EFFECT OF WORK HARDENED INNER SURFACE LAYERS ON STRESS CORROSION CRACKING OF TYPE 316 STAINLESS STEEL AND TT ALLOY 690 IN SIMULATED PWR PRIMARY WATER

摘要

In this study, a comprehensive study was made of the relationship between the stress corrosion cracking (SCC) growth rate and Vickers hardness for Type 316 stainless steel and thermally treated (TT) Alloy 690 at various temperatures in simulated pressurized water reactor (PWR) primary water. In addition, intergranular SCC (IGSCC) growth rate measurement tests were conducted using so-called functionally graded cold rolled specimens made of Type 316 stainless steel and TT Alloy 690, in simulated PWR primary water. The purpose of these latter specimens was to evaluate the effect of heavily cold worked layers on the inner surface of components made of Type 316 stainless steel or TT Alloy 690 on the possibility that IGSCC could penetrate through the wall thickness. From the test data, it is considered that the work hardened inner surface does not always have a detrimental effect on SCC susceptibility. However, if any surface cracks exist within the work hardened inner surface layer of any components, the stress at the crack tip becomes very large and SCC easily initiates. Nevertheless, even if IGSCC initiates from a heavily cold worked layer at inner surface, it is considered that the IGSCC growth rate in Type 316 SS and TT Alloy 690 eventually becomes negligibly small or arrests in the soft base material.