Sadato Hiratsuka

Effect of Casting Skin Condition on Fatigue Strength of Gray Cast Iron

The microstructure around the casting skin of cast iron changes according to conditions in the mold, wash material and cooling speed. When a self-hardened mold was used, a matrix microstructure containing all pearlite was obtained in the casting skin. When a greensand mold was used, the matrix microstructure was a mixture of pearlite and ferrite. In this study, tests were conducted to determine the influence of a casting skin on fatigue strength in gray cast iron with one sample containing a fully pearlitic matrix compared with another having a ferrite–pearlite mixture. For comparison, fatigue tests were also conducted on the sample with a pearlitic matrix taken from inside the sample and machined. The surface roughness of the test piece with casting skin was rougher than the test piece with the machined surface. The fatigue strength of the test piece with coarser surface roughness was lower. In a smaller eutectic cell, fatigue strength became higher. The fracture path was observed to be along the interface of graphite. It was considered that the fracture propagation was suppressed by smaller eutectic cells. On the other hand, a little ferrite generated in a casting skin made the fatigue strength lower.

Aging of NR-brass cord adherends in moisture environments.

天然ゴムースチールコード接着物の湿潤劣化性に及ぼす硫黄添加量, 促進剤の種類および配合の種類などの影響をはく離強度とゴム被覆率の変化から検討した. 低硫黄基本配合の接着物における初期の湿潤劣化速度は小さいが, 長期になると劣化速度が増加した. 高硫黄配合においては初期の劣化速度は大きいが長期になると減少した. Co配合の接着物は, 高硫黄配合の接着物において基本配合より劣化速度が低かった. スチーム劣化はCo配合の接着物において水中劣化より高い劣化速度を与えた. 湿潤劣化性に及ぼす促進剤アミンの影響を知る目的で, スルフェンアミド系促進剤とチアゾール系促進剤の影響を検討した結果, 前者はどの場合もはく離強度とゴム被覆率を著しく減少させるが, 後者は長期の劣化においてもゴム被覆率が高くスチールコードが腐食し難いことが分かった. 劣化試験後の剥離面のSEM観察とEPMA分析をゴム側とコード側について行った結果, 高硫黄配合の接着物について破壊は先ずコードの黄銅層で起こっておりゴム側に金属腐食成分の存在が確認され, 湿潤劣化が黄銅層の応力腐食割れに始まることが明らかとなった.

The corrosion inhibition of magnetic iron powders by triazine dithiols

Abstract The surface treatment of ultra fine magnetic iron powders with 6-substituted-1,3,5-triazine-2,4-dithiols (RTD) and their corrosion inhibition were investigated. The amount of RTD adsorbed was influenced by treating time and temperature, solvent, type of RTD and magnetic iron powder. Non-polar solvents and RTD with long alkyl chains in 6-substituted groups provided RTD films with a high layer number on the surface of the powders. Basic and Co-alloyed iron powders also had RTD films with a high layer number in the surface treatment of the powders. They showed lower corrosion rates than acidic magnetic iron powder. Magnetic iron powder changed to a mixture of Fe2O3 and FeOOH during aging in moist air. RTD treatment was very effective for preventing the corrosion of magnetic iron powder and decreasing its saturated magnetization. The preventive effect increased with RTD film thickness as well as water repellency and insulation. RTD treatment also prevented rapid exothermic reaction of iron powder in air.