Bainite Transformation in a Silicon Steel.

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  • Jung Yun Chul
    Graduate Student, Ehime University
  • Ohmori Yasuya
    Department of Materials Science and Engineering, Faculty of Engineering, Ehime University
  • Nakai Kiyomichi
    Department of Materials Science and Engineering, Faculty of Engineering, Ehime University
  • Ohtsubo Hiroyuki
    Department of Materials Science and Engineering, Faculty of Engineering, Ehime University

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Abstract

The processes of upper bainite formation, the crystallographic aspects and the internal structure in a 1.83 % silicon steel have been investigated. The T-T-T diagram is separated into two C-curves as in the case of steels containing strong carbide forming elements. In the early stage of upper bainitic transformation, very fine needlelike ferrite subunits with the parallelogram cross sections elongated in a <110>γ //<111>α direction form on a {111}γ sheet in a side-by-side fashion. In the later stage of transformation, these subunits are coalesced on a {111}γ plane and produces upper bainite laths. This bainite is always related to the parent austenite with the Kurdjumov-Sachs relationship and accompanies the surface reliefs. ε carbide particles precipitate mainly after the ferrite subunits formation or after the coalescence of them. Therefore, the carbide precipitation is not a fundamental characteristic of bainite transformation but is a secondary effect. ε carbide needles precipitating within a bainite lath by long time holding are aligned almost parallel to the <112>α with almost constant intervals and are related to the ferrite by the Jack relationship. These aspects are exactly similar to those in tempered martensite. Such an ε carbide configuration is thought to arise from the precipitation on the dislocations introduced during transformation.

Journal

  • ISIJ International

    ISIJ International 37 (8), 789-796, 1997

    The Iron and Steel Institute of Japan

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