Papers by Keyword: Cold Rolling

Abstract: Cold rolling forces are strongly affected by lubrication and material properties, and maypotentially be used to estimate material property variations along the coil. The 1D slab method iscommonly used to estimate rolling forces as it is computationally inexpensive. By model definition,the pressure distribution as modelled in the slab method has a single peak or friction hill in the rollbite. However, it has been observed in several studies that multiple local peaks can appear in thepressure distribution in the roll bite. Additionally, material anisotropy also affects the contact pressuredistribution and steady state roll force. In the present work, a 2D plane strain finite element rollingmodel is used for a detailed sensitivity study of the multitude of parameters that affect the verticalpressure distribution and the steady state roll force. The considered model parameters are materialanisotropy, entry sheet thickness, roll radius, tensions, coefficient of friction and roll gap.

Abstract: The Ti-13Nb-1.5Mo-3Ta alloy is a recently developed biocompatible metastable β-Ti alloy designed for biomedical application. In this present work, the influence of cold rolling and subsequent annealing heat treatment on grain refinement of Ti-13Nb-1.5Mo-3Ta alloy was investigated. The alloy was cold rolled (CR) to 60% and 90% thickness reductions at room temperature followed by recrystallization annealing at different temperature (800°C-900°C) and time (1.5mins-10mins) before ice-water quenching. X-ray diffraction (XRD) and optical microscopy (OM) were used to characterize the alloy, and microhardness tests were carried out using the Vickers microhardness tester. The results revealed that the annealed alloys exhibited a fully β-phase, while those subjected to cold rolling displayed introduction of stress induced martensite (SIM) α′′-phase along with β-phase. The microhardness of the 60% and 90%CR samples increased significantly to 253 and 283 Vickers hardness (HV), respectively, from an initial value of 198 HV. Annealed samples exhibited a recrystallized microstructure containing fine equiaxed grains with average size of 10-50μm for 60%CR and 8-34μm for 90%CR. The grain refinement mechanisms are probably attributed to the reversal of the SIM α′′-phase back to the more stable β-phase and the recrystallization of the deformed β-phase.

Abstract: Improved understanding of friction during cold rolling is crucial to further optimize the rolling process, to accurate analyse cold rolling defects and to increase model accuracy enabling an improved mill setup during industrial operation. Classical slab rolling models make use of the Coulomb friction law, assuming a constant coefficient of friction in the roll bite. In the last decades, mixed-lubrication models have been developed that explicitly take the lubricant action into account. These models have greatly increased the understanding of factors that influence friction during cold rolling, but quantitatively the model results should still be further improved before such models can be used as an online tool for setting up the cold rolling mill. This article describes a mixed-lubrication model to simulate cold rolling of low-carbon steel. Especially the tribological core of the model is extended and improved compared to state-of-the-art models. Friction mechanisms now also include a viscous shear stress and ploughing friction. The quantification of viscous shear stress was reported in a previous work [1], this work focuses on the quantification of ploughing friction. Material Point Method (MPM) simulations were carried out to determine the work piece strain-hardening and strainrate-hardening under a ploughing indenter. These simulations result in an ‘Surface Ploughing Resistance’ and finally in a quantification of the contribution of ploughing friction to the overall friction in the roll bite. The description of the various friction mechanisms (ploughing, adhesive and viscous shear) is implemented in the mixed-lubrication model. This article concludes by presenting typical results of the developed model. One of the main conclusions is that the contribution of ploughing friction in a cold rolling process cannot a priori be neglected.

Abstract: Oil-in-water emulsions (O/W-emulsions) are generally used to lubricate the cold rolling process of low-carbon steel. Besides the obvious advantages of efficient lubrication and cooling of the process, there are also some disadvantages mainly related to emulsion bath maintenance, subsequent production steps and waste disposal. In some application areas, Oil Free Lubricants (OFL’s) have shown to be at least equally effective in decreasing friction and wear as conventional lubricants, while resulting in benefits related to waste disposal. In 2018 a project (acronym ‘RollOilFree’) was started with funding from the Research Fund for Coal and Steel (RFCS). The objective of this project was to develop an OFL as a lubricant for the cold rolling process of low-carbon steel and hot rolling of aluminium. A cold rolling lubricant can be evaluated based on many criteria; for some criteria the OFL even outperformed the oil-based emulsion, but it was found that for some rolling conditions the coefficient of friction with the OFL was still too high. In September 2023 a follow-up project, “Transfer of aqueous oil free lubricants into steel cold rolling practice” (acronym ‘RollOilFreeII’) has begun, also in the RFCS-framework. This article briefly recapitulates the findings in the RollOilFree-project and describes the objectives and benefits of the RollOilFreeII-project. Furthermore, the main activities in the project will be discussed.

