| Popis: |
For manufacturing the critical landing gear parts of aircrafts “AN” 30CrMnSiNi2Mo high-strength steel, UTS=1900 MPa, is used. The maximal operation stresses in the landing gear units are 854 MPa. At operation for 15 years, in spite of insignificant stresses, cases of failures by means of a corrosion mechanism (intergranular brittle fracture) and by means of corrosion-fatigue mechanism had taken place. The researches have shown that the failure of parts was provided by technology factors — the presence of a decarburized layer etc. Based on the analysis of operating conditions of the parts, their fractures the followed conclusion was drawn: the steel applied behaves on a limit of its capabilities, does not have a margin of plasticity, is sensitive to presence of surface defects, has low corrosion resistance and is not the best material for the loaded units with long term of operation. In last aircrafts “AN” for the loaded landing gear units a high-strength titanium alloy VT22 and maraging steel VKS-170 are used which have the much greater resistance for corrosion cracking. |
