Determination of Hydrogen Diffusivity in Rail Steels by Sub-Scale Microhardness Profiling Technique
Hydrogen diffusivity was estimated in three different eutectoid rail steels (C-Mn, Cu-Mo and Ni-Cu-Cr) at ambient temperatures using the technique of sub-surface microhardness profiling after cathodic hydrogen charging in 0.5mol/l sulphuric acid at a current density of 0.1A/cm2 for 24 hours. The increase in the concentration of hydrogen at a certain depth below the surface was related to the microhardness increase at this location as compared to the bulk value. The procedure used to obtain the diffusion coefficient of hydrogen from the microhardness profiles is discussed. The hydrogen diffusivity values in all of the rail steels were found to be similar (of the order of 10-13m2/sec). The estimated hydrogen diffusivity in the rail steel was lower than in pure iron (10-8m2/sec). Possible reasons for the difference are discussed.
David J. Fisher
A. Moon and R. Balasubramaniam, "Determination of Hydrogen Diffusivity in Rail Steels by Sub-Scale Microhardness Profiling Technique", Defect and Diffusion Forum, Vol. 293, pp. 41-45, 2009