Structure and Tribological Characteristics of Steels After Liquid Boriding with Additions of Rare Earth Oxides

The effect of borating on the structure and tribological characteristics of VKS-5, Kh12MF, 40Kh steels was studied. The samples were processed in a melt based on sodium tetraborate and boron carbide with the addition of lanthanum, yttrium and scandium oxides in an amount of 5 %. It was shown that this type of CTT is an effective means of increasing the tribological efficiency of steel joints for operating conditions without a lubricant. When testing the friction pair of VKS-5 steel — SS440 steel, the maximum decrease in the friction coefficient is observed if the steel is borated in the melt with the addition of Y₂O₃, the smallest — with the addition of La₂O₃. The values of the friction coefficient in the steady-state mode are: ≈ 0.45 for the original (not subjected to CTT) surface, steel after borating in a standard melt and in a melt with the addition of La₂O₃; ≈ 0.20 — for steel after borating with the addition of Sc₂O₃; ≈ 0.14 — for steel borated in a melt with the addition of Y₂O₃. The wear of VKS-5 steel decreases by ≈ 6.7 times after treatment in a standard melt, by 5.0, 4.2 and 3.6 times, respectively, in a melt with the addition of La₂O₃, Sc₂O₃ and Y₂O₃. Borating of Kh12MF steel in a standard melt reduces the friction coefficient by 1.7 times, and wear by 1.8 times compared to steel without CTT. The average value of the friction coefficient decreases by 2.9, 2.7 and 2 times in melts with the addition of La₂O₃, Y₂O₃ and Sc₂O₃, respectively; the wear intensity in the melt with La₂O₃ does not increase significantly, with Y₂O₃ it decreases by 1.6 times, and with the addition of Sc₂O₃ it decreases by 1.3 times. Borating forms wear-resistant diffusion layers on the surface of steel 40Kh. The best results in the combination of two tribotechnical characteristics (wear intensity and friction coefficient) for the friction pair steel 40Kh — steel SS440 were obtained under conditions when the steel was borated in a melt of standard composition.

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