Abstract
The present study investigated the effects of the austempering process far below Ms (martensite start temperature) on the microstructural evolution and impact toughness of bainitic steel with ultrahigh impact toughness and compared the results with the tempered martensitic steel. The results revealed that the lamellar bainitic steel composed of bainitic ferrite laths and retained austenite films is obtained by austempering far below Ms temperature. The obtained steel exhibited the Charpy V-notch impact absorbed energy of up to 131 ± 6 J, which was 2.7 times higher than that of the tempered martensitic steel (49 ± 1 J). The ultra-high impact toughness of bainitic steel was attributed to the deflection of the crack propagation direction by the refined bainitic ferrite laths and the passivation of the crack tip by the retained austenite films. Furthermore, the proportion of V2, V3, and V5 variants increased and formed HAGBs (high-angle grain boundaries) with the V1 variant in the austempered bainitic steel B-32. These HAGBs inhibited crack propagation effectively, thereby significantly improving the impact toughness of the austempered bainitic steel.
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
