To achieve a high rate injection of pulverized coal into a blast furnace, it is so important to increase a combustion efficiency of pulverized coal. Enhancement of particle dispersion is one of the measures to increase combustion efficiency by accelerating oxygen-coal particle mixture in blowpipe to tuyere region. To realize this, it is found that convergent - divergent injection lance designed on the basis of fluid dynamics has superior characteristics. Divergence angle of the lance is optimized as the maximum angle free from the flow separation phenomenon in the boundary layer and convergence angle of the lance is optimized considering the inertia of coal particle in the gas-solid two phase flow. Optimum divergence angle and convergence angle is found to be 7 and 5 degrees respectively. Direct observation results by offline apparatus, hot model experiments and even in the actual blast furnace proves that dispersion of pulverized coal particles is enhanced considerably.
It is confirmed that permeability is improved at an actual blast furnace when the developed lances are installed. This result suggests that high combustion efficiency had been achieved by the enhancement of particle dispersibility.
It is thought that the convergent - divergent lance can be one of the practical solutions for the stable operation with high rate injection of pulverized coal because the lance can be installed almost all blast furnaces easily by its simple configuration without a large amount of investment.
Polyester films have been used widely as laminate films of beverage and food cans due to their excellent properties of formability, corrosion resistance, and adhesion to steel sheets. Recently, excellent formability under the condition of a higher processing degree has been required in laminated steel sheets for drawn and ironing (DI) cans, which are used as beverage and food cans. Therefore, polyester films which are almost amorphous are used since high formability is needed in the laminate film. In this study, we investigated the thermal crystallization behaviors of a near-amorphous oriented polyester film and non-oriented film by thermal analysis and Raman spectroscopy. We found that the two types of films display different thermal crystallization behaviors.
Understanding of γ→α transformation during intercritical annealing is important to achieve precise control over the mechanical properties of low-carbon steels. And control of the carbon contents in the phases is the most important factor in alloy design for achieving high strength and high ductility. However, it is unusually difficult to determine the carbon contents in multiphase structures with high accuracy. So, we have developed new methods for suppressing hydrocarbon contamination during field emission (FE) EPMA measurements.
Carbon enrichment at γ/α interface and carbon concentration of γ phase in Fe-0.15%C-2%Si-(1.5, 2.0)%Mn steels isothermally transformed at 750 and 800°C was measured using developed FE-EPMA. The paraequilibrium (PE) model gives much better predictions for carbon enrichment in 1.5%Mn steel for 15 s. The NPLE/PLE transition model of local equilibrium gives much better predictions in 2.0%Mn steel. But the interfacial carbon concentration agrees with the composition of PLE/NPLE transition line in all alloys annealing for 1800 s. Furthermore, carbon enrichment shifted from the PE to NPLE model during annealing.
In order to obtain basic information for maintenance, repair and reinforcement of aged steel bridges, mechanical properties and weldability of steels used in aged bridges were investigated.
The contents of sulfur were relatively much in steels used in bridges constructed before 1960. The mechanical properties of aged steels were almost the same as those of SS400 and SM400. However, the Charpy absorbed energy of aged steels at 0°C were extremely low. Welding defects were observed in the repair welded parts of aged steel bridges. Although a weld cracking test was performed on the same steel of which the chemical compositions were not suitable for welding, weld crack was not generated. That might be because of the small thickness of steel and the mechanical conditions of welded joints. That is, patch plate welded joints with small thickness generated the small restraint during welding. The results indicated the importance of investigating chemical compositions and the mechanical conditions of welded joints for evaluation of the weldability of aged steels.
