To achieve stable operation of coke oven battery, numerical model for estimating clearance between coke cake and coke oven wall were developed. By developed model, influence of temperature distribution in combustion chamber on coke cake contraction was investigated. As a results, following findings were obtained.

1) Drop of temperature in coke side (CS) gives higher drop of clearance at the end of coke chamber compared with machine side (MS).

2) Drop of clearance at the end of CS causes higher pushing load of coke cake. Therefore, improvement of CS flue temperature is important for lowering pushing force of coke cake, particularly.

It is indispensable to construct sinter pot in large-scale and to apply material segregation charging equipment, for there exist several significant dissimilarities between practical and lab-scale sinter facilities. From the issue, sinter pot for 300 kg material mixture with segregation charging system called ‘sinter simulator’ is developed. The system allows segregated materials being charged into fixed pot with proper sequential order, according to the result of stacking properties. In this paper, it is reported that stable and proper sintering procedure is obtained, and phenomena more precise to practical process is also simulated, confirming the results of product yield recovered with core sampler.

Various methods were employed to measure the austenite volume fraction in a 1.5Mn-1.5Si-0.2C steel. It has been confirmed that the volume fractions determined by transmission electron microscopy, scanning electron microscopy/electron back scatter diffraction, X-ray diffraction and neutron diffraction exhibit a general trend to become larger in this order, although the values obtained by X-ray and neutron diffraction are similar in the present steel because austenite is relatively stable. The austenite volume fractions determined by diffraction methods have been found to be affected by the measuring specimen direction, i.e., texture, even by applying the conventional correcting procedure. To avoid this influence, it is recommended to measure both of volume fraction and texture simultaneously using neutron diffraction. Although synchrotron X-ray shows higher angle resolution, its small incident beam size brings poor statistic reliability. The influence of texture cannot be avoided for transmission Bragg edge measurement, either, which must be overcome to realize 2D or 3D volume fraction mapping.

Better balance of strength and toughness is a strong demand for the ASTM A707 L5 grade steel. In the present study, therefore, the combination of hardening by Cu precipitates and toughening by quenching from a dual-phase (α+γ) region, so-called intercritical quenching or lamellarizing, has been investigated for a better balance of strength and toughness. The combination procedure resulted in a drastic increase in toughness at low temperatures with a slight decrease in yield strength.

The lamellarizing brought about a complicated microstructure with meandered high angle grain boundaries (HAGB) and fine grains bordered by the HAGB. The final microstructure was composed of granular bainitic ferrites without retained γ and basically dual of a softer phase and a harder phase. The softer phase inherited the not-transformed α phase region in lamellarizing and contained coarse Cu precipitates. The harder phase inherited the transformed γ phase region in lamellarizing and contained no Cu precipitates. Hence, over-aging of Cu precipitation in the softer phase might result in the slight decrease in yield strength.

In the present steel, the retained γ has nothing to do with the improved toughness. Hence, the effective grain size (d_EFF) approach was verified to account for the microstructural effect on toughness. The unit microstructure to determine the d_EFF was identified to be the bainitic ferrite grain bordered by the HAGB. The refinement of the d_EFF through lamellarizing can be attributed to the improved toughness.

Simple shear tests and hydraulic bulge tests of IF steel sheet, 590 and 980 MPa grade dual phase high strength steel sheets were carried out to investigate the work-hardening behavior, i.e. equivalent stress-equivalent plastic strain curves and Instantaneous n-values, in large strain region over uniform elongation. Parameter κ that correlates simple shear (or bulge) stress to uniaxial tensile stress used to obtain the equivalent stress-equivalent plastic strain curve. The work-hardening behaviors obtained by simple shear tests and bulge test were good agreement with those of uniaxial tensile test. On the other hands, work-hardening equations proposed by previous studies were less likely to reproduce behaviors of the Instantaneous n-value, i.e. a strain dependency of the n-value, in a variety of steel sheets. Thus a new work-hardening equation that can reproduce the strain dependency of the n-value proposed. This equation can reproduce the work-hardening behavior of a variety of steel sheets.

High-speed deformation behavior and their strain rate dependence on mechanical properties of 1 GPa-grade TRIP-aided multi-phase (TRIP) steels were studied. The strain rate range in this study was between 3.3×10^–6 and 10³ s^–1, and the effect of retained austenite (γ_R) shapes on TRIP effect in the 1 GPa-grade TRIP steel was also focused on. The effects of strain rate on tensile strength and flow stress in the TRIP steels were small whereas that on uniform elongation was large. The strain rate dependences on tensile strength and uniform elongation in the TRIP steels were more closely to those of the metastable austenitic stainless steels than the conventional TRIP and dual-phase steels. The 1 GPa-grade TRIP steel with the γ_R shape of needle-like showed better tensile properties and absorbed energy in the present strain rate range. The volume fraction of γ_R more than 20% and the matrix microstructure of martensite seem to be important factors in the high-strength TRIP steels.

Gas injection systems are extensively employed in the steelmaking industry for mixing molten metal baths and, hence, for removing impurities and nonmetallic inclusions such as C, P, S, and Al₂O₃. A bath subjected to bottom gas injection is sometimes accompanied by a swirl motion of the deep-water wave type when the aspect ratio of the bath, H_L/D, ranges from about 0.3 to about unity. Here, H_L is the bath depth and D is the bath diameter. Although the swirl motion has high mixing ability, it causes vessel oscillations in the vertical and horizontal directions. Accordingly, the conventional refining processes are usually operated in the absence of the swirl motions. In a previous water model study a method of suppressing the swirl motion was proposed. A circular disk was set in contact with the surface of a water bath. The size of the disk capable of suppressing the swirl motion was experimentally clarified. In this study a circular disk was immersed in the bath to investigate the possibility of suppressing the swirl motion more effectively.