Steel Ingots Research Articles

Fast and accurate detection of surface defect based on improved YOLOv4

PurposeThe current popular image processing technologies based on convolutional neural network have the characteristics of large computation, high storage cost and low accuracy for tiny defect detection, which is contrary to the high real-time and accuracy, limited computing resources and storage required by industrial applications. Therefore, an improved YOLOv4 named as YOLOv4-Defect is proposed aim to solve the above problems.Design/methodology/approachOn the one hand, this study performs multi-dimensional compression processing on the feature extraction network of YOLOv4 to simplify the model and improve the feature extraction ability of the model through knowledge distillation. On the other hand, a prediction scale with more detailed receptive field is added to optimize the model structure, which can improve the detection performance for tiny defects.FindingsThe effectiveness of the method is verified by public data sets NEU-CLS and DAGM 2007, and the steel ingot data set collected in the actual industrial field. The experimental results demonstrated that the proposed YOLOv4-Defect method can greatly improve the recognition efficiency and accuracy and reduce the size and computation consumption of the model.Originality/valueThis paper proposed an improved YOLOv4 named as YOLOv4-Defect for the detection of surface defect, which is conducive to application in various industrial scenarios with limited storage and computing resources, and meets the requirements of high real-time and precision.

Flow accelerated corrosion of carbon steel containing chromium under water chemistry conditions of boiling water reactor applying mitigation techniques of corrosive environment

ABSTRACT The effects of exposure to oxygenated water on flow accelerated corrosion of carbon steel containing chromium were investigated by alternately and repeatedly exposing specimens to low dissolved oxygen water with <3 μg L−1 of dissolved oxygen and oxygenated water with 30–50 μg L−1 at 190°C and 2 m s−1 flow velocity. First, carbon steel ingot and several carbon steel ingots containing chromium were prepared in a vacuum melting furnace and hot forged. The forged ingots were machined to make tube test specimens. After exposure to the oxygenated water condition, the thinning rate of carbon steel containing chromium under the low dissolved oxygen condition was found to depend on chromium concentration. For carbon steel containing less than 0.052 wt% chromium, thinning rate after exposure to the oxygenated water condition was almost the same as that before exposure to the oxygenated water condition. That is, no adverse effects by exposure to the oxygenated water condition were observed. For carbon steel containing more than 0.13 wt% chromium, thinning rate decreased to the undetected level by exposure to the oxygenated water condition. That is, corrosion resistance was improved by exposure to the oxygenated water.

Effect of Ni addition on bainite microstructure of low-carbon special bar quality steels and its influence on CCT diagrams

This work presents the effect of Ni content on the bainite morphology and in the mechanical properties of low-carbon special bar quality steels. Four steel ingots with the same base chemical composition, having only Ni content as their main difference, were melted in a pilot scale vacuum induction melting furnace, hot forged into square bars followed by cooling in still air to room temperature. Samples for Charpy-V notch tests of every steel were tempered to equalize their hardness level. Through dilatometry tests, it was found that Ni slows down the transformation kinetics of ferrite and pearlite phases, and, acts in favor of bainite and martensite formation. In low-carbon bainitic steels, Ni also favors the formation of lower bainite at the expanse of upper bainite. The steels with lower Ni contents, 0.03 % and 0.70 %, have their microstructures mostly composed of upper bainite, with clusters of alloy carbides precipitated in the boundaries of the bainitic ferrite packages. The clusters of hard carbides act as stress raisers, facilitating the propagation of cracks, and, reducing the toughness of the steels. The other two steels studied with higher Ni, 1.40 % and 2.75 %, showed superior hardenability and predominant microstructures of lower bainite and martensite, respectively. The steels composed of lower bainite and martensite have higher toughness than the steels with upper bainite due to their more refined microstructure and homogenous dispersion of the alloy carbides in the steel matrix. It was also observed in the bainitic steels that tempering does not influence the location where the alloy carbides precipitated during bainite transformation. After tempering, these carbides remain at the bainitic ferrite boundaries or dispersed in the bainitic ferrite packages depending on the type of bainite formed.

