Study of the Precipitation of X-carbide in Tempered Medium and Low Carbon Steels(Metallurgy)

Observations by transmission electron microscopy have been made on quenched and tempered carbon steels containing 0.017%, 0.15% and 0.48% carbon to investigate the precipitation behaviours of X-carbide in lower carbon steels with regard to those already clarified for high carbon steels by the present authors. The main results obtained are summarized as follows : (1) There exists X-carbide in the tempering process of low (0.017%, 0.15%C) and medium (0.48%C) carbon steels. (2) The habit plane of the X-carbide in the medium carbon steel is {112}_a, suggesting that the carbide precipitates preferentially on martensite twin boundaries. (3) The orientation relationship of the X-carbide with ferrite matrix of low and medium carbon steel is approximately expressed as (100)_x//(121)_a, (010)_x//(101)_a, and [001]_x//[111]_a