Fatigue behavior of DIN 1.4307 and DIN 1.4306 stainless steels under high frequency loading

ScienceDirect Available online at www.sciencedirect.com Procedia Structural Integrity 43 (2023) 142–147 2452-3216 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under the responsibility of MSMF10 organizers. 10.1016/j.prostr.2022.12.249 10.1016/j.prostr.2022.12.249 2452-3216 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( https://creativecommons.org/licenses/by-nc-nd/4.0 ) Peer-review under the responsibility of MSMF10 organizers. Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000–000 www.elsevier.com/locate/procedia 2452-3216 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under the responsibility of MSMF10 organizers. 10th International Conference on Materials Structure and Micromechanics of Fracture Fatigue behavior of DIN 1.4307 and DIN 1.4306 stainless steels under high frequency loading Jan Klusáka* , Kamila Kozákováa,b, Michal Jambora, Stanislav Seitla a Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 513/22, 616 00 Brno, Czech Republic b Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69 Brno, Czech Republic Abstract Two stainless steels DIN 1.4307 and DIN 1.4306 were tested by an ultrasonic fatigue loading device under push-pull mode (stress ratio R = -1). Life-time curves were determined in the high and very high cycle fatigue regions. The time dependence of frequency was monitored and evaluated. At the beginning of the tests (up to 1107 cycles), an increase of the frequency was observed, followed by a slow frequency decrease. It relates to changes of microstructure. No failure occurred in the region between 1109 and 11010 cycles. The steel 1.4306 exhibits a higher fatigue life-time than the steel 1.4307. This is caused by the difference in the chemical composition of the two steels, namely by the higher nickel content in the 1.4306 steel. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under the responsibility of MSMF10 organizers. Keywords: very high cyle fatigue; stainless steels; frequency changes; plastic deformation; 1. Introduction Both stainless steels AISI 304L 1.4306 and 1.4307 are chrome-nickel steels with very low content of carbon. Thus, they are highly resistant to intergranular corrosion and suitable for food and chemical industry, in design and architecture as well as for outdoor constructions (Lo et al., 2009). Fatigue properties of these steels are analyzed in this paper, where we have focused on the mechanical properties in high cycle and very high cycle fatigue regions. The study follows our previous investigation of fatigue crack growth in AISI 304L steel (Jambor et al. 2021, Šmíd et al. * Corresponding author. Tel.: +420-532-290-348 E-mail address: [email protected] Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000–000 www.elsevier.com/locate/procedia 2452-3216 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under the responsibility of MSMF10 organizers. 10th International Conference on Materials Structure and Micromechanics of Fracture Fatigue behavior of DIN 1.4307 and DIN 1.4306 stainless steels under high frequency loading Jan Klusáka* , Kamila Kozákováa,b, Michal Jambora, Stanislav Seitla a Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 513/22, 616 00 Brno, Czech Republic b Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69 Brno, Czech Republic Abstract Two stainless steels DIN 1.4307 and DIN 1.4306 were tested by an ultrasonic fatigue loading device under push-pull mode (stress ratio R = -1). Life-time curves were determined in the high and very high cycle fatigue regions. The time dependence of frequency was monitored and evaluated. At the beginning of the tests (up to 1107 cycles), an increase of the frequency was observed, followed by a slow frequency decrease. It relates to changes of microstructure. No failure occurred in the region between 1109 and 11010 cycles. The steel 1.4306 exhibits a higher fatigue life-time than the steel 1.4307. This is caused by the difference in the chemical composition of the two steels, namely by the higher nickel content in the 1.4306 steel. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under the responsibility of MSMF10 organizers. Keywords: very high cyle fatigue; stainless steels; frequency changes; plastic deformation; 1. Introduction Both stainless steels AISI 304L 1.4306 and 1.4307 are chrome-nickel steels with very low content of carbon. Thus, they are highly resistant to intergranular corrosion and suitable for food and chemical industry, in design and architecture as well as for outdoor constructions (Lo et al., 2009). Fatigue properties of these steels are analyzed in this paper, where we have focused on the mechanical properties in high cycle and very high cycle fatigue regions. The study follows our previous investigation of fatigue crack growth in AISI 304L steel (Jambor et al. 2021, Šmíd et al. * Corresponding author. Tel.: +420-532-290-348 E-mail address: [email protected] 2 Author name / Structural Integrity Procedia 00 (2022) 000–000 2021, Trávníček et al. 2021, Seitl et al. 2022) and