eJournals Tribologie und Schmierungstechnik 69/1

Tribologie und Schmierungstechnik
0724-3472
2941-0908
expert verlag Tübingen
10.24053/TuS-2022-0004
High interstitial austenitic stainless CrMn steels are characterised by significantly increased work hardening ability and strength compared with conventional CrNi austenites, yet maintaining very high ductility and toughness. The machining of high interstitial CrMnCN steels is challenging in terms of process stability and economic efficiency. In this context, unfavourable chip forms, high thermomechanical loads and the superposition of different wear mechanisms in particular lead to challenges in turning operations. In the following article, different lubricant strategies are analysed for machining of CrMnN and CrMnCN austenitic stainless steels regarding chip form, mechanical tool loads and wear. Furthermore, the workpiece properties are considered with regard to surface roughness and microstructural changes
2022
691 Jungk

Turning of high strength, austenitic stainless steels

2022
Timo Rinschede
Nils Felinks
Dirk Biermann
Janis Kimm
Sebastian Weber
Philipp Niederhofer
Clara Herrera
Martin Kalveram
Aus Wissenschaft und Forschung 33 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 Turning of high strength, austenitic stainless steels Timo Rinschede, Nils Felinks, Dirk Biermann, Janis Kimm, Sebastian Weber, Philipp Niederhofer, Clara Herrera, Martin Kalveram* Eingereicht: 6.9.2021 Nach Begutachtung angenommen: 12.2.2022 Dieser Beitrag wurde im Rahmen der 62. Tribologie-Fachtagung 2021 der Gesellschaft für Tribologie (GfT) eingereicht. Drehbearbeitung hochfester, austenitischer Werkstoffe Nichtrostende, austenitische CrMn-Stähle zeichnen sich durch ein deutlich höheres Kaltverfestigungsvermögen und sowie eine gesteigerte Festigkeit im Vergleich zu konventionellen CrNi-Austeniten aus, wobei sie eine sehr hohe Duktilität und Zähigkeit aufweisen. Die Zerspanung von CrMnCN-Stählen gestaltet sich in Bezug auf Prozessstabilität und Wirtschaftlichkeit dabei als sehr herausfordernd. In diesem Zusammenhang führen insbesondere ungünstige Spanformen, hohe thermomechanische Belastungen und die Überlagerung verschiedener Verschleißmechanismen zu Herausforderungen bei der Drehbearbeitung. Nachfolgend werden zwei unterschiedliche Schmierstoffstrategien für die Zerspanung von austenitischen CrMnN- und CrMnCN- Edelstählen hinsichtlich Spanform, mechanischer Werkzeugbelastung und Verschleiß analysiert. Darüber hinaus werden die Werkstückeigenschaften im Hinblick auf Oberflächenrauheit und Gefügeveränderungen betrachtet. Schlüsselwörter Hochfeste Werkstoffe; Nichtrostender, austenitischer Stahl; Kühlschmierstoffe; Korrosionsbeständigkeit; Interstitielle Elemente; Kaltverfestigung; Drehbearbeitung High interstitial austenitic stainless CrMn steels are characterised by significantly increased work hardening ability and strength compared with conventional CrNi austenites, yet maintaining very high ductility and toughness. The machining of high interstitial CrMnCN steels is challenging in terms of process stability and economic efficiency. In this context, unfavourable chip forms, high thermomechanical loads and the superposition of different wear mechanisms in particular lead to challenges in turning operations. In the following article, different lubricant strategies are analysed for machining of CrMnN and CrMnCN austenitic stainless steels regarding chip form, mechanical tool loads and wear. Furthermore, the workpiece properties are considered with regard to surface roughness and microstructural changes. Keywords High-strength materials; stainless austenitic steels; cooling lubricants; corrosion resistance; Interstitials; work hardening; turning Kurzfassung Abstract * Timo Rinschede M.Sc. - Corresponding author Orcid-ID: https: / / orcid.org/ 0000-0002-8771-6479 Nils Felinks M.Sc. Orcid-ID: https: / / orcid.org/ 0000-0002-7232-0367 Prof. Dr.-Ing. Prof. h.c. Dirk Biermann Orcid-ID: https: / / orcid.org/ 0000-0001-8215-0093 Technische Universität Dortmund Institute of Machining Technology 44227 Dortmund, Germany Janis Kimm M.Sc. Orcid-ID: https: / / orcid.org/ 0000-0002-9875-3910 Prof. Dr.-Ing. Sebastian Weber Orcid-ID: https: / / orcid.org/ 0000-0002-4168-3480 Ruhr-Universität Bochum, Chair of Materials Technology 44780 Bochum, Germany Dr.-Ing. Philipp Niederhofer Orcid-ID: https: / / orcid.org/ 0000-0001-7619-8840 Dr.-Ing. Clara Herrera Orcid-ID: https: / / orcid.org/ 0000-0002-7505-149X Deutsche Edelstahlwerke Specialty Steel GmbH & Co. KG 58452 Witten, Germany Dr.