The Structure of the Diffusion Boride Layer Obtained as a Result of Repair of a Worn-Out Boride Coating

This paper presents the results of a study of the repeated complex diffusion saturation of a “thrust plain bearing” part made of Steel 45 after its repair. Repair of a bearing after simultaneous complex diffusion saturation with boron, chromium, and titanium, which wore out after 18 months of operation, has been carried out by removing the hardening coating by grinding to a depth of 0.15 mm on a flat grinding machine. The witness specimen, which had previously hardened simultaneously with this bearing, was subjected to a similar procedure at the same time. After carrying out the operation of chemical-thermal treatment of the bearing and the witness sample, control and measurement of the thickness and characteristics of the diffusion coating have been performed on the witness sample. The diffusion coating on the bearing before its repair had a thickness of 120–150 µm. The transition zone mainly consists of 450-µm-thick pearlite. Thus, the total thickness of the diffusion coating is of the order of 600 μm. The thickness of the diffusion coating on the bearing increased to 0.9–1 mm after repair, of which approximately 0.7–0.8 mm is in the transition zone. The boride-layer thickness also increased to 180–200 µm. The surface hardness of the boride layer increased by 60%–from 1100 to 1800 HV 0.1 . At the same time, in general, the hardness of the diffusion coating, measured by the Vickers method with a load of 1 kg, increased from 2243 to 2764 HV 1 , i.e., by 23%. Higher surface hardness and, moreover, microhardness will allow significantly reducing the wear of the boride layer and, as a result, significantly increasing the service life of the plain bearing after its repair.