Effect of Mechanical Activation of the Powder Mixture on the Structure and Properties of Boro-Aluminized Low-Carbon Steels

Abstract

Introduction. Boro-aluminizing is one of the most effective ways to improve the performance properties (corrosion resistance, heat and wear resistance) of low-carbon steels. Solid-phase methods of thermochemical treatment (TCT) are carried out from saturating mixtures based on powder materials. Preliminary mechanical activation of these powders is one of the ways to improve the properties of the resulting diffusion layer. The purpose of this work is to determine the effect of preliminary mechanical activation of the powder mixture on the structure and properties of the boro-aluminized layer on the surface of low-carbon steels. Methods: The paper considers the results of research on the preliminary mechanical activation of the saturating mixture in the TCT of low-carbon steels (for example, St3 and 3Kh2V8F) based on powdered boron and aluminum carbide. The results of experiments on preliminary mechanical activation of the saturating mixture are shown, and the dependence of the particle size of the initial mixture on the duration of mechanical activation is established. Samples of steels with a diffusion layer after TCT are obtained. It is found that the process temperature has a significant effect on the thickness of the layers obtained. With an increase in temperature from 950 ° C to 1050 ° C on St3 steel samples, the layer thickness increases from 120 to 150 μm, on 3Kh2V8F steel samples – 105 and 140 μm with a holding time of 2 h and 4 h, respectively. The microstructure of the obtained samples is investigated; dependence diagrams of the microhardness distribution on the depth of diffusion layers are shown. The distribution of Al over the depth of the resulting boro-aluminized layer is established. As additional studies, the saturation capacity of the mixture after a single application in the TCT process is studied. Results and discussions. The principal possibility of using mechanical activation in TCT to obtain diffusion layers with specified strength characteristics is established. An increase in the duration and temperature of TCT in mechanically activated mixtures leads to an increase in the aluminum content in the layer.