In this paper, the two kinds of precipitations in ferrite and cementite of iron or steel are described. These precipitations were observed by means of an electron microscope. (Reference Photo. 1 to Photo. 8).
With these precipitations the following results were obtained by metallurgical considerations with respect to C, Si, Mn, P, S, N and O in iron or steel. (1) Ferrite contains many spherical precipitations, most of which are Fe3Si2 particles. (2) Fe3Si2 particles are about 550 Å in average. But this size grows in proportion as the Si content in iron or steel increases, and then they group with other kinds of particles. (3) Fe3Si2 particles are precipitated in a field of γ solid solution and their distribution is dense at the grain boundary but not in the interior of the crystal grains. (4) Cementite is a combination of Fe3C and Mn3C. (5) Spherical particles of MnSi are precipitated in a very small quantity from cementite. They are about 400 A on the average. (6) Growth of pearlite cementite is partially disturbed by the Fe3Si2 particles. (Reference Photo. 8). (7) As compared with ferrite of plain carbon steel, silico-ferrite contains much more Fe3Si2 particles.
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