Artificial Inclusion Environments—Replicating Industry in the Laboratory

The authors present a series of complementary test methods which were developed and used to investigate reactions between high aluminium steel and silica rich inclusions. Non-metallic inclusions (NMIs) cause many defects in the final steel product, therefore the ability to track their size, morphology and composition and correlate this with fundamental reaction kinetics provides important knowledge to support the production of clean quality steel products. Novel steel grades such as TRIP, TWIP and low-density steels have high aluminium contents; aluminium is a readily oxidisable species presenting the potential for instability and excessive reaction with commonly used mould powders that contain silica. A novel combination of techniques including HT-CLSM (High-Temperature Confocal Laser Scanning Microscope), XCT (X-ray computed tomography) and SEM/EDS (scanning electron microscopy/electron dispersive spectroscopy) have been used to study the interaction of entrained mould powder inclusions with steel at high temperatures simulating industrial conditions. This report presents a discussion on the development of techniques and samples to achieve representative and repeatable results that can provide information on the complex chemical and physical interaction phenomena with confidence. Each experimental technique had its own learning points and consequent results. Outcomes presented include possible confirmation of the chemical reaction rate controlling step being aluminium mass transfer; heterogeneous local environmental conditions including fluidity and chemical composition; and occurrence of spontaneous emulsification where the mould powder inclusion breaks apart into a cloud of smaller fragments.

Non-metallic Inclusions in Different Ferroalloys and Their Effect on the Steel Quality: A Review

Ferroalloys have become increasingly important due to their indispensable role in steelmaking. In addition, the demand for improved steel qualities has increased considerably, which in turn highlights the quality of ferroalloys. This is due to the fact that the impurities in ferroalloys directly and significantly influence the quality of steel products. To gain a better understanding of the main trace elements and inclusions in ferroalloys (such as FeSi, FeMn, SiMn, FeTi, FeCr, FeMo, FeNb, FeV, FeB, some complex ferroalloys) and their behaviours in steel melt after the additions of these ferroalloys, information from a large number of previous results on this topic was extensively reviewed in this work. The applications of different ferroalloys and their production trends were discussed. In addition, the effects of some trace element impurities from ferroalloys on the inclusion characteristics in steel were also discussed. The possible harmful inclusions in different ferroalloys were identified. Overall, the results showed that the inclusions present in ferroalloys had the following influence on the final steel cleanliness: (1) MnO, MnS and MnO–SiO2–MnS inclusions from FeMn and SiMn alloys have a temporary influence on the steel quality; (2) the effect of large size SiO2 inclusions (up to 200 μm) in FeSi and FeMo alloys on the steel cleanliness is not fully understood. The effect of Al, Ca contents should be considered before the addition of FeSi alloys. In addition, Al2O3 inclusions and relatively high Al content are commonly found in FeTi, FeNb and FeV alloys due to their production process. This information should be paid more attention to when these ferroalloys are added to steel; (3) except for the existing inclusions in these alloys, the Ti-rich, Nb-rich, V-rich carbides and nitrides, which have important effects on the steel properties also should be studied further; and (4) specific alloys containing REM oxides, Cr–C–N, Cr–Mn–O, Al2O3, Al–Ti–O, TiS and Ti(C, N) have not been studied enough to enable a judgement on their influence on the steel cleanliness. Finally, some suggestions were given for further studies for the development of ferroalloy productions.

Peculiarities of application of natural and man-caused materials for steel alloying and modifying

Considerable reserves of improvement of steel quality and reduction of costs of its production are concealed in a possibility of active and purposeful formation their structure and the properties by introduction into the melt modifiers, alloying and microalloying additives. Due to the task of decreasing costs, studies on alloying and modifying of metal by natural and man-caused materials are very actual. Thermodynamic regularities of steel alloying and modifying processes by natural and man-caused materials, including manganese ores of various structures, BOF vanadium slag, barium- strontium modifier, obtained from the complex ores containing barium and strontium considered. Possibilities of wide application of various structure manganese ores for steel alloying by manganese without use of standard manganese alloys as well as vanadium slag for microalloying by vanadium demonstrated. Metallurgical properties barium-strontium natural modifier obtained and the possible mechanism of the modifying impact of barium and strontium on quality of metal studied. It was determined, that the effect of modifying by barium can revealed in steels, deoxidized only by silicon, and for modifying by strontium or joint modifying by barium and strontium it is necessary to apply aluminum as deoxidizing agent. Industrial testing of the above-stated materials showed reliability of studies, accomplished at thermodynamic modeling and laboratory studies of calculations and conclusions. Recommendations on optimization of technologies of steel alloying and modifying made. It was proved that use of the materials of the study allows to improve technical and economic indices of the process of production of steels and to increase considerably quality of final steel products. Conclusions on significant expansion of natural and man-caused materials prospects worded.

Modification of Non-Metallic Inclusions in Oil-Pipeline Steels by Ca-Treatment

Corrosion rate in different steel grades (including oilfield pipeline steels) is determined by the presence of non-metallic inclusions (NMI) in steels. Specifically, the effect of different inclusions on the quality of steels depends on their characteristics such as size, number, morphology, composition, and physical properties, as well as their location in the steel matrix. Therefore, the optimization and control of NMI in steels are very important today to obtain an improvement of the material properties of the final steel products. It is well known that a Ca-treatment of liquid steels in ladle before casting is an effective method for modification of non-metallic inclusions for improvement of the steel properties. Therefore, the NMI characteristics were evaluated in industrial steel samples of low carbon Ca-treated steel used for production of oil-pipelines. An electrolytic extraction technique was used for extraction of NMI from the steel samples followed by three-dimensional investigations of different inclusions and clusters by using SEM in combination with EDS. Moreover, the number and compositions of corrosion active non-metallic inclusions were estimated in hot rolled steel samples from two different heats. Finally, the corrosion resistance of these steels can be discussed depending on the characteristics of non-metallic inclusions present in the steel.