-Ing. Martin Kalveram Orcid-ID: https: / / orcid.org/ 0000-0003-4561-8106 Seco Tools GmbH 40699 Erkrath, Germany they are non-magnetic. Consequently, they can be used in demanding environments like e.g. oiland gas-exploration, submarine environments, or medical applications. On the other hand, mechanical properties of HNS and HIS, in particular the combination of high toughness and intense cold work hardening, are prone to cause issues for machining of such alloys, e.g. concerning chip formation or tool wear. Thus, in this study, two different high strength austenitic stainless steels are investigated aiming at finding optimized parameters for efficient machining. Experimental setup Workpiece materials Two different high strength austenitic stainless steels were chosen for the investigations. X3MnCrNiMoN is a commercially available HNS, which is used e.g. for oiland gas-exploration. X30CrMnN18-18 is a newly developed HIS, which can be used e.g. as a stainless bearing steel, but also in similar applications as mentioned above. Both steels were supplied as round bars with a diameter of 60 mm. They were tested in solution annealed condition, which ensures a fully austenitic microstructure free of precipitates. The resulting mechanical properties along with the chemical compositions and microstructural images can be found in Figure 1. Tools In the experimental investigations, specific inserts for machining austenitic steels from Seco Tools were used, as is shown in Figure 2. The cutting insert type CNMG120408-MF4 TM2501 was used for roughing and type VBMT160404-F1 TM2501 for finishing tests. Both inserts are made of the same cutting material and Aus Wissenschaft und Forschung 34 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 Introduction Conventional austenitic stainless steels (Fe-18Cr-8Ni) are alloyed with chromium, which ensures corrosion resistance, and nickel, which is required for stabilization of the austenitic phase. In order to improve resistance to localized corrosion, molybdenum can be added [1]. While featuring superior resistance to attack of corrosive media as well as very high toughness and ductility, conventional FeCrNi austenites suffer from rather low strength, which is unfavorable for many applications. Strength can be increased by applying cold work strengthening, which, however, can be accompanied by deformation-induced phase transformation from austenite to martensite. Another possibility is the addition of interstitial elements, most likely nitrogen, which results in increased strength, improved cold work hardening ability, and stabilization of the austenitic phase. However, the solubility of nitrogen is limited in FeCrNi steels, and the precipitation of most probably chromium-rich nitrides is undesired since it is linked with deterioration of corrosion resistance and mechanical properties. Nitrogen solubility in austenitic stainless steels can be enhanced by a (partial) substitution of nickel by manganese (FeCrMn(Ni)). Thus, higher amounts of nitrogen can be added (“high nitrogen steels”, HNS), which improves mechanical properties as well as resistance to localized corrosion [2]. High nitrogen contents however may require pressurized metallurgy, which is expensive. Thus, recent developments aimed at introduction of high amounts of interstitial elements at ambient pressure, which was achieved by partial replacement of nitrogen by carbon. The so called austenitic “high interstitial steels” (HIS) combine superior mechanical properties with good corrosion resistance and can be produced by conventional metallurgy [3]. HNS and HIS remain fully austenitic even at high degrees of cold deformation, which in turn means, that Figure 1: Mechanical properties and chemical composition of the investigated steel grades provide high cutting-edge stability and wear resistance for machining austenitic stainless steel grades. The coating system, comprising TiCN and Al 2 O 3 , is applied to the tools in a CVD process with a maximum thickness of 7 µm, which enables the preparation of sharp cutting edges. For roughing, a corner radius of r ε = 0.8 mm was applied to increase the cutting stability. In order to realize small cutting depths as well as to machine complex contours, a decreased corner radius of r ε = 0.4 mm was selected for finishing inserts. The tool type CNMG120408-MF4 is characterised by an open, negative geometry with a tool orthogonal clearance of α = 0 ° and a rounded cutting-edge radius of r β = 36 mm. In comparison, the positive finishing insert type VBMT160404-F1 has a similar cutting-edge radius but a tool orthogonal clearance of α = 5 °. Machines and lubricants The tests were carried out on two different CNC lathes in order to apply various cooling lubricant strategies. One test series was performed with oil