Control of cryogenic intergranular fracture in high-manganese austenitic steels
The sources of cryogenic intergranular embrittlement in high-Mn austenitic steels and the conditions necessary for its control are examined. It is shown that the high-Mn alloys are inherently susceptible to intergranular embrittlement due to both their low grain boundary cohesion and heterogeneous deformation characteristics. Extrinsic sources of embrittlement which could account for the transition behavior are not observed. An Auger electron spectroscopy (AES) study shows no indication of impurity-segregation-induced embrittlement. No grain boundary precipitation is observed, and austenite stabilization does not ensure ductile fracture. The influence of chemistry modifications on the ductile-to-brittle transition behavior were also examined through additions of N, Cr, and C to binary Fe-31 Mn. Nitrogen additions increase the 77K yield strength at a rate of 2200 MPa per weight percent N, and increase the austenite stability, but also increase the susceptibility of ternary alloys to intergranular fracture. Quaternary Cr additions are effective in increasing the N solubility, and lower the transition temperature. Carbon additions result in complete suppression of intergranular fracture at 77K. Qualitatively significant changes in the deformation heterogeneity with chemistry modifications are not observed. The temper-toughening of Fe-Mn-Cr-N alloys is associated with the grain boundary segregation of boron and the redistribution of N. Both boron and carbon are expected to inhibit intergranular fracture through increases in grain boundary cohesion.
- Research Organization:
- California Univ., Berkeley (USA). Dept. of Materials Science and Mineral Engineering
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6738367
- Report Number(s):
- LBL-22650; ON: DE87008226
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
AUGER ELECTRON SPECTROSCOPY
AUSTENITIC STEELS
CHARPY TEST
CHEMICAL COMPOSITION
CHROMIUM ALLOYS
CRYSTAL STRUCTURE
DEFORMATION
DESTRUCTIVE TESTING
DUCTILE-BRITTLE TRANSITIONS
ELECTRON SPECTROSCOPY
EMBRITTLEMENT
FRACTURE PROPERTIES
GRAIN BOUNDARIES
IMPACT TESTS
IRON ALLOYS
IRON BASE ALLOYS
MANGANESE ALLOYS
MANGANESE STEELS
MATERIALS TESTING
MECHANICAL PROPERTIES
MECHANICAL TESTS
MICROSTRUCTURE
NITROGEN ADDITIONS
PHYSICAL PROPERTIES
QUANTITY RATIO
SPECTROSCOPY
STEELS
TENSILE PROPERTIES
TESTING
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
YIELD STRENGTH