Abstract
In order to clarify the effect of dissolution of MnS inclusions on environmentally assisted cracking of low alloy steel in high temperature water, dissolution behavior of MnS inclusions was investigated. The effects of temperature, dissolved oxygen concentration, specimen orientation and the composition of the test environments are discussed. Corrosion tests in high temperature water were carried out by using coupon specimens with crevice and without crevice to simulate the conditions of inside and outside of the cracks. Marked MnS inclusions were observed before and after 72 hours corrosion by a scanning electron microscope. The MnS inclusions dissolved at temperatures higher than 473K in crevice. The dissolution of MnS was accelerated by crevice and temperature up. Dissolved oxygen accelerated the dissolution of matrix around MnS inclusions but took little effect on dissolution of MnS inclusions. Specimen orientations and a simulated PWR environment showed little effect. The dissolution of MnS inclusions is considered to accelerate fatigue crack growth at temperatures higher than 473K.
