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The effects of thermal and thermomechanical treatments on sliding wear of graphite crystallised white cast iron (GWCI) were studied. Due to the inherent embrittlement of GWCI, a laminated metal in which the GWCI is cladded by low carbon steel was prepared for this study. Three cylindrical samples (GWCI-A, GWCI-B and GWCI-C) were machined from the same laminate. GWCI-A was kept in as-cast state while GWCI-B and GWCI-C underwent the thermal and thermomechanical treatments, respectively. The pin-on-disc type sliding wear tests were performed on the GWCI layers at room temperature. The microstructures and wear mechanisms were analysed by optical microscope, scanning electron microscope and the Vickers hardness test. Experimental results demonstrated that the GWCI, after laminating with ductile steel, can be deformed at high temperature with crack-free. The thermomechanical treatment produced a finer microstructure and crushed primary carbides in GWCI-C. Both GWCI-B and GWCI-C displayed plenty of secondary carbides in supercooled austenitic matrix, which was more favourable to squeeze the graphite and form the oxide layers than the matrix of martensite plus retained austenite in GWCI-A. The wear resistance of GWCI-C was superior to that of GWCI-A and GWCI-B because the oxidational wear rather than delamination dominated the sliding wear process.

In cold strip or foil rolling, flatness control is an integral part of modern mill. This paper introduces two typical flatness control systems, pattern recognisation flatness control system and multivariable flatness control. It is found that the latter is effective and has wider application fields. The FEM models of its core parameters, flatness actuator efficiency, are constructed. Influencing factors, such as the rolling force, bending force as well as the tilting force are discussed. Control strategies are proposed for foil rolling. The results demonstrate that the control strategies can reduce flatness error and improve flatness quality. © (2013) Trans Tech Publications, Switzerland.

As limited results were reported in terms of the evolution of sliding friction with growth of oxide layer in thickness during running-in, a pin-on-disc wear test was carried out in this study. 4.8Ni-1.Cr cast iron as core layer and low carbon steel as outer layers, were thermo-mechanically processed via three different routes. For samples with lower hardness due to their predominantly austenitic or martensite retarded matrices, we found that initially rapid increase of thickness of oxide layer continually lowers the sliding friction. However, after the oxide layer was beyond a certain thickness, the sliding friction began to increase consecutively. After a fluctuation of friction caused by the break-down of oxide, a mild equilibrium wear with roughly constant friction followed.

As an important parameter of surface quality for metal manufacturing products, surface roughness is affected by the following parameters: original roughness, friction, grain size, grain orientation, stress- strain state, and work hardening. Previously, effects of friction and gauged reduction and wavelength on surface roughness have already been studied by a 2D surface asperity model in uniaxial planar compression. On the basis of previous results, a 3D surface asperity model is developed by employing rate-dependent crystal plasticity constitutive model in finite element software ABAQUS. Results from electron back scatter diffraction(EBSD) and atomic force microscope(AFM) experiments have also been input into the 3D model. Influences of strain rate and texture have been discussed in this paper. The calculated results show a good agreement with experimental results. With an increase of reduction, the surface asperity flattening under a lower strain rate tends to accelerate; grain size and roughness decrease while hardness and stress increase. Under the same reduction, surface roughness with higher strain rate 0.01 s1 has a larger flattening rate (lower roughness Ra) than that of surface roughness with lower strain rate 0.001 s1. In this study, increased strain rate has no obvious effect on texture.

When the common deformation processes are scaled down to micro/meso dimensions, size effect is the particular phenomena in microforming, which is related to the dominant influence of single grains inside the micropart. The conventional cross wedge rolling (CWR) is introduced into the micro scale in order to take the advantages of CWR. The micro cross wedge rolling (MCWR) has to confront with the phenomena of size effect that occurs in the common microforming processes inevitably. One of the approaches to compensate size effect is to increase the deforming temperature. An increased formability is achieved because more slip systems of polycrystal metal are activated at the elevated temperature. This reduces the anisotropic material behavior resulting in a more homogeneous forming with improved reproducibility. In this study, a YAG laser beam is applied to heat the workpiece. Finite element model (FEM) associated with a material constitutive formulation considering dislocation mechanics is set up to simulate the MCWR of pure copper utilizing the laser heating. The surface asperity as an indication of material heterogeneity in micro scale is quantitatively analysed. The simulation results show a good agreement with experimental results in terms of the surface asperity.

