In this work we consider the issue of influence of initial state of tool steel P6M5 surface on thickness and microhardness of hardened layer during ion nitriding in the glow discharge. It is established that the application of intense plastic deformation torsion before ion nitriding in the glow discharge increases the rate of nitrogen diffusion deep into the tool steel R6M5, and increases the thickness of the hardened layer by 2.5 times.
This work is devoted to the study of the effect of the duration of ion nitriding by glow discharge on the physical and mechanical properties of tool steel with different initial structure. We used specimens of R6M5 tool steel with a coarse-grained structure obtained after annealing at a temperature of 850°C and with a fine-grained structure obtained after severe plastic deformation by torsion discharge. With an increase in the duration of ion nitriding, the thickness of the hardened layer and wear resistance increase. The combination of plastic deformation with ion nitriding by glow discharge increases the adsorption and diffusion rate of the saturating element due to the creation of a highly fragmented and disoriented fine-grained structure and contributed to reduction in processing time.
Asymmetric rolling is a process based on purposefully created differences in the circumferential speeds of the work rolls. For such a process, a degree of asymmetry is defined by a speed ratio (SR) of the work rolls. This research presents the experimental results of the effect of asymmetric rolling with high speed ratio (SR = 2.0; 2.5; 3.0) on the HSS AISI M2 behaviour during processing and on the change in the mechanical properties. Two types of asymmetric rolling were studied: 1) asymmetric warm rolling at temperatures 400, 500, 600, 700, 800 °C; 2) asymmetric hot rolling at 1100 °C. It was shown, that asymmetric rolling can be used as an effective technology for processing difficult-to-deform high-speed steels. Due to asymmetric rolling the number of passes was decreased by 5 times and at the same time the rolling force was also decreased by about 5 times compared with conventional (symmetric) rolling at the same temperature. The highest value of microhardness 790 HV (3 times higher than the initial value of microhardness) was achieved in HSS M2 after asymmetric hot rolling at 1100 °С and SR = 3. Carbides refinement with uniform distribution of them was also achieved. The results of investigation can be used for design of effective technology of manufacturing high-speed steels with improved microstructure and mechanical properties.
This paper examines the influence of plastic deformation of the HSS M2 surface on the characteristics of the hardened layer after ion-plasma nitriding in the glow discharge. In the study it was found that the plastic deformation of the steel surface increases the rate of nitrogen diffusion deep into the material, due to an increase in dislocation density and the formation of microdefects, due to a highly refined grain-like ultrafine grain structure. It was also found that the plastic deformation of the steel surface before ion-plasma nitriding leads to a 2-fold increase in the thickness of the hardened layer HSS M2, due to an increase in surface free energy, which contributes to increased adsorption of the saturation element and the formation of nitrides in the near-surface layer of nitrided material.
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