In recent years, techniques of blast furnace operation have considerably advanced, such as fuel injection, high top pressure, oxygen enrichment, etc.These new techniques have cut down coke consumption and increased productivity.In this connection qualities of sinter acquire greater importance to blast furnace operation.We studied on degradation of sinter during chemical reduction at low temperature below 650°C, and effects of degradation of sinter on blast furnace condition
The results obtained are as follows:
(i) Operational data of the commercial blast furnace at degradation of sinter leads to lower productivity of blast furnace.
(ii) Sinter was remarkably degraded at about 500°C, and also with an increase of heating rate.
(iii) There was no relationship between shatter index and degradation of sinter.
(iv) Degradation of sinter during chemical reduction can be avoided by increase of FeO or slag components of sinter.
(v) It was presumed that degradation of sinter was related with chemical reduction and carbon deposition reactions.

抄録全体を表示

In order to study decarburization in an oxygen converter, a comparison was made between the reactions in a converter and in an open hearth furnace, and further the decarburizing reaction in our 160 tons oxygen converter was discussed by calculating the carbon loss in exhaust gas, as the converter was equipped with unburned gas recovery system.The results.obtained are summarized as follows:
(1) The C-0 relation in a converter is not in the“steady-state”which has been assumed for an open hearth furnace.
(2) It is probable that the decarburiz ng reaction mostly takes place at the oxygen gasmetal interface during oxygen blowing, including the bessemerizing period in an open hearth furnace.
(3) In a converter, almost 100% of oxygen blown into bath is used for decarburization when C content is over 1% except Si blowing period.
(4) The rate of decarburization or the oxygen efficiency for decarburization decreases with the decrease of C content from 1%, and considerable depression is observed below 0.3% C.
(5) This fact suggests that the amount of oxygen which affects other furnace reactions will rapidly increase in that stage, and it is found that its effect on the increase of total iron content in slag is most notable.

抄録全体を表示

In order to make a systematic survey on the behavior of sulfur in solid steel, the precipitated sulfide inclusions in solid steel were studied microscopically through their heat treatment and the electrolytically isolated sulfide inclusions were investigated by the electron diffraction method and the electron probe method.
It was shown that sulfide inclusions were precipitated in solid steel below about 1200°C, when the steel was cooled from the temperature above the solution temperature of the preprecipitated cipitated sulfide inclusion at a slower rate than 60°C/min.The precipitated sulfide inclusions had two forms: a plate-like inclusion which had a widmastätten structure and was preci-pitated on plane {100}γ of austenitic grain, and a very fine particle inclusion which was precipitated at the grain boundary of austenite.As the result of impact test over the temperature range of 800°C to 1350°C of steels which were slow-cooled from 1405°C, it was found that the brittleness of the steel below 1200°C was induced by precipitation hardening of austenitic grain and reduction of grain boundary cohesion, and it did not vanish even at the temperature below Ar₃.
When the steel in which the precipitation of sulfide inclusions had been suppressed by rapid cooling from the high temperature was reheated at austenitizing temperature, the uncompleted plate-like inclusion at grain and the very fine particle inclusion at grain boundary were precipitated.
When the steel in which the precipitation of sulfide inclusion had occurred through slow cooling from a high temperature to the room temperature was reheated at austenitizing temperature, the plate-like inclusion in it was decomposed rapidly to a very fine particle inclusion. But when the steel which had been slow-cooled to the temperature of lower austenitic region from the high temperature was reheated, the plate-like inclusion in it was not decomposed and kept its shape up to the solution temperature.
The results of electron diffraction analysis and electron probe analysis on the electrolytically isolated plate-like sulfide inclusion show that the plate-like inclusion was composed of single crystal of α-MnS solid solution containing 23 wt% FeS and matched the lattice of austenite on plane {100}γ, and the phenomena of decomposition of the plate-like inclusion in reheated steel occurred due to lack of cohesion between lattices of the plate-like inclusion and refreshed austenite.
In the steel containing up to about 0.7% manganese, precipitated sulfide inclusions were observed, but in the steel with 0.03% manganese they were in molten state at the temperature and migrated into grain boundary of austenite.
The solution temperature of the precipitated sulfide inclusion was affected by contents of manganese and carbon in steel.In low manganese steel (0'1%), the solution temperature was 1290°C independently of content of carbon and in steel containing 0.2-0.4% manganese, the higher the carbon content of (0.1-0.8%C) steel the lower the solution temperature was (1400-1320°C).But, the precipitation temperature of sulfide inclusion was almost constant (1180-1200°C), independently of contents of manganese and carbon in steel.

抄録全体を表示