| Bainitic transformation structure in a low carbon alloy steel, 0.13C-1.8Ni-1.6Cr-0.5Mo-0.07V, has been studied by electron microscopy. Bainitic structure was obtained by isothermal transformation in the salt bath holding at 400℃, 450℃ and 500℃, Bainitic transformation has already begun at the initial cooling stage, from the austenitizing temperature to the respective transformation temperature. In the case of isothermal treatment at 450℃ and 500℃, mixed structure of coarse bainitic ferrite lath and retained austenite was observed in the specimens of short transformation time, for example, 200 sec. As the isothermal transformation time increased, the region of retained austenite was replaced gradually by finer bainitic ferrite lath, and carbide was precipitated in the revious coarse bainitic ferrite lath. Detailed microstructural features of the bainitic structure, produced at the initial cooling stage and at the later isothermal treatment stage, were studied, respectively. At the transformation temperature of 400℃, somewhat different microstructure, so-called granular type bainite, was developed. |
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