Designing of the formation process of recyclable eco-steels

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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.