During the heat treatment of springs for railway bogies, phase transformations and oxidation occur and it is important to know transformation temperatures and oxidation rates to optimise the process. Oxidation and decarburisation can adversely affect the surface properties of steel when not limited to the bare minimum. The oxidation rates and material-specific phase transformation of the spring steels were evaluated by means of differential scanning calorimetry. Three spring steels with known mass were heated and cooled. The change in the corresponding heat flow was evaluated. The materials were also subjected to a regular spring steel heat treatment process in order to determine the relationship between oxidation rate and decarburisation. This allowed for the observation of phase transition and oxidation rate for each steel. The results of these investigations showed that there is a nonlinear relationship between oxidation and decarburisation. The three materials analysed showed distinct properties; therefore, understanding of the material characteristics is important. Material A showed a high oxidation rate with decreased decarburisation, whereas material B showed less oxidation and higher decarburisation due to higher silicon contents.