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© 2016 Trans Tech Publications, Switzerland. In hot rolling, metal oxides formed on steel surface can generally be classified as primary, secondary and tertiary oxide scales, corresponding to the reheating stages, the roughing stages and the finishing passes of continuous mills, respectively. The tertiary oxide scale grows into the final products on the hot-rolled steel strip during the finishing rolling and the subsequent cooling down to ambient temperature. We provide here a systematic overview of the oxidation mechanism, microstructure and microtexture development of the tertiary oxide scale. Mechanism of oxidation and Fe3O4 precipitation in tertiary oxide has been given as the fundamental theory. Three main sections has been divided in this review. The first section includes experimental investigations on microstructure evolution from the formation of oxide scale during hot rolling, then through continuous cooling, to Fe3O4 precipitation behaviour in storage cooling of hot-coiled strip. By using electron backscatter diffraction (EBSD) to characterise both the steel substrate and the oxide scale concurrently, the second section has further dealed with the texture-based analysis of oxide scale: phase identification, orientation analysis and coincident site lattice (CSL) boundaries. The third section has provided the general type of crystallographic texture and its evolutions in deformed Fe3O4 and steel substrate. Finally, the upcoming challenges have been addressed in this intriguing and promising research field.

Strip profile control during rolling is required to assure the dimensional quality of rolled thin strip is acceptable for customers. Throughout rolling, the strip profile is controlled by using the advanced shape control rolling mill, such as the combination of work roll crossing and shifting during asymmetrical rolling, the one of the valuable methods to control the strip profile quality in rolling process. In this paper, the influences of cold rolling parameters such as the crossing angle and axial shifting value of work rolls on the strip profile are analysed. The strip shape control is discussed under both symmetrical and asymmetrical rolling conditions. The obtained results are appropriate to control the rolled thin strip profile in practice. © (2014) Trans Tech Publications, Switzerland.

Titanium and its alloys have excellent properties and are promising biomaterial in medical engineering field. A bioactive surface on a Ti substrate is a prerequisite for great performance and long service life of implants. Based on the mechanism for inducing cell/tissue responses, three kinds of methods, namely morphological, physicochemical and biochemical methods, are reviewed in this paper. Hybrid methods that integrate individual methods or have additional functions are also discussed. © (2014) Trans Tech Publications, Switzerland.

To understand the high temperature flow behaviour of a novel pearlitic steel (PS) and low carbon steel (LCS) bimetal, hot compression tests in a wide range of temperature and strain rate were conducted on a Gleeble 3500 thermo mechanical simulator, and the constitutive model was developed based on the experimental data. The measured true stress-strain curves exhibited three types of variation patterns, which are (i) a plateau type, (ii) single peak type and (iii) multi peaks type. These patterns well displayed the effects of the deformation temperature, strain rate and plastic strain on the flow behaviour of the bimetal. By incorporating the Zener-Hollomon parameter and material parameter functions of α(ε), n(ε), Q(ε) and A(ε) into Arrhenius-type constitutive equation, the flow stress values predicted by the proposed model show a good agreement with experimental results by the evidence of reproducing true stress-strain curves accurately, high value of correlation coefficient (R=0.9873) and low value of average absolute relative error (AARE=4.81%). The proposed constitutive equation can be used to realise numerical simulation and determine processing parameters during hot-working of the PS/LCS bimetal. © 2013 Elsevier B.V.

Controlling cold strip profile is a difficult and significant problem has been found in industry during thin strip rolling. At present choosing the new type of strip rolling mill is the one of main methods to control the strip shape quality in cold rolling. The influences of rolling process parameters such as the work roll cross angle and work roll shifting on the strip shape and profile of thin strip are recognised throughout this study. The results show that the roll crossing and shifting is efficient way to control the strip shape. The increase of the work roll crossing angle would lead to improve the strip profile significantly by decreasing the exit strip crown and edge drop. The strip profile would be enhanced if the axial roll shifting was increased. Moreover, the total rolling force was analysed in detail by changing the roll cross angle and axial shifting roll. © (2014) Trans Tech Publications, Switzerland.

