In this study, we investigate the diffusion of carbon (C) and other elements into steel substrates (Impax Supreme™) during diamond chemical vapour deposition (CVD). The substrate temperature varied from 700 to 850ºC by plasma power manipulations to enable the correlation of substrate temperature with diffusion length and depth of the above mentioned critical elements into steel during film growth conditions. Methane concentration is also a parameter which has been considered during the parametric analysis. The crystalline compounds formed during the diamond growth process were studied using XRD analysis. In addition, SIMS technique is used with depth profiling to monitor the diffusion of elements induced by the process. The results obtained enabled to improve traditional understanding about the mechanisms relating to diamond deposition on steel substrates using CVD processes.