Behaviors of Lanthanum and Cerium on Grain Boundaries in Carbon Manganese Clean Steel

The behaviors of La and Ce on gram boundaries in carbon manganese clean steel were investigated by high-reso- lution transmission elecetron microscope （HRTEM）, scanning elecetron microscopy（SEM ）, energy dispersive spectrometer （EDS） and X-ray diffraction（XRD） analysis. The existing forms of rare earths （RE） in clean steel were as follows： dissolved in sohd solution, forming inclusion or second phase containing RE （RE-Fe-P, La-P, Fe-La eutectic and Fe-Ce phase）. The dissolved La or Ce segregated at grain boundaries. The segregation of both S and P at gram boundaries was reduced with suitable RE content. The impact toughness of the steel was improved obviously. La and Ce had effecets on purifying molten steel and modifying inclusions in clean steel, whereas with excessive La or Ce, La-Fe-P, La-P and Fe-La eutecetic phase or Ce-Fe-P and Fe-Ce intermetallic compound would form along grain boundaries, causing the impact energy to decrease significantly.

Current Situation and Development of Refractories for Clean Steel Production

The low cost and high efficient clean steels metallur- gy has been focused much attention in China. Among the factors affecting the cleanliness and consequent quali- ty of steel products, refractories are one of the key fac- tors. Meanwhile the restriction of resource, energy and environment is getting stronger, thus the improvement of refractories becontes much more important. In this paper, refractories selection principle Jbr clean steel production according to their thermodynamic features was ex- plained; refractories for tundLsh and flow control in con- tinuous casting, which play important roles in prohibi- ring secondary contamination of molten steel, were intro- duced. Moreover, new development of low-carbon and carbon-free refractory materials was also described.

Effect of Rare Earths on Corrosion Resisting Properties of Carbon-Manganese Clean Steels

Electrochemistry experiments were made on carbon-manganese clean steel with rare earths Ce and La respectively to observe corrosion parameters such as corrosion current i_(corr), and characteristic potential of pitting E_b. The results indicate that the rare earths have effect on corrosion resisting properties of carbon-manganese clean steel, and the optimum contents of La is about 0.011% (mass fraction) and Ce about 0.014% (mass fraction) respectively. The change of corrosion resistance is related to the action of rare earths on microstructure and effect on surface state of samples in the process of polarization.

Roles and Progress of Refractories for Clean Steel Technology

This paper presents a general survey of roles and progress of fundamental and fitnctional refractories applied in seco Mal：y steelmaking, tundish and mold tnetallurgy along with the evolution of clean steel technology, focusing on refractories that are to create clean environments, benefit cleanliness and productive efficiency for the clean steal production, in particular, reducing the total oxygen content and inclusion defects in steel. All that arguments have revealed in abundant that the interaction between the clean steel technology and inno vation of refractories is so intimate that the philosophy of clean steel technology would not be accomplished without functioning of the innovated state of the arts refractories in it.

RESEARCH ON AS-CAST GRAIN REFINING TECHNOLOGY BY INOCULATING CLEAN STEEL WITH TITANIUM OXIDE

Precipitation condition and nucleation of Ti2O3 during solidification of clean steel have been studied. The behavior of Ti2O3 during solidification as well as possibility of using Ti2O3 to refine as-cast grains as heterogeneous nucleation sites is discussed. It is shown that Ti2O3 can be formed provided that the steelmaking and solidification process is controlled strictly. And inoculating clean steel with Ti2O3 is an effective way to refine as-cast grains.

Kinetics Analysis of Pre-Eutectoid Transformation of Austenite in Carbon-Manganese Clean Steel with Rare Earths

By means of rapid cool dilatometry, the influence of rare earths on kinetics of pre-eutectoid transformation of austenite of carbon-manganese clean steel was studied. While the content of rare earths were proper, the nucleation of pre-eutectoid ferrite on the grain boundary of austenite was accelerated and the incubation period of pre-eutectoid transformation was shortened. But while rare earths were excessive, opposite actions appeared. Rare earths decreased transformation velocity constant in the process of transformation from austenite to ferrite, which meant that the growth of per-eutectoid ferrite became slow. The reason above varieties was related to effect of rare earth on grain boundary constitution of austenite and diffusion of carbon element.

