Effect of retained austenite on the mechanical properties of medium-strength steels

The effect of retained austenite on the mechanical properties of high-strength steels is associated with decleration of crack motion in the austenite layers positioned between martenstie laths. Decelertation of crack motion is also provided by the growth of the plasticity due to the development of the gamma - > alpha transformation in the course of a tensile test (the PNP-effect). The kinetics of the decomposition of retained austenite in the deformation process and the properties of the structures formed as a result have a great influence on the results of mechanical tests of medium-strength steels. Since such steels are used quite widely in basic engineering, evaluation of the effect of the amount of retained austenite on their mechanical properties is of considerable interest. It is expedient to study the effect of retained austenite on the mechanical properties of steels under conditions where the properties of the steel matrices are at virturally the same level but the amount of retained austenite differs. Even stabilization of retained austenite in an isothermal bainitic transformation cannot give unambiguous results due to the complexity of evaluation of the differences in the properties of the matrices. In addition, the redistribution of carbon between the alpha - and gamma -phases in the process of the bainitic transformation introduces an additional uncertainty due to the difference in the properties of retained austenite and the products of its decomposition under strain that are enriched with carbon to different degrees. Material studied: 06Kh12N3D.