Nucleation of Proeutectoid Ferrite on Complex Precipitates in Austenite

Abstract:

Effect of various intragranular inclusions or precipitates (MnS, VC and V(C,N)) on the microstructure and kinetics of intragranular ferrite transformation at the temperatures between 973 and 823 K was studied using various Fe–2Mn–(0.13, 0.2)C(mass%) alloys with the small addition of sulfur, vanadium, and nitrogen. In Fe–2Mn–0.13C–50ppmS and Fe–2Mn–0.2C–470ppmS alloys, MnS particles, mostly incoherent in austenite, do not act as effective nucleation sites of ferrite. V addition slightly improves the potency of MnS as ferrite nucleation site by forming MnSVC complex precipitates. The addition of both V and N largely enhances the intragranular nucleation of ferrite idiomorph on the MnSV(C,N) complex precipitate. It is considered that two factors, i.e., (1) the advantage in the balance of interphase boundary energy and (2) the increase in the fraction of V(C,N) precipitate by the addition of nitrogen, are mainly responsible for the promotion of intragranular ferrite formation on the MnSV(C,N) complex precipitate.

Keywords:

phase transformation, precipitation, steel, austenite, ferrite, carbide, nitride, sulphide, inclusion, crystallography, interphase boundary.

Author:

T. Furuhara (1), J. Yamaguchi (2), N. Sugita (3), G. Miyamoto (4) and T. Maki (1)

Affiiation

  1. Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto, 606-8501 Japan
  2. Formerly Graduate Student, Kyoto University, now at Nippon Steel Corp., Nagoya Works, Tokai 851-0392 Japan
  3. Formerly Graduate Student, Kyoto University, now at Hitachi, Ltd., Kodaira Operation, Kodaira, Tokyo 187-8588 Japan
  4. Graduate Student, Kyoto University, Sakyo-ku, Kyoto, 606-8501 Japan

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Source:

ISIJ International, Vol. 43, No. 10, 2003, pp.1630–1639