Engineers have been interested in a thorough understanding of how a case-hardened steel components, consisting of soft substrate (or core) and hard surface, behaves under various types of loads, ranging from extremely destructive load to mild-cyclic loads. The use of numeric simulation, such as well known finite element method, has made it much easier to achieve this. Throughout this investigation, the author proposes a methodology to treat such a case-hardened part as multi-laminated metal with a relative thin, outer layers whose ultimate tensile strength may be several times as high as its inside core material. In the case studies to demonstrate the technique, a representative automotive component is subject to various loads due to not only the inertia of its own but also that imparted from heavy springs housed within it. A comparison was made between three approaches to account for the hardness transition often encountered, more or less, between the hard layer and soft core. It is interesting to find the two approaches have yielded noticeably different outcomes and the third with more refinement in the hardness transition zone does not seem to benefit much in coming up with more accuracy in the stiffness. The most interesting finding provided by this study is that the failure due to mild cyclic loads may be a little different from due to destructive loads. In particular, when it is subject to extremely high and steady loads, the failure usually occurs on the high-strength outer layer The method presented here is so broad that it is not limited to the components for power train and is of significance for designing case-hardened structures for their better durability.