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.