TWI Industrial Member Report Summary 351/1987
By G S Booth, A Maresca and R J Pargeter
A significant part of the life of a fatigue crack propagating from a weld toe may be spent in a hardened heat affected zone. As it is believed that hydrogen from corrosion or cathodic protection is responsible for accelerated fatigue crack growth rates in normalised steels in seawater, it is important to know the effect of this environment on crack growth rates in hardened HAZ microstructures, which are inherently more susceptible to hydrogen embrittlement. To investigate this, fatigue crack growth data were obtained from a simulated HAZ microstructure, produced by quenching BS 4360 Grade 50D steel from 1200ºC. Tests were performed for R = 0 and 0.5 in air, and in seawater under freely corroding conditions and with both normal and over-protection by cathodic polarisation. Test material strength and microstructure were characterised and fracture surfaces were examined in section, and directly in the scanning electron microscope.