on a Monforts RNC200A lathe, which has a drive power of P max = 13 kW. The Index ABC65 machine tool was used for the tests under emulsion and has a drive power of P max = 35 kW. The cutting oil type Blasomill13 from Blaser Swisslube GmbH is mineral-based. The high lubricating effect is provided by anti-wear and extremepressure-additives. A water-miscible cooling lubricant based on ester oil of type Blaser Vaso 6000 was applied for machining tests under emulsion. The content was adjusted to 12 % in order to achieve a sufficient lubricating effect in addition to the cooling qualities. Methods of analysis Specific multicomponent dynamometers type Kistler 9121 and Kistler 9119 respectively were used to measure the mechanical tool loads while machining. The tool wear was analysed by a digital microscope type Keyence VHX 5000 and surface quality was measured with a tactile surface roughness tester type Hommel Etamic W5 in cutting time periods of Δ th = 3 min. In addition, chip formation was analysed by a highspeed microscope type Keyence Highspeed VW9000. Samples that were cut from the machined parts were embedded in epoxy, and carefully ground by hand to a mesh size of 1000 using SiC grinding paper. Afterwards they were polished down to a grain size of 1 μm with a diamond suspension and then etched in V2Aetching solution to develop deformation features and microstructures. The microhardness was measured with the KB30s automatic hardness tester (KB Prüftechnik) with a load of 0.1 kg. Further, a microhardness tester type Shimadzu HMV-G was used to analyse the subsurface zone after sample preparation process. Results and discussion Roughing In the experimental tests the machinability in turning, both roughing and finishing, of the stainless, non-magnetic steel grades were analysed experimentally. Initially, tests on varying cutting speed, feed rate and cutting depth were performed in order to work out favourable cutting parameters. The primary criteria of these analyses were high productivity as well as process reliability. Concerning finishing, a high surface quality was intended. The machinabilities of these steel grades are negatively influenced by their high ductility in particular. This effects chip breaking and favours the formation of chip balls. The experimental test on tool life, presented in the following, is based on the results of initial tests, in which cutting parameters were varied. In roughing, inserts of type CNMG120408-MF4 TM2501 were used at a feed rate of f = 0.3 mm, a cutting depth of a p = 1.5 mm and a cutting speed of v c = 50 m/ min. The mechanical tool loads and tool wear were presented along the performed cutting time of t h = 18 min. Figure 3 displays the results for the regarded materials depending on lubricant types. With regard to the mechanical tool loads, it is shown that no significant deviations of cutting forces were measured for most experiments. Rising mechanical tool loads over machining time were only observed in roughing X30CrMnN18-18 under the use of emulsion-based cool- Aus Wissenschaft und Forschung 35 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 Figure 2: Turning tools used for roughing and finishing X30CrMnN18-18 under these conditions causes increased loadings on the cutting edge. In particular, abrasive wear forms can be observed, which is induced by the impact of interstitial particles [5, 6]. Furthermore, cutting material spalling and plastic deformation, especially under emulsion, can be observed, which is the reason for increasing cutting forces. In comparison to the steel grade X3MnCrNiMoN19-16-5-3, increased notch wear on the main cutting edge as well as lower thermal load marks were analysed in the turning tests under emulsion. The occurring tool loads and the resulting tool wear can be influenced by microstructural changes in form of strain hardening, besides other factors [3]. In order to investigate this correlation more precisely in the context of processing the investigated steel grades, metallographic analyses of the previously machined workpiece subsurface zones were carried out. By these analyses, the microscopic changes in the subsurface zones were to be detected in order to enable a reference to the previously presented results of machining tests. Figure 4 shows the results of microhardness tests in the workpiece’s subsurface zones, starting from the machined surface. Aus Wissenschaft und Forschung 36 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 ing lubricant. In general, a favourable ratio of cutting, feed and passive force could be achieved with the performed cutting parameters. In comparison, machining X30CrMnN18-18 is characterised by a