A high carbon steel (HCS) and low carbon steel (LCS) bimetal was fabricated by centrifugal composite casting. Two different thermomechanical treatments (TMT1 and TMT2) were employed to improve the mechanical properties of the bimetal. TMT1 process includes 60% of overall reduction by hot compression with temperatures of 1100 and 800 °C, respectively. While TMT2 process involves 60% of overall reduction using the two-step deformation method, which is a combination of non-isothermal compression cooling from 1100 to 800 °C and isothermal compression at 800 °C. The flow stress behavior, microstructural evolution and microhardness variation were analysed. Experimental results show that both TMT processes contributed to the improvement in mechanical properties resulting from a refinement of the grain size and an increase of density of pearlitic lamella in HCS layer. However, TMT2 process gave a better efficiency and a more significance in improvement of properties with the evidence of the same overall reduction leading to a higher microhardness. © (2014) Trans Tech Publications, Switzerland.

© (2014) Trans Tech Publications, Switzerland. The dry sliding wear behaviour of the full pearlite in a novel bimetal consisting of low carbon steel and hypoeutectoid steel has been studied by means of pin-on-disc type wear tests at room temperature. Thermomechanical treatments were performed on the bimetallic samples to obtain different interlamellar spacings. It was found that interlamellar spacing decreased with an increase in plastic strain to a great extent initially and followed by a lower extent of decrease. This decrease not only increases the hardness and strain hardening capacity of the fully pearlitic microstructure, but also is in favor of stabilizing the friction coefficient during sliding process. The observations of wear tracks show that delamination dominated the wear process when interlamellar spacing is higher than 200 nm, while pronounced oxidational wear occurred with interlamellar spacing below 200 nm.

The precipitates and hydrogen permeation behavior in three kinds of hot rolled low carbon heavy plate steels for enameling were analyzed; then, both sides of the steels were enameled. The experimental results show that a large amount of coarse Ti4C2S2 and fine Ti(C, N) particles exist in the optimized Ti-bearing steel, quite a lot of fine Ti(C, N) particles exist in the optimized carbon steel, but only a little bit fine Ti(C, N) particles exist in the carbon steel. The fishscaling resistance of the steels can be correlated to the effective hydrogen diffusion coefficient, and a model of correlation between the effective hydrogen diffusion coefficient and the volume fraction of the precipitates was established and verified. The effective hydrogen diffusion coefficient should be lower than 3. 96 × 10 6 cm2/s to avoid fishscaling in heavy plate steels. © 2014 Central Iron and Steel Research Institute.

© (2014) Trans Tech Publications, Switzerland. A novel microforming process - Micro Cross Wedge Rolling (MCWR) has been developed. It is a very promising technology in the field of microforming due to its advantages such as high product rate and minimised material consumption. How to control geometrical accuracy of the produced micro parts is one of the major challenges in the development of microforming technology. Geometrical accuracy was still concentrated in term of springback. When the wedge tools loads are removed after forming step, a portion of the deformation recovers, which causes a change in the shape of micro parts. In other word, springback happens, which should be determined and controlled especially in microforming technology. A series of MCWR experiments of pure copper and aluminium have been carried out using the machine designed by authors in this study. Cylindrical workpieces were deformed into stepped shafts with cross-sectional area reductions of 35, 52.73 and 75%. Corresponding finite element simulation has also been conducted in consideration of the size effect on the material flow. The springback was proposed to account for the geometrical error of micro products. The effect of grained heterogeneity on the height of surface asperity after rolling was assessed quantitatively.

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.

High temperature oxidation of ferritic stainless steel 21Cr-0.6Mo-Nb-Ti was carried out isothermally at 1100 °C 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. © (2013) Trans Tech Publications, Switzerland.

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 0.01s-1 has a larger flattening rate (lower roughness Ra) than that of surface roughness with lower strain rate 0.001s-1. In this study, increased strain rate has no obvious effect on texture. © 2013 Elsevier B.V.

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. © 2012 Elsevier B.V.

