On the Symmetry Among the Diffusional Transformation Products of Austenite
2011 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 42A, no 6, 1558-1574 p.Article in journal (Refereed) Published
Information on the diffusional transformation products of austenite in high-carbon steels is reviewed and supplemented with new microscopic studies. A comparison with transformation products in low-carbon steels indicates that there is a symmetry with pearlite in the middle, where ferrite and cementite are equal partners, and with acicular ferrite or cementite on each side. They both form with a surface relief, and at lower temperatures, each one is the leading phase in a eutectoid microstructure, bainite and inverse bainite, respectively. However, there is an asymmetry because at low temperatures bainite appears in high-carbon steels but inverse bainite never appears in low-carbon steels. At a constant high carbon content, there is another kind of symmetry, which is related to temperature. At intermediate temperatures the eutectoid reaction results in spherical nodules in which the cementite constituent originates from Widmanstatten plates. It turns spiky at both higher and lower temperatures with the leading phase in the spikes being cementite at higher temperatures and ferrite at lower temperatures. In the first kind of symmetry, there is an abrupt change among the three reaction products; in the second kind of symmetry, there is a gradual change. Accepting that all the eutectoid microstructures form by diffusion of carbon, one may explain the existence of both symmetries by the variation of the ratio of the supersaturations of ferrite and cementite with carbon content and with temperature.
Place, publisher, year, edition, pages
2011. Vol. 42A, no 6, 1558-1574 p.
HYPEREUTECTOID STEELS; LOWER BAINITE; DECOMPOSITION; MORPHOLOGY; ALLOYS; CARBON
IdentifiersURN: urn:nbn:se:kth:diva-33964DOI: 10.1007/s11661-010-0539-1ISI: 000290176100021ScopusID: 2-s2.0-79958786497OAI: oai:DiVA.org:kth-33964DiVA: diva2:420142
QC 201105312011-05-312011-05-232013-05-03Bibliographically approved