ON THE STABILIZATION OF RETAINED AUSTENITE

F.B.   Abudaia

doi:10.66411/jer.v5i5.390

Authors

F.B. Abudaia Department of Materials and Metallurgical Engineering, Al-Fateh University B.O. Box 13430, Tripoli, Libya Author

DOI:

https://doi.org/10.66411/jer.v5i5.390

Keywords:

Retained austenite, Deep freezing, Carburization, X-ray diffraction pattern, Aging

Abstract

Carburized layers in quenched steel components usually contain few percent of retained austenite (RA). Deep freezing treatment by dipping in liquid nitrogen is usually carried out when it is required to reduce the amount of retained austenite to very low levels. Stability of retained austenite due to aging was assessed by the difficulty of transformation of retained austenite to martensite when subjected to sub-zero treatment. In this work the case material was simulated by carburizing thin specimens of 1mm thick to obtain full through hardening by carburization. Retained austenite was found to stabilize with aging. Even in the absence of the effect of the core material, the retained austenite become under small compressive stresses induced by previously transformed austenite. This state of stress opposes further transformation resulting in incomplete transformation of austenite to martensite. X-Ray Diffraction (XRD) patterns from aged and non-aged specimens do not reveal any austenite carbon enrichment with aging. Indication of carbon atoms redistribution during aging is observed by disappearance of peak doublets of martensite lines on XRD diffraction patterns. Impeding mobility of α / γ interface migration by of carbon atoms to dislocation arrays is more likely to occur. Stability of retained austenite could therefore be attributed to the lowered mobility of the α / γ interface

References

[1] Kern R.F., Metals Progress, vol.166, no.1, July, 1972.

[2] Magner S.H., Weins W.N. and Makinsons J.D., 19th Heat Treating Society Proceedings, Oct.1999.

[3] Krauss G., Adv. Matl. & Proc. HTP, Sept.1995.

[4] Wilson B.M. and Weins W.N., 2000, 20th ASM Heat Treating Society Conference Proceedings, 9-12 October 2000, St. Louis, MO, ASM International.

[5] Cullity B.D., Elements of X-Ray diffraction, 2nd edition, Addison- Wesley, 1978. [6] Ruhl R.C. and Cohen M., Trans. AIME 245, 1969

[7] Pearson W.B., A Handbook of Lattice Spacing and Structure of Metals and Alloys, Pergamon press, Oxford, 1958.

[8] Averbach B.L. and Cohen M., Trans. AME176, 1948.

[9] Sarikaya M., Thomas G., Steeds J.W., Barnard S.J. and Smith G.D.W., In proceeding of an International conference on solid-solid phase transformations August 10-14-1981, Metallurigical society of AIME 1982.

[10] Wang J. and Van Der Zwaag S., Metallurgical and Materials Transaction A, vol.32A, June 2001 DOI: https://doi.org/10.1007/s11661-001-0240-5