A new iron ore agglomeration process was experimentally evaluated in comparison with the sinter process on the basis of permeability and heat transfer characteristics in the bed. Desirable operating conditions for the new process were also investigated. The main results obtained are as follows :
(1) The productivity of the new process increased linearly in proportion to the gas volume passing through bed, while the maximum productivity of the sinter process was estimated at 1.6 t/m² h due to the limit of the permeability in the bed by the capacity of the suction blower.
(2) According to the sintering test results for the two processes using a pot made of a transparent silica glass tube, the new process's melting zone temperature seemed to be higher than that of the sinter process, owing to be the efficient combustion of fine coke coated on the green ball.
(3) An evaluation of gas flow characteristics in the bed by a mathematical model, the productive yield for the new process seemed to be superior to that of the siner process, in that it controlled excessive gas flow near the side plate.
(4) It was proved by both mathematical and experimental evaluations that the size of the green balls should be mainly controlled between 5 and 10 mm in order to achieve sufficient heat conduction within the pellet.

抄録全体を表示

It is important to understand the desulfurization mechanism by solid CaO for improving its desulfurizing power of hot metal.
From the standpoint described above, desulfurization experiment of hot metal was carried out by CaO calcined under various conditions. Experimental results were discussed with CaO properties.
Results obtained are as follows.
No correlation between utilization factor (η_S) which has been regarded as a desulfurizing power and CaO properties was found.
On the other hand, a good correlation between desulfurization efficiency (dη_S /dt) defined by the authors and pore size distribution of CaO used was found, namely higher desulfurization efficiency of early stage in the reaction was given by rather lower porosity CaO having pores with wide diameter, than by higher porosity CaO having a number of pores with small diameter.

抄録全体を表示

The dephosphorization of hot metal with CaO-Al₂O₃-Fe_xO_y, flux was studied at 1 350°C to develop a new kind of flux to be substituted for the Na₂CO₃-based and CaO-Calcium halides-Fe_xO_y, fluxes, which are commonly used in hot metal treatment. The most suitable composition for dephosphorization was (38-45)CaO-(12-5)Al₂O₃-50Fe_xO_y, by weight percentage. The apparent phosphorus distribution ratio, (%P)/[%P], was 150, and the dephosphorization ratio was 80% with the consumption of 40 kg per ton of hot metal. These results were almost similar to those of CaO-Calcium halides-Fe_xO_y, flux, but the desulphurization ratio of the new flux was about 20%.

抄録全体を表示

The effect of additives such as CaO, SiO₂, MnO, MgO, Na₂O, P₂O₅, Al₂O₃, TiO₂, FeS, CaF₂ and CaCl₂ on the reduction rate of liquid iron oxide contained in an iron crucible with CO has been measured using a thermobalance as a fundamental study for the smelting reduction process. The effect of mass transfer in both the gas and liquid phase on the overall reduction rate was carefully estimated to learn the rate of chemical reaction on the surface.
It was found that the reduction rate was greatly affected by the ratio of Fe³⁺ /Fe² in the melts. An empirical rate equation was derived to express the rate of chemical reaction on the surface as follows :
r= (N²_FeO1.5/N³_FeO) ^1/3 (P_CO-P_CO2/K'_C)exp(-138000/RT-6.37)(kg/m²s)
Where, K'_C=(P_CO2/P_CO)_eq.. Since phosphate acted like a surface active species and retarded the reduction rate markedly, the rate equation mentioned above could not be applied to the liquid iron-phosphate system. The reduction rate of liquid iron oxide containing FeS, CaF₂ or CaCl₂ was also investigated to discuss the effect of coexisiting anions on the chemical reaction rate. It was concluded that the reduction rate was mainly affected by cations and the effect of anions was very small.

抄録全体を表示

Removal of copper and tin in molten steel was investigated in a laboratory scale plasma furnace. It was found that the removal of copper and tin proceeded by both argon-hydrogen plasma and argon plasma even at 10⁵ Pa. The degrees of removal of those elements were much greater at reduced pressures, at higher hydrogen contents in the plasma gas, and at higher plasma gas flow rates. Maximum degrees of removal of copper and tin were about 90 and 60% respectively in 2 h.
The removal of copper is thought to take place through accelerated evaporation at the very high temperature hot spot created by the plasma. However, the removal rate is assumed to be controlled by the transport of gaseous species evaporating from the melt surface.

