The Effect of Pre-Strain on the Resistance to Hydrogen Embrittlement in 316L Austenitic Stainless Steel

Abstract

The effect of pre-strain before hydrogen charging on the resistance to hydrogen embrittlement (HE) in the 316L austenitic stainless steel was investigated through the slow strain rate tensile test (SSRT), transmission electron microscopy, and thermal desorption analysis (TDA). The pre-strain suppressed mechanical twinning during the SSRT, regardless of hydrogen charging. However, it accelerated the ¾-martensitic transformation in hydrogen-charged specimens. The TDA revealed that whereas hydrogen atoms migrated from grain boundaries and dislocations mainly to the austenite (£)/¾ interfaces in pre-strained specimens during the SSRTs, they moved to the boundaries of fresh mechanical twins, which newly formed during the SSRTs, in the annealed specimen. The elongation loss by hydrogen charging became greater with increasing the pre-strain, indicating that pre-straining deteriorated the resistance to HE. This elongation loss by pre-strain resulted from both the increase in fraction of ¾-martensite with pre-strain and the segregation of hydrogen atoms to the £/¾ interfaces.

The advantage of grain refinement in the hydrogen embrittlement of Fe–18Mn–0.6C twinning-induced plasticity steel

“…2a). Instead, the 2nd peak, which is known to be generated by hydrogen atoms detrapped from twin boundaries [16,28], newly appeared at temperatures ranging between approximately 500 K and 600 K. This result implies that hydrogen atoms were transported from grain boundaries, dislocations, and lattices (the 1st peak) to twin boundaries (the 2nd peak) during the SSRTs, which shows good agreement with previous results obtained using other TWIP steels [16,31] and austenitic stainless steels [28,29]. The height of the 2nd peak increased with increasing grain size, implying that the migration of hydrogen atoms was more active in coarse-grained specimens most likely due to the high volume fraction of mechanical twins.…”

“…The hydrogen desorption rate was measured by TDA before and after the SSRTs during continuous heating at a constant rate of 100 K h À1 from room temperature to 650 K. The hydrogen desorption rate was normalized to the surface area of each sample. Each peak on the hydrogen desorption rate curve was converted to a hydrogen concentration [11,18,29,31].…”

“…The annealed tensile specimens were electrochemically charged with hydrogen in a 3% NaCl aqueous solution containing 0.3% NH 4 SCN with a current density of 50 A m À2 for 48 h at room temperature [28,29]. A platinum wire was used as a counter-electrode.…”

“…However, in the case of TWIP steel, grain refinement increases not only the area of grain boundaries but also reduces the volume fraction of mechanical twins [5,6,27], which provide strong sites for hydrogen trapping [16,28,29] and crack formation [30]. Accordingly, the resistance to HE of Fe-Mn-C TWIP steels is anticipated to be improved by grain refinement without the addition of Al.…”

The effect of Ti precipitates on hydrogen embrittlement of Fe–18Mn–0.6C–2Al–xTi twinning-induced plasticity steel

“…Therefore, the migration of hydrogen atoms toward the interfaces of Ti particles instead of twin boundaries implies that hydrogen atoms eventually migrate to trapping sites with a stronger binding energy with themselves. Recently, the migration of hydrogen between different trapping sites during the SSRT has been investigated by observing the changes in hydrogen desorption peaks [44,45]. It is reported that hydrogen migrates to the stronger trapping site through mobile dislocations during deformation [32,35].…”