Numerical Simulation Research on Mandrel reaming of Ring Steel Ingot

The mandrel reaming forging is of great significance to the billeting of the ring ingot. Through the analysis of the reaming deformation of the ring steel ingot mandrel, it is concluded that the ring steel ingot reaming deformation exists in the radial, axial and tangential directions, which are similar to the rigid zone, active plastic deformation zone and passive plastic deformation zone in the upsetting theory. Numerical simulation methods are used to analyze the reaming of the ring steel ingot mandrel, and it is verified that the ring steel ingot reaming deformation has a rigid zone, an active plastic deformation zone and a passive plastic deformation zone in the radial, axial and tangential directions. At the same time, the reduction rate is found has a greater impact on the three regions.

Influence of thermally grown oxide layers thickness on temperature evolution during the forging of large size steel ingots

Medium carbon low alloy specialty steels are preheated in gas-fired furnaces before undergoing open die forging operation. Oxide layers with different thicknesses and compositions are formed on the surface and significantly influence the temperature evolution during the forging process. In the present work, the kinetics of oxide growth of two high-strength medium carbon steels with different Ni concentrations, were determined. Four oxidation temperatures and five oxidation times were used to simulate various forging and intermediate heat treatment conditions. Three distinct oxide layers with different thicknesses were identified and correlated with the applied thermal cycles. The results indicated that the kinetics of oxidation varied with the Ni concentration of the alloys, but interestingly the fractions of different layers were the same at different oxidation temperatures. A 3D finite element model (3D-FEM) was developed, and the effect of the oxide layer investigated on the temperature evolution of the ingots. Correlations are made between the thickness of the oxide layers and the cooling pattern of the ingots, as well as their impact on the forging die temperature. The 3D-FEM predicted critical temperatures were validated by experimental temperature measurements on the ingot during the forging process.

The Effect of Rare Earth Metals Alloying on the Internal Quality of Industrially Produced Heavy Steel Forgings.

The paper presented the findings obtained by industrial research and experimental development on the use of rare earth metals (REMs) in the production of heavy steel ingots and their impact on the internal quality of the 42CrMo4 grade steel forging. REMs alloying was carried out after vacuuming the steel. A relatively large melting loss of cerium (about 50%) and its further decrease in casting due to reoxidation were observed. Refinement of structure and better mechanical properties of forged bar containing about 0.02 wt.% of Ce compared to that of the standard production were not achieved. The wind power shaft with content of about 0.06 wt.% of Ce showed high amount of REM inclusions, which were locally chained, and in some cases, initiated cracks. Four stoichiometrically different types of REM inclusions were detected in forgings, namely (La-Ce)2O2S + (La-Ce)O2 + SiO2 (minority); oxygen, phosphorus, arsenic, and antimony bound to lanthanum and cerium probably bonded with iron oxides La + Ce, MgO, Al2O3 a SiO2; (La-Ce)2O2S, FeO, SiO2, and CaO or CaS.

Rapid Prototyping of Carbon‐Bonded Alumina Filters with Flame‐Sprayed Alumina Coating for Bottom‐Teeming Steel Ingot Casting

Although continuous casting is the state‐of‐the‐art casting method in steelmaking, ingot casting by bottom teeming has kept its relevance, for example, in the area of specialty steels. The main challenge is to meet the ever‐increasing quality requirements demanded by the customers. Regarding high‐performance steel applications, the purity with respect to the content of nonmetallic inclusions thereby is of special interest. Herein, foam templates with tailored geometry are designed and manufactured by selective laser sintering. Different coating techniques based on carbon‐bonded alumina slurries are applied to replicate foam structures with miniature cube geometry and cylindrical geometry. The techniques are evaluated regarding the porosity, pore size distribution, bulk density, mechanical strength, and shrinkage of the resulting filters. Suitable processing routes are selected to manufacture prototype batches with near‐net‐shape geometry. Finally, the feasibility of applying a flame spray coating is tested. First samples of the prototype batch are tested in industrial bottom‐teeming ingot casting.

Optimization Steel ingot Mould’ Riser Height Based on Solidification Simulation

Solidification process of 13.5t P91 steel ingot with different riser heights were simulated by software and predicted the distribution of shrinkage cavity. The simulation results showed the shrinkage cavity in the precedent ingots is much deeper. The simulation results is agreement well with experiment results. Therefore, the riser height was designed by solidifation simulation and verified by experiments and the results showed that optimized riser height can eliminate shrikage cavity and improve the quality of steel ingot.

