EFFECT OF ELECTRON BEAM TREATMENT ON THE STRUCTURE AND PROPERTIES OF PLASMA COATING OF HIGH-SPEED MOLYBDENUM STEEL

The structure and properties of the surface of a plasma-deposited layer in a nitrogen environment of high-speed molybdenum steel on a substrate of medium-carbon steel grade 30KhGSA were studied using modern physical materials science methods. The deposited layer was irradiated with pulsed electron beams with the following parameters: energy density of 30 J/cm², duration of one exposure of 50 μs, frequency of 0.3 Hz, number of pulses of 10. In the initial state, the surface layers contain a polycrystalline structure of the dendritic type with a non-uniform distribution of molybdenum, chromium, aluminum, nitrogen and oxygen, surrounded by a developed network of ledeburite eutectic. The relative content of elements (except for Mn, C and O₂) decreases as it approaches the substrate. The microhardness of the deposited layer is 5.6 MPa, which increases to 6.2 MPa after a single high-temperature tempering, and to 7.2 MPa after a double tempering. Electron-beam pulsed action performed after a double high-temperature tempering modifies the structure and properties. A quasi-homogeneous distribution of alloying elements, the formation of a fine-grained structure with a grain size of 4 ‒ 6 μm, in the volume of which lamellar martensite was found, were revealed. The previously formed structure of dendritic crystallization is not observed. The microhardness of the deposited layer after electron-beam treatment increases and reaches 8.7 MPa, which is almost 2 times higher than the microhardness of the substrate. The revealed patterns of change in nanohardness and Young's modulus from the distance to the irradiation surface confirm the developed ideas about the nature of hardening of the plasma deposited layer of high-speed molybdenum steel.