FORMATION OF A DIFFUSION LAYER ON STEEL 45 WITH SIMULTANEOUS SATURATION WITH BORON, CHROME AND TITANIUM

doi: 10.25712/ASTU.2072-8921.2021.02.031

Abstract

Single-component hardening of steel products (boriding, chromium plating, nitriding, carburizing) increases wear resistance, while it increases surface brittleness, reduces resistance to heavy cyclic loads, and has a relatively low corrosion resistance. Multicomponent coatings obtained by complex saturation of steels and alloys with boron, chromium and titanium at the same time, have excellent characteristics of wear resistance, ductility and corrosion resistance. Research has been carried out to determine the kinetics of coating formation on steel 45 with simultaneous diffusion saturation with boron, chromium and titanium. It was found that the experimental parameters of the boride diffusion layer thickness in time exceed the calculated values. The diffusion layer has a thickness of 120 μm with a saturation time of 2.5 hours, 155 μm with a saturation time of 5 hours, and 180 μm with a saturation time of 7.5 hours. The maximum microhardness of the diffusion coating is observed not on the surface, but at some distance from it (on average, at a depth of 45-60 µm from the surface), and reaches values ​​ of about 3200 HV0.1. In this case, on the surface of the samples, the microhardness takes on a minimum value of about 1800 HV0.1. The developed method and composition makes it possible to obtain high-quality boride coatings. The uncharacteristic distribution of microhardness with an increase from the surface to the middle of the layer makes it possible to use finishing (grinding and / or polishing) without significant loss of properties inherent in diffusion boride layers, which makes it possible to significantly expand the scope of boriding of critical machine parts that have high requirements for dimensional accuracy and surface quality.