Influence of eutectic phase precipitation on cracking susceptibility during forging of a martensitic stainless steel for turbine shaft applications

The presence of the eutectic phase (delta ferrite + M23C6) in martensitic stainless steels brings significant deterioration of the in-service mechanical properties of the critical components such as turbine shaft made of these alloys. In the present study, thermodynamic and kinetics of eutectic phase formation during solidification and the reheating stages before forging of a large size X38CrMo16 martensitic stainless steel ingot are investigated. Material characterization and microstructural evolution were characterized in three different zones of a large size ingot. It was observed that the forging temperature and the solidification rate were the two most effective parameters influencing the volume fraction of the eutectic phase and its morphology. Optical and electron microscopy observations along with Energy Dispersion Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD) measurements were used in the investigation. The results showed that the eutectic phase precipitated primarily at the grain boundaries. Furthermore, a clear evolution on the morphology and volume fraction of the eutectic phase including thin film-like and skeleton-like carbides was found from the outer surface to the center of the ingot along the radial direction. EDS analysis revealed the substantial presence of chromium, molybdenum, and carbon within the M23C6 along the grain boundaries. Phase transformation and the precipitation phase sequences were analyzed as a function of temperature and composition of eutectic transformation using the Thermo-Calc software and the predictions were validated with experimental findings.

Devising manufacturing techniques to control the process of zonal segregation in large steel ingots

A method of physical modeling was applied to study the effect of external actions on the processes of crystallization and the formation of the structure of ingots. A brief review of existing hypotheses about the evolution of physical, structural, and chemical heterogeneities in large steel ingots is given. The parameters of the structure and the two-phase zone have been determined, as well as the nature of the distribution of segregated materials along the cross-section of ingots, depending on the conditions of their curing. The decisive importance of convective and capillary mass transfer in the interdendritic channels of hardening ingots on the formation of a zonal heterogeneity at their cross-section has been proven. Experimentally, when crystallizing a model environment (camphene), it has been visually confirmed that the flow of segregated materials in interdendritic channels occurs when a certain amount of impurities accumulates in them. A clear dependence of the speed of this flow on the rate of melt crystallization has been established. With an increase of the hardened part of the melt, the rate of segregated material movement (Vl) increases while the rate of crystallization (R) decreases due to worsening heat release conditions. At a certain distance from the ingot’s surface, these rates become equal, and impurities are carried to the curing border, which is the main cause of the formation of zonal segregation. The results reported here show that the evolution of zonal segregation in ingots can be controlled using various techniques involving external influence on the hardening melt. This study has demonstrated that the adjustable intensity of heat removal from an ingot, as well as the addition of external excess pressure on the hardening melt, could be used as such tools. In the study, to obtain ingots with a minimum level of chemical heterogeneity, it would suffice to provide the following conditions for the curing of the alloy: a value of the alloy crystallization speeds at the level of Rcr ≥ 9·10–2 mm/s, or external pressure on the free surface of ingots Рext. ≥ 135 kPa. The industrial implementation of the reported results could make it possible to improve the technology of obtaining large blacksmith ingots, provide savings in materials and energy resources, increase the yield of a suitable metal, and improve its quality

A journey of over 200 years: early studies on wootz ingots and new evidence from Konasamudram, India

Recent new evidence emerged from the crucible steel production site of Konasamudram, Telangana, India. A hoard of 60 crucible steel ingots from this site offers a unique opportunity to study details of the early large-scale production of this fabled material, beginning with a detailed documentation of the weights and sizes of 45 of them. Historically, Konasamudram has been an important pre-modern crucible steel manufacturing and trading centre in India, as reported by Persian and European travelogues, and may have been the source of many of the early ingots studied during the past 200 years. The aim of this work is to present a dimensional analysis of these ingots and interpret the data in the context of earlier studies, to address questions of consistency in manufacturing, standardization of weights and other physical attributes. The newly-discovered ingots show considerable uniformity in shape, size and weights, indicative of a single production event during the heydays of crucible steel making, while the ingots previously reported in the literature vary much more widely.