抄録全体を表示

A post combustion (P·C) nozzle which accomplishes high P·C and heat transfer efficiency in a converter was developed through studies of both nozzle profile for maintaining stable P·C and appropriate P·C regin. By applying the abrupt expansion P·C nozzle to the 180t LD-KGC converters of Kawasaki Steel Corp., the following results were obtained.
1) In order to enhance heat transfer to molten steel, it is desirable to form the P·C region in a space near the molten steel surface and approximately more than 1.0 m inside the furnace wall refractories.
2) It is estimated that the P·C nozzle forms diffusion combustion due to the collision between oxygen jet and carbon monoxide gas. Therefore the oxygen flow velocity into the combustion region should be controlled under 10 m/s. For this purpose, it is required to keep the initial jet velocity from the nozzle within 100 m/s.
3) The P·C ratio increases with the lance height but the heat transfer ratio is almost constant at 60% regardless of the lance height.
4) The scrap ratio increased by 6% when P·C oxygen of 0.5 Nm³/min·t is supplied.
5) The developed abrupt expansion P·C nozzle has no significant effects on metallurgical reactions, and the values of (T-Fe) and (P)/ [P] are almost the same as those in the conventional process.

抄録全体を表示

Quality of forging products is greatly affected by macrosegregations such as "A" segregation which tends to appear in large ingots. From the points of quality control and assurance, therefore, it is important to establish a method to predict formation of "A" segregation in ingots. For this purpose, twelve commerical ingots of different sizes and steel grades are investigated. Further experiments are carried out, by producing "A" segregation in small ingots, to study the effects of alloying elements. The results show that the critical location of the formation of "A" segregation differs with grades of steel. The location is determined not only by the liquid density difference but also by the coarseness of dendrites. In the case of lowalloy steels, secondary dendrite arm spacings have to be as big as 560 micron meters for the formation of the segregation. Meanwhile the vanishing location of the segregation in the center of ingots is determined by the radius of ingot regardless of grades of steel.

抄録全体を表示

Since "A" segregation in forging ingots has adverse effects on the quality of products, it is important to determine quantitatively the number, the size, and the extent of segregation of "A" segregation in ingots. For this purpose eleven commercial ingots of different sizes and steel grades were examined. The results show that "A" segregation spots distribute in a region surrounded by two coaxial circles and that the peak of the number of spots is around the center of the region, in the cross section of ingots. The increase in the number from the outer circle toward the peak is determined by the size of the dendrite, and the decrease from the peak toward the inner circle is determined by the decrease in liquid fraction at the ingot center while it is solidifying. The size of the spots tends to increase with increasing the size of ingot and is proved to be dependent of the coarseness of the dendrites. Finally the enrichment of solute in "A" segregation is found to differ among elements and also with steel grades. It is proved that the enrichment is determined by the patition ratio of each alloying element and by the coarseness of dendritic structure.

抄録全体を表示

During potentiostatic corrosion fatigue test, fluctuation of polarization current which is synchronized with the cyclic tension-compression loading was observed. This current fluctuation means that the corrosion rate was accelerated by the cyclic loading. Using Fourier transformation, we separated the current component of this accelerating which is synchronized with the cyclic loading from the polarization current. We named this component of the current "Stress Synchronized Polarization Current (SSPC)" and compared it with the fatigue life.
Corrosion fatigue test for high tension steel HT60 was carried out in artificial seawater solution and in borate solution under the condition of bend type specimen potentiostatically. In the artificial seawater, except the potential range where prominent general corrosion or hydrogen embrittlement occurred, there was a good correlation between SSPC and the fatigue life. Under the potential where SSPC was low, corrosion fatigue damage was also small and then fatigue life was longer. This correlation is further clear in the borate solution in which the passive film formed. The result suggests that the SSPC, which can be measured at the early stage of fatigue test, is useful to estimate the corrosion fatigue damage quantitatively.

