Minoru Kogawara

The Effect of Transformation Plasticity on Prediction of Tooth Distortion of Heat-Treated Helical Gear

The displacement profile in a shank and dedendum-addendum circle of helical gear made of through-hardened S45C carbon steel and carburized-hardened SCr420H low alloy steel by gas carburizing was measured and predicted using a finite element method of DEFORM-HT. Both gears were quenched into same oil quenchant. Heat Transfer Coefficient (HTC) was taken by measuring thermal history inside of firstly silver probe and secondly stainless steel SUS304 gear blank. Uniform HTC of silver probe was calculated by lumped heat capacity method, whereas zone-based HTC of SUS304 gear blank was calculated by iterative modification method. Transformation plasticity was included and excluded to predict the tendency of distortion. Simulation results were analyzed and compared to the experimental results to validate the influence of transformation plasticity on the prediction of distortion during the martensitic and bainitic/pearlitic transformation. However, more accurate distortion profiles require detailed HTC by taking thermal history on the surface of the tooth.

Iterative Modification of Lumped Heat Capacity Method on Predicting Residual Stress and Distortion of Still-Quenched S45C Steel Cylinder

Computer simulation can be utilized to predict the property and quality of heat-treated products. The prediction accuracy depends upon the thermal boundary condition and the thermal history from which surface heat transfer coefficient (HTC) is derived. Variables studied are thermal boundary and the surface HTC. Zone-based thermal boundary is set with and without edge effect. Lumped heat capacity method is used to predict HTC of silver probe (1st step), then iterative modification method is applied to the prediction of HTC of SUS304 cylinder (2nd step) and S45C cylinder itself (3rd step). Using FEM tool of DEFORM-HT combined with lumped heat program LUMPPROB, this research is intended to obtain the number of thermal boundary and iterative modification step. The higher accuracy is obtained by employing the edge effect of thermal boundary. The 2nd step significantly increases the prediction accuracy of radial distortion and residual stress distribution. However, 3rd step does not significantly increase the prediction accuracy.