Thermal Conductivity Of Steel Research Articles

OPTIMAL PROFILE FOR A FIN OF CONSTANT CROSS SECTION WITH MODELATION OF THE THERMOPHYSICAL PROPERTIES

The dependence of the temperature and composition on thermal conductivity of steel, and its influence in the optimal profile for a fin of constant cross section to be used in air cooled condenser is presented. In Air Cooled Condensers (ACC), air is used as refrigerant, which forces the need for fins to improve the heat transfer process leading to appreciable increments in the costs of the installation. Therefore, developing better fins profile will allow optimizing the operation, maximizing the heat transfer and minimizing the manufacturing cost of the fins. To this objective, in the present paper, three geometric parameters, thickness, height and surface of heat transfer of the fin, this parameters influence directly the optimal obtained profile for conditions of maximum heat flux and optimal Biot number. The study was accomplished for fins of constant cross section. In a future work, fins of variable cross sections will be considered.

Experimental and Numerical Study of the Ice Storage Process and Material Properties of Ice Storage Coils

The coiled ice-storage-based air conditioning system plays a significant role in enhancing grid peak regulation and improving cooling economy. This paper presents theoretical and experimental studies conducted on the ice storage process of coiled ice storage air conditioning technology. The cooling of water is divided into two stages:10.0 °C to 4.0 °C and 4.0 °C to below 0.0 °C. Initially, the ice storage process forms an ice layer with a thickness of 2.50 mm on the lower surface of the coil, but eventually, the ice layer on the upper surface becomes 3.85 mm thicker than the lower surface as a result of the natural convection of water and density reversal at 4.0 °C. Furthermore, the impact of three coils with different thermal conductivity on the ice storage process was evaluated. It was observed that the thermal conductivity of R-HDPE (reinforced high-density polyethylene) was only 2.6 W/(m·K) higher than HDPE (high-density polyethylene), yet it reduced the freezing time by 34.85%, while the thermal conductivity of steel was 37.4 W/(m·K) higher than R-HDPE, but only decreased the freezing time by 9.40%. The results demonstrated that the rate of ice accumulation increased with thermal conductivity. However, when the coil material’s thermal conductivity surpassed that of ice, the further increase of thermal conductivity gradually weakened its impact on the ice storage rate.

Structure, thermal stability and transport properties of heat-resistant high-entropy ZrTiHfNb alloy

The problem of phase stability is one of the key problems in the study of high-entropy alloys. Here we address this issue for a heat-resistant high-entropy TiZrHfNb alloy with a bcc structure. The evolution of the structure of this alloy is studied during isothermal annealing at T=400oC. It was found that the as-cast alloy consists of two coexisting bcc phases with similar unit cell parameters. This state is homogenized during annealing. Still, the highly stressed nanostructured state is retained and the texture is enhanced. The thermal conductivity of the alloy in the temperature range of 20-400oC changes in the range of 8-16 W/m·K, which is comparable in order of magnitude with the thermal conductivity of steels. Keywords: high-entropy alloys, heat-resistant alloys, phase stability.

Effect of debris material composition on post accidental heat removal in a sodium cooled fast reactor

