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Oil-in-water (O/W) emulsion is widely applied as a lubricant during hot rolling process. For reducing environmental impact caused by O/W emulsion, a novel nano-TiO 2 additive O/W lubricant with improved stability and reduced coefficient of friction (COF) is developed. Little research, however, has been focused on the growth behaviour of oxide scale formed on the workpiece surface and its effects on the tribological property of nano-TiO 2 additive O/W lubricant. In the current work, oxidation tests of high strength steel were conducted to investigate the growth behaviour of oxide scale and obtain different surface morphologies of the oxide scale. Ball-on-disk tribological tests under a temperature of 80 °C were carried out to investigate the effects of surface morphology of oxide scale on the tribological behaviour under nano-TiO 2 additive O/W lubrication. The performance of the new developed lubricant was evaluated by hot rolling process. The growth mechanism of oxide scale and the modified oxide scale growth model were proposed. Tribological results indicate that oxide scale plays an important role in the tribological behaviour of nano-TiO 2 additive O/W lubricant. A reduction in surface roughness can result in a decrease of COF, while the COF will increase if the surface roughness reduces too much because some of the nano-TiO 2 particles cannot go through the contact area to play a positive role in lubrication. [ABSTRACT FROM AUTHOR]

Electron backscatter diffraction (EBSD) of the microtexture in the tertiary oxide scale after hot rolling were investigated. The surface asperity flattening and grain refinement of Fe 3 O 4 were produced at a thickness reduction of 28% and a cooling rate of 28 °C/s. Microtexture development of Fe 3 O 4 manifests as a strong θ fibre parallel to oxide growth, including the {100}<001> and {001}<110> textured components, whereas the {0001}<10 1 ̅ 0> component dominates in α -Fe 2 O 3 as the favoured basal slip. The tribological effect of α -Fe 2 O 3 at the contact surface of steel and rolls was considered at low and high thickness reductions. The propagation of cracks along the Fe 3 O 4 grain boundaries could create a dish to collect nanoparticles during lubrication and thereby changed the wear rates. [ABSTRACT FROM AUTHOR]

Severe sticking occurs in the hot rolling of ferritic stainless steel B445J1M. The characteristics of the oxide scale on the steel in hot rolling are associated with this phenomenon. The tensile failure of the oxide scale formed on the steel B445J1M was investigated by using a Gleeble 3500 thermo-mechanical simulator over temperature range from 1000 to 1150 °C in humid air. Two passes hot rolling were carried out on a 2-high Hille 100 experimental rolling mill. The results show that the temperature is a significant factor for the formed thickness of the oxide scale and its failure in tensile stress. On the specimen before hot rolling, irregular spinels are extruded from the surface of a thin oxide scale with Cr 2 O 3 as its main component, which are hard and brittle at lower rolling temperature. [ABSTRACT FROM AUTHOR]