Two-high Rolling Mill Research Articles

Vacuum melting of compressed powders and hot rolling of the as-cast Ti-48Al-2Nb-0.7Cr-0.3Si intermetallic alloy: Mechanical properties and microstructural analysis

The amalgamated effect of hot-rolling, rapid cooling and heat treatment on the grain refinement and the resultant mechanical properties of an intermetallic sheet of nominal composition Ti-48Al-2Nb-0.7Cr-0.3Si was investigated. The sheet of 4 mm thickness was fabricated by hot-pack rolling from the vacuum arc remelted (VAR) ingot using a conventional two-high rolling mill. After the final rolling pass, the canned specimen was rapidly cooled in the air to room temperature followed by heat treatment in the α + γ region. The scanning electron microscopy (SEM) micrographs of the as-rolled sheet revealed slightly elongated grains of a typical “duplex (DP)” microstructure with a mean grain size of about 3 μm which grew to about 4 μm and became more equiaxed and homogeneous after heat treatment. Moreover, the EBSD micro-texture indicated a weak cube texture in the rolled + heat-treated sheet. Furthermore, the results from the profilometry-based indentation plastometry of the rolled + heat treated specimen illustrated the balanced and improved mechanical properties compared to the as-cast and as-rolled samples, and also those of similar alloy systems found in the literature.

Tribological and Lubrication Performances of Nano-WO3 and CaWO4 Contained in Water-Based Fluid for Steel Strip during Hot Forming

CaWO4 and WO3 nanoparticles were prepared by the sol-gel method and Pechini method. The morphology and structure of nano-CaWO4 and nano-WO3 were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tribological, hot forming, and hot rolling lubrication properties of nano-CaWO4, nano-WO3, and mixed nano-CaWO4-WO3 as antiwear additives in water-based fluid were investigated using a four-ball friction and wear testing machine, Gleeble tester, and two-high rolling mill, respectively. Results showed that 0.3 wt% mixed nano-CaWO4-WO3 has excellent tribological properties in water-based fluid. The average wear scar diameter values decreased from 0.62 to 0.37 mm (mixed WO3-CaWO4) and the coefficient of friction value reduced from 0.080 to 0.064. This was due to the formation of a tribofilm (∼30 nm) on the worn surface during the forming process, avoiding direct contact between the metals. During Gleeble hot forming, the lubrication effect of the mixed nano-CaWO4-WO3 was the best. The nano-WO3-CaWO4 particles were relatively dispersed and dis not bond together under high temperature and pressure conditions, which played a role in reducing friction resistance between friction pairs. With the addition of 0.3 wt% mixed WO3-CaWO4 nanofluid, the surface quality was improved and it had the lowest surface roughness in the hot rolling process.

POWDER CHARACTERISTICS BLENDING AND MICROSTRUCTURAL ANALYSIS OF A HOT-PACK ROLLED VACUUM ARC-MELTED gamma-TIAL-BASED SHEET

In the quest for cost-effective fabrication processes capable of producing sound gamma-TiAl products, the microstructure and mechanical properties of a modified second-generation hot-rolled gamma-TiAl-based alloy with nominal composition Ti-48Al-2Nb-0.7Cr-0.3Si were investigated in this work. The alloy was fabricated using a processing route that involved uniaxial cold-pressing of powders and vacuum arc re-melting. Prior to the cold pressing, the elemental powder characteristics, such as particle sizes and morphologies, were blended to minimise porosity in the compact that might be inherited by the final ingot. A hot-pack rolling process was carried out directly from the melted button-ingot using a conventional two-high rolling mill to produce a 4 mm-thick sheet. The relative density results of both as-compacted and as-melted alloy parts showed a significant reduction of porosity in the alloy. In addition, both the optical and the scanning electron microscopy micrographs of the rolled sheet revealed a typical ‘duplex’ microstructure with a mean grain size of about 9 µm. Moreover, the results from a room-temperature indentation plastometry test of the hot-rolled sheet indicated good mechanical properties with recorded yield strength of about 600 MPa, an ultimate tensile strength of about 850 MPa, and a true plastic strain of about 3%.

