G80T steel is a special type of M50 steel smelted by electroslag directional solidification. It is a medium-temperature second-generation wear-resistant plate that can withstand 350°C. Judging from the current literature reported at home and abroad, M50 steel is still the main material for manufacturing aero-engine spindle bearings, and the maximum operating temperature can reach 315°C. The ever-increasing DN value (the product of bearing diameter and bearing speed) requires the engine main bearing to have higher bending and torsion resistance, which places higher requirements on the toughness of the bearing material. Existing research results show that the original material of G80T steel can be refined through dynamic recrystallization, thereby improving the toughness of the bearing material and increasing the material strength. In order to ensure that the grains of hot-deformed G80T steel have both fine grains and higher hardness after solution treatment, researchers selected G80T steel with refined structural grains through dynamic recrystallization as raw materials and studied the austenitization temperature. and the effect of austenitization time on structural properties.
The test material is a cast high-temperature wear-resistant plate G80T steel ingot with a diameter of Φ150cm smelted by directional electroslag remelting. Its composition (mass fraction, %) is C0.82, Cr4.11, Mo4.19, V0.97, and the balance Fe.
After the ingot is subjected to high-temperature diffusion annealing for 5 hours, samples are taken and processed into Φ8mm×15mm cylindrical specimens. In order to refine the grain size through dynamic recrystallization, after holding at 1200°C for 2 minutes on the thermal simulation testing machine Gleeble-3800, it was cooled to 1050°C at 5°C/min, and 60% compression was performed at a deformation rate of 10s-1. Deform, then cool to 600°C at 5°C/min and then cool to room temperature to obtain a deformed sample.
The hot-compressed samples were solid solution treated in a box-type resistance furnace at temperatures of 950, 1000, 1050, 1100, 1150, and 1200°C, and then loaded into the furnace when the temperature was reached. The holding times were 5, 10, 30, and 60 min. Quickly oil quench after coming out of the oven. The sample was uniformly cut in half longitudinally along the direction of pressure loading during thermal compression, and the structure and hardness of the center of the longitudinal section were observed.
The results show that as the solid solution temperature increases, the austenite grain size first slowly increases to about 7 to 8 μm before 1050°C, and then grows abnormally as the solid solution temperature further increases. The microhardness of the test steel first increased and then decreased with the solid solution temperature. The microhardness reached 921HV0.2 at 1050°C solid solution, which was caused by the combined effects of fine grain strengthening and carbide precipitation strengthening. Thermodynamic calculation results show that the grain growth behavior of 60% hot-compressed G80T steel during the re-austenitization process is controlled by the diffusion of alloy elements, and its diffusion activation energy is 333kJ/mol.
