Nitridation technology specifics of high-alloy corrosion-resistant steels of aviation purposes

Metallurgy and Material Science

Material science


DOI: 10.34759/vst-2021-2-206-215

Аuthors

Bibikov P. S.1*, Belashova I. S.2**, Prokof'ev M. V.1***

1. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
2. Moscow Automobile and Road Construction State Technical University (MADI), MADI, 64, Leningradsky Prospect, Moscow, 125319, Russia

*e-mail: bpetrserg@gmail.com
**e-mail: irina455@inbox.ru.
***e-mail: mikepro1953@rambler.ru

Abstract

The article is devoted to a new gas nitridation method, which allows obtaining high-quality diffusion layers, meeting the requirements for operation of the products that running under severe conditions of sharp temperature changes and large sign-changing loads, particularly, for aircraft parts. The method consists in a combination of various temperature regimes at the ammonia and air concentration change in the furnace working part.

The authors propose the three-stage technology for the 03Cr11Ni10Mo2Ti steel nitridation. The first state ensures the surface restoration, oxides destruction, and guaranteed nitrided layer creation.

The high activity of the saturating atmosphere is being achieved by reducing the ammonia dissociation degree, as well as air oxygen binding with hydrogen while the ammonia decomposition. These processes ensure forming continuous nitrided layer on the surface The second stage ensures the passage of intense diffusion processes at a temperature of 550-600°C due to additional thermal cycling when concentration of the working mixture changing.

The second stage duration is being determined by the required thickness of the diffusion zone. In the atmosphere of the pure ammonia, the third stage allows resolving to a certain extent the hard and brittle high-nitrogen surface layer, which itself becomes the source of nitrogen at the low activity of the saturating atmosphere. Nitrogen reflux inward the metal and reduction of its content on the surface begins herewith. The stage of diffusion allows the phase content changing of the surface, and reduce its brittleness due to the certain hardness decrease and plasticity increase, which excludes micro-cracks appearing on the ready parts, i.e. fulfill the task set by the industry.

Keywords:

gas nitridation, micro-cycling, depassivation, thermal cycling, nitrogen potential

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