Abstract. Structure-phase state and tribological properties of the coating deposited on Hardox 450 martensitic low-carbon steel by flux-cored wire Fe-C-Cr-Nb-W and modified by subsequent electron-beam processing were studied. It is shown that the electron beam processing of ~ 5 mm thick deposited layer leads to the formation of ~ 20 µm thick modified surface layer with the main phases of α-Fe and NbC, Fe3C and M6C(Fe3W3C) carbides. Wear resistance of the weld layer is 70 times higher than the one of the original steel. IntroductionThe production of coatings with high service properties making possible the increase in service durability of the articles in the extreme conditions of high wear, corrosion, mechanical loads and temperatures is the important fundamental problem. The thorough analysis of the relation «wear parameters -hardness -microstructure» is necessary in scientific and practical use of various kinds of surfacing in the critical articles. Only in this case it is possible to produce the articles with high service parameters [1 -8].The purpose of the research is the analysis of structure and tribological properties of the layer formed on Hardox 450 steel by electrocontact surfacing of powder wire of system Fe-C-Cr-Nb-W and modified by high intensity pulsed electron beam irradiation.Hardox 450 steel (weight %): (0.19-0.26 C; 0.70 Si; 1.6 Mn; 0.025 P; 0.010 S; 0.25 Cr; 0.25 Mo; 0.004 B; balance -Fe) was used as a test material. The surfaced electrode 1.6 mm in diameter had the following chemical composition (weight %): 1.3 C; 7.0 Cr; 8.5 Nb; 1.4 W; 0.9 Mn; 1.1 Si, balance -Fe.The testing techniques of the surfacing by methods of modern physical material science are presented in [1].

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The decay mechanism of silicon particles in silumin in the thermal effect zone of low-energy high-current electron beam is proposed. Its essence consists in the fact that under the effect of the mechanical stresses the interface of silicon inclusion with aluminum matrix becomes instable resulting in the decay of silicon particle. It was supposed that the instability was the analog of Rayleigh-Taylor instability. The mechanical stresses arising due to the discrepancy of the elastic moduli and the linear expansion coefficients of the inclusion and the matrix are the analogs of gravity force. The analysis of the initial stage of instability within the frameworks of the visco-potential approximation has shown that the dependence of the rate of perturbations’ growth has only one maximum which falls on the wave length of the order ≈ 500 nm that is 5-fold higher than that of the experimental data. Such a discrepancy may be explained by the fact that when developing the model the temperature of the silicon inclusion and the aluminum matrix was considered to be constant, similar and being equal to the eutectic temperature of silumin. In fact, the temperatures of the inclusion and the matrix are different. To take into account the influence of these facts on the instability of the interface the new investigations are necessary.

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