Enhanced clean steel tapping on BOF vessels with the interstop converter gate type CG series

Trends in today' s steel production show increasing demands for highly-sophisticated steel grades. Therefore,the steel industry will eventually be required to install best performing technologies to meet governmental specifications designed to significantly reduce environmental emissions.Such efforts are supported by innovative new solutions in the entire steel making process.One process that will need to be addressed is the cleanliness of the steel in the liquid steel phase,especially during the BOF-tapping process. The new converter gate(CG)(Fig.1) best supports the slide gate tapping technology for converters in terms of clean steel,productivity,yield and availability-at reduced costs. The CG gate introduces a unique feature for converter slide gates:The bottom plate can be exchanged while the gate remains mounted on the converter.This new feature allows for an increased utilisation of the refractory parts and a significant reduction of the downtime of the converter.This 'designed efficiency' is achieved with a refractory set consisting of three identical plates-two bottom plates and one slider plate-and a nozzle.A number of other improvements such as automatic cylinder coupling using the Interstop SNAP technology and a two step tensioning system have also been implemented. The new system is designed to meet minimal space requirements and therefore will adapt to most BOF shops.To perform preparation,service and maintenance work the modular CG gate can be dismounted from the converter and simultaneously replaced by a ready-to-use unit.The degree of automation for dismounting and mounting as well as for off-line preparation has been enhanced and reduces manual efforts. This paper provides a solution to the obvious trend towards efficient and controlled production of clean steel,in general,and especially at BOF shops.Moreover,it specifically describes the operational results of this innovative BOF tapping equipment at Salzgitter Flachstahl GmbH,Germany.

Progress of Production Technology of Clean Steel in Baosteel

The progress in control technology of carbon, nitrogen, total oxygen, phosphorus, and sulphur as well as ()inclusions in steel is discussed at Baosteel. The purity obtained in IF steel and pipeline steel is introduced.

Effects of Rare Earth on Structure and Mechanical Properties of Clean BNbRE Steel

The mechanisms of RE in clean BNbRE steel were studied by means of experimental measurement, microstructural observation and theoretical analysis. For BNbRE steel, the state and the content of RE were measured, and the effects and the mechanisms of RE on sulfide inclusions, microstructure and properties of steel were determined. On the condition of increasing the cleanliness of steel, the mechanisms of RE in steel were changed to certain degree. Small amount of RE has the effect of cleaning, modifying inclusions and alloying in clean steel, too. With increasing the cleanliness of BNbRE steel, addition of RE should be decreased properly. Under experimental conditions, the optimum addition of RE is -0.01 % （mass fraction） for clean BNbRE steel, while RE can evidently improve plasticity and impact toughness of BNbRE steel.

Reviews and Prospects of Clean Steel Production Practices in Ansteel

It summarizes the recognition of clean steel through the reviews the historical development and production practices of clean steel of Ansteel in this paper.The technological characteristic,equipment,controlling capability and new exploratory of clean steel production of Ansteel are introduced.It has also made a new appraisal to the production line of different clean steel from the angle of high efficiency,stabilization and low-cost.The prospects of new production technology of clean steel are introduced at the end of the paper.

Overview:Development of Clean Steel Production at Baosteel

The development of clean steel technology at Baosteel can be dated back to the first production of IF steels and pipeline steels in the early 1990s.Now the technology has gradually covered nearly the whole range of products.This progressive development is introduced in the overview including the levels of cleanliness for some steel grades at Baosteel.The technologies at different processes for the production of clean steel and the removal of some impurity elements in molten steel are also discussed.Suggestions are given on the future research and development of clean steel technology at Baosteel in the aim to keep a sustainable development,which should focus on the basic research,inclusion control and making efficient use of inclusions,as well as stable and reliable low-cost manufacturing technology,removal of harmful residual elements,and the expanding of the technology to stainless steels and special steels.

