Investigation of the Diffusion Rate of Boron Atom in AISI D3 Steel
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Investigation of the Diffusion Rate of Boron Atom in AISI D3 Steel Atila Gürhan Çelik* Department of Civil Engineering, Engineering Faculty, Giresun University, Giresun, 28200 Turkey *e-mail: [email protected] Received May 29, 2019; revised December 19, 2019; accepted March 15, 2020
Abstract—The present study reports on the kinetics of borided AISI D3 steel. Boriding thermochemical treatment was carried out in a solid medium consisting of B4C, SiC and KBF4 powders mixture at 1123, 1173 and 1223 K for 2, 4 and 6 h, respectively. The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe2B, CrB and Cr2B compounds. The thickness of the boride layer increased with an increase of the boriding time and the temperature. The hardness of the boride compounds formed on the surface of the steels ranged from 1652 to 1984 HV0.05, whereas Vickers hardness values of the untreated the steels was 608 HV0.05. The boron activation energy (Q) was estimated as equal to 174.261 kJ/mol for the borided AISI D3 steel. The growth kinetics of boride layers forming on the borided AISI D3 steel was also analyzed. Keywords: AISI D3 steel, XRD, micro-hardness, kinetics, activation energy DOI: 10.1134/S2070205120040103
1. INTRODUCTION Boronizing refers to a surface diffusion treatment by which a boride coating is formed on the component surfaces. By this treatment, a multi-phase layer consisting of iron and metallic borides can be obtained in the case of ferrous alloys. In boriding process, boron atoms diffuse into the surface of the workpiece to produce hard boride layers without requiring high technology. As a consequence, the formation of boride layers improves the surface properties such as: a high hardness, resistance against wear and corrosion in some acids or alkali media. It exists many boriding methods to produce the boride layers. Particularly, the pack-boriding is one of the more common boriding methods due to its simplicity and cost effectiveness [1–3]. The boride layer may be either a single phase layer (Fe2B) or a double phase layer (FeB and Fe2B) depending on the boriding conditions. The presence of the FeB phase in the layers leads to their brittleness and high stress intensity at the (FeB/Fe2B) interface, due to the significant differences between the expansion coefficients of both iron borides [4, 5]. Thermal diffusion treatments of boron compounds used to form iron borides typically require process temperatures of 973 and 1323 K for 1 to 12 h. The process can be carried out in solid powder (boronizing compound), liquid, gaseous, electrochemical or plasma medium Boriding of high carbon steels with high alloy content has been somewhat difficult in the past [6–11].
The powder mixture used in the literature is 5% by weight. B4C, which acts as a borate donor, is 5% by weight. KBF4 acting as activator and 90% by weight
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