Keisaku Ogi

Suppression of ignition and burning of molten Mg alloys by Ca bearing stable oxide film

Abstracts are not published in this journal

Sliding wear behaviour of Al-Si-Cu composites reinforced with SiC particles

Abstract The sliding wear behaviours of an unreinforced monolithic Al-Si-Cu alloy and SiC particles reinforced composites containing 5, 13, 38 and 50 vol.-% with diameters of 5.5, 11.5 and 57μm were investigated. The results showed that the wear resistance of the composites is much higher than the monolithic alloy, and the larger and the more SiC particles, the higher the enhancement of the wear resistance. Metallographic examinations revealed that the subsurface of worn composites was composed of both fragmented particles and deformed matrix alloy. The depth of the particle fracture zone in the subsurface varied in the range of 20-35 μm at a sliding distance of 1.8 km, while the plastic deformation zone of the worn subsurface on monolithic alloy was more than 100 μm. Scanning electron microanalyses of the worn surface, subsurface microstructure and debris suggested that the depth of the particle fracture zone became smaller as the diameter of SiC particles increased. Increasing the hardness and decreasing the applied wear stress changed the debris morphology from flake to very small lumps.

Quantitative evaluation of the fatigue limit of a metal with an arbitrary crack under a stress controlled condition – Stress Ratio R=−1

In this paper, the result from rotating bending fatigue tests of notched specimens are carried out on aluminum cast alloys and high strength steels with HB≃600 are reported. The threshold stress intensity factor range under a stress controlled condition, ΔKw, is introduced for the purpose of predicting the fatigue limit of a metal with an arbitrary crack. The ΔKw value of a long crack, ΔKwUL, is obtained from the fatigue crack propagation limit σw2 of specimens with a sharp and deep notch; ΔKw increases with crack length, and ΔKwUL is an upper limit of ΔKw. Since there are few σw2 data of steels with HB≥400, the σw2 values are evaluated by the fatigue crack initiation limit predicted using Linear Notch Mechanics and the relation between σw1 and σw2 at the branch point. Using ΔKwUL values of many metals with a long crack, the ΔKwUL values are approximated with a simple formula. Moreover the lower limit value of ΔKw versus the crack length, ΔKwLL, is proposed. Then using the ΔKw and ΔKwUL formulae and the ΔKwLL value, the smallness of a fatigue crack is clarified.

Estimation of Particle Size Distribution in Materials in the Case of Spheroidal Particles Using Quantitative Microscopy

In this paper, an estimation method is proposed for the size distribution of particles in materials. The configuration of particles is assumed to be spheroidal and all observed information is gathered from cutting planes. The apparent size distribution measured from 2D is corrected to the 3D true size distribution, then the expected size distribution can be estimated from a small size up to an extreme size. This estimation method is most versatile, and involves Saltycovs method and extreme statistics at the same time. The procedure is applied to an artificial material with a given particle size distribution in computer simulation in order to examine its validity. The estimated results are compared with the given distribution, and the validity of the method is confirmed.

The fibre distribution of Al2O3/Al–Cu alloy composites

Two methods which rely on direct microstructural measurements to assess the fibre distribution in alumina continuous fibre-reinforced Al–Cu alloy composites produced via an infiltration process, are outlined. The first is based on distance analysis, i.e. the distance distribution of nearest neighbours; and the second is based on fibre–cell structures. Specimens with two fibre volume fractions, 0.39 and 0.50, were employed in this study. It was found that the fibres in both kinds of specimen appear to have a rough thread-like distributions, and the local volume fraction of the fibres varies over a larger range in the specimen with lower fibre volume fraction than does that in the specimen with the larger one. Quantitative relationships between fibre distribution and the composite defects are deduced. Some data on the microsegregation of copper and the macrosegregation of eutectic phase are given in relation to the fibre distributions. The reasons for the uneven fibre distributions are also discussed.

