The use of high reactivity coke is proposed to realize low reducing agent rate blast furnace operation. The reducing agent rate was reduced by use of high reactivity coke in an actual blast furnace. The reduction of reducing agent rate is caused by the improvement of the reaction efficiency due to the decrease of the thermal reserve zone temperature. On the other hand, it is suggested that sinter reducibility will affect on the effect of the high reactivity coke. Therefore, in this paper, the quality of high reducibility sinter and the effectiveness of high reactivity coke coexistence of high reducibility sinter were verified by the experimental blast furnace and following results were obtained. 1) The top gas utilization was improved and the reducing agent rate was reduced by use of high reducibility sinter. 2) The permeability was improved by use of high reducibility sinter. The improvement of permeability will be expected in actual blast furnaces. 3)The top gas utilization was improved by use of high reactivity coke. The improvement was caused by the improvement of reaction efficiency due to the decrease of the thermal reserve zone temperature. 4) The degradation of coke was decreased due to the decrease of the amount of reaction. 5) The high reactivity coke works effectively when high reducibility sinter co-exists.
In this paper, a control problem of temperature dispersion in steel cooling is formulated as model predictive control (MPC) of a probability density function (PDF). The input of MPC is optimized for dynamics of the PDF approximated by the Monte Carlo method, which is called particle MPC (PMPC). Simulation results of PMPC are presented to show the potential effectiveness of dispersion control.
By using polyester/ iso-cyanate resin solutions as model paints, the relation between the hardening behavior of the paint film heated on the steel sheet and the maximum film thickness without bubble defect (the popping) occurring was examined by using the TBA (Torsional Braid Analysis) method. The results were as follows. 1)In the cure process of the paint film, two dimensional crosslinking reactions are firstly begun, and subsequently, three dimensional crosslinking reactions are begun. The evaporation of volatile elements such as solvents did not receive a big influence from the two dimensional crosslinking reactions, and was started being obstructed after the three-dimensional crosslinking reactions were begun. 2)In the comparison of the resin solutions, the lower the starting temperature of the three-dimensional crosslinking reaction (T3) was, the more easily the popping occurred. The more the numbers of functional groups of resin were, the lower the T3 value was. Furthermore, when the number of functional groups were same, the higher the Tg value of the resin was, the lower the T3 value was.
The influence of volatile elements on the popping of polyester resin solutions on the substrate steel sheet was investigated by heating substrate with various patterns of rising temperature. The results were as follows. 1) When using the resin solution which did not include any hardener, the bubbles which were generated at comparatively low temperature were deleted with the rise of the temperature. This is because the diffusion barrier for the volatile elements in the resin solution film was very low. On the other hand, in the case where the hardener exists, the bubbles were not deleted. Therefore, for the purpose of the popping prevention of thermal hardening type-polyester resin solutions, it is necessary not to generate any bubbles into the film during the heating process within all ranges of the temperature. 2) In the heating process of the resin solution film, the temperature range where the bubble occurs existed. When this range was heated at low-speed, the popping was controlled. This temperature range was almost corresponding to the evaporation temperatures of the volatile elements (solvents and reaction products) of the resin solution inside. However, when strictly seeing, this range was being shifted a little to the low temperature side than the evaporation temperatures. It is thought that the diffusion of the volatile elements was obstructed along with the rising of viscosity of the resin solution, and the partial pressures of the volatile elements were relatively risen in the resin solution.
The internal reversible hydrogen embrittlement (IRHE) of austenitic Fe(10-20)Ni17Cr2Mo alloys based on type 316 stainless steel hydrogen-charged as 40 mass ppm was investigated by tensile tests using the slow strain rate technique from 80 to 300 K. IRHE occurred below a Ni content of 15% (Ni equivalent of 29%), increased with decreasing temperature, reached a maximum at 200 K, and decreased with further decreasing temperature. The susceptibility to IRHE depended on Ni content. Hydrogen-induced fracture of IRHE occurred in brittle transgranular mode associated with the strain-induced α’ martensite structure from 200 to 300 K and mixed with twin boundary fracture at 200 and 250 K, and changed to dimple rupture mode due to hydrogen segregation at 150 K. IRHE was controlled by the amount of strain-induced α’ martensite above 200 K, whereas it was controlled by the hydrogen diffusion below 200 K.
Automotive parts made of steel sheets normally have sheared edges, which have been reported to decrease hydrogen embrittlement (HE) resistance of ultra-high strength steel (UHSS) sheets. However the mechanism on the detrimental effect of the sheared edge on HE resistance has not been clearly understood yet. In this study, the influence of the edge condition in UHSS sheets on HE property was investigated using an 1180MPa grade steel sheet. HE resistance of specimens with the edges ground or as-sheared was evaluated by the U-bend method. Two types of as-sheared specimens with the burnished surface or the fracture surface bent to be the outer side were prepared. The specimens with the ground edges did not fracture at any conditions. Fracture stress of fracture surface specimens was significantly lower than that of burnished surface specimens. Micro cracks were observed at the edge of the specimens except for the ground specimens, and larger micro cracks were observed in the fracture surface specimen. Fracture stress was drastically decreased with the increase in micro crack length. Threshold of stress intensity factor K was decreased with increasing the diffusible hydrogen content. When threshold stress intensity factor at each diffusible hydrogen content was defined as KH, fracture condition was described as K > KH. The reason why the fracture stress in the as-sheared specimen decreased was considered that K increased due to the micro crack introduced by the bending.
A study to evaluate the effect of pre-strain on crack growth is carried out based on fracture mechanical method using 3 point bend test. Two kinds of hot rolled high tensile strength steel sheets were used as samples. One has relatively uniform microstructure strengthened by precipitates, and the other has relatively non-uniform microstructure strengthened by hard secondary phase particles. The effect of pre-strain on fracture mechanical resistance to crack growth was measured, and the mechanism involved in the result was discussed. And the following conclusions were obtained. 1) The steel sheet with uniform microstructure has a higher resistance to initiation of crack growth (Jq), and tearing modulus (Tmat) than the other. Pre-strain reduces the resistance to initiation of crack growth of the both steel sheets. However, the decrease in Jq due to pre-strain is more significant in steel sheets with non-uniform microstructure. 2) The main factors determining crack growth in steel sheet with uniform microstructure are large precipitates and inclusions, and that for the other steel sheet is the secondary hard phase. 3) The reason for decline of Jq due to pre-strain is attributed to the increase of density of voids in the vicinity of crack front due to pre-straining. The difference in the influence of pre-strain on Jq may be understood as the difference in the density of void nucleation sites. Namely, larger density of void nucleation sites in the steel with non-uniform microstructure leads to lower Jq.
Austenitic stainless steel is widely used in important industries since it has excellent mechanical and chemical properties such as anti-corrosion, high ductility and high strength. In the past, it was reported that its extremely high energy absorption can be measured by the Charpy impact test. The mechanism of its energy absorption characteristic is still unclear and its rate sensitivity has not been discussed. In the present study, a rate sensitivity of energy absorption characteristic of austenitic stainless steel will be discussed experimentally by measuring J-integral under 3-point bending condition for a wide range of displacement rate. In the experiment, the direct current potential difference method is employed for sensing an onset of a stable crack extension. As a result, the positive rate sensitivity on the energy absorption can be observed and high energy absorption can be achieved by the high ductility of the steel.