We have proposed a technology of swirling flow formation in submerged entry nozzle as a fundamental and effective measure for controlling flow pattern in continuous casting mold. A joint study started in 1997 with Nippon Institute of Technology, Osaka University, Kyushu Refractories and Sumitomo Metal Industries to develop a swirling flow submerged entry nozzle with a swirling blade for steel casting. As a result of the collaboration, the swirling flow submerged entry nozzle for wide slab casting has developed in Wakayama Works, which improve productivity and surface quality of slabs and coils. Swirling flow formation in the submerged entry nozzle can be effective for controlling flow pattern in the mold in the case with optimum design of outlet port. The outlet port of the swirling flow submerged entry nozzle should be designed adapting a characteristic of swirling downward flow in the nozzle. As a result of full-scale water model experiment, we achieved a conclusion of outlet port design that the narrow width of the outlet port is optimum for the swirling flow submerged entry nozzle. Otherwise, outlet flow from the port extends widely and stagnates in the mold.
In this paper, an auto-tuning system to attenuate the periodical mold level fluctuation caused by unstedy bulging of continuous caster is shown. This system tunes the parameter of the Q-paramter design controller proposed by the author. This auto-tuning system uses the frequency distribution of the estimated disturbance to the molten steel outflow from the mold. The auto-tuning system is compared with the auto-tuning system using the mold level instead of the estimated disturbance by numerical simualations. Stability of the paramters for the attenuation performance and their variable range provide several evidences of advantage of this auto-tuning system. An experimental result in an actual continuous caster is shown.
The heat fatigue characteristic and the high temperature oxidization characteristic were examined about the typical cermet and metal type sprayed coatings as a part which aims at the life extension by applying thermal spraying technology to the components used in the intermediate temperature region of a diesel engine etc. And most suitable sprayed coatings was collected. The result is summarized below. (1) The high temperature fatigue characteristic of Hasteloy C sprayed coating was superior to Cr3C2-25%NiCr sprayed coating and was more than or as same as that of steel coating. (2) From a high temperature oxidization examination result, it became clear that the high temperature oxidization characteristic of Hasteloy C sprayed coating was superior to steel casting and was equivalent to Cr3C2-25%NiCr sprayed coating. (3) From (1) and (2), it was shown clear that Hasteloy C psrayed coating having the both excellent ability of the High temperature fatigue characteristic and the high temperature oxidization characteristic excelled in the environment-proof property of components in the intermediate temperature region.
Decomposition behavior of cementite in high carbon steel wires during drawing and aging was investigated by atom probe field ion microscope, transmission electron microscope and tensile testing. Cementite decomposition proceeds with the drawing strain. At the same drawing strain, the carbon concentration of the dry drawn wire is higher than that of the wet drawn. In addition, cementite decomposition proceeds in low temperature aging after drawing. It may be concluded that the carbon atoms segregate to dislocations or cell boundaries and dislocation locking by carbon atoms plays an important role in the work hardening and strain age hardening. The mechanisms of cementite decomposition can be considered as follows. When the wire is drawn, carbon atoms in ferrite move within the dislocation strain fields, and the carbon concentration around dislocations is lowered locally. On the other hand, the matrix carbon concentration should be in equilibrium with the cementite. Accordingly, the diffusion of carbon atoms into the depleted region around dislocations leads to a general decrease of the carbon concentration, and cementite then dissolves tending to maintain the local equilibrium in the matrix carbon content. The highly dense dislocations which act as trapping sites of carbon atoms, and the heat generation of the drawing process which increases the diffusion rate of carbon are prerequisite for cementite decomposition. The rate-determining step of cementite decomposition may be carbon diffusion under the condition of constant dislocation density.
It is well known that tungsten (W) is the key element for creep strength of the advanced martensitic heat resistant steels developed for main steam pipe in ultra-super critical power plant. W is found to suppress coarsening of M23C6 type carbide during creep at elevated temperatures, which can never be predicted according to the conventional Ostwald ripening model for a Fe-X-C system in αFe. In this study, therefore, the effect of W on the coarsening of M23C6 during aging has been analyzed in a detailed experiment and modeled using a modified Ostwald ripening equation for Fe-X1-X2-C system. It is found that W substitutes only for Cr in M23C6 lattice to form [Fe4(Cr, W)19]C6. Using the modified Ostwald ripening equation the coarsening of M23C6 is found to be controlled by the lattice-diffusion of W, resulting in the coarsening rate reduced about one order of magnitude by 1% W addition.
Forming temperature dependence of formability in 0.20C-1.51Si-1.51Mn ultra high-strength TRIP-aided sheet steels with bainitic ferrite matrix (TBF steel) which were austempered at 375 or 450°C was investigated for automotive applications. Warm formings at 20-50°C and 100°C respectively enhanced the stretch-formability and the deep drawability of the TBF steel through the TRIP effect due to the strain-induced martensite transformation of retained austenite. The stretch-flangeability became maximum by warm forming at 20-50°C and 100-200°C in the TBF steels austempered at 375°C and 450°C, respectively. Further good stretch-flangeability was completed by warm punching at 100-200°C and subsequent cold expanding at 20°C in the TBF steel austempered at 450°C. The mechanisms improving these formabilities by warm forming were proposed in terms of retained austenite characteristics and microstructural properties.
Circumferentially notched and smooth round tension tests were conducted at room temperature with or without compressive prestrain in hotrolled ferrite-pearlite SM490B steel. And the effects of compressive prestrain and notch acuity on plastic deformation limit were investigated. Plastic deformation limit was defined as the termination point in the true stress-true strain relationship, caused by ductile or cleavage fracture. The average stress-true strain relationship was varied with prestrain and notch acuity, but the true stress-true strain relationship was not. The true strain at the onset of plastic instability was determined by the work hardening exponent, regardless of prestrain and notch acuity. On the other hand, the plastic deformation limit in terms of true strain was varied with prestrain and notch acuity. It was found that the plastic deformation limit can be estimated by the axial stress criterion. The axial stress at plastic deformation limit was about 1300 MPa, regardless of ductile and cleavage fracture.
Aging behavior of low Carbon steel depends on over aging condition and chemical compositions. Over aged samples with Mo after quenching are tensile tested and the effect by Mo on aging parameters are investigated. The following results are obtained: 1) Bake Hardenability of Mo added samples show high value at early stage of over aging than as quenched samples, 2) Tensile strength and Yield strength of the samples with Mo show higher value than those of the sample without Mo for 230 ppm carbon steel, 3) Snoek Peak Height of the samples with Mo show lower value than those of the sample without Mo for 70 ppm carbon steel, but show higher for 230 ppm carbon steel. 4) These phenomena can be explained by assuming the presence of Mo-C-Va cluster which are made during quenching.
A continuous monitoring system for gas generation in coke oven has been established with the Fourier-transform infrared spectroscopic analyzer (FT-IR) as a detector. Coke oven gas (COG) was sampled in an ascension pipe by a pump. COG, passed through traps for removing tar and mist, was led to the detector located about 20 m from the sampling position. COG was monitored with 50 times dilution by nitrogen gas because the concentrations of component gases are too high for the FT-IR measurement. Using this system, the COG of a coke oven was measured continuously for about 20 h. By monitoring the generation behavior of COG, it was possible to characterize the details of the coking reaction in a coke oven. It was shown that different combinations of coals result in different COG generation behavior.