抄録全体を表示

With offshore structures being increasingly installed in frigid regions and deeper waters, it is important to clarify the effects of temperature and dissolved oxygen (DO) content of seawater on fatigue strength. The effect of applied potential for high tensile strength steel should also be clarified, as hydrogen can be introduced under cathodic protection (CP).
In this study, fatigue tests were conducted on welded Tee joints of a 600 MPa-strength steel, by controlling temperature and DO concentration in synthetic seawater with and without CP. The temperature was kept at 30 or 4°C, and the DO concentration was 0 ppm, 5 ppm or of air-saturated state. In the tests with CP, the potential of -0.8, -1.0 or -1.2 V (vs. SCE) was applied on the toes of welded joints.
While the effect of temperature was not remarkable, lowering DO content increased the fatigue strength for the steel under free corrosion. In longer fatigue endurance region, CP of -0.8 or -1.0 V (vs. SCE) improved the fatigue strength in seawater to exceed that in the air. However, cathodic protection at -1.2 V decreased the fatigue strength regardless of DO content.

抄録全体を表示

Effect of phosphorus on the hardenability and the pearlite transformation behavior in high-purity 0.35% carbon steels has been investigated.
It was confirmed by Jominy end-quench testing, dilatometric measurement, and metallography that phosphorus increased the hardenability. The Jominy distance parabolically increased with phosphorus content, and the phosphorus effect tended to saturate at high phosphorus content around 0.04%. Metallography showed that the hardenability was limited by the pearlite (degenerate pearlite) transformation at around 820 K. The growth rate of pearlite nodules at 823 K markedly decreased by addition of phosphorus, but the nucleation rate did not. It was concluded that the enhancement of hardenability by phosphorus addition was caused by the retardation of pearlite growth because of solute drag effect.

抄録全体を表示

The effects of manganese and sulphur on the grain growth and texture development during isochronal annealing have been investigated for cold rolled 0.5% Si steel. Although both manganese and sulphur affect the grain growth, its dependency on Mn content is influenced by the S level. In steels containing 0.004% to 0.017% S, an increase in Mn content leads to marked grain growth through coarsening of manganese sulphide particles. In ultra-low S steels containing less than 0.001% S, however, the grain growth is inhibited by fine precipitates of manganese silicon nitride (MnSiN₂). On the other hand, the texture development during grain growth depends only on Mn content, a higher Mn content results in an increase in {222} texture component and a decrease in {110} texture component. This fact is considered to be related to the change in solute N content being counter-balanced with MnSiN₂ precipitation.

抄録全体を表示

An influence of boron and nitrogen contents on the strength and toughness of 0.03%C-1.50%Mn-0.15%Mo-0.07%V-0.04%Nb-0.02%Ti-B steel, finish-rolled at 720°C, then acceleratedly-cooled after heating at 1 050°C was studied.
The strength and toughness can be estimated by the content of calcurated free-boron. The microstructure changes from coarse ferrite to fine ferrite, or from fine ferrite to bainite by increasing of free-boron content, or cooling rate after controlled-rolling, consequently the tensile strength increases. The toughness increases by the change to fine ferrite, but decreases by the change to upper bainite. The decrease of toughness is caused by increase of a unit crack path. Optimum free boron content to obtain both high strength and high toughness is less than 7 ppm.

抄録全体を表示

The influence of hot working and heat treatment conditions, impurity elements and test temperature on the fracture toughness of Ti-6Al-4V alloy was systematically examined. The fracture mechanism of this alloy was also discussed on the result of the detail observation of cracking behavior at the notch-tip of COD test specimens unloaded prior to the maximum load.
At 0°C, microstructure has a more influence on the strength-toughness relationship than impurity content. The βtreated specimens with acicular microstructure show a better strength-toughness combination than α+β treated specimenes with equiaxed microstructure at any strength level.
At -196°C, the impurity content has a great influence on the strength-toughness relationship and specimens with low impurity contents, ELI, have a better strength-toughness combination than those with standard impurity contents, regardless of their strength.
These tendencies in the strength-toughness relationship are proved to be closely related with both the occurrence of microcracks and their length at the notch-tip of the specimens before the final unstable fracture. It is found that a specimen shows higher fracture toughness, when microcraks are developed at the notch-tip through void coalescence below the maximum load and their propagation is hindered or distorted by lath-colony boundaries, grain boundaries or phase boundaries.

