The influence of the tempering temperature on hydrogen embrittlement in carbonitrided modified SAE 10B22 steel C. S. Brandolt*, F. V. Gonc ¸alves, I. D. Savaris, R. M. Schroeder and C. F. Malfatti The modified SAE 10B22 steel has high hardenability, which provides its use in special engineering applications, such as in self-drilling screws, with carbonitrided layer, quenched and tempered. However, these components are susceptible to hydrogen embrittlement, which can cause damage to structural components. In addition, the study of the behavior regarding to hydrogen embrittlement of components with carbonitrided layer has not been done hitherto. In this work the tempering temperature influence on hydrogen embrittlement of modified SAE 10B22 steel, was evaluated after a carbonitriding process. Standard samples and M4 Â 50 screws were tested. A galvanostatic circuit was used for hydrogen charging of the samples, which were characterized by low-strain tensile test and the samples fracture were analyzed by SEM. The obtained results demonstrate that by lowering tempering temperatures, the hydrogen-loaded samples presented a greater loss of mechanical properties and greater changes of the micromechanics of fracture. In addition, the geometry of the screw was more prone to the deleterious effects of the hydrogen charging than the conventional specimens. 1 Introduction Fasteners are very important components for mechanical engineering, and they are commonly used in the automotive industry, in the making of furniture manufacturing, in construction and other areas. Their application varies from simple connections between two parts of larger equipment, to their use as strength multipliers, as machining tools (self-drilling screws) or as safety items. In general, these components do not add great value to the product, but serious problems may occur when their function is not properly fulfilled. These malfunctions encourage the testing of techniques to improve the properties of the components, such as wear and corrosion resistance [1,2]. Besides, the behavior in fracture of fixation elements has been extensively studied in the literature, due their structural importance [3–6]. Surface hardening techniques such as carburizing, nitriding and boronizing, among others, have been widely used in metallic materials with the aim of improving surface hardness, wear resistance, fatigue strength, corrosion resistance and oxidation resistance of components [7–9]. Carbonitriding is one of these techniques, which is a thermochemical treatment that has the objective of enriching the surface of materials with carbon and nitrogen, followed by quenching and tempering processes employed in order to adjust the surface properties for the application in which the component will be used [10]. The tempering temperature is a key factor in determining the mechanical properties of treated bolts, especially when the materials present different properties and different chemical compositions from its surface in relation to its core, which is the case of the carbonitrided materials. Among the steels used in the fasteners manufacturing processes, the modified SAE 10B22 steel is more widely applied [11] for replacing medium carbon steels or conventional low alloy steels, such as the SAE 5135 steel [12]. The chemical composition, containing considerable amounts of boron and manganese confers to modified SAE 10B22 good hardenability and excellent response to thermochemical processes, such as carburizing and carbonitriding, thus combining the properties of hardness and wear resistance with toughness and ductility [13]. However, when these alloys are subjected to different processes such as stripping, electroplating, electrochemical corrosion and cathodic protection, a hydrogen introduction may occur, making these materials susceptible to hydrogen embrittlement [10]. The hydrogen embrittlement is a failure caused by the action of hydrogen in combination with residual stresses present and/or C. S. Brandolt, F. V. Gonc ¸alves, I. D. Savaris, R. M. Schroeder, C. F. Malfatti LAPEC, Federal University of Rio Grande do Sul—UFRGS, Avenida Bento Gonc ¸alves, 9500, Porto Alegre—RS (Brazil) E-mail: cristiane.brandolt@ufrgs.br Materials and Corrosion 2016, 67, No. 5 DOI: 10.1002/maco.201508607 449 www.matcorr.com wileyonlinelibrary.com © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim