Characteristic features of the embrittlement occurring in the temperature range from 1 000 to 600°C in various kinds of steels were examined by hot stage tensile test as well as fractographic analysis, and the mechanism of this embrittlement is discussed.
The embrittlement is caused by the slower strain rate of the tensile test and fracture occurs along the austenite grain boundary by either grain boundary sliding or by localization of strain in the film-like proeutectoid ferrite produced by the γ-α transformation.
Steels such as ferritic steel and electrolytic iron do not have this embrittlement, while carbon steels containing 0.05 to 0.4% carbon and fully austenitic steels reveal this embrittlement. In the case of carbon steels, sulfur, nitrogen and niobium are detrimental elements while aluminum and phosphorus suppress it depending on their content and state of existence in the steels.
The stress-strain analysis by an Instron type machine shows that the restoration process either by dynamic recovery or by dynamic recrystallization plays an important role in this embrittlement. Another finding is that proeutectoid ferrite deforms preferentially in the austenite plus ferrite region because of very low levels of flow stress and work hardening rate in this ferrite.
Thus, factors governing this embrittlement are the degree of ease of the recrystallization in austenitic steel relating to the grain boundary sliding, and the formation of film-like proeutectoid ferrite produced by the γ-α transformation in the case of carbon steels. Grain boundary precipitates such as sulfides and carbonitrides act as nuclei of voids and thus promote this embrittlement.

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The mineral structure of sinter is strongly affected by the heat pattern in the sintering process. For this reason, the control of heat pattern in sintering bed is an important operating factor in the sintering process of iron ore. In the theoretical investigation of sintering process, a simulation model which is considering the coke breeze size distribution, the moisture condensation reaction, the FeO formation/reoxidation reaction and other reactions are considered was developed. Many useful findings on an actual sintering operation were obtained from the study of the effects of various operating factors on the heat pattern with the aid of this simulation model.

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For a stable operation of blast furnace and a decrease in fuel rate, the improvement of the qualities of sinter which is the principal charging material is very important. At Wakamatsu Sinter Plant of Nippon Steel Corporation which is equipped with a double-layer charging system, the plant experiment has been made to improve the reducibility of sinter by making uniform and ideal heat pattern in the sintering bed. In this experiment, sinter with excellent properties, 3.7% FeO, 70% JIS RI, good high-temperature properties has been manufactured. Findings obtained are summarized as follows:
(1) An effective means o f improving the sinter reducibility is to cause porous ore to remain as unmelted ore by lowering the sintering temperature at about 1250 to 1300°C and by increasing the temperature-rise rate in the high-temperature zone.
(2) Compact ore should have fine grains to improve the sinter reducibility.
(3) The reduction degradation index (RDI) of sinter can be improved by reducing the ratio of Al₂O₃/SiO₂ in fine raw mix and by lowering the sintering temperature.

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Previous studies concerned with the drainage of the blast furnace hearth have assumed that the iron-slag interface remains horizontal and fixed at the level of the taphole during the outflow of the slag phase. As a consequence they have ignored the presence of the iron phase and its effect on the drainage characteristics of the slag phase.
In this study we examine the validity of the above assumption using a novel two-dimensional experimental drainage apparatus which allows a clear visualisation o f the drainage behaviour of two immiscible fluids. The results of the study suggest that in most cases the iron and slag phases may be expected to flow simultaneously from the taphole and that the iron-slag interface will not remain horizontal and fixed at the level of the taphole as has been previously assumed.
It is shown that the drainage process is characterised by a down-ward tilting of the gas-slag interface towards the taphole and a simultaneous downward tilting of the iron-slag interface away from the taphole. The experiments show that it is possible to drain the iron phase down to levels considerably below the level of the taphole. The volume of iron removed below the level of the taphole increases with increasing slag drainage rate. Calculations are presented which suggest that under actual blast furnace conditions this volume may be of the same order as the volume of residual slag remaining above the level of the taphole at the end of tapping.
Finally, it is concluded that existing predictions of slag residual ratio based on studies which have neglected the presence of the lower iron phase may lead to a serious underprediction of the residual ratio particularly at higher slag drainage rates.

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In order to describe the effects of solute-interactions on the equilibrium distributions of solute elements between solid and liquid phases in iron base ternary system, Distribution Interaction Coefficient (DIC), k^j_i, was defined in this work. The coefficient k^j_i is shown as the ratio of the equilibrium distribution coefficient of solute i in Fe-i-j ternary system to that in Fe-i binary one and this is considered to be the parameter indicating the change of the equilibrium distribution coefficient of solute i with the additon of the alloying element j. The influences of solute-interaction on the equilibrium distributions of some solutes in Fe-C, Fe-N, Fe-H, Fe-P and Fe-S base ternary systems could be discussed by the use of the coefficient DIC.

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To analyze non-flatness (edge wave) of hot rolled steel strip after cooling, a numerical method for the prediction of temperature and thermal stress has been developed by taking phase transformation into consideration. It has been confirmed that the temperature during cooling and the residual stress calculated by the present method agree well with the measured ones. Using this method, the occurrence of edge wave in a thin and wide hot strip (3.24×2 173mm) has been studied.
The results obtained are as follows:
(1) The edge wave occurs when compressive residual stress in the edge becomes greater than the critical buckling stress.
(2) The residual stress becomes small when the transverse distributions of finishing temperature and of water-cooling rate after rolling are small. Water-cooling of the hot strip in the latter stage of the runout table and high coiling temperature are beneficial to reduce the residual stress.
(3) The most effective measure of preventing the occurrence of edge wave is to cool the strip uniformly in the transverse direction by controlling the distribution of water-supply of the cooling device after rolling.

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An asymmetric cluster mill has been developed modifying an existing four-high mill to attain higher reduction than four-high mill or six-high mill. The upper part of the mill is of six-cluster roll structure with a small work roll, two intermediate rolls and three backup rolls. The lower part is of two-roll structure with a large work roll and a backup roll. Furthermore, this mill has a crown-bender and an intermediate roll-bender to control strip shape over a wide range from edge waving to center buckling or from center-edge buckling to quarter buckling. It is considered that the asymmetric cluster mill will show excellent shape controllability to reduce shape faults, especially quarter buckling which occurs in the wide strip rolled by a four-high mill.

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