Papers by Author: Keisaku Ogi

Abstract: Lubricated reciprocating tests were conducted on an SRV tester to investigate effects of stroke and frequency on frictional and wear properties of flaky graphite cast iron used for marine cylinder liner by varying frequency and stroke under a given sliding velocity in boundary and mixed lubrication regime. It was clarified that changes in coefficient of friction were significantly dependent on stroke and frequency: in boundary lubrication, coefficient of friction at steady state showed a lower value at a combination of lower frequency and therefore larger stroke. In mixed lubrication, however, a combination of lower frequency and larger stroke produced a higher friction. In boundary lubrication where no run-in process was observed, higher frequency contributed to producing rougher surfaces resulting in higher friction. In mixed lubrication bordering on boundary lubrication higher frequency promoted run-in, enhancing film formation and lowering friction. Effects of frequency and stroke also reflected on wear, changes in separation voltage between a disk and a ball specimen, which were in accordance with changes in friction.

Abstract: A series of abrasion tests on high Cr-V-Nb cast irons revealed that the addition of MC type carbide formers, V and Nb, remarkably enhances the abrasion resistance of high Cr cast iron, and the abrasion resistance becomes higher with the increase in MC type carbides[1]. Therefore, hyper eutectic Fe-4.7%C-15%Cr-7%V-5%Nb-5%Mo alloy melt was poured into 30kg and 1kg sand mold castings to distribute different sizes of primary and eutectic carbides in hardenable matrix. The abrasion test specimens cut from each casting were austenitized at 1323K for 1h then cooled in air. These specimens were tempered at 773K for 1h followed by air cooling. The hardness of specimens was 1015-1018HV50. The rubber wheel abrasion test, a typical 3 body type one, was performed on these quenched and tempered specimens with 56-107, 107-150 and 297 μm dia. silica grit. The testing load was 86.3N and 172.5N, and the rubber wheel rotation speed was varied from 1s-1 to 4s-1. Though the higher testing load increases the wear loss, the wear rate expressed by the wear volume/( testing load × wear distance) changes depending on the wear condition and the microstructure. In case of 30kg cast specimen, the silica grit preferentially attack and scrape off the matrix, and the wear rate increases with the increase in the testing load. The fine carbides in 1kg cast specimens effectively protect the matrix from the attack of silica grit, and the wear rate decreases with increasing load which causes silica grit blunt and fracture. However, fine carbides tend to be fractured by silica grit and diminish the protective effect. Based on the worn surface structures, the abrasion mechanism is discussed comparing those of steel and eutectic 25%Cr cast iron.

Abstract: 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.