Research On Microstructures And Properties Of Fe-Ni-Mo-Cr Based Sintered Low-alloy Steels

Abstract:In this thesis, Fe-2.5Ni-1Cr-0.6Si-0.3Mo-0.1Mn-0.6C alloy powder was prepared with water atomized alloy steel powder LAP100.29A4(Fe-0.5Mo) by adding other alloy element powder, and studies the influence of pressing force and different pre-diffusion thermodynamic state on organization and performance of sintered parts. Finally, by quench and temper alloy specimens, to study the effect of different quenching temperature on the microstructure and properties of sintered parts.The results show:the improvement of the pressing force can contribute to the molding of the green compacts, make the density of the green compacts and sintered parts density increased, porosity decreases, closed porosity increased, the tensile strength of the sintered samples is variable. When the pressure is800MPa, the green density and sintered density of alloys are6.99g/cm3and7.11g/cm3, the porosity can be reduced to9.53%, closed pore can reach7.77%, the tensile strength of sintered sample can be reached730MPa.Ferrochromium Steel powder pre-diffusion treatment can effectively increase the proliferation ability of Cr element. Compared with the conventional mixed sintered samples, when the pre-diffusion temperature was750℃,800℃and820℃,the green density and sintered density increase with the pre-diffusion temperature increasing as well as the hardness after heat treatment, then density declined at850℃; and the tensile strength slightly decreased as the pre-diffusion temperature increasing and obviously decreased at850℃. The powder which is produced from diffusion treatment using Ferrochrome powder and pure iron powder at800℃, can be used to make sintered samples with balanced property, and the hardness of sintered samples can be reach30HRC, while tensile strength remain in783MPa.Optimal quenching temperature is studied by the samples produce from diffusion treatment using Ferrochrome powder and pure iron powder at800℃, and find that the hardness and the tensile strength of the alloy increasing with the rise of the quenching temperature before925℃and then the tensile strength decreased significantly。 The specimen can be fully martensitic structure when quenching at925℃, the hardness reaches32.5HRC, the tensile strength reaches840MPa.