CRACK INITIATION AND CRACK PROPAGATION IN COPPER POWDER MIXED PM STEEL

This paper presents a detailed study of the crack initiation site and initial crack walk in two copper containing PM steels sintered at 1120 o C. Material A is plain copper – carbon PM steel Fe2Cu0.8C. Material B is based on 1.5% Mo pre-alloyed powder mixed with Ni, Cu and C. Material A contains pearlite, fine pearlite and a small amount of ferrite. The crack initiation and crack walk in material A is mainly obtained through the relatively coarser pearlite and along the interface between fine pearlite and pearlite. The upper/lower bainitic particle cores of material B are stronger, and crack initiation and crack walk is mainly obtained along the interface between the Cu-rich martensite and bainite, but also through the martensite or bainite.