چكيده به لاتين
During the last few decades, nanostructured bainite steels have received special attention due to their special mechanical properties, including high strength and hardness, acceptable toughness, and relatively low productioncosts. The biggest problem for the industrialization of this class of steels is the relatively long period of isothermal transformation of bainite, which increases production time and costs. Therefore, during recent years, by doing different things such as changing the composition of the steel alloy, changing the temperature and time of isothermal transformation, or doing additional work before and after the transformation, such as applying mechanical work and momentary quenching, it has been tried to reduce the production time. In this research, it has been tried to select the composition of the researched steel in such a way that in addition to achieving the usual physical and mechanical properties of nanobainite steels, it also has good kinetic properties. As a result, steel with the composition of0.79C-0.32Si-1.57Mn-0.57Cr-0.35Mo-3.5Al (%Wt.)was designed and prepared. After casting, the ingot was subjected to hot rolling and homogenization. To perform austempering heat treatment, the samples were austenitized at 950℃ for 60 minutes and subjected to bainite transformation at three temperatures of 250℃, 275℃ and 300℃ at different times and then cooled in air. Microstructural investigations were carried out using optical and scanning electron microscopes and phase investigations by X-ray diffraction. Finally, the austempered samples were tested for hardness and the tensile behavior of some of them was investigated. The results of the microstructural investigations showed that depending on the temperature of Austemper, microstructures with nanometer components can be obtained; So, after transformation at temperatures of 250℃, 275℃ and 300℃, bainite ferrite plates with a thickness of about 50nm, 55nm and 65nm were observed. The values of yield strength, ultimate tensile strength and elongation were obtained in the range of 1200-1600 MPa, 1600-2000 MPa and 12-20% depending on the temperature and time of the austempering process. Hardness measurement results also indicated high hardness for Austemper samples in the range of 544-456HV.
