Sintering of Ni-Mo-W steels and their properties

Purpose: The paper focuses on microstructural and mechanical characteristics of Ni-Mo and Ni-Mo-W sintered steels with increasing amount of tungsten, low and high addition of carbon. Design/methodology/approach: Prepared mixes of powders have been compacted at 700 MPa and sintered in a vacuum furnace with argon backfilling at 1120°C for 60 minutes; after sintering rapid cooling has been applied with an average cooling rate of 2,5°C/s. Produced sets of samples have been studied by scanning electron microscopy (SEM) with EDS for phase distribution and mapping and light optical microscopy (LOM) for microstructure observations. Mechanical properties such as impact energy, microhardness and wear rates were evaluated depending on chemical composition and the effect of applied sintering process with rapid cooling. Wear resistance was investigated using both pin on disk and disk on disk tests. Findings: The highest value of impact energy was achieved for set of steels with smaller amount of carbon. It was noticed that the presence of tungsten didn't differ much the results. The situation was opposite in the case of microhardness, where the best results were obtained for set with addition of 0.6%C and reached 452 HV0.1. The microstructure of all investigated alloys was mainly martensitic with minor presence of bainite in the set of steels containing low addition of carbon. Research limitations/implications: According to the powders characteristic, the applied cooling rate seems to be a good compromise for mechanical properties and microstructures, nevertheless further tests should be carried out in order to examine different cooling rates and parameters of tempering process. Originality/value: The effect of small additions of W and WC to low alloyed steels, especially in terms of hardenability and wear resistance, was investigated.