Rolling Heat Research Articles

Rational chemical composition and heat treatment models of rails made from E76HF steel using the heat of rolling heating

On the pilot plant the experiments in the differentiated heat treatment by air using the heat of rolling heating of rails produced from steel E76HF with three chemical compositions comprising various contents of chromium, manganese and silicon were carried out. The effect of heat treatment parameters on the structure and properties of rails was examined. According to the results of experiments the rational chemical composition was determined, as well as the heat treatment modes recommended for a mass production of differentially thermo-strengthened rails of DT350 category.

EFFECTS OF BLEND RATIO AND SBR TYPE ON PROPERTIES OF SILICA-FILLED SBR/NR TIRE TREAD COMPOUNDS

ABSTRACT The influences of blend ratio between SBR and NR and SBR type, emulsion SBR (E-SBR) and solution SBR (S-SBR), on properties of silica-filled passenger car tire tread–based compounds were investigated. Results reveal that, with increasing NR proportion, cure time and most mechanical and dynamic properties, for example, tensile strength, tear strength, modulus, abrasion resistance, and wet skid resistance of the compounds and vulcanizates, are reduced, whereas the improvements in elongation at break and crack growth resistance are observed. The unexpectedly impaired mechanical and dynamic properties identified in the presence of NR are mainly caused by thermal degradation of NR taking place during the mixing process at high temperature. Compared with E-SBR, S-SBR provides superior properties in many aspects, that is, higher modulus and greater abrasion and wet skid resistances as well as lower heat buildup and rolling resistance. However, E-SBR gives greater tear strength than S-SBR.

Optimization of spray drying process for Bi-2223 precursor powders fabrication

Precursor powders for the fabrication of Bi2Sr2Ca2Cu3O10+δ (Bi-2223) tapes were fabricated with spray drying technique combined with a one-step calcination process. During the spray drying process, the effects of spray temperature on both the morphology and carbon content of collected powders were systematically analyzed. And the uniformity of chemical composition of these powders was confirmed with EDX mapping. By optimizing the calcination temperature, precursor powders with the major phases of Bi2Sr2CaCu2O8+δ (Bi-2212) and alkali earth cuprates (AEC, (Ca, Sr)xCuyOz), proper Pb content, and uniform morphology were obtained. Powder in tube process was adopted for the fabrication of 37-filament Bi-2223 tapes and a traditional heat treatment process involving the first heat treatment, intermediate rolling and second heat treatment was performed, during which textured Bi-2223 phase was obtained. With the optimized fabrication parameters and spray dried precursor powders, 37-filament Bi-2223 tape was achieved with high critical current of Ic ~ 125 A. Further optimization involving with the over-pressure heat treatment process is on the way.

Production of Directly Quenched High-Strength Hot-Rolled Strip Steels - Influence of Rolling and Cooling Conditions on Mechanical Properties and Flatness

The production of hot-rolled sheets of high-strength and wear-resistant special structural steels by direct quenching from the rolling heat is a cost effective and energy-saving alternative to traditional production via downstream quenching the previously cut-to-length plates. Reaching the required strength and toughness parameters in combination with best flatness of the sheets requires strict compliance with the pre-set rolling and cooling conditions over the entire strip width. Using two high-strength low-alloyed steels, plant trials have been carried out to study the effect of the cooling conditions and the coiling temperature on mechanical properties, impact toughness and flatness of cut-to-length sheets made of hot-rolled strip. The results showed that by applying optimized cooling pattern and low coiling temperatures, high-strength steel sheets with outstanding mechanical properties and good flatness can be produced.

Development of Modern Steels for Strain Based Design Pipe Lines and Simulation Results

Due to the exploration of gas and oil sources in remote regions with harsh environment, the pipe line designers are faced with the challenging conditions. Especially in the cases where displacement-controlled loads are the predominant design condition, such as ground movement, strain-based design is applied instead of stress-based design to build safer pipelines and to assure the integrity of the lines along their lifetimes. It requires steels to have a large strain hardening capacity, long uniform elongation, and good toughness to achieve a well-defined and sufficient plastic deformation. In order to fulfil the requirements, all the processing steps are supposed to be well designed, for example, the chemical composition, microstructural design, thermo-mechanical controlled process (TMCP) and heat treatment, etc. In general pipe line steel has a low carbon, high manganese content combined with a certain amount of micro-alloying elements as Nb, Ti and sometimes B. Using Thermo-mechanical rolling and cooling schedules excellent combinations of strength and toughness can be established. To successfully produce steel plates for strain based design pipe lines the actual heating rolling and cooling technologies must be developed further as well as the equipment to produce such steel. The paper gives an overview about modern plate mill equipment and new setup strategies for the production of heavy plates X70 to X100 as well as thethermo-dynamic simulations used during the development.

