Sinter-hardening of Ni-Mo pre-alloyed powders with tungsten addition

Purpose: Purpose of this paper was to present the benefits of powder metallurgy technology and development of sinter-hardening process. The mechanical properties, focusing in particular on hardness and wear resistance, of two different carbon levels pre-alloyed steel powders processed with sinter-hardening method, were described. Microstructure characteristic of produced sinter-hardened Ni-Mo steels with increasing amount of tungsten (from 0 to 0.3% wt.) was taken under consideration. Design/methodology/approach: Different compositions have been tested in order to investigate the influence of various tungsten additions into low (0.4%) and high (0.6%) carbon content of pre-alloyed steel powders. Powders, with addition of 0.7% lubricant, were pressed in a 2000 kN hydraulic press. De-waxing process at 550 degrees centigrade for 60 minutes in a fully nitrogen atmosphere was performed before the sintering. Sinering was carried out in vacuum furnace with argon backfilling. The furnace was equipped with a cooling zone to provide accelerated cooling from the sintering temperature. Green compacts were sintered at the temperature 1120 degrees centigrade for 1 hour and rapidly cooled with a rate 2.5 degrees centigrade/s. Findings: The applied sinter-hardening process with achievement of material characterized by good wear resistance. The investigation of Ni-Mo and Ni-Mo-W sinter-hardened steels with low and high carbon content proved that applied process of sintering under vacuum and rapid cooling brought expected outcome. Research limitations/implications: Considering the achieved outcome, it was revealed that chemical composition and applied process of steels preparation, sinter-hardening with the cooling rate 2.5 degree centigrade/s, results in achieving materials with relatively high hardness and significant resistance to abrasion. Anyhow, further research should be performed. Originality/value: Sinter-hardening of Ni-Mo pre-alloyed powders with the addition of different additions of tungsten, especially in terms of hardenability and wear resistance, was investigated.