Effects of Thermal Processing History on Microstructure and Local Hardness in a Bainitic TRIP Steel - Tom Bell Young Author Award Candidate

Carbide free bainitic microstructures can be developed via different thermal processing routes, and the route taken largely affects the scale and morphology of microstructural constituents. In this study, bainitic microstructures are formed by either a controlled cooling process or an austempering process to understand the relationship between microstructure and mechanical properties in a 0.2C - 2.1Mn - 1.5Si - 0.8Cr steel containing small amounts of Nb, Ti, B, and N. The resulting microstructures are characterized with scanning electron microscopy and X-ray diffraction. When compared to microstructures produced via austempering, microstructures produced with a controlled cool exhibit increased inhomogeneity, specifically regarding size and distribution of bainitic and martensite-austenite constituents within a lath-like bainitic ferrite matrix. Nanoindentation testing is employed to assess and compare local variations in properties of microconstituents produced under these different thermal processing conditions. Tensile testing is employed to observe the effects of microstructural inhomogeneity on bulk material strength.