| Abstract: | Influence of various annealing temperatures on the long-term strength under corrosion of a molybdenum alloyed 13% chromium steel in chloride containing media Corrosion fatigue tests were performed at varied levels of tensile strength of the material X 20 CrMo 13 at temperatures of 150 and 200 °C in 0.01 n solution of NaCl. A considerable decrease in the resistance to corrosion fatigue could be observed with increasing tensile strength of the material. As expected, the material shows a distinct sensitivity to stress corrosion at the highest tensile strength. Additional investigations of the morphology of the fracture proved that stress corrosion mechanisms are not directly controlling the formation of fracture surfaces. Spots of pitting corrosion on the surface of the samples can be coordinated with the amount of stressing. Pitting and fracture initiation under corrosion fatigue conditions, however, cannot be coordinated. Analyses of the microstructure reveal a layer on the samples which is expected to have a good protective effect against corrosion. Obviously the course of the fatigue corrosion depends on the rebuilding time of passivity which should be influenced by alloying of molybdenum. Under the selected testing conditions, however, the alloying of molybdenum was not yet sufficient to obtain a distinct improvement of the resistance to corrosion fatigue. The investigations will he carried on with the chosen material with higher amounts of alloyed molybdenum. |
