厚肉球状黒鉛鋳鉄の衝撃特性に及ぼすMn含有量とCE値の影響

抄録

  The purpose of this study is to carry out Charpy impact test of heavy section spheroidal graphite cast iron with varying Mn content and carbon equivalent (CE), and to investigate the influence of Mn content and carbon equivalent on impact characteristics. The Charpy impact specimen was cut out from a large ingot of spheroidal graphite cast iron equivalent to FCD400 and instrumented Charpy impact test was conducted. The hammer angle of fall was 140° and the test atmosphere was room temperature in air. The tests were conducted 14 times per material. The impact value was determined from the absorbed energy obtained from the measured voltage-time diagram. As a result, at any CE, the absorbed energy decreased with the increase in the Mn content. For materials with high Mn content, the absorbed energy decreased with decreasing CE, but for materials with low Mn content, the carbon equivalent did not affect the absorbed energy.

  In order to investigate the cause of the decrease in the absorbed energy, all fracture surfaces were observed after the test by electron microscope, and the percent of brittle fracture, which indicates the percent of cleavage fracture, was calculated. As a result, the percent of brittle fracture rate increased with the increase in the Mn content. Moreover, the brittle fracture rate increased as the CE decreased at the same Mn content. Since most of the part showing brittle fracture on fracture surface was pearlite, the pearlite area on the fracture surface was calculated. Good correlation between the brittle fracture rate and pearlite area rate on the fracture surface was seen. These findings suggest that the reasons for the decrease in absorbed energy depends on the pearlite amount.