The placement control of iron ore and carbon in the blast furnace is one of the effective methods to improve the reaction efficiency and permeability. To clarify the increasing the reaction rate and decreasing the high temperature gas flow resistance, softening-melting test which changed the placement conditions in the packed bed of carbon composite iron-ore and the mixture of coke and ore was carried out. The effect of placement (i.e. packing structure) and reactivity of iron-ore and carbon on soften-melting properties at lower part of blast furnace were evaluated, and following results were obtained.

1) The starting temperature of solution loss reaction decreased using high reactivity coke by close placement between iron-ore and carbon (i.e. by using carbon composite iron-ore and coke and ore mixture in packed bed).

2) The final reduction degree of iron-ore with iron-ore rise by high reactivity coke or iron-ore and close placement between iron-ore and carbon and the high temperature gas flow resistance decreased

3) The shrinkage resistance at high temperature decreased by using a carbon composite, and increased by using mixture of coke and ore.

Steelmaking slag is recycled and reused, but its utilization is restricted due to its chemical properties. On the other hand, steelmaking slag is considered to be a promising resource of iron and phosphorus in Japan. In this work, reduction of (Fe_tO) and (P₂O₅) in steelmaking slag and recovery of iron and phosphorus resources were investigated with the aim of developing a new recycling process for steelmaking slag. In order to investigate the effect of slag basicity (%CaO/%SiO₂) and Fe_tO content in slag on phosphorus separation from steelmaking slag, steelmaking slags were reduced by carbonaceous material at high temperature by using an induction furnace. From the results, the effects of slag composition, temperature and oxygen partial pressure on phosphorus separation from steelmaking slag were discussed.

LIDAR (light detection and ranging) system was applied to a plate flatness evaluation system. Plate flatness surfaces are reconstructed from many points generated by LIDAR with a smoothing spline method. We defined a smoothing spline functional with sampling measure weights. The equivalent number of parameters defined on this functional does not depend on the distributions of samples. The approximation of the equivalent number of parameters is derived when the number of samples becomes infinity. This approximation greatly reduced the calculation time needed to estimate the optimal smoothing. The smoothing spline calculation cost was so high that new algorithms (FMM: fast multi-pole method) were introduced and we developed the smoothing engine, which was applied to practical problems. The engine generated clear surfaces and was robust to various dirty points cloud.

Steel scraps are used as a resource of electric steel making. However, reuse of the scrap leads to increase the amount of tramp elements such as Cu and Sn. In hot rolling process, Cu segregates at the scale/steel interface. Furthermore, this Cu segregation layer causes surface cracking. This brittleness is called surface hot shortness. Previous studies have shown that surface hot shortness is suppressed by addition of Ni. However, the addition of Ni increases in the cost of steel making.

The authors have reported the influence of shot peening on suppression of surface hot shortness in pervious study. After hot oxidation, the shot peened scale/steel interface was rugged. The rugged scale/steel interface occluded the segregated Cu into the scale. The surface hot shortness was suppressed by the shot peening. However, the influence of shot peening didn’t completely suppressed surface hot shortness. Whereat, this paper shows the influences of hot Ni shot peening on surface hot shortness.

The shot peening grid was changed from cast iron to Ni. Surface hot shortness was suppressed by the hot Ni shot peening. After the hot Ni shot peening process, Ni diffused phase at the surface of specimens were observed with the Cu segregated layer by EDX analysis. The melting temperature of Cu segregated layer was increased by Cu-Ni alloying. In addition, the refined grains at the surface of specimens were observed by optical microscope. This suggests that the refined grains and increased lattice defects such as dislocations are developed the microscopically heterogeneous oxidation. Consequently, the hot Ni shot peening can suppress the surface hot shortness by Ni enrichment and grain refinement in surface layer.

The effect of the Al oxide layer which segregated on the surface of hot dip galvanized steel sheet (GI) with aging on the frictional properties of the GI was investigated.

Conventional GI with the Zn coating weight of 67 g/m² including 0.36 mass% Al were used as test specimens. It was found that an Al oxide layer grew on the GI surface with aging after production, and the friction coefficient tended to decrease due to the existence of this Al oxide. However, the tendency was clearer under the sliding conditions with shorter tool length and higher contact pressure than with longer tool length and lower contact pressure.

In order to clarify the mechanism, surface observation and analysis of both the test specimens and the tools after sliding were carried out by SEM, EDX and EPMA. Both Al oxide and metallic Zn were detected as adhesions on the tool surface after sliding, and the surface of the adhesions was covered with Al oxide. It is thought that the adhesions on the tool had the effects of reducing the stickiness between metallic Zn of GI and the tool, and reducing the tool roughness. These effects led to a lower friction coefficient because both shearing and plowing resistance were decreased. In addition, the area on the tool which was covered by the adhesions depended on the tool length. This is thought to be the reason why the effect of the Al oxide layer on the friction coefficient depended on the sliding conditions.

