EFFECT OF HYDROGEN ON THE MECHANICAL-PROPERTIES OF HIGH-PURITY IRON .1. SOFTENING AND HARDENING OF HIGH-PURITY IRON BY HYDROGEN CHARGING DURING TENSILE DEFORMATION

Tensile tests were performed on high purity iron during hydrogen charging. The flow stress was increased by hydrogen charging below 190 K and was decreased reversibly above 190 K. Hydrogen charging caused no, or only very few, blisters on the surface of specimens with a residual resistivity ratio (RRRH) larger than 3600 but an appreciable number of blisters on less pure specimens (RRRR ≈ 1800). The less pure specimens were hardened rather than softened by hydrogen charging at room temperature. Several mechanisms for the softening are discussed, and it is concluded that the softening and hardening observed in the high purity specimens are the inherent effect of hydrogen on the mechanical properties of iron. The softening and hardening are interpreted as the results of hydrogen-dislocation interactions; it is proposed that hydrogen atoms trapped at the core of a screw dislocation increase its mobility and that hydrogen atoms hinder the motion of edge dislocations at sufficiently low temperatures. © 1979.