抄録全体を表示

Internal crack initiation in high cycle fatigue at cryogenic temperatures has been investigated for Ti-5A1-2.5Sn ELI alloy. The fatigue crack initiation site changed from the sample surface to the sample interior at about 10⁵ cycles. Neither defects nor foreign material was detected at the internal nucleation sites. However, the region of the nucleation site had a grain morphology and composition different from that of the bulk material. From observation it is concluded that internal cracks initiate in small a grain regions with a low Al content and an Fe enriched second phase at their grain boundaries.
At maximum stress lower than three-quarters yield strength, where internal fatigue crack initiation occurred, dislocation pile-ups were primarily on prism planes and were blocked at the grain boundaries. The piled-up dislocations are believed to produce a high stress concentration in the small a grain regions. This stress concentration may provide a site for internal crack initiation. At higher maximum stress the dislocation pile-ups are more homogeneously distributed in the material and the dislocation arrays can pass through the grain boundaries. As a result, fatigue crack initiation must occur at the specimen surface.

抄録全体を表示

Creep rupture tests were carried out at 1 000°C in air on the Ni-26Cr-W alloys containing small amount of B and/or Zr, and the effect of the minor elements addition on the creep rupture properties was investigated in relation to the microstructure. The results obtained were summarized as follows ;
1. A minimum creep rate was decreased remarkably through small addition of B. This is attributed to the uniform and fine dispersion of M₂₃C₆ in a grain during creep deformation. The state was kept at least up to 2 500 h.
2. A rupture ductility was improved by a small addition of Zr. This seems to result from the increase of the surface energy for cracking at the grain boundary through the Zr addition.
3. Owing to (1) and (2), the alloy containing a small amount of B and Zr showed better creep rupture properties than the alloys solely with B or Zr. Its rupture life was longer than that of 113MA (Ni-23Cr-18W) and the life difference was apt to become larger with decreasing in the applied stress.

抄録全体を表示

It is necessary to grasp the behavior of hydrogen in refining process accurately and rapidly, in order to produce low hydrogen steel by degasification treatment. From this viewpoint, a study was made, through comparison of hydrogen analytical value using double tube sampler and that using conventional quartz tube sampler to establish the technique for accurate determination of hydrogen in molten steel.
(1) Hydrogen analytical value using double tube sampler is more accurate than that using quartz tube sampler, because double tube sampler can catch almost perfectly evolved hydrogen in solidification and cooling processes of the sample. Hydrogen analytical value by double tube sampler is 2.5 to 3.5 times that by quartz tube sampler in molten steel containing 0.05%C.
(2) Fraction of diffusible hydrogen to total hydrogen is different depending on C, Cr and Ni contents in molten steel.
(3) Reliability of this method expressed by the standard deviation is 0.11-0.25 ppm and these values are good enough for application to actual production control of refining process.

抄録全体を表示

A rapid potentiometric titration mothod of free sulfuric acid in the colouring solution for stainless steels is described.
The solution was composed of chromic acid (CrO₃, 250 g/l), sulfuric acid (H₂SO₄, 500 g/l) and metallic sulfate ions as Fe₂ (SO₄)₃, Cr₂( SO₄)₃ etc.
For the control of the tints and qualities of coloured films, the determination of free sulfuric acid was needed. But the conventional procedures could not be employed because of co-precipitation of both sulfuric acid and metallic sulfate as BaSO₄.
It was found the follwing procedure was effective to take away the interference of the metallic sulfate ions.
(1) At first, total [H⁺] at 1st titration end point of H₂SO₄ and H₂Cr₂O₇ in the sample solution was determined with potentiometric titration method after addition of Zn-EDTA for masking metallic ions.
(2) Free sulfuric acid concentration was determined after subtraction of [H⁺]_CrO3 of 1st dissociation of CrO₃ from total [H], which was determined by the another chemical analysis of Cr(VI).
The time required for this method was about 30 minutes for one sample and the results were accurate and reproducible.

抄録全体を表示