In this report, a few recent topics relating to blast furnaces in Japan-low productivity operation-high fuel ratio operation of large blast furnaces (1.0-1.5t/day3•m3 inner volume), the life of blast furnaces and recent new technology-the injection of pulverized coal and low silicon operation, are mentioned.

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For the safety design of various kinds of large-sized welded structures, it is necessary to establish a method of evaluating the strength of their structural stress concentrated regions against brittle fracture. In the previous paper, basic analysis was made on the basis of the COD concept on small-sized structural models with artificial slits made in their structural stress concentrated regions.
In this paper, the applicability of the strength evaluation method based on the COD concept to the regions where structural stress concentration is combined with residual stress and material deterioration due to welding is investigated using large structural models. Furthermore, the results of tests carried out on stress concentrated regions with complicated strain gradients using various kinds of structural models with different slit lengths are reported and a new strength evaluation method having generality is shown.

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For viscosity measurements in CaO-FeO-Fe₂O₃SiO₂ slags at temperatures up to 1700°C a viscosimeter with high accuracy was constructed and built. Measurements were undertaken mainly at 1600°C under air and carbon dioxide atmospheres at CaO/SiO₂-ratios of 0.66, 1.00 and 1.50. Additional measurements were carried out at 1500 and 1700°C under air. The results are:
(1) At low iron oxide contents the viscosity strongly depends on the basicity. The highest viscosities are found in acid slags.
(2) Increasing iron oxide content decreases the viscosity. The decrease is stronger in acid than in basic slags since at high iron oxide contents the viscosity values approach each other.
(3) The degree of oxidation influences the viscosity only a little.
(4) At Fe₂O₃/(FeO+CaO)=0.5 the viscosity changes due to a change in the atomic structure of the slag.
The results could be interpreted by the slag structure. The viscosity depends on the size and the concentration of the atomic structural units of viscous flow. These units are the silicate and the ferrite anions. Their size and concentration are influenced by the slag composition.

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A method of spectrochemical analysis by means of G. P. (giant pulse) laser has been applied to the analysis of C, Si, and Mn in solid steel and the most suitable condition for its application has been studied. The following results have been obtained:
(1) In atmosphere for the analysis, Ar or Ar+3%H₂ is better than N₂ and air from the point of view of spectral intensity and SN ratio.
(2) As a result of examination of the influence of laser energy on spectral intensity and intensity ratio, it has been found that it is generally suitable to set up laser energy above 0.3J. And for the purpose of minimization in variations of each analysis, intensity ratio to Fell 271.4nm should be used.
(3) Calibration curves have been made under the most suitable condition described above, and its relative errors of analysis have been evaluated.
(4) As a result of the time profile studies of the spectral lines obtained in Ar atmosphere, it has been shown that the separation of line and background is possible, and so that SN ratio of the analysis is much improved by this technique.

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For the purpose of the process control in continuous steelmaking, a new method of G. P. (Giant Pulse) laser direct spectrochemical analysis of C, Si, and Mn in liquid iron has been developed. This method is characterized by coincidence of optical axes of laser and spectrometer. In this study, fundamental conditions for the analysis of C, Si, and Mn, especially taking a serious view of C, have been studied. The following results have been obtained:
(1) Influence of variations in the level of liquid iron surface on spectral intensities and intensity ratios has been evaluated. It has been shown that, for the purpose of minimization of these influences, intensity ratio should be used.
(2) Si and Mn analyses are possible with the use of cylinder type and cone type atmosphere controlling apparatus.
(3) In C analysis, it has been shown that CO gas generated in the surface of liquid iron has effects upon spectral intensity of CI 193.1nm, and these effects can be eliminated by using cone type atmosphere controlling apparatus. C analysis is possible with the use of this apparatus.

