Sinter-hardening of ferrous astloy Mo and distaloy DH alloys

In this study, the effect of sinter-hardening operation on the mechanical properties of water atomized and prealloyed Distaloy DH (Fe-2.0Cu-1.5Mo) with 0.6%C addition, prealloyed Astaloy Mo (Fe-1.5Mo) with 2%Cu and 0.6%C additions, Astaloy Mo (Fe-1.5Mo) with 2%Cu and 0.7%C additions, and prealloyed Astaloy 85 Mo (Fe-0.85Mo) with 2%Cu and 0.8%C additions was examined. The samples were pressed under 600 MPa and were sintered at 1120°C for 20 minutes in an industrial belt sintering furnaces under endogas atmosphere. After the sintering process, 0.5°C/s, 1.5°C/s, 3°C/s cooling rates were applied to the samples. The study showed that sinter-hardening led to an increase in the hardness due to the transformation of martensite and bainite but a decrease in the transverse rupture strength and tensile strength values due to the irregular pores in the microstructure. In addition to the sinter hardening studies, the effect of the secondary heat treatment on the mechanical properties was also examined. The samples were sintered at 1120°C for 45 minutes under 90%N2-10%H2 atmosphere after pressing under 600 MPa. The sintered samples were annealed at 1070°C for 20 minutes under nitrogen atmosphere. After annealing, the effect of normalizing, quenching and tempering on the microstructure and mechanical properties were studied. An increase in the hardness values of the heat treated samples was observed due to the increase of cooling rate. The increased hardness has led to an important decrease on the transversal rupture values in Astaloy Mo specimens due to the notch effect. Little and more spherical pores of Distaloy DH specimens has diminished the affectivity of the notch effect and led to higher TRS values.