Effect of Nonmetallic Inclusions on Impact Property of Steels

Abstract

In order to study the relationship between FeO type inclusions and impact property of steels, 30-kg U-notched charpy impact test of specimens with different oxygen content was carried out. The fracture surfaces obtained by this test were observed with an electron microscope by two-steps carbon replica technique or directly with a scanning electron microscope and the profiles of these fracture surfaces were observed with an optical microscope. A quantitative estimation was made on the degree of effect of FeO type inclusions on impact property of steels, on the basis of the relationship between absorbed energy in impact test and the number of inclusious associated with the fracture surface.
Some of the results obtained are as follows:
1) Impact property becomes worse with an increase in inclusion content. But the effect of inclusion content on absorbed energy in brittle fracture range can not be recognized.
2) FeO type inclusions seem, in some cases, to act as barriers to the propagation of cleavage crack.
3) The degree of effect of FeO type inlusions on impact fracture increases with an increace in grain size of specimen.