Abstract: An important aspect of New Product Development (NPD) is the determination of the expected product dimensional window, describing the maximum strip width, that can be produced for a given strip thickness. The estimation of the product dimensional window is used to safely execute first rolling trials. In addition, one can verify in advance whether customer geometry specifications of the final strip can be reached. For this purpose, offline simulation tools are used for hot rolling as well as cold rolling. An accurate prediction of the deformation resistance and interstand softening behaviour of the new steel grade is key in the determination of the dimensional window. Preferably, the deformation resistance model is validated with experimental data, for example from tensile tests or laboratory mini-mills. Rolling simulations are performed, using prescribed process conditions with respect to for example load distributions, temperature and rolling speed requirements. The dimensional windows of respectively the hot strip mill and the cold strip mill are merged, resulting in a final product dimensional window, indicating the maximum strip width at a final, customer specified, strip thickness.

Abstract: Severe plastic deformation processing and subsequent aging treatment have been known to be effective for achieving higher strength than the conventional aging treatment in aluminum alloys. This study prepared the Al-Cu-Mg-based alloy sample, Al-5.3Cu-2.8Mg (mass%). The alloys were solution treated at 480, 495 and 505°C, and cold-rolled by 90%. The effect of process condition and test environment on tensile properties in cold-rolled Al-Cu-Mg alloys was investigated. Results confirm that strength and ductility were improved with increasing the solution heat treatment temperature regardless of test environment. 0.2% proof stress and ultimate tensile strength were higher than aging treatment specimens, but elongation to failure was lower than aged one. Hydrogen embrittlement susceptibility increased with increasing solution treatment temperature. Ductile fracture with many dimples is observed in both cold-rolled and aged specimens. Second-phase particles were observed at the bottom of the dimples. There was no significant difference in fracture surface between the different test environments.

Abstract: Powder metallurgy (PM) is an alternative approach to ingot metallurgy (IM) in the production of metal products. It is of paramount importance for PM to be able to produce fully dense products for it to make headway in becoming an equal alternative to IM and be a better option economy-wise. Cold rolling is an inexpensive post-sintering densification option that enables the lowering of sintering conditions. Experiments were carried out in this study to investigate cold rolling parameters on the densification of titanium brown compacts with a starting relative density of 89.3 %. The highest relative density obtained during the cold rolling experiments was 97.7 % without any annealing. It was found that the density increases with an increase in the percentage reduction of cold rolling. High percentage reductions reduce the number of roll passes needed to increase the density up to a limit where the brown compacts become susceptible to severe rolling defects. It was also found that the total increase in density increases with a decrease in cold rolling speed. An increase in the relative density of 8.36 % was observed at the cold rolling speed of 1 rpm, whereas the highest increase recorded at 10 rpm was 5.83 %.

Abstract: Ni/Al energetic structural materials were prepared by vacuum hot-pressing method and then treated by secondary treatment of cold rolling or cold isostatic pressing. The effects of secondary treatment on the surface morphology, the phase composition, density, exothermic properties and tensile properties of Ni/Al energetic structural materials were investigated. The results showed that the density, the reaction energy density and the sensitivity of energetic materials improved significantly by the secondary treatment of cold rolling or cold isostatic pressing. It was also found that, after cold rolling and cold isostatic pressing, the energy density increased from 780 J/g to 1089 J/g and 993 J/g, respectively, and the initial reaction temperature was advanced by 46 °C and 14°C simultaneously. This is related to the increased in the contact area between Al particles and Ni particles. Meanwhile, the tensile strength increased from 166.7 MPa to 254.8 MPa and 211.3 MPa, respectively.

Abstract: On the example of shape memory alloys in coarse-grained and ultrafine-grained states there is demonstrated an influence of pulse current on deformation behavior, microstructure and mechanical properties during cold rolling. The combination of cold rolling with the introduction of a pulsed current stimulates an increase in the deformation ability and strong structural refinement into the region of nanograins in a hard-deformed shape memory TiNi alloy. For both coarse-grained and ultrafine-grained structural states, the maximum achievable one-time and the total degree of deformation are higher in the case of using a pulsed current. Subsequent annealing improves the strength and functional properties. It has been shown that effect of pulsed current on deformability during cold rolling is higher in an alloy with a high content of impurities.

Abstract: The effects of different cold rolling deformations on the microstructure and mechanical properties of high nitrogen and low nickel alloys were investigated. The microstructure of high nitrogen alloys with different rolling deformations were characterized by EBSD and TEM. The tensile mechanical properties of the high nitrogen alloys at room temperature were tested. The results showed that the microstructure of the cold rolled high nitrogen alloy with deformation of 0% to 70% shows a twinning process. The twin thickness of the high nitrogen alloy without deformation is micron degree. When the rolling deformation is over 50%, the average thickness of the deformation twin is 23nm. When the rolling deformation increases to 70%, the average thickness of the twin is 14nm. When the rolling deformation increases from 0% to 70%, the cold rolled high nitrogen alloy exhibits high strength (1001-2236 MPa) and excellent plasticity (5.9%-64.1%). It is beneficial to have a good combination of strength and plasticity after rolling deformation.