The Precipitation of χ-carbide in the Tempering Process of High Carbon Steels

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To make clear the precipitation behaviour of iron-carbides, especially to show if χ-carbide precipitates or not, in the tempering process of steels, observations were made by transmission electron microscopy on some quenched and tempered high carbon steels containing 0.86, 1.11, and 1.34 wt% carbon. Thermomagnetic and thermal dilatational measurements were also made for comparison's sake. The main results obtained are summarized as follows : (1) In the high carbon steels tempered under appropriate conditions, χ-carbide was observed by transmission electron microscopy. (2) The habit plane of χ-carbide was determined to be {112}_α, suggesting that the carbide may precipitate preferentially on twin boundary in martensite. (3) In electron micrographs, the morphology and the growth direction of χ-carbide were different from those of ε-carbide, but were very similar to those of θ-carbide which precipitates on {112}_α. From these observations, it was supposed that the transitions of ε→χ andχ→θ were due to a separate nucleation and an in situ transformation, respectively. θ-carbide precipitated on {110}_α was also found, suggesting the precipitation to take place by a separate nucleation directly from ε-carbide. (4) Using indices of main crystal planes and a direction in χ-carbide, i.e., (100)_x, (010)_x, and [001]_x, the orientation relationship of the carbide with ferrite matrix was expressed as (100)_x//(121)_α, (010)_x//(101)_α, and [001]_x//[111]_α. (5) The precipitation of χ-carbide was also detected by thermomagnetic and thermal dilatational measurements on the high carbon steels tempered under the most favourable condition to obtain χ-carbide.
東北大学の論文

The Precipitation of χ-carbide in the Tempering Process of High Carbon Steels

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