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The aim of this study is to explore the potential engineering application of a thermally grown chromium oxide scale on a ferritic stainless steel. The friction and wear behaviour of the oxide scale were investigated by scratch and pin-on-disk tests. The failure mechanisms of the oxide scale subjected to scratch tests under both progressive and constant loading were investigated. It shows that the oxide scale adheres well to the steel substrate and is in a ductile failure. The oxide scale leads to an increase in the coefficient of friction (COF) under different constant loads when compared to what occurs when there is no oxide scale in the scratch test. The pin-on-disk tribological tests show that the chromium oxide scale on the ferritic stainless steel causes abrasive wear of the high-speed steel (HSS) pin, but it enhances the wear resistance of the ferritic stainless steel disk. The COF is slightly lower when there is oxide scale on the disk which is different from that by the scratch test. The ferritic steel substrate fine wear particles generated during the dry sliding and the formation of new compound layers on the surface can stabilise the COF. The wear mechanism is proposed and the tribological properties of the thermally grown chromium oxide by the two techniques are discussed. • Scratch behaviour of stainless steel with a chromia scale by oxidation. • The chromia scale showed adhesion strength with a significant variation. • Two different wear was observed with a similar COF. • The ferritic stainless steel substrate powder-like particles play a role in COF. [ABSTRACT FROM AUTHOR]

Some defects on the surface of carbon steel do not need to be removed before hot rolling because the surface will be vigorously oxidised in a reheating environment. Thus the defects can be minimised by oxidising and then removed by the de-scaling process. The defects on the surface of ferritic stainless steels, however, are not easily removed by oxidation when a high chromium concentration is used. In this paper, a ferritic stainless steel grade 445 was selected as a research material. The effects of different surface features on oxidation and tribological behaviour in the hot rolling process were investigated. Three surface states were prepared, namely, smooth surface, surface with 45° grinding marks and surface with oscillation marks. The samples were put into an electric furnace at 1100 °C for reheating. Hot rolling tests were carried out on a 2-high Hille 100 experimental rolling mill. Rolling forces were measured, and the coefficient of friction was calculated and compared under various rolling parameters. It was found that the original surface profiles with grinding marks were still maintained during oxidation. The original oxide scale on the surface with oscillation marks caused the formation of irregular oxide nodules and the spallation of the oxide scale. Surface morphology and the reduction in thickness had a significant impact on the oxide scale integrity and coefficient of friction in the hot rolling process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Cr 2 O 3 scale underneath the Fe–Cr spinel display better adhesion without showing pores at the metal–scale interface. [ABSTRACT FROM AUTHOR]

The tribological behaviour of innovative TiO 2 nano-additive water-based lubricant on ferritic stainless steel (FSS) 445 was characterised on a ball-on-disk tribometer. Non-oxidised (clean) and pre-oxidised FSS 445 disks with original rough surfaces were both applied in the tribological tests at room temperature. The results show that the water-based nanolubricants with concentrations of 0.4–8.0 wt% TiO 2 can significantly reduce the coefficient of friction (COF) on the two types of disks. The 4.0 wt% TiO 2 lubricant exhibits optimal tribological properties, including the lowest COF and the strongest anti-wear ability on the applied balls under all lubrication conditions. The lubrication mechanisms are primarily ascribed to the formation of tribofilm and the ball-bearing effect of the TiO 2 nanoparticles, respectively, on the two different disks. [ABSTRACT FROM AUTHOR]

In this paper, wear and friction behaviour of high-speed steel (HSS) and indefinite chill (IC) material for rolling a ferritic stainless steel were investigated on a tribometer. A disk specimen of the ferritic stainless steel-B445J1M was pre-oxidised at 1100 °C for 30 min, and then rotated against a pin at 500 °C for 30 min. The pin was made of HSS or IC material. It was found that the friction coefficient of the IC was lower than that of the HSS, but the mass loss of the HSS pin was less than that of the IC pin. The oxide scale of the disk was more easily worn out and attached on the HSS pin than that of the IC pin. [ABSTRACT FROM AUTHOR]