%0 Journal Article
%T Microstructure and cleavage in lath martensitic steels
%A John W Morris Jr
%A Chris Kinney
%A Ken Pytlewski and Y Adachi
%J Science and Technology of Advanced Materials
%D 2013
%I Institute of Physics, National Institute for Materials Science
%X In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni) steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recently identified 'classic' lath martensite structure: prior austenite grains are divided into packets, packets are subdivided into blocks, and blocks contain interleaved laths whose variants are the two Kurjumov¨CSachs relations that share the same Bain axis of the transformation. When the steel is fractured in brittle cleavage, the laths in the block share {100} cleavage planes and cleave as a unit. However, cleavage cracks deflect or blunt at the boundaries between blocks with different Bain axes. It follows that, as predicted, the block size governs the effective grain size for cleavage.
%U http://dx.doi.org/10.1088/1468-6996/14/1/014208