Aging of Iron-Based Martensites at Low Temperatures

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School of Engineering | Doctoral thesis (article-based) | Defence date: 1992-06-25
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In the present work aging of iron-based martensites, defined as all the phenomena preceding the first stage of tempering, is studied using various methods. In some alloys aging was observed to start at very low temperatures, even near 4 K. Abnormally high or abnormally low tetragonality is observed in freshly formed martensite alloyed with Ni or Mn, respectively. The reason for high tetragonality obviously lies in the coherency at the interface between the martensite and the retained austenite. It is shown in the present work that the coherency is broken during aging in the temperature range of 100 - 200 K and it is accompanied by a decrease of tetragonality (first stage of aging). The new internal friction peak centered at 145 K corresponds to the movement of the coherent interface and the break of coherency. Some evidence for correlation between short range atomic ordering in austenite and the high tetragonality of the virgin martensite is given and a contribution of nontransformed ordered austenitic regions inside martensite plates to tetragonality is discussed. It is shown that the second stage of aging at temperatures about 200 - 270 K is controlled by the pinning of the dislocations by carbon atoms and the third stage (mainly above 250 K) by the clustering of carbon atoms in a solid solution. By means of Mössbauer spectroscopy, electrical resistivity and magnetic susceptibility measurements, a striking difference is shown between the redistribution of carbon and nitrogen atoms above 200 K. Evidence for the clustering of carbon and ordering of nitrogen is given and discussed. The dynamics of clustering was studied by means of small angle neutron scattering. Deformation of martensite at subambient temperatures reduced the tetragonality of martensite to cubic and changed the redistribution of carbon atoms. According to different measurements, practically no aging was observed below room temperature in the deformed martensite.
Supervising professor
Pietikäinen, Juha
Hänninen, Hannu
martensite, aging, low temperature, deformation, X-ray diffraction, neutron scattering, Mössbauer spectroscopy, internal friction, positron annihilation, electrical resistivity, magnetic susceptibility, dilatometry, shear modulus
Other note
  • [Publication 1]: K. Ullakko and V.G. Gavriljuk, Effects of coherent interfaces in the freshly formed iron–nickel–carbon martensites, Acta Metallurgica et Materialia, Overview No. 99, Vol. 40, No. 10, pp. 2471-2482, 1992.
    DOI: 10.1016/0956-7151(92)90316-7 View at publisher
  • [Publication 2]: O. Antson, V.G. Gavrilyuk, V.A. Kudryashov, V.M. Nadutov, H. Pöyry, J. Pietikäinen, A. Tiitta, V.A. Trudnov, K. Ullakko, V.A. Ul'yanov, P. Hiismäki and Yu.P. Chernenkov, Neutron diffraction study of the martensitic transformation in Fe–Ni–C alloys, Physics of Metals and Metallography, Vol. 70, No. 4, pp. 108-115, 1990.
  • [Publication 3]: V.G. Gavrilyuk, V.M. Nadutov, S.P. Oshkaderov, J. Pietikäinen and K. Ullakko, Phase and magnetic transformations in the Fe–Ni–C alloy at low temperatures, Physics of Metals and Metallography, Vol. 70, No. 1, pp. 120-125, 1990.
  • [Publication 4]: V. Gavriljuk, V. Duz' and K. Ullakko, Internal friction of tempered ferrous martensites, Scripta Metallurgica et Materialia, Vol. 26, pp. 667-672, 1992.
    DOI: 10.1016/0956-716X(92)90303-V View at publisher
  • [Publication 5]: V.G. Gavriljuk, V.M. Nadutov and K. Ullakko, Low temperature ageing of Fe-N martensite, Scripta Metallurgica et Materialia, Vol. 25, pp. 905-910, 1991.
    DOI: 10.1016/0956-716X(91)90246-W View at publisher
  • [Publication 6]: V.V. Runov, A.I. Okorokov, A.D. Tretjakov, L.V. Grigorjev, V.A. Uljanov, K. Ullakko and V.G. Gavriljuk, Observation of a relaxation phenomenon during ageing of Fe-Ni-C martensite by means of small angle neutron scattering, Scripta Metallurgica et Materialia, Vol. 26, pp. 661-665, 1992.
    DOI: 10.1016/0956-716X(92)90302-U View at publisher
  • [Publication 7]: M. Kajatkari, K. Ullakko and J. Pietikäinen, On the aging of Fe-Ni-C and Fe-Mn-C martensites, Journal de Physique, Colloque C4, Supplément au no 18, Tome 43, décembre 1982, pp. 461-466.
    DOI: 10.1051/jphyscol:1982471 View at publisher
  • [Publication 8]: K. Ullakko, M. Nieminen and J. Pietikäinen, Effects of low temperature deformation on the lattice structure and carbon distribution in Fe-Ni-C martensite, Materials Science Forum, Vols. 56-58 (1990), pp. 191-196.
    DOI: 10.4028/ View at publisher