Search

Cast steel parts can realize rapid prototyping effectively, which is suitable for complex structural design. However, due to the large residual stress, the problem of mechanical property degradation is more obvious. In order to solve this problem, a high temperature excitation vibration treatment scheme is proposed in this paper. By applying different excitation frequencies and impact forces, the effects of mechanical properties and stress corrosion properties are studied and verified. Based on the finite element software ANSYS, the modal shape and resonant frequency of the cast steel parts are obtained, and verified by the sweep frequency module in the excitation vibration system. According to the characteristics of modal shape, five typical detection paths are set, and stress sensors are arranged every 200 mm. In order to obtain the specific effects of excitation frequency and impact force amplitude on mechanical properties, nine parts samples were prepared on the same production line according to the matching requirements of test parameters. In addition, the main external parameters that remain unchanged during vibration excitation are set as initial 750 ℃ and vibration excitation time of 60 s, which can fully affect the effect of austenite transformation. Keeping the synchronization of test parameters in different samples, the distribution rules of residual stress under different excitation frequencies and forces are obtained and analyzed. In the aspect of mechanical properties, the microstructure, hardness, yield strength and tensile strength of the specimens subjected to vibration were compared and analyzed. In the aspect of stress corrosion performance research, stress corrosion cracking test was carried out in weak acid environment to obtain the tensile stress curve and fracture morphology of the specimen. The results show that the excitation vibration at high temperature can effectively eliminate the residual stress of cast steel parts, but the increase of excitation frequency does not correspond to the effect of residual stress elimination. When the exciting force exceeds a certain value, the stress relief effect cannot be further improved. Excitation vibration can reduce the internal hardness of cast steel parts to a certain extent, and improve the yield strength and tensile strength. At the same time, it has a positive role in promoting the improvement of stress corrosion resistance. [ABSTRACT FROM AUTHOR]

The submerged entry nozzle (SEN) plays an important role in the continuous casting production process. It is a cast refractory pipe fitting installed in the lower part of the tundish and inserted below the molten steel level of the mold. It not only affects the speed of molten steel flow, but is also prone to nodules and affects production. In the present work, the flow behavior of molten steel in a traditional nozzle and that in a new type of nozzle whose inner wall was distributed with arrays of hemispherical crowns were studied by means of both physical simulation (using a water model) and numerical simulation (using ANSYS CFX) based on the prototype of a production continuous casting slab mold. Both experimental and numerical simulation results show that, compared with the traditional nozzle, the impact depth generated by the new-type nozzle in the mold is reduced by 21.06–26.03 cm, the impact angle is reduced by 14–17 degrees, and swirl flow was generated inside the new-type nozzle, which not only improves the flow characteristics inside the submerged entry nozzle and changes the dead zone size in the submerged entry nozzle, but also improves the velocity distribution at the outlet of the nozzle and minimizes the possibility of nodulation. In addition, in contrast to the traditional nozzle that generates flat body-shaped jets of molten steel flow, the new-type nozzle produces baseball glove-shaped jets that penetrate shallower into the molten steel bath in the mold, which significantly reduces the outlet velocity and is conducive to the floating of inclusions. [ABSTRACT FROM AUTHOR]

This research was devoted to unveiling the strain rate sensitivity (SRS) of G18NiCrMo3-6 cast steel in tension/compression asymmetry. For that purpose, detailed mechanical characterization tests were conducted providing a process window covering quasi-static and medium strain rate regimes (0.001, 0.1, 10 [s−1]) in tension and compression states. Through this experimental effort, the SRS of the material could be extracted by a function of strain and the strain rate which enabled us to create a mathematical expression to easily be implemented as a state variable for constitutive material modeling. Finally, a pressure- and rate-dependent constitutive material model on the basis of the Cocks'89 yield locus definition was created using a subroutine (UMAT) file and the material parameters were verified with respect to the experimental data. The UMAT file also takes into account the tension/compression asymmetry in yielding to handle the effect of the porous media plasticity concept. The predictions of the proposed material model are in line with the experimental outputs. [ABSTRACT FROM AUTHOR]

In this paper, a micromechanical model was developed to predict the residual stress–strain state that is generated around nodules of a ferritic ductile cast iron during solidification. A finite element analysis was performed on a reference volume element of the material to analyze the local strain development, having modeled both matrix and nodule as deformable bodies in contact. The behavior of the nodule was assumed linear–elastic because of the low stresses to which it is subjected during cooling. On the other hand, elasto-plastic viscous behavior was considered for the matrix, considering both the primary and secondary creep regimes. To make up for the lack of information on the physical–thermomechanical properties of the constituents, the available literature data were integrated with the results obtained from the CALPHAD methodology applied to both cast iron and the steel that constitutes its matrix. The micromechanical model was validated by comparing the resulting residual strains with experimental data available in the literature for a ferritic ductile cast iron. Then, it was used for analyzing the correlation between the solidification history and the mechanical response of cast iron in terms of the uniaxial stress–strain curve. [ABSTRACT FROM AUTHOR]

The submitted article deals with the use of physical and numerical modelling to study the process of the steel flow in an asymmetric five-strand tundish that continuously casts steel. For the purposes of physical modelling, a 1:4-scale plexiglass model was used as the operating tundish, and for numerical modelling, the geometry of the operating tundish was created on a 1:1 scale. A model liquid (water) was used in the physical modelling of the melt flow process, while liquid steel was used as the standard flowing medium in the numerical modelling. We assessed the relevant operating parameters influencing the characteristics of the flow of the bath in the tundish—the shape of the turbulence inhibitor, the position of the ladle shroud in relation to the turbulence inhibitor and the distance between the ladle shroud orifice and the bottom of the turbulence inhibitor. The preliminary results show that optimal steel flow characteristic results are achieved by using the TI3-C configuration. The results from both modelling methods achieved the same characteristics, therefore verifying the results of each other and demonstrating that when taken together, the results of physical and numerical modelling can be considered sufficiently informative. [ABSTRACT FROM AUTHOR]

