Numerical simulation and experimental verification of carburizing-quenching process of SCr420H steel helical gear

Using DEFORM 2D ver. 9.0 and 3D ver. 6.0, a finite-element model was developed to study the prediction accuracy for the modeling of carburized-quenched helical gear. The helical gear model incorporates phase transformation kinetics during heating, carburizing, diffusing and quenching process. Carbon- and temperature-dependent material properties of austenite, martensite and bainite including transformation-induced volume change, latent heat and transformation plasticity are considered in calculating the stress–strain distribution. The total strain is divided into individual strain which are thermal, elastic, plastic, phase transformation and transformation plastic strain, respectively. There are 2 thermal boundary conditions employed which are uniform heat transfer coefficient (HTC) that is estimated from an oil-quenched silver probe by using the lumped-heat capacity method, and zone-based HTC that is estimated from an oil-quenched SUS304 gear blank by using the iterative modification method. The aim of this study is to evaluate the prediction accuracy of the simulated results when both methods of HTC are employed. The results of the simulation and experiment e.g., cooling curves, cooling rate curves, radial displacement, hardness, diffused carbon layer, residual stress and strain distribution are presented. The summary is that although zone-based HTC gives a more accurate prediction of thermal history than uniform HTC, it does not give significant accuracy in the prediction of hardness, distortion and residual stress.