Rolled Layers Research Articles

Microstructural Evolution, Hardness and Wear Resistance of WC-Co-Ni Composite Coatings Fabricated by Laser Cladding.

This study investigated how process parameters of laser cladding affect the microstructure and mechanical properties of WC-12Co composite coating for use as a protective layer of continuous caster rolls. WC-Co powders, WC-Ni powders, and Ni-Cr alloy powder with various wear resistance characteristics were evaluated in order to determine their applicability for use as cladding materials for continuous caster roll coating. The cladding process was conducted with various parameters, including laser powers, cladding speeds, and powder feeding rates, then the phases, microstructure, and micro-hardness of the cladding layer were analyzed in each specimen. Results indicate that, to increase the hardness of the cladding layer in WC-Co composite coating, the dilution of the cladding layer by dissolution of Fe from the substrate should be minimized, and the formation of the Fe-Co alloy phase should be prevented. The mechanical properties and wear resistance of each powder with the same process parameters were compared and analyzed. The microstructure and mechanical properties of the laser cladding layer depend not only on the process parameters, but also on the powder characteristics, such as WC particle size and the type of binder material. Additionally, depending on the degree of thermal decomposition of WC particles and evolution of W distribution within the cladding layer, the hardness of each powder can differ significantly, and the wear mechanism can change.

ОЦІНКА НАПРУЖЕНОГО СТАНУ РОБОЧОГО ШАРУ ВАЛКІВ КОЕРЦИТИМЕТРИЧНИМ ЕКСПРЕС-МЕТОДОМ

The purpose of the work is the problem of researching the influence of chemical composition and structure on the indicators of operational stability of centrifugal two-layer rolling rolls made of high chromium cast iron by the coercimetric express method. In order to ensure the achievement of this goal, the following tasks were set and solved: conducting an analysis of the causes of the destruction of the surface layer of rolls; building a mathematical model for studying the influence of the chemical composition and structure of cast iron on the level of hardness and coercive force; using the coercimetric method to analyze the quality of rolled rolls. Conclusions. Forecasting the behavior of the rolls during operation is inextricably linked to the analysis of the main factors on which the level of properties and operational stability of the working layer depend. The properties of high-chromium alloys are closely related to the type of phases formed and their ratio. The amount of residual austenite and martensite in the structure of the alloy has the greatest influence on the properties of the alloy (in the studied interval of changes in the proportion of phases). The operational layer of two-layer high-chromium rolls is characterized by a high level of residual stresses. Exceeding the permissible level of stresses or their unfavorable distribution can cause premature destruction during the operation of the roll. With the help of the coercimetric express method, it is possible to solve a fairly wide range of tasks of quality control of rolls, related to the determination of the level and distribution of residual stresses in the working layer of the rolls. This is because the intensity of the process of formation of thermal cracks under conditions of thermo-cyclic loading largely depends on the level of residual compressive stresses. Too high a level of stresses or their unfavorable distribution can cause premature destruction of the working layer of the roll, because the typical type of destruction due to an unbalanced distribution of stresses is cracking. A local increase in the level of coercive force can be the basis of the prediction of crack formation.

PREDICTION OF THE STRUCTURAL STATE OF THE WORKING LAYER OF LARGE-SIZE ROLLS DURING THERMAL HARDENING

Problem statement. High-carbon steels, which are additionally alloyed with chromium, molybdenum, and vanadium, are used during the production of large-sized rolling rolls for hot deformation. Rolling rolls are subjected to significant loads during operation, so they must have sufficient hardness and resistance to wear. Steels of the type 65Cr3SiMoV, 80Cr3MoV, 80Cr5MoV have recently been used for the production of hot-formed rolling rolls, but despite this, their resistance to wear in harsh operating conditions is insufficient. There is no information in the literature about the peculiarities of the austenite decay kinetics of the specified rolled steels, therefore, this direction requires appropriate comprehensive research. Purpose. Development of a methodology for predicting the structural state of the working layer of large rolling rolls in the process of thermal strengthening of high-carbon alloy steels, taking into account the determining parameters of the manufacturing technology. Results. A methodology for modeling phase-structural transformations in the process of continuous cooling of high-carbon alloy steels was developed. For steels 65Cr3SiMoV, 80Cr3MoV, 80Cr5MoV were constructed thermokinetic diagrams and on their basis, the peculiarities of the formation of the structural state of the working layer of large rolling rolls (support, working) during thermal hardening were investigated. It has been established that the method of hardening by volumetric heating of support rolls made of 65Cr3SiMoV steel ensures the formation of a bainite structure over the entire normalized depth of their working layer. For working rolls made of 80Cr3MoV and 80Cr5MoV steels, the most effective method is hardening with differentiated heating, while in the latter case continuous cooling should be carried out at a slower speed.