Erosion testing was conducted on cast steel and spheroidal graphite cast iron specimens containing large amounts of manganese and several other ferrous materials in molten aluminum alloys. Based on the results, the erosion resistance of ferrous materials with a high-Mn content was quantified, and the resistance mechanism was investigated. The erosion ratios of high-Mn-containing ferrous specimens were lower than those of specimens that did not contain a high amount of Mn. An analysis of the chemical compositions in the vicinity of the contact interfaces of the high-Mn-containing specimens after testing revealed that the manganese-to-iron content ratios in the intermetallic layers were largely the same as those in the specimens and that the ratios in the melts (solidified) were greater than those in the specimens and intermetallic layers. This small-scale enrichment of manganese could be attributed to its lower diffusion rate compared to iron. In addition, the calculated isothermal phase diagrams corresponding to the testing temperature showed that the apparent saturation solubility of iron in the molten aluminum alloys decreased with the manganese content, irrespective of the silicon content in the melts. These results suggest that the local decrease in the saturation solubility of iron in the melts owing to the small-scale enrichment of manganese in the vicinity of the solid–liquid interface can improve the erosion resistance of specimens containing a high amount of manganese. [ABSTRACT FROM AUTHOR]

The paper presents the research results on duplex corrosion-resistant chromium–nickel–molybdenum cast steel of the GX2CrNiMoCuN 25-6-3-3 grade. The aim was to determine the effect of the soaking temperature for the hyperquenching process Tp, that is, 950 to 1200 °C, on the microstructure and mechanical properties, that is UTS tensile strength, the yield strength, HB Brinell hardness, the elongation EL and impact strength KV of the steel, cast under industrial conditions with the minimum content of Cr, Ni, Mo and Cu according to the PN-EN 10283 standard. On the basis of the results, it was confirmed that the hyperquenching guarantees the elimination of the brittle intermetallic phase in the steel microstructure. In addition, the most favorable strength-to-ductility ratio of the steel with an almost equal amount of austenite γ and ferrite α in its microstructure was obtained using the soak temperature of 1080 °C, which was considered optimal for the above-mentioned duplex cast steel. [ABSTRACT FROM AUTHOR]

Transverse corner cracks were encountered in plain carbon-manganese structural grades with 0.16–0.18% C during continuous casting. The thermo-mechanical stresses present during bending and straightening in secondary cooling regime along with ductility drop in specific temperature ranges was suspected to be the major aggravating factor leading to corner cracks in slabs. Their role was investigated through two-step compression tests wherein the specimens are deformed in two stages to generate secondary tensile strains similar to the ones present at slab corners during continuous casting. The tendency for corner cracking was found to be very high in the temperature range of 850–750 °C. The cracks were found to be intergranular occurring post austenite to ferrite transformation start temperature. The presence of non-metallic inclusions along the grain boundary leads to the formation of micro-fissures which coalesce under the action of external stresses and lead to cracks. It was identified that specimens failed at hoop strains much higher than the critical limit. The presence of excessively high thermo-mechanical stresses due to misalignment of caster roll segments was identified as the major factor causing corner cracks. Accordingly, corrective actions were taken which resulted in reducing the problem in all the affected grades. [ABSTRACT FROM AUTHOR]

The potential impact of concrete mixtures containing steel slag (SS) as a partial replacement of natural aggregates (NA) on the terrestrial ecosystem was assessed using a battery of plant‐based bioassays. Leaching tests were conducted on four concrete mixtures and one mixture containing only NA (reference concrete). Leachates were tested for phytotoxicity using seeds of Lepidium sativum, Cucumis sativus, and Allium cepa. Emerging seedlings of L. sativum and A. cepa were used to assess DNA damage (comet test). The genotoxicity of the leachates was also analyzed with bulbs of A. cepa using the comet and chromosome aberration tests. None of the samples caused phytotoxic effects. On the contrary, almost all the samples supported the seedlings; and two leachates, one from the SS‐containing concrete and the other from the reference concrete, promoted the growth of C. sativus and A. cepa. The DNA damage of L. sativum and A. cepa seedlings was significantly increased only by the reference concrete sample. In contrast, the DNA damage in A. cepa bulbs was significantly enhanced by the reference concrete but also by that of a concrete sample with SS. Furthermore, all leachates caused an increase in chromosomal aberrations in A. cepa bulbs. Despite some genotoxic effects of the concrete on plant cells, the partial replacement of SS does not seem to make the concrete more hazardous than the reference concrete, suggesting the potential use of SS as a reliable recycled material. Environ Toxicol Chem 2023;42:2193–2200. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The new cast steel with a chemical composition of Fe-(0.85-0.95)C-(1.50-1.60)Si-(2.40-2.60)Mn-(1.0-1.2)Al-(0.30-0.40)- Mo-(0.10-0.15)V-(1.0-1.1)Ni (all in wt.%) was investigated in aspect of formation of the multiphase microstructure leading to high strength and ductility. Two types of heat treatment technologies were developed. The first one involves softening annealing at a temperature of 650°C for 4 hours, heating up to 950°C and holding for 2 hours, and then fast cooling down to 200°C and isothermally treated for 2 hours. The second one involves homogenizing annealing at 1100°C for 6 hours, then cooling with furnace down to 950°C and holding for 2 hours, then fast cooling down to 200°C and isothermally treated for 2 hours. A unique microstructure of cast steel consisting of martensite and retained austenite plates of various thicknesses and volume fractions was obtained. Additionally, nanometric transition carbides were noticed after the above-mentioned heat treatments. This microstructure ensures high hardness, strength and plasticity (Rm = 1426 MPa and A = 9.5%), respectively, due to the fact that TWIP/TRIP processes occur during deformation related to the high volume fraction of retained austenite, which the stacking fault energy is above 15 mJ/m–2 resulting from the chemical composition of the investigated cast steel. [ABSTRACT FROM AUTHOR]

The corrosion fatigue crack propagation (FCP) of the butt weld with G20Mn5QT cast steel and Q355D steel in 3.5‐wt% NaCl solution was investigated experimentally. Considering the influences of stress ratio and loading frequency, the corrosion FCP rate curve was obtained. The results indicated that the corrosion FCP rate in the corrosion environment is three times that in air. Increasing the stress ratio or decreasing the loading frequency will increase the corrosion FCP rate. The fracture morphology of the specimens in the corrosion environment had more corrosion pits and intergranular characteristics due to anodic dissolution than that in air. Anodic dissolution and hydrogen embrittlement jointly promoted the corrosion FCP of butt weld in simulated seawater. The corrosion FCP rate model was established considering the effects of stress ratio and loading frequency. Highlights: Corrosion accelerated corrosion fatigue crack propagation (FCP) significantly.The corrosion FCP rate increases with the increase of R and the decrease of f.The mathematical model of corrosion FCP rate of butt weld is proposed. [ABSTRACT FROM AUTHOR]