Thermodynamics and Industrial Trial on Increasing the Carbon Content at the BOF Endpoint to Produce Ultra-Low Carbon IF Steel by BOF-RH-CSP Process

Thermodynamic analysis was performed to obtain the relation between the carbon content at the BOF endpoint and the dissolved oxygen content in liquid steel and the (FeO + MnO) content in the slag with the help of thermodynamic calculation software FactSage. It finds that both the [O] and (FeO + MnO) content increase with decreasing the carbon content at the BOF endpoint and the increasing rate is larger when the carbon content is lower. In addition, in the case of the higher temperature at the BOF endpoint the [O] in liquid steel increase and the (FeO + MnO) in the slag increase as well. The consumption of O2 for decarbonization at the BOF endpoint is much more than that in RH degasser since the majority of the blowing O2 at the BOF endpoint will produce FeO into the slag, thus it increase the metal loss and deteriorate the steel cleanness during the consequent refining process. As a result, the carbon content at the BOF endpoint should be properly increased within the RH decarbonization ability. At last, industrial trials were carried out and confirmed that total oxygen consumption decrease obviously and the (FeO + MnO) of final BOF slag decline as well with increasing carbon content at BOF endpoint from 0.042% to 0.081%. In addition, it almost does not slow down the RH process and the carbon content in final steel all met the demand of the ultra-low carbon steel. In addition, mechanical properties of IF steel with higher carbon content at the endpoint of BOF are almost all more superior to those of heat with lower carbon content at BOF endpoint.

A numerical model for considering the bond-slip effect in axially loaded circular concrete-filled tube columns

This article introduces a numerical model that simulates the bond-slip behaviour in axially loaded circular concrete-filled tube columns without applying double nodes required in the use of the classical bond-link element. After calculating the nodal displacements of in-filled concrete, the deformation in the steel tube at each node has been found through the back-substitution technique from the first to the final steel element using a governing equation constructed on the basis of the force equilibrium and displacement compatibility at each node. Finally, correlation studies between analytical and experimental results are conducted to verify the efficiency and applicability of the introduced model.

Experimental Study on the Behavior of TiN and Ti2O3 Inclusions in Contact with CaO‐Al2O3‐SiO2‐MgO Slags

TiN and Ti2O3 are the predominant inclusion types in Ti-alloyed ferritic chromium stainless steels. In order to ensure the required steel cleanness level, an effective removal of such inclusions in the slag during secondary metallurgy is essential. This inclusion removal predominantly takes place via dissolution of the inclusion in the slag. The dissolution behavior of TiN and Ti2O3 in CaO-SiO2-Al2O3-MgO slags as well as their agglomeration behavior in the liquid steel is investigated using High Temperature Laser Scanning Confocal Microscopy and Tammann Furnace experiments. Thermodynamic calculations are performed using FactSage 7.0. The behavior of TiN is observed to be completely different to that of oxides. Ti2O3 dissolves quickly in slags, and its dissolution behavior is comparable to that of other already well examined oxides. In contrast, TiN shows a very intense gas reaction which is attributed to the release of nitrogen during contact with slag. Slags with higher SiO2 content show a significantly higher ability for the dissolution of TiN as compared to Al2O3-rich slags. The gas reaction is found to also significantly influence the final steel cleanness. Despite the easy absorption of TiN in the slag, the formed nitrogen supports the formation of pinholes in the steel.

Hot Rolled Coil Property Heterogeneities due to Coil Cooling: Impact and Prediction

The importance of coil cooling conditions on mechanical properties uniformity of HSLA and AHSS steel grades is discussed. It is namely shown that hot rolled coil under conventional industrial production can be cooled non-uniformly. That is why to predict correctly the final steel microstructure and mechanical properties of hot-rolled products an accurate description of not only run-out table condition but also of coil cooling should be done. Two solutions to provide accurate description of coil cooling were tested. First one is to use 2D finite element (FE) thermal model. When coupled with the ArcelorMittal metallurgical model to predict hot-rolled microstructure and properties (TACSI) it matches well the industrial data within +/-15-20MPa both for the tensile and yield strength. However, this approach is recognized to be heavy and time consuming. A second solution, a new 2D coil cooling simplified model incorporated in TACSI model, proved to be quite efficient, as it leads to performances similar to the more detailed first solution. Moreover, it is able to compute the coupling between the thermal evolution of the hot band and the kinetics of phase transformation during coil coiling and cooling, and will enable a better evaluation of the final mechanical properties especially for the grades for which the phase transformation is not completed before hot band coiling.

Industrial Experiments of Using Limestone Instead of Lime for Slagging during LD-Steelmaking Process

Some industrial trials of utilizing limestone as a new kind of slag-making agent instead of lime for slagging during LD-steelmaking process are discussed and analyzed in the present work. The results indicate that with oxygen blowing time being unchanged, slag forming rate increased significantly and final steel compositions and temperature reached the required standard during the steelmaking process with limestone used, compared with the process by using lime. The preliminary success achieved from industrial tests gave strong evidence that the idea of using limestone instead of lime for slagging is feasible and this new steelmaking method with limestone used, which saves energy and reduces CO2 emissions, can be successfully applied into industrial production. Thus, the application of this new method can not only sharply reduce energy consumption and emission of dust and CO2, but also bring significant environmental and economic benefits.