Thermodynamic Analysis Of Eutectoid Transformation And Process Of GCr15Steel Divorced

Spheroidizing annealing process is an important preliminary heat treatment process for GCrl5bearing steel, because good ball of tissue has a siganificance impacts on subsequent heat treatment process. Traditional annealing process is not only time consuming, but the effect is not good. Divorced Eutectoid Transformation is a process under specific heating system and cooling system and granular substance are precipitated from granular carbide, so as to get the purpose of quick ball. Therefore, The study of mechanism of divorced eutectoid and explore the remaining carbide reaction can generate significant influence of bearing steel ball annealing process.GCrl5steel cold carbide two different decomposition products (flake and spherical) thermodynamic and kinetic model were established based on the solid phase transformation, thermodynamics and diffusion theory.Growth of equations of carbon atoms attached dissolved carbon nucleation and simultaneously corresponding theoretical calculations was constructed.Finally, by quenching experiments and ball annealing experiments, The conclusions are drawed as follows:(1) Thermodynamic model calculation show that when the austenite in normal eutectoid decomposition, and the isothermal temperature below966k, the generated flake carbides grow up rate is greater than the granular carbides, so the relative to the granular carbides formed more easily.(2) When divorced eutectoid transformation occurs, the residual carbides increased the system interface area, priority will be attached to the rest of the carbide carbide nucleation grew up.(3) Through the quenching experiment data analysis and calculation, get the rest of the carbide volume fraction and average particle size of relationship is Vt=8.141×10-4+0.0427r剩0.5207; Remaining carbide volume fraction and the austenitizing heating process is relationship Vt=0.96-(0.96-101.36-1480/T)×[1-exp [2.8×106exp(-0.1938T) t1/2]]. Also concluded that the rest of the carbide volume fraction is about5%(that is, the austenitizing temperature is800℃, holding20min), the income is not soluble carbide morphology of granular and dot, in line with granular carbide forming conditions when divorced eutectoid transformation.(4) Spheroidizing annealing experiments show that the austenitizing temperature is800℃, holding20min, then in the710℃furnace isothermal30min, in25℃/h after the oven to650℃cold air cooling residual carbide volume fraction (about5%), the organization obtained the average particle size is about0.2537um, hardness of about202.95HBW, meet the GB/T18254-18254standard after spheroidizing hardness range, the total time used in heat treatment of about3.3h.