Following a core meltdown accident in a pool type sodium cooled fast breeder reactor (SFR), a debris bed is formed over the core catcher. The influence of initial material composition of the debris bed (consisting of fuel and steel) on the post accidental heat removal processes has been investigated in view of reactor safety. A one dimensional transient multiphase thermal model has been developed and employed for this purpose. The model includes sodium boiling, steel melting, fuel melting, slumping of molten particles and formation of molten pool. The overall steel fraction in the debris bed, the extent of steel stratification in the bed due to density difference between the debris particles and the overall porosity of the debris bed are considered as main parameters. It is seen that the assumption of a homogeneous initial mixture of fuel and steel in the debris bed yields a low core catcher plate (CCP) temperature compared to stratified debris beds where steel fraction increases with debris height. In a debris mixture with a low steel content (20% steel and 40% fuel), the peak temperature experienced by the CCP increases only marginally, from 872 K for homogeneous mixture to 900 K for a highly stratified mixture. But, in a debris mixture rich in steel content (30% steel and 30% fuel) the corresponding peak temperatures experienced by CCP are 886 K and 932 K respectively, suggesting that material stratification has significant effect in steel-rich debris mixture. For identical steel stratification profiles, the peak CCP temperature in a steel lean debris mixture is lower than that in a steel rich debris mixture. For 20% overall steel fraction, the peak temperature experienced by CCP is less than the creep limit of 923 K even for the worst stratification. But for 30% overall steel fraction, increasing the extent of steel stratification above a specific value results in CCP peak temperature exceeding the safe limit based on creep failure. Thus, the thermal load on the CCP increases with steel content though the thermal conductivity of steel is much higher than that of the fuel.

Структура, термическая стабильность и транспортные свойства жаропрочного высокоэнтропийного сплава ZrTiHfNb

The problem of phase stability is one of the key problems in the study of high-entropy alloys. Here we address this issue for a heat-resistant high-entropy TiZrHfNb alloy with a bcc structure. The evolution of the structure of this alloy is studied during isothermal annealing at T = 400 °C. It was found that the as-cast alloy consists of two coexisting bcc phases with similar unit cell parameters. This state is homogenized during annealing. Still, the highly stressed nanostructured state is retained and the texture is enhanced. The thermal conductivity of the alloy in the temperature range of 20–400 °C changes in the range of 8–16 W m K, which is comparable in order of magnitude with the thermal conductivity of steels.

SIMULATION OF FLUIDITY AND DENSITY OF CAST STEELS

As a result of the analysis of the formation processes of fluidity and the conditions for feeding the castings during cooling after solidification, a significant effect of the properties of the melt and the dispersion of the primary structure on the fluidity and density of steel was established. It is theoretically substantiated and experimentally confirmed that the level of fluidity and density is determined by the dispersion of the dendritic structure, the magnitude of the melt overheating over the liquidus temperature, as well as the properties of the liquid metal, the thermal conductivity of steel at the solidus temperature, crystallization heat and crystallization interval. The established quantitative laws describe the real process with a probability more than 95% and a high degree of reliability (R = 0,709-0,837; ð = 1,2 – 13,8%). The article shows that in order to increase the effectiveness of the influence of integral factors on the fluidity of structural steels, they can be arranged in the following sequence: thermophysical conditions of solidification, dispersion of the dendritic structure, properties of liquid metal. In this case, an increase in fluidity occurs with an increase in the overheating of the melt above the liquidus temperature, the heat of crystallization and the dispersion of the dendritic structure. An increase in the values of other factors leads to the opposite effect. Alloying elements are arranged in the following sequence: Si, Cr, Mn, C, V, N, V + N according to the specific efficiency of increasing fluidity. The results of the studies performed show that according to the effectiveness of the influence of the considered factors on the steel density, they can be arranged in the following sequence: dispersion of the dendritic structure, properties of liquid metal and thermalphysic conditions of solidification. Alloying elements affect these parameters in such a way that a complex multiextremal change in density is observed during alloying of steel. The general trend is that carbon and chromium decrease, while silicon, manganese, vanadium, nitrogen, and co-alloying with nitrogen and vanadium increase the density of the steel. Alloying elements can be arranged in the following sequence: V, Cr, Mn, Si, N, N + V, C to increase the specific efficiency of changing the density.