Construction of High-Efficiency and Low-Cost Clean Steel Production System in Shougang Jingtang

This paper analyzes the technology for clean steel production in modern iron and steel plant,a philosophy with production efficiency,manufacturing cost and product performance in its core.It also makes a review on functions of high-efficiency,low-cost and high-quality steel products manufactured by the new generation iron and steel plant,in combination with the study on design of steelmaking-continuous casting process of Shougang Jingtang iron and steel Plant.By applying precise and dynamic design system to optimize and allocate systems and working procedures of hot metal pretreatment,converter smelting,secondary refining,continuous casting process,etc,a platform of high-efficiency,low-cost and high-quality clean steel production is built.

Oxide Inclusions in Ferromanganese and Its Influence on the Quality of Clean Steels

Low and medium carbon ferromanganese produced by oxygen decarburization process and electric silicothermic process was briefly introduced, and the quality of products by these two processes was analyzed. Results showed that the total oxygen content in medium carbon ferromanganese by electric silicothermic process in China, which ranged from 0.039% to 0.171%, was between those of the common and refined products by oxygen decarburization process outside of China. The increments of total oxygen content in liquid steel were estimated when ferromanganese was added for the purpose of Mn element adjustment at the end of smelting. Refined low and medium carbon ferromanganese, which had low total oxygen content, was recommended for composition adjustment of clean steels during final stage of a heat. It is possible that the inclusions in the ferromanganese alloy greatly influenced the quality of clean steel indirectly by affecting the amount, size and composition of inclusions in steel.

Research on Refining Technology of Clean Steel in a Plasma Ladle Furnace

The clean steel refining tests carried out in a 100 kg plasma ladle furnace(PLF)were to show the metallurgical effects of the different plasma gases such as Ar-H_2 and Ar-CO_2.The variations of carbon,nitrogen contents in steels and the mechanism of denitrogenation were studied.Compared with the conventional ladle furnace,when the plasma gases were injected into the ladle furnace,there was a decarburization process,the carburetion rates were reduced obviously. The carburetion rate is 3.6×10^(-6) per minute for the steel heated by conventional LF,and is 2.20 and 1.35 times of the heats blown 85%Ar-15%H_2 and 85%Ar-15%CO_2,respectively.When the plasma ladle furnace operated with Ar-H_2 plasma gas, the denitrogenation of the molten steel occurs.The lowest denitrogenation rate is 0.30×10^(-6)per minute when Ar-H_2 gas mixtures were used.The main reactant gas is monatomic hydrogen and the main product of denitrogenation is NH_3 for Ar-H_2 injection.

Control of Sulfur Content in the Production of Clean Steel in Panzhihua Steel

This article mainly introduced the process of clean steel with different ways in Panzhihua Steel based on high sulfur content hot metal. With the development and application of sulfur control technologies in hot metal pretreatment, converter steel-making and refining processes, Panzhihua Steel had achieved the production of clean steel such as 350km/h steel for high speed railway, electric steel, etc.

Low-Cost and Large-Scale Clean Steel Production Technology

As the market demand for clean steel increased,a number of new technologies for clean steel production have been developed in some domestic and foreign steelmaking plants.Based on the existing equipments and technical conditions in the No.1 steelmaking plant of Ansteel,a series of clean steel technologies have been integrated including single bay duplex-dephosphorization in steelmaking control technology,high efficiency desulfurization technology,the control technology for nitrogen content during the whole process,the control technology for hydrogen content in VD,and the systematic control technology for oxygen content.A series of process for all kinds of ultra-low phosphorus,ultra-low sulfur and relative low level of inclusions have been designed in clean steel production.This process include hot metal desulfurization and slag-off,single bay duplex-dephosphorization in BOF,molten steel slag-off,LF processing,VD processing,and continuous casting with protection,then a stable,low-cost and large-scale production process has been formed.Applying this integrative technology,the sum of 5 major elements including phosphorus,sulfur,oxygen,nitrogen,hydrogen is less than 80×10-6 in high alloy steel scale production,and the industrial applications for clean steel technology have been achieved.

