Role of Interlath Austenite in Microstructural Strain Localization in Martensitic Stainless Steels

In this work, we introduce reverted austenite with various stacking fault energies in a PH17-4 stainless steel to study its mechanical effects via integrated in-situ scanning electron microscopy and in-situ synchrotron diffraction tests, as well as nanoindentation experiments. These experiments demonstrate that the proper tuning of size, stability, and chemistry of austenite can be an effective measure to overcome the strength-ductility tradeoff in martensitic stainless steels. Most intriguingly, we observe that the austenite does not always lead to softening when introduced in the highly-defected body centered tetragonal (BCT) martensitic matrix. The causes and consequences of this observation are discussed critically, leading to design considerations for martensitic stainless steels.