Crystal Structure of Martensite

Abstract

IT was first shown by W. L. Fink and E. D. Campbell (Trans. Am. Soc. Steel Treat., 9, 717; 1926), and independently by N. Seljakow, J. Kurdumoff, and N. Goodtzow (NATURE, 119, 494; 1927), that quenched carbon steels contain a phase with a tetragonal crystal structure, which might be considered as a deformation of the body-centred cubic structure of α-iron. This has been confirmed by other investigators, and our present knowledge of the tetragonal martensite may be briefly summarised as follows. The axial ratio increases from about 1.03 at 0.8 per cent carbon to 1.06 at 1.4 per cent carbon. At lower contents of carbon the interference doublets corresponding to the tetragonal lattice are not resolved, but in photograms of very rapidly cooled specimens the α-Fe-lines are slightly displaced in such a way as to indicate a tetragonal deformation. The higher the carbon content and the higher the axial ratio, the larger is also the volume of the unit cell.