Ignatenko O. The initiation mechanism of hydrogen induced cracking The initiation mechanism of hydrogen induced cracking.

The thesis is devoted to researches of initiation mechanism of hydrogen induced cracking in welded joints of high-strength low alloy steels. To solve this problem theoretical studies and numerical simulations of processes, which occur in bcc metal grain at initiation and growth of submicrocrack, were carried out. A mathematical model of hydrogen transportation by moving edge dislocations is put forward. Influence of metal temperature, edge dislocation movement rate and diffusion hydrogen concentration on hydrogen quantity transported by edge dislocation to submicrocrack initiation place was studied. Zener-Stroh's model of submicrocrack initiation on dislocation mechanism was improved. Having applied numeric method the temperature-speed dependence of hydrogen embrittlement degree ?(Т) was investigated. The calculation results were compared to experimental data. A calculation-experimental methods were put forward to determine parameters of energy traps for hydrogen in weld metal, such as hydrogen trap density and their interaction energy. Influence of the energy trap parameters on diffusion kinetics and redistribution of hydrogen in welded joint was analyzed. Recommendations are given to avoid the initiation of hydrogen induced cold cracking in welded joints at microlevel.