Billet Samples Research Articles

Effects of mold electromagnetic stirring on heat transfer, species transfer and solidification characteristics of continuous casting round billet

In this study, the temperature distribution, species transfer, and solidification behavior in round billet continuous casting with mold electromagnetic stirring (M-EMS) was numerically investigated. The joule heat induced by the M-EMS and the liquid fraction profiles in the mushy zone were observed, whereby it was found that increasing current intensity caused further increase in electromagnetic force, which reduced the impact depth of liquid steel while accelerating the dissipation of superheat. The high liquid fraction in the mushy zone at the exit of the secondary cooling zone were 68.1% (case 1) and 77.1% (case 6). The central carbon contents of the round billets were 0.337 wt% (case 1) and 0.335 wt% (case 6). Moreover, the proportion of solidification microstructure and secondary dendrite arm spacing of the round billet samples were compared, which revealed that increasing the current intensity, casting speed, and cooling intensity, were all conducive to improving the uniformity of carbon distribution and compactness of the solidification structure.

Mechanical Properties of Hot Rolled Ribbed and Plain Steel Rods

This study focuses on microstructure and mechanical behaviour of 3PS (Semi-killed mild steel) hot rolled ribbed and plain carbon steel. 3PS billet steel samples and hot rolled ribbed and plain steel rods of different heat numbers and profiles were characterized for its chemical composition, microstructure, and tensile behaviour. The composition analysis of 5 (five) 3PS billet samples shows that there was no appreciable variation in chemical composition of the hot-rolled plain and ribbed steel rods. The microstructures of as-received steel billet (3PS) examination revealed large grains of ferrite and pearlite while those of hot-rolled 3 PS mild steel samples of different heat numbers contain smaller grains of ferrite and some amount of pearlite. The results also indicated that yield and ultimate tensile strength reach maximum values (492 and 361 N/mm2) at 0.31% elongation for heat number 43 while maximum values for heat number 56 (478 and 362 N/mm2) at 0.33 % respectively. The ribbed steel rod of the same diameter as plain steel exhibit slightly better mechanical properties with higher values of yield and ultimate tensile strength. There is consistency in the chemical composition of the as-received billet and the hot rolled products.

Geospatial Management and Analysis of Microstructural Data from San Andreas Fault Observatory at Depth (SAFOD) Core Samples

Core samples obtained from scientific drilling could provide large volumes of direct microstructural and compositional data, but generating results via the traditional treatment of such data is often time-consuming and inefficient. Unifying microstructural data within a spatially referenced Geographic Information System (GIS) environment provides an opportunity to readily locate, visualize, correlate, and apply remote sensing techniques to the data. Using 26 core billet samples from the San Andreas Fault Observatory at Depth (SAFOD), this study developed GIS-based procedures for: 1. Spatially referenced visualization and storage of various microstructural data from core billets; 2. 3D modeling of billets and thin section positions within each billet, which serve as a digital record after irreversible fragmentation of the physical billets; and 3. Vector feature creation and unsupervised classification of a multi-generation calcite vein network from cathodluminescence (CL) imagery. Building on existing work which is predominantly limited to the 2D space of single thin sections, our results indicate that a GIS can facilitate spatial treatment of data even at centimeter to nanometer scales, but also revealed challenges involving intensive 3D representations and complex matrix transformations required to create geographically translated forms of the within-billet coordinate systems, which are suggested for consideration in future studies.

