Investigation on the effect of multi-layered boriding on the mechanical and tribological properties of barrel steels

In this study, the effect of boronizing, titanizing, and borotitanizing coating processes on the surface properties and wear behaviour of 42CrMo4 and 32CrMoV12-10 barrel steels were systematically investigated and compared with their uncoated and commercially nitrided conditions. The surface properties of coated steels were determined by microscopic examinations, hardness, Rockwell-C adhesion, scratch, and wear tests. The coating processes led to the formation of hard Fe₂B, FeB, TiC, and TiB₂ layers on the surface of steels. It was observed that the TiC layer had the poorest adhesion strength quality among the coatings. The highest scratch resistance was obtained from the 42CrMo4 steel having a single-phase boride layer on its surface. On the other hand, the borotitanizing process caused the transformation of the FeB phase to Fe₂B. Nitrided steels exhibited the highest wear resistance at room temperature wear tests, but the wear resistance of the borotitanized steels was determined to be superior at elevated temperature. Boronizing and borotitanizing coatings were performed on inner surfaces of barrel samples produced from 42CrMo4 steel; however, a proper coating at the inner surface of the sample was achieved with boronizing.