MICROSTRUCTURE AND MECHANICAL PROPERTIES OF FINE-GRAINED IRON PROCESSED BY HYDROEXTRUSION

The aim of this study was to characterize the microstructure and properties of fine-grained iron. The samples were prepared by sintering at 1000 degrees C +/- 5 degrees C for 30 minutes, followed by Severe Plastic Deformation via Hydrostatic Extrusion (HE). After the sintering the rod samples were capsulated to prevent damage during extrusion. HE has been applied as a final consolidation process of iron powders. The HE process was carried out on two extrusion passes. The rods of 8 mm in diameter were obtained as a final product after hydroextrusion. The total cumulative strain was 2.3. Materials in three states were investigated: sintered, sintered and deformed by one hydrostatic extrusion pass, and two hydrostatic extrusion passes. The results were compared with the results obtained for coarse-grained Armco iron. The measurements showed that the grain size was reduced from 3.5 mu m after sintering to 180 +/- 81 nm after the 2nd extrusion pass. The tensile strength and microhardeness increased with cumulative strain of the material. The impact test carried out at -196 degrees C showed transformation of the fracture mechanism from cleavage for coarse-grained structure to ductile for extruded material.