EFFECT OF HYDROGENATION ON THE FRACTURE MODE OF A REACTOR PRESSURE-VESSEL STEEL

The conditions for hydrogen-induced intergranular fracture in an artificially embrittled, low-alloy reactor pressure-vessel steel were investigated by using fracture toughness and stress-corrosion cracking tests. The specimens were taken from two locations: the heat-affected zone beneath the cladding and the base material directly below the heat-affected zone. A hydrogenating system allowed the tests to be carried out on both prehydrogenated specimens and with continuous hydrogenation in the course of the tests. In total, the results demonstrate a detrimental effect of hydrogen on the subcritical crack-growth resistance of both materials. At 120 degrees C (close to the upper shelf), it led to a lower energy ductile fracture mode and isolated events of transgranular fracture. At ambient temperature (in the ductile-to-brittle transition mode) some mixed intergranular and transgranular subcritical crack growth was observed.