Interface adhesion between cast iron substrate and oxide layer formed during dry unidirectional sliding wear was studied by using thermo-mechanically processed 4.8Ni-1.5Cr cast iron. The purpose of the present work is to reveal the difference of the adhesion behaviour between martensitic matrix with a higher hardness and austenitic matrix with low hardness. The 4.8Ni-1.5Cr alloy was sandwiched as a middle layer with low carbon steel as outer layers and thermo-mechanically processed via (1) hot rolling (HR), (2) hot rolling and heat treatment (HT), and (3) hot rolling, heat treatment and hot compression (HC), respectively. The applied normal loads were 20 and 40. N, and the sliding speeds were 45 and 78. mm/s in sliding wear test. The durations of the wear test were 2 and 7. min, respectively for different testing rounds. It was found that the wear after running-in was always mild under the conditions of 20. N and 45. mm/s or 20. N and 78. mm/s for all the tested samples. Prior to the transition into mild oxidational wear, negative displacements of pins were observed for HT and HC samples when the applied load was raised to 40. N at the sliding speed of 78. mm/s. No similar response was observed for HR sample under the same testing condition. The possible mechanisms for the negative displacement of pin in the test are discussed in terms of the microstructure and phases of the testing samples. The effect of the hardness of the substrate on the growth and integrity of the oxide film formed during the sliding and the interface adhesion between the oxide film and substrate are also discussed. © 2012 Elsevier B.V.

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.

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. © (2012) Trans Tech Publications, Switzerland.

In order to develop the relationship between surface roughness, friction and texture in the uniaxial planar compression, Al 6061 samples are compressed in a channel-die to conduct plane-strain compression experiments. Molly bond is selected as a lubricant in a group of samples. The other group of samples is compressed without lubrication. The tool is polished smoothly; all the samples are prepared with the same method to retain the same surface roughness. Finite element modelling of the surface asperity flattening is carried out with ABAQUS under the same experimental conditions, original random textures are employed in the two dimensional model. The same surface roughness (Ra) obtained from the experiment is also employed on the top surface of the sample. The constitutive model and time-integration procedure have been implemented into the implicit finite element code ABAQUS using user material subroutine UMAT. Both the calculated results and the experimental results show a same tendency: the lubrication can constrain the process of surface asperity flattening. When the reduction is less than 10%, the effect of lubrication on surface asperity flattening is not significant. If the reduction is 10-40%, the lubrication plays a satisfactory role during the compression. With an increase of reduction, the lubrication will be damaged, and then the sample compressed with and without lubrication keeps a similar tendency of change. © 2011 Elsevier B.V.

Friction is one of the most significant physical phenomena influencing metal forming. The deformation or fracture of oxide scale significantly affects the roll-strip interface behaviour. Sticking occurs frequently during hot rolling of stainless steels especially ferritic stainless steels, which causes surface defects of both steel products and rolls. It is important to characterize the features of the oxide scale in hot rolling of stainless steel strips, but few studies have been carried out. This paper focuses on the deformation of oxide scale and roll-strip interface characteristics in hot rolling of austenitic stainless steel 304L and ferritic stainless steel 430. Oxidation tests in a short time in humid air with water vapour content of 7.0. vol.% were carried out using Gleeble 3500 thermo-mechanical simulator, and the oxidation characteristics of 304L and 430 steels were obtained. The deformation, surface morphology of oxide scale of the steels, and the friction in hot rolling were studied in hot rolling tests. Thick oxide scale of 304L steel shows high lubricative effect while the breaking of thin oxide scales of 430 steel may make the steel substrate to contact with the roll, which counteracts the lubricative effect of the oxide scale and results in friction coefficient increasing with an increase of reduction. A FEM simulation has been developed to analyse the deformation behaviour of oxide scale and surface roughness transfer during hot rolling of stainless steels and the model describing the rough surface profiles of the scales and steel has been integrated into the simulation. © 2011 Elsevier B.V.

