Cyclic surface deformation behaviour of ZrH₂-purified iron: Effects of solute carbon, strain amplitude, strain rate and environment

The surface deformation behaviour in ZrH₂-purified interstitial-free iron was studied during fatigue in the push-pull plastic strain control mode under various combinations of plastic strain amplitude (5×10^-4, 5×10^-3), strain rate (5×10^-4, 3× 10^-2s^-1) and environment (ultrahigh vacuum, oxygen). Comparative tests of vacuum-melted commercially pure iron (CPI) containing 170 p.p.m. C were also conducted to investigate the effect of interstitials. At a plastic strain amplitude of 5×10^-4, the environmental effect is clearly exhibited regardless of the strain rate and the presence of interstitials. Fatigue in ultrahigh vacuum produces very fine slip lines not only in interstitial-free iron but also in vacuum-melted CPI. In the presence of oxygen, fatigue produces prominent slip lines, but those developed in CPI are more intense and coarser than those developed in interstitial-free iron. At the higher plastic strain amplitude of 5×10^-3, the gaseous environmental effect on the cyclic surface deformation is insignificant. The surface deformation behaviour is discussed in terms of the environmental effect and the basic mechanisms that govern the cyclic plasticity of iron.