Role of Oxide and Sulfide Particles on Charpy Impact Properties in 10Ni-8Co Alloy Steels

Abstract

The influence of second phase particles such as oxide and sulfide on Charpy impact absorbed energy of 10Ni-8Co alloy steels (HT180) with various sulfur (0.002-0.015%) and oxygen (0.0006-0.0095%) contents was studied. The role of these particles in ductile fractures was discussed to be based on the variation of the dimple size and the relation between the impact energy and volume fractions of the particles. Charpy impact absorbed energy (E_v) in these steels decreases remarkably with an increase of the volume fraction (V_p) of oxide and sulfide. The relation between E_v and V_p is expressed by E_v=A·V_p^-n, where nvalue indicating the dependence of E_v on V_p is 0.95 of 1/3 according to the change of size and spacing of the particles observed. When the dimple size on the fractured surface correpsonds to the spacing the particles obsE_ved, n-value is 0.95. When the dimple size smaller than the spacing of the paricles, n-value decreases to 1/3. The latter is the case for the coarse oxide. This can be explained by the fact that the voids nucleated by the coarse oxide are linked by the smaller voids nucleated by sulfide.