Quantitative evaluation on wear resistance of aluminum alloy composites densely packed with SiC particles

Abstract Wear behaviour was investigated for high volume fraction SiC particulate reinforced aluminum alloy composites by considering the shear stress acting on the specimen and the wear debris formed during sliding wear. The SEM morphology of worn subsurfaces showed that particles are fragmented, mechanically mixed, and then aligned in the wear direction caused by normal and tangential stresses. Wear debris were initially tiny lumps but finally delaminated due to the shear stress. A theoretical wear model was proposed for plastically deformable specimens worn by a rigid non-deformable steel ring by analysing the interspacing of SiC particles and the tangential stress applied to the worn surface. Predictions of this theoretical wear model were in good agreement with experimental results.

Control of graphite formation in solidification of white cast iron

Abstract Graphite formation should be strictly suppressed for the most abrasion resistant white cast irons, since austenite (γ)+graphite eutectic structure shows lower hardness and selectively wears thus deteriorates the abrasion resistance even though the austenite transform to hard phase such as martensite. On the other hand, a small amount of fine graphite is desired to distribute in rolls for hot steel mills to suppress the scoring. However, strong carbide formers such as Cr, V, Nb have been increasingly added to rolls, in order to crystallise more harder carbides. As γ+carbide eutectic grows, the residual liquid among eutectic cells becomes poor in carbide formers and rich in elements which promote graphite formation. Therefore an appropriate alloy design is essential for the hot steel milling rolls. In this study, the graphite formation mechanisms are discussed for chromium cast iron, high speed steel type cast iron and Ni hard type cast iron.

Thermodynamic evaluation of solidification structure of high chromium white cast iron

The partition coefficients of chromium kCr and carbon kc of high chromium cast irons were measured and also calculated using ThermoCalc. The experimental values were similar to the calculated values, though the experimental kCr were a little larger at higher chromium content. The solidification theories give a good estimation for the redistribution of chromium and carbon in the solidification structure as well as for the amount and composition of non-equilibrium eutectic carbide, if the most accurate k values are employed, which change depending on the chemical composition of residual liquid. The equilibrium chromium and carbon contents of austenite; at a destabilising temperature were also evaluated by ThermoCalc. They can provide the suitable destabilising temperature for higher hardness. IJCMR/440

Control of Carbides and Graphite in Ni-hard Type Cast Iron for Hot Strip Mills

The carbide and graphite formation and redistribution of alloy elements during solidification were investigated on Ni-hard type cast iron (Fe-C-Si-Ni-Cr-Mo) to develop higher quality rolls for hot steel strip mills. By the control of Ni and Si contents of iron, eutectic graphite flakes crystallize even in cast irons containing strong carbide formers such as V, Nb and Cr. The crystallization of Ni-hard type cast iron with V and Nb proceeds in the order of primary , + MC, + M3C and + graphite eutectic. Since the influence of each alloying element on graphite formation is estimated based on the solubility of C in molten iron, the change in graphite forming tendency of residual liquid is evaluated by the parameter expressing the solubility limit of C to molten iron. The amount of graphite increases with the decreasing of solubility parameter. In addition, inoculation with ferrosilicon effectively increases the graphite flakes.

Alloy design for heat and abrasion resistant high alloy cast iron

Influences of Mo, Nb, V on the microstructure, the oxidization behavior and the high-temperature compressive strength of 35–40%Cr-9%Ni cast irons were investigated. The addition of Mo raises the compressive strength at higher temperature, since Mo distributes into the matrix and enhances the high temperature strength. The crystallization of fine eutectic M7C3 and M2C type carbides should also contribute to the higher strength. The MC type carbide formers such as V and Nb can significantly improve the abrasion resistance at lower temperature. However, these elements also promote the oxidization of alloys. Especially V causes abnormally severe in both matrix and the hard phases. On the other hand, Nb preferentially distributes to NbC, the oxidation behaviors of M7C3 and matrix are little influenced by the addition of Nb. Among the trial alloys, Fe-2.2 4.5%C-35 40%Cr-9%Ni-5%Mo-0/7%Nb maintain 900Mpa of compressive strength even at 1073K, while the strength of conventional heat resistant alloys and high Cr cast irons drop below 500MPa at the temperature from 873K to 923K. The developed alloys show high oxidation resistance and superior high temperature wear resistance.