An understanding of the dynamic behaviors of poorly-wetted fine particles penetrating into molten steel is of essential importance for the enhancement of steel refining efficiency. Many water model experiments have been carried out on a poorly-wetted single sphere penetrating into molten steel. Information on the behaviors of more than two particles, however, is very limited. In this study, the behaviors of a pair of spheres penetrating into a water bath are observed with a high-speed camera. Particular attention is paid to an air cavity or air cavities formed behind the spheres because the cavity length affects the penetration depth which is closely associated with the refining efficiency.
Alumina adhesion to the submerged entry nozzle (SEN) causes serious problems in continuous casting, as it has a negative influence on the flow pattern in the mold and causes inflow of alumina inclusions to mold. The purpose of this research is to prevent alumina adhesion to the SEN. A new type of SEN which enables control of the interfacial tension gradient at the interface of the SEN and molten steel was developed. Removing sulfur on the SEN interface controlled interfacial tension, preventing alumina adhesion. Various experiments were performed to evaluate the quality of the SEN material. As a result, the optimum refractory material for preventing alumina adhesion was clarified. After evaluating the thermal shock characteristics of nozzles using the developed material, experiments were performed at an actual continuous casting machine, and reduced alumina adhesion was confirmed under commercial operating conditions.
As a technology to manufacture fine-grained steel, accumulative bending process after hot rolling was proposed, and multi-bending equipment of laboratory scale were established. The effects of accumulative bending on microstructure and ferrite grain size by changing the thermomechanical conditions were investigated. As the results, a microstructure with the grain size of 2.2μm was obtained at specimen surface by accumulative bending after hot rolling in the optimized thermal condition. By the results of FE analysis, it was cleared that equivalent strain was accumulated on not only surface but also center of thickness.
Solution nitriding was applied to conventional 12%Cr stainless steels such as JIS SUS410L, SUS410, SUS420J1 and SUS420J2, and then the microstructure and hardness were examined for the as-quenched specimens as well as tempered ones. Nitrogen concentration was increased to around 0.28 mass% under the solution nitriding condition of 1473K-0.1MPa N2 in all of the 12%Cr steels regardless of the carbon content. Solid solution strengthening by nitrogen was relatively small compared with that by carbon in as-quenched martensite. However, solutionnitrided steels exhibited a remarkably large secondary hardening during tempering, which hardly appears in conventional martensitic stainless steels without nitrogen. TEM observation and X-ray analysis for extracted residue indicated that the secondary hardening by nitrogen was caused by precipitation of fine CrN nitride.
The correlation between ESSO test results and Charpy impact properties has been empirically proposed to qualify brittle crack arrest toughness, Kca of structural steels. The brittle crack arrest temperature TK6000 at Kca=6000N/mm3/2, conventionally used as a measure of crack arrest property, is interrelated generally with the Charpy transition temperature vTrs. However, ESSO test results occasionally deviates from the TK6000-vTrs correlation in some TMCP steels. Considering a thickness effect in ESSO test results, TK6000 was converted to a reference temperature 25TK6000 for 25mm thickness. Nevertheless, a scatter is found in 25TK6000-vTrs correlation. This study focuses on the effect of texture intensity on crack arrest properties. It is found that steel plates with texture show lower 25TK6000 than other steels without texture, even if the transition temperatures vTrs of these steels are on the same level. The role of the (211) texture is more significant than the (100) texture. A new parameter, vTrs (°C) -12X(100) -22X(211), is proposed in this study to correlate the crack arrest temperature 25TK6000 with the material properties of structural steels, where X(100) : pole density of (100) parallel to surface of steel plate, X(211): pole density of (211) parallel to surface of steel plate.