Effect of billet microstructure and deformation on austenite grain growth in forging heating of a medium-carbon microalloyed steel

We prepared samples with different ferrite-pearlite characteristics and deformation by heat treatment and Gleeble thermocompression respectively. Then, the different samples are rapidly heated to 1200 °C for 60 s to study the austenite grain growth. The study results show that the ferrite-pearlite characteristics has little effect on austenite grain growth. With the mean austenite grain size (MAGS) of billet microstructure increasing from 14 µm to 56 µm, the MAGS after heating only increases from 47 µm to 56 µm. With the cooling rate of billet samples increasing from 0.1 °C/s to 1.0 °C/s, the MAGS after heating has basically no change. However, the deformation of billet samples has significant effect on the austenite grain growth. With the deformation at 1150 °C increasing from 10% to 50%, the MAGS after heating decreases from 63 µm to 31 µm. In the meanwhile, the mean distance between element segregation bands decreases from 115 µm to 33 µm, and the mean width of element segregation bands decreases from 70 µm to 20 µm. Electron probe microanalysis shows that the segregation region has higher Si, Cr, Mn and V contents, which generate stronger solute drag effect on austenite grain boundaries. Deformation can crush the as-cast grains and make the segregation bands fine and dispersed, further refining the austenite grains after heating.

Successful Integrated Pest Management Minimizes the Economic Impact of Diatraea saccharalis (Lepidoptera: Crambidae) on the Louisiana Sugarcane Industry.

The sugarcane borer, Diatraea saccharalis (F.), is the primary pest of sugarcane, Saccharum spp., in Louisiana. Recent evidence suggests an integrated pest management (IPM) program has reduced the pest's impact, but the success of this program has not been assessed across the industry. The level of D. saccharalis injury present at harvest was recorded from 388 billet samples from five sugar mills from 2017 to 2019. These results were used to estimate direct and indirect revenue losses from D. saccharalis on the Louisiana sugarcane industry. Insecticide use records were used to estimate control costs and determine total economic impact. The mean percentage of bored internodes was 1.1, 0.3, and 1.7% for 2017, 2018, and 2019, respectively. Direct losses from reduced sugar yield averaged US$4.6 million across years. Indirect losses across years accounted for US$3.0 million and $463,000 for insecticidal control costs and reduced milling efficiency, respectively. The total economic impact of D. saccharalis averaged $8.0 million annually during the three-year study period. This study demonstrates the efficacy of pest management implementation in reducing D. saccharalis injury and highlights the value of IPM. Our findings provide new support for the emergence of D. saccharalis management in the Louisiana sugarcane industry as a modern IPM success story.

Tuning the microstructure morphology and genetic mechanical properties of 2219 Al alloy with ultrasonic treatment

Some defects i.e. dendrite, coarse eutectic phases, and serious macro-segregation were hard to eliminate when the ultra-large aluminum alloy was manufactured by conventional technique. An effective method with ultrasonic sonotrode was inserted into the direct-cooling casting system to manufacture the 2219 Al alloy billet (Φ1100 mm × 5400 mm), followed by multidirectional forging and solution-aging (MSA) treatment. A comparative study of the morphology of α-Al grains, eutectic phases, and precipitates, as well as the mechanical properties were investigated. The results indicated that more coarse eutectic networks agglomerated together in the center position compared with billet samples without ultrasonic treatment (NUT) and with ultrasonic treatment (UT). They were difficult to completely dissolve into the matrix in the downstream MSA process, and acted as preferential nucleation sites for micro-cracks, thereby decreasing the mechanical properties. The average grain sizes of billet were generally refined induced by UT. And a greater density of tinier, uniform distributed precipitates was obtained from the UT billet and MSA samples. The mechanical properties were obviously increased by ultrasonic treatment in the billet samples. Based on the present results and proposed hypotheses in previous works, the dominant mechanisms of UT on major microstructures and genetic effects on mechanical properties were discussed.

