Sinter hardening of astaloy CrA alloys

In this study, the effect of sinter-hardening operation on the mechanical properties of water atomized Astaloy CrA-0,5C, Astaloy CrA-1Ni-0,5C, Astaloy CrA-1Cu-0,5C, Astaloy CrA-2Cu-0,5C powder alloys 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 sintering, 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 whereas 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 was studied. An increase in the hardness and transverse rupture strength values of the heat treated samples was observed due to the increase of cooling rate and decarburization layer which was formed during secondary heat treatment.