Nanoparticle influence into the structure of structural steel

Abstract

It is shown in result of the analysis of nanoparticle production processes that among the numerous methods of metal nanoparticle producing, the electrospark granule processing in liquids allows to obtain nano-objects at high temperatures, pressures, and cooling rates, ie nanoparticles with high energy saturation and as a consequence with effective modifying ability. Nanoparticles obtained by electrospark treatment of iron granules in liquids, taking into account the high energy saturation. Nanoparticle influence was investigated on the structure of low carbon low-alloy structural steel 25GSL.
The results are shown of the study of the iron nanoparticles effect in a shell of Fe₂O₃ oxide, which when introduced into the melt it heating to the melt temperature and it converted into Fe₃O₄ oxide, on the formation of the dendritic and ferrite-pearlite structure of 25GSL steel during cooling after solidification and at normalization.  It is shown that the introduction of 3.65×10¹² nanoparticles into the melt results in grinding of globular dendrites in 2.5-2.8 times, austenite grains size reduces 1.4-1.8 times, perlite grains 1.7-2, 0 times, ferrite - 1.4-1.5 times, the amount of perlite 1.4-1.5 times, and the ferrite amount increases in 1.8-2.0 times. Cementite plate length increases and thickness decrease, respectively, in 1.8-2.0 and 1.7-1.8 times, and the distance decreases between the cementite plates in 2.7-3.0 times.
Modification changes the form of cementite in perlite from lamellar for the original steel to spherical in the modified one. The cementite plate length and the shape factor changes, respectively, from 2.9 - 5.0 (average - 4) μm and 8.9 - 22.0 (average - 14.7) for the original steel to 0.20 - 0.82 (average 0.41) µm and 1.1 to 3.0 (average 1.7) for modified steel.
The nanoparticle influence mechanism is mainly due to action as crystallization centers, and recrystallization during the formation of δ-Fe phases and transformations δ-Fe → γ-Fe during cooling after solidification and phase transformations of austenite into perlite during cooling and perlite into austenite during heating at normalization on thermokinetic parameters of phase transformations and steel structure during solidification, cooling after solidification and heating, holding and cooling during normalization.