Distortion from heat treatment is a main concern because heat treatment is often one of the last steps in the manufacturing process. Excessive distortion can ruin hours of work on parts that are machined and hardened. Reworking the parts may be challenging, and scrapping the parts leads to lost revenue. In 1995, the German Research Association of Drive Engineering estimated annual losses of ~850M Euros to remove distortion from manufacturing [1]. Around the same time DANTE, a heat-treatment process modeling tool, was born from a project with the American automotive industry, academia, and the national labs, to combat distortion in excess of hundreds of millions of dollars annually. All distortion from heat treatment can be broken down into two categories: shape change and size change. Size-change distortion is caused by the reorientation of the crystal structure as the steel changes phase and is unavoidable. Shape change is the difference in part dimensions before and after hardening, assuming no volume change. Shape and size change is caused by material, geometry, and process effects. Material effects refer to the initial state of the steel, including the microstructure phases, chemical composition, carbide phases and sizes, alloy segregation, grain size, and the effects from the material fabrication process. Part geometry affects distortion due to differences in heating and cooling between thick and thin sections, causing material strain. Process uniformity and consistency directly affect part distortion during heating and cooling due to the accompanying phase transformations. Chemical gradients of carbon and nitrogen play a role in nonuniform phase transformations due to their effect on martensite start temperature. The volume change from tempering martensite can have a similar effect if the thermal gradient is high. Process consistency and residual stresses from previous processes also impact process distortion.