The degradation induced by the presence of hydrogen in some steels may be reduced or eliminated by the addition of palladium, but the mechanism for this effect is not fully understood. Little is known about the distribution of the palladium in such modified steels so a recently published study by M. K. Miller, of the Oak Ridge National Laboratory, and S. S. Brenner and M. G. Burke, of the University of Pittsburg, used high resolution atom probe field-ion microscopy and conventional transmission electron microscopy to examine the microstructure and microchemistry of laboratory melted low carbon alloy steels containing 0.31 and 0.65 atomic per cent palladium (Metall. Trans.A, 1987, 18A, (4), 519–523).

The authors concluded that the solubility of palladium in the tempered steel was between 0.25 and 0.5 atomic per cent, considerably less than indicated by the iron-palladium phase diagram. Although most of the palladium remained in solution in the ferrite, some had segregated to the ferrite-ferrite lath boundaries where it formed a mono-atomically thick adsorbate layer. Palladium-manganese precipitates were detected both at lath boundaries and in the ferrite matrix.