Basic indicators of steel industry of Russia operation in 2020

The spread of the coronavirus has had a significant impact on the ferrous metallurgy of Russia. Extensive analysis of steel industry of Russia status in 2020 presented. Dynamics and structure of production of basic products of Russian and world steel industries was shown. By results of 2020 year operation, Russia moved to the fourth position from the fifth one among the biggest steel producers in the world with the volume of production of 72.8 million tons, which accounts for 4% of world steel production. Data on production dynamics of basic products of steel industry of Russia in 2019–2020 presented. In 2020 metallurgical enterprises of Russia produced 52 million tons of cast iron, which is higher of that in 2019 by 1.5%. Production of finished rolled products accounted for 61.8 million tons (increase by 0.5%), steel production also increased by 1.1%. In 2020 the share of BOF steel and EAF steel in total volume of steel produced accounted for 97.8% (at the level of 2019). In 2020 the total value volume of export of raw materials (ores and iron ore concentrates, coke, steel scrap and wastes), ferroalloys, steel ingots, billets and rolled products accounted for USD 18.47 billion and decreased by 11.8% comparing with the value volume of 2019 (USD 20.95 billion). The total value volume of raw materials import (ores and iron ore concentrates, ferroalloys, steel ingots, billets and rolled products) decreased comparing with the value volume of 2019 and accounted for USD 3.9 billion. Economic indices of basic steel-works operation presented, as well as data on utilization of material and energy resources and their investment activity in 2020.

Effect of Pressure on Dendrite Structure and Characteristics of Carbides during Solidification Process of H13 Die Steel Ingot

Effect of Pressure on Dendrite Structure and Characteristics of Carbides during Solidification Process of H13 Die Steel Ingot

Inducing mechanism and model of the critical oxygen content in homogenized steel

Macrosegregation is the key issue in the solidification field. Oxygen and its inclusions play the important role in driving the melt flow and the resulting macrosegregation in steel. Here, to reveal the inducing mechanism and quantitative model of oxygen content in real industrial steel ingots, we demonstrate for the first time that there exists the critical oxygen content in triggering the formation of channel-type segregation, the most undesirable macrosegregation type in steel. Our multiscale simulations from density functional theory calculations to multiphase/multicomponent macromodel, clarify the quantitative conditions initializing channel-type segregation and reveal two typical growth modes via oxide flotation. The oxygen content model and criterion to induce the channel onset is built accordingly, which are validated by the numerous full ingot dissections and experimental characterizations including the in situ electrolysis of inclusions, X-ray microtomography, scanning electron microscope, large-scale measurement system of inclusions and chemical analysis. With oxygen controlled below this critical value of 0.0008 wt%, channel disappears. This study quantitatively uncovers the novel role of oxygen in steel, changes the traditional sole concept of cleanliness, and highlights an innovative and controlling-effective route to fabricate homogenized steel.

Application of Heat Absorption Method to Improve Quality of Large Steel Ingot

The heat absorption method (HAM) was proposed to improve the quality of a large steel ingot. The CaO–CaF2 inorganic material rods was used to reduce 5 K superheat of the 6-ton GCr15 molten steel. The quality of the steel ingots with and without the HAM was compared. In comparison with conventional casting, the HAM not only significantly alleviated the A- and V-segregation and the segregation levels of carbon and sulfur, but also reduced the number of inclusions and the shrinkage porosity zone in the 6-ton steel ingot. The simulation results demonstrated that the molten steel could quickly be cooled from within by the inorganic material rods, which is the main reason for the reduction of macrosegregation. Additionally, the majority of inclusions could be absorbed and removed when the liquid inorganic material floated up in the molten steel.

Carbides Modification and Mechanical Properties Enhancement of Cr12MoV Die Steel by Magnetically Controlled Electroslag Remelting

The effects of an axial static magnetic field (ASMF) on the carbides and mechanical properties of electroslag-remelted (ESR) Cr12MoV die steel were investigated. The superimposition of a 30 mT ASMF induced unidirectional rotation in the molten slag pool, resulting in a more uniform temperature distribution at the front of the dendrite solid–liquid interface. The size of the grains and carbides in the ESR Cr12MoV steel ingot became smaller. The sulfur content of the ingots decreased and the mechanical properties (hardness and impact energy) increased after applying the ASMF. A new mechanism was proposed that the unidirectional flow was mainly due to the coupled thermoelectric magnetic force induced in the melt between dendrites, which promoted the refinement of grains and carbides, as well as the desulfurization process, thereby resulting in the enhanced mechanical properties of the Cr12MoV die steel.

