Stress corrosion cracking of the chromium steel X 210 Cr 12 in chloride and sulphate containing solutions: part II: influence of media on SCC-behaviour

摘要

The stress corrosion cracking behaviour of the cold work steel X 210 Cr 12 with both martensitic andpearlitic structure has been investigated in distilled water as well as in aqueous sodium chloride andsulphate solutions at room temperature by means of fracture mechanical and electrochemicalmethods. In the used test solutions both materials are not in the state of passivity despite of their relativelyhigh chromium contant (12 w.-%) and sensitive to SCC-cracking. The K{sub}(ISCC)-value amountsto 10-11 Mpa sqrt(m) for the martensitic material and 26-29 MPa sqrt(m) for the pearlitic steel in thetest media. The dependence of the K{sub}(ISCC)-values on the media can be explained by formation ofporous layers consisting of ferrous hydroxide and ferrous sulphate, respectively. These layers inhibitthe anodic metal dissolution and the hydrogen absorption and so the corrosion process. Sulfatesinhibit the SCC above a material depending threshold concentration reflected by an increasedK{sub}(ISCC)-value. However, at a sulfate concentration below the threshold value the conductivityof the test solutions forces the corrosion process and so a decrease of the K{sub}(ISCC)-value.