Effect Of Residual Carbide Morphology Before Divorced Eutectioid Transformation On Spheroidized Microstructures Of GCr15

The original microstructure of hot-rolled high-carbon chromium bearing steel GCr15 is consisted of fine-lamellar pearlite which has high hardness,low plasticity and poor processing performance.At the same time the net-work carbide will separate out along austenite boundaries.The spheroidization annealing is designed to obtain the spheroidised pearlite.However,conventional spheroidizing requires long annealing time of 10?15 hours,which gets energy-consumed and low-productivity.In this paper,the influence of the cooling rate to the network carbide precipitation was researched by the thermal simulation experiments on GLEEBLE-3500 and developped a reasonable normalizing process.The study shows that network carbide can be effectively suppressed after hot rolling deformation of 40%at 980 ?,a speed of greater than 100?/s cooling rate to room temperature.The key to bring out DET is guarantee enough diffuse residual carbide particles as cores.The research on three main austenitizing processing parameters have shown austenitizing temperature of 790 ?,heating time 10min and dual-phase region cooling rate of 30 ?/h?120 ?/h ensures enough diffuse residual carbide particles in austenitization and more uniform.The number of residual carbide particles per square millimeter is 71.9×105 and the particles size between 0.1 ?m to 0.3 ?m is more than 50%,which shows the good uniformity and distribution and may be propitious to rapid isothermal spheroidizing annealing.The research on cycle spheroidizing annealing process parameters as well as austenitizing processing parameters to the residual carbide particles shows that with the increase of cycles,there will be more residual carbide particles,a nd the austenitizing temperature of 790 ?,heating time 10min and 3cycles can get the maximum number of residual carbide particles.This article formulated the rapid isothermal spheroidized and cycle spheroidized annealing for experimental steel.The total time of optimized rapid isothermal spheroidized annealing is 3.5h,and the cycle spheroidized annealing is 5.5h.Saving 30%more time than the conventional process.The spheroid level and hardness meets the requirements of the GB.