Fluctuation characteristic of billet region gas consumption in reheating furnace based on energy apportionment model

To master the fluctuation characteristic of billet gas consumption in different regions of reheating furnace, a system analysis method about fluctuation degree of billet region gas consumption (BRGC) is put forward in accordance with energy apportionment model. And this system analysis method mainly includes: (i) The space division of reheating furnace; (ii) The simplification of energy apportionment model in reheating furnace; (iii) The classification of billet samples; (iv) The establishment of BRGC standard deviation (BRGCSD) analysis model. A case study shows that (i) the BRGC fluctuates greatly in low temperature area, and fluctuates smoothly in high temperature area; (ii) The volatility degree of BRGC is intensified because of the lower loading temperature; (iii) It is very reasonable that the residence time of billets is controlled in (3,4] and (4,5] range, and the average fluctuation degree is about 0.01 and 0.012 respectively; (iv) The fluctuation of BRGC is amplified in some regions because of mixed charging. The analysis results show that some measures can reduce the fluctuation of BRGC, such as the stable operation of tiny positive pressure, the control of production rhythm, the improvement of billet loading temperature, the optimization of loading plan.

Bottleneck of slab thermal efficiency in reheating furnace based on energy apportionment model

To reveal distribution of slab thermal efficiency (STE) and its bottlenecks, a slab region thermal efficiency (SRTE) model and an STE model were established based on the energy apportionment model of a reheating furnace in this paper. The bottleneck index of the slab thermal efficiency (BISTE), which could be used to assess the influence of SRTE on STE in a particular region, was proposed. First, the regional energy balance equation was listed based on reheating furnace region division. Next, the SRTE and STE models were established. Second, the bottleneck of slab thermal efficiency (BSTE) was achieved through a partial correlation analysis (PCA) of billet samples, which were obtained according to the difference between billet loading temperature and its residence time in the reheating furnace. Next, the BISTE was advanced to accurately determine the BSTE. Finally, several suggestions or measures, that could improve SRTE, were proposed. The case study has demonstrated the validation of these models, and the BISTE was 42% (Preheating), 19% (Heating II), 18% (Soaking), 11% (Heating I) and 10% (Preheating & Heating), respectively. Therefore, the preheating zone is the key region used to improve STE.

Utilization of hot deformation to trigger strain induced boundary migration (SIBM) in Ni-base superalloys

The effect of strain on the resultant microstructure of an experimental low stacking fault energy Nickel based superalloy containing 24 wt. pct. Co was investigated. Billets subjected to a preliminary heat treatment at 1110 °C were compressed to strain limits of 0.15 and 0.5 at strain rates ranging from 0.1/s to 0.01/s and temperatures at 1020 °C and 1060 °C. The as-deformed microstructures were assessed and characterized using electron backscatter diffraction, as were microstructures corresponding to a super-solvus anneal heat treatment at 1160 °C for one hour. This study sought to identify a critical strain limit at which conditions indicative of Strain induced boundary migration (SIBM) could be effectively triggered for the experimental Ni-based superalloy over a set range of thermal-mechanical parameters. Microstructures corresponding to SIBM were then compared to more extensively deformed billets which contained notable fractions of dynamically recrystallized grains to quantify differences in the length fraction and density of ∑3 twin boundaries of the respective microstructures. Though billet samples deformed to both 0.15 and 0.5 contained notable magnitudes of stored strain energy, microstructures deformed to 0.15 were noted as having maintained larger length fractions of ∑3 twins due to a predominant absence of dynamic recrystallization. Annealed samples originally deformed to 0.15 yielded annealing twin length fractions as high as 59% when compared a sample deformed to the 0.5 strain limit under equivalent thermal-mechanical conditions that resulted in a twin length fraction of 50%. Although samples deformed to the lower strain limit exhibited higher length fractions of annealing twins, samples deformed to the higher strain limit of 0.5 were noted to yield ∑3 densities as high as 0.65 μm−1, whereas the annealed sample deformed under equivalent thermal-mechanical parameters to the 0.15 strain limit produced ∑3 densities as low as 0.32 μm−1.

