On the Grain Growth Kinetics of a Low Density Steel

The grain growth kinetics of an age-hardenable Fe-Mn-Al-C steel were investigated. Kinetics of grain growth were determined between 1173 and 1348 K (900–1075 °C) to obtain a range of grain sizes from 30 to 475 μm. It was found that grain growth was negligible at 1173 K (900 °C) for times up to 15 h. The activation energy for grain growth was found to be 467 kJ/mol. The hardness and mean linear intercept (L3) were correlated to follow a traditional Hall-Petch relationship. Tensile properties of the alloy were determined after various solution treatments performed for 2 h followed by water quenching. Tensile strength increased from 810 to 960 MPa and ductility was reduced from 80 to 60% as the grain size decreased from 200 μm to 30 μm as grain coarsening was mitigated by lowering the solution treatment temperature

Alloy Partitioning Effect on Strength and Toughness of κ-Carbide Strengthened Steels

Alloy partitioning during heat treatment in a lightweight precipitation hardened steel was investigated using transmission electron microscopy and atom probe tomography. The mechanical properties are discussed as a function of the effect of solution treatment temperature and aging time, giving rise to variations in chemical modulation. A wrought lightweight steel alloy with a nominal composition of Fe-30Mn-9Al-1Si-1C-0.5Mo (wt. %) was solution-treated between 1173–1273 K and aged at 773 K. Lower solution treatment temperatures retained a finer grain size and accelerated age hardening response that also produced an improved work hardening behavior with a tensile strength of −1460 MPa at 0.4 true strain. Atom probe tomography indicated these conditions also had reduced modulation in the Si and Al content due to the reduced aging time preventing silicon from diffusing out of the κ-carbide into the austenite. This work provides the framework for heat-treating lightweight, age hardenable steels with high strength and improved energy absorption