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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2007

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On low temperature ion nitriding of austenitic stainless steel AISI 316

Toshkov V., Russev R., Madjarov T., Russeva E.

Journal of Achievements in Materials and Manufacturing Engineering

2007

Vol. 25, nr 1

71-74

Purpose: The purpose of this paper is to discuss some problems concerning the extremely high values of the nitride layer hardness and the features of so called S-phase which are formed after low-temperature ion nitriding of high-alloyed austenitic (austenitic-ferritic) steels. Design/methodology/approach: The investigations are performed mainly by using of ray diffraction method after ion nitrided 316 (AISI) steel. Findings: As a result of the work some data, concerning the structure and substructure, the phase composition of the S-phase, crystal lattice, the broadening of diffraction reflexes, mechanism of transformation of gamma'- phase into S-phase, its high hardness etc. of the nitrided layer are obtained. It could be concluded that S-phase could be classified as a modified gamma'-phase. The extremely high values of the hardness could be explained by the high nitrogen concentration in the solid solution and by the presence of increased density of the defects in the austenitic volume, which is transformed in the new S-phase. Research limitations/implications: The potencionstatic investigations of the electrochemical properties of the nitriding probes, performed by us, confirmed the data, obtained by the literature, but this problem will be discussed in some of the next publications. Originality/value: The high micro- and macro-deformations of the lattice of S-phase could be explained by the considerable registered expansions and the angle replacements of the slope (psi) on the ray diffraction maxima. The registered macro deformations could reach immense values, in the range of (1.4 - 2.1)x10-2, which corresponds to macro deformations around 1900 - 2300 MPa (if we accept, for the austenite, the usual module of elasticity of 2.1x105 MPa). For such final decision it is necessary to obtain also some other confirmation facts.