MoS2–Al2O3 nanofluid-induced microstructure evolution and corrosion resistance enhancement of hot-rolled steel surface

The influence of MoS2–Al2O3 nanofluid as a functional lubricant on the microstructure and corrosion resistance of hot-rolled steel surface was studied. Because of the excellent lubrication performance of the nanofluid, the rolled surface quality improved with a 18.2% and 69.5% reduction in surface roughness and oxide scale thickness, respectively, when compared with the base-fluid without nanoparticles. The further microstructure characterization determined that the grain size, local misorientation and deformed grain fraction of the steel decreased significantly. A diffusion layer of Al2O3, FeS and FeMo4S6 was found in the outer oxide layer of rolled surface. Closely arranged Al2O3 grains inhibited the oxidation of steel strips that the oxidation activation energy was increased by about 14.5%. Through density functional theory (DFT) calculation, the formation of FeS and FeMo4S6 was attributed to the migration of Mo and S atoms from MoS2 into the Fe lattice through substitutional and interstitial diffusion, respectively, with the energy barrier of 0.84 eV and 0.54 eV. Finally, the protection of diffusion layer, reduction in surface defects, and alleviation of residual stress and deformation resulted in the enhancement of corrosion resistance. This study provides a possible route to achieve surface enhancement during the hot rolling process.