Rolling Contact Fatigue of Austempered Cast Irons with Different Graphite Shapes.

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  • 黒鉛形状の異なるオーステンパ処理鋳鉄のころがり疲労
  • コクエン ケイジョウ ノ コトナル オーステンパ ショリ チュウテツ ノ コロ

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Abstract

  The effects of graphite shapes and matrix structure on the rolling contact fatigue strength of cast iron were investigated using a Nishihara-type wear test machine with gear oil lubricant. Two kinds of spheroidal graphite cast irons with different graphite diameters, compacted vermicular (CV) cast iron and the flake graphite cast iron were austempered at 648K, 573K and 513K for 7.2 ks. They were also quenched from 1123K and tempered at 825K and 552K for 7.2 ks. The rolling contact fatigue limit (F∗) of austempered irons are much higher than those of quenched and tempered irons with the similar graphite morphology and matrix hardness. The morphology of graphite has also large on F∗, and F∗ tends to increase in the order of flake, CV and spheroidal graphite cast iron under the same heat treatment condition. Two types of fatigue cracks were observed : one generated from the contact surface and the other from inside of the specimen. The latter type appeared only in the CV cast iron and the flake graphite cast iron austempered at 648K. The mode of cracking should depend on both the strength and toughness of matrix and the morphology of graphite.

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