Hydrogen Distribution in a Duplex Stainless Steel Investigated by Means of Hydrogen Microprint Technique

Cracking Process Related to Hydrogen Behavior in a Duplex Stainless Steel

“…To approve the mentioned opinion, the cross section of the hydrogen charged specimen was subjected to the HMPT by author's group. 34) Hydrogen was detected both in the ferrite matrix and phase boundary on the surface (charged side) and in the middle portion of thickness with different volume fraction. The results confirmed that some of the charged hydrogen atoms diffuse according to the hydrogen concentration gradient toward the other side, leaving the interphase boundary to the ferrite matrix.…”

“…From the HMPT result (v), hydrogen atoms can migrate from the charged side to the other, but the diffusion condition is somewhat different from that in the tensile test. In the HMPT, the sample was hydrogen-charged, emulsioncovered, tensile loaded, unloaded and then kept for 24 h at room temperature, while in the tensile test, the test piece was hydrogen-charged and then tensile-tested up to fracture, which took about 0.75 h. The authors' group 34) made HMPT on the cross section of the sample hydrogen-charged and kept in the same condition as in the present paper but with no elastic stress loading, and found silver particles with area fraction of 1.7%, which is about twice of the value of the present study of the sample loaded with 30% of the proof stress. Considering the distance from the charged surface, the loading with 30% of the proof stress is thought to have no effect.…”

“…Further discussion on the hydrogen diffusion path has been shown elsewhere. 34) Turnbull and Hutchings 41) also reported that interphase boundaries in DSS are effective trapping sites and can be responsible for the reduced diffusivity in electrochemically hydrogen-charged DSS specimens, based on hydrogen atom transport theory in a two-phase alloy. In contrast, Luu et al 38) visualised most of hydrogen in ferrite phase by means of HMPT.…”

“…Therefore, it is presumed that a certain amount of charged hydrogen migrates during the deformation into a new trapping site with lower binding energy. Although there has been no report on TDS result in DSS, phase boundary will be a stronger trapping site than those inside the ferrite phase such as the interstitial site (matrix), dislocation and ferrite/ferrite grain boundary according to the recent study 34) by the authors' group. Thus, it is presumed that the trapping site in the as-charged specimen is phase boundary and that the new trapping site in the deformed specimen is dislocations inside the ferrite phase, considering the too small trapping energy for the ferrite matrix that cannot be shown in the normal TDS, 35) far lower fraction of ferrite/ferrite grain boundary in DSS than in ferrite base iron and steels, and high dislocation density after deformation.…”

Evaluation of Hydrogen-induced Cracking Behavior in Duplex Stainless Steel by Numerical Simulation of Stress and Diffusible Hydrogen Distribution at the Microstructural Scale

“…are: the phase ratio of the ferrite to the austenite phase, [12][13][14] the grain size, 15) the difference in steel microstructure with respect to the hydrogen penetration direction, [16][17][18][19] the difference in the hydrogen diffusion path due to the difference in microstructure, [20][21][22][23] and the effect of prestrain. 24,25) The distribution of stress and diffusible hydrogen concentration at the microstructure scale should be assessed based on their relatedness to the occurrence of hydrogen cracking.…”