Evaluation of the Possibility of Retarding Steel Recrystallization During Hot Rolling with Precipitation of Manganese Sulfide Particles

The article is devoted to finding new production methods making it possible to prepare rolled product of carbon or low-alloy steels with a fine-grained structure, and this means greater strength with limitation or exclusion of expensive alloying with niobium. The possibility is considered of retarding recrystallization during hot rolling as a result of reprecipitation of manganese sulfide particles previously dissolved on heating for rolling. Laboratory tests are performed with the aim of determining the optimum heating temperature for rolling in order to implement the mechanism described.

“Bainitic Refinement” of Machine Steels Microalloyed with Vanadium and Nitrogen

The effect of microalloying additions of N, V, Ti, Al, and Nb on structure formation and properties of medium-carbon steels alloyed mainly with chromium (30Kh2AF–40Kh2FABT type) is considered. Steel microalloying makes it possible to provide marked austenite structure refinement due to grain growth limitation by (Ti, V)N particles, retardation of austenite recrystallization and grain growth during stamping by Nb(C, N) particles (and Nb in solid solution), which leads to the formation of a fine final steel structure, as a result of which there is improvement of both strength properties and impact strength. Steel of the class in question may be produced by economic controlled stamping technology with cooling from rolling heating and subsequent tempering instead of heat treatment with quenching and separate heating and tempering. As a result, a unique set of properties is achieved: mechanical properties, brittle failure resistance, corrosion resistance, seismic resistance, fire resistance of long rolled product, building structure components, engineering components, oil recovery equipment, etc.

DEVELOPMENT AND COMMERCIAL INTRODUCTION OF TECHNOLOGY FOR DIFFERENTIATED HEAT TREATMENT OF RAILWAY RAILS WITH ROLLING HEAT UTILIZATION

The article presents the research results obtained during working out and industrial development of technology of the differentiated thermal treatment by air of railway rails with the use of heat of rolling heating. The work was performed in the conditions of JSC «EVRAZ ZSMK» during reconstruction of the rail manufacture. In the paper the authors describe the results of investigation of the influence of a chemical compound, modes of plastic deformation and thermal processing on the position of polymorphic transformation points, as well as the construction of thermokinetic diagrams of steels of a skilled chemical compound. Cooling rate on the section of a rail head depending on heat treatment parameters was investigated. The rational chemical compound and modes of thermal processing are defined. The experiments on thermal treatment of rail tests of rails were made directly after rolling. According to the results of the theoretical and laboratory data, the recommendations are developed for industrial introduction of technology of the differentiated hardening. The conducted industrial tests have shown high quality of rail production on all parameters of the specifications and technical documentation corresponding to the requirements.

Modeling of a Thermal Massive Body Depending on the Cooling Liquid Volume, as Exemplified by Rolls for a Hot-rolling Mill

Setting metal cooling systems at the development of the technology for rolling of thin strips is much more topical problem at the functional hot rolling mill. The solution of this problem was modernization of mill cooling systems. The next step after modernization is to adjust this system. At the same time, an important factor is also the thermal condition of a working roll for hot rolling. Various approaches are currently known including two main ones: the heat balance method and the thermal conductivity equation use.The heat balance method allows calculation of the average integral temperature of a roll blanket which is most subject to a temperature change. This method will allow definition of a roll heat intensity and the average integral temperature which are required for use of the following method.The thermal conductivity equation method allows operation of the factors influencing roll temperature at the mathematical level.Due to the reconstruction of cooling systems there are restrictions of cooling liquid volumes.In that way, at the moment, it is required to make a mathematical model of the “stand — cooling means” system. To develop the working system model, we have used the Scilab software environment.By means of the created model, data on the average temperature of a working roll blanket and the coolant flow to a stand in time have been obtained.Introduction of this model for production will allow reduction of the average working roll temperature by 4 – 8 on average, and also to reduce a coolant flow by 7 - 10 percent.

Technology of roll production for cold rolling of strip using electroslag remelting method

The article is concerned with the description of the manufacture of rolls for cold rolling of strip using electroslag remelting process and decommissioned rolls. It also describes modes of initial and final thermal treatment of work rolls providing the necessary hardness of the roll barrel and depth of the hardened layer. The article offers the scheme and experimental results aimed at electroslag remelting of decommissioned rolls in plant conditions at an industrial electroslag installation. The research group found the relationship between the slag bath height variation and the descending rate of the decommissioned roll acting as a consumable electrode into the molten slag bath in electroslag remelting process. The mold of new design for electroslag remelting was offered to provide higher surface quality of the cast ingot and to improve the quality of roll neck metal. The mode of enhanced roll production was developed to obtain a uniform fine-grain pearlite structure, which is necessary for the final thermal treatment. The offered mathematical models of the final thermal treatment make it possible to determine the optimal modes of roll thermal treatment, which will provide higher hardness of the roll face and the necessary structure of the hardened layer as well as its phase composition. The offered mathematical model of thermal cycling and roll heating for hardening allowed the authors to give theoretical justification of rational thermal treatment conditions, which contribute to formation of an active layer of the predetermined depth and hardness in the roll without causing its breakdown.

