Dynamic Study On Effect Of Austenitizing Process On Spheroidizing Annealing Of GCr15

The original lamellar structure of GCr15 bearing steel is characterized by high hardness,low plasticity and poor processability.It is usually improved by long-time isothermal annealing spheroidization,which takes a long time,has poor spheroidizing effect and consumes high energy.The morphology of carbides before isothermal annealing affects the final spheroidizing effect.Based on the principle of "segregation eutectoid",the austenitizing process is optimized.At this stage,a large number of spheroidized and spheroidized carbides are retained as the nucleation particles of subsequent spheroidization.The traditional way to study the high temperature structure of austenitizing by water quenching is to avoid a part of structural transformation in the rapid cooling process,so it is impossible to study the real-time dynamic microstructure transformation.The high temperature laser confocal microscope can precisely study the carbide morphology changes in austenitizing process in real time and dynamically.According to the dynamic research results,the traditional spheroidizing annealing process can be optimized,and the spheroidizing time can be saved under the premise of ensuring the spheroidizing effect.The results of high temperature laser confocal specimen preparation show that the pearlite in the original structure of GCr15 can be clearly observed under the combined polishing conditions of 3 ? m slurry polishing for 20 min + 1 ? m slurry polishing for 20 min + 50% silica sol polishing for 20 min,and the phase interface is continuous and free of corrosion products.The dynamic study of high temperature laser confocal microscope shows that the effect of austenitizing temperature on the morphology of GCr15 carbide is greater than that of austenitizing heating time.When the austenitizing heating temperature is 790 ?and holding for 10 min,enough dispersed cementite particles can be obtained as the core particles of subsequent spheroidizing nucleation.When the cooling rate of the dual phase zone is-180 ? / h,the distribution of undissolved carbide particles can be ensured,which is conducive to the subsequent spheroidizing annealing.It is found that the nucleation number of cementite will also increase and the distribution tends to be uniform when the number of cycles is properly increased in the early stage of austenitizing parameter determination.According to the austenitizing parameters obtained from dynamic experiments of high temperature laser confocal microscope,the annealing process was optimized.Finally,the optimized continuous annealing process is obtained,and the spheroidizing rating and hardness meet the national standard,and the total time is about3.5H;in the optimized periodic spheroidizing annealing process,the spheroidizing rating and hardness with cycle number of 3 meet the production requirements,and the time consumption is about 6.5h.Compared with the traditional process,the two annealing processes can save 30 ? 35% of the time and meet the production requirements.