Abstract
Fatigue crack growth tests were conducted by using CT specimens of butt welded joint of low alloy pressure vessel steel A508 cl. 3 in high temperature pressurized water simulated BWR environments. The butt welded joint was obtained by a submerged arc-welding method. Microstructures of base metal, welded metal and HAZ were all bainitic ones. Grain size of the HAZ was greater than that of the base metal. The welded metal showed dendritic microstructure. Residual stress of the butt welded joint was about 200MPa in maximum and the values of Vickers hardness of the HAZ and the welded metal were higher by 20% than that of the base metal. As the results of the tests, there was no specific difference in fatigue crack growth behaviour of these three microstructures irrespective of grain size, residual stress, specimen orientation and so on. It is, therefore, concluded that fatigue crack growth rate in butt welded joint may be represented by that of the base metal. The tests also revealed that the material used in this work has a sufficient safety margin compared to the reference curves in ASME Boiler and Pressure Vessel Code Sec. XI.
