THE INVESTIGATION OF STRENGTH AND PLASTICITY CHARACTERISTICS OF COMPOSITE LAYERS IN AUSTENITIC STAINLESS STEEL SUBJECTED TO ION-PLASMA TREATMENT USING THE NANOINDENTATION METHOD

One of the main issues of austenitic stainless steel is low strength properties and low wear-resistance. It can be partially or fully eliminated by the product surface modification and the creation of hardened surface layers. The ion-plasma saturation of alloys with interstitials, which is carried out in a mixture of gases with different compositions is an available and effective method of surface hardening of complex structural parts. At the same time, the mechanical and plastic characteristics of the processed materials are determined by the complex of properties of the base alloy and the hardened surface, and it is not always possible to identify their influence on the mechanical and plastic properties of each component of the composite material. The nanoindentation method allows determining local mechanical and plastic characteristics in certain areas of hardened materials (base alloy and surface) by the dynamic loading of the local microscopic areas. In this paper, using the nanoindentation method, the authors identified the mechanical and plastic characteristics of hardened layers produced by the ion-plasma treatment of austenitic 01H17N13M3 stainless steel with the grain-subgrain and coarse-grain structures. The ion-plasma treatment of steel specimens facilitates surface hardening and the formation of a composite surface layer of ≈20-25 μm in thickness. High values of nano-hardness in a composite layer are caused by the complex hardening of specimens: solid-solution hardening of austenite with nitrogen and carbon, the dispersion hardening and the formation of different nitrides and carbonitrides and the ferrite low fraction. The experimental results show that the strength properties and plasticity characteristics of such a layer strongly depend on the base material initial microstructure - the formation of a highly-defective grain-subgrain structure promotes the formation of a more enforced surface layer compared to the coarse-grained specimens.

austenitic steel, ion-plasma treatment, nanoindentation, Oliver-Pharr method, plasticity characteristics, nanohardness, 01H17N13M3 steel