Effect of Si Content on the Formation of {100} <uvw> Orientation in 0.27% Al Non-oriented Electrical Steel during Cell-to-Dendrite Transition Process

The effects of Si content (0.73%, 2.23%, 4.57%) and solidification rate (10 µm/s, 35 µm/s, 80 µm/s) on the as-cast microstructure and crystal orientation of 0.27% Al non-oriented electrical steel have been studied by directional solidification technology. Si atoms were inclined to segregate on the trunks and stems of cells and dendrites, and precipitate in the form of quadrilateral Fe-Si particles with size less than 4 μm. Increasing Si content would lead to a decrease in thermal conductivity of steel and directly cause an increase in temperature gradient of liquid steel, and as a result, make solid–liquid interface more stable and easier to grow as cell crystal. Moreover, decreasing solidification rate could further aggravate Si segregation at solid–liquid interface. Higher Si content (4.57%) together with lower solidification rate (10 µm/s) was more beneficial to the grain nucleation with {100} orientation, whereas higher solidification rate (80 µm/s) played a major role in the grain nucleation with {110} orientation.

Effects of alloying elements and temperature on thermal conductivity of ferrite

The thermal conductivity of steel and cast iron is often much lower than that of pure ferrite. One of the main reasons is the addition of alloying elements, which reduces the thermal conductivity of ferrite. Based on the theory of metal heat conduction, relationships between the thermal conductivity of ferrite and contents of alloying elements as well as temperature are established. Then, the effects of alloying elements and temperature on the thermal conductivity of ferrite are quantitatively and qualitatively analyzed, respectively. At 300 K, the effects of Si and Al on the thermal conductivity of ferrite are significant, while the effects of Mn, Cr, and Mo are relatively small and that of W is the weakest. However, the superposition of another element may change the influence of an alloying element on the thermal conductivity of ferrite. Within 300–800 K, the temperature dependence of electrical resistivity for alloyed ferrite is much weaker than that of pure ferrite. Although the phonon thermal conductivity of ferrite decreases monotonously with temperature, the electron thermal conductivity of ferrite changes from monotonic decreasing to monotonic increasing with the addition of alloying elements. The overall impact will make the thermal conductivity of alloyed ferrite with temperature decrease monotonously at low alloying content, and the latter increase first then decrease at medium alloying content, and finally increase monotonously at high alloying content.

The possibility of simplified modelling of radiation heat transfer within a steel porous charge

The article refers to the problem of calculating the effective thermal conductivity kef of a steel porous charge. In proposed approach for each heat transfer mechanism, which occurs in the considered medium, the corresponding thermal resistance is assigned. The model values of the kef coefficient were determined twice for the same input data (geometric dimensions, emissivity, temperature, thermal conductivity of steel and gas). The difference between successive calculations depended on the use of two different methods to determine the thermal radiation resistance Rrd. In the first approach the resistance Rrd was calculated using the exact method and in the second approach the simplified, approximate method was used. The discrepancy between the obtained results of kef in both approaches provides the evidence to use the approximate method to determine the resistance Rrd. A bundle of square steel sections were used to demonstrate the challenge. In the exact method, data regarding the temperature distribution within a single profile was used. These data were obtained based on experimental research using a guarded hot plate apparatus. The calculations were performed using a temperature range between 200ºC and 800ºC for two sections: 60×60mm and 80×80mm and three emissivities: 0.5, 0.7 and 0.9.

Diffusion processes during cementite precipitation and their impact on electrical and thermal conductivity of a heat-treatable steel

The thermal conductivity of heat-treatable steels is highly dependent on their thermo-mechanical history and the alloying degree. Besides phase transformations like the martensitic upgamma rightarrow upalpha ^{prime } or the degree of deformation, the precipitation of carbides exerts a strong influence on the thermal conductivity of these steels. In the current work, thermal and electrical conductivity of a 0.45 mass% C steel is investigated during an isothermal heat treatment at 700 ^{circ }C and correlated with the precipitation kinetics of cementite. To include processes in the short-term as well as in the long-term range, annealing times from 1 s to 200 h are applied. This investigation includes microstructural characterization, diffusion simulations, and electrical and thermal conductivity measurements. The precipitation of carbides is connected with various microstructural processes which separately influence the thermophysical properties of the steel from the solution state to the short-term and long-term annealing states. In the early stages of cementite growth, an interstitial-dominated diffusion reaction takes place (carbon diffusion in the metastable condition of local equilibrium non-partitioning). Afterwards, substitutional-dominated diffusion controls the kinetics of the reaction. The electrical and thermal conductivity increase differently during the two stages of the carbide precipitation. The increment is associated to the binding of alloying elements into the carbides and to the reduction of the distortion of the martensitic matrix. Both factors increase the electron density and reduce the electron and phonon scattering. The correlation of the precipitation kinetics and the thermophysical properties are of general interest for the design of heat-treatable steels.

