Stress Corrosion Cracking in High-Temperature Pure Water and Selective Corrosion of Nickel-Bearing 13Cr Martensitic Stainless Steels

Mechanical and corrosion properties of 13 mass%Cr martensitic stainless steels containing 2∼5 mass% nickel were studied in various tempered states. Effects of metallurgical variable were examined by the following tests: (a) Conventional mechanical and metallurgical tests, (b) selective corrosion test in 0.88 kmol/m3 HNO3 at 293 K, and (c) slow strain rate stress corrosion cracking test in high purity water at 561 K. The following results are obtained:(1) The 13%Cr martensitic stainless steels containing 3.5∼5 mass% nickel shows superior mechanical properties and machinability to those with 0∼2 mass% nickel.(2) However, a higher nickel addition lowers the Ac1 point to the actual tempering temperature range. This makes it difficult to choose the tempering condition which satifies the mechanical properties needed for hydraulic machinery.(3) The susceptibility to selective corrosion increases with increasing nickel content and selective corrosion occurs in a wide temperature range and consequently the selection of the tempering temperature range is limited.(4) Active path type stress corrosion cracking behavior is closely related to the selective corrosion behavior.In conclusion, it is desirable to lower the nickel and carbon contents in the steel and to carefully select the tempering temperature yielding good mechanical properties without giving rise to susceptibility to selective corrosion.