Multi-walled carbon nanotubes promote the accumulation, distribution, and assimilation of 15N-KNO3 in Malus hupehensis by entering the roots.

Multi-walled nanotubes(MWCNTs)consistofmultiplerolled layersofgraphene. Nitrogen plays an important role in apple growth. The effect of MWCNTs on nitrogen utilization in apple needs to be further investigated. In this study, the woody plant Malus hupehensis seedlings were used as plant materials, the distribution of MWCNTs in the roots was observed, and the effects of MWCNTs on the accumulation, distribution, and assimilation of nitrate by the seedlings were explored. The results showed that MWCNTs could penetrate the roots of Malus hupehensis seedlings, and the 50, 100, and 200 µg·mL-1 MWCNTs significantly promoted the root growth of seedlings, increased root number, root activity, fresh weight, and nitrate content of seedlings, and also increased nitrate reductase activity, free amino acid, and soluble protein content of roots and leaves. 15N tracer experiments indicated that MWCNTs decreased the distribution ratio of 15N-KNO3 in Malus hupehensis roots but increased its distribution ratio in stems and leaves. MWCNTs improved the utilization ratio of 15N-KNO3 in Malus hupehensis seedlings, with the values being increased by 16.19%, 53.04%, and 86.44% following the 50, 100, and 200 µg·mL-1 MWCNTs, respectively. The RT-qPCR analysis showed that MWCNTs significantly affected the expression of genes (MhNRTs) related to nitrate uptake and transport in roots and leaves, and MhNRT1.4, MhNRT1.7, MhNRT1.8, MhNRT2.1, MhNRT2.5, and MhNRT2.7 were notably up-regulated in response to 200 µg·mL-1 MWCNTs. Raman analysis and transmission electron microscopy images indicated that MWCNTs could enter the root tissue of Malus hupehensis and were distributed between the cell wall and cytoplasmic membrane. Pearson correlation analysis showed that root tip number, root fractal dimension, and root activity were the main factors affecting root uptake and assimilation of nitrate. These findings suggest that MWCNTs promoted root growth by entering the root, stimulated the expression of MhNRTs, and increased NR activity, thereby enhancing the uptake, distribution, and assimilation of nitrate by root, and ultimately improved the utilization of 15N-KNO3 by Malus hupehensis seedlings.

Influence of cast iron vacuuming on the level of mechanical characteristics of the material of the working layer of double-layer chromium-nickel rolls

The object of research is chromium-nickel cast iron of the working layer of two-layer sheet-rolling rolls of the LPKhNd design. At present, chromium-nickel cast iron is widely used for the manufacture of rolls for sheet and section rolling mills. One of the ways to improve the operational properties of products made of chromium-nickel cast iron is the refining of molten metal by vacuum. The existing problem is that information on the effect of vacuuming on the performance of chromium-nickel iron is very limited. Rolls with the most characteristic concentration of alloying elements for LPKhNd performance were selected for the study. When evaluating the properties of vacuumed cast iron and cast iron by traditional technology, the level of strength, hardness, as well as special properties were determined, the study of which is caused by the peculiarities of the operation of rolling rolls (thermal wear resistance and crack resistance). It has been established that there is no significant difference in the structures of rolls made of vacuumed and non-vacuumed cast iron. The structure of the rolls consists of martensite, bainite and carbides. With an increase in the content of graphite-forming elements (C, Si, Ni), graphite inclusions appear in the structure, and with their decrease, individual troostite colonies appear. The physical and mechanical properties of vacuumed and non-vacuumed cast iron are on the same level. The crack resistance of the chilled zone of vacuum cast iron is 12.35 % higher than that of cast iron of the traditional production method, and the transition zone is 11.96 %. The thermal endurance of the chilled zone of the roll material increased by 14.95 % as a result of vacuuming of the molten metal, and the transition zone – by 14.56 %. An increase in crack resistance and heat resistance can help reduce the chipping of the working layer of chromium-nickel rolls of sheet mills during operation and increase their resource indicators. The obtained results of research indicate a positive effect of vacuuming on individual indicators (crack resistance and heat resistance) of the working layer of the forming tools of sheet rolling mills.

