The influences of the immersion of sinter into calcium halide aqueous solutions or suspensions and the subsequent drying of sinter on the reduction degradation index (RDI) and relative reducibility index (RI) were investigated.
The immersion treatments of sinters were carried out at a room temperature in air and in vacuum. The calcium halide concentration of aqueous solution or suspension was changed from 1.0 to 10.0 wt%.
When sinter was immersed into CaCl₂ and CaBr₂ aqueous solutions, RI remained at the same value of the original sinter, while the value of RDI decreased, in other words, the degradation during reduction was improved, particularly in case of CaBr₂.
On the other hand, when sinter was immersed into CaF₂ suspension, the effect of the immersion treatment on RI and RDI was scarcely detected.

View full abstract

Removal of impurities in fine-grained iron ore with Na₂O-B₂O₃ flux and its mechanism have been investigated. The flux leaching method in which the oversaturated amount of powdery iron ore is treated with the flux has been used in the temperature range from 850 to 950°C. The recrystallization method has also been used in the temperature range from 1 400 to 1 450°C. The isolated impurities as well as those on the surface of ore particles were removed by the former method, while the inclusions present inside the particles together with the above-mentioned impurities were removed by the latter method. The high yield of iron oxide and the low content of impurities were obtained at the flux compositions of Na₂O·2B₂O₃ and 2Na₂O·5B₂O₃. The contents of Si, Al, Ca, Mg, Mn, and V decreased with increasing temperature from 850 to 1 450°C; these observations were explained by the break up of ore particles and the increase of the amount of recrystallized iron oxide. About 80% of iron oxide yield was obtained in both flux treatments by use of the Na₂O·2B₂O₃ flux.

View full abstract

Surface tension and density of molten CaF₂-based binary system were measured. From the measurement, the following results were obtained.
(1) Molar volumes of the melts in the systems CaF₂-NaF, and CaF₂-BaF₂ are deviated positively from the additive rule, while for CaF₂-LiF and CaF₂-MgF₂ melts negative deviation from the additive rule on volume is found, but CaF₂-SrF₂ melt behaves ideally on volume.
(2) Surface tensions of the melts in the binary systems can be expressed by Guggenheim's equation for regular solution, if a suitable interaction energy ω of each binary system is selected.
(3) The interaction energy ω, estimated from surface tension of binary fluoride systems, is related to the excess volume on mixing for CaF₂-M_xF₂ equi-molar composition (x=1 for divalent and x=2 for monovalent fluoride).
(4) Liquidus lines for the systems, calculated from the interaction energy ω in combination with the thermochemical data are fairly in good agreement with those reported, but that for CaF₂-NaF system is exceptional.
(5) Surface tensions of binary fluoride melts are strongly depended on packing density of fluorine ions on the surface.

View full abstract

Drop generation due to a jet impinging on a liquid was investigated in 3D single phase (water) and two phase (mercury/glycerine) models. It was found that the bottom flow affects the criterion for transition of the mechanisms of the drop generation. A peak of drop production is obtained at a certain lance height. "Apparent tuyere position" should be taken into account. Weber number as a link between model and prototype is clearly indicated.

View full abstract

Transverse surface cracks were metallographically investigated and the local segregation was found to be the origin of transverse surface cracks on continuously cast slabs. The positive segregation spreaded over an oscillation mark and showed high phosphorous content. At the same time, the sharp negative segregation was also seen adjacent to the positive segregation along the mark. This positive segregation penetrated deeply into austenite grain boundaries, through which transverse cracks propagated. The fractured surface was smooth and the precipitates of MnS was found.
Based on the observation, a mechanism of the formation of cracks was proposed. At the meniscus, when the tip of partially solidified shell is bent down periodically during mould oscillation, interdendritic "dirty" liquid is squeezed out and accumulated at the valley of an oscillation mark. In other case, bulk liquid overflows on the tip of the shell and again interdendritic "dirty" liquid spreads out and accumulates there. In any case, the local segregation forms at the valley of an oscillation mark. The cracks lead to initiate at this weak part of the shell under any external stresses. Thus so called internal cracks forms below the oscillation mark and propagates along austenite grain boundaries. Finally a large transverse crack forms on the above-mentioned defect. Some industrial measure were summarized to prevent both the segregation and the cracks to form.

View full abstract

Flash butt welding of 3.7 mm thick Mn-Cr-Mo dual phase steel is carried out at different final jaw distances, where various post weld cooling systems such as the normal machine cooling, forced air cooling and water spray cooling are used. The energy input during welding such as the current and voltage are kept constant. The intention of this investigation is limited to study the influence of various weld thermal cycle on the behaviour of phase transformation at weld centre and different regions of HAZ. Under different conditions of welding the weld thermal cycle is analysed and the behaviour of phase transformation at different regions of the weldment is determined with the help of welding CCT diagram. A detail microstructural study is carried out under optical and scanning electron microscopes. A special attention is paid to study the behaviour of tempered martensite region of HAZ, which is identified earlier as the weakest region of HAZ, under different welding conditions. The weakening of tempered martensite region is estimated by measuring its microhardness under different conditions of welding.

View full abstract

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 Mn and S 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 promotes the grain growth through decreasing the amount of fine manganese sulphide particles. In ultra-low S steels containing less than 0.001% S, however, the grain growth is inhibited with Mn addition by the precipitation of manganese silicon nitride (MnSiN₂). On the other hand, the changes in recrystallization texture being accompanied by grain growth depend only on Mn content, a higher Mn content results in an increase in {222} component. This fact is considered to be related to the change in solute N content being counterbalanced with MnSiN₂ precipitation.

View full abstract

This study examined the effects of ceramic tool materials on the surface roughness and cutting force when low-carbon resulfurized free-machining steels were plunge-machined. The Tool materials used for the study were 9 kinds in total; 7 kinds ceramics-TiN, TiC, HfO₂, ZrN, Al₂O₃, ZrO₂ and La₂O₃-and a high-speed steel (Fe₃C) and a cemented carbide (WC+Co).
(1) Surface roughness and cutting force are the smallest in the ZrO₂ tool, increasing in the order of TiN, ZrN, Al₂O₃, TiC, HfO₂, WC+Co, La₂O₃ and Fe₃C tools.
(2) ZrO₂, TiN, ZrN and Al₂O₃ tend to adhere selectively to manganese sulfide inclusions in steels, resulting in the formation of MnS films over the rake face of tools. On the other hand, HfO₂, WC+Co, Fe₃C and La₂O₃ tend to adhere selectively to the ferrite phase, forming a kind of built-up edge, whereas TiC hardly to manganese sulfide inclusions and ferrite phase.
(3) Surface roughness and cutting force decrease in proportion to the area percentage of MnS films formed over the rake face of tools, because the MnS films play a role as a lubricant.
(4) Adhesion of manganese sulfide inclusions to tools may not only stem from physical properties such as surface roughness of the tools but also from chemical bonding.

View full abstract