Gallium as a Metrology Substance for Measuring Thermal Conductivity of Metals

In the presented work the effective thermal conductivity of steel was received from the simple experiment in which the change of phase metrology-matter was applied [1]. As the metrology-matter gallium was used.The change of phase process plays role of the heat source. During the change of phase period the temperature is constant. A quasi-stationary temperature fields allows to use the stationary model of heat transfer calculations. The model is a cylindrical rod of finite length losing heat out one face to melting-substance and by radiation from surface, respectively. All process measurement was carried out in vacuum. Measurement of thermal conductivity quasi-stationery method is practiced at the Department of Thermodynamics at Rzeszow University of Technology. This method has application in measurement of thermal conductivity of good conductors.

EXPERIMENTAL STUDY OF THE ROLLING–SLIDING CONTACT CONDITIONS IN A PA66/STEEL GEAR USING TWIN-DISC TEST RIG: FRICTION AND WEAR ANALYSIS

This study investigates the effects of sliding ratio on the tribological response of the contact between the teeth of a metal/polymer gear in the regions close to the pitch point. For this purpose, a new twin-disc test rig was developed on the basis of two discs of different diameters rotating one above the other at the same angular speed. Two different materials were used: non-alloyed structural steel (C45) and polyamide (PA66). The effect of the slip ratio (4%, 12%, 20% and 28%) was studied at a constant pressure of 34 MPa and a constant angular speed of 300 rpm. In addition, the contact conditions were controlled with measurements of the two discs surface temperatures. The results indicate that the wear and the friction are closely related to the contact temperature generated by the sliding phenomenon. At low slip ratio (4% and 12%), the coefficient of friction and the temperature are characterized by a quasi-linear increase with time, and the wear increases slowly. At higher slip ratio (20% and 28%), the coefficient of friction and the temperature presents a steady state, and the wear increases dramatically. During the test, a film of transferred PA66 is formed on the steel surface causing the development of adhesive interactions between the contacting discs which increase the friction coefficient and the contact temperature. The high thermal conductivity of steel as compared to that of the polymer can reduce enormously the contact temperature generated by the sliding process.

Effects of calculation approaches for thermal conductivity on the simulation accuracy of billet continuous casting

An unsteady, two-dimensional, explicitly solved finite difference heat transfer model of a billet caster was presented to clarify the influence of the thermal conductivity of steel on model accuracy. Different approaches were utilized for calculating the thermal conductivity of solid, mushy and liquid steels. Model results predicted by these approaches were compared, and the advantages of advocated approaches were discussed. It is found that the approach for calculating the thermal conductivity of solid steel notably influences model predictions. Convection effects of liquid steel should be considered properly while calculating the thermal conductivity of mushy steel. Different values of the effective thermal conductivity of liquid steel adopted could partly be explained by the fact that different models adopted dissimilar approaches for calculating the thermal conductivity of solid and mushy steels.

