Features of formation of diffusion zone obtained on steel 20 by boriding in induction furnace

Shevchuk E.P. Plotnikov V.A. Makarov S.V.
2022 National University of Science and Technology MISIS

Izvestiya Ferrous Metallurgy
2022 #65 Issue 2 98 - 105 pp.

The article presents data on studies of iron borides synthesis during induction heating to 1000°C for 5 min of steel 20 samples with a coating from a charge containing Fe - H₃BO₃. Content of boric acid in the charge varied from 25 to 75 % wt. Charge in the experiments could be diluted with a solution of liquid glass in water with addition of small amount of ammonium hydroxide and coal. Study of the surface layer microhardness showed that during saturation of the surface layer of carbon steel 20 with boron, a macroscopically extensive difusion zone 900-1000 μm in size is formed, in which the boride content gradually decreases when moving deeper into the matrix. Such a size of the difusion zone indicates an anomalously high mass transfer during boriding of steel 20. Indeed, the calculated difusion coefcient during boriding under induction conditions (about 1.35·10-⁹m²/s) is two orders of magnitude higher than the difusion coefcient in the classical boriding. X-ray studies showed that, under the considered conditions, Fe₂B and FeB borides are synthesized, and a solid solution of boron in α-iron is also formed. An analysis of phase composition of the difusion zone structural components indicates that, from the surface to the matrix, formation of boride phases occurs in the following sequence: FeB → Fe₂B → (α-phase + B) → base metal. Microstructure of the difusion zone consists of more or less pronounced layers consisting of FeB and Fe₂B boride phases. On the whole, especially deep-lying regions of the difusion zone are a composite material consisting of plastic α-phase and iron boride crystals. Crystals in FeB and Fe₂B in the layer are oriented mainly perpendicular to the difusion front. Perhaps, this is due to the rapid predominant growth of the boride phase under conditions of high difusion mobility of boron atoms in one direction and hindered in others.

boration , boride layers , boron mixture , difusion coefcient , difusion zone , microhardness , microstructure , phase composition

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Eastern Kazakhstan State University, 34 30-i Gvardeiskoi divizii Str., Eastern Kazakhstan Region, Ust-Kamenogorsk, 070020, Kazakhstan
Altai State University, 61 Lenina Ave., Altai Territory, Barnaul, 656049, Russian Federation

Eastern Kazakhstan State University
Altai State University

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