In this study, we conducted a low-cycle fatigue testing in a Fe-28Mn-6Si-5Cr-0.5NbC (FMS) alloy and a SUS304 steel. The fatigue tests were made using a servo hydraulic fatigue testing machine of capacity 50 kN, at maximum total strain amplitudes (ε_ta) of 2.0%, 1.4%, 0.9%, 0.6%. In the SUS304 steel, with decrease in applied strain amplitude, stress-strain hysteresis loop is reduced. On the other hand, the stress response of the FMS alloy is almost unchanged, irrespective of the applied strain amplitude. The rupture life of the FMS alloy is 4 times higher at ε_ta=0.6%, and twice at ε_ta=0.9% and at ε_ta=1.4% than the SUS304 steel. In addition, the stress amplitude of the FMS alloy is 1.5 times higher at ε_ta=0.9%, and twice at ε_ta=0.6% than the SUS304 steel. The prolonged fatigue life of the FMS alloy is attributable to the reversible deformation associated with the transformation pseudo-elasticity that can reduce the accumulated strain.

Recently, 5% Mn steel has been focused on as one of the promising candidates for third generation AHSS by showing an excellent TS-El relationship. The excellent TS-El relationship is brought about by a large volume fraction of retained austenite through the enrichment of austenite stabilizing elements such as C and Mn in reverted austenite. The effect of the microstructure of mother hot band on the changes in microstructure and mechanical properties was compared with the intercritical annealing time in this study. The steel containing about 10% of retained austenite in a mother hot band exhibited a higher volume fraction of retained austenite and higher strength. On the other hand, the steel which did not contain retained austenite in a mother hot band exhibited excellent strength-elongation combination. The difference of work hardening behavior in these steels was analyzed and thought to be brought about by the difference of transformation behavior during deformation determined by the stability of retained austenite affected by Mn concentration.

States of hydrogen present in high-strength steels for use as bearing steel SUJ2 and hydrogen embrittlement susceptibility were examined using thermal desorption analysis (TDA) and tensile tests. SUJ2 specimens containing retained austenite phase (γ_R) in the martensite phase exhibited three hydrogen desorption peaks in the TDA profile. Two of the peaks desorbed at higher temperatures decreased with a decreasing amount of γ_R, indicating they corresponded to desorption associated with γ_R. Fracture strength in the presence of hydrogen increased with a decreasing amount of γ_R and with an increasing strain rate. When the specimens contained γ_R and hydrogen, a flat facet at the crack initiation site and a quasi-cleavage (QC) fracture in the initial crack propagation area were observed on the fracture surface. Local characterization using electron back-scattered diffraction (EBSD) revealed that the flat facet on the fracture surface corresponded not to γ_R but to stress-induced martensite. In addition, the facet was {112} plane of martensite, which is the slip plane or deformation twin plane of body-centered-cubic metals. The reason for high hydrogen embrittlement susceptibility of the specimens containing γ_R was attributed to the stress-induced phase transformation at the crack initiation site of the flat facet and in the initial crack propagation area of the QC fracture. Furthermore, the strain rate dependency of hydrogen embrittlement susceptibility is presumably ascribable to local plastic deformation, i.e., the interaction between dislocations and hydrogen.

To clarify the controlling factors affecting fatigue crack initiation life in poly-crystal ferritic steel, we first observed the initiated fatigue crack morphology during four-point in-plane cyclic bending tests using bcc Fe-16 mass% Cr alloy with a huge grain. The experimental slip trace analyses were compared with those of the calculated shear stress among 24 slip systems based on finite element analysis (FEA). The focus was placed upon the relationship between fatigue crack initiation and the operated slip system. Under the high-cycle-fatigue condition, the inhomogeneous stress distribution was predicted by taking into account the elastic anisotropy. It was clarified that the fatigue cracks tend to initiate at sites where stress concentration was predicted by FEA, Furthermore, the slip trace near fatigue cracks was confirmed to correspond to the dominant slip systems identified by shear stress analysis. However, the fatigue initiation life depended not only on the applied stress amplitude and/or shear stress on the primary slip system, but also on the characteristics of the active slip systems, which were classified into two types. The fatigue crack initiation life, in the case of the cross slip dislocation type was longer than that in the case of the Lomer-Cottrell locking dislocation type. It was inferred that the nature in the dislocation interaction leads to the difference in the fatigue crack initiation life.