Strain Partitioning & Mechanical Stability of Retained Austenite Joo Hyun Ryu a Dong-Ik Kim b Hyoung Seop Kim c H. K. D. H. Bhadeshia a,d Dong-Woo Suh a a Graduate Institute of Ferrous Technology, POSTECH, Pohang 790-784, Korea b Korea Institute of Science and Technology, Seoul, 136–791, Korea c Department of Materials Science and Engineering, POSTECH, Pohang 790-784, Korea d Materials Science and Metallurgy, University of Cambridge, CB2 3QZ, U.K. Abstract The mechanical stability of austenite in steels which rely on transformation–induced plasticity is usually attributed to its chemical composition, size and shape. We demonstrate here that another factor, the partitioning of strain between phases with different mechanical properties, can dramatically influence the stability. Key words: TRIP steel, retained austenite, stability, strain partitioning Many modern steels rely on a microstructure containing some retained austen- ite which transforms into martensite during the course of deformation [1,2]. This stress or strain–induced transformation leads to additional plasticity which enables strong steels to be formed into complex shapes. Critical in this behaviour is the mechanical stability of the austenite; if transformation is exhausted at small plastic strains then the protection against a necking in- stability is lost, and if the austenite is too stable then it does not contribute to strain hardening at stress concentrations. The importance of the stability of retained austenite in the design of transfor- mation induced plasticity (TRIP) steels is well understood and the chemical composition [3–8], size [9,10] and shape [11] of the austenite are the main factors that have been researched in this context. In most cases, TRIP steels are only partly austenitic because this phase is retained without using expensive solutes by ensuring that the carbon that is Email address: dongwoo1@postech.ac.kr (Dong-Woo Suh). Preprint submitted to Elsevier 26 May 2010 Scripta Materialia 63 (2010) 297-299