Cold rolling is one of the most essential elements in the manufacture of flat products of metals. Work roll wear is always a topic of interest to many researchers. In this paper, the disc-to-disc tests of the material with 4% Cr and that with 4% Cr+Ti were carried out respectively under the conditions of dry contact and emulsion lubricant of 3.9% Quakerol N680-2-DPD. The wear and friction patterns were discussed by correlating the disc surface morphologies and the microstructures of both materials. The surface roughness of the disk of the material with 4% Cr+Ti deteriorates much slower than that with 4% Cr under the condition of lubrication. The material with 4% Cr+Ti is characterised as carbonitrades precipitated in a fine tempered martensite matrix while coarse carbides (M7C3) exist in the material with 4% Cr. The disk of the material with 4% Cr+Ti wears differently to that with 4% Cr. Delamination may become an important wear mechanism earlier in the case of 4% Cr than that of 4% Cr+Ti. Micro spalling and pitting occur after 120min of wear in the case of 4% Cr, but not in the case of 4% Cr+Ti until 330min. Detached carbides are responsible for the abrasive wear on both discs at the late stage. Ti alters the friction pattern due to surface regeneration that resulted from the abrasive effect of carbonitrades. Generally, the wear-resistance of roll material may be improved by 175% by introducing added Ti. The outcome is beneficial for developing new materials for prolonging the service life of the cold work roll. © 2011 Elsevier B.V.

The as-rolled and enamel fired microstructure and mechanical properties of two low carbon steels with different compositions were analysed in the paper. The results show that the grains do not coarsen in lab firing process, and could be refined after industrial enamel firing process. The strength can keep stable in the firing process and the impact energy could be enhanced greatly under the industrial enamel firing process. The surface decarburized layer was occurred as a result of chemical reaction among the carbon in steel and water, oxides in the enamel frit. © (2011) Trans Tech Publications.

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 authors show that the friction coefficient decreases with an increase of oxide scale thickness for stainless steel 304L. Copyright © 2011, IGI Global.

Edge crack is one common phenomenon in cold rolling of thin strip which affects qualities of the rolled strip. A three-dimensional elastic-plastic finite element (FE) model for cold flat product rolling has been developed to simulate the edge crack propagation during rolling. Stress field is investigated around the edge crack tip, and the effects of the friction coefficient, the initial crack size, reductions on crack propagation are analysed. The FE simulation provides a better understanding of the crack growth at the edge of thin strip, and could be helpful in developing of cold rolled strip with high performance mechanical properties. The optimum condition to eliminate defects is discussed, and the proposed prediction method of surface defect can be utilised to make defect free products in rolling processes. © 2010 American Institute of Physics.

The friction is a key factor that influences the surface quality in metal forming. To figure out the relationship between the friction and the surface roughening, a finite element model is employed in the commercial finite element software ABAQUS to simulate the surface roughness of top side of Al plate during uniaxial planar compression. With the change of friction conditions, the surface roughening varies. The average surface roughness (Ra) shows a relationship with the friction coefficient. During the surface roughening process, the grain slip takes place in the "soft orientation", and the "hard orientations" become the barrier of the slip. © Trans Tech Publications.

The demand of thin gauge strip with good quality such as the strip shape and surface finish is significantly increasing. In this study, finite element model of the strip shape during cold rolling of thin strip in asymmetrical rolling was developed, and the finite element simulation of the thin strip shape has been carried out in LS-DYNA. The effects of reduction and speed ratio on the strip shape and profile and the strip edge drop have been obtained. The developed finite element model has been verified with the experimental data. The obtained results are applicable to the control of the rolled thin strip shape in rolling practice. © (2010) Trans Tech Publications.

Strip shape is an important factor affecting the strip quality significantly during cold rolling of thin strip. In the paper, finite element simulation models of the strip shape in cold rolling for both symmetrical and asymmetrical rolling cases were successfully developed. The strip edge drop and the effect of the rolling force on the strip shape (the thickness distribution along the strip width) have been obtained. The developed finite element model has been verified with the experimental value, which shows they are in good agreement. The obtained results are applicable to control the rolled thin strip shape during cold rolling practice. © (2010) Trans Tech Publications, Switzerland.