This paper investigates a novel joint method for connecting rectangular hollow section (RHS) members in reticulated shells. It is proposed to overcome the problem of connecting rectangular tubes using the traditional joint (cast steel joint) under dead and snow load. A case study is a structure in the eastern region of Turkey that was built on August 20, 2019. This museum-style structure is 40 meters long and 20 meters wide, with an oval shape. In the middle of the building, five tree-shaped columns were used. ANSYS is used to create a refined 3D solid model of the RHS joint. The moment-rotation results show that the proposed RHS joint (plate steel joint) for connecting rectangular hollow section members can be considered a semi-rigid connection and preferred due to its lower cost and weight. Moreover, the dissipated energy capacity has been raised by approximately 3.22 times when the plate steel type model has been used instead of the cast steel type. The stress ratios indicate that the connection stress in the Cast steel type model is lower than the stress in the Plate steel type model. As a result, the Cast steel type model is determined to be incredibly safe and more rigid than plate steel. Furthermore, since the resulting stress rates are lower than those of S355 steel, both models (cast and plate steel type models) can be used for connecting RHS. [ABSTRACT FROM AUTHOR]

Cast martensitic alloy steel is used for the production of parts and components of machines operating under conditions of abrasive wear. One of the most popular grades is cast steel GX70CrMnSiNiMo2 steel, which is used in many industries, but primarily in the mining and material processing sectors for rings and balls operating in the grinding sets of coal mills. To improve the abrasion resistance of cast alloy tool steel, primary titanium carbides were produced in the metallurgical process by increasing the carbon content to 1.78 wt.% and adding 5.00 wt.% of titanium to test castings. After alloy solidification, the result was the formation of a microstructure consisting of a martensitic matrix with areas of residual austenite and primary titanium carbides evenly distributed in this matrix. The measured as-cast hardness of the samples was 660HV and it increased to as much as 800HV after heat treatment. The abrasion resistance of the sample hardened in a 15% polymer solution increased at least three times compared to the reference sample after quenching and tempering. [ABSTRACT FROM AUTHOR]

The article presents the results of metallographic and tribological tests on GX120MnCr13 cast steel that was previously subjected to heat treatment (including solution treatment from 1100°C and isothermal holding at 250, 400, and 600°C for 100 hours). The temperatures of the isothermal holding process were selected in order to reflect the possible working conditions of the cast elements that can be made of this cast steel. Wear tests were carried out under dry friction conditions using the ball-on-disc method using a ZrO2 ball as a counter-sample. The tests were carried out with a load of 5 N. The influence of the long-term isothermal holding process on the microstructure of the tested cast steel was analysed by light and scanning microscopy; however, abrasion marks were also examined using a confocal microscope. Based on the tests conducted, it was found that in the microstructures of the sample after solution treatment and samples that were held in isothermal condition at 250 and 400°C, the grain boundary areas were enriched in Mn and Cr compared to the areas inside the grains. Pearlite appeared in the sample that was heated (or held in isothermal holding) at 600°C; its share reached 41.6%. The presence of pearlite in the austenitic matrix increased the hardness to 351.4 HV10. The hardness of the remaining tested samples was within a range of 221.8-229.1 HV10. Increasing the hardness of the tested cast steel directly resulted in a reduction in the degree of wear as well as the volume, area, and width of the abrasion marks. A microscopic analysis of the wear marks showed that the dominant process of the abrasive wear of the tested friction pair was the detachment and displacement of the tested material through the indentation as a result of the cyclical impact of the countersample. [ABSTRACT FROM AUTHOR]

In this paper, an experimental Mg-Al-RE-type magnesium alloy, named AEZ951, is presented. The chemical composition of the investigated alloy was ca. 9 wt% Al, 5 wt% RE (rare earth elements), 0.7 wt% Zn and 3 wt% Mn. The experimental material was gravity cast into a cold steel mould. Microstructure analyses were carried out by light microscopy, along with X-ray phase analysis and scanning electron microscopy with an energy-dispersive X-ray spectrometer (SEM + EDX). Detailed investigations disclosed the presence of primary dendrites of an α(Mg) solid solution and Al11RE3, γ and Al10RE2Mn7 intermetallic compounds in the alloy microstructure. The volume fraction of the Al11RE3 phase and α+γ eutectic was also presented. The hardness, impact strength, tensile strength as well as the yield strength of the alloy were examined in tests at room temperature. The examined experimental Mg-Al-RE-type magnesium alloy exhibited higher mechanical properties than the commercial AZ91 alloy (cast in the same conditions). [ABSTRACT FROM AUTHOR]

In this study, a droplet solidification technique was used to simulate the process of sub-rapid solidification and film deposition phenomenon in strip casting of boron-containing steel, and studied the effect of boron on the formation of the naturally deposited film and its corresponding interfacial heat transfer behavior. The results indicated that boron modified the surface tension of molten steel, thus increasing the interfacial wettability between the molten steel and substrate surface with the final contact angle decreasing from 102 to 89 deg, and improving the related heat transfer with maximum heat flux increasing from 6.23 to 9.11 MW/m2. The deposited film was mainly composed of elements O, Fe, Si, Mn, B, and Cr. The increasing boron content made the deposited film particles melt faster and fuse more easily. Furthermore, the deposited films of the experiments with high boron content were thicker under the same deposition times; meanwhile, with the increase of boron content, the surface roughness of the deposited film increased gradually. In addition, the interfacial heat transfer behavior was mainly related to interfacial wettability and deposited film. Also, the deposited film composed of uniformly distributed small particles was better than tiny floccule or large clusters, and the relatively good film thickness was about 3.3–4.0 μm [ABSTRACT FROM AUTHOR]

The area around the solidification hook for low-carbon steel continuous casting slab is divided into four zones: zone A (the overflow zone), zone B (the capture zone), zone C (the zone between oscillation marks) and zone D (the oscillation mark zone without hook). The inclusions and microstructures in the zones of A, B, C and D are observed and detected. The results indicate that the inclusions captured by the solidification hook are Al2O3, MnO and MnO + MnS. The number densities of Al2O3, MnO and MnO + MnS in the zone B are all higher than those of the same types of inclusions in the other zones, indicating that the solidification hook have no tendency to just catch a certain type of inclusions. The proportion of the inclusions greater than 5 μm in the zone B is close to 40 pct, and those in the other zones are less than 12 pct, indicating that the solidification hook is easy to capture the inclusions greater than 5 μm. Besides, the grains near the oscillation marks on the zones of A, B and D are mostly with <111> orientation, while the grains in the zone C are mainly with <101> orientation and the proportion of the grain boundaries with low angle in the zone C is the largest. Thus, the grain orientations and grain boundary angles are affected by the oscillation marks. There are lots of small grains in the zone B because inclusions can hinder the movement of grain boundaries during grain growth. The temperature marangoni force and buoyancy force are the decisive forces whether the solidification hook can capture the large inclusions or not. [ABSTRACT FROM AUTHOR]

