Hydrogen degradation of spheroidized AISI 1020 steel
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The authors gratefully acknowledge the suggestion by one of the reviewers of this article to use more explicit notations for the activity coefficients at infinite dilution. This work was supported in part by the American Society for Metals under Grant FG-104-1A and in part by the National Science Foundation through the Joint Program on Critical Compilation of Physical and Chemical Data coordinated through the Office of Standard Reference Data, National Bureau of Standards. REFERENCES 1. J.P. Neumann, T. Zhong, and Y.A. Chang: Bull. Alloy Phase Diagrams, 1984, vol. 5, pp. 136-40. 2. M. Venkatraman, J.P. Neumann, and Y.A. Chang: J. Electrochem. Soc., 1986, vol. 133, pp. 634-38. 3. C. Wagner: Thermodynamics of Alloys, Addison-Wesley, Reading, MA, 1952, ch. 2. 4. J. Chipman: J. Iron Steel Inst., 1955, vol. 180, pp. 97-106. 5. W. Stichel: Dissertation, Technische Universit~it, Berlin, 1967. 6. J. Osterwald, G. Reimann, and W. Stichel: Z. Phys. Chem. (Wiesbaden), 1969, vol. 66, pp. 1-7. 7. P. Taskinen: Acta Polytech. Stand. Chem., Incl. Metall. Ser., 1981, vol. Ch. 145, pp. 1-45.
Hydrogen Degradation of Spheroidized AISI 1020 Steel S.C. CHANG and J. P. HIRTH In a previous study of the influence of hydrogen on the properties of spheroidized AISI 1090 steel, the major effect of precharged hydrogen in plane-strain tension and bend tests was to promote plastic instability form of localized shear. 1 The instability was manifested by enhanced surface roughening, the development of bulk shear bands emanating S. C. CHANG is Associate Professor, Department of Materials Science, National Tsing-Hua University, Hsinchu, Taiwan. J.P. HIRTH is Professor, Department of Metallurgical Engineering, The Ohio State University, Columbus, OH 43210. Manuscript submitted August 15, 1985.
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from the surface, the formation of surface microcracks at reentrant regions of the roughened surface, and mixed mode I-II failure. The mixed mode cracks 2 followed shear bands, the characteristic slip lines of plasticity theory, but also had normal stresses acting to open the cracks. The critical strains for all of the above stages of development of plastic instability were lowered by about a factor of two in the presence of precharged hydrogen at high fugacity. ~'3 Cross sections of tested specimens revealed voids aligned along the shear band traces once bulk shear bands formed, but a major cause for these was shown to be the incompatibility stresses developed at carbide interfaces by the localized plastic flow.l'3 Once formed, voids further enhance flow localization and vice v e r s a , and failure ensues. The mechanism of enhancement of plastic instability occurred at a sizescale too fine to be resolved in the above experiments, but possibilities include a direct effect of hydrogen on the planarity of slip in the matrix or the development near the surface of a few carbide-interface decohesion events that trigger the interactive failure mechanism described above. In contrast, in uniaxially tensile loaded notched or unnotched rou
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