Study of the influence of strengthening electron-beam processing on the structure of high-alloyed tool steels

Abstract

The work investigated the effect of hardening electron beam treatment on the microstructure and microhardness of the surface layers of high-speed and stamping steels. The limit modes of processing were established experimentally, at which the maximum microhardness of the surface layer is achieved, and at the same time, surface melting is prevented. It is proposed to use the power density of the electron beam as a complex parameter of the processing mode, which determines the nature of heating and cooling of the tool during its processing with an electron beam. The power density of the electron beam includes all the other main parameters of the electron beam treatment mode, namely the diameter, power, and speed of the electron beam moving relative to the product to be treated. It was established that the maximum microhardness of the hardened layer is achieved in the case of high-temperature quenching without remelting. At the same time, the maximum dispersion of the structure is ensured almost throughout the depth of the reinforced layer. Surface melting of the tool during electron beam processing is extremely undesirable. Under such processing conditions, there is a sharp decrease in the microhardness of the surface layer, which contains a significant amount of residual austenite. Hardening with the formation of a significant amount of residual austenite leads to a sharp decrease in the content of carbides. An insufficient content of carbides and an excessive content of residual austenite leads to a decrease in the wear resistance of the tool. At the same time, the tool's resistance to plastic deformation worsens at elevated temperatures. It was established that the depth of the hardened layer formed during electron beam treatment of high-speed cutting and stamping steels is significantly affected by the initial microstructure of these steels. In order to obtain the maximum depth of the hardened layer during electron-beam processing of high-speed cutting and stamping steels, these steels should be subjected to preliminary heat treatment in the form of volume hardening and tempering. The optimal values of the overlap coefficient during electron beam processing, which ensures the minimum width of the tempering zones, have been determined.