Niyama and solid fraction criteria are used to predict the solidification porosity and microporosity in computing simulation of casting processes. The solid fraction permits us to determine the areas that solidify last and that are a candidate for presenting porosity if a feeding system is not correctly designed. The Niyama criterion is locally obtained based on the thermal and cooling gradients at a point of the liquid casting. The Niyama value at a casting point varies rapidly from low rates to high ones during the last part of the metal solidification, which demands that the percentage of solidification of the metal is defined to determine the Niyama number. In addition, the Niyama threshold that establishes the soundness of the workpiece can vary according to the nature of the metal or the casting system. In this paper, a methodology to determine the solidification percentage is presented. The method is based on the Niyama number evolution during the solidification process at different key points. These points are validated by the solid fraction criterion as healthy or, on the contrary, as candidates for containing porosity. In addition, some considerations of the solid fraction criterion are visited since the threshold value for which the isolation of the last solidification areas can be defined is not clear. The research is validated by the empirical casting criteria existing in the literature for obtaining sound parts and applied to low-carbon steel bars produced by sand casting. [ABSTRACT FROM AUTHOR]

Previous studies have underlined the importance of establishing a database of high‐fidelity benchmark experimental test results under random loading histories such as earthquake excitations for both existing structural systems as well as newly proposed ones. Such experimental results are useful for understanding the limitations of previously developed numerical models, proposing new numerical models for more recently developed structural systems, better assessing the ultra‐low cycle fatigue (ULCF) life of energy dissipative components, and improving the loading protocols used for element assessments or developments of numerical model. This paper presents experimental results from pseudo‐dynamic hybrid simulations on steel eccentrically braced frames (EBF) equipped with novel cast steel replaceable modular yielding links. The first set of experiments are carried out on a four‐story EBF, with the first‐floor yielding link physically tested in the laboratory. The second set of experiments are performed on a two‐story EBF where the second‐floor link is physically tested in the laboratory, while considering axial loads due to the imbalanced distribution of the seismic weight in the building. Each building structure is subjected to three Maximum Credible Event (MCE) level earthquakes. A framework for performing hybrid simulations on EBFs is proposed where the response of the yielding link is physically captured in a single degree of freedom control system, with or without axial loads. A substructuring strategy is proposed in conjunction with a modeling approach in the integration module. The results confirm the effectiveness of the hybrid simulation framework, which can be adopted in similar studies. Two numerical models are proposed for capturing the response of cast steel links using a simplified and a more advanced approach. The models are first calibrated using incremental reversed‐cyclic experimental test results, and then refined using the hybrid simulation test results. The effects of this calibration improvement are quantified through critically comparing the response prediction for different response parameters before and after improving the calibration with the experimental results. The numerical model which captures the physical mechanism of the cast steel links provides a more accurate response prediction compared to the simplified numerical model using a phenomenological truss with calibrated force‐deformation. The remaining ULCF life of the tested yielding links is experimentally investigated after having sustained three MCE level earthquakes, which indicates a large reserve ductility capacity which is more than twice the required plastic rotation capacity for cast steel links after seismic events. [ABSTRACT FROM AUTHOR]

Steel is mainly produced through continuous casting; molten steel flows into the mold from the tundish, where it cools and then enters the secondary cooling zone, ultimately solidifying into a billet. During the continuous casting production process, the quality of the casting billet is mainly related to the lubrication state of the coated slag. In the upper part of the mold, the consumption of liquid protective slag directly affects the friction state of the initial solidified billet shell. Therefore, the flow and fluctuation characteristics of coated slag in the meniscus area are very important. There is limited research on the flow and fluctuation characteristics of coated slag in the meniscus area, and little consideration has been given to the shape of the meniscus. In this work, a two-dimensional numerical model for the flow and fluctuation of coated slag in the meniscus region was established, and the transient flow velocity of protective slag and molten steel at each moment of the vibration cycle was obtained, as well as the fluctuation of the slag/steel interface in the meniscus region. The results show that when the surface mold vibrated upwards, the protective slag in the meniscus area flowed clockwise. When the mold moved downwards, the protective slag in the slag pool generated a counterclockwise flow vortex. When the mold was in a positive slip state, the negative pressure formed by the upward flow of the protective slag on the meniscus and the inertia force of steel liquid pushed the meniscus toward the inner wall of the mold. During negative slip, the flow of coated slag generated positive pressure on the slag/steel interface, pushing the meniscus toward the steel liquid, and at the initial moment of negative slip, the steel liquid overflowed into the slag channel. This model could provide a theoretical basis for the flow control of protective slag. [ABSTRACT FROM AUTHOR]

Two novel concepts, recently developed in North America, are presented for bolted splices between Rectangular Hollow Section (RHS) column members. Single‐sided bolting through the RHS wall is performed, but using regular high‐strength bolts rather than "blind bolts". The first concept employs nut‐holding devices, called "Shurikens", that are pre‐installed on four splice plates fitted to the inside of the two RHS columns. The second innovation is a custom‐designed, hollow, cast steel insert – made of nut‐quality steel – that extends into both the upper and lower columns and has threaded holes to receive the inserted bolts, in lieu of nuts. This "internal plug" is a pre‐engineered solution, tailored to a particular RHS size, and requires no connection design. For both concepts, a bolted shear connection with little protruding steelwork is the result. [ABSTRACT FROM AUTHOR]