Size effect is a special phenomenon in metal micro-forming process. As the deformation process is scale down to micro/mesoscale, the characteristics of single grain involved in the deformed region play a significant role on the material mechanical behaviours resulting in the invalidation of classical theories in microforming. This paper presents a newly developed material model in microscale on the basis of the grained heterogeneity (e.g. grain size, shape and deformability) and specimen dimension. Voronoi tessellation has been employed to describe the polycrystalline aggregate. The grain shape is controlled by the centroidal-voronoi algorithm to drive grains into steady state. Hardness of the grains obtained from Nano-indentation is used to identify the scatter of the grained deformability. Applying the new material model, the micro-compression test of pure copper is numerically simulated by finite element method (FEM). The influences of grain size and feature size on the deformation behaviours are discussed. The numerical simulation results are in good agreement with the experimental results in terms of the flow stress curves and profile of deformed parts. Based on the novel material model, a FE model of microcross wedge rolling is established and the obtained results show the strain of specimen core region increases with the magnification of grain size. © 2013 Elsevier B.V. All rights reserved.

Strip profile control in cold rolling of thin strip is a difficult and challenge problem found in industry. Currently using the novel type of strip rolling mill, such as the work roll crossing and shifting is the one of the main methods to control the strip profile quality in cold rolling. In this paper, 3-D finite element simulation models of the thin strip profile in cold rolling for the work roll crossing and shifting system were successfully developed. The strip profile and edge drop are discussed considering both crossing angle and shifting value of the work rolls. The research shows that the combination of the work rolls crossing and shifting can effectively improve the strip profile. The developed 3D- finite element model has been verified with the measured values. The obtain result are applicable to control the rolled thin strip profile during cold rolling process.

Paper presented at 19th International Conference on Wear of Materials, 14-18 Apr 2013.

The bubble structures, fishscaling resistance, adhesion and its mechanism of vitreous enamel to low carbon steels were evaluated by microscopic methods. The results show that the microalloying elements deteriorates the adhesion but suppress the fishscaling tendency, the enamel-steel interface adhesion could be explained as mainly the mechanical interlocking and chemical bonding during the firing process; the lower carbon substrate causes higher proportion of bigger bubbles in the enamel layer and subsequently causes the lower fishscaling susceptibility.

A cast iron/low carbon steel sandwich-structured bimetal fabricated through composite casting, followed by hot rolling and hot compression (40% reduction) in a vacuum, and water quenched using Gleeble 3500 thermomechanical simulator. The microstructure of a predominantly martensitic structure is transferred to a matrix with an amount of austenite. The measured results show that the macro-hardness is significantly lower due to the evolution of matrix. A considerable amount of secondary carbides were precipitated from the matrix. This study also shows that a significant difference in the value of coefficient of friction (COF) at the end when hot rolling (HR) was tested under three sets of sliding wear conditions, while those for hot rolling and heat treatment (HT) tends to be merged. An increased wear resistance of interfacial zone is expectable.

The oxidation of stainless steels 304 and 304L during hot rolling is studied in this paper. Results show the oxide scale thickness decreases significantly with an increase of reduction, and the oxide scales of both 304 and 304L stainless steels were found more deformable than the steel substrate. Surface roughness shows a complicated transfer during the hot rolling process due to the complexity of oxide scale characteristics. Also, surface roughness decreases with an increase of reduction. The friction coefficient increases with reduction in all cases, and the increase is more significant in the case of the 304 stainless steel than that of 304L stainless steel.

Asymmetric rolling can reduce the thickness of rolled strip and rolling load significantly. In this paper, the asymmetric cold rolling of thin strip with roll edge kiss was analysed theoretically and the rolling pressure, intermediate force between the work roll and backup roll, the work roll edge kiss force, the strip profile after rolling are obtained for this special asymmetric rolling. The rolling pressure, intermediate force, roll edge kiss force and the strip profile are compared for various roll speed ratios, reduction and friction coefficients. Simulation result shows that the roll speed ratio and reduction have significant influence on the profile of rolled strip, and the calculated rolling forces are consistent with the measured values. The effect of friction in the roll bite on mechanics of the asymmetric cold rolling of thin strip with roll edge kiss is also discussed.