INFLUENCE OF STRUCTURAL PARAMETERS ON MECHANICAL PROPERTIES OF R6M5 STEEL UNDER THE CONDITIONS OF STRENGTHENING SURFACE TREATMENT

摘要

The work is devoted to investigation of structural-phase changes in surface layers of high-speed steel R6M5 after strengthening pulsed-plasma surface treatment in various modes and influence of forming structure parameters on tool performance. As a result of comprehensive investigations and calculation-analytical prediction of strength properties, fracture toughness coefficient and crack resistance of surfaces, strengthened in various technological modes, it was established that optimum properties of subsurface layers are ensured at recommended modes of pulsed-plasma surface treatment, increasing the total strength level by 25%, compared with base metal due to refinement of grain structure (by 1.5 to 2 times), increase of the contribution of substructural, grain, dislocation and dispersion strengthening mechanism. Here, the level of local inner stresses in the treated layer is equal to -0.018 to 0.44 of the theoretical strength of material that is not dangerous in terms of crack formation, because of the absence of abrupt gradients as to inner stresses and uniformly increased dislocation density (10~(11)-2.10~(11) cm~(-2)) compared to base metal. It is shown that at a significant strengthening of treated layers of high-speed steel, the value of fracture toughness coefficient is by 15% higher compared to base metal. Thus, application of recommended modes of pulsed-plasma surface treatment leads to modifying the structural-phase state of the surface layer and improvement of its mechanical properties.