Sinteraustempering Of Two Mo-(Cu)-(Cr)-(Ni)-(Mn)-C Steels In A Semi-Closed Container In Flowing Nitrogen

Three types of heat treatment, sinteraustempering in 500 ◦ C, 400 ◦ C and 350 ◦ C; sinterhardening and sintering with cooling at the rate 10K/min) as the final operation, on steels sintered semi-closed container were investigated. Results of mechanical properties, microstructure investigations and fracture and EDX analyses are reported. The study involved two PM steels: DH-1 (Fe-2%Cu-1.5%Mo-0.5%C) and 34HNM (Fe-0.2%Mo-0.8%Mn-1.5%Cr-1.5Ni-0.4%C). Prealloyed H ¨ ogan ¨ as DH (Direct Hardening) iron powder and graphite powder (grade C-UF) were used to produce DH-1 steel. Prealloyed Astaloy CrL iron powder, low carbon ferromanganese, elemental nickel and graphite grade C-UF powder were the starting powders of 34HNM steel. Pressing was in rigid dies at 660MPa according to PN-EN ISO 2740 standard. After compaction, green compacts were sintered in a specially designed semi-closed container at 1120 ◦ C for 60 minutes in a nitrogen atmosphere. The chemical composition of the sintering atmosphere was modified by adding ferromanganese and/or activator into the container. All specimens were tested for tensile strength (UTS), elongation (A), yield offset strength (R 0 , 2 ), TRS, apparent surface and cross section hardness (HV 30). The best combination of strength and plasticity for both steels was achieved after sinteraustempering at 500 ◦ C. The results show that, using the specially designed semi-closed container, sinteraustempering in N 2 atmosphere offers the same or even better mechanical properties in comparison with sinteraustempering in vacuum. It means that sinteraustempering in N 2 atmosphere is a very interesting process in terms of cost in comparison with vacuum sinteraustempering.