Bruchmechanische Charakterisierung austenitischer Edelstähle bei chloridinduzierter Spannungsrisskorrosion

Translated title of the contribution: Using fracture mechanics on investigation of chloride induced stress corrosion cracking of austenitic stainless steels

Beate Wagner

Research output: ThesisDiploma Thesis

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Abstract

In hot chloride containing environments, austenitic stainless steels are highly suscebtible of Stress Corrosion Cracking (SCC). Stress corrosion occurs when a metal is attacked by the simultanious action of a corrosive environment and tensile stress, which results in the formation of a crack, often followed by service failures. SCC undergoes two different states: Formation and propagation of a crack. The most common investigation methodes like constant load tests, can not give the necessary information to distinguish between these two states. Using the fracture mechanics approach to SCC, stress corrosion crack velocities can be measured, because of the application of preckracked sampels. Thereby the location of both, crackforming and direction of the crackgrowth are predetermined. In this work fracture mechanics methods have been used to investigate the SCC behavior of two different types of steels: CrNiMo- and CrMnN-steels. Therefore constant load tests on notched samels have been carried out in 45 wt% MgCl2-solution at 145 °C. The results are obtained in in the form of stress corrosion crack velocity versus stress intensity curves. The CrNiMo-alloy with the highest content of Ni and Mo showed the lowest crack velocity of 7 E-09 m/s. The crack velocities of the CrNiMo-steel with lower content of Ni and Mo, as well as the CrMnN-alloy of highest strength were nearly the same at about 1 E-07 m/s. The lower strength of the CrNiMo-steels results in crackbranching, which in turn lowers the driving force for furher crack prolongation. For both, the CrNiMo-steels and CrMnN-steels the crackmorphology of the SCC was transgranular, irrespective of the initial applied stress intensity. In this work the mainly influencing factor of the stess corrosion crack velocities was the chemical composition of the alloys, consequently the stability of the passive layer. Related to the slip-step-disolution-model it can be assumed, that the anodic dissolution takes the leading part according to the SCC stability of these investigatet stainless steels.
Translated title of the contributionUsing fracture mechanics on investigation of chloride induced stress corrosion cracking of austenitic stainless steels
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Mori, Gregor Karl, Supervisor (internal)
Award date26 Jun 2009
Publication statusPublished - 2009

Bibliographical note

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Keywords

  • stress corrosion cracking fracture mechanics stress corrosion crack velocity austenitic stainless steels

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