A STUDY OF PHYSICO-CHEMICAL MECHANISMS RESPONSIBLE FOR DAMAGE OF HEAT TREATED AND AS-CAST FERRITIC SPHEROIDAL GRAPHITE CAST IRONS

摘要

Today, ferritic spheroidal graphite cast irons are more and more used for mechanical applications. The ferritic matrix can be obtained either during the casting process or after additional heat treatment which aims at transforming pearlite into ferrite and graphite. The final microslructure seems to be the same but some mechanical characteristics appear to be very different (for example K1C of 80 MPa for the as-cast and 30 for the heat treated) (1). This difference is usually attributed to a matrix-graphite interface brittlcncss. In fact, two damage initiation sites are reported in the littcrature (2-12): at the matrix-graphite interface and within the graphite.