Steels have made remarkable progress in order to meet the strict requirements of today’s society. Such progress is based on scientific elucidation of the functions of alloying elements, their effective utilization, and the innovative production processes. Since natural resources are limited, it is important to increase their productivity for the continuous development of our society. Therefore, proper management taking into account the element strategy is becoming extremely important. Steel industries are highly dependent on rare metals. Therefore, they are easily influenced by the hazards of rare metals, avoidance of which is extremely crucial. This paper focuses on steels such as flat-rolled product, plate, pipe & tube and stainless steel, and historically reviews them from the aspect of changes in the surrounding market together with the technological developments such as new steel products and exploitation of rare metals for them. The functions of rare metals are classified into three types, i.e. the control of a) microstructures, b) mechanical properties and c) anti-corrosion properties, and the present understanding of them is discussed from a scientific perspective. Furthermore, the concrete future scientific and technological problems are surveyed. It is revealed that there are still many issues that need to be addressed. Exploitation of the advanced analytical techniques together with computational science is expected to contribute to solving the long standing problems and to stimulate a breakthrough in this field.
Various activities performed by the ISIJ social engineering division from 1995 to present is briefly summarized focusing on its contribution to environmental researches in steel science and engineering. Totally 10 forums including the young scientist forum and 8 research-projects in this division made extremely fruitful works. From 2010, this division has merged with another tentative division, “Environment and Energy division” to start a new division named “environmental, energy and social engineering, where environmental issues have been discussed more extensively.
In recent years, while comparing materials has been actively performed by utilizing LCA, in consideration of the lifecycle of a material, recycling is an important factor that influences the overall lifecycle of the materials. However, there is little material of which statistical data in the recycling industry, in other words the venous industry, is arranged. In addition, a definition of the recycling and an amount of material being recycled are different for each material and further, even though it is the same material, the definition of the recycling and the amount of material being recycled are greatly different depending on publicized reports. Among the materials, qualitatively, steel material is said to have high recycling performance but there is not much statistical data regarding recycling thereof. Thus, it is often to indicate a quantitative recycling rate as Recycled Content (a ratio of using steel scrap). However, the Recycled Content of steel manufacturing in Japan is as low as 30%, in accordance with a recent increase in steel consumption, which gives an impression departing from the original meaning of qualitatively “high recycling performance”. Based on the above background, we have collected the quantitative data regarding steel manufacturing for each country of the world and estimated world steel stock (accumulated) in 2008 using the collected data in consideration of a loss or the like in the steel making process. As a result of the estimation, the world steel stock (accumulated) in 2008 was 22 billion tons including the amount of loss. This amount was converted into an amount in terms of Fe and it was estimated that there was 20.8 billion tons excluding the amount of loss. In this review, the recycling rate is considered to be an obsolete scrap recovery ratio and the idea and the estimation method are presented. As a result of collecting data for a long period of time, verifying data and examining the inspection method, material balance of the steel is confirmed and a world steel recycling circuit can be created.
Recently, the issue of sustainable management of resources has been increasingly recognized. Accordingly, the issue to understand the relationship between natural resources consumption and product supply chain in the world has been also increasing. Material flow analysis (MFA) is a useful tool to understand the resource consumption and material cycle in national economy. However, detailed MFA studies of the materials embedded in foreign trade flows are rare. This study identified global trade flow of iron embedded in every bilateral trade between 231 countries by multiplying the trade volume of the commodity in BACI (Base pour l’Analyse du Commerce International) database and the iron content of each commodity. Moreover, we focused on the case of Japan, China, and United State, and estimated each mass of iron embedded in the imports and export. The identified total flows of iron embedded in international trade is 1.15×109 t-Fe, and 35.2% of the flows is concentrated in three countries, which is Japan, China and United State known as crude steel production countries.
In this study, a random sample of 107 steel bars from Japan and 26 steel bars from China were studied. Each specimen’s elemental composition of tramp elements, such as Cu, Cr, Ni, and Sn, was analyzed. By using the compositions of specific tramp elements, 99 of the 107 samples and 16 of the 26 samples were recognized as electric arc furnace steel. The distributions of the tramp element composition were obtained for the Japanese steel bars and represent a larger number of samples than previous studies. Those for the Chinese samples are the first published data. The compositions of Cu, Cr, Ni, and Sn in the Japanese bars are statistically significantly higher than those in the Chinese bars. Owing to the large gap between the Cu contents of the Japanese and Chinese samples, and the statistically significantly differences between the ratios of Cu to both Ni and Cr in the Japanese and Chinese samples, it is highly likely that copper-based materials are separated from steel scrap at a higher rate in China. The relationship between the Cu and Cr compositions suggested that the mixing of copper-based materials and special steels, which contribute to Cr contamination, differs between Japan and China. The distributions of the Cr composition for each country had larger standard deviations than the distributions of other elements. The ratio of the Cr and Ni compositions in the Chinese samples is less than 2.25, resulting in 18% Cr and 8% Ni in stainless steel. It was found that Ni from materials other than stainless steel was likely to have been included.
To realize the removal of Cu from iron scraps by a segregation during solidification, we demonstrated the Cu segregation in Fe-C-Cu alloy by unidirectional solidification of utilizing a temperature gradient. The effect of cooling rate and initial Cu content of Fe-C-Cu alloy on the segregation behavior of Cu was investigated in the present work. The segregation ratio of Cu between solid and liquid was determined based on the experimental data. We found out that the unidirectional solidification of Fe-C-Cu melts results in the Cu segregation in solidified alloy. The segregation coefficient of Cu was 1.2 for the unidirectional solidification of molten Fe–4.2 mass%C–0.5~3.7 mass%Cu alloy.
