A comparison of mechanical properties and microstructures of PM steels with chemical compositions Fe-(1-3)%Mn-0.8%C

Abstract

Mechanical properties of sintered steels containing 1, 1.5, 2, 2.5 and 3%Mn and 0.8%C, candidate materials for structural parts, are compared with actually used PM steels. Höganäs iron powder grade NC 100.24, low-carbon ferromanganese Elkem and graphite powder grade C-UF were used as the starting powders. Powder mixtures were prepared in a Turbula mixer for 30 minutes and “dog bone” compacts were single pressed at 660 MPa, according to PN-EN ISO 2740 standard. Sinterhardening was carried out in a semi-closed container in a laboratory tube furnace at 1120°C and 1250°C for 60 minutes in a mixture of 95%N2-5%H2. Microstructures consisted of pearlite and ferrite, sometimes bainite and martensite, depending on the Mn content. Yield, tensile and three point bend strengths and Vickers' microhardness were determined and metallographic observations carried out. The best combination of properties was for 2.5% Mn steel: yield strength 620 MPa and 3.7% elongation. The tensile properties of 2.5/3%Mn-0.8%C are not inferior to the best Ni-Cr-Mo-Cu type PM steels in MPIF Standard 35.