Effect of Retained Austenite on Hydrogen Embrittlement of Steels.
Abstract
Ultrahigh strength steel alloys heat treated to 200,000 psi yield strength levels are notoriously sensitive to hydrogen induced delayed failure. In this program the effects of microstructure, especially that of retained austenite, on hydrogen induced (a) threshold stress intensity level, (b) crack growth rate, and (c) fatigue crack growth rate have been investigated. Microstructural variables investigated included prior austenite grain size, twinning, carbides, retained austenite, and indirectly, segregation. Emphasis in this study has been placed on the contribution of and stability of retained austenite. Optical, scanning electron microscopy, and transmission electron microscopy have been employed to establish microstructural details. Compact tension and bolt loaded fracture toughness specimens were used throughout the program. Precision hydrogen measurement were carried out by the Boeing Company. It was necessary to measure the hydrogen content for each sample, since it was not possible to introduce consistent hydrogen levels by cathodically charging. The influence of retained austenite is limited by its instability at the crack tip, where it has been shown to transform due to the intense stresses and strains in the plastic zone. Acoustic emission analysis was employed to detect and study the microscopic nature of crack growth as well as to establish a threshold stress intensity level. Test results showed that retained austenite, grain size, and probable segregation each contribute towards altering the hydrogen induced delayed failure characteristics. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 14, 1979
- Accession Number
- ADA078988
Entities
People
- W. E. Wood