Tailoring the surface characteristics and mechanical behavior of Ti-Nb stabilized IF steel through controlled shot peening coverage

The rising demand for a qualitative surface opens a new window of research in the domain of mechanical surface treatment, known as severe shot peening, especially in the automotive industry. The effectiveness of this method is usually affiliated with various process parameters, of which peening coverage is the most sought-after. It is anticipated to elevate the surface characteristics by proficiently optimizing the peening coverage. On this ground, the current investigation tries to gather the beneficial effect of peening coverage on the surface properties of Ti-Nb stabilized interstitial-free steel subjected to severe shot peening by considering four different coverages (100 %, 500 %, 1000 %, and 2000 %). The work attempts to interpret the impact of peening coverage on grain refinement and dislocation-induced microstructures at different depths of the as-treated sample. The crossectional microscopy unveiled a prominent grain refinement hardening and dislocation hardening in 2000 % peening coverage up to a depth of 90-120 mu m, firmly agreeing with the microhardness depth profile. The optical microscopy identified four zones of deformation (severe deformation, deformation, transition, and undeformed zone) in the sample treated with the highest coverage. The transmission electron microscopy demonstrated the dominance of certain dislocation-derived features like dislocation forest, dislocation cells, tangled dislocations, dislocation bands, nanocrystalline region, stress concentration region, etc., at the deformed zone of the treated samples. Interestingly, the trace of these features was detected at a greater depth for the highest-peened sample than the lowest-peened sample, affirming the beneficial aspect of higher peening coverage. The stored energy and thermal stability assessment in the as-received and as-treated sample was done in the differential scanning calorimeter, revealing the favorable impact of severe peening on the substrate. The surface topographical study in a 3D profilometer also unveils the variation in the surface roughness and functional volume parameters. The present investigation also analyzed the maximum depth and mean density of furrows to verify the severe plastic deformation in the as-treated sample.