The morphology of (α+β) dual-phase structure in Ti-4%Cr alloy was controlled to be plate-like and equiaxed types by aging treatment and warm rolling, respectively. Tensile testing for the specimens with different morphology revealed that the equiaxed specimen was much superior to the plate-like one in elongation and reduction of area. The inhomogeneous and hierarchical strain distribution was quantitatively visualized for these specimens by DIC method, and it was found that the plastic strain is preferentially introduced into the softer phase of α, which results in a marked strain partitioning between α and β phases, particularly in the plate-like specimen. There were three conditions for preferential plastic deformation in the plate-like specimen: 1. α plate is aligned nearly in the direction of maximum shear stress, 2. the length and width of α plate is relatively large, and 3. Schmidt factor for prismatic slips is relatively large. As a result, the plastic strain is increased in such α plates and expanded along the plate, leading to a void formation at plate/plate or plate/β grain boundary junctions. On the other hand, the equiaxed specimen deforms uniformly with a less strain partitioning, and also, the strained regions are formed separately and hard to connect each other. Since the void formation is significantly delayed due to those reasons, the equiaxed specimen can continue plastic deformation to a higher strain regime.
The existence of small amount of retained austenite in precipitation hardening stainless steels (PHSS) is known to be effective to improve the ductility caused by transformation-induced plasticity. However, the detailed mechanism is yet inadequately understood. In the present study, two types of PHSS are prepared and solution heat treated with different cooling rate to systematically change the amount of retained austenite in the PHSS. The amount of retained austenite was investigated by XRD analysis, microstructure was observed by TEM and EBSD, and micro Vickers hardness test and tensile test were carried out in order to elucidate the relationship between the amount of retained austenite and mechanical properties. As a result, retained austenite is finely distributed with a block or film shape along the martensite lath boundaries. The excess amount of retained austenite forms large blocks in several ten μm in the vicinity of grain boundaries and hence inhomogeneous microstructure and hardness. 0.2% proof stress decreases and rupture elongation increases with increasing the amount of retained austenite. On the other hand, tensile properties of the 3Co steel with a large amount of retained austenite do not change in spite of the precipitation in the martensite matrix by the aging treatment. It is considered by the effect of percolation phenomenon of retained austenite with low mechanical strength. Further improvement of mechanical properties of PHSS will be achieved by controlling not only amount of retained austenite but also microstructure especially focused on the connectedness of retained austenite.
A single peak in thermal desorption profiles of hydrogen, which are measured in low-temperature thermal desorption spectrometry (L-TDS) for a very thin plate specimen of tempered martensitic steel, was reproduced successfully to evaluate the peak temperature by the superposition of two Gaussian distributions. We calculated the parameters concerning the detrapping rate constants for both peaks, which are the trap energy and pre-exponential factor, from the Choo-Lee plot. We confirmed that the Kissinger model incorporating the obtained parameters could simulate the two peaks. In addition, the single peak was also well reproduced by the reaction-diffusion equation based on the McNabb-Foster model incorporating the obtained parameters. From the trapping energy and the trap site concentration which were used for reproducing the single peak, we interpreted that one peak corresponded to dislocation and the other was to grain-boundary.
The coaxing effect has been recognized as a phenomenon that enhances the fatigue resistance associated with work hardening and strain-age hardening. To uncover the intrinsic factors that affect the degree of coaxing effect, rotating bending fatigue tests including a process of stepwise stress increases every 107 cycles were carried out at ambient temperature in interstitial free steel and binary Fe-C ferritic alloys. The effects of the work hardening capacity, aging time, stress amplitude increment, and carbon concentration were examined in this simple alloy system. The work hardening capacity was changed by controlling carbon state in a Fe-0.017C (wt%) steel. However, the degree of coaxing effect did not show a significant correlation with work hardening capacity. For the effect of aging time, a fatigue test at a high stress amplitude was interrupted, aged for 2 weeks, and subsequently restarted. Although this process is sufficient to induce strain-age hardening in terms of aging time and plastic strain, a fatigue life of the aged steel was not comparable to that with the coaxing effect. Moreover, an increase in stress increment for each step deteriorated a degree of coaxing effect. It was concluded that the effect of work hardening is minor, and the other factors affecting strain-age hardening must be optimized simultaneously to show a coaxing effect. In addition, the degree of coaxing effect of smooth steel specimens was predominantly controlled by the intergranular fatigue crack initiation behavior. Consequently, a considerable amount of solute carbon and an alternate process for the stress amplitude increment and aging time are required for strain-age hardening that suppresses intergranular fatigue crack initiation.