The laws governing the influence of a hydrogen atmosphere at a pressure of up to 15 MPa with controlled total oxygen and water vapor content of up to 0.004 g/m3 and pre-absorbed hydrogen on the strength and ductility characteristics, short-term and long-term static crack resistance of 05Kh13N8M3 cast martensitic steel (in wt.%: 0.045 C, 0.38 Si, 12.9 Cr, 2.69 Mo, 0.43 Mn, 7.8 Ni, 0.057 La) at room temperature were studied. After hydrogen pre-charging for 4 h at a temperature of 773 K and a pressure of 5, 10, and 15 MPa, the hydrogen content of the specimens determined with a LECO TCH 600 device by infrared adsorption with melting was 3.3, 4.9, and 7.6 ppm, respectively. It was found that under short-term loading, the intensity of the effect of hydrogen on the fracture toughness of steel increases with an increase in the absorbed hydrogen content, crack sharpness, and a decrease in the loading rate. At the maximum hydrogen concentration of 7.6 ppm and a tensile rate of 0.1 mm/min, the relative elongation, lateral contraction ratio of smooth 25 mm long cylindrical specimens with a test portion diameter of 5 mm and the critical stress intensity factor of beam specimens measuring 20×10×100 mm with a relative length of the pre-induced crack of ε = 0.53 decrease almost twofold. At the same concentration, hydrogen does not affect the stress intensity factor of cracked specimens at a rate of 10 mm/min and specimens with a stress concentrator in the form of a notch with a tip radius of 0.065 mm at a rate of 0.1 mm/min. Under long-term static loading with a test duration of 300 h of double-cantilever beam specimens in the form of a rectangular plate 10 mm thick with milled grooves 3 mm deep and a tip angle of 60°, the threshold value of the stress intensity factor decreases. The rate of subcritical crack growth in the second portion of the hydrogen cracking diagram increases in proportion to the logarithm of hydrogen concentration. [ABSTRACT FROM AUTHOR]

The structure and mechanical properties of 4Kh4N5M4F2 steel in thermodeformed and cast states after quenching and tempering, and additional heating are investigated. After additional heating of hardened and tempered 4Kh4N5M4F2 steel, which models the operating conditions of the equipment (operating temperature during quasi-stationary exposure), at 630–650°C steel softens, which is associated with the formation of Me7C3 carbides. Such carbide phase in the metal structure of the cast steel under mentioned conditions is absent and is accompanied by the increase in its heat resistance. The expansion of the operating temperature range of cast 4Kh4N5M4F2 steel after the optimal mode of hardening and tempering allows using a tool made of this steel up to the operating temperature of 650°C. It is recommended not to use such steel in the cast and thermodeformed states for the manufacture of tools for hot deformation of non-ferrous metals and alloys, which operate under cyclic impact loading. [ABSTRACT FROM AUTHOR]

The clogging behavior of submerged entry nozzle (SEN) is the main reason restricting the continuous casting of steel, which seriously affects the application and popularization of rare‐earth (RE) steel. Through literature analysis, herein, the main influencing factors and mechanism of RE steel continuous casting immersion outlet clogging, and sorts out the main ideas and practices of relevant Japanese enterprises in solving SEN clogging in recent years, are summarized, mainly including the following: 1) optimizing SEN materials to reduce nozzle clogging reactions; 2) using Ar‐blowing SEN; 3) applying electromagnetic field to eliminate charge and inhibiting clogging reaction; and 4) and regulating the composition of molten steel to reduce the possibility of clogging, etc. The combination of these advantages and measures is a feasible way to solve the nozzle clogging of RE steel continuous casting nozzle. [ABSTRACT FROM AUTHOR]

Many structural components and devices in combustion and automotive engineering undergo highly intensive cyclic thermal and mechanical loading during their operation, which leads to low cycle (LCF) or thermomechanical (TMF) fatigue crack growth. This behavior is often characterized by large scale plastic deformations and creep around the crack, so that concepts of linear-elastic fracture mechanics fail. The finite element software ProCrackPlast has been developed at TU Bergakademie Freiberg for the automated simulation of fatigue crack growth in arbitrarily loaded three-dimensional components with large scale plastic deformations, in particular under cyclic thermomechanical loading. ProCrackPlast consists of a bundle of Python routines, which manage finite element pre-processing, crack analysis, and post-processing in combination with the commercial software Abaqus. ProCrackPlast is based on a crack growth procedure which adaptively updates the crack size in finite increments. Crack growth is controlled by the cyclic crack tip opening displacement Δ CTOD, which is considered as the appropriate fracture-mechanical parameter in case of large scale yielding. The three-dimensional Δ CTOD concept and its effective numerical calculation by means of special crack-tip elements are introduced at first. Next, the program structure, the underlying numerical algorithms and calculation schemes of ProCrackPlast are outlined in detail, which capture the plastic deformation history along with the moving crack. In all simulations, a viscoplastic cyclic material law is used within a large strain setting. The numerical performance of this software is studied for a single edge notch tension (SENT) specimen under isothermal cyclic loading and compared to common finite element techniques for fatigue crack simulation. The capability of this software is featured in two application examples showing crack growth under mixed-mode LCF and TMF in a typical austenite cast steel, Ni-Resist. In combination with a crack growth law identified in terms of Δ CTOD for a specific material, the tool ProCrackPlast is able to predict the crack evolution in a 3D component for a given thermomechanical loading scenario. [ABSTRACT FROM AUTHOR]

The fatigue strength of cast steel components is severely affected by manufacturing process-based bulk and surface imperfections. As these defect structures possess an arbitrary spatial shape, the utilization of local assessment methods is encouraged to design for service strength. This work applies the elastic–plastic strain energy density concept to study the fatigue strength properties of a high-strength cast steel alloy G12MnMo7-4+QT. A fatigue design limit curve is derived based on non-linear finite element analyses which merges experimental high-cycle fatigue results of unnotched and notched small-scale specimens tested at three different stress ratios into a unique narrow scatter band characterized by a scatter index of 1:TΔW¯(t)=2.43. A comparison to the linear–elastic assessment conducted in a preceding study reveals a significant improvement in prediction accuracy which is assigned to the consideration of the elastic–plastic material behaviour. In order to reduce computational effort, a novel approximation is presented which facilitates the calculation of the elastic–plastic strain energy density based on linear–elastic finite element results and Neuber’s concept. Validation of the assessment framework reveals a satisfying agreement to non-linear simulation results, showing an average root mean square deviation of only approximately eight percent in terms of total strain energy density. In order to study the effect of bulk and surface imperfections on the fatigue strength of cast steel components, defect-afflicted large-scale specimens are assessed by the presented elastic–plastic framework, yielding fatigue strength results which merge into the scatter band of the derived design limit curve. As the conducted fatigue assessment is based solely on linear–elastic two-dimensional simulations, the computational effort is substantially decreased. Within the present study, a reduction of approximately 400 times in computation time is observed. Hence, the established assessment framework presents an engineering-feasible method to evaluate the fatigue life of imperfective cast steel components based on rapid total strain energy density calculations.

