مهربد مدرسي عالم

Bearing steels are steels that have high hardness, good strength, very good wear resistance and high fatigue resistance. Among them, steel 52100 or 100Cr6 is used much more than other types. The structure in these steels is mostly martensitic structure with a little residual austenite, which have high hardness and good wear resistance. However, the low toughness and the presence of residual tensile stresses in this structure are problems that reduce the life of the equipment. In recent years, ultra-fine grain bainite steels have been the focus of researchers and large companies producing these steels by creating alternate structures of bainite ferrite and residual austenite. The main problem in this method is the long time required for the transformation of the astemper. It seems that increasing the nucleation sites for the transformation of ferrite can be effective in this regard. For this purpose, in this project, by using thermomechanical operations, the parts are austenitized at two temperatures of 900 and 1100 degrees Celsius and with different values of 5, 10, 15 and 20 The percentage of deformation was subjected to the rolling process and the parts were austempered at 300 degrees Celsius. To check the microstructure of the samples, they were examined with an optical microscope and a scanning electron microscope, and to eva‎luate the percentage of austenite in the structure and to detect the time of completion of the transformation from X-ray diffraction and to calculate the hardness. And strength and elongation were used from hardness test and tensile test. The results show that in 24 hours and by 15%, the transformation of bainite is complete and the strength of the pieces compared to the original piece which has a final strength of 663 MPa is 2-3 times, but the increase in length due to the brittleness of the pieces was reduced to For example, the austenitized sample at a temperature of 1100 degrees Celsius with a deformation percentage of 7% and austempering for 24 hours has reached a final strength of 1803 MPa. And also, based on the results, the increase in percentage of deformation has a direct relationship with strength and hardness and increase in elongation.

بينيت , نورد , آستمپرينگ , آستنيت , درصدتغييرشكل

Bainite , rolling , austempering , austenite , deformation percentage

Mehrbod Modarresi Alam

Roohollah Rahmanifard