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In hot rolled H-beams, putting heat-insulator on the upper surface of the web (web-insulating) and cooling the outer surface of the flange by water (flange-cooling) after the finishing rolling are considered effective measures for reducing the residual stress. To confirm this, the relation between the residual stress and the times of their treatments under various finishing temperature conditions was investigated using an analytical method for the thermal stress. This method is characterized by taking phase transformation into consideration.
The outline of results obtained is as follows;
(1) The longer the times of the web-insulating or of the flange-cooling are and the smaller the difference in finishing temperature between the flange and web is, the smaller the tensile residual stress in the flange and the compressive residual stress in the web are. Namely the residual stress is reduced in all cross-sectional areas in these cases.
(2) In the case of a typical large size H-beam (H: 900×300×16× 28mm), the time of the flange-cooling (heat transfer coefficient during water-cooling: 250kcal/m²•h•°C) after rolling for reducing the residual stress in the web is about a quarter of that of the web-insulating.
(3) It is possible to reduce the residual stress below a required value by combining the control of the difference in finishing temperature with the control of the difference in cooling rate between the flange and web after rolling.
(4) The choice of either web-insulating or flange-cooling after rolling should be made by considering the influence on the metallurgical quality and the ease of control as well as the effect of reducing the residual stress.

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A new method for thickness measurement of C.C. powder film on a slab surface was studied.
We showed that the C.C. powder film thickness could be determined by measuring thermal radiation energy from the powder surface at different two wavelengths.
Assuming that radiation energy spectrum characteristics of the powder can be measured beforehand, and the emissivity of the hot slab surface at a certain wavelength is constant in the operation temperature range, we would obtain experimental results of the powder thickness with an accuracy of ±10% in laboratory test.

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Under the present situation which is forced to reduce the productivity of the all coke operation, it is important to establish such a distribution adjusting technique as to maintain an adequate peripheral gas flow and a sharp central gas flow simultaneously. The gas distribution in a furnace equipped with a bell-armour in comparison with that of the bell-less top has a tendency to flatten owing to the difference in size segregation behaviour in the radial direction, thus posing a problem in micro-control of the burden distribution.
The authors have recently developed a new technique of controlling the burden distribution by the movable armour and applied it to Chiba No. 5 Blast Furnace. The technique is aimed at improving the layer thickness and promoting the particle size segregation in the radial direction, slowing down the raw material discharging rate from the bell by controlling the bell stroke and speed.
By the application of this technique, it has made possible to strengthen both the peripheral gas flow and central gas flow simultaneously, and thus has greatly contributed to stabilizing the furnace condition and extention of the permitted limit for operation under the recent circumstances of reduced production.

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The composite cold pellet consisted of manganese ore, iron ore, fine coke and ferro-manganese slag based on their charging ratio at the silico-manganese production in an electric furnace was produced without additional binders by a pilot plant.
The physical properties of the composite cold pellet produced, such as decrepitation, reduction disintegration, reducibility and resistivity were remarkably improved in comparison with the original manganese ore.
Only one thirds of energy of ordinary firing agglomeration process is expected to be required to the pellet production. Moreover, the energy under 200°C like plant exhaust heat is sufficient to the processing and this process is expected to be pollution free.
By replacing 40% of manganese lump ore to the composite cold pellet 243kWh/t of electricity saving, 123kg/t of nut coke substitution by fine coke including 23kg/t of net saving and 1.2% increase of manganese yield in metal were achieved in silico-manganese production test.

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An analytical technique for determining the amounts of boron over 0.1 ppm in steel was investigated.
The sample (0.5g) was first dissolved with 10ml of hot nitric acid (35%), and then thoroughly dissolved with 10ml of hot mixed acid which consisted of three portions of phosphoric acid and one portion of sulfuric acid. Boron was separated by distillation as methyl borate. The methyl borate solution was transferred to a platinum dish, and heated up to 85± 5°C in an evaporating apparatus to decompose the methyl-borate into sodium borate with sodium hydroxide solution. This solution was evaporated completely using a water bath at the above temperature. 25ml of water was added to dissolve the residue, and the amounts of boron were determined from the intensity of the spectral line of 249.77nm by using an inductively coupled argon plasma (ICP) emission spectrometer.
This method exhibited good precision for the steel samples containing from 0.1ppm to 0.4% boron.
The coefficient of variation at 5ppm level was 4.0%.

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