The continuous steel casting process must simultaneously meet the requirements for production performance, quality and safety against breakouts. Knowing the thickness of the solidified shell, particularly at the exit of the mould, is useful for the casting process control and breakout prevention. Shell thickness is difficult to measure during casting; in practice, it is predicted by indirect methods and models. But after undesired rupture of the shell and leakage of the liquid steel, it is possible to measure the shell thickness directly. This article is focused on the problem of the growth and measurement of the solid shell obtained after the breakout of a round block with a diameter of 410 mm. An original methodology was developed in which a surface mesh of points was created from the individual scanned parts of the block using a 3D laser scanner. Research has shown differences of up to 6 mm between the maximum and minimum shell thickness at the mould exit. A regression function of the average shell thickness on time was found. The results of the real shell growth were further used for the verification of the original numerical model of cooling and solidification of the round block. [ABSTRACT FROM AUTHOR]

Postfire mechanical properties and fracture resistance of G20MnQT cast steels were investigated experimentally and effects of different cooling procedures were studied. G20Mn5QT cast steels were heated to 600°C, 700°C, 800°C, and 900°C and cooled to ambient temperature in air or in water. Metallographic examination found significant phase transformations only in G20Mn5QT cast steels cooled quickly in water from elevated temperatures of 800°C (800W) and 900°C (900W). Original ferrite and pearlite transformed to harder phases, such as martensite and bainite, in these two postfire materials. Vickers hardness tests, Charpy impact tests, and tension coupon tests were conducted on original and postfire G20Mn5QT cast steels. All test results confirmed the findings about phase transformation in metallographic examination. The martensite and bainite generated in phase transformation caused significant hardening of 800W and 900W. With no significant phase transformation, most mechanical properties of 600A, 600W, 700A, 700W, 800A, and 900A varied within ±15% compared with those of the original material, and the postfire Charpy impact energies increased moderately due to improvement of material homogeneity. Smooth notched tensile specimens were tested and material parameters in the void growth model were calibrated to evaluate the postfire fracture resistance of G20Mn5QT cast steels at high stress triaxialities. It was found that the fracture of 600A, 600W, 700A, 700W, 800A, and 900A was almost as ductile as that of the original G20Mn5QT cast steels, whereas 800W and 900W fractured brittlely, and had fracture resistance 87.6% and 78.4% lower than that of the original material. [ABSTRACT FROM AUTHOR]

To reduce the occurrence of stickers and longitudinal cracks during continuous casting (CC) of peritectic steel, herein, the use of a mold slag with high basicity and adequate lubrication is proposed. Laboratory results indicate that the mold slag with a basicity of 1.75 and 2.3 wt% Li2O content exhibits a lower break and melting temperatures and relatively fast crystallization rate. The proposed mold slag can rapidly induce crystallization to control the heat flux, and the residual flux after crystallization and formation of the solid slag still exhibits excellent lubrication on the initial shell. Thus, coordination control of heat transfer and lubrication during CC of peritectic steel can be achieved. Industrial trials obtain satisfactory results, the application of the designed mold slag reduces the occurrence of stickers, and longitudinal cracks are reduced at the initial stage of one sequence casting. [ABSTRACT FROM AUTHOR]

The solidification structure of a continuous-casting slab of high-SiMnTi steel at different drawing speeds was predicted by performing experiments using a thermal-simulation device for dendrite growth. The microstructure of a characteristic cell of the solidified steel was mainly composed of fine equiaxed crystals in the chilling region, coarse equiaxed crystals in the core, and columnar crystals in between. Increasing the drawing speed of continuous casting improved the quality of the slab. When the drawing speed reached 1.2 m/min, the proportion of equiaxed crystals in the core was approximately 64.2%, and the degrees of segregation of the major solute elements, C, Mn, Si, and Ti, were the lowest (1.02, 0.98, 0.74, and 1.13, respectively). Our strategy to optimize the continuous-casting process was to adjust the parameters such that the slab more easily experienced CET transformation and had a larger chemical supercooling width. Therefore, our study provides an effective means of characterizing and a technical reference for the continuous casting of high-SiMnTi steel, and enables its process optimization. [ABSTRACT FROM AUTHOR]

We study metal samples taken from two batches of hot-rolled, semi-finished steel products and two batches of grade HC340LA cold-rolled steel, annealed in bell-type furnaces, produced from transitional slabs obtained by continuous casting of the developed high-strength, low-alloy, microalloyed, auto-sheet steel microalloyed with titanium (Ti) onto steel microalloyed with niobium (Nb). Based on the results obtained, for the first time, the possibility of continuous casting of the developed high-strength, low-alloy, auto-sheet steel microalloyed with Ti onto steel microalloyed with Nb is established. It is revealed that both grade S420MS hot-rolled steel according to EN 10149 and grade HC340LA cold-rolled steel, annealed in bell-type furnaces, can be simultaneously produced from transitional slabs while meeting EN 10268 requirements with reduced costs. [ABSTRACT FROM AUTHOR]

The crankshaft, as the main detail in internal combustion engines, is subjected to a variable load caused by the dynamic forces of the combustion process and its rotation. As a result, its surface layers are loaded successively in tension and compression, which causes fatigue of the material. The destruction of crankshafts is a serious problem in the operation of internal combustion engines and creates serious costs for the maintenance of the vehicle fleet. In this research paper are presents the results of a study of damaged crankshafts from internal combustion engines. The failure mechanisms of steel and cast iron crankshafts were established, and penetrant testing was conducted to identify other fatigue cracks. The hardness of the material from which the crankshafts are made was measured, and no significant changes were found. The study was conducted on broken crankshafts from gasoline and diesel engines, and the fracture surface, hardness and local deformations of the main journals and crank pin journals were examined. The crankshafts are made of steel and cast iron, having been dismantled from a car with a mileage of about 300,000 km, a truck with a mileage of about 250,000 km and a forklift with about 8,000 motor hours. [ABSTRACT FROM AUTHOR]

