Influence of the Chemical Composition of Steel on the Structure and Properties of Diffusion Coatings Obtained by Simultaneous Saturation of Structural Steels with Boron, Chromium, and Titanium

The paper presents a comparative analysis of the microstructure of diffusion coatings on steels 45 and 38Kh2MYuA obtained by simultaneous diffusion saturation with boron, chromium and titanium. The saturation was performed by packing the saturable samples with sizes of 15 × 15 × 50 mm in a heat-resistant container with a powder saturating medium. At saturation of steel 45, the thickness of the diffusion layer is 120–140 µm, while at saturation of steel 38Kh2MYuA, the thickness of the diffusion coating is in the range of 70–80 µm, which is 58% less. The transition zone of the sample made of steel 38Kh2MYuA contains up to 20 vol % ferrite, while, in the case of steel 45, the transition zone is represented only by pearlite. The maximum microhardness of the diffusion layer on steel 38Kh2MYuA is 1.8 times lower than the indicator of the maximum microhardness of the diffusion layer on steel 45. At the same time, the surface microhardness on both steels is practically the same and is in the region of 1500 HV_0.1. The microhardness of the transition zone in the case of steel 45 is higher than in the case of steel 38Kh2MYuA due to the almost complete absence of the ferrite phase. According to the data of durometric analysis, the thickness of the diffusion layer on steel 38Kh2MYuA does not exceed 85 μm, the thickness of the diffusion layer on steel 45 is 120 μm, which correlates with the results of metallographic analysis. Parts made of 38Kh2MYuA steel strengthened by complex boron–chromium–titanizing, having a lower surface hardness than parts made of steel 45, have high prospects for use as one of the parts that make up the friction pair of critical units. As the second part, it is possible to use boronized steel 45.