Effects of hydrogen on the plastic properties of medium-Carbon steels

Abstract

The effect of hydrogen on the plastic deformation of pearlitic and spheroidized 1045 steels is examined. We find that hyrogen in the dissolved state invariably hardens 1045 steel. Luders band formation and propagation require greater applied stress, the slope of the stress-strain curve is increased, and the amount of plastic deformation over a given stress-time history is decreased by dissolved hydrogen. We find, however, that microvoids, the population of which at a given degree of strain is increased by hydrogen of themselves are a softening influence. Furthermore, because hydrogen at very high input activity has the additional effect of generating very large gas pressures within the microvoids, such hydrogen produces an apparent softening effect. Some prior results in the literature are considered, and a reasonably consistent rationalization is given of the results in terms of the effects here described. An attempt is made to relate the hardening and softening effects to dislocation behavior. It is argued that the increase by hydrogen of the number of microcavities by decohesion, the reduction of the Peierls barrier to dislocation motion observable only in iron of very high purity, and the reduction of cross slip of screw dislocations are all manifestations of the reduction by hydrogen of the cohesive force between metal atoms.