Synthesis, characterization and lubrication performance of reduced graphene oxide-Al2O3 nanofluid for strips cold rolling

A novel nanomaterial reduced graphene oxide-Al2O3 nanocomposite (rGO-Al2O3) was synthesized through the hydrothermal method. The nanofluid containing rGO-Al2O3 nanocomposite was prepared as lubricant and exhibited superior dispersion stability. To clarify the lubrication mechanism of rGO-Al2O3 nanofluid, tribological tests and cold rolling lubrication experiments were conducted using the four-ball tribometer and two-high rolling mill. The results indicated that excellent anti-wear and friction-reducing properties as well as desired strip surface topography could be obtained under the lubrication of 0.20 wt% rGO-Al2O3 nanofluid. Induced by the interfacial tribochemical reaction, a bilayer lubrication film composed of adsorption film and reaction layer was formed at the friction interface. Through theoretical calculation and experimental characterizations, the thickness of lubrication film was about 25 nm. The adsorption film, dominated by nano-Al2O3 and graphene oxide fragments, played a vital role in synergistic lubrication. Meanwhile the reaction layer contained iron oxides (primarily Fe2O3 and FeO) with high mechanical properties. This bilayer structure ensured the denseness and continuity of the lubrication film, thus achieving significant lubrication performance.

Superior lubrication performance of MoS2-Al2O3 composite nanofluid in strips hot rolling

Abstract The novel composite material MoS2-Al2O3 nanoparticles were synthesized via mussel-inspired chemistry of dopamine. Hot rolling lubrication performance of MoS2-Al2O3 in water-based fluid was evaluated using a two-high rolling mill. Results showed that the synthesized MoS2-Al2O3 nanofluid exhibited optimum hot rolling lubrication performance. The finish rolling thickness and rolled surface roughness reached lowest. Meanwhile the rolling force and oxide scale thickness of strips were respectively reduced by 26.9 % and 54.2 % compared with base-fluid lubricating condition. The ratio of Fe2O3 in oxide scale has lowered when rolled with nanofluids, owing to the antioxidation effect of nanoparticles during lubrication. MoS2 has partially oxidized to MoO3 and the excellent lubrication performance of MoS2-Al2O3 nanofluid resulted from the lubricating film formed by these three nanoparticles.

Finite Element Analysis of Dynamic Recrystallization of Casting Slabs during Hot-Core Heavy Reduction Rolling Process

Hot-core heavy reduction rolling (HHR2) is an innovative technology, where a two-high rolling mill is installed after the solidification end of a strand, which can significantly eliminate the core defects of the slab. The mill exhibits a heavy reduction ratio, which promotes the dynamic recrystallization (DRX) of the slab. This study aims to optimize the parameters of the HHR2 process considering the effect of DRX on microstructure homogeneity. The secondary development of commercial software DEFORM-3D is conducted to calculate the deformation and DRX behavior of HHR2 for different reduction ratios. The parameters of DRX volume fraction and DRX grain size are compared, and finer DRX grains are obtained when the greater reduction ratios are conducted in HHR2. Then, corresponding to the deformation conditions in the HHR2, the thermal–mechanical simulations are conducted on the Gleeble3800 to obtain the average grain sizes before and after this process. When the reduction amount increases from 20 mm to 50 mm, the difference of average grain size between the core and the surface reduces by 52%. In other words, appropriately enhancing the reduction ratio is helpful to reduce the average austenite grain and promote the microstructure uniformity of the slab. These results provide some valuable information on the design of deformation parameters for HHR2.