In order to develop a practical method of Cu removal from the viewpoints of promoting utilization of scrap procured in the market and reduction of energy consumption, it is necessary to develop a practical method of Cu removal. In this study, Cu removal from hot metal by sulfidation of Cu was identified as a potential candidate for industrial use and was investigated in laboratory experiments using ferrous sulfide (FeS) and sodium carbonate (Na2CO3) as commercially-available fluxes. A laboratory experiment on removal of Cu from hot metal was carried out using a 10 kg-scale furnace. Cu removal occurred while feeding the Na2CO3-FeS fluxes, and stopped after the end of flux feed. In the experimental temperature range, lower temperatures were advantageous for Cu removal reflecting the exothermic nature of Cu sulfidation. The dependence of Cu removal on the composition of the hot metal was also confirmed based on the analysis in terms of Cu partition ratio.
In this study, the concept of total material requirement (TMR) has been introduced to quantify the recyclability of scrap steel from end-of-life (EoL) vehicle. The TMRs for the recycling of scrap steels (urban ore TMR, UO-TMR) from the EoL vehicle have been estimated for four cases; conventional press-method, shredder and separation method, additional recycling of scrap steel from automobile shredder residue (ASR) and all-recycling using the press method, and the trade-off between the increase in function of recycled steel (in other words, decrease in influence of copper as contaminant) and the additional inputs such as pig iron or nickel required to create the increase in function were evaluated. As the results, the estimated UO-TMR ranged 3.7~4.0 kg/kg and the factors of “material itself” and “melting” were dominant. The effect of ASR input into electric arc furnace aiming the all-recycling was found to be canceled by additional lime input and energy to heat glass materials. Considering the dilution process by cold pig iron, the shredder and separation method is most effective in terms of TMR. Further the effectiveness of both dilution process using pig iron and nickel addition to suppress surface hot shortness is discussed.
Over the last decade, regulations regarding end-of-life vehicle (ELV) recycling have been introduced in many countries, leading to an increased recycling rate of ELVs. However, steel scrap from ELVs is recycled as a secondary iron source in the steelmaking process with rare consideration of alloying elements loss. Consequently, dissipation to slag and contamination in metals with alloying elements during the steel recycling process are likely to occur, but very few open data about destination of alloying elements which is available for stakeholders of ELV recycling. The purpose of this study is to obtain information about the amounts of alloying elements associated with ELV scrap and its allocation ratio between metal and slag phases in an electric arc furnace (EAF) steel making process. Our results indicate that, over half a kilogram of chromium and manganese are contained in a unit of ELV. 10% of chromium and 20-40% of manganese are transferred to slag during the dissolution process, and more alloying elements are expected to be lost depend on the condition of oxidation pressure.
Various alloying elements are used in vehicle manufacture to reduce environmental impacts and advance technology. After being used in human economic activities, end-of-life vehicles (ELVs) return to the steel industry as scrap containing rare metals and are subjected to the electric arc furnace process. However, at present, these steel scraps are recovered with insufficient concern for alloying elements mainly because of economic reasons. The objective of this study is to analyze the cost and benefit of scrap sorting system with explicitly considering alloying elements. Sorting of six parts, drive shaft, rear axle, disk rotor, rear exhaust piece, catalyst unit, and exhaust pipe, are analyzed from the sorting cost and benefit of deduction of ferroalloy input for EAF steel making process. Our results indicate that the sorting of exhaust pipe and catalyst unit deduce 711 ton and 1280 ton of ferrochromium in maximum, and 7.2 ton and 26.4 ton of ferronickel, and the sorting of rear exhaust piece is a feasible option from the cost and benefit perspective, while this amount is 0.1 kg per unit.
The water granulation conditions for producing high density, coarse granulated blast furnace slag were investigated in a laboratory-scale experiment. The influence of the slag temperature, water temperature and nozzle shape on the density and grain size of the granulated slag was clarified. The influence of these factors on the density and grain size of the slag was confirmed by using various nozzles in the slag water granulation system. Neural network computation was applied to estimation of the density and grain size of granulated blast furnace slag. The influence of the water granulation conditions on the density and grain size predicted by neural network computation corresponded closely to the results of the laboratory-scale experiment. Based on the results of this research, we proposed a new slag granulation system and manufactured a high density, coarse blast furnace slag fine aggregate.
The decomposition of polychlorobiphenyls (PCBs) by means of basic molten salts was investigated in order to construct a safe, simple andhighly efficient waste treatment system for PCBs. PCBs (mono, di, tri, tetra, penta, hexa, hepta-chlorobiphenyls) solution was injected intobasic molten salts (KOH-K2CO3 or NaOH-Na2CO3) at 773~973 K with oxygen or imitation air. The mass of residual PCBs in the exhaust afterthe decomposition and the mass of PCBs condensed inside the reaction vessel were measured by using gas chromatograph mass spectrometry,and the decomposition efficiency of PCBs was determined. The decomposition efficiency was also determined from the residual concentrationof PCBs in the exhaust in some experiments. The decomposition efficiency was high regardless of the number of chlorine contained in PCBsand reached to very high of 99.999% in an optimum condition. Chlorine of PCBs was captured in basic molten salts, and organic compoundscontaining chlorine was not emitted from the molten salts. Some by-products comprising benzene rings were found at 773~873 K, but the byproductsdisappeared at 973 K.