Effect of MnS Inclusions on Stress Corrosion Cracking in Low-Alloy Steels

Abstract

Effect of MnS inclusions on the stress corrosion cracking (SCC) of low-alloy steel in 288°C oxygenated pure water was studied using slow strain rate tensile (SSRT) test. MnS inclusions dissolve and can act as starting points of SCC. At high amounts of dissolved oxygen (about 8 ppm), pitting corrosion and MnS inclusions act as starting points of SCC, while at low amounts of dissolved oxygen (about 0.2 ppm), MnS inclusions dominate the SCC initiation. The probability of MnS inclusions existing on the specimen side surface is an important factor for SCC initiation susceptibility of the material. The number of SCC starting points in intermediate sulfur content material (about 0.015 wt%S) is larger than that in low-sulfur content material (about 0.004 wt%S). The existence of MnS inclusions also affects the SCC propagation, particularly at low, dissolved oxygen (about 0.2 ppm).