Internal nitration in iron−chromium (manganese) nitride powder systems

Abstract

The effect of the internal nitration of powder iron is examined by the introduction of nitrogen in the form of alloying additives such as chromium and manganese nitrides. It is established that the phase composition of these materials includes residual manganese and chromium nitrides and a solid solution of nitrogen in iron. To obtain a porousless or low-porosity hot-pressed material with evenly distributed fine inclusions of secondary nitrides and to maintain the composition, hot-pressed materials must be annealed in conditions that prevent nitrogen loss.Keywords: internal nitration, chromium nitride, manganese nitride, hot-pressed material, fine powders.Nitrogen, as an alloying element, is increasingly used to harden powder metallurgy parts [1−4]. The use of structural austenite nitride steels is reasonable to reach high strength, adequate high-temperature wear resistance and intercrystallite corrosion resistance. To harden cast structural steels, use is made of nitrides of mainly transition metals such as titanium, vanadium, chromium, zirconium, tantalum, silicon, beryllium, and aluminum [5].The partial replacement of nickel with α-iron in powder stainless steels when nitrogen is introduced will extend the austenite range. In addition, austenite will be stabilized under microstructural changes [6] resulting from the formation and growth of particulate nitrides and from the pinning and retardation of dislocations. In spite of the obvious interest in nitrogen as an alloying element, the effect of nitrides on the properties of iron-based alloys has not been examined on a systematic basis. There are only data on the nitration of porous powder materials [3].The Central Research Institute for Ferrous Metallurgy (Moscow, Russia) developed a process [2] to produce high-strength tool steels and functional alloys by chemical nitrogen doping of iron-based matrix powders under pressure and subsequent hot pressing. The materials obtained are characterized by high performance characteristics at elevated temperatures.There are data on the capability of high-nitrogenous iron-based powders produced by thermal-diffusion alloying and nitration to serve as an initial component to obtain nitrogen-containing steels [1]. In addition, such powders can be used to produce nitride-hardened composite materials.The objective of this paper is to examine the interaction of chromium and manganese nitrides with powder iron and associated processes of internal nitration of iron with impermanent nitrides.