MATHEMATICAL MODELING OF THE THERMO-STRESSED CONDITION IN THE COLD WORK ROLLS DURING FAST HEATING IN THE CHAMBER FURNACE

A physical-and-mathematical pattern of calculation of the thermo-stressed condition of the cold work roll, being heated in the chamber fast (gradient) heating furnace for hardening of the working layer of the certain depth, has been demonstrated. The heating furnace consists of two sliding halves and is connected with the spraying unit. A roll subjected to heating runs on rollers and rotates during heating and hardening. Two heating conditions: forced one and more rational one, under which a speed of the roll heating is limited at the initial stage, have been compared. The authors have offered a steptype schedule of increasing the heating medium temperature during roll heating at which the maximum tensile stress does not exceed an acceptable value of 300 MPa. It is recommended to limit a heating speed at the initial stage of heat treatment to reduce the thermal stress.

Deep drawability improvement of two steps asymmetrically rolled and heat-treated AA7075 Al alloy sheet

AA7075 Al alloy sheet shows low r-value (plastic strain ratio) and low deep drawability. To increase average r-value ( -value) of AA7075 Al alloy sheets, the sheets were asymmetrically rolled and subsequently heat treated in a salt bath as the first action, followed by the second asymmetry rolling and subsequent heat treatment in a salt bath. The second 22% asymmetrically rolled and subsequent heat-treated AA7075 Al sheet shows 1·41 times higher average r-value (-value) than that of initial specimen. This result could be explained by the texture changes of AA7075 Al alloy sheet after two steps asymmetry rolling and subsequent heat treatment.

DEVELOPMENT OF METALL-SAVING MODES IN CONTINUOUS FURNACES FOR HEATING OF CONTINUOUSLY CAST BILLETS OF 60Si2CrA STEEL

Abstract. The paper presents the results of laboratory studies of scaling laws, the kinetics of high-temperature oxidation and decarbonization of 60Si2CrA steel. It has been established that the waste is intensifi ed sharply when the temperature of the metal is about 1000 °C. The appearance of the fi rst liquid-phase areas in the scale occurs at temperatures of 1270 – 1280 °C, and the melting of the scale, accompanied it to the runoff in metal surface begins at 1300 °C. The temperature range of the most intense decarbonization of steel is 950 – 1100 °C; at 1175 °C and above on the metal surface, the formation of the mixed zone thickness of 0,030 – 0,045 mm, complicating remove scale from the surface of the metal. The received empirical dependence helps to forecast the waste of metal during heating for rolling. For practical use, based on a deterministic mathematical model, a metal-saving temperature mode for heating of continuously cast billets in continuous walking-beam furnaces has been developed.

Effect of segregations on mechanical properties and crack propagation in spring steel

Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR) of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM) and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel.

Numerical investigation of roll heat pipe type for heat exchangers thermal management

Heat pipes cooling technology is currently spreading out for many applications such as electronic, solar energy, air conditioning systems, space applications, telecommunications, food industries, geothermal systems, heat recovery etc.In this work, two numerical studies have been developed to investigate the thermal performance of a novel type of heat pipe called “Roll heat pipe (RHP)”. Results show that RHP performs better than annular pipes often used in heat exchangers. The effect of boundary conditions on the heat pipe thermal resistance is investigated. Results reveal that the RHP thermal resistance decreases with the heat input and RHP thermal performance is controlled by the outer surface temperature. Heat transfer inside RHP can be enhanced when heat is extracted quickly from the condenser region. Result reveals also that a higher grade of isothermalisation can be obtained compared with conventional tubular heat exchanger for uniform or localized heat inputs in the evaporator region. The objective of this study is to better understand the thermal performance of RHP type for further heat exchanger applications or other designs processes that are transient or steady.

Characterization of Precipitates in 3xxx Series Alloys with Zirconium

The study presents the results of microstructure examinations and phase identification of precipitates in AlMn alloys containing zirconium after heat treatment and rolling. Chemical composition in microareas was determined by Energy Dispersive Spectrometry (EDS) microanalysis performed in Scanning Electron Microscope (SEM-EDS) and Scanning Transmission Electron Microscope (STEM-EDS) modes. Phase identification was carried out using Electron Backscatter Diffraction (EBSD) method. Studies have shown that Al6Mn and α- Al17(Fe3.2Mn0.8)Si2 phases were formed in the melt. Microstructure examined by TEM showed the presence of finely dispersed spherical precipitates of zirconium. In the alloy with an addition of silicon and magnesium, numerous precipitates of an Mg2Si phase were also found.

