The occurrence of fine intergranular surface cracks is investigated for the case of bloom section 260×260mm cast on a low head curved mold type four strand machine with 8m radius, based on EAF steel supply.
Crack incidence depends on residual elements primarily and can be reduced below critical levels by limiting the Cu content to max. 0.22% provided the application of optimized casting conditions.
The latter consist of a casting speed limit at about 1.0m/min, connected with a minimum mold powder consumption of 0.3kg/m². Furthermore, high stability of mold level control and pouring stream directed toward the meniscus as well as soft indirect secondary cooling below the mold are also important, and, at low casting speeds, an increased mold taper appears to be beneficial, too.
On the other hand, soft mold cooling by reduced water velocity and increased wall thickness as well as wall plating and also total spray cooling intensity do not show significant effects. Replacement of mold powder by oil lubrication indicates a lesser sensitivity to residual content but is not practical due to occurrence of large depressions. No effect of C-content becomes apparent but increasing Al-content seems to enhance crack susceptibility.

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Ridging phenomenon of 18% Cr stainless steel is studied in connection with the segregation-pattern of Cr and C which shows undulations very similar to the ridging on the transverse section of hot rolled and cold rolled sheet.
(1) A laminated segregation pattern is observed at the center layer of transverse cross-section of hot rolled sheet. The segregation-pattern becomes wavy and extends through the thickness of cold rolled and annealed sheet.
(2) The segregation-pattern shows undulations very similar to the profile of ridging after stretching of 20% in the rolling direction.
(3) The height of ridging is well correlated with that of undulated segregation-pattern.
(4) Ridging phenomenon is thought to be a manifestation of underlying pattern of undulated segregation of Cr and C, which is farmed and retained in the hot and cold rolling process, by tensile elongation.

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Stress generation behavior in a steel-scale system and its relations to the structural and compositional changes of the oxide scale and the steel during high temperature oxidation were investigated by an X-ray method. A high temperature furnace capable of in situ measurement of elastic strains by X-ray diffraction up to 900°C under controlled atmosphere was newly designed. With the furnace, mild steel SS 41A(1.19% Mn, 0.2% C) was oxidized in air over a temperature range of 250-500°C, the stresses and lattice constants of the steel and oxide were measured by using the sine ψ method with Kα₁ radiations of Cr and Co. The stresses in the steel measured by Cr-Kα₁ X-ray during oxidation at 500°C were found to become compressive after 100h oxidation, while those of pure iron, and of the steel measured by Co-Kα₁ X-ray remained tensile under the same oxidation condition. A gradual decrease of lattice constant was observed in the steel after prolonged time of oxidation at 500°C, while those of the pure iron, and of the steel measured by Co-Kα₁ X-ray were nearly constant. Those differences were attributed to the compositional changes of some constituents in the steel near the steel-scale interface.

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Yielding and strain aging behaviors of an Fe-0.070-1.7Mn dual phase steel were investigated by tensile testing after various cooling schedules from intercritical annealing.
Mechanical properties did not vary much with cooling rates between 20°C/sec and 100°C/sec when cooled from annealing at 720°C. At slower cooling rates than 20°C/sec discontinuous yielding was observed. The discontinuous yielding seemed to be caused by diffusion of interstitial solute to mobile dislocations below the austenite-martensite transformation temperature. Existence of pearlite did not affect the yielding behavior of the dual-phase steel.
Aging experiment between 60°C and 230°C with 2% prestrain showed that two stages of strain aging appeared with prolonged aging even at a constant temperature. The activation energies for the first and the second stages aging were estimated as 17 000cal/mol and 28 000cal/mol, respectively. The first stage was related to carbon diffusion to mobile dislocations and the second stage was explained to be due to precipitation growth. Manganese alloying did not affect the diffusion rate of carbon atoms at the aging process.