The endurance limit of structural mechanical components is affected by the residual stress state, which depends strongly on the manufacturing process. In general, compressive residual stresses tend to result in an increased fatigue strength. Post-manufacturing processes such as shot peening or vibratory finishing may achieve such a compressive residual stress state. But within complex components, manufacturing-process-based imperfections severely limit the fatigue strength. Thus, the interactions of imperfections, residual stress state and material strength are key aspects in fatigue design. In this work, cast steel and aluminium alloys are investigated, each of them in vibratory finished and polished surface condition. A layer-based fatigue assessment concept is extended towards stable effective mean stress state considering the elastic–plastic material behaviour. Murakami's concept was applied to incorporate the effect of hardness change and residual stress state. Residual stress relaxation is determined by elastic–plastic simulations invoking a combined hardening model. If the effective stress ratio within the local layer-based fatigue strength is evaluated as critical distance value, a sound calculation of fatigue strength can be achieved. Summing up, the layer-based fatigue strength design is extended and features an enhanced understanding of the effective stabilized mean stress state during cyclic loading. [ABSTRACT FROM AUTHOR]

The article presents results of research on fume emission in relation to various arc welding methods (MAG standard, CMT, ColdArc and ColdArc Puls) and laser welding techniques (heat conduction and deep penetration welding). Research - related tests involved manifold elements and a turbine housing made of cast stainless steel. The shielding gas used during arc welding was a mixture containing 97,5 % of Ar and 2,5 % of CO2. In turn, laser welding processes were shielded by argon. The analysis of test results aimed to identify the effect of arc/laser welding methods on the total emission of welding fume. [ABSTRACT FROM AUTHOR]

This research study proposes the hot-cold tip thermoelectric power (TEP) method to estimate alloying elements segregation and the microstructure variation of high carbon steel cast in a mold. Optical emission spectrometry (OES) showed a higher concentration of carbon, nickel, chromium and aluminum at the ingot center. That elemental saturation produced an increase in perlite content as well as hardness. The nondestructive technique of thermoelectric power was applied varying the hot tip temperature (40, 50, 60, 70°C), where higher temperature values showed to be more sensitive to segregation and microstructural changes. The statistical analysis showed that the thermoelectric power technique is more sensitive to detect the nickel and chromium concentration changes. [ABSTRACT FROM AUTHOR]

Steel slag is a melted by-product that mainly consists of calcium carbonate and metal oxides generated in the process of steel manufacturing. The main objectives of this study are to evaluate the effectiveness of steel slags as fine and coarse aggregates in concrete and to determine the optimum quantity of steel slag as fine and coarse aggregates to enhance the strength of concrete. Concrete cubes were cast by mixing steel slag as replacement (i.e. 0%, 10%, 25%, 50%, 75% and 100%) for fine and coarse aggregate, separately. Abrasion test, sieve analysis, water absorption and specific gravity test were conducted to determine the properties of raw materials. Unit weight, workability, compressive strength, splitting tensile strength and the possibility of corrosion were experimentally evaluated to determine the effectiveness of steel slag. It is found that 75% steel slag mixed concrete indicates improvements in compressive strength, splitting tensile strength and unit weight, respectively. Further, it was noted that steel slag aggregates were not corroded after conducting the Accelerated Corrosion Test Method (ACTM). Therefore, the use of steel slag as fine and coarse aggregates for concrete would improve the mechanical properties of concrete and reduce the adverse environmental impact. [ABSTRACT FROM AUTHOR]

Acquiring small-scale experimental techniques that allow analysis of casting defect in large-scale ingot is beneficial to understanding its phenomena. In this study, we report an experimental technique using sand mold to analyze (reproduce and evaluate) casting defect that occur in large-scale ingot. We cast carbon steel (500 kg) by top pouring into a sand mold in which a chill plate (SS400) was installed to enhance cooling of a part of the mold, and observed structure and segregation. Equiaxed crystals were formed in the lower part of the ingot, and negative segregation of carbon was formed in the region of the equiaxed crystals. Al2O3 inclusions were present in the region of negative segregation. This meant that solid movement was generated during the solidification process. Additionally, porosities and shrinkage were also formed in the ingots. This experimental technique using sand mold is expected to be used as an experimental technique that can analyze casting defect that occur in large-scale ingot. [ABSTRACT FROM AUTHOR]

In recent years, numerical simulations have been playing an increasingly important role in the process of casting optimization. The reliability and validity of numerical simulation results are significantly determined by the accuracy setting of the interfacial heat transfer coefficient (IHTC). In this paper, the change law of IHTC between ring type castings and cores under different conditions is systematically investigated by using the Beck inverse algorithm, numerical simulation method and temperature field measurement data with AISI1045 steel as casting material and no-bake furan resin bonded sand as core material. The results show that the change of IHTC with time is in the form of "bimodal" after the cavity is poured, and the value increases rapidly to the maximum after pouring, and then decreases gradually to the minimum, followed by a slow increase and slow decrease process. The accuracy of the calculated IHTC was verified by using Procast software. [ABSTRACT FROM AUTHOR]

The application of steel castings in earthquake engineering has increased significantly in recent years, and steel casting technology has been proven as a viable solution for the design and development of energy dissipative yielding elements. The first-generation of cast steel replaceable modular yielding links were recently proposed as an off-the-shelf energy dissipative product line for use in steel eccentrically braced frames (EBF). The performance of the links was validated through an extensive full-scale experimental program. These links featured a design approach in which the effective length of all links across the product line was identical. As a result of this design approach, a wide range was observed in the ductility capacity, with the smaller- to medium-capacity links achieving larger rotation capacities than the larger-capacity links. This paper presents the design and experimental validation of an alternative design of cast steel replaceable yielding links where, rather than ensuring equal length across the product line, a similar link ductility capacity is targeted for all link sizes. The new cast steel links with targeted ductility capacity are presented, and the performance of two link sizes is validated through large-scale experiments to confirm that the proposed design achieved the targeted design ductility. Each link size was tested twice: once as a standalone element and once as part of a one-story EBF system that imparted a large axial load to the link. Based on the results, the effect of axial load on the performance of EBF links is discussed. [ABSTRACT FROM AUTHOR]

Steel eccentrically braced frames (EBFs) combine the advantages of both moment-resisting frames and concentrically braced frames and provide an attractive seismic design solution. Shear-critical replaceable links were developed about a decade ago to improve the performance, design process, construction, and postearthquake repair process in EBFs. However, replaceable shear links are still susceptible to the commonly observed limit states in EBF links such as web fracture close to web stiffeners, local buckling, and lateral torsional buckling. This paper presents the experimental validation of a new generation of optimized cast steel replaceable yielding links for use in EBFs, which address the shortcomings of conventional and fabricated replaceable links. The performance of the proposed cast steel links is investigated through nine large-scale component-level and system-level experiments, covering a range of link sizes and loading conditions, while also studying the impact of other phenomena influencing the response such as the presence of axial load, the level of axial restraint in the links and the presence of a concrete slab. The tested series of cast links demonstrated enhanced ductility levels and low-cycle fatigue life when compared to fabricated links, achieving up to 0.21 radians of link rotation under the AISC protocol used for the qualification of EBF links. [ABSTRACT FROM AUTHOR]

