MECHANISM OF HYDROGEN-INDUCED INTERGRANULAR CRACKING OF TUBULAR STEELS

Hydrogen could be enriched on grain boundaries by stress induction and other traps. The enriched hydrogen facilitated emission and movement of dislocations and lowered plastic work. Consequently, fracture occur red easily along grain boundary. A normalized threshold value of hydro gen-induced cracking (HIC) along grain boundary is given as (K-IH/K-IC )(2) = 1 - 0.162 x 10(-3) beta(H)C(sigma)(H)G(H)/2 gamma(s) - gamma(b) - 0.16 x 10(-3) Sigma beta(i)C(i)G(j)), where beta(H) and beta(i) are the enrichment factors of hydrogen and other elements on grain bounda ries, respectively; C-sigma(H) is hydrogen concentration induced by st ress; C-i is the average concentration of an element in the steel; G(H ) and G(i) are factors of fracture work along grain boundary with hydr ogen and other elements, and gamma(s) and gamma(b) are surface free en ergy and grain boundary energy of Fe. For tubular steel, the calculate d K-H/K-IC is 0.23 while the determined value is 0.26. The theoretical threshold Value is well consistent with the experimental one.