higher level of cutting force components, due to comparatively increased mechanical strength as well as a higher content of interstitial elements nitrogen and carbon. Due to this, this material causes intense mechanical loadings. Furthermore, tool wear increases in form of abrasive wear at the cutting edges. Especially in terms of tool wear, there are significant differences between the materials as well as between the applied cooling lubricant types. The material X3MnCrNiMoN19-16-5-3 causes less abrasive wear on the flank face and a reduced width of flank wear land (VB). The main cutting edge and the corner were rounded, so the cutting edge durability decreases in consequence. However, these phenomena do not affect the mechanical tool loads and the chip shape along the regarded cutting time t h . Due to the low thermal conductivity of austenitic steels [1], high thermal tool loads can be implied at roughing under oil. Because of the increased cooling qualities, thermal loadings can be significantly reduced by using a coolant emulsion [4]. By applying oil as lubricant concept, a burr was formed at the level of the cutting depth, regarded as sign of wear. Turning Figure 3: Mechanical tool loads and wear behaviour in roughing under oil and emulsion Basically, the materials differ in terms of the measured bulk hardness: A micro hardness of 290 HV0.1 was detected for the material X30CrMnN18-18, which is about 50 HV0.1 higher than for X3MnCrNiMoN19-16-5-3. Additional to the bulk hardness, rough turning causes a hardening of the subsurface zone to the depth of s = 0.2 mm. These cold hardening phenomena are favoured by the influence of the solved interstitial elements, which hinder dislocations in the crystal lattice. The level of bulk hardness as well as hardening results correlates with the mechanical tool loads and tool wear, observed in the performed machining test. In this context, the increased strength for X30CrMnN18-18 causes higher mechanical tool loads as well as more extensive abrasive wear. Moreover, the choice of cooling lubricant does not have a significant effect on the subsurface zone’s strength. In summary, it can be said that the observed hardening effects induced by rough machining can thus be used effectively in application purposes in form of an increased surfaced integrity. In this context special wear resistance properties arise for the presented choice of cutting tools and the parameters. The comparison of the tool wear along the regarded cutting time demonstrates the differences in the use of different cooling lubricants. Due to the higher thermal conductivity and capacity of water-mixed lubricants compared to oil, the point of contact can be cooled more ef- Aus Wissenschaft und Forschung 37 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 Figure 5: Resulting tool wear and micro hardness analysis at increased cutting parameters for roughing using a coolant emulsion Figure 4: Results of micro hardness analyses in the subsurface zones of the roughed workpieces differentiated between material and lubricant Finishing In addition to roughing, experiments on finish-turning for the regarded steel grades were also investigated. In these tests, inserts type VMBT160404-F1 TM2501 were applied. In terms of technological analysis of finishing processes a high reliability, especially with regard to chip shape and chip removal as well as a high surface quality, was adduced primarily. Especially under these aspects, the coolant types oil and emulsion were compared experimentally in initial tests. Due to the superior lubrication effect [4], it can be said that higher surface qualities were measured in the tests under oil. An increased thermal tool load did not occur due to the small chip cross-section during finishing, so that an increased cooling effect was not necessary. In this context, machining under emulsion does not generate significant advantages. For this reason, only the results for finishing under oil are presented below. The tool wear and the surface quality were documented over a cutting time of t h = 18 min, and the subsurface zone of the finished surface was also analysed. Figure 6 shows these results for both materials. The finishing process was performed at a feed rate of f = 0.1 mm and a cutting depth of a p = 0.4 mm. Under these cutting parameters, ribbon chips were shaped by the chip former geometry. They move away from point of contact into feed direction and finally are removed reliably. Chip breakage cannot be achieved due to the material’s high ductility and the low chip cross-section area. Under the performed conditions, it was possible to reach Aus Wissenschaft und Forschung 38 