潜在物理现象开发的，并已通过实验数据进行了验证。本工作的目的是建立一个完整的微观结构模型，以充分描述奥氏体分解为多边形铁素体和贝氏体的动力学，从而对于模拟工业实践的复杂热路径，可以合理地获得高级高强度钢的最终微观结构。预料到的。这特别适用于热轧DP和TRIP钢，在这些钢中，由于临界铁素体对后续贝氏体形成的开始和动力学的关键影响，其间的临界铁素体析出必须精确定量。临界奥氏体的计算分数，尺寸和空间碳分布被用作输入，以充分表征贝氏体反应的动力学。与铁素体形成有关，在混合模式方法的基础上建立了一种基于现象学的物理模型。该模型涉及生长阶段，因为在工业处理过程中很可能会达到先前奥氏体晶界的成核位点饱和。针对超平衡评估了动力学模型的热力学边界条件。在模型中严格考虑了合金原子与运动的铁素体-奥氏体界面之间的潜在相互作用，称为溶质拖曳效应。为了量化溶质阻力压力，在将Purdy-Brechet方法实施到模型之前对其进行了修改。 （摘要由UMI缩短。）

著录项

  • 作者

    Fazeli, Fateh.;

  • 作者单位

    The University of British Columbia (Canada).;

  • 授予单位 The University of British Columbia (Canada).;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 202 p.
  • 总页数 202
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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