Study of the Precipitation of χ-carbide in the Tempering Process of Some Low and Medium Carbon Steels

Abstract

Observations by transmission electron microscopy have been made on some quenched and tempered carbon steels containing 0.017%, 0.15%, and 0.48% carbon, to clarify the precipitation of χ-carbide in lower carbon steels, which was clearly found during tempering of some high carbon steel by the present authors.
The main results obtained are summarized as follows:
(1) There exists X-carbide in the tempering processes of low (0.017%, 0.15%C) and medium (0.48%C) carbon steels.
(2) The habit plane of the χ-carbide in the medium carbon steel is (112) a, suggesting that the carbide may precipitate preferentially on martensite twin boundaries.
(3) The orientation relationship of the χ-carbide with ferrite matrix of low and medium carbon steels is approximately expressed as (100)χ//(121)α, (010)χ//(101)α, and [001]χ//[111]α.