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 fectively when using an emulsion. By this, the intensive thermal loadings on the tool can be reduced significantly. For this reason, increased cutting parameters for turning under emulsion were applied in further experimental tests. The material removal rate and thus also the productivity are to be increased by rising the cutting speed to v c = 75 m/ min and the feed rate to f = 0.35 mm. The test results describing tool wear and the micro hardness in the subsurface zones are shown in Figure 5. For the material X3MnCrNiMoN19-16-5-3 the enhanced machining strategy, a high process stability and comparable signs of wear were observed. More precisely, minor material removing signs at the main cutting edge and corner as well as notch wear at the level of the cutting depth could be analysed after processing. When considering the subsurface zone, the process adjustments primarily affect the hardening depth, but not the degree of hardening. Furthermore, turning the material X30CrMnN18-18 under the same machining conditions, both the degree of hardening and the hardening depth significantly increase. Strong mechanical loads attend this on the cutting tool, so that plastic deformation and abrasive wear was detected. As a result of increased tool loading, a tool breakage occurs after a cutting time of t h = 15 min. In summary, it can be said that the thermal tool loading can be reduced significantly by the increased cooling effect of an emulsion towards oil for the regarded steel grades. However, the investigated cutting parameters for roughing can be applied productively in turning X30CrMnN18-18 because of increased strain hardening effects and mechanical loadings. Figure 6: Surface quality, influence on subsurface zone and tool wear for finishing under oil an average roughness depth Rz ≈ 4 µm and a centre roughness value Ra ≤ 1 µm along the entire process. The small chip cross-section during finishing does not lead to any significant changes in the surface integrity and thus only a slight hardening in the subsurface zone. Using a micro hardness analysis, it was shown that there are slight increases towards the bulk hardness for both investigated materials. Low thermal and mechanical tool loads were accompanied by minor tool wear signs in form of abrasive cutting-face wear. In summary, the finishing process of the considered non-magnetic austenitic steel grades can be entirely realised using cutting oil as a cooling lubricant in accordance with the defined targets. Chip formation In the context of turning austenitic steel grades, the resulting chip shape and its removal are particularly important in order to reach a high process quality [7]. The high ductility of austenitic steels results from the facecentred cubic crystal structure, which favours plastic deformability due to a high number of slip systems [8]. In terms of machining, these properties lead to the use of a small cutting-edge radius in order to improve material separation and reduce plastic deformation in the subsurface zone. However, the cutting edge also provides sufficient stability to avoid any chipping of cutting material. Consequently, smaller cutting-edge roundings should be used for finishing. In contrast, more stable machining tools with an increased rounding should be used for roughing [9]. Due to their good plastic deformability, austenitic steels tend to form long continuous chips, which are accompanied by turning the risk of chip nests on the tool and workpiece while machining. For this reason, the chips must be moved away from the cutting edge reliably. This can be achieved in particular by suitable adjustment of the cutting parameters, the corner radius and the chip former. For a precise analysis of chip formation, a high-speed microscope was used to record sequences of roughing and finishing processes for both steel grades (see Figure 7). By the technological analysis of the recorded pictures, it can be proven that the specific combination of cutting parameters and tool selection for roughing and finishing is appropriate to guide the material intentionally from chip former in an angle of about 45 °. Afterwards, the chips are led in feed direction, which was attended to prevent collisions to the previously machined surface. The specific cutting edge geometry provides stable material separation of the ductile workpiece material without chipping of the cutting edge, as the high-speed pictures show. With a focus on the roughing process, it can be said that the extreme deformation rates in consequence of the large area of the undeformed chip cause a transgression of break stress at frequent intervals. Thus, the