To evaluate high temperature properties of blast furnace burdens, a series of reduction under load tests was carried out under the conditions simulating blast furnace processes, using sinter, self-fluxed pellets and acid pellets.
To investigate the softening and melting mechanism, structural analysis was conducted on those samples taken after interrupting the test.
The results obtained are summarized as follows:
(1) Generation of molten slag is involved in the assimilation process of slag during softening and melting of samples, and the basic path for this assimilation is considered to be toward the final composition (average gangue composition before reduction) along the direction expanding the liquid phase area with heating.
(2) The difference in softening and melting behavior of these burden materials is directly due to the quantity of molten slag formed in the slag assimilation process. It is indirectly due to the differences in reducibility at about 1000°C in addition to the composition and volume of gangue before reduction.

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Fbeen concluded that the thermal degradation and the attack by inorganic compounds contribute considerably to the drastic degradation at the position of 3-5m above the tuyere level, and that the contribution to the deteriorations by CO₂ reaction is smaller than the former.
On the base of these findings, the coke degradation through blast furnace has been tried to determine by measuring the difference of coke size between before charging and at the tuyere during the operation with very low fuel rate (396kg/pig-t). The result obtained implies that the less thermal level of the lower part of blast furnace brings the less degradations of coke through blast furnace.
Another blast furnace trial has been conducted with the low CSR (coke strength after CO₂ reaction) cokes with enough JIS drum strength (more than 92.0 in DI³⁰₁₅) which are produced mainly by lowering the flue temperature of coke ovens. Any serious problems have not been encountered such as frequent slips and scaffold formations during the operation. A clear relation is recognized between the slag discharging speed and the hot drum index (1500°C) of charged coke.
To confirm what kind of coke shows the less thermal degradation, the apparatus for measuring the indirect tensile strength at high temperatures (2300°C) has been developed. It is found that the optimum inerts and the high micro strength are indispensable to get the coke with less thermal degradation.

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Tine titanium nitride (TiN) particles precipitated in steel slabs suppress the growth of austenite grains on heating and consequently improve the low-temperature toughness of controlled-rolled steel plates by grain refinement. It was found, however, that the austenite grain size depends on the chemical composition of the steel, or in other words, the microstructure of the slab prior to heating. When a slab of extremely coarse bainitic microstructure was slowly heated, it developed an unusual transformation and formed duplex austenite grains. This unusual transformation can be prevented if the microstructure of the slab is properly refined.

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An in-line direct solution heat treatment process for austenitic stainless steel wire rods has been developed. This process utilizes the rolling sensible heat of wire rods. The results of the fundamental research on the recrystallization and the growth of austenite grains after hot rolling are described. The direct solution heat treatment line designed and built on the basis of the results of this fundamental study is outlined, and the quality of wire rods treated by the line is summarized. In the direct solution heat treatment process, the wire rod finish rolled at a high speed and a high temperature is first held in a high-temperature furnace for a short time and then cooled rapidly in a water box. These treatments are continuously performed in a short time in-line with the wire rod mill. The quality of wire rods thus treated is better than that of off-line annealed wire rods, enabling the elimination of solution heat treatment prior to drawing into wire.

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Dephosphorization of molten stainless steel by the addition of metallic calcium has been studied by using a laboratory scale high frequency furnace and an industrial scale electric arc furnace. Safety treatments of dephosphorization slag have also been examined. The results obtained are summarized as follows:
(1) From the laboratory scale test, it is found that there is a relation between the activities of carbon and oxygen (a_C and a_O) in molten steels and dephosphorization ratios. Favorable conditions under which the dephosphorization ratio exceeds 50% are a_C<0.92 and a_O<4×10^-4 at 1480°C.
(2) For an efficient dephosphorization of 18Cr8Ni steel, it is necessary to control the carbon and oxygen contents of molten metal in the range of 0.3%<C<1.0% and O<60ppm at 1480°C.
(3) The dephosphorization ratio and the desulfurization ratio determined by the industrial scale experiment of 13Cr5Ni steel are 33% and 55%, respectively, when the addition of calcium is 10.6kg/t steel.
(4) The concentrations of PH₃ and H₂S gases generated from the dephosphorization slag have been measured. The maximum concentrations are 160ppm/g for PH₃ and 400ppm/g for H₂S before safety treatment. After safety treatment, the maximum concentrations decrease to 2ppm/g for PH₃ and 11ppm/g for H₂S.

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Considering the application of a ferritic stainless steel as heat exchanger tubing for a moisture separator reheater of light water reactors, stress corrosion cracking behavior at the weldment of commercial ferritic stainless steels in high temperature pure water was studied. Double U-bend method was used for the study and the relationship with microstructure was discussed.
Welded joint of Type 439SS containing 0.021% C, 0.025% N and 0.27% Ti with In-82 type filler metal was susceptible to intergranular stress corrosion cracking if a tight crevice was provided by inserting a teflon sheet between the inner and outer specimens of double U-bend. This was attributable to the formation of chromium depleted zone due to the precipitation of chromium carbides/nitrides along ferrite grain boundaries.
On the other hand welded joint of Type 444SS with 0.007% C, 0.010% N and 0.26% Nb was immune to stress corrosion cracking, and this might be attributed to the higher ratio of Nb/(C+N) content.

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The aging of Fe-C-Ni martensite was studied using acoustic emission and optical microscopy. It was observed that the bursts of acoustic emission were very discrete. The cumulative counts of acoustic emission as a function of the logarithm of the aging time increased linearly. The slope of the previous curves decreased as the grain size of austenite, or the test temperature decreased. The pre-aged martensite greatly influenced the number and rate of the acoustic emission counts and the number of the microcracks in the specimen.

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Optical emission spectrometry is superior to other analytical methods in its rapidity. Therefore, it plays an important role in the field of elemental analysis at the steel making plants. However, further speedup and labor saving of the analysis by automation are required to progress of continuous steel making process. An apparatus has been developed to meet this need, and the following results were obtained.
(1) Analytical procedure was fully automated, from the receipt of samples to the transmission of analytical results. The time required for the analysis of a sample is 50sec.
(2) Automatic standardization and automatic selection of working curves were also provided.
(3) Better precision results were obtained than by the conventional integration method in the analysis of routine steel samples taken from a converter by employing the pulse height distribution analysis method.

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