Effect of Chemical Compositions on IGSCC Resistance for Strain Hardened Low Carbon Austenitic Stainless Steels in High Temperature Water

摘要

In order to clarify the mechanisms and develop the alternative materials on intergranular stress corrosion cracking (IGSCC) for the non-sensitized and strain hardened low carbon austenitic stainless steel in oxygenated water, the SCC resistance was studied for 24 laboratory melted steels and commercial type 3I0S stainless steel by the SCC propagation tests. From this study, it is concluded that the SCC resistance of the strain hardened low carbon austenitic stainless steel in high temperature water mainly increases with increasing of nickel contents and nickel equivalent value. The effects of chromium content, chromium equivalent value on the SCC resistance were hidden by the effects of the nickel contents and nickel equivalent value, in this study. The effects of the carbon content, nitrogen content, minor elements, hardness, grain size, delta ferrite content etc. on the SCC resistance were not so pronounced in this study. Non-cracked materials in this study showed the highest stacking fault energy (SFE) value which was calculated from the literature equations. It is strongly suggested that the SFE value is a key parameter for the SCC resistance of the non-sensitized and strain hardened low carbon austenitic stainless steels. From these test results, low carbon - low nitrogen - low silicon - low manganese - 20 % nickel - 25 % chromium -2.5 % molybdenum steel is recommended as an alternative high SCC resistant low carbon austenitic stainless steel. Following future works are recommended. 1) To develop a reliable calculation formula for SFE value of the austenitic stainless steels according to chemical compositions 2) To verify the superiority of the above new alternative stainless steel under practical fabrication 3) To develop an IGSCC resistant stainless steels within chemical composition range specified in JIS or ASTM material standard