The effects of chemical composition variations on microstructure and mechanical properties of nanostructured, low temperature bainitic steels

Abstract

Bainitic transformation at low transformation temperatures leads to a microstructure involving fine plates of bainitic ferrite and thin films of retained austenite. This microstructure has shown ultimate tensile strength of about 2.2 GPa, noticeable uniform elongation in the range of 5 to 30%, hardness values of about 600 to 670 HV and impact toughness in the range of 30 to 40 MPa m1/2. With careful design of the chemical composition of steel, suitable mechanical properties with lower cost production could be achieved. In the current work, the microstructure and mechanical properties of two steels with different chemical compositions have been evaluated using XRD, SEM, TEM, tensile and Charpy impact tests. The results of this study suggest that without trial and error, it is possible to design a new steel with unique microstructure and mechanical properties. The achieved mechanical properties are due to the microstructural characteristics which evolved during isothermal transformation.