Investigation on the Welding Temperature Field Measurement in Gas Tungsten Arc Welding

Based on the gas tungsten arc welding process this paper investigated the welding temperature field measurement and simulation of 945 steel plate and AZ31B magnesium alloy, using a non-contact and fast response measured temperature method-Infrared Radiation (IR)-which utilized the baffle to remove the arc and hot tungsten electrode interference, the top-face temperature of AZ31B magnesium alloy plate and 945 steel plate. The results indicated that the lengthwise isothermal map of 945 steel plate is much longer than that of AZ31B magnesium alloy plate, which leads to the most temperature field information loss, this is because the thermal conductivity of steel is small and decreases with temperature increase, the thermal conductivity of AZ31B magnesium alloy is much bigger that that of the 945 steel, about 1.5 times of 945 steel, and increased with temperature increase. The results also showed using IR to measure the welding temperature of magnesium alloy is more difficult than 945 steel. Keywords: magnesium alloy, high strength steel, welding temperature field, IR

Low-energy high-current electron beam heating of target with second-phase microinclusions

The temperature field generated by microsecond pulsed low-energy high-current electron beam (LEHCEB) in the surface layer of a stainless-steel target containing second-phase (manganese sulfide, MnS) microinclusions has been numerically simulated. The results of calculations show that the temperature is nonuniformly distributed over the target surface. By the end of the LEHCEB pulse, the temperature in the regions of MnS inclusions significantly exceeds that of the steel matrix. This nonuniformity is related to (i) markedly greater thermal conductivity of steel compared to that of MnS and (ii) the pulsed character of the electron-beam-induced heating of the target surface. It is also established that LEHCEB-induced melting begins at the inclusion-steel interface and then involves the inclusion and spreads over the entire irradiated surface. The dependence of the characteristics of the irradiation-induced temperature field on the parameters of the pulsed electron beam has been studied.

Effect of Firing Method on the Acoustic Properties of Carbon Billets and their Uniformity

The advantage is demonstrated of container firing of large billets of electrode graphite compared with the traditional firing method for such billets in carbon packing, distinguished by considerable thermal inertia as a result of low thermal conductivity. Firing in containers makes in possible to increase billet uniformity and reduce the level of their defects as a result of reducing temperature drops provided by the high thermal conductivity of steel from which the container is manufactured. An increase in billet uniformity in this case is convincingly demonstrated by ultrasonic studies.

Electrical resistivity and thermal conductivity of tool steels at operating temperatures

1. In the annealed and heat treated condition steel R18 has the lowest thermal conductivity. 2. Reduction of the tungsten content (R9) increases the thermal conductivity at low temperatures. 3. Replacing part of the tungsten with molybdenum substantially increases the thermal conductivity at low temperatures. 4. The lower the thermal conductivity at low temperatures, the higher the temperature coefficient of thermal conductivity, which holds true for austenitic, highly alloyed, and carbon steels (in the latter the temperature coefficient of thermal conductivity is negative). 5. During heating the thermal conductivity of the high-speed steels investigated (except for those with cobalt) becomes almost identical. At 800–900°C, i.e., near the critical points, steels R18, R9, and R6M3 have approximately the same thermal conductivity. In the heat treated condition the thermal conductivity of these steels is already approximately the same at 550–600°C. 6. The addition of cobalt to high-speed steels slightly increases the thermal conductivity at room temperature and strongly increases the temperature coefficient of thermal conductivity. At operating temperatures of 500–600°C the thermal conductivity of heat treated steel R9K10 is 30% above that of R18 at the same temperatures, which is responsible (along with the higher red hardness) for the higher cutting properties of cobalt high-speed steels.

Thermal conductivity of some steels at low temperatures

Synopsis The measurements made in the Kamerlingh Onnes Laboratory on the thermal conductivity of steels at low temperatures were extended to liquid helium temperatures and the technique was improved. Five specimen of different composition and heat treatment have been investigated. The lattice conductivity is approximately proportional to T1.2. With increasing nickel content from 2% to 27% (Ni + Cr) it decreases by about 60, 58 and 37% at the temperatures 70, 20 and 4k respectively. The electronic thermal conductivity decreases by about 80% for the mentioned temperatures.