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A ball-on-disk tribometer was employed to evaluate the lubrication performance and mechanisms of innovative TiO2 nano-additive water-based lubricants. Two experimental methods were applied to determine the optimal mass fraction of TiO2. In the method I, lubricants were added onto the worn disk tracks at a predetermined time interval. In the method II, the disks were immersed in the lubricants continuously during the whole process of tribological tests. The results both indicate that the water-based lubricants can significantly reduce the coefficient of friction (COF). The 0.8 wt% TiO2 lubricant demonstrates excellent tribological properties including the lowest COF and the strongest wear resistance under all lubrication conditions. The lubrication mechanisms are attributed to the rolling and mending effects of the TiO2 nanoparticles.

The aim of this study is to investigate the effect of zinc dialkyl dithio phosphate (ZDDP) films on sticking during hot rolling of a ferritic stainless steel strip. The surface characterization and crack propagation of the oxide scale are very important for understanding the mechanism of the sticking. The high-temperature oxidation of one typical ferritic stainless was conducted at 1373 K (1100 °C) for understanding its microstructure and surface morphology. Hot-rolling tests of a ferritic stainless steel strip show that no obvious cracks among the oxide scale were observed with the application of ZDDP. A finite element method model was constructed with taking into consideration different crack size ratios among the oxide scale, surface profile, and ZDDP films. The simulation results show that the width of the crack tends to be reduced with the introduction of ZDDP films, which is beneficial for improving sticking.

The tribological tests of a ferritic stainless steel (FSS) 445 in contact with high-speed steel (HSS) were performed on a high-temperature pin-on-disc tribometer. Wear exhibited significant difference when the FSS 445 was oxidised with a Cr-rich oxide scale on the surface. The HSS pin displayed adhesive wear when there was no oxide scale on the stainless steel disc, and in the early stages, the coefficient of friction fluctuated significantly, but the level of wear changed as Cr2O3 particles formed. The wear was then reduced, and the coefficient of friction remained stable. The Cr-rich oxide scale which formed on the stainless steel was able to stabilise the coefficient of friction, to reduce the wear rate and to help form a glazed layer on the HSS surface. The abrasive wear of the HSS pin took place at 850 °C, indicating that the hardness of the Cr-rich oxide scale increased as the temperature decreased.

High-speed steel (HSS) materials are universally used as work rolls for the hot rolling of stainless steels. Their use has increased the output of the rolling mill and decreased roll material consumption and grinding. Sticking defects often occur, however, during the hot rolling process. In this article, extreme pressure (EP) additives were dropped on the HSS samples at high temperature. Zinc dialkyl dithiophosphate (ZDDP) was chosen as the most effective EP additive by scratch tests on the HSS samples. In order to determine the optimum proportion of ZDDP in the lubricant, two reduction rates were tested on a Hille 100 experimental rolling mill by hot rolling ferritic stainless steel 445J1M at five different concentrations of ZDDP. The mechanism of EP additive action during the hot rolling process was also investigated. By analyzing the deformation behavior of the oxide scale of samples after hot rolling using different proportions of ZDDP, it was found that 20% ZDDP in the lubricant is the preferred concentration for industrial application.

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 Cr2O3 as its main component, which are hard and brittle at lower rolling temperature.

The oxidation kinetics of ferritic stainless steel 430 was studied in dry and humid air at 1090 °C by Thermo Gravimetric Analysis (TGA). Different atmospheres and heating times were adopted for reheating to obtain different compositions and thickness of the oxide scale. Hot rolling was performed on a 2-high Hille 100 experimental rolling mill at various reductions. Oxide scale thickness and composition were analysed with optical microscopy (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The surface profiles were examined by a digital microscope, and the topographic features of the thin oxide scale surface were examined with an atomic force microscope (AFM) before and after rolling. The oxide scale surface and steel/oxide interface roughness were measured after rolling. Inverse calculation of the coefficient of friction was employed to analyse and the effect of oxide scale on friction in hot rolling. The coefficient of friction depends not only on the thickness of the oxide scale, but also on its composition and surface topography before hot rolling.

The various chemical compositions of stainless steels can result in complication of the formation of oxide scales in hot rolling process. The time for formation of tertiary oxide scale during finishing rolling is short. In the present study, the oxidation tests with short time period were carried out on eight stainless steel grades by Gleeble 3500 thermal mechanical simulator in a simulated water mist environment. Multi-layers of oxide scale have been developed on all the steel grades during short time oxidation. Internal and intergranular oxides were formed in the steel matrix underneath the inner spinel oxide layer. The cross section of the oxide scales were examined and measured by SEM to understand the oxide scale cross section morphology and thickness.

An experimental method was developed to examine oxidations of austenitic and martensitic stainless steels. The results show that the surface roughness along both rolling and transverse directions decreases with an increase of reduction. When the reheating time is increased, the average thickness of oxide scales of stainless steels increases, which results in relatively rough surface after hot rolling. The effects of oxide scale on the friction condition and surface roughness transfer in hot rolling depend on the oxide scale generated during reheating. The calculated surface roughness is close to the experimental results, which verifies the developed FEM model. (2014) Trans Tech Publications, Switzerland.

The aim of this study is to optimise the stainless steel oxidation behaviours during hot rolling. The high temperature oxidation behaviours of ferritic stainless steels B443NT and B445J1M were studied over the temperature range from 1000 to 1150 °C in a humid atmosphere containing 18% water vapour, as measured by a thermogravimetric analyser (TGA). The results indicate that breakaway oxidation occurs at 1090 °C for the B443NT steel, which is 60 °C lower than that for the B445J1M steel. The occurrence of iron oxide nodules on the steels marks the onset of breakaway oxidation; however, the breakaway oxidation phenomenon of B445J1M is different from that of B443NT due to a compact and continuous Mn-Cr spinel which is formed on the surface of B445J1M. The oxide nodules with regenerated Cr2O3 scale underneath the Fe-Cr spinel display better adhesion without showing pores at the metal-scale interface.

High temperature oxidation of ferritic stainless steel 21Cr-0.6Mo-Nb-Ti was carried out isothermally at 1100 oC under different water vapour content conditions in an electrical furnace. Water vapour does accelerate the formation of oxide scale of stainless steel 21Cr-0.6Mo-Nb-Ti, however, it is not significant. Some oxide grains consist of spinel crystal structure, which should be spinel Manganese Chromite. In dry air atmosphere, the grain of the spinel is more and bigger than that in wet air. No breakaway oxidation occurs in the experiment indicating that 21Cr-0.6Mo-Nb-Ti has very high oxidation resistance, which might be contributed by the formation of MnCr2O4 and compact protective chromia. In addition, continuous silica formed along and accumulated at the oxide metal interface performs like a diffusion barrier.

To investigate roll bite behaviors in cold foil rolling process, a 2D elasto-plastic finite model is established using FEM software ABAQUS. Contact pressure distribution and roll contour in roll bite are also presented, which demonstrate that foil rolling process is different from conventional strip rolling process. The contact area is composed of entry elastic zone, entry plastic zone, an extensive neutral zone, exit plastic zone and exit elastic zone. It conforms to the results of Fleck foil rolling theory. Elastic deformation and work hardening of foil in roll bite are taken into account. The effect of rolling parameters, such as friction coefficient, entry thickness and reduction rate on distribution of contact pressure and vertical displacement are also discussed.