Fracture mechanics SSC testing of weldments

Stress corrosion cracking (SCC) studies of shielded metal arc (SMAW) weld joints of a C-Mn steel were performed using a fracture mechanics based test technique. The specimens contained multipass ferritic weldments with two nitrogen contents and were tested in the As-Welded (AW) condition. Fatigue precracked compact tension (CT) specimens with the cracks in the weld metals were subjected to slow rising displacement rates in the order of 1 #mu#m/h, measured in the load lines of the specimens. The tests were conducted at room temperature in ASTM substitute ocean water under conditions of hydrogen charging (cathodic polarization at -900 mV vs Ag/AgCl, de-aerated solution). Results obtained in these tests in terms of CTOD-R curves are compared with corresponding data obtained in standardized fracture mechanics tests performed in laboratory air. The aim of this work was to assess the feasibility of a rising displacement type of test for SCC testing of weldments. It was also intended to compare the influences of the nitrogen content on the fracture behaviour of these welds in air and under conditions of environmentally assisted cracking by using fracture mechanics concept. The evaluation of the rising displacement SCC tests shows that differences in the fracture behaviour observed for testing in laboratory air which could be attributed to the effect of nitrogen is almost completely overidden by the influence of the corrosive environment. Investigations of the fracture surfaces show that the uptake of hydrogen from the aqueous environment in both cases led to a strong embrittlement which is responsible for the decrease in fracture toughness. (orig.)Reprinted from 'Proceedings of the 13th international conference on offshore mechanics and Arctic engineering', Salama, M.M.; Toyoda, M.; Lui, S.; Dos Santos, J.F.; Kocak, M.; Patterson, E.A.; Berge, S. (eds.). ASME book no. H00898 - 1994 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman