Iron ore sinter feeds are granulated with water to improve permeability of the bed during sintering. The permeability of a packed bed is a complex function of the effective mean diameter of the granules and the void fraction of the bed.
This paper describes a technique for measuring the void fraction of a bed of granulated iron ore sinter feed by filling the voids, under vacuum with kerosene. Kerosene, being immiscible with water, does not penetrate the moist granules.
For the hematite ore studied, bed void fraction increased initially as the amount of water used for granulation was increased. This was due most likely to the narrowing of the size distribution of the granules. A maximum void fraction of 0.49 occurred at about 5.3% water. Thereafter, additional water used for granulation resulted in a decrease in bed void fraction due probably to slumping of the granules as they were packed to form a bed.
Bulk density measurements on the granulated mixes confirmed the shape of the voidage vs. moisture content relation obtained by kerosene displacement and a satisfactory matching of void fraction values by the two methods was obtained using a value of 4.08g/cm³ for the density of dry sinter feed. This value agreed favourably with the experimentally determined value of 4.03g/cm³ and suggests, for the sinter feed studied, all the internal porosity of granules is filled with water.

View full abstract

Effects of potassium chloride on the reduction of iron oxides were investigated by using dense hematite, magnetite, and wustite samples prepared by the oxidation of electrolytic iron plates.
The addition of small amount of KCl to the surfaces of oxide samples was found to greatly increase the reduction rate of all the reduction steps: Fe₂O₃ →Fe₃O₄, Fe₃O₄→FeO, and FeO→Fe.
Reduction of hematite with KCl addition produced very porous magnetite having larger contact area with reducing gas. In the reduction of magnetite with KCl addition, the grain boundary on the surface was strongly eroded and distorted wustite crystals were formed on the magnetite surface. These phenomena were considered to be responsible for the accelerating effects of KCl on the reduction of hematite and magnetite. However, the accelerating effect of KCl on wustite reduction could not be clarified in terms of morphology.

View full abstract

The information about thermodynamic properties of phosphorus in lime bearing slags at relatively low temperatures is required in connection with the recent progress of hot metal treatment.
In the present study, the equilibrium distribution ratio of phosphorus (L_P) between CaO-CaF₂-SiO₂ melts saturated with CaO, 3CaO•SiO₂ and/or 2CaO•SiO₂ and carbon-saturated iron has been measured under a CO atmosphere at temperatures ranging from 1200 to 1400°C, keeping in mind that the industrial flux always contains some undissolved solids.
The results are summarized as follows:
(1) The distribution ratio, L_P increases with increasing CaO content and has a maximum when the slag is doubly saturated with CaO and 3CaO•SiO₂.
(2) The phosphate capacity is confirmed to be independent of the partial pressure of oxygen in the case that iron-carbon melts are equilibrated with austenite and CO at 1300°C. The phosphate capacity in basic regions of this system is much greater than that of other lime bearing slaps.
(3) CaF₂ is more effective for dephosphorization than CaCl₂, probably because the interaction between fluorine and phosphorus and between fluorine and calcium is stronger than that between chlorine and phosphorus and between chlorine and calcium.
(4) The distribution ratio, L_P increases significantly with a small Na₂O addition to the CaO-CaF₂-SiO₂ system, indicating that the costly soda ash treatment can be replaced by lime-based flux containing a little soda ash.

View full abstract

Experiments have been made to study the phosphorus distribution between carbon-saturated iron and lime-based melts containing MnO, BaO, Na₂O in the temperature range of 1250-1350°C under a CO atmosphere.
The results are summarized as follows:
(1) The phosphorus equilibrium distribution between CaO-CaF₂ SiO₂-MnO melts and carbon-saturated iron decreases with increasing manganese oxide content in slaps.
(2) BaO and Na₂O have a beneficial effect on the phosphate capacity of the slags for the systems: CaO-CaF₂-SiO₂-MnO-BaO and CaO-CaF₂-SiO₂-MnO-Na₂O.
(3) Increasing CaF₂ content in the range of 25 to 40% decreases the phosphorus equilibrium distribution.
(4) The temperature dependence of equilibrium phosphorus distributions can be expressed as follows: log L_p=13300/T-8.84
The heat of reaction of dephosphorization was -130kcal per mole of Ca_1.5PO₄.

View full abstract

Two types of wustite micropellets; wustite I (chemically pure) and wustite II (2.1% SiO₂-containing wustite), were isothermally reduced at 900-1100°C in the flowing hydrogen, carbon monoxide and their mixtures. Surface area, optical and scanning electron microscopes and X-ray and carbon analyses were used to characterise the structural changes and to elucidate the possible mechanism of reduction. The highest rate at the initial stages was obtained in H₂ and the slowest was in CO. With mixtures of gases, the rate did not vary with gas composition in a simple manner. The presence of silica enhanced the reduction in CO and retarded the reduction in H₂. The addition of silica led to a significant slowing down at the latter stages of reduction in H₂. The addition of small amount of CO to H₂ eliminated this slowing down.

View full abstract

The effect of C on hot ductility of low alloy steels has been studied in view of surface cracking of continuously cast (CC) slabs. As the ductility was not affected by C content in hot tensile test of the reheated specimens, the well-known C dependency of surface cracking susceptibility in CC slabs can be ascribed to the microstructural change during the solidification process. Austenite grain size of as-cast materials was found to depend largely on C content, i.e., the maximum grain size in 0.10-0.15% C region. This can be explained by the higher austenite formation temperature in these C region. Austenite grain growth rapidly occurred after the complete transformation or solidification into γ phase, as the strong pinning effect of the second phase such as δ-ferrite or liquid phase on γ grain boundary migration was relieved. Carbon dependency of γ grain size became more marked with increasing cooling rate up to that of ordinary continuous casting.
Such coarsening of γ grains enhanced intergranular fracture, resulting in ductility loss inversely proportional to the γ grain size. Uneven surface solidification in the mold due to the peritectic reaction will produce much coarse γ structure because of the local delay of cooling. Surface cracking susceptibility will also be largely accelerated by this mechanism. Carbon range where surface cracking susceptibility was the largest varied with the chemical compositions. This shift can be explained in terms of the effect of alloying elements such as Mn on the peritectic composition.

View full abstract

The susceptibility to temper embrittlement of 21/4Cr-1Mo cast steels was compared with that of forged steels. The degree of temper embrittlement of cast steels is closely related to the parameter, (Si+Mn)×(P+Sn)×10⁴, and is much greater than that of forged steels. Difference in temper embrittlement susceptibility between cast steels and forged steels is caused by difference in Mn content and solute segregation. Moderated dendritic solute segregation due to soaking lowers the susceptibility to temper embrittlement when heated at temperatures above 1100°C.

View full abstract

This report is concerned with the capability of manufacturing by direct-quench and tempering of seamless steel pipes for grades HT60 (TS≥60 kg/mm²) to HT80 (TS≥80kg/mm²) and API 5L X60 to U80. Although pipes of the strength level of these grades can be produced with low alloy steels, toughness of the direct-quenched and tempered pipes has not been satisfactory. A series of studies on the effect of alloying additives on the hardenability of steels have shown that titanium addition to the boron steel yields the maximum hardenability effect. To improve toughness, controlling the amount of titanium in the range of 0.008wt% to 0.011wt% has been found effective for the content of nitrogen between 25ppm and 45ppm. This range of nitrogen is determined to retain toughness in the welded joint. The direct quenching, thus, enables the production of high-strength seamless steel pipes with markedly improved toughness in both pipes and welded joints, when the content of titanium in the boron steel is chosen within the optimum range.

View full abstract

Wire-shaped austenite (γ) alloys of Fe-Mn-Cr-Al-C system exhibiting high strength and large elongation have been produced by the technique of melt spinning in rotating water. The formation range of γ phase is limited to about 0 to 20 at% Cr, 2 to 9 at% Al, 1 to 6 at% C and above 6 at% Mn. The wires have a circular cross section whose diameter is in the range of 80 to 200μm. The average grain size of the γ wires is as small as about 0.8μm. The yield strength (σ_y) and the tensile strength (σ_f) of the wires increase to 480MPa and 900MPa, respectively, with increasing amounts of Cr, Al and/or C, while elongation increases to 20% with the decrease in Cr, Al and/or C. The high strength and good ductility of the metastable γ wires produced by the melt-quenching technique have been interpreted as due to the suppression of the phase transformation of γ to a mixed structure of ferrite+M₇C₃ carbide, in addition to the refinement of grain size. Furthermore, the cold-drawing to about 90% reduction in area has been found to result in a very significant increase of tensile strength from 835 to 3850MPa, through the fibrous formation of the strain-induced lath martensite (α'L) phase and a remarkable work-hardening ability of γ and α'L phases.

View full abstract

The fatigue fracture surface analysis map of a 18 Ni maraging steel (see Fig. 1) is presented for the aging temperature of 482°C and the stress ratio of 0.10. The map consists of the quantitative information obtained from the analysis of fatigue fracture surface and the curve of macroscopic crack growth rate vs. stress intensity factor reported in Ref. 4). It is aimed to estimate the mode of fatigue fracture and the rate and the direction of crack growth from a fracture surface of which a cause is unknown. The effectivity of the map for the above aim is confirmed under other kinds of testing conditions, such as with the prior austenitic grain sizes of 11 μm and 25μm, the aging temperatures of 482°C and 432°C, and the stress ratios of 0.10 and 0.70.

View full abstract

The creep rupture properties of nickel base heat resisting alloys are investigated in two types of impure helium o f He-2 and PNP-He at 1000 °C, simulating a high temperature gas-cooled reactor (HTGR) environment. The alloys examined are four new alloys developed for heat exchangers of nuclear steelmaking system using HTGR.
All the alloys are decarburized in some extent in PNP-He, while some of them are carburized in He-2 during the creep rupture testing, indicating that carbon activity of the gases is lower in PNP-He than in He-2 at 1000°C.
Decarburization is found to be the most important of the environmental effects deteriorating the creep rupture properties of the alloys. The environmental effects of the formation of internal oxides and the depletion of gamma prime and α-W precipitates beneath the alloy surface are also examined.

View full abstract