Tribological performances of SiO2/graphene combinations as water-based lubricant additives for magnesium alloy rolling

The tribological performances and rolling lubrication properties of SiO2/graphene combinations as water-based lubricant additives were evaluated using a reciprocating ball-on-plate tribometer and two-high rolling mill. The results obtained therein revealed that dispersion of the SiO2/graphene combinations in water is conducive to the reduction of the friction coefficient and wear volume and the increase in the load-bearing capacity, which were superior to the results obtained for the graphene nanofluids or SiO2 nanofluids separately. In the best case, the addition of 0.1 wt% nano-SiO2 mixed with 0.4 wt% graphene in water reduced the friction coefficient by 48.5% and the wear volume by 79% compared with the addition of 0.5 wt% graphene. Transmission electron microscopy images of the SiO2/graphene combinations additives after friction testing showed that nano-SiO2 supports the graphene layers as pillars and prevent assembly between the graphene layers. The synergistic effect of the components considerably enhanced the SiO2/graphene combination. Additionally, the preliminary application of the SiO2/graphene combination nanofluids in magnesium alloy rolling effectively decreased the rolling force and improved the surface quality of sheets.

Preparation, characterization and lubrication performances of graphene oxide-TiO2 nanofluid in rolling strips

Graphene oxide (GO) and anatase TiO2 are tried as lubricating additives for nanofluids due to their unique structure and physical properties. In this article, anatase TiO2 modified GO (GO-TiO2) have been synthesized via an improved and facile solvothermal method. The physical and chemical properties of as-prepared samples were characterized by means of X-ray diffraction, Fourier transformed infrared spectra, Raman spectra and transmission electron microscopy. The tribological properties and rolling lubrication performance of the control group and 0.5 wt% of GO, TiO2, GO + TiO2, GO-TiO2 nanofluids were investigated using a four-ball tribometer and two-high rolling mill. The microscopic morphologies of the rolled strips were measured and analyzed by a series of physical characterizations. The results showed that spherical TiO2 was successfully anchored on GO nanosheets. 0.5 wt% of GO-TiO2 nanofluid had excellent friction reducing and wear resistance. It had the largest film thickness and was nanoscale (28.07 nm). And the rolled strip lubricated by 0.5 wt% of GO-TiO2 nanofluid had few defects and minimal roughness. The superior lubricating properties of GO-TiO2 nanocomposites were attributed to the excellent dispersion stability and the formation of absorption films, carbonaceous protective films and transfer films.

Influence of the Deformation Method on the Microstructure Changes in AZ31 Magnesium Alloy Round Rods Obtained by the Rolling Process

This paper presents the research results of the microstructure changes of the round rods of AZ31 magnesium alloy in the hot rolling processes. The rolling was conducted in duo mill and a three-high skew rolling mill. Numerical modelling of the AZ31 magnesium alloy round rods rolling process was conducted using a computer program Forge 2011®. The verification of the results of numerical modelling was carried out during laboratory tests in a two-high rolling mill D150 and a three-high skew rolling mill RSP 40/14. Distributions of the total effective strain and temperature during AZ31 rods rolling process were determined on the basis of the theoretical analysis. Microstructure and texture changes during both analysed processes were studied.

The initiation and propagation of edge cracks of silicon steel during tandem cold rolling process based on the Gurson–Tvergaard–Needleman damage model

Edge cracking is a commonly observed phenomenon during the cold rolling process of silicon steel, which may cause the rupture of strips in the rolling mill. In this paper the initiation and propagation of edge cracks under the tandem cold rolling condition were investigated by using the Gurson–Tvergaard–Needleman damage model. The damage parameters were obtained from the tensile tests data and the SEM analyses. Different cold rolling experiments were carried out by a non-reversing two-high rolling mill and the experimental results agreed well with the finite element calculation results. Parametric studies were carried out and revealed that the crack propagation increases with the increasing of total reduction, friction coefficient, and unit tension. A bigger work roll is beneficial to reduce the edge crack growth as well.

