Effects of thermal aging on Stress Corrosion Cracking and mechanical properties of stainless steel weld metals

Abstract

Stress Corrosion Cracking (SCC) in and around primary loop piping welds in Boiling Water Reactors has been observed worldwide as plants continue to operate at temperatures and pressures near 2880C (5500F) and 6.9 MPa (1000 PSI). An experimental program was designed to explore the effect of thermal aging on the SCC crack growth rate in weld materials for type 316 and 304 stainless steels. An autoclave facility was designed and constructed for the measurement of SCC crack growth rates under BWR conditions and testing was underway at the time of this writing. The effects of composition and thermal aging on mechanical properties (i.e. tensile, micro-hardness, nano-hardness, Jic, and Charpy-impact toughness) was in process and initial results show an increase in yield strength and a decrease in fracture toughness after aging for 1000 hours at 430 and 400 *C. Thermal aging results in no discernable changes to the 6-ferrite morphology when viewed optically at 500 X agnifications and in the scanning electron microscope.