A Comparative Study of Kinetic Models Regarding Bainitic Transformation Behavior in Carburized Case Hardening Steel 20MnCr5
A Comparative Study of Kinetic Models Regarding Bainitic Transformation Behavior in Carburized Case Hardening Steel 20MnCr5
复制标题
DOI：
10.1007/s11661-018-5004-6
复制
发表时间：
2018-11
期刊：
影响因子：
--
通讯作者：
J. Damon;F. Mühl;S. Dietrich;V. Schulze
中科院分区：
文献类型：
--
作者：
J. Damon;F. Mühl;S. Dietrich;V. Schulze
本文对碳含量在0.2 ~ 0.8wt%范围内的20 MnCr 5表面硬化钢进行了等温贝氏体相变动力学研究。选择多个奥氏体化温度来研究奥氏体晶粒粗化对相变动力学的影响。在60多条转化曲线上对Johnson-Mehl-Avrami-Kolmogorov（JMAK）方程、Austin-Rickett（AR）方程以及货车Bohemen提出的自催化（AC）模型进行了评价。在拟合质量方面，AR动力学是上级的，虽然所有的模型显示出良好的符合实验数据。结果表明，整体活化能的解释可能是高度模糊的。此外，增长指数的JMAK/AR方程被发现与分散的值之间的1.5-4.5和2.0-6.0，分别增加。这一发现表明，不能用贝氏体亚基的生长尺寸来解释生长指数的值。此外，对无扩散方法的动力学模型进行了评价，并将活化能与货车Bohemen的工作进行了比较。由于考虑到晶粒尺寸对相变延迟的影响，对每种合金都评估了令人惊讶的恒定OAE，而与奥氏体化温度无关。此外，发现OAE值接近货车Bohemen的发现，约。190至200 kJ/mol。最后，提出了自催化因子与碳含量的指数依赖关系。
Isothermal bainite transformation kinetics have been carried out and evaluated for the case hardening steel 20MnCr5 with the carbon content ranging between 0.2 and 0.8 wt pct in a wide span of isothermal temperatures. Multiple austenitization temperatures were chosen to investigate the effect of austenitic grain coarsening on the effect of transformation kinetics. Three well-known transformation kinetic equations were evaluated on more than 60 transformation curves, the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation, the Austin–Rickett (AR) equation, as well as an autocatalytic (AC) model proposed by van Bohemen. In terms of fit quality, the AR kinetic is superior, although all models show a good accordance with experimental data. The results demonstrate that the interpretability of overall activation energies can be highly ambiguous. Also, an increase for the growth exponent of JMAK/AR equations was found with a scatter of values between 1.5–4.5 and 2.0–6.0, respectively. This finding demonstrates that the value of the growth exponent cannot be interpreted in terms of growth dimension of the bainitic subunits. Furthermore, the kinetic model on a diffusionless approach was evaluated, and the activation energies were compared to work from van Bohemen. Due to the consideration of the grain size on the delay of transformation a surprisingly constant OAE was evaluated for every alloy irrespective of the austenitization temperature. Also, found OAE values are close to findings by van Bohemen with approx. 190 to 200 kJ/mol. Finally, an exponential dependency of the autocatalytic factor with respect to carbon content was proposed.