Effects of Nitriding Subsequent Titanaliting of Steels

Abstract

The paper presents the results of nitriding in partially dissociated ammonia of the pure technical iron, respectively 34CrAlMo5 steel after titanaliting in powdery solid medium, with direct reference on the growth kinetics of the layers, the phase composition and the morphology of the resulting layers. Thermodynamics was anticipated and experimentally demonstrated that the layers of titanium aluminide formed on the surfaces of the two metallic materials considered do not constitute barriers to nitrogen diffusion during the nitriding process, but actively participate in the formation of simple or complex nitrides of the two elements, titanium and aluminum. On the other hand, in the presence of these layers, the flux of nitrogen atoms is slightly diminished with repercussions on the dimensions of the structural components of the layer. The conclusion of the experimental research was that the role of titanaliting prior to nitriding is to increase the proportion of the hardening phases in the surface layers of thermochemically processed metal products after nitriding.

The Effects of Modifying the Activity of Nitriding Media by Diluting Ammonia with Nitrogen

“…In the absence of dilution gas (nitrogen, argon, etc. ), experimental research shows a significant influence of the variation of this quantity on the layer growth kinetics [ 6 , 7 , 8 , 18 , 32 ]. The mathematical model obtained, according to Equation (21), passed the concordance test as it is presented in Table 7 , and its graphical expressions, drawn in Figure 6 , express quite suggestively the effect of the variation of the two parameters with statistically significant influence, temperature, and ammonia dilution degree on the total thickness of the nitrided layer.…”

Nitriding in ammonia-nitrogen gaseous mixtures, after the simultaneous saturation with Ti and Al

“…in the surface areas of the layer, as they showed Kogan, 1976, 1982;Lahtin et al, 1991;Winter, 2009;Edenhofer et al, 2008) b By introducing in the general thermochemical processing flow of the products, prior to nitriding, some processing stages generating hardening phases, which later, during nitriding, by partial or total conversion into nitrides, to ensure an increase in the proportion of phases of interest in the areas surface of the layer. Achieving such a goal can be ensured by applying a titanisation or simultaneously saturation with Ti and Al, as they showed (Cojocaru et al, 2021;Bu et al, 2012;Ozkan and Saduman, 2012;Xua et al, 2020;Ghinea et al, 2020). Maintaining the tenacity of the central areas of thermochemically processed products, because titanisation or simultaneous saturation with Ti and Al is performed at temperatures higher then tempering, can be ensured by interposing a martensitic quenching in the neutral mediums or vacuum that preserve the composition of the phases, whether followed by high tempering, its effect being like the application of nitriding.…”