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Licensed Unlicensed Requires Authentication Published by De Gruyter December 29, 2021

Microstructure Selection in Laser Remelted Fe–C–Si Alloys

Milton S. F. Lima, P. Gilgien and Wilfried Kurz

Abstract

Laser surface remelting at various velocities has been employed to study the selection of microstructures of high-purity Fe–C–Si alloys containing nominally 3.2 to 4.2 wt.% C and 1 to 3 wt.% Si. The microstructure of the remelted region consisted of metastable Fe–Fe3C eutectic (ledeburite) or austenite dendrites, with interdendritic eutectic. Furthermore, ledeburite presents two solid-liquid interface morphologies: planar and cellular. The competition between the austenite dendrites and the ledeburite eutectic as a function of solidification rate has been experimentally determined. The critical velocity which destabilizes the planar Fe–Fe3C eutectic with respect to primary austenite dendrites, was of the order of several mm/s and depends on the initial composition of the alloy. The critical velocity for the destabilization of the eutectic interface leading to two-phase cells was 0.44 mm/s, for the alloy containing 4.2 wt.% C and 1 wt.% Si. Theoretical calculations of the coupled zone have been performed using current microstructure selection models. The results of the simulation were then used to construct a microstructure map which was compared with experimental results.


M. S. F. Lima[1)], W. Kurz Department of Materials Swiss Federal Institute of Technology CH-1015 Lausanne, Switzerland
P. Gilgien Cornell University Ithaca N. Y., U.S.A

  1. The authors thank J.-D. Wagniére for technical assistance. The research of MSFL had been partially financed by the Swiss Government under a CFBEE Scholarship.

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Appendix: Thermophysical constants values*

Constant Symbol Value Unity Reference:
Thermal conductivity K 44 W m–1 K–1 [19]
Thermal diffusivity α 8.9 · 10–6 m2 s–1 [19]
Densities at 24 °C ρFe 7400 kg m–3 [20]
  ρFe3C 7200 kg m–3 [20]
Gibbs-Thomson coefficients ΓFe 1.9 · 10–7 m K [21]
  ΓFe3C 2.4 · 10–7 m K [21]
Contact angle of the eutectic θFe/θFe3C 50/55 Degrees [21]
Solute diffusivities D 3 · 10–9 m2 s–1  

  1. *

    The phase diagram data (e.g. liquidus slopes, partition coefficients and reference temperatures) were obtained directly from ThermoCalc Database [8] and vary for each alloy.

Received: 1998-08-11
Published Online: 2021-12-29

© 1998 Carl Hanser Verlag, München