Model for multiple stress affected martensitic transformations, microstructural entropy and consequences on scatter in properties

Abstract

Building on previous work on stress affected martensitic transformations, a simple theory is presented to enable the calculation of the volume fractions of each martensite variant in an austenite grain, as a function of temperature. Polycrystalline austenite is dealt with by introducing specific textures, so that the orientation of the martensite in any region of the sample is defined. The calculations show that there is strong variant selection even with relatively small applied stresses, and the evolution of overall volume fraction is dominated by the favoured variants. The notion of microstructural entropy, which indicates the level of heterogeneity in the microstructure, is then used to indicate consequences on properties such as the scatter to be expected in toughness. These and further detailed consequences of stress affected transformation are described.

Keywords:

• Martensite
• Stress affected
• Simultaneous transformations
• Microstructural entropy
• Mechanical free energy

The authors are grateful to Professor D. W. Suh of GIFT, POSTECH, for helpful discussions and comments. Drs Kundu and Chintha acknowledge support from Tata Steel Ltd. HKDHB is grateful to the World Class University Programme of the National Research Foundation of Korea, Ministry of Education, Science and Technology, project no. R32-2008-000-10147-0.