An influence of gaseous-atmosphere composition on the formation of nitride layers on deformed iron alloys

Using the complex methods, including microstructure, microdurometric, X-ray, differential thermomagnetic (in strong fields), and electron probe analysis, there is investigated the influence of preliminary plastic deformation (PPD) on phase composition, structure, and some mechanical properties of diffusion layers formed on deformed (to 0-30%) samples of Fe + 2.2% Cr + 2.2% Ti alloy after chemical and heat treatments (CHT) within ammonia-propane-butane mixture with different components' relation in gaseous atmosphere af 853 K during 1.44.10(4) s (4 h). It is established that optimal relation of gases in saturating atmosphere, when there is reached the maximal PPD influence on the interstitial elements' diffusion during CHT, is as follows: 90 vol.% ammonia and 10% propane-butane. For such a gaseous relation, there is observed the maximum increase of the diffusion-layer depth (approximate to 1.5 times) and surface microhardness (approximate to 1.1 times) on the samples deformed with 25-30% degrees in comparison with initial samples. According to X-ray and magnetic analysis data, the diffusion zone consists of alloyed layer of carbonitride phases of the cementite type on the samples' surface, nitrogen-carbon solid solution within alpha- and gamma'-phases. gamma'-phase is mainly formed on grain boundaries.