Recent research that emphasizes electron backscatter diffraction ( EBSD) as a characterization tool has clarified the microstructure of dislocated martensitic steel formed by quenching moderate to large-grained austenite.The present paper specifically reports results for conventional 9Ni steel.Typically,each transformed prior austenite grain contains martensite laths that have all of the 24 distinct variants of the Kurdjumov-Sachs ( KS ) orientation relation.These are organized into 4 distinct packets,each of which contains laths in the 6 KS variants that share a common { 111 } γ = { 110} α plane.The laths are organized into 3 distinct blocks,each of which is a composite mixture of the 2 KS variants of the packet that share a common Bain axis.The blocks are plates with habit planes very near { 110}α;their boundaries are 120° twist boundaries about the common < 110 > α axis.While complex,this microstructural pattern can be understood and predicted by applying the Khachaturyan theory of dislocated martensite;it is the structure that minimizes elastic energy both during the transformation and in the final state of the transformed,polygranular body.