Finite element analysis (FEA) is widely used in mechanical design to predict part performance under various loading conditions. However, traditional loading models often assume uniform, isotropic, material properties and overlook the residual stresses and property changes introduced by heat treatment. This can be significant for case-hardened components such as gears or bearings. Heat treatment can alter phase composition, introduce compressive residual surface stresses, and change mechanical properties such as yield strength. Residual stresses in case-hardened parts develop due to complex interactions of phase transformation and temperature gradients during quenching. During quenching of carburized parts, martensite forms earlier in the low-carbon core than in the high-carbon case. This transformation sequence results in compressive stresses at the surface which are beneficial for fatigue performance. Figure 1 shows the stress reversals during a quench with (a) martensite transformation starting under the case, pushing the surface into tension and (b), residual compressive stresses at the surface after the case transforms.