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Nitrocarburizing of low-carbon unalloyed steel

Part 2 Positron annihilation studies

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Abstract

Low-carbon unalloyed steel has been investigated after nitriding accomplished by either the salt-bath method (Tenifer) or the gas method (Nitroc). The resulting changes in the position annihilation parameters are reported in this paper, while changes in the mechanical properties are reported in the preceding paper. The positron lifetime measurements show that small vacancy clusters in which the positron lifetime is ∼ 240 psec are present in the steel and that they are thermally stable even up to 570° C. A fast cooling from this temperature appears to freeze in monovacancy-impurity complexes. Positrons annihilating in the surface layer (formed by the nitriding processes and consisting of Fe2–3N) reveal that a high concentration of large vacancy clusters can be present in the outermost 4μm of this layer. The Tenifer treatment appears to result in the presence of more clusters than in the Nitroc treatment. The positron lifetime in these clusters is ∼ 300 psec and this component disappears upon annealing at 100° C. Positrons annihilating in the diffusion zone below the surface layer indicate that dislocations are created around Fe16N2 and Fe4N precipitates. The interpretation of the positron data provides a physical understanding of the mechanical data presented in the preceding paper.

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Dannefaer, S., Hogg, B. & Kerr, D. Nitrocarburizing of low-carbon unalloyed steel. J Mater Sci 19, 1099–1108 (1984). https://doi.org/10.1007/BF01120018

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Keywords

  • Fast Cool
  • Diffusion Zone
  • Lifetime Measurement
  • Preceding Paper
  • Mechanical Data