a study of construction steels S355 (Klusák et al. 2021, Seitl et al. 2018, Seitl et al. 2018a) Ultrasonic testing device was used to generate high frequency loading at 20 kHz. Thus, we could reach high number of cycles in real time. Fully reversed push-pull loading cycle with the stress ratio R = -1 was applied. Nomenclature A Coefficient of Basquin’s law B Coefficient of Basquin’s law Ed Dynamic modulus of elasticity [GPa] fn Intrinsic frequency of the specimen [Hz] R Stress ratio Sf Stress factor [MPa/m]  Poisson’s ratio [-]  Density [kg/m3] σf Fatigue limit 2. Experimental testing Fatigue lifetime of the studied steels is described by S-N curves, that were obtained from tests of cyclic loading at ultrasonic frequency. The specimens were designed to exhibit their intrinsic frequency close to the frequency of the loading device. Firstly, basic material properties had to be determined. Dynamic modulus of elasticity was ascertained by means of an impulse excitation technique, and together with the Poisson’s ratio and density, the properties are in Table 1. Dynamic modulus, Poisson’s ratio and density of materials enter to the modal analysis performed in the finite element software ANSYS. Thus, the dimensions and the intrinsic frequency of the specimens were adjusted and calculated, see Table 1 and Fig. 1. Finally, the stress factor Sf of the specimens were calculated by the harmonic analysis, and they are also stated in Table 1. To observe the materials microstructure, the fatigue samples were cut longitudinally. Specimens for the microstructure characterization were ground using sandpaper followed by electrolytic polishing in solution of 600 ml methanol, 360 ml ethylene glycol monobuthyl ether and 60 ml perchloric acid. Using Tescan Lyra 3 XMU scanning electron microscope, the gauge lengths and the specimens' heads were observed. The deformation structures were observed using the electron channeling contrast imaging technique (ECCI), while the microstructures in as-delivered conditions were characterized using electron back-scattered diffraction (EBSD). Microstructures of both experimental materials are shown in Fig. 2. Both materials exhibited similar microstructure with equiaxed austenitic grains, containing many annealing twins and delta ferrite stringers along the rolling direction. Area-weighted mean grain size was 59.78 μm for 1.4306 steel and 57.92 μm for 1.4307 steel. No preferential crystallographic orientation was recorded. Table 1. Properties of the materials and the stress factors of the test specimens. Material Dynamic modulus Ed [GPa] Poisson’s ratio  [-] Density  [kg/m3] Intrinsic frequency fn [Hz] Stress factor Sf [MPa/m] 304L/4306 199 0.3 7899 20005 26.3 304L/4307 198 0.3 7884 19974 26.2 After machining, the test samples were polished electrolytically to get fine surface without defects and traces of machining. High frequency measurements are performed at resonant frequency of 20 kHz. Cyclic loading of austenitic steels leads to high heat generation. For this reason, the specimens must be efficiently cooled. In our case, cooling by water in a closed circuit was used, see Fig. 3. Jan Klusák et al. / Procedia Structural Integrity 43 (2023) 142–147 143 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000–000 www.elsevier.com/locate/procedia 2452-3216 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under the responsibility of MSMF10 organizers. 10th International Conference on Materials Structure and Micromechanics of Fracture Fatigue behavior of DIN 1.4307 and DIN 1.4306 stainless steels under high frequency loading Jan Klusáka* , Kamila Kozákováa,b, Michal Jambora, Stanislav Seitla a Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 513/22, 616 00 Brno, Czech Republic b Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69 Brno, Czech Republic Abstract Two stainless steels DIN 1.4307 and DIN 1.4306 were tested by an ultrasonic fatigue loading device under push-pull mode (stress ratio R = -1). Life-time curves were determined in the high and very high cycle fatigue regions. The time dependence of frequency was monitored and evaluated. At the beginning of the tests (up to 1107 cycles), an increase of the frequency was observed, followed by a slow frequency decrease. It relates to changes of microstructure. No failure occurred in the region between 1109 and 11010 cycles. The steel 1.4306 exhibits a higher fatigue life-time than the steel 1.4307. This is caused by the difference in the chemical composition of the two steels, namely by the higher nickel content in the 1.4306 steel. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under the responsibility of MSMF10 organizers. Keywords: very high cyle fatigue; stainless steels; frequency changes; plastic deformation; 1. Introduction Both stainless steels AISI 304L 1.4306 and 1.4307 are chrome-nickel steels with very low content of carbon. Thus, they are highly resistant to intergranular corrosion and suitable for food and chemical industry, in design and architecture as well as for outdoor constructions (Lo et al., 2009). Fatigue properties of these steels are analyzed in this paper, where we have focused on the mechanical properties in high cycle and very high cycle fatigue regions. The study follows our previous investigation of fatigue crack growth in AISI 304L steel (Jambor et al. 2021, Šmíd et al. * Corresponding author. Tel.: +420-532-290-348 E-mail address: [email protected] Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000–000 www.elsevier.com/locate/procedia 2452-3216 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under the responsibility of MSMF10 organizers. 10th International Conference on Materials Structure and Micromechanics of Fracture Fatigue behavior of DIN 1.4307 and DIN 1.4306 stainless steels under high frequency loading Jan Klusáka* , Kamila Kozákováa,b, Michal Jambora, Stanislav Seitla a Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 513/22, 616 00 Brno, Czech Republic b Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69 Brno, Czech Republic Abstract Two stainless steels DIN 1.4307 and DIN 1.4306 were tested by an ultrasonic fatigue loading device under push-pull mode (stress ratio R = -1). Life-time curves were determined in the high and very high cycle fatigue regions. The time dependence of frequency was monitored and evaluated. At the beginning of the tests (up to 1107 cycles), an increase of the frequency was observed, followed by a slow frequency decrease. It relates to changes of microstructure. No failure occurred in the region between 1109 and 11010 cycles. The steel 1.4306 exhibits a higher fatigue life-time than the steel 1.4307. This is caused by the difference in the chemical composition of the two steels, namely by the higher nickel content in the 1.4306 steel. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under the responsibility of MSMF10 organizers. Keywords: very high cyle fatigue; stainless steels; frequency changes; plastic deformation; 1. Introduction Both stainless steels AISI 304L 1.4306 and 1.4307 are chrome-nickel steels with very low content of carbon. Thus, they are highly resistant to intergranular corrosion and suitable for food and chemical industry, in design and architecture as well as for outdoor constructions (Lo et al., 2009). Fatigue properties of these steels are analyzed in this paper, where we have focused on the mechanical properties in high cycle and very high cycle fatigue regions. The study follows our previous investigation of fatigue crack growth in AISI 304L steel (Jambor et al. 2021, Šmíd et al. * Corresponding author. Tel.: +420-532-290-348 E-mail address: [email protected] 2 Author name / Structural Integrity Procedia 00 (2022) 000–000 2021, Trávníček et al. 2021, Seitl et al. 2022) and a study of construction steels S355 (Klusák et al. 2021, Seitl et al. 2018, Seitl et al. 2018a) Ultrasonic testing device was used to generate high frequency loading at 20 kHz. Thus, we could reach high number of cycles in real time. Fully reversed push-pull loading cycle with the stress ratio R = -1 was applied. Nomenclature A Coefficient of Basquin’s law B Coefficient of Basquin’s law Ed Dynamic modulus of elasticity [GPa] fn Intrinsic frequency of the specimen [Hz] R Stress ratio Sf Stress factor [MPa/m]  Poisson’s ratio [-]  Density [kg/m3] σf Fatigue limit 2. Experimental testing Fatigue lifetime of the studied steels is described by S-N curves, that were obtained from tests of cyclic loading at ultrasonic frequency. The specimens were designed to exhibit their intrinsic frequency close to the frequency of the loading device. Firstly, basic material properties had to be determined. Dynamic modulus of elasticity was ascertained by means of an impulse excitation technique, and together with the Poisson’s ratio and density, the properties are in Table 1. Dynamic modulus, Poisson’s ratio and density of materials enter to the modal analysis performed in the finite element software ANSYS. Thus, the dimensions and the intrinsic frequency of the specimens were adjusted and calculated, see Table 1 and Fig. 1. Finally, the stress factor Sf of the specimens were calculated by the harmonic analysis, and they are also stated in Table 1. To observe the materials microstructure, the fatigue samples were cut longitudinally. Specimens for the microstructure characterization were ground using sandpaper followed by electrolytic polishing in solution of 600 ml methanol, 360 ml ethylene glycol monobuthyl ether and 60 ml perchloric acid. Using Tescan Lyra 3 XMU scanning electron microscope, the gauge lengths and the specimens' heads were observed. The deformation structures were observed using the electron channeling contrast imaging technique (ECCI), while the microstructures in as-delivered conditions were characterized using electron back-scattered diffraction (EBSD). Microstructures of both experimental materials are shown in Fig. 2. Both materials exhibited similar microstructure with equiaxed austenitic grains, containing many annealing twins and delta ferrite stringers along the rolling direction. Area-weighted mean grain size was 59.78 μm for 1.4306 steel and 57.92 μm for 1.4307 steel. No preferential crystallographic orientation was recorded. Table 1. Properties of the materials and the stress factors of the test specimens. Material Dynamic modulus E d [GPa] Poisson’s ratio  [-] Density  [kg/m3] Intrinsic frequency f n [Hz] Stress factor S f [MPa/m] 304L/4306 199 0.3 7899 20005 26.3 304L/4307 198 0.3 7884 19974 26.2 After machining, the test samples were polished electrolytically to get fine surface without defects and traces of machining. High frequency measurements are performed at resonant frequency of 20 kHz. Cyclic loading of austenitic steels leads to high heat generation. For this reason, the specimens must be efficiently cooled. In our case, cooling by water in a closed circuit was used, see Fig. 3. 