chips break in small sections, as shown in Figure 7. With regard to the finishing process, it is evident that cylindrical helical chips are formed under the regarded conditions. Although the chips do not break in segments, they leave from the point of cutting as well as from the machined part of the workpiece, so that no negative process influences can be ascertained. Summary In the presented studies, turning processes of two nonmagnetic austenitic stainless steels (X30CrMnN18-18 and X3MnCrNiMoN19-16-5-3) were analysed technologically with special regard to varied cooling lubricants. Aus Wissenschaft und Forschung 39 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 Figure 7: Chip formation and chip shape in roughing and finishing operations stainless steels have a great potential for high-tech applications, where high strength and corrosion resistance is required. References [1] Berns, H.; Theisen, W.: Eisenwerkstoffe Stahl und Gusseisen. 4. Auflage, Springer Verlag, Berlin 2008 [2] Gavriljuk, V.; Berns, H.: High Nitrogen Steels, Springer Verlag, Berlin 1999 [3] Berns, H.; Gavriljuk, V.; Riedner, S.: High Interstitial Stainless Austenitic Steels. Springer Verlag, Berlin Heidelberg 2013, https: / / doi.org/ 10.1007/ 978-3-642-33701-7 [4] Weinert, K.: Trockenbearbeitung und Minimalmengenkühlschmierung. 1. Auflage, Springer Verlag, Berlin Heidelberg 1998 [5] Niederhofer, P.: Hochlegierte Stähle für den Einsatz bei Verschleiß- und Korrosionsbeanspruchung. Dissertation, Ruhr-Universität Bochum 2015 [6] Forke, E.; Niederhofer, P.; Albrecht, M.; Hüllmann, A.; Kräusel, V.; Schneiders, T.; Gehde, M.: Profile Cross Rolling of High-Interstitial Austenitic Stainless Steels for Application in Plastics Extrusion. Steel research international, Volume 91, Issue 5, Special Issue: Tooling 2019, 2019. https: / / doi.org/ 10.1002/ srin.201900417 [7] Maruda R.W.; Krolczyk, G.M.; Niesłony, P.; Krolczyk, J.B.; Legutko, S.: Chip Formation Zone Analysis During the Turning of Austenitic Stainless Steel 316L under MQCL Cooling Condition, Procedia Engineering, Volume 149, 2016, pp. 297-304, https: / / doi.org/ 10.1016/ j.proeng.2016.06.670 [8] Tobler, R.; Meyn, D.: Cleavage-like fracture along slip planes in Fe-18Cr-3Ni-13Mn-0.37N austenitic stainless steel at liquid helium temperature. Metallurgical Transactions A19 6. 1988, pp. 1626-1631 [9] Klocke, F.: Fertigungsverfahren 1 - Zerspanung mit geometrisch bestimmter Schneide. 9. Auflage, Springer Verlag, Berlin 2018 Aus Wissenschaft und Forschung 40 Tribologie + Schmierungstechnik · 69. Jahrgang · 1/ 2022 DOI 10.24053/ TuS-2022-0004 It was proven that the investigated materials - in comparison to conventional austenitic stainless steels - can be characterised as difficult-to-machine due to its comparatively high content of nitrogen and carbon. These interstitially dissolved elements increase the material’s mechanical properties. Regarding its machinability, a direct correlation between C+N-content and loadings was proven. The microstructural analysis of the rough turned X30CrMnN18-18 samples revealed that there was no influence of the applied lubricant type. Furthermore, a significant influence of the cutting parameters used can be declared. The comparably increased material’s strength limits the maximum cutting parameters that can be applied under performed conditions. With regard to thermal aspects, the choice between oil and emulsion should be considered according to the targeted application. The coolant type has a specific influence effect on tool loads and achievable surface quality. The thermal loadings occurred less due to the comparatively higher cooling effect of water-based lubricant, especially during roughing under emulsion. In consequence, it was feasible to increase cutting speed and feed for machining X3MnCrNiMoN19-16-5-3 and succeed in the same tool life. In contrast, using oil provides a higher lubrication effect, which has a particular effect in finishing. In comparison to the analogous process under water-based lubricant a higher surface quality was reached. Concerning the resulting surface integrity, there were no differences between the metalworking fluids evaluated. Looking ahead to further investigations, the work hardening potential of the regarded steel grades can be utilised by means of mechanical post-processing in order to influence the surface integrity specifically. By the presented investigations, it was shown that by applying specific cutting parameters, tool types and cooling lubricant, it is possible to turn difficult-to-machine austenitic steels with comparatively reduced productivity and at a high surface quality. Therefore, non-magnetic, austenitic