There are iron ore and coal resources to supply raw materials for ironmaking for many years. Recent developments, such as the consolidation of raw materials suppliers and increase of iron ore imports in China, influence the present and future availability of raw materials. Carajas iron ore, pisolitic iron ore and "semi-soft" coking coal are the accomplishment of about 20 years' cooperative development of new sources and raw materials utilization by Japanese steel mills. To adopt the changes and natural resources availability, the next targets are Marra Mamba and high P Brockman iron ores from Western Australia for iron ore and less usage of prime coking coal for coal. In future, utilization of scrap is a key for steel industries.
In welded structures, welds are required to have performances equivalent to base metals in wrought and annealed conditions. To achieve the performance required, various microstructure controls have been developed and applied for steel weld metals and heat-affected zone to minimize the coarse, heterogeneous and brittle structures. In this article, these microstructure controls are reviewed with a particular emphasis on the toughness of carbon-manganese and low-alloy steel welds. The control of inclusions and the optimization of steel compositions for the improved microstructure refinement are discussed, since the refinement of weld microstructure has been achieved by the inclusion-assisted grain refinement of prior austenite and the enhancement of intra-granular ferrite formation. The discussions are extended to the role of inclusions as pinning particles and as preferential nucleation sites of ferrite, which is important for further improvement of the technology. Toughness degradation due to martensite-austenite constituent in welds is also referred. Current understandings of the microstructure controls in carbon-manganese and low-alloy steels welds and issues to be solved are summarized.
The heat resistant steel is a structural material for the high temperature of thermal power generation etc. As mechanical property for the heat resistant steel, high temperature strength should be high, and the rupture time be long. But, the structure of the steel remakably change during long time creep deformation because diffusion easily occurs at the high temperature. Therefore, it is necessary to control the structural change during creep deformation to maintain strength for a long time at the high temperature. In this paper, at first the origin of high temperature sterngth of the heat resistant steel is described in view point of high-temperature deformation mechanism. Next, the grain boundaries in martensitic structure which are the fundamental structure of the heat resistant steel is described, and the change of these boundaries during creep deformation is described. The structure control of a further making of the heat resisting steel to high strength is described by using these findings.
Currently, a number of waste treatment technologies have been developed. Among them, melting treatment has drawn more and more attentions due to merits such as low environmental pollution, high volume reduction and widespread treatment capacity for various waste materials. In this study, a two-dimensional mathematical model of high-temperature gasification and melting furnace was developed. This model considers motion; heat transfer and mass transfer of gas, solid and liquid phases in the furnace. Furthermore, this model did take into account the possible chemical reactions and phase transformations. The governing equations include inter-phase exchange of mass, momentum and heat, and consist of strongly coupled set of simultaneous partial differential equations. The model was applied to a gasification-melting furnace having packed bed for gasification and melting of wastes, and freeboard for secondary combustion of pyrolyzed gas. The computational results clearly showed regions of gasification, combustion and melting in the furnace as well as the flow field distributions of temperature, component concentration and other process variables.
We examined the methods for determining trace amount of tramp elements contained in iron and steels using the graphite furnace atomic absorption spectrometry (GF-AAS). We also investigated the graphite furnace heating conditions for no-loss ashing and high-efficiency atomization of tramp elements by the graphite furnace atomic absorption method. Vaporization of each element was observed for various heating conditions by using the electrothermal vaporization /ICP mass analysis method, which used the same type of graphite furnace as the one used for the atomic absorption method. As a result, we confirmed that all elements could only be observed by the atomizing step. Assuming the lower detection limit of this method to be 3σ, the detection limit for 1 g of specimen was 0.05ppm for As, 0.025ppm for Bi, 0.017 ppm for Pb, 0.022 ppm for Sb, 0.020 ppm for Sn, and 0.003 ppm for Zn. This method was demonstrated to be an accurate and fast tramp element analyzing method.
Polycyclic aromatic hydrocarbons (PAHs) were analyzed by gas chromatography/mass spectrometry (GC/MS) using electron ionization (El), positive ion chemical ionization (CI) and negative ion chemical ionization (N-CI) mass spectrometry. PAHs are major constituents of coal tar, and GC/MS technique is a useful analysis method for complex mixture of PAHs such as coal tar. El and Cl methods give similar sensitivities for each PAHs in reconstructed ion chromatograms (RIC). N-CI method gives different sensitivities in RIC for structural isomers and alkyl-side chain compounds. The results of GC/MS analysis of coal tar, RIC by El and N-CI method were quite different. It was confirmed that N-CI method is useful for analysis of PAHs mixture, because of good selectivity for PAHs structural isomers.
High-temperature nitridation behavior of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (alloy 909) has been investigated in a flowing nitrogen gas atmosphere at 1073 to 1273K using metallographic, X-ray diffraction and electron probe microanalysis techniques. The scales consist of an external scale and a subscale. The former is composed of reaction products on the alloy. The latter is composed a mixture of intragranular reaction products and an un-reacted alloy matrix. The reaction products in these scales are identified as TiN, NbN and Nb2N including small amounts of Fe3O4, α-Fe2O3 and CoFe2O4. The rate constants for the subscale formation in this alloy are about 200600 times as large as those in CMSX-2, CMSX-6 and SRR99 reported previously. At all the temperatures the external scale and the subscale grow according to a parabolic rate law and apparent activation energies for these scale growth are estimated to be 123 kJ/mol and 158 kJ/mol, respectively. The rate determining diffusion element for subscale growth is considered to be N in the alloy matrix.
Effects of niobium addition on strengthening, hydrogen absorption and hydrogen embrittlement have been investigated paying attentions to carbides morphologies by using laboratory melted clean steels. Addition of niobium and austenitizing at high temperature enhanced temper softening resistance due to fine niobium carbide precipitation during subsequent tempering. Addition of both niobium and vanadium improved temper softening resistance furthermore. High niobium steel absorbed less hydrogen in corrosive media than high vanadium steel. It would attribute to small size and incoherency of niobium carbide. High niobium steel showed good resistance to hydrogen embrittlement. It would be due to both uniform dispersion of cementite by high temperature tempering and low hydrogen absorption.