Abstract
The aim of the study is to investigate the effects on impact toughness properties of powder metallurgy (P/M) steels depending on different nickel ratios. For this purpose, ferrous P/M alloy samples containing 1.2 wt.% carbon and different nickel contents (0.5–5 wt.%) were compacted under 700 MPa pressure and sintered at 1200 °C under 5 × 10^–2 Pa vacuum atmosphere. Following sintering, the densification rate and macrohardness (HV2) measurements of the samples were carried out. Fracture morphologies of the samples having different nickel content following impact toughness tests at various temperature (–40 to 40 °C) were imaged by scanning electron microscopy (SEM). Metallurgical characterizations of the samples with different nickel content were analyzed SEM and X-ray diffractometer (XRD). It was understood that pearlitic transformation was suppressed with the formation of nickel-rich austenitic areas in the microstructure of nickel-doped P/M steels. The hardness and impact toughness values of PM steel samples with 5 % nickel addition were increased by approximately 121 and 247 %, respectively, compared to samples without nickel addition, at all test temperatures.

Key words
powder metallurgy steel, nickel, impact transition temperature, microstructure and hardness

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