Effects of warm compaction on mechanical properties of sintered P/M steels

The green and sintered densities, and tensile strength of sintered P/M steels produced by cold compaction, warm compaction, warm compaction combined with die wall lubrication (DWL) were measured under various compaction pressures using polytetrafluoroethylene (PTFE) emulsion as the die wall lubricant. The effects of warm compaction on the mechanical properties were studied. The tensile fracture behaviors of cold compaction and warm compaction were studied using scanning electron microscope (SEM). The results show that the density of sintered P/M steel prepared by warm compaction or warm compaction with DWL is higher than that by cold compaction under all compaction pressures. Meanwhile, the highest tensile strength is obtained by combination of warm compaction and die wall lubrication under all compaction pressures. The SEM results show that the fracture modes of the sintered samples prepared by cold compaction and warm compaction at 700 MPa are the mixed mode of ductile fracture and brittle fracture, and obvious dimples can be found in some regions. The fracture of sample prepared by cold compaction is uneven and has irregular and big pores, but that by warm compaction is relatively even and the pores are round mostly, and the samples have many obvious dimples on the whole fracture surface.