M. A. Flores-Rentería, M. Ortiz-Domínguez, M. Keddam*, O. Damián-Mejía, M. Elias-Espinosa, M. A. Flores-González, S. A. Medina-Moreno, A. Cruz-Avilés and M. Villanueva-Ibañez A Simple Kinetic Model for the Growth of Fe 2 B Layers on AISI 1026 Steel During the Powder-pack Boriding Abstract: This work focused on the determination of boron diffusion coefficient through the Fe 2 B layers on AISI 1026 steel using a mathematical model. The suggested model solves the mass balance equation at the (Fe 2 B/substrate) interface. This thermochemical treatment was carried out in the temperature range of 1123–1273 K for a treatment time ranging from 2 to 8 h. The generated boride layers were characterized by different experimental techniques such as light optical microscopy, scanning electron mi- croscopy, XRD analysis and the Daimler-Benz Rockwell-C indentation technique. As a result, the boron activation energy for AISI 1026 steel was estimated as 178.4 kJ/mol. Furthermore, this kinetic model was validated by compar- ing the experimental Fe 2 B layer thickness with the pre- dicted one at a temperature of 1253 K for 5 h of treatment. A contour diagram relating the layer thickness to the boriding parameters was proposed to be used in practical applications. Keywords: boriding, incubation time, kinetic model, acti- vation energy, adherence PACS ® (2010). 68.47.De, 68.55.A-, 68.55.jd *Corresponding author: M. Keddam: Département de Sciences des Matériaux, Faculté de Génie Mécanique et Génie des Procédés, USTHB, B.P. No. 32, 16111 El-Alia, Bab-Ezzouar, Algiers, Algeria. E-mail: keddam@yahoo.fr M. A. Flores-Rentería, M. A. Flores-González, S. A. Medina-Moreno, A. Cruz-Avilés, M. Villanueva-Ibañez: Universidad Politécnica de Pachuca-UPP, Carretera Pachuca-Cd. Sahagún km. 20, Ex Hacienda de Santa Bárbara, CP 43830, México, Hidalgo M. Ortiz-Domínguez: Universidad Autónoma del Estado de Hidalgo, Campus Sahagún, Carretera Cd. Sahagún-Otumba s/n, México, Hidalgo O. Damián-Mejía: Universidad Nacional Autónoma de México-UNAM, Instituto de Investigación en Materiales, Circuito Exterior, s/n Ciudad Universitaria, Coyoacán, CP 04510, México, D. F. M. Elias-Espinosa: Instituto Tecnológico y de Estudios Superiores de Monterrey-ITESM Campus Santa Fe, Av. Carlos Lazo No. 100, Del. Álvaro Obregón, CP. 01389, México, D. F. 1 Introduction Boriding is the most widely used thermochemical surface treatment to enhance the mechanical properties such as high surface harness, wear resistance and corrosion resis- tance of ferrous alloys [1]. The boriding process involves the diffusion of atomic boron into the base steel. This diffusion takes place in the temperature range of 800– 1050 °C for a treatment time ranging from 0.5 to 10 h. Due to its small size and high mobility, the atomic boron dif- fuses into the base steel, and reacts with Fe to form iron borides (i.e. Fe 2 B and FeB) in gaseous, solid, or salt media. Several boriding methods are available such as gas borid- ing, liquid boriding, plasma boriding and plasma paste boriding. Among these boriding methods, the powder- pack boriding possesses some important advantages in terms of easy handling, the flexibility with respect to the composition of the powder, minimal equipment and low cost [2–4]. In the powder-pack boriding, the boriding agent is placed in a heat resistant box and samples are embedded in the mixture of powder. In practice, a single Fe 2 B is preferred to the bilayer configuration (FeB + Fe 2 B) which gives rise to cracking and scaling due to difference in coefficients of thermal expansion of borides and that of base steel [5–7]. The modeling of the growth kinetics in the boriding process was considered as a tool to optimize the boride layer thickness according to the practical use of the borided material. For this purpose, different models were reported in the literature to simulate the growth kinetics of Fe 2 B layers grown on different substrates. Some of them assumed a linear boron concentration profile through the Fe 2 B layers with and without the inclusion of boride incu- bation times for Fe 2 B phase [8–20]. The aim of the present work was to characterize the boride layers formed on AISI 1026 steel by powder-pack boriding in the temperature range of 1123–1273 K. The kinetic studies were performed to analyze the growth of Fe 2 B layers on AISI 1026 steel. A simple kinetic model, based on the mass balance equation at the (Fe 2 B/substrate) interface, was used to estimate the boron diffusion DOI 10.1515/htmp-201 0 High Temp. Mater. Proc. 2015; 34(1): – 4- 004 1 11