IRRADIATION ASSISTED STRESS-CORROSION CRACKING OF CONTROLLED PURITY 304L STAINLESS-STEELS

The effect of chromium, phosphorus, silicon and sulfur on the stress c orrosion cracking of 304L stainless steel in CERT tests in high purity water or argon at 288-degrees-C following irradiation with 3.4 MeV pr otons at 400-degrees-C to 1 dpa, has been investigated using ultrahigh purity alloys (UHP) with controlled impurity additions. Grain boundar y segregation of phosphorus or silicon due to proton irradiation was q uantified using both Auger electron spectroscopy and scanning transmis sion electron microscopy, and the alloys with impurity element additio ns were observed to have greater grain boundary chromium depletion and nickel enrichment than the UHP alloy. The UHP alloy suffered severe c racking in CERT tests in water. Less cracking was found after CERT tes ts of irradiated UHP+P or UHP+Si alloys, despite greater chromium depl etion. This suggests a mitigating effect of phosphorus and silicon at grain boundaries. No cracking was found in argon tests, eliminating a purely mechanical embrittlement mechanism, but not eliminating a contr ibution from radiation hardening. Implanted hydrogen was not a factor in the intergranular cracking found.