EFFECT OF CRACK-TIP HYDROGEN PROFILES ON THE EMBRITTLED FRACTURE TOUGHNESS OF A STAINLESS STEEL

As part of ongoing work to determine the bounds of transferability of hydrogen embrittled fracture toughness test data, this paper investigates the sensitivity of hydrogen embrittled fracture toughness to modification of the crack tip hydrogen field. Compact tension fracture specimens manufactured from 21Cr-6Ni-9Mn stainless steel are preconditioned in 63 MPa hydrogen at 300 degrees C to achieve a uniform internal hydrogen concentration. Once uniformly preconditioned, the pressure and temperature are controlled to partially remove hydrogen from the crack tip subsurface, creating a hydrogen profile in the region in which the plastic strains are expected to be highest during the fracture test. Standard J-R curve fracture toughness tests are then performed on each specimen in ambient air. Differing fracture toughness between specimens with different hydrogen profiles would be evidence that the hydrogen affected fracture mechanism is active mainly within the large plastic strain region ahead of the crack tip and is sensitive to these concentration perturbations. This knowledge would then provide insight into whether toughness data obtained using hydrogen preconditioned specimens is transferable to components in hydrogen service.