With the technology advancement, crystal plasticity finite element modeling becomes more and more popular in the simulation of metal forming process. In order to obtain a better understanding of the difference between the Taylor model and finite element model during the simulation of metal forming process, an implicit time-integration procedure with the two polycrystal models is applied in the commercial finite element code ABAQUS to simulate the plane strain compression separately. FCC metal is used in this study. The simulation shows that the two polycrystal models both can predict the compression process approximately. The two modelling results of surface roughness show an agreement with that of the experimental results. However, the side profile calculated by the Taylor polycrystal model is much steeper and straighter than that of finite element polycrystal model. The experimental surface roughness curve shows a high frequency fluctuation. It is much steeper than those of the two models. The simulation results also show that the von Mises stress from the Taylor model is much higher than that of the finite element model.

Surface roughness plays an important role in determining the tribological behaviour of mechanical components (e.g. gears and roller bearings etc.) under full-film and mixed (or partial) elastohydrodynamic lubrication conditions. This paper describes a detailed mechanics analysis of the surface roughness transformation of thin strip which has been cold rolled on an experimental mill. Low carbon steel strips were rolled at various speeds and reductions, and the effects of rolling parameters on surface roughness are studied. The results of surface roughness can provide important information to optimise the rolling schedule and to improve the rolled strip quality.

In rolling process, the contact friction is of crucial importance for accurate modeling, optimum design and control of industrial rolling processes. It is important to characterize the features of the oxide scale of stainless steel in hot strip rolling because the scale on the strip surface affects friction coefficient and thermal conductivity coefficient. To some extent, the rolling force and friction condition depend on the thickness and the microstructure of the oxide scale. Oxidation tests of stainless steels 304 and 304L were carried out in a high temperature electric resistance furnace. The humid air in which the water vapour content can be controlled was generated and remained to flow into the chamber of the furnace in 2.5 × 10-4 m3/s to study the effect of humidity on the oxidation of stainless steels. The microstructure and thickness of oxide scale layer of stainless steels were obtained and two or three oxide layers can be found. The humid air has a significant effect on the growth of oxide scale. Hot rolling tests were carried out on Hille 100 rolling mill. The friction condition at the roll-strip interface during hot rolling of stainless steel was determined and the transfer of surface roughness was discussed. © 2009 Elsevier B.V. All rights reserved.

Both longitudinal and transverse frictions arising from plane strain during cold metal forming are of crucial importance for the accurate modelling, optimum design, and control of industrial processes. However, the influence of the friction and roughness along the transverse direction has been neglected in much previous research. Oblique roughness textures are considered, and the scale of roughness asperities is enlarged in this study. Four types of prism patterns, in which the angles between the longitudinal direction and the top line of prism are 90°, 60°, 30°, and 0°, and three types of pyramid patterns, in which the top angles are 151.9°, 161.1°, and 168.6°, were designed and manufactured using samples of annealed Al 6060T5. All compression tests were completed in 10 passes, and the total displacement of the pressure head was 5.4 mm. The first five passes were carried out on an Instron 8033 Materials Testing Machine, and the last five passes on a 500-ton compression-testing machine. The surface morphologies of the deformed peak were analysed, and the top areas of the deformed peak were measured. The effects of the angle between the longitudinal direction and the top line of the prism texture or the top angle of the pyramid texture on the surface morphology of the deformed peak are not obvious. The angles have a relatively significant effect on the deformation behaviour of the surface layer during cold metal forming when the deformation is small. The pattern with a top angle of 161.1°, which is the closest to the real value, shows the highest deformation resistance when the displacement of the pressure head is less than 1.2 mm. © 2009 Elsevier B.V. All rights reserved.

Taylor-type and finite element polycrstal models have been embedded into the commercial finite element code ABAQUS to carry out the crystal plasticity finite element modelling of BCC deformation texture based on rate dependent crystal constitutive equations. Initial orientations measured by EBSD were directly used in crystal plasticity finite element model to simulate the development of rolling texture of IF steel under various reductions. The calculated results are in good agreement with the experimental values. The predicted and measured textures tend to sharper with an increase of reduction, and the texture obtained from the Taylor-type model is much stronger than that by finite element model. The rolling textures calculated with 48 {110}〈110〉, {112}〈111〉 and {123}〈111〉 slip systems are close to the EBSD results.