Validity of Heat Transfer Coefficient based on Cooling Time, Cooling Rate, and Heat Flux on Jominy End Quench Test

摘要

Jominy end-quenched test is one of tools to know the hardenability character of a steel being hardened by heat treatment. As a coupon test, successful prediction of mechanical property and microstructure on Jominy test piece will increase the accuracy prediction of actual hardened steel parts. In this study, two-dimensional finite-element analysis was performed to predict thermal history and radial distortion of end-quenched steel bar using FEM-based software DEFORM-HT. It incorporates transformation-induced volume change, latent heat, transformation plasticity, and temperature-dependent material properties of individual phase of austenite, pearlite, bainite, and martensite. The following assumption was made, simplified diffusion at heating, diffusional transformation from autenite to bainite and pearlite at slow cooling, and diffusionless transformation from austenite to martensite at fast cooling. There are two thermal boundary condition used in this study i.e. water cooled area and still-air cooled area of the Jominy model. To study the validity of Heat Transfer Coefficient (HTC) employed on water-cooled area, the HTC was taken from several works of Narazaki, Homberg, Shorin, Inoue, and Hunkel. Measured and predicted cooling time and cooling rate curve inside Jominy stainless steel 304 then is compared to validate the accuracy of the HTC. Time-dependent heat flux is also reported to analyze the heat transfer mechanism. The most accurate employed HTC, Narazaki and Shorin method, then is applied on Jominy carbon steel S45C and alloy steel SCr420H. Predicted cooling curve, Jominy hardness and Jominy cooling time, and radial distortion then is compared to the measured one with relatively good agreement.