Hydrogen Diffusion and Hydrogen Embrittlement Failure Behavior of AH36 Marine Steel Subjected to High Heat Input Welding

Abstract

AH36 marine steel processed through high heat-input welding is subjected to microstructural characterization, hydrogen permeation test, internal friction test, and slow strain rate tensile test to reveal its hydrogen diffusion and hydrogen embrittlement failure behaviors. Compared with the base metal, the coarsegrained heat-affected zone (CGHAZ) exhibits a significantly coarsened microstructure and decreased hydrogen trap density, resulting in a high hydrogen diffusion coefficient and short hydrogen permeation time. The presence of hydrogen yields a hydrogen-induced Snoek internal friction peak and promotes the movement of the Snoek-Kê-Köster internal friction peak to the lowtemperature region. In addition, B and Kê peaks, which are not found in the base metal, appear in the CGHAZ. With increasing hydrogen content, the plastic loss and brittle fracture of the AH36 marine steel become increasingly significant, and the hydrogen embrittlement sensitivity of the heat-affected zone increases compared with that of the base metal. The discontinuous yield phenomenon gradually disappears under slow strain rate tension owing to the weak pinning effect of the Cottrell atmosphere on mobile dislocations.

Effect of Slow Strain Rates on the Hydrogen Migration and Different Crack Propagation Modes in Pipeline Steel

“…The yield strength of the CHG and NCHG SSRT samples increased for all SSRTs at three strain rates. This result agrees well with the work of Zhang et al [53] work, which focused on materials with an obvious yield platform. [54,55] With hydrogen 4.4 Â 10 À6 cm s À1 [59] 0.25 nm [37] 25 kJ mol À1 [39] 8.314 J (mol K) À1 298 K 1 Â 10 8 cm À12 [60] 1 10 -4 s -1 1 10 -5 s -1 1 10 -6 s -1 charging during the SSRT, hydrogen atoms further gathered around dislocations and retarded the mobility of dislocations at the yield platform, resulting in increased plastic deformation stress.…”