Strain-induced ε-martensite transformation during nanoindentation of high-nitrogen steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 598; pp. 56 - 61
• Main Authors: AHN, Tae-Hong, SUNG BO LEE, PARK, Kyung-Tae, KYU HWAN OH, HEUNG NAM HAN
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 26.03.2014
• Subjects: Applied sciences; Austenite; Compressive properties; Cross-disciplinary physics: materials science; rheology; Dislocations; Exact sciences and technology; Martensitic transformations; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure; Nanoindentation; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Quantitative analysis; Stainless steels; Strain; Transformations; Nanohardness; Austenite transformation; Metastable states; Nanoindentation; Martensitic transformations; Mechanical properties; Displacement(deformation); Plastic deformation; Partial dislocation; Shockley partial dislocation; High nitrogen steels; Orientation relation; High-nitrogen stainless steel; Compressive stress; Pop-in; Hardness testing; High nitrogen steel; ε-martensite; Stress effects; Hardness indentation; Microstructure; Martensite; Quantitative chemical analysis
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2014.01.030

The strain-induced austenite-to- epsilon -martensite transformation during nanoindentation of metastable austenite in a high-nitrogen stainless steel was investigated by observation of the microstructural changes underneath the indent. In the nanoindentation load-displacement curve, several small pop-ins were detected at the beginning stage of plastic deformation. The presence of epsilon -martensite bands underneath the indent and their orientation relationship with the parent austenite strongly suggest that the pop-ins in the load-displacement curve correspond to the transformation from austenite to epsilon -martensite. A quantitative analysis on the massive movement of Shockley partial dislocations during the transformation was performed to obtain the contraction strain under compressive stress conditions during nanoindentation. It was confirmed that the calculated contraction strain along the indenting direction matches well with the measured length of the pop-ins.