Continuous CoolingTransformation Behavior of Flake Graphite Cast Iron During Heat Treatment

概要

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The purpose of this paper is to draw CCT diagrams for heat treatment and clarify the continuous cooling transformation behavior of flake graphite cast irons containing 1.6 and 2.5mass%Si. A metallographic method is used to draw the CCT diagrams, and the Ac1, Ac3 and Ms temperatures are measured by the dilatometoric method. The austenitizing condition is 1223K × 900s, and the range of cooling time from the austenitizing temperature to 773K is about 0.5s to 4000s. Ferrite, pearlite, and martensite transformation regions exist in both the CCT diagrams of 1.6%Si and 2.5%Si cast irons. Cementite and bainite transformation regions do not exist in both CCT diagrams, and hypereutectic cementite and bainite are not observed in any of the specimens after cooling in this study. The ferrite transformation region in both CCT diagrams exists in the pearlite transformation region. This phenomenon is considered to occur due to insoluble cementite in the steadite, and that pearllte starting to precipitate from this cementite before ferrite precipitation in the austenite surrounding the graphite. The ferrite transformation curve and Ms temperature shift to a higher temperature with the increase in the Si content. The hardenability of the 2.5%Si cast iron is greater than that of the 1.6%Si cast iron.
Japan Foundry Engineering Societyの論文