Microstructures and Mechanical Properties of Ti-6Al-4V Alloy Processed by Multi-Process

Abstract To understand the relationship among the processes, mechanical properties and microstructures of the Ti-6Al-4V alloy processed by the different combinations of ring rolling, bulging and different heat treatments, the correlation between the α- and β-phase morphologies, the strength and plasticity properties of tensile tests at ambient temperature and elevated temperature were investigated. Researches indicate that adding the second procedure, bulging, is necessary after the rolling process under the condition of the appropriate heat treatment. The tensile properties are closely related to the size and the volume fraction of the primary α-phase, the size and the thickness of the secondary α-phase. Furthermore, the bulging after heat treatment mainly affects firstly the size of primary α-phase, and the compositions of α- and β-phase, secondarily the size and the quantity of the secondary platelet α-phase. The elongation decreases when the primary α-phase transforms from the small equiaxed to the thick multilateral shape. As the volume fraction of the primary α-phase decreases and the proportions of both untransformed β structure and the dispersed secondary α-phase increase, the alloy strength increases. Fracture modes of the elevated temperature tensile fracture samples were determined as the ductile fracture. Poor plastic deformation ability is attributed to the casting micro-defects on the fracture surface.

Hydrogen Diffusion Characteristics in the TRIP 800 C-Mn-Si Steel

The presented paper is devoted to the study of hydrogen diffusion characteristics in the C-Mn-Si TRIP 800 steel. The steel was tested in three different states: in as-received state after hot and cold rolling and subsequent heat treatment; and furthermore after 5% and 10% tensile deformation. Hydrogen diffusion characteristics were studied by means of electrochemical permeation method. Two build up transients corresponding to lower and higher charging current densities as well as a decay transient were recorded during experiment. The lowest values of hydrogen diffusion coefficient (from 1 to 3.5.10-7 cm2.s-1) were observed during the first build up transient; the value of 3.5.10-7 cm2.s-1 corresponded to 10% tensile deformation. During the 2nd build up transient corresponding to the higher charging current density, hydrogen diffusion coefficients increased markedly reflecting thus the fact that hydrogen trapping was less pronounced. For decay transients hydrogen diffusion coefficients were situated between values obtained for the 1st and 2nd build up transients. In all studied states, a rather high sub-surface hydrogen concentration was observed during the 1st build up transient rising to 12.6 ppm of hydrogen in as-received state. The obtained results are explained taking into account steel microstructure and hydrogen trapping.

Microstructural Features Controlling Mechanical Properties in Nb-Mo Microalloyed Steels. Part II: Impact Toughness

The present paper is the final part of a two-part paper where the influence of coiling temperature on the final microstructure and mechanical properties of Nb-Mo microalloyed steels is described. More specifically, this second paper deals with the different mechanisms affecting impact toughness. A detailed microstructural characterization and the relations linking the microstructural parameters and the tensile properties have already been discussed in Part I. Using these results as a starting point, the present work takes a step forward and develops a methodology for consistently incorporating the effect of the microstructural heterogeneity into the existing relations that link the Charpy impact toughness to the microstructure. In conventional heat treatments or rolling schedules, the microstructure can be properly described by its mean attributes, and the ductile–brittle transition temperatures measured by Charpy tests can be properly predicted. However, when different microalloying elements are added and multiphase microstructures are formed, the influences of microstructural heterogeneity and secondary hard phases have to be included in a modified equation in order to accurately predict the DB transition temperature in Nb and Nb-Mo microalloyed steels.

Preparation of high-strength Al-Mg-Si-Cu-Fe alloy via heat treatment and rolling

Abstract An Al-Mg-Si-Cu-Fe alloy was solid-solution treated at 560°C for 3 h and then cooled by water quenching or furnace cooling. The alloy samples which underwent cooling by these two methods were rolled at different temperatures. The microstructure and mechanical properties of the rolled alloys were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and tensile testing. For the water-quenched alloys, the peak tensile strength and elongation occurred at a rolling temperature of 180°C. For the furnace-cooled alloys, the tensile strength decreased initially, until the rolling temperature of 420°C, and then increased; the elongation increased consistently with increasing rolling temperature. The effects of grain boundary hardening and dislocation hardening on the mechanical properties of these rolled alloys decreased with increases in rolling temperature. The mechanical properties of the 180°C rolling water-quenched alloy were also improved by the presence of β″ phase. Above 420°C, the effect of solid-solution hardening on the mechanical properties of the rolled alloys increased with increases in rolling temperature.