Effect of Carbon and Oxygen on the Fracture of Iron

Abstract

Specimens were prepared from three kinds of electrolytic iron, which initially contained 0.012–0.015 % carbon and 0.002, 0.012, and 0.016% oxygen, respectively. After their grain size had been controlled by vacuum-annealing at 930°C, a number of the specimens were subjected to various degrees of decarburization by hydrogen-annealing at 700°C, during which the oxygen contents changed very little. In a slowly cooled condition, the specimens were extended at 22, −75, and −196°C. At carbon levels around and above 0.005 %, elongation of ∼ 50–60% was observed at both 22 and −75°C, while rather brittle cleavage fracture occurred around or above 55 kg/mm² at - 196°C. When the carbon content was reduced to 0.0014–0.0012%, intergranular fracture took place at all test temperatures after < ∼ 25% elongation and at < ∼ 20 kg/mm² stress. There was a sharp transition in tensile properties at around 0.0021 % carbon. On the other hand, the tensile properties were hardly affected by oxygen content in the range examined, which is considered to be higher than the solubility limit for the specimens tested.