Hardening of surface layer of cold rolls by multilayer plasma surfacing in nitrogen atmosphere

High service properties of cold rolling working rolls can be provided by plasma surfacing in protective-alloying nitrogen atmosphere with heat-resistant alloys (such as steel R18Yu). The distributions of hardness, microhardness and the structure of the surface layer of the deposited working rolls of cold rolling, which have impact on their performance, are studied. It is established that the surfacing technology and the surfacing material make it possible to obtain high-quality surfaced alloy without cracks, pores, slag inclusions and macro- and microstructure defects. Additional contribution to the hardening is made by high-temperature tempering of the deposited metal. The deposited alloy is pearlitic grains, along the boundaries and joints of the grains are carbonitrides based on iron, tungsten, chromium, molybdenum, aluminum (Me6NC and AlN).

Analyzing recrystallization behavior of heterogeneous structures single-phase Al alloys

In this research, mixed structures are created so that they have regions where dislocations accumulate and a region that is, to some extent, free from dislocations. These heterogeneous structures that bring together both soft and hard domains in a single sample are presumed to produce a fine recrystallized grain and recovered large grain structures if they are subsequently heated, leading to limited recrystallization. In the present work, the 3D Potts model has been modified to tailor and model complex problems such as heterogeneous structure recrystallization. This is done by introducing a limited fraction of nucleating grains to the structure where the highest geometrically necessary dislocation density distributions develop in the rolled layers at early simulation time as well as by controlling structure evolution in the undeformed structure layer using grain boundary energy criteria. Additionally, the designed microstructures were investigated using electron backscatter diffraction measurements and an in-situ heating stage performed on material with various degrees of deformation.

Analyzing Recrystallization Behavior of Heterogeneous Structures Single-Phase Al Alloys

In this research, mixed structures are created so that they have regions where dislocations accumulate and a region that is, to some extent, free from dislocations. These heterogeneous structures that bring together both soft and hard domains in a single sample are presumed to produce a fine recrystallized grain and recovered large grain structures if they are subsequently heated, leading to limited recrystallization. In the present work, the 3D Potts model has been modified to tailor and model complex problems such as heterogeneous structure recrystallization. This is done by introducing a limited fraction of nucleating grains to the structure where the highest geometrically necessary dislocation density distributions develop in the rolled layers at early simulation time as well as by controlling structure evolution in the undeformed structure layer using grain boundary energy criteria. Additionally, the designed microstructures were investigated using electron backscatter diffraction measurements and an in-situ heating stage performed on material with various degrees of deformation.

Graphite flake cast iron surface hardening

The influence of the operating parameters of electric arc heat treatment of the surface layer of graphite flake cast iron type CП-61 on the structure, microhardness of structural components and the size of the hardening zone is studied. It is shown that controlling the arc power, its speed and the degree of overlap of local hardening zones allows purposefully forming modified structural States with properties most suitable for specific operating conditions in the surface working layer of cast iron. Overlapping of local hardening zones allows purposefully forming modified structures with suitable properties for specific operating conditions in the surface working layer of cast iron rolls. According to the research results, regularities of formation of the structure and phase composition and properties of the surface layer of cast iron type CП-61 under the influence of electric arc heat treatment were obtained. Control of parameters of the processing mode (power and speed of the arc, the degree of overlap of local hardening zones) allows you to purposefully form modified structures with suitable properties for specific operating conditions in the surface working layer of cast iron.

