Abstract
The effects of nickel, cobalt and molybdenum on the characteristics of sintering and also on the age-hardenability of sintered maraging steels were investigated. Specimens were prepared by mixing reduced iron powder with alloying element powders, and then compacted at 6t/cm2 and sintered for 1-3 hrs at 1300°C in hydrogen. Subsequently, the sintered compacts were aged for 5 hrs at 500°C. The results obtained are summarized as follows ;
1) The densification during sintering was slightly accelerated with the increase of nickel or cobalt content, but it was restrained with molybdenum content.
2) Up to a critical amount of alloying elements the aged hardness of compacts steadily increased. When these elements were added in excess, however, there was retained austenite in the martensitic structure of sintered compact, while the aged hardness decreased considerably.
It was, therefore, confirmed that the optimum base composition for the maraging steel sintered at 1300°C was of 18% nickel, 7% cobalt and 5% molybdenum.
3) Line analysis data by X-ray microanalyzer for Fe-18 Ni-7Co-5Mo compact (sintering: 1300°C× 3hrs) showed that the variations of the average concentrations were ±2% for nickel, ±3% for cobalt and ±0.5% for molybdenum.
4) The mechanical properties of sintered compacts are given in table 1, where it is observed that the sintering time and alloy composition have marked effects on mechanical strength, and that sintering at a temperature of 1300°C for the economical time of 1hr gives fairly good results.