Detection of Non-metallic Inclusions in Centrifugal Continuous Casting Steel Billets

In the current study, automated particle analysis was employed to detect non-metallic inclusions in steel during a centrifugal continuous casting process of a high-strength low alloy steel. The morphology, composition, size, area fraction, amount, and spatial distribution of inclusions in steel were obtained. Etching experiment was performed to reveal the dendrite structure of the billet and to discuss the effect of centrifugal force on the distribution of oxide inclusions in the final solidified steel by comparing the solidification velocity with the critical velocity reported in literature. It was found that the amount of inclusions was highest in samples from the tundish (~250 per mm2), followed by samples from the mold (~200 per mm2), and lowest in billet samples (~86 per mm2). In all samples, over 90 pct of the inclusions were smaller than 2μm. In steel billets, the content of oxides, dual-phase oxide–sulfides, and sulfides in inclusions were found to be 10, 30, and 60 pct, respectively. The dual-phase inclusions were oxides with sulfides precipitated on the outer surface. Oxide inclusions consisted of high Al2O3 and high MnO which were solid at the molten steel temperature, implying that the calcium treatment was insufficient. Small oxide inclusions very uniformly distributed on the cross section of the billet, while there were more sulfide inclusions showing a banded structure at the outside 25 mm layer of the billet. The calculated solidification velocity was higher than the upper limit at which inclusions were entrapped by the solidifying front, revealing that for oxide inclusions smaller than 8μm in this study, the centrifugal force had little influence on its final distribution in billets. Instead, oxide inclusions were rapidly entrapped by solidifying front.

Analysis of structural changes when processing aluminum alloy roll billets produced by ingotless rolling

The paper reviews structural changes after processing the roll billet manufactured of lightweight Al–Mn–Fe–Si aluminum alloys by ingotless rolling. It was also proposed to identify the texture by the generalized pole density index and to set the structural element dimensions depending on the field of coherent X -rays scattering. Correlating the findings with the phases of the material, as well as evaluating the matching of hardening with the cold rolling plastic deformation, the place of annealing between the passes was defined by selection and due to convergence of the generalized pole density value after its determination by X -ray patterns of the roll billet samples and the strip after each pass.

Dimensional Structure of Non-Metallic Inclusions in High-Grade Medium Carbon Steel Melted in an Electric Furnace and Subjected to Desulfurization

Non-metallic inclusions may be introduced to liquid steel from the outside, usually with charge material, or they may be produced in the metallurgical process. According to literature, if evenly distributed, non-metallic inclusions may affect the functional properties of steel, mainly its fatigue strength. The aim of this study was to determine the quantity and dimensional structure of non-metallic inclusions in high-grade medium carbon steel melted in an electric furnace and subjected to desulfurization. The experimental material consisted of semi-finished products of high-grade, medium-carbon constructional steel containing manganese, chromium, nickel, molybdenum, and boron. The levels of phosphorus and sulphur impurities did not exceed 0.02%. Billet samples were collected to determine the chemical composition, microstructure, the relative volume of non-metallic inclusions, and the size of impurities. The results were processed and presented in graphic form.

Homogenization of direct chill cast AlSi1MgMn billets

Abstract The homogenization practice for direct chill cast AlSi1MgMn billets was investigated. It takes 8 h at 570 °C and at least 4 h at 580 °C to even out the Mg and Si distribution in the aluminium matrix and to obtain relatively small discrete αc-Al12(Fe, Mn)3Si particles with a “necklace” configuration. Once Mg and Si are solutionized, the equilibrium β-Mg2Si phase precipitates during post-soaking cooling at ≥ 500 K h–1. β′-Mg2Si precipitates are also identified in samples cooled at ≤ 250 K h−1. Hardness produced in this cooling rate range is relatively lower suggesting improved extrudability. These billet samples are fully solutionized at 500 °C during billet pre-heating. Typical press exit temperatures may suffice for adequate age hardening in billet samples soaked at 580 °C for 8 h and subsequently cooled at 250 K h−1. This is a very attractive feature as it implies a full age hardening capacity even without the need for a separate solution heat treatment.