Development Technology for Prevention of Macro-segregation in Casting of Steel Ingot by Insert Casting in Vacuum Atmosphere

Development Technology for Prevention of Macro-segregation in Casting of Steel Ingot by Insert Casting in Vacuum Atmosphere

Impact of Solidification on Inclusion Morphology in ESR and PESR Remelted Martensitic Stainless Steel Ingots

This study focuses on the impact of solidification on the inclusion morphologies in different sizes of production-scale electro-slag remelting (ESR) and electro-slag remelting under a protected pressure-controlled atmosphere, (PESR), ingots, in a common martensitic stainless steel grade. The investigation has been carried out to increase the knowledge of the solidification and change in inclusion morphologies during ESR and PESR remelting. In order to optimize process routes for different steel grades, it is important to define the advantages of different processes. A comparison is made between an electrode, ESR, and PESR ingots with different production-scale ingot sizes, from 400 mm square to 1050 mm in diameter. The electrode and two of the smallest ingots are from the same electrode charge. The samples are taken from both the electrode, ingots, and rolled/forged material. The solidification structure, dendrite arm spacing, chemical analyzes, and inclusion number on ingots and/or forged/rolled material are studied. The results show that the larger the ingot and the further towards the center of the ingot, the larger inclusions are found. As long as an ingot solidifies with a columnar dendritic structure (DS), the increase in inclusion number and size with ingot diameter is approximately linear. However, at the ingot size (1050 mm in diameter in this study) when the center of the ingot converts to solidification in the equiaxial mode (EQ), the increase in number and size of the inclusions is much higher. The transition between a dendritic and an equiaxial solidification in the center of the ingots in this steel grade takes place in the region between the ingot diameters of 800 and 1050 mm.

Internal shrinkage crack in a 10 t water-cooled steel ingot with a large height-to-diameter ratio

Steel ingot with a large height-to-diameter ratio is utilized to produce multiple products by one stock in practice. Water cooling is a usual way to enhance production efficiency. However, the combination of the two factors will generate internal defects, such as shrinkage porosity and hot crack. The characteristic of internal shrinkage crack in a 10 t water-cooled steel ingot with a large height-to-diameter ratio was examined by an ultrasonic test. A slice was sectioned from the ingot middle part where billets containing star-like crack were further extracted. The billets were examined by X-ray high energy industrial CT, and the compactness was reconstructed in three dimensions. Microstructure near the crack was observed using scanning electron microscopy, and the solidification process and grain size were studied by high temperature confocal microscopy. Moreover, thermomechanical simulation and post-processing were carried out to analyze the formation of shrinkage porosity and hot crack. A new criterion considering mushy zone mechanical behavior in brittle temperature as well as grain size distribution was proposed to evaluate hot cracking potential in the ingot. The results show that a deep shrinkage porosity band easily forms in the center line of such an ingot with a large height-to-diameter ratio, and water-cooling further generates excessive tensile stress tearing the liquid films around the porosities. Then, hot cracks begin to propagate along grain boundaries. The grain size in the upper and center of the ingot is large, which leads to an inverted cone shape defects zone in the ingot center.

Numerical Simulation of Macrosegregation Formation in a 2.45 ton Steel Ingot Using a Three-Phase Equiaxed Solidification Model

In the present work macrosegregation during solidification of a 2.45 ton steel ingot is simulated with a pure equiaxed model, which was tested previously via modeling of a benchmark experiment. While the columnar structure is not taken into account, a packed layer formed over inner walls of the mold at an early stage of solidification reproduces to some extent phenomena generally related to zones of columnar dendrites. Furthermore, it is demonstrated that interaction of free-floating equiaxed grains with ascending convective flow in the bulk liquid results in flow instabilities. This defines the irregular form of the negative segregation zone, the formation of which at the ingot bottom corresponds to experimental observation. Vertical channels reported in experimental measurements are reproduced in simulations. It is confirmed that intensification of ingot cooling may decrease segregation in the ingot.