More Discussion on High Efficiency & Low Cost Clean Steel Production Platform

The construction of high efficiency, low cost clean steel platform is one of the common key technologies concerning efficiency, quality and cost. It is basic and universal and not only applicable in the R&D and production of "high-end" products, but also in the production of bulk ordinary steel products. The platform of high efficiency, low cost clean steel is the important direction of modern steel technology progress and has great significance on the competitiveness of each steel plant. The research of high efficiency, low cost platform not only involves the production and management of the steel plant, but also the academic research field (process engineering and dynamic operation) and theories and methods innovation of engineering design (theory and method of dynamic-precision design). The integrated theory and method of high efficiency and low cost clean steel platform is the binding point of metallurgical process engineering and material engineering. Different types of high efficiency, low cost clean steel platform should combine with the corresponding rolling process and iron making process so that high efficiency, low cost clean steel manufacturing system would come into being.

Progress on statistical models of evaluating inclusions in clean steels

Non-metallic inclusions are critical for the fatigue failure of clean steels in service;especially,the large and hard inclusions are detrimental.Since it is not possible to measure all the inclusions in the large-volume clean steels,statistical models have been developed to evaluate inclusions,aiming at predicting the maximum inclusion size in the large volume from the data of inclusions,which are derived from the limited observations on small-volume specimens.Different statistical models were reviewed together with their supporting theories.In particular,the block maxima and the threshold types of models were discussed through a thorough comparison as they are both widely used and based on the extreme value theory.The predicted results not only are used to distinguish the different cleanliness levels of steels,but also help to estimate fatigue strength.Finally,future research is proposed to focus on tackling the present difficulties encountered by statistical models,including the sufficient credibility of obtained results and the robustness of models for applications.

Clean Production of Steel and Refractories in China's Steel Industry

The paper describes the importance of clean production of steel and the relationships amongst sustaining development of steel industry, environment protection and the role of refractories in the clean production of steel. The main achievements and main shortcomings in the clean production of China ' s steel industry have been reviewed together with the introduction of the policy supporting system and the future development of clean production in China ' s steel industry.

Inclusion control of ultra clean ferritic stainless steel

The most important characteristics of the ultra clean ferritic stainless steel is that the carbon,nitrogen and other interstitial elements are very low.The ultra clean ferritic stainless steel has been widely used for household appliances,auto exhaust system,elevator,water treatment system,building roof and other various fields,because of its low cost,pro-environment,excellent properties.They can replace some traditional austenitic stainless steel.such 304 and 316L.The addition of titanium to liquid steel has become common for stabilizing nitrogen and carbon in steel.Titanium reacts with nitrogen,carbon,and oxygen to form titanium nitride,carbide, carbonitride and oxide.These inclusions may have a deleterious effect on the properties such as toughness, ductility,weldability and corrosion.In addition,the inclusions can also agglomerate and cause surface quality problem of the slab and clogging of the submerged entry nozzle during continuous casting process. The formation rules of inclusions in ultra clean ferritic stainless steel were investigated by the thermodynamic calculation,and methods of controlling inclusions were put forward to improve the quality of product.The composition,type,amount,size and distribution of the inclusions in the slab are investigated by optical microscope and scanning electron microscope.The results can be concluded as follows.(1) In the slab,the main original inclusions,with size of larger than 2μm,are Al_2O_3,TiN or Ti(CN) and complex TiN or Ti(CN) inclusion with core of MgO,MgO-Al_2O_3 and Ti_2o_3,which will not affect the performance of the steel if they are in diffusing distribution.The size of these inclusions are less than 10μm except some Al_2O_3 inclusions in size of 10-40μm.(2) Foreign inclusions are Ti_2O_3-Al_2O_3-MgO-SiO_2 in size above 50μm covered by TiN or Ti (CN).Although these inclusions are few,they do harm to the surface quality of stainless steel.It is able to reduce the risk of forming this kind of inclusion by aluminium deoxidation with increasing Al content to restrain the formation of Ti_2O_3.(3 ) TiN or Ti(CN) is easy to precipitate on inclusions such as MgO,MgO-Al_2O_3 and Ti_2O_3,except Al_2O_3.Controlling the content of[Ti]and[N]and the formation of the oxides can be used to control the precipitation of TiN or Ti(CN).