Designing of the formation process of recyclable eco-steels

这项工作旨在提供选择适合回收的钢(生态钢)的指导原则，并建议满足所要求的机械性能的化学成分和生产工艺。1)得到了钢的化学成分与热处理和力学性能之间的数值关系，针对Fe-C-Si-Mn等适合回收利用的简单化学成分，用回归方法得到了力学性能(应力-应变曲线、YS、TS、均匀伸长率、断裂伸长率)与化学成分和热处理之间的关系。2)提出了一种预测力学性能的新方法--机械热力学方法，并证明了该方法的适用性，指出决定材料强度的主要因素是结构自由能。认为材料的强度与结构自由能的平方根成正比。当组织由相变产生时，结构自由能是相变驱动力的一定比例，因此可以利用相变驱动力来预测材料的强度。这就是机械热力学。结果表明，珠光体钢的流动应力与相变驱动力的平方根之间存在良好的线性关系。所得相关系数远高于显微组织观察所得的相关系数。最后得出了贝氏体钢和马氏体钢的相变驱动力与强度之间的关系。

This work was aimed to present the guide line to select steels suitable for recycle (eco-steel) and suggest chemical compositions and production process to satisfy the required mechanical properties. The main results obtained were as follows :1) The numerical relationship between the chemical compositions and thermal treatment and mechanical properties of steels were obtained.About the simple chemical composition of steels such as Fe-C-Si-Mn which are suitable for recycle, the relationships between the mechanical properties (stress-strain curve, YS,TS,uniform elongation, fracture elongation) and chemical compositions and thermal treatments were obtained using regression method. Using the obtained equations, the method to calculate the mechanical properties of any given simple chemical compositions of steels after any thermal treatments was established.2) A new method to predict mechanical properties, mechano-thermodynamics, was proposed and the usage of it was proved.It was noted that the main factor which determines the strength of materials was structural free energy. It was considered out that the strength of materials is proportional to the square root of the structural free energy. When the microstructure is produced by phase transformation, the structural free energy is a certain fraction of the transformation driving force.Therefore it is possible to predict the strength of materials using the transformation driving force. This was maned mechano-thermodynamics. It was shown in pearlite steels that good linear relationships exist between the flow stress and the square root of the transformation driving force. The obtained correlation factor was much higher than that obtained from the observation of microstructure. Finally the relationships between the transformation driving force and strength were derived for bainite and martensite steels.