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A simulation model for the burden distribution at blast furnace top was used for the quantitative evaluation of the effects of various charging conditions on the burden distribution and was applied to the actual operations at Kokura #2BF in cases of the control of hot spot occurrence at lower shaft and the control of furnace wall 'activeness'.
Among three charging conditions, that is, coke base, charged O/C, and stock level, coke base has the most significant effect on the burden distribution. The decrease in charged O/C at furnace center was accelerated by the mixed layer formation during ore dumping in cases of the increase in coke base and charged O/C. On the other hand, the rise of stock level resulted in the increase in charged O/C at furnace center, which differs from the previous knowledge.
For the restraint of hot spot occurrence, both suitable selection of movable armor notch based on the model computation and the mortar injection are important. To enhance wall 'activeness' the movable armor operation was successfully performed on the basis of the model computation. Through these applications of the model to actual operations, the effectiveness and the usefulness of the model was confirmed.

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The effect of carrying out gaseous reduction of iron oxide under external pressure cycling has been investigated. When the reduction is carried out at 800°C with pellets of 30% porosity, relatively moderate pressure cycling with an amplitude of 0.5atm and frequency of 0.5cps can lead to about 25% higher reduction within 20min from the start of reaction. A threefold improvement in initial conversion rate can be obtained if higher amplitude and frequency of cycling are used. Computation shows that, for pellets and naturally occurring hematite ore, viscous flow effects can be neglected.
The results of the investigation provide justification for further research in the use of external pressure cycling to overcome diffusional resistances in gas-solid reaction systems.

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Compression-casting where a cast slab is straightened under compressive stress along cast direction has been successfully applied to the conventional continuous casters, minimizing internal cracks. In a rotary type continuous caster, a cast slab is to be straightened just after leaning the mold, when shell thickness is small. In order to study effects of compressive force on internal crack formation of a cast slab of small shell thickness, a static casting experiment was carried out. It was shown that, by applying compressive force to a cast ingot, internal crack formation could be prevented.

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To analyze longitudinal residual stress in hot rolled H-beams, a numerical method for the prediction of temperature and thermal stress has been developed by taking phase transformation into account. The temperature during cooling and the residual stress calculated by the present method agree well with the measured ones. The influence of finishing temperature and cross-sectional size on the residual stress was investigated by using this method. The results obtained are as follows;
(1) The larger the thickness ratio of flange to web (t_f/t_w) is, the larger the stress is.
(2) The larger the difference in finishing temperature between web and flange (T_f0-T_w0) is, the larger the stress is.
(3) The larger the ratio of cross-sectional area of flange to web (S_f/S_w) is, the smaller the tensile stress in the flange is and the larger the compressive stress in the web is.
(4) Immediately after rolling, the less the non-transformed phase (austenite) in the web is and the more the phase in the flange is, the larger the stress is.
(5) The larger the compressive stress in the web is and the larger the ratio of inner width to thickness in the web (B_w/t_w) is, the more frequently the web-buckling occurs.

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In order to investigate the role of inclusions as sources for delamination wear in liquidized nitrogen (L.N₂), the rubbing wear tests of SUS316 type stainless steels including various amounts of sulfide inclusion against quench-hardened or tempered SUS440A type stainless steels were carried out in air at R. T. and in L.N₂. Results are summarized as follows: With increasing sulfur content, the wear-loss of SUS316 specimens increased and that of the tempered companions decreased, but the weight of hardened companions increased by adhesion. MoS₂ is a superior lubricant available for use in L.N₂.

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Since 1971, Daido Steel Co., Ltd. has developed the LF process, a ladle refining process which depends primarily on slag refining, aiming an ideal performance of reduction refining instead of electric arc furnace. The main feature of this ladle technology exists in refining under non-oxidizing atmosphere and acceleration of slag-metal reaction through stirring by Ar gas injection, for a desired long time due to the temperature compensation by arc heating. It is possible to obtain clean materials having low oxygen and sulfur levels around 10ppm, or inclusion rating of approximately 1.0 to 0 for every type specified by ASTM-A.
At the early stage of development, several LF units were applied only for the production of high grade steels. In recent years, the application has extended to whole steel industry not only for the quality improvement, but for cost reduction, production increase and especially ladle-CC matching in sequence casting. In 1983, there are 24 LF installations in domestic steel works including 3 integrated steelmakers and the total LF steel will exceed 7 million t.
Many steelplants in Japan are now equipped with FAF(BOF)-LF-RH-CC combined line for high quality steels, in which reduction refining is exclusively entrusted to LF. The portion of special steels produced by this steelmaking process is expected to increase still further.

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