The subject of the work are modern composite materials with increased wear resistance intended for elements of machines operating in difficult conditions in the construction and mining industries. The study determined the effect of zone reinforcement of GX120Mn13 cast steel with macroparticles (Al2O3 + ZrO2) on the corrosion resistance and abrasion wear of the composite thus obtained. SEM studies have shown that at interface between two phases, and more precisely on the surface of particles (Al2O3 + ZrO2) a durable diffusion layers are formed. During the corrosion tests, no significant differences were found between the obtained parameters defining the corrosion processes of GX120Mn13 cast steel and GX120Mn13 with particles (Al2O3 + ZrO2) composite. No intergranular corrosion was observed in the matrix of the composite material, nor traces of pitting corrosion at both phases interface. This is very important in terms of tested material’s service life. Reinforcement of cast steel with particles (Al2O3 + ZrO2) resulted in a very significant improvement in the abrasion resistance of the composite – by about 70%. After corrosion tests, both materials were subjected to further operational investigations. These examinations consisted in determining the impact of corrosion processes on the durability of the composite in terms of abrasion. The obtained results indicate that corrosion processes did not significantly deteriorate the wear resistance of both the cast steel and the composite. [ABSTRACT FROM AUTHOR]

The paper presents the results of research conducted in the field of crystallization and microstructure of duplex alloy cast steel GX2CrNiMoCuN 25-6-3-3 grade. The material for research was the above-mentioned cast steel with a chemical composition compliant with the relevant PN-EN 10283 standard, but melted at the lowest standard allowable concentration of alloying additives (some in short supply and expensive), i.e. Cr, Ni, Mn, Mo, Cu and N. The analysis of the crystallization process was performed based on the DTA (Derivative Thermal Analysis) method for a stepped casting with a thickness of individual steps of 10, 20, 40 and 60 mm. The influence of wall thickness was also taken into account in the cast steel microstructure testing, both in the as-cast state and after solution heat treatment. The phase composition of the cast steel microstructure was determined by using an optical microscope and X-ray phase analysis. The analysis of test results shows that the crystallization of tested cast steel uses the ferritic mechanism, while austenite is formed as a result of solid state transformation. The cast steel under analysis in the as-cast state tends to precipitate the undesirable σ-type Fe-Cr intermetallic phase in the microstructure, regardless of its wall thickness. However, the casting wall thickness in the as-cast state affects the austenite grain size, i.e. the thicker the casting wall, the wider the γ phase grains. The above-mentioned defects of the tested duplex alloy cast steel microstructure can be effectively eliminated by subjecting it to heat treatment of type hyperquenching. [ABSTRACT FROM AUTHOR]

Cast steel nodes are widely used as important components of offshore platform, owing to their better performance than welded nodes. In this paper, the mold filling and solidification process of cast steel nodes were numerically simulated and verified by the finite element analysis commercial software package—ProCAST, and the occurrence of shrinkage porosity was quantitatively predicted based on the simulation results. The numerical simulation results of the preliminary design showed that the overall filling was stable with bottom gated system, agreeing well with the design requirements. However, the shrinkage porosities in the intersection of lower tubes and main tube were evident due to the insufficient feeding. Optimization of the casting design was carried out through repeated computer simulation. By incorporating chills in the cores, the optimized design showed that the shrinkage porosities in the intersection of lower tubes and main tube were effectively eliminated. In view of these aforementioned optimizations, the casting steel can meet the technical requirements in an actual production. [ABSTRACT FROM AUTHOR]

A great variety of tuning forks survive in collections around the world, from departments of physics, phonetics, and psychology to medical settings, conservatories, and museum collections. Their ubiquity speaks to their iconic status, while their diversity points to the multifaceted cultures of materiality that shaped and formed around these objects. This essay traces the complex supply chains of nineteenth-century tuning forks, from the gathering and processing of iron ore and crucible steel, to their sites of manufacture, to their various uses. By probing further into these nodes of supply and use, the essay uncovers a chain of values and contingencies that reveal the interdependencies between extracting, commercial, scientific, and artistic practices of the past. [ABSTRACT FROM AUTHOR]

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A three-dimensional species transport model in continuous casting mold has been developed to describe the interfacial reaction behavior and to clarify the evolution of composition and properties of the mold flux for high-Al steel. The reaction experiment and plant trial were conducted to verify the model predictions. The results show that the interfacial reaction rate is the main factor affecting the composition distribution of the mold flux. The reaction interface above the upflow zone of molten steel has a fast update rate, resulting in a rapid increase in the Al2O3 content in mold flux in this area. In addition, the mold flux near the nozzle stays in the liquid pool for a longer time to react with the molten steel, leading to the accumulation of Al2O3. The Al2O3 content in the solid film is slightly lower than that of the liquid pool due to the solidification of liquid mold flux in the early stage. The interfacial reaction increases the viscosity of the mold flux and reduces the thickness of the liquid film, thereby reducing the flux consumption. [ABSTRACT FROM AUTHOR]

A heat transfer model for covers in steel continuous casting process has been established. In the model, the boundary temperature of bloom is firstly calculated by a calibrated three dimensional heat transfer model for continuous casting strand. The cover model has been developed based on heat transfer and surface to surface radiation, and most important, the cover effect is evaluated by specially designed probes placed close to the bloom surface. Then the influences of cover's thermo-physical properties and geometry have been fully studied, including the emissivity, thermal conductivity, specific heat, size, shape and structure. And then some principles for cover design have been presented. According to the numerical model and analytical analysis, the final emissivity reduction of cover is determined by cover's emissivity, bloom's emissivity, the gap between bloom and cover, and cover's thermal conductivity. Besides, the transient time is proportional to the cover's density, cover's specific heat and cover's thickness. Finally, the cover model has been applied to improve the cover effect and improve the heat transfer model of strand. Results indicate that the improved model is much better agreeing with the measurements, by reducing the maximum error from ± 30 °C to ± 16 °C. [ABSTRACT FROM AUTHOR]