Effects of Copper and Phosphorus Impurity Content and Thermal Aging on the Corrosion Fatigue Behaviour of A533B Pressure Vessel Steel

摘要

The effects of thermal ageing of fatigue crack growth behavior have been evaluated in three experimental melts of ASTM A533B MnMoNi steel containing differing amounts of copper and phosphorus. Tests have been conducted under vacuum and in a high purity, low oxygen water environment at 50 C. The results show that environmentally enhanced growth is generally restricted to a limited range of alternating stress intensity Delta k and that the phosphorus segregation extends the range to lower stress intensities. The maximum environmental enhancement is similar in all three casts and occurs in the aged condition. All tests in water exhibited fractographic features not observed in vacuum tests, namely varying amounts of intergranular failure and transgranular failure showing a marked dependence on underlying grain orientation. The changes in fracture mode and growth rate are consistent with hydrogen induced cracking mechanisms observed under static loading conditions.