Microstructure evolution and densification behavior of iron-based powder metallurgy materials by surface rolling densification technology

Fe–2Cu–0.6C powder metallurgy materials with the different density were treated by surface rolling process under the different pressure. The effects of material density and rolling pressure on the densification behavior were investigated. The results show that, the rolling pressure and material density are the main parameters on the surface densification. With the increase of rolling pressure, the densification depth and surface hardness increase significantly. The effect of material density on the surface densification decreases with the increase of rolling pressure. The surface densification depth and surface hardness increase with the increase of material density under a low rolling pressure. However, the values of densification depth and surface hardness for the materials with the different density are approximately equal under a high rolling pressure. After rolling process, the pearlite in the surface layer bends along the rolling direction, the lamellar spacing near the surface becomes smaller, some of the laminates are twisted and wavy, and even some cementite breaks. Ferrite is stretched along the rolling direction, and the grains are refined. Massive dislocation tangle and dislocation walls exist at the grain boundary of ferrite. The refinement of ferrite and deformation of pearlite provide the favorable conditions for improving surface strengthen.