Control of Macrosegregation Behavior by Applying Final Electromagnetic Stirring for Continuously Cast High Carbon Steel Billet

Solidification behavior of continuously cast high carbon steel billets was investigated with an objective of producing high quality billets by determining the optimum final electromagnetic stirring (F-EMS) parameters. Characteristics of centerline segregation were analyzed for lots of billet samples collected from the plant through obtaining the carbon concentrations of drill chips, which were correlated with the operating parameters of the caster and stirrers, but a problem occurred that segregation control results of trial billets with the same casting and stirring parameters often have drastic fluctuations. An attempt was made to find out the induced reasons of this problem by measuring the electromagnetic torque, analyzing the secondary dendrite arm spacing (SDAS) and the corresponding cooling rate of the typical specimens, and observing the longitudinal profile of etched billet samples. Then a simple dynamic secondary cooling model was developed based on the solidified shell thickness control mode, by which the maximum carbon segregation index was reduced effectively, and thus the segregation fluctuation problem was basically solved. Finally, the most favourable stirring parameters were determined as the casting speed of 1.65 m/min, the liquid core thickness of 40 mm, stirring current of 360 A and frequency of 12 Hz.

Thermodynamic Evaluation of Inclusion Formation during Cooling and Solidification of Low Carbon Si-Mn Killed Steel

The primary endogenous inclusions are inherent and specific to the deoxidation process and may contribute significantly to the steel properties besides affecting its castability during continuous casting. Additional (secondary) inclusions form during cooling and subsequent freezing of liquid steel during continuous casting operation. Therefore, in order to produce clean steel it is extremely important to understand clearly their formation mechanisms. Rejection of solutes by the solidifying dendrites causes segregation of solutes in the interdendritic liquid with consequent build-up of their thermodynamic super saturation. Rejected solute elements subsequently react to give rise to secondary inclusions in the solidifying liquid steel. The present investigation aimed at development of an appropriate thermodynamic calculation procedure for the prediction of inclusion compositions formed during cooling and solidification of liquid steel. The model has been applied to an inclusion sensitive grade of steel. Segregation of various solutes with progress of freezing was calculated using the Clyne–Kurz microsegregation equation. A sequential computation procedure involving segregation equation and thermodynamic equilibrium calculations by the Factsage-06 thermodynamic software was developed. Compositions of inclusions at various stages of solidification were calculated. Model predictions were finally compared with literature as well as with observed inclusion compositions determined in several continuously cast billet samples using SEM-EDS. Reasonably good correspondence between model predictions and observed inclusions have been obtained. The model has provided deeper insight into the formation mechanisms of various nonmetallic inclusions in steel and provided the required guidance for controlling them.

The Effect of the Production Process and Heat Processing Parameters on the Fatigue Strength of High-Grade Medium-Carbon Steel

The experimental material consisted of semi-finished products of high-grade, medium-carbon constructional steel with: manganese, chromium, nickel, molybdenum and boron. The experimental material consisted of steel products obtained in three metallurgical processes: electric and desulfurized (E), electric and desulfurized with argon-refined (EA) and oxygen converter with vacuum degassed of steel (KP). The production process involved two melting technologies: in a 140-ton basic arc furnace with desulphurisation and argon refining variants, and in a 100-ton oxygen converter. Billet samples were collected to analyze: relative volume of impurities, microstructure and fatigue tests. The samples were quenched and austenitized at a temperature of 880 o C for 30 minutes. They were then cooled in water and tempered by holding the sections at a temperature of 200, 300, 400, 500 and 600 o C for 120 minutes and air-cooled. Fatigue tests were performed with the use of a rotary bending machine at a frequency of 6000 cpm. The results were statistical processed and presented in graphic form. This paper discusses the results of microstructural analyses, the distribution of the relative volume of impurities in different size ranges, the fatigue strength characteristics of different production processes, the average number of sampledamaging cycles and the average values of the fatigue strength coefficient for various heat processing options.