New Processing Technology of Twin Roll Strip Casting of AZ31B Magnesium Strip

In order to improve the poor workability and solve the problem of difficult roughing rolling of magnesium billet, the twin roll strip castor (TRSC) was used for the manufacture of magnesium thin strip directly from its molten metal. Since the cooling rates achieved by TRSC casting process are in the range of five hundred to several thousands of degrees per second and the strip is formed under the pressure, therefore, this near- rapid solidification process can leads to homogeneity of microstructures, refined grain size and increased solid solubility. The experiments were carried out on the existing equipments at State Key Laboratory of Rolling and Automation (RAL), Northeastern University. Strip samples 200~350 mm wide and 1.5~3.5 mm thick have been successfully cast in standard AZ31B alloy. The surface of the as cast magnesium strip was smooth and the edge was tidy. The microstructure analysis of the as cast magnesium strip showed that the gain size was much refined compared to that of ingot samples, and there was no segregation in the strip. The tensile strength of the strip in the cast state was about 220 MPa. The as cast magnesium strips were cold rolled directly on a two-high rolling mill, the total reduction up to 40% can be reached. X- ray diffraction result showed that the main phase in the as cast state AZ31B magnesium strip was a (Mg), the g (Mg17Al12) phase existing in the conventional wrought magnesium AZ31B sheet was vanished, therefore, the ductility of the strip increased.

Nanoscale brass/steel multilayer composites produced by cold rolling

Metallic multilayer composites are of interest due to their attractive combination of strength and fracture resistance, tq These composites have been produced by a number of techniques including coextrusion and wire drawing,t2] vapor deposition,t3] and electrodepositionJ 4] On the other hand, cold rolling is a potential method for continuous mass production of microlaminate sheets, since the technology to cold roll strips of various metals already exists. In spite of this potential, application of cold rolling to produce nanoscale multilayer composites is yet to be performed. The primary objective of the present study was to explore the feasibility of fabricating nanolaminate composites, having different layer thicknesses, by cold rolling. The brass/steel system was selected, due to the limited mutual solid solubility, ease of deformability, and material availability at low cost. The deformation behavior during rolling and the evolution of microstructure and texture were studied. It is to be noted that this is the first attempt toward the fabrication of nanoscale multilayer composites by cold rolling. The starting materials for the fabrication of laminate composites were 25.4-/xm-thick sheets of AISI 1010 steel and CDA 260 cartridge brass (70 pct Cu-30 pct Zn). These sheets were degreased with acetone, sliced into 40 x 40mm pieces, and stacked alternately to form a multilayer composite. To reduce the friction as well as to prevent the bonding between the stack and the platen, top and bottom surfaces of the stack were sprayed with graphite lubricating powder. Diffusion bonding of the stack was done at 510 ~ for 4 hours with a pressure of 16 MPa, followed by air cooling to room temperature. Typically, there was a reduction of 30 to 35 pct in the thickness during the diffusion bonding process. The bonded composites were sliced into blanks of size 40 x 20 mm and polished by SiC abrasive papers. They were then cold rolled in a two-high rolling mill, with a roll diameter of 150 mm. The specimens were given an intermediate annealing treatment at 400 ~ for 15 minutes, after a level of reduction ranging from 30 to 60 pct. Specimens were cut at different rolling stages to obtain specimens with different percentage reductions and, hence, different layer thicknesses. The rolled specimens were sectioned and metallographically polished. The steel layers were preferentially etched with a 2 pct nital solution to enhance the contrast between layers for observation in the light microscope. Microstructural examinations and chemical analyses were performed

A study of the rolling of I-section beams

The shape rolling processes for an I-section beam are simulated by the simplified three-dimensional finite element method and experimented with a model material. Computer simulation results of the four passes in I-section beam rolling include the grid distortions, the cross-sectional area changes, the roll separating forces, and the roll torques. Experiments with plasticine as a model material are performed on the experimental two-high rolling mill. The experimental and the numerical results showed good agreements in the flow pattern and the strain distributions. It is shown that optimally designing the roll pass schedule for I-section beam rolling is possible.

Laboratory investigation of the continuous seamless-tube rolling process (Mandrel mill process) using models

This paper reports the results of an experimental investigation into the dependence of the tube-shape and -dimensions on the variation of mandrel velocity and on the values of the tension and the back-tension in the rolling of aluminium tubes in a laboratory two-high rolling mill. The causes of wall-thickness and diameter variations in the rolled tube are identified and the possibilities of controlling the cross-section of the tube are explored.