Effect of chemical composition on the performance of centrifugally cast indefinite chilled cast iron rolls

Problem Statement (Relevance): An urgent task of rolling mill operators includes minimizing the cost of manufactured products while ensuring the required quality. To accomplish the task, measures are being taken to optimize the rolling process aimed at increasing the duration of the rolling campaigns and reducing the number of roll regrinds. The performance of the rolls is influenced by the properties of the working layer material which determine wear resistance, formation and development of fire cracks, as well as resistance to metal sticking. Finishing mill rolls dictate the surface quality of the rolled steel. That is why it is important to make timely regrinds in order to completely remove the fire crack layer. The removal depth and the acceptable duration of the campaigns depend on the properties of the roll working layer material. To improve the properties of the rolls, the roll manufacturers need the actual roll operation data to be able to analyze how the chemical composition and the structure of the roll working layer is related to the roll performance. Such analysis will help improve the structure and properties of the materials used, as well as develop new ones. Objectives: The objective of this research is to understand how the chemical composition of the working layer of indefinite chilled cast iron rolls used in finishing mills dictates the roll performance, to evaluate the effect of each chemical element, and to determine what concentrations of the chemical elements could most effectively benefit the performance of indefinite chilled cast iron rolls. Methods Applied: The methods applied include building a database of the finishing mill indefinite chilled cast iron rolls and using artificial neural networks based on a dual-function algorithm. Originality: The authors built a neuromodel which can help understand the effect of the chemical composition of the roll working layer and predict the performance of indefinite chilled cast iron rolls. The authors studied the effect of carbon, silicon, manganese, chromium, nickel, molybdenum, vanadium, niobium and boron on the performance of indefinite chilled cast iron rolls. Findings: Graphic diagrams were built which demonstrate the effect of each chemical element on the performance of indefinite chilled cast iron rolls at constant concentrations of the remaining elements. The authors looked at the relationship between the chemical elements and the roll performance in terms of the impact of the former on the structure of indefinite chilled cast iron rolls. The effective concentrations of the chemical elements were also determined. Practical Relevance: The authors developed a new chemical composition of indefinite chilled cast iron to be used for the working layer of finishing mill rolls. As a result, a 12–14% increase in the roll performance was achieved.

Optimization of parameters and modes of operation of the spiral-screw roller

The method of planning a two-factor experiment substantiates the optimal parameters and operation mode of the spiral-helical roller for compacting the soil in order to create its optimum density in the sowing layer, which ensures friendly shoots of the sown seeds of cultivated plants and their sustainable development. The studies were carried out using the provisions of the experiment planning theory and the main measurement methods written in the regulatory documentation. The quantitative factors of the mathematical planning method are the design parameters and operating modes of the press roller. The Vк (plan) was used for its optimization, and the density of the soil in the rolled layer was taken as the optimization criterion (response), which depends on the size of the ballast weight attached to the frame of the roller and the operating speed of the unit. The levels of variation of the factors are chosen so that their optimal values, calculated theoretically, fall into the center of the interval of variation. Using the obtained regression equations in canonical form, we obtained hypersurfaces of dependence of soil density in the sowing layer on the operating speed of the aggregate and ballast weights, as well as dependencies of two-dimensional sections of soil density. The center of the experiment lies within the scope of the experiment. The value of the optimum density of the soil in the sowing layer of 1,25 g/сm3 at a working speed of the unit of 7,6 km/h and a ballast weight of 42,4 kg was obtained.