Hot Working of Ti Aluminide Made through Reaction Synthesis

Hot working of titanium aluminide made through reaction synthesis (RS) has been studied. Hot isostatic pressing under argon, isothermal pressing under vacuum, open die forging and pack forging was carried out. Hot worked billet samples were characterized for density and microstructure evolution. Presence of refined grains and dynamically recrystallized grains were observed. In case of open die forging, presence of twins was also found. From the present study, near isothermal working through near conventional processes has been confirmed. However, role of isothermal working in obtaining crack free sound deformed product has also been noted.

Mathematical Modeling of Hot Tearing in the Solidification of Continuously Cast Round Billets

Billets produced by continuous casting sometimes show the presence of subsurface cracks that can compromise the quality of the final product. The presence of these cracks is revealed by Baumann prints of billet cross sections in which the chill zone is visible and the short radial cracks are located only where the chill zone thickness is thinner. This experimental finding induces the hypothesis that cracks are formed as a result of the presence of unevenness in the mold heat extraction around the billet perimeter. Cracks start to open in the dendritic front in regions where the shell growth in the mold is slower. The study presented in this article focused on steels with a sulfur content of about 300 ppm. The Baumann prints taken from billet samples of numerous different heats allowed detecting the presence of subsurface cracks and their location nearby visible chill zone thinning areas. To understand the mechanisms of crack formation and to define the possible corrections, a modeling activity has been carried out using the finite element technique on 148-mm diameter billets continuously cast at TenarisDalmine (Dalmine, Italy). The model performs a two-dimensional thermomechanical analysis of the solidification in the mold and within about 4 cm below the mold exit, along which the shell surface is cooled only by radiation to the environment, before the sprays of the first ring impact on the strand. The model includes the contact of the shell with the mold inner surface, which moves according to taper and distortion (this last part is calculated by means of a separate mold model); the steel creep behavior; the calculation of the heat transfer through the gap depending on the local mutual distance between the two surfaces; the effect of the liquid steel fluid dynamics on the solidification growth as a result of the temperature distribution; and the calculation of a hot tearing indicator represented by the porosity fraction caused by mechanical strains applied at the dendrite roots. From the simulation results, it is concluded that subsurface cracks are generated in the space between the mold exit and the first cooling ring; the involved mechanisms of formation also are withdrawn. Nucleation of MnS precipitates of large dimensions is an additional cause of defectiveness in controlled sulfur steels. As a final conclusion of this work, the most important actions to eliminate subsurface cracks are derived.

Design and implementation of an automated secondary cooling system for the continuous casting of billets

This paper describes a heat transfer model based automatic secondary cooling system for a billet caster. The model aims to minimize the variation in surface temperature and excessive reheating of the billet strands. It is also used to avoid the low ductility trough of the solidifying steel, which aggravates the tendency of steel to crack. The system has been designed and implemented in an integrated steel plant. A Programmable Logic Controller (PLC) based automation system has been developed to control the water flow in the secondary cooling zones of the strand. The results obtained through field trials have shown complete elimination of internal and off-corner cracks for the fifty billet samples that were monitored.

Quantification of the Solidification Microstructure in Continuously-Cast High-Carbon Steel Billets

In this work, an attempt has been made to investigate the relationship between the cast microstructure and solidification variables in industrial scale, continuously-cast (CC) high-carbon steel billets. Toward these, theoretical and experimental studies are undertaken to predict the evolution of dendrite arm spacing (DAS) in the columnar zone of CC billets. Several billet samples collected from the continuous casting shop of Tata Steel are used to characterize the solidification microstructure, and interdendritic arm spacings (both primary and secondary) are measured. Macrostructural examination of the billet samples indicates predominantly columnar structure in all billets. Dendrite arm spacings vary over a wide range indicating nonuniform secondary cooling. A mathematical model is also developed to describe the relationship between dendrite structures and solidification parameters. The model considers the effect of change of volume on solidification and provides a quantitative estimation of variation of DAS as a function of distance from the product surface. Results predicted by the mathematical model are compared with the experimental measurements and good agreement can be observed in this regard, thereby establishing the authenticity of the proposed formulation.