Effects of alloying elements on stress corrosion cracking (SCC) resistance of 19Cr-9Ni steel in dilute NaCl solution were investigated. SCC tests were conducted with spot welded specimen in 50ppm Cl- solution at various temperatures, which allowed determination of critical temperature for SCC. Decreasing P content below 30ppm was effective in increasing SCC resistance. Critical temperature for SCC of 19Cr-9Ni steel with 10ppm P was 100°C, which was higher than that of 50°C for SUS 304 (0.07C-19Cr-9Ni-0.028P-0.027N). Addition of Cu had beneficial effect on SCC resistance. Critical temperature for SCC of 19Cr-9Ni-1Cu steel with 20ppm P was 140°C and that of 19Cr-9Ni-2Cu steel with 200-300ppm P was 100°C. Increasing N content had no significant effect on SCC resistance, while Mo showed detrimental effect on SCC resistance. Based on the corrosion morphology observations after immersion tests, competition was observed between SCC and crevice corrosion and SCC was enhanced under the condition which suppressed the dissolution by crevice corrosion. It is thought that beneficial effect of decreasing P content on SCC resistance is attributable to the result that it promotes metal dissolution in a crevice. On the other hand, addition of Cu makes the corrosion potential in a crevice more noble, resulting in increasing SCC resistance by making to shift to more noble potential region of the SCC occurrence.
In order to meet with severer regulations of exhaust emission, FFV (Flexible Fuel Vehicle) operated by a blend fuel of gasoline and methanol are now under intensive development. However, critical failures can be expected to occur on the surface of SUS 440 C valve seat of fuel injector operated by the blend fuel M 85. Metallographic observations, FFV on-board durability tests, injector fuel-jet durability tests, and corrosion tests were carried out to confirm that failures caused by corrosion wear occur as expected, and the corrosive power of fuel becomes strong by blending with methanol in the case of trespassing of chloric acid in exhaust gas on the fuel. In order to supress the corrosion wear of the surface of valve seat, it is necessary to exclude the source of chloride ions, and apply new valve seat material with higher performance of anticorrosion than conventional SUS 440 C.
Anodic polarization behavior of Al-4.5Mg-0.3Cu alloy was studied in 0.008, 0.04 and 0.2g/l NH4F solutions and compared with that of pure aluminum at room temperature. It was found that fluoride ions stimulate the anodic dissolution of the aluminum alloy and pure aluminum and that the anodic dissolution is controlled by fluoride ion transport process. The higher the NH4F concentration, the larger the dissolution current density. The pitting potential increases as the concentration of NH4F increses, and at the same time the density of pits increases. It seems that the pits initiate at the precipitates of intermetallic compounds (Al3(Fe, Cu), Al6(Fe, Cu)) under the anodic polarization and that the amount of the compounds exposed on the alloy surface increases in highly concentrated NH4F solution. Higher pore density at higher F- concentrations can be explained in terms of the exposure of intermetallic compounds.
Stereo image processing technique has been applied to measure a three dimensional shape of corroded surface. Stereo photographs were taken at the front of view and the inclined view of a sample. The three dimensional height was calculated from the difference in position of an image between two photographs and the inclination angle. A newly developed algorithm was applied for correcting a distortion of inclined image. Mutual correlation coefficient methed was applied to calculate the corresponding points. The depth precision of this method is about 0.1mm, when photographic amplification is 2 and resolution of image scanner is 400dpi. Results from this method agree with the data measured by point micrometers. This method doesn't require any special measuring tools but a camera, and can be used as non-destructive and non-contact tests.
Surface analysis methods like XPS, static SIMS, AES, and RA-FTIR can provide valuable information on the structure and composition of interface between metal and polymer. Examples of their application are the investigations of bonding mechanisms such as surface primary bonding. This paper reviews the ability of these surface analysis methods for the interface study, particularlly for the interface between pretreated metals and polymeric materials for structural bonding.