Abstract
In our previous studies on the 4600 steels produced by conventional powder metallurgy (P/M) process using mixed elemental powders, the fine heterogeneous microstructure caused by the agglomeration of Ni powders was reported to be significantly effective for the improvement of mechanical properties. This study has been performed to obtain the high densified compacts using the double press and sintering, and the bimodal powders, and moreover to investigate the relationship between the mechanical properties and the heterogeneous microstructure of the compacts (4600grade, 0.4 mass%C).
The tensile strength of the steels with bimodal powders (coarse : fine = 8 : 2) was improved the most significantly with increasing Ni content to 6 mass%, without loss of the ductility. This seemed to be due to the solution strengthening and the mezzo-heterogeneous microstructure which were consisted of Ni rich martensite surrounded by a network of tempered martensite. However, the tensile strength of the steels with bimodal powders (coarse : fine = 9 : 1) added 6 mass% Ni were dropped by the increase of retained austenite.
