Hydrogen diffusion and trapping effects in multiphase steels are modelled using the recently developed Svoboda-Fischer-Kozeschnik diffusion model. Diffusion of interstitials in these steels cannot be described by the standard diffusion equation because of their trapping on defects (dislocations, carbides etc.), as well as the enormous hydrogen solubility and diffusivity differences between the constituent ferrite and austenite phases. We explore the correlations between densities of various defects and austenite morphology on hydrogen diffusion properties. We also explore how to avoid explicit descriptions of fine phase mixtures, such as in the case of bainite, during steady state diffusion and extract an effective diffusion coefficient using the effective medium theory.