Enhanced Fracture Strength in the Working Layer of Rolls Manufactured in Ni-Hard Cast Iron Alloyed with Mo, Nb and Mg

One of the main in-service failure mechanisms of the work-rolls used in hot strip mill finishing stands is surface spalling. The indefinite chill double-poured rolls usually comprise of a peripheral working layer made of crushed Ni-hard cast iron and a grey cast iron core, mostly pearlitic matrix with spheroidal graphite. To enhance its wear resistance, the working layer can be alloyed with Mo and Nb. The possible cracking and spalling of the surfaces of these work-rolls is strongly influenced by the presence of carbides and the continuity of their network. The flexural and impact toughness tests are reliable testing methods to assess these properties. The aim of this paper is to identify those manufacturing factors that have a significant effect on the flexural strength and toughness of this material, correlating the results with the volume fraction of precipitated carbides. It is worth highlighting, among the analysed factors are the liquidus temperature, the %Si, the use of an inoculant with traces of Lanthanum, and inoculation with different amounts of FeB, SiCa and Mg. Inoculation with SiCa is found to have a positive effect on the toughness of the material, breaking up the continuity of the carbide network, while FeB is found to act as a heterogeneous nucleant for NbC precipitation. However, high FeB contents reduce flexural strength and do not have a significant effect on the hardness of the material. To enhance the fracture toughness of the working layer, a liquidus temperature in the 1270–1275 °C range is recommended, as well as inoculating the ladle with Mg, 3 kg/T FeB and 0.6 kg/T SiCa.

Optimization of Graphite Morphology in Mottled Nihard Cast Irons Inoculated with Feb and Manufactured by Centrifugal Casting

The present research was focused on the identification of manufacturing factors that have an active influence on the graphite phase formation in Nihard cast irons inoculated with FeB, constituting the outer layer of duplex work rolls. These rolls are used in the finishing stands of hot-strip steel mills where the following are desired: (a) between 2.5 and 4 vol % of graphite; (b) homogeneous graphite distribution across the layer section; and, (c) a reasonable high number of graphite particles across the layer. The research methodology that followed consisted of the application of a saturated design of experiments (DOE), with seven factors, eight experiments, and resolution III. The analyzed responses obtained by quantitative metallographic techniques were: the volume fraction of graphite, Vv; the number of counts per unit area of graphite, NA; and the graphite morphology across the layer thickness. Increasing the addition of FeB from 6 to 10 kg/T reduced the graphite volume fraction and the count number, but had no influence on its morphology. However, an increase of the liquidus temperature from 1225–1230 to 1250–1255 °C, and an increase in the amount of SiCaMn added to the ladle from 0.3 to 0.6 kg/T produced the desired compact graphite morphology.

Hardening Roll Surface by Plasma Nitriding with Subsequent Hardfacing

The wear of the surface layer of rolls after ion nitriding in glow discharge, followed by a coating of TiN -TiAlN plasma arc are studied and simulated. stress-strain state of the material rolls under asymmetric rolling with ultra-high shear deformations is simulated. The effect of thermal fields, formed upon contact of the tool and a deformable sheet, the structure of aluminum alloys, are considered.

Effective Technological Process of Crystallization of Turning Rollers' Massive Castings: Development and Analysis

The paper describes a new method of maximum reducing residual stresses and stabilization of the structure, hardness of the working layer of massive sheet rolls from alloyed cast irons during their crystallization due to controlled decomposition of retained austenite. It is achieved by programmable preheating of the metal form to the temperature of magnetic transformation of doped cementite or special carbides of the castings (depending on the material being processed); meanwhile it is provided an optimum cooling rate with an exposure of up to 6 hours in this interval and maximizes decomposition of retained austenite, minimizes stresses in the working layer. This casting technology is also accompanied by appropriate structural changes. Inhomogeneity of the dislocation structure is noted in various constituent phases. Polygonization and fragmentation along dislocation walls are revealed in the carbide phase. To evaluate the occurring processes, a new method of optical and mathematical description of the phases being formed is used. As a criterion describing the changes in the dislocation structure, we use the parameter - a power dissipation power function. The proposed casting technology for rolls is particularly effective when the proportion of the carbide phase is at least 25%. In this case, the heat treatment of the rolls to relieve stress does not change the stably achieved properties. It is shown that the quality control on the stability of the achieved indicators can be carried out by the coercive force and the level of hardness.

