Abstract
Strengthening of machine parts and units, increased reliability and longer service life is an important task of modern industry. As promising materials for protective-strengthening coatings, matrix composites based on the ternary system Fe-B-FenB are offered. The article proposes the complex heating of steel being borated and imbued medium by high frequency currents (HFC). We also proposed to combine the diffusion boriding from liquid and solid media and the transition of the diffusion boriding to chemical interaction between the elements of Fe and B. We determined the main components of the reaction-boronizing system, as well as their roles and possible processes that lead to the implementation of topochemical boriding initiated by HFC-heating. We confirmed the course of the reaction leading to the occurrence of reducing agents Ca, Si and active boron in the boronizing mixture.
Highlights
Finite element modeling was applied to simulate the yield strength of the FeB layer on a low-alloy steel substrate; the resultant values ranged from 5 to 7 GPa [13]. The mechanical properties such as fracture toughness, compressive residual stresses, and the indentation size effect (ISE) were evaluated in the tips of the needles of the Fe2B layer using the Berkovich nanoindentation technique [15]; the results showed an apparent hardness of approximately 14 GPa with a fracture toughness between 2.4 and 2.7 MPa, and the compressive residual stresses were between 351 and 471 MP
The thermal study of boronizing mixtures showed, firstly, that all processes in the system at temperatures above 540-550 °C occur in the pseudo-liquid environment of the P0.66 borate flux melt, which already facilitates the boriding and delivery of active boron to the steel surface
It confirmed the course of the reaction leading to the occurrence of reducing agents Ca, Si and active boron in the boronizing mixture
Summary
It is well established that nitrocarburising and boriding treatment of steels generate surfaces which causes considerable modification in the mechanical, tribological and corrosion properties [1, 2].In boronizing process, diffusion of boron into the steel surface leads to the formation of boride layer, which includes either a single-phase layer of Fe2B or two-phase layer of Fe2B and FeB [3,4,5,6].Boride layers formed on the diffusion boriding steel parts considerably (5-30 fold) increase the abrasion resistance, heat resistance (1.5 - 2 fold) and corrosion resistance, which improves the life of the hardened product [7].After the "classic" boriding, the coating microstructure, most often, is coalescent at the bottom of boride needles, that form a coating layer. It is well established that nitrocarburising and boriding treatment of steels generate surfaces which causes considerable modification in the mechanical, tribological and corrosion properties [1, 2]. Diffusion of boron into the steel surface leads to the formation of boride layer, which includes either a single-phase layer of Fe2B or two-phase layer of Fe2B and FeB [3,4,5,6]. Boride layers formed on the diffusion boriding steel parts considerably (5-30 fold) increase the abrasion resistance, heat resistance (1.5 - 2 fold) and corrosion resistance, which improves the life of the hardened product [7]. After the "classic" boriding, the coating microstructure, most often, is coalescent at the bottom of boride needles, that form a coating layer. Resulting internal tensile stresses in the borated coating significantly reduce their plasticity, peeling and chipping of such a hardening coating occur, until its complete destruction, at relatively small bending, shock or compressive stresses and especially reversed loads and vibrations.
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