Effect of hydrogen on low cycle fatigue properties and deformation behavior of a tempered martensitic high strength steel

摘要

The cyclic deformation characteristics and fatigue behavior of a tempered martensitic high strength steel have been investigated in air and under cathodic polarization in de-aerated NaCI solution. Detailed studies were performed on cyclic hardening-softening behavior, hysteresis loops, fatigue lifetime and internal stresses as well as effective stresses during cyclic straining in the plastic strain amplitude range of 0.2 10~(-2) - 2.0 10~(-2) and at constant plastic strain rate. Special attention is paid on the role of hydrogen on the evolution of the internal and effective stresses according to plastic strain amplitude. For all plastic strain amplitudes and both in air and under cathodic polarization, an immediate cyclic softening takes place during the first cycles. Then a stationary state develops with only a weak decrease of the peak stresses. In air, the effective stresses develop like the total stresses with a slightly more important decrease, while the internal stresses reach a plateau in the early cycles. Furthermore, increasing the plastic strain amplitude increases the effective stresses but not the internal stresses. Under cathodic polarization, internal stresses show a strong decreasing before reaching a steady state on a plateau, but at a higher level than in air. Effective stresses continuously decrease with a higher rate and lower values than in air. These results are discussed in terms of developing dislocation structures and how hydrogen interferes in these mechanisms.