Hydrogen-Assisted Crack Propagation in Austenitic Stainless Steel Fusion Welds

Abstract

The objective of this study was to characterize hydrogen-assisted crack propagation in gastungsten arc (GTA) welds of the nitrogen-strengthened, austenitic stainless steel 21Cr-6Ni-9Mn (21-6-9), using fracture mechanics methods. The fracture initiation toughness and crack growth resistance curves were measured using fracture mechanics specimens that were thermally precharged with 230 wppm (1.3 at. pct) hydrogen. The fracture initiation toughness and slope of the crack growth resistance curve for the hydrogen-precharged weld were reduced by as much as 60 and 90 pct, respectively, relative to the noncharged weld. A physical model for hydrogenassisted crack propagation in the welds was formulated from microscopy evidence and finiteelement modeling. Hydrogen-assisted crack propagation proceeded by a sequence of microcrack formation at the weld ferrite, intense shear deformation in the ligaments separating microcracks, and then fracture of the ligaments. One salient role of hydrogen in the crack propagation process was promoting microcrack formation at austenite/ferrite interfaces and within the ferrite. In addition, hydrogen may have facilitated intense shear deformation in the ligaments separating microcracks. The intense shear deformation could be related to the development of a nonuniform distribution of hydrogen trapped at dislocations between microcracks, which in turn created a gradient in the local flow stress.

Effects of Thermal Aging on Material Properties, Stress Corrosion Cracking, and Fracture Toughness of AISI 316L Weld Metal

“…), the common factor is that the effect of hydrogen is accompanied by a change in fracture morphology. The effect of hydrogen on toughness and tearing modulus of stainless steel weld metal reported by Somerday et al [34] is similar as observed here in in situ fracture toughness testing. For confirming the presence of hydrogen in the specimens, the hydrogen contents of the as-welded specimens and after high-temperature water exposure were determined by hot extraction using a Leybold-Heraeus H2A 2002 hydrogen analyzer where the sample is heated up to 1373 K (1100°C) and the total amount of evolving hydrogen is analyzed by a thermal conductivity detector.…”

“…Luppo et al [33] have shown that the d-ferrite-austenite interface acts as a strong hydrogen trap. The results from Somerday et al [34] show a significant degradation (60 to 90 pct) of both the initiation toughness and tearing modulus (dJ/da) by hydrogen in weld metals of 21Cr-6Ni-9Mn stainless steel. Their results show that hydrogen promotes micro-crack formation at the d-ferrite-austenite interface.…”

Effects of Strength and Microstructure on Hydrogen-Assisted Crack Propagation in 22Cr-13Ni-5Mn Stainless Steel Forgings

“…This observation resulted from a study on hydrogenprecharged welds of 21Cr-6Ni-9Mn stainless steel, which exhibited steps on the fracture surface similar to those in Figure 5. [32] In the case of 21Cr-6Ni-9Mn welds, parallel microcracks formed at d-ferrite then linked due to intense shear deformation in the connecting ligaments, resulting in steps on the fracture surface. In the hydrogen-precharged condition, the shear in the ligaments was substantially more intense relative to the noncharged condition for a fixed remote applied strain.…”

Effect of Anneal Temperature on Microstructure and Mechanical Properties of 0Cr21Ni6Mn9N cold Drawn Pipe

“…However, the effects of annealing treatment on the microstructure and mechanical properties of 21-6-9 austenitic stainless steel are seldom reported. [11][12][13][14][15] In this study, the microstructure and mechanical properties of 21-6-9 austenitic stainless steel were investigated carefully after annealing at different temperatures. The effect of anneal temperature on grains size and shape, second phases and mechanical properties was studied.…”