Prevention of Corrosion-Resistant Austenitic Steel Cladding Layer Surface Defects

Reasons are studied for surface defect formation (rolling crystallization cracks) for a bimetallic rolled product cladding layer of austenitic class corrosion-resistant steel prepared by electroslag welding. An unfavorable effect of liquation during welded layer steel crystallization is established for surface quality. Possibilities and examples are established for preventing the occurrence of surface defects by optimizing welded steel chemical composition, and also bimetallic rolled product start-to-finish manufacturing technology parameters.

Освоение технологии термической обработки центробежнолитых валков с рабочим слоем из хромникельмолибденового чугуна

The paper is dedicated to analysis of heat treatment of cast iron products. It is noted that heat treatment is performed for reduction of internal stresses, graphitization, decarurization, to change structure and properties. During the experiments technological parameters of heat treatment of centrifugally cast rolls with working layer of chromium-nickel-molybdenum cast iron have been determined. They are necessary to develop effective process in special car bottom gas furnaces. It is shown that such treatment contributes to reduction of residual stresses in the rolls after casting. The aim of this paper was to study the effect of heat treatment on the structure, hardness level and stress state of sheet-rolling rolls. Studies of as-cast rolls showed that various combinations of matrix with secondary carbide inclusions were observed depending of proportions of chemical components in the analyzed cast iron and cooling rate of the cast billet. Hardness level changed depending on their quantitative relations. Results of stressed state study of castings by means of coercive force measurement showed a non-uniform distribution of its values along the working surface of roll barrels. A regime of low-temperature ( T = 673 K) annealing proposed in the work permitted to obtain a more uniform structure of the working layer of rolls. As a result, inhomogeneity of properties along working layer surface decreased two times compared to as-cast state.

Structure and Properties of Cast Iron DESIGNATED for Working Layer of Rolls

<p class="1Body">The formation of the structure and properties of cast irons designated for the working layer during solidification and subsequent tempering of Indefinite Chill Double Poured Centrifugal Casting Rolls (ICDP) has been studied.</p><p class="1Body">Graphitization of cast irons designated for the working layer of rolls occurs under isothermal conditions at high temperatures, which vary over the cross section and resulted from casting the roll core. At subsequent slow cooling, secondary carbides precipitate and austenite partially transforms into martensite; the resulting end structure consists of martensite and austenite metallic base (primary austenite dendrites) with 11.4 per cent of retained austenite, 26 per cent of eutectic and secondary carbides, and 2.6 per cent of flake graphite.<em> </em></p><p class="1Body">The amount of retained austenite in the metallic base of the cast structure of cast iron designated for the working layer, heated to 430 °C, decreases<strong> </strong>from 11.4 per cent to 3.2 per cent due to the partial transformation into bainite. The martensite tetragonality decreases due to the carbide precipitation; the existing excess phases grow and the new ones are formed; the total volume fraction of the carbide phase increases to 29.8 per cent and graphite to 3.7 per cent.</p>

Исследование влияния продувки азотом на формирование структуры металла рабочего слоя прокатных валков исполнения ЛПХНМдц

The information about the extra-furnace chrome-nickel hot iron processing for active layer of two-layer rolls. The analysis of the technological parameters of the casting rolls. It is found that the nitrogen purge in a ladle for an active layer of a chrome-nickel hot iron rolls helps to reduce the content of non-metallic inclusions in the active layer, also the proportion of retained austenite and contributes to generate thin martensite needles, which improves the operational durability of the rolls in 7.7 %.

Radial buckling of multi-walled carbon nanotubes under hydrostatic pressure

Radial buckling stresses of carbon nanotubes (CNTs) need to be studied in high-pressure resonance Raman scattering spectrum. In this work, the closed-form expression of the critical buckling stress of multi-walled carbon nanotubes (MWCNTs) under hydrostatic pressure is derived that can be conveniently employed. Using the derived formulae, the critical buckling stresses of single-walled carbon nanotubes and double-walled carbon nanotubes with different diameters are calculated. The results are in good agreement with other reported literatures. In addition, the critical buckling stresses of each layer of a quintuple-walled CNT in different buckling modes are predicted, showing that the buckling instability can occur not only in the outermost rolled layer, but also in other rolled layer of MWCNTs by considering different diameters and buckling modes.