The effect of boriding process on impact sliding wear behavior of electrochemical borided 1020 steel

Impact-sliding wear, which is caused by impact and sliding motions, is a common type of composite wear that can quickly lead to rapid wear failure of parts and has a very complex damage process. This type of wear is common in a wide range of industrial equipment, including high-speed railway catenary systems, nuclear power plants, bearings, gears, valve seats, drag bits, artificial joints, railway track system turnouts, and other components. Wear failure as a type of surface damage reduces the service life of the part, raises the running costs of the equipment, and can even lead to catastrophic accidents owing to the breakdown of crucial components. Surface strengthening techniques that do not modify the properties of the base material are increasingly being explored and implemented to improve the wear resistance of parts. Boriding is typically used to improve the surface properties of steels by forming layers of hard iron boride composed of dual FeB and Fe2B phases. However, structural distinctions between these borides, specifically the thermal expansion coefficients and brittleness of FeB, restrict the use of borided steels on contact surfaces under cyclic loads. Even though numerous studies on conventional boriding applications on AISI 1020 steels via pack boriding or plasma paste boriding have been published, their results cannot be implemented in industry due to the presence of FeB in the grown coatings. The purpose of this study is to improve the surface properties of AISI 1020 steel by applying cathodic reduction and thermal diffusion-based boriding by forming thick single-phase Fe2B layer and dual phase boride structures composed of Fe2B (inner) and FeB (outer) on AISI 1020 steel, and then to examine the impact sliding wear behavior of samples. In the present study, the influence of boriding on the wear resistance of AISI 1020 steel was investigated by a homemade impact-sliding wear tester. Structural characterization of borided and bare samples was conducted using an X-ray diffractometer and optical microscope, along with hardness measurements. Wear tracks of samples subjected to an impact-sliding wear test at room temperature were examined under an optical microscope in order to determine their wear mechanism. A 2-D profilometer was also used to measure the wear loss. Results of these examinations revealed that boriding leads to an increment in the impact-sliding wear resistance of AISI 1020 steel at room temperature. On the basis of the microstructure and microhardness analysis results, it has been determined that a single-layered (Fe2B) borided structure with a thickness of approximately 40 μm and a surface hardness of 1450±50 HV0.05 is formed on the surface of low carbon steel during 15 min at 950 °C with 45 min of soaking time. At EB in 30 min at 950 °C with 45 min of soaking time, however, a two-layered (FeB+Fe2B) borided structure with an approximate thickness of 140 μm and a surface hardness of 1900±50 HV0.05 is formed on the surface of the low-carbon steel. In summary, the wear resistance of the borided structures differed in the impact and sliding zones. The single-layered (Fe2B) structure showed better performance in the impact zone due to its toughness and ductility, resulting in less wear depth. Conversely, the two-layered (FeB+Fe2B) structure performed better in the sliding zone due to its higher hardness, but this led to more wear on the steel ball surface.