The isothermal precipitation behavior in a low-carbon steel at low temperatures investigated by internal friction
- Erich-Schmid-Inst. fuer Festkorperphysik der Osterreichischen Akademie der Wissenschaften, Leoben (Austria) Inst. fuer Metallphysik der Montanuniversitat, Leoben (Austria)
The precipitation behavior of metals is commonly demonstrated in continuous or in isothermal time-temperature transformation diagrams. Best known are such diagrams for steel with carbon concentrations above 0.2 wt%. Isothermal TTT''-diagrams are used to show the aging properties of aluminium alloys. Conventional methods to establish TTT-diagrams comprise the analysis of the microstructure, strength measurements, dilatometric observations and the measurement of the electrical resistivity. All these methods measure directly the results of precipitation. Except for the last of these methods, all others may fail to work when the amount of the precipitated phase is too small for detection. A very sensitive way to assess the state of precipitation in an interstitional alloy with a b.c.c. structure is measuring the internal friction at the Snoek peak which is caused by the anelastic relaxation of interstitially dissolved atoms. Complementary structure analysis should be used to distinguish the different precipitates of one interstitial. A further way of distinction, when precipitates form directly from still dissolved interstitial atoms, is to observe the precipitation kinetics. However, any later structural changes of the first precipitate are not recognized unless they are accompanied by intermittent reversion phenomena. An attempt to produce a TTT-diagram by internal friction may be worthwhile when all other methods are not accurate enough because the carbon concentration is too low as, for instance, in low-carbon steels. The steel used to study the precipitation behavior contained, in wt.%, 0.043 C, 0.02 Si, 0.22 Mn, 0.008 P, 0.012 S, 0.061 Al, 0.02 Cr, 0.027 Cu and 0.02 Ni.
- OSTI ID:
- 5455168
- Journal Information:
- Scripta Metallurgica et Materialia; (United States), Vol. 30:3; ISSN 0956-716X
- Country of Publication:
- United States
- Language:
- English
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