Intricate morphologies of laths and blocks in low-carbon martensitic steels

Publication date: 15 September 2018
Source:Materials & Design, Volume 154
Author(s): Cyril Cayron, Annick Baur, Roland Logé
Low-carbon martensitic steels are made of intricate assemblies of martensitic laths: the twenty-four lath variants are grouped into packets on the four {111}fcc planes, and each packet is composed of three blocks of pairs of low-misoriented variants. The orientation relationship between the laths and their parent austenitic grains ranges from Kurdjumov-Sachs toward Nishiyama-Wassermann. The paper presents electron microscopy investigations that confirm that the habit planes of the laths are the {557} planes that contain the common fcc-bcc dense directions. The morphology of many blocks appears as a bifoliate structure made of the habit planes of the two low-misoriented lath variants they contain. A theoretical model is proposed to discuss the results. The average of the two Kurdjumov-Sachs distortions associated with the variants in a block is a Nishiyama-Wassermann distortion. The {557} lath plane of each of the two variants in a block is untilted by the Nishiyama-Wassermann distortion of one of the two neighboring blocks in the packet. Complete self-accommodation is also obtained in individual packets. These results could explain simultaneously the {557} lath planes and the lath/block intricacy in the packets.

Graphical abstract

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