THE STRESS-CORROSION CRACKING OF AS-QUENCHED-4340 AND 3.5NICRMOV STEELS UNDER STRESS RATE CONTROL IN DISTILLED WATER AT 90-DEGREES-C

This paper presents experimental results from the Linearly Increasing Stress Test (LIST) applied to the stress corrosion cracking (SCC) of a s-quenched 4340 and 3.5NiCrMoV turbine rotor steel in aerated distille d water at 90-degrees-C. Experiments were performed at applied stress rates ranging from 2.1 x 10(-4) to 2.1 x 10(2) MPas-1. Parameters meas ured included the threshold stress, the fracture stress, the average c rack velocity and the strain rate at the threshold stress. The crack t ip strain rates were evaluated using expressions derived from the lite rature. Stress corrosion was observed at all applied stress rates in 4 340 steel but not at applied stress rates higher than 0.034 MPas-1 for the turbine rotor steel. In both steels, the crack velocity was stron gly dependent on the applied stress rate. The fracture surface morphol ogy was intergranular in all cases. Corrosion pits influenced stress c orrosion crack initiation.