Accelerated Austempering Kinetics in a Low-Cost Alloy: Simulation, Processing, and Microstructural Analysis

The industrial adoption of ultrafine bainitic steels is limited by excessively long heat treatment times. This study presents a new, low-cost alloy designed to overcome this limitation by achieving accelerated austempering kinetics. First, a composition of Fe-0.6C-1.5Si-1.0Mn-0.25Cr-0.02Nb (wt%) was designed using thermodynamic simulation, and then manufactured and heat-treated. The resulting microstructures were characterized in detail using optical and scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, X-ray diffraction with Rietveld refinement, Vickers hardness testing and tensile testing. After ∼2 h of austempering at 320 °C, the hardness increased by ∼90% compared to the non-austempered condition. The alloy achieved competitive hardness of 557 ± 10 HV and ultimate tensile strength (UTS) of 1.57 ± 0.20 GPa, which are comparable to those of conventional ultrafine bainitic steels requiring much longer processing times.