高炭素鋼の焼戻し過程におけるX-炭化物析出

抄録

In order to make clear the precipitation behaviour of iron-carbides, especially the existence or non existence of X-carbide, in the tempering process of steels, observations were made of some quenched and tempered high carbon steels containing 0.86-1.34 wt pct carbon by transmission electron microscopy. 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, X-carbide can be observed by transmission electron microscope.
(2) Habit plane of X-carbide is determined to be {112}α suggesting that the carbide may precipitate preferentially on martensite twin boundary.
(3) In electron micrographs, morphology and growth direction of X-carbide are different from those of ε-carbide, but are very similar to those of θ-carbide which precipitates on {112}α. From these observations, separate nucleation and in situ transformation are supposed for ε→x and Xθ transition, respectively.θ-carbide precipitating on {110}α a is also found, and is suggested to take place by separate nucleation directly from ε-carbide.
(4) Using three main crystal indices of planes and direction in X-carbide, i. e., (100)x, (010)x, and [001]x, the orientation relationship of the carbide with ferrite matrix is approximately expressed as (100)z≈//(121)α, (010)x≈//(101)α, and [001]x≈//[111]α.
(5) By thermomagnetic and thermal dilatational measurements, the precipitation of X-carbide is also detected on the high carbon steels tempered under the most favourable condition to obtain X-carbide.