HYDROGEN TRAPPING ENERGY LEVELS OF DUPLEX STAINLESS STEELS AT DIFFERENT STARIN RATES

The susceptibility of materials to hydrogen embrittlement is directly related to the interaction between traps (defects) and hydrogen. Hydrogen effects are being studied by a thermal desorption spectrometry (TDS) process. In this research we determine the mechanical properties of different duplex stainless steels (DSS) alloys with hydrogen, at low and high strain rates (~10^-7 s^-1 and ~10⁵ s^-1, respectively) using quasi-static and dynamic experiments, respectively. Dynamic experiments were applied for the first time to DSS alloys with and without of hydrogen. The dynamic experiments include dynamic yield stress and spall strength. We used an analytical model to describe the hydrogen bubble growth and coalescence under ductile deformation in a wide range of tensile loading stresses. Our results give new insight to the hydrogen enhanced local plasticity (HELP) model (hydrogen embrittlement model) regarding high strain rate and high Hugoniot pressures (dynamic pressures), ~9 GPa.

In this research we prove that at high strain rates and high dynamic pressures the dislocations velocity is higher than the diffusion of hydrogen; it is concluded that the HELP model is not applicable in these dynamic pressures. It was shown using dynamic experiments that hydrogen changes the dynamic yield strength depending on strain rate. Hydrogen trapping phenomenon was increased when strain rates were higher. Calculations performed by TDS showed ~40 % differences in trapping energies of quasi-static and dynamic experiments. The possible mechanism for hydrogen trapping in DSS is discussed in detail.