PSI - Issue 20

Valeriy Lepov et al. / Procedia Structural Integrity 20 (2019) 24–29 Valeriy Lepov et al / Structural Integrity Procedia 00 (2019) 000 – 000

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4. Result and discussion Assuming that the ions of hydrogen dissolved in the lattice are capable to lower the Peierls barrier for dislocation sliding, and the molecular hydrogen remaining in traps does not participate in embrittlement process the improved model of hydrogen transport by Arkhangelskaja et al (2001) could be complemented by (1) or (2). The improved model allows to understand the dependence of fracture nature from hydrogen content of temperature range during the impact toughness and static tension tests for known and new steels, including the fine-grained materials. However the problem of hydrogen effect on generation of dislocations is still open. Nevertheless, it is obvious that hydrogen forms own subsystem in a metal lattice with own frequencies of fluctuations out of a phonon range of a crystal. Then the phonon-dislocation theory of DBT in bcc-metals by Achikasova and Lepov (2015) can be expanded also on the phenomenon of hydrogen embrittlement. The activation energy of microplastic shear would decrease due to interaction with lattice hydrogen, then taking into account (3), it could be receive: (4) The average activation energy here should takes into account a contribution of the ionized hydrogen dissolved in a crystal lattice and lowering of shear threshold with a temperature caused by DBT mechanism. The values of activation energy for different materials are known or could by obtained experimentally, as by Petrov and Razuvaeva (2011). The results of numerical modeling according (1)-(4) for locomotive steel with  b =1050 MPa and activation energy U 0 =4.2 eV lead to the following conclusions: 1) High rate of damage accumulation occurs at moderate and high stress level; decrease of temperature causes an accelerated damages accumulation as well the as the energy of activation drop (see Fig.1, a); 2) The energy activation of microplastic shear decrease due to lattice hydrogen content in a metal and considerably accelerates process of damage accumulation at low temperature environment of operation and small levels of tension (see Fig.1, b) f( С ,T,  ) = ехр ( –  /kT).