The paper presents an assessment of the wear rate of turning tool blades during machining of steels applied in medical industry. The subjects of the research were stainless steels X20Cr13 (1.4021) and X8CrNiS18-9 (1.4305) used in production of surgical instruments. An experiment was carried out to assess the wear of multi-edge turning inserts with CVD coatings (Pafana CNMG 12 04 08 ZSZ and Sandvik CNMA 12 04 12-KR 3205), and an uncoated turning insert (Sandvik CNGA 12 04 08 T0102 WG 650). The

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... ar was measured by the direct wear indicator VB C . On the basis of the results obtained for both X20Cr13 and X8CrNiS18-9, it was found that the Pafana CNMG 12 04 08 ZSZ turning insert had the best wear resistance during machining. The cutting path of Pafana CNMG 12 04 08 ZSZ was about 25 % longer than Sandvik CNMA 12 04 12-KR 3205 and about 300 % longer than Sandvik CNGA 12 04 08 T0102 WG 650. It was also found that each turning insert revealed a linear wear. Keywords: tool blade durability, tool blade wear, turning, steel, surgical instruments. [1][2][3][4][5]. New surgical robots use many types of instruments [6] [7] [8] [9] . Widely used materials for surgical instruments are high-quality grades of stainless steel, especially austenitic and martensitic ones. These steel grades exhibit high resistance to air, moisture, and weak solutions of salts and acids. Corrosion resistance is endowed to a steel material by its feasibility to be passivated, which directly depends on the chemical composition. Passivation gives an oxide layer, which protects its substrate against ambient conditions and can replenish itself. In stainless steel, this effect is caused by chromium as an alloy additive, and only when its content is 10.5 % or higher. With the chromium content corrosion resistance grows [10] . Stainless steel grades vary in machinability. Ferritic and martensitic steels are relatively well machinable, while high-alloy austenitic grades exhibit a very poor machinability. Machinability of these steels depends first on high tendency to strain hardening, creating a build-up edge, low heat conductivity and capacity, accelerated cutting edge wear, and chip control problems. It is then critical to choose the correct machining parameters, materials and geometry of tools. CAD/CAM systems are recommended to use for modelling 3D virtual product and for generating a cutting path [11] [12] [13] [14] [15] . Cemented carbide tools are commonly used for machining of stainless steel workpieces. Additionally, they are protected with coatings to inhibit wear. Cutting tools made from cemented carbide with multi-layer coatings (with up to several dozen coating layers) have been increasingly popular. Another trend in cutting tools is their preservation with single-layer coatings of polycrystalline diamond (PCD) or common boron nitride (CBN). The protective coatings can be deposited to the working surfaces of cutting tools with two methods: CVD (Chemical Vapour Deposition) or PVD (Physical Vapour Deposition) [16] [17] . The cutting ability and operation of cutting tools are largely affected by the protective coating material. Protective coatings increase the machining efficiency (which means higher technological parameters) and extend the cutting edge durability [18] [19] . Stainless steel machining is recommended to be done with multi-edge tool inserts, the wear of which should be monitored. The wear of a cutting edge is determined by its loss of cutting ability properties over time. This process is very complex and defined by many factors. Wear occurs near the cutting edge over the flank face and/or the tool face. Several types of wear exist: abrasive, chemical, adhesive, thermal, and mechanical. During stainless steel machining, the following wear phenomena