144 Jan Klusák et al. / Procedia Structural Integrity 43 (2023) 142–147 Author name / Structural Integrity Procedia 00 (2022) 000–000 3 Fig. 1. Shape and dimensions of the test samples. Fig. 2. Microstructures of experimental materials. Fig. 3. Water cooling of the specimen during testing. 4 Author name / Structural Integrity Procedia 00 (2022) 000–000 3. Results of fatigue tests 3.1. Fatigue life curves The fatigue lifetime of the studied steels is presented in S-N curves, see Fig. 4. The results of fatigue life of both steels are comparable, where the steel 1.4306 exhibits slightly higher numbers of cycles to fracture than 1.4307. The main difference between both steels is the presence of two step S-N curve in the case of 1.4306 steel. It is apparent that the life-time of the specimens loaded by 270 and 280 MPa failed in two regions: below 1106 cycles (high cycle fatigue region - HCF) and between 1107 and 1109 cycles (very high cycle fatigue region - VHCF). In the case of 1.4306 steel, no failure was observed in VHCF region. The fatigue limit was determined from the samples capable to withstand 11010 loading cycles without failure. The slope of the curve in high cycle fatigue region (below 1107) can be described by the Basquin’s law in the form: , (1) where the coefficients A and B of the relation (1) are in the Table 2. Table 2. Coefficients of the Basquin’s law relation and the fatigue limit. Material A B σf [MPa] 304L/4306 750 -0.078 255 304L/4307 553 -0.055 245 3.2. Frequency dependence During fatigue tests, frequency was monitored and evaluated. We have observed frequency changes related to changes of stiffness of the materials tested. During the initial phases of the tests an increase of frequency was observed with the following very slow frequency decrease. The initial growth lasted about 10 million cycles, while the decrease in frequency lasted billions of cycles. The frequency dependence on the number of cycles in logarithmic scale is shown in Fig. 5. There are records of tests of the 1.4307 specimens No. 09 and 10, run outs at 240 and 245 MPa, respectively. Fig. 4. S-N curves of fatigue data measured on steels 304L/4306 and 304L/4307. Jan Klusák et al. / Procedia Structural Integrity 43 (2023) 142–147 145 Author name / Structural Integrity Procedia 00 (2022) 000–000 3 Fig. 1. Shape and dimensions of the test samples. Fig. 2. Microstructures of experimental materials. Fig. 3. Water cooling of the specimen during testing. 4 Author name / Structural Integrity Procedia 00 (2022) 000–000 3. Results of fatigue tests 3.1. Fatigue life curves The fatigue lifetime of the studied steels is presented in S-N curves, see Fig. 4. The results of fatigue life of both steels are comparable, where the steel 1.4306 exhibits slightly higher numbers of cycles to fracture than 1.4307. The main difference between both steels is the presence of two step S-N curve in the case of 1.4306 steel. It is apparent that the life-time of the specimens loaded by 270 and 280 MPa failed in two regions: below 1106 cycles (high cycle fatigue region - HCF) and between 1107 and 1109 cycles (very high cycle fatigue region - VHCF). In the case of 1.4306 steel, no failure was observed in VHCF region. The fatigue limit was determined from the samples capable to withstand 11010 loading cycles without failure. The slope of the curve in high cycle fatigue region (below 1107) can be described by the Basquin’s law in the form: , (1) where the coefficients A and B of the relation (1) are in the Table 2. Table 2. Coefficients of the Basquin’s law relation and the fatigue limit. Material A B σ f [MPa] 304L/4306 750 -0.078 255 304L/4307 553 -0.055 245 3.2. Frequency dependence During fatigue tests, frequency was monitored and evaluated. We have observed frequency changes related to changes of stiffness of the materials tested. During the initial phases of the tests an increase of frequency was observed with the following very slow frequency decrease. The initial growth lasted about 10 million cycles, while the decrease in frequency lasted billions of cycles. The frequency dependence on the number of cycles in logarithmic scale is shown in Fig. 5. There are records of tests of the 1.4307 specimens No. 09 and 10, run outs at 240 and 245 MPa, respectively. Fig. 4. S-N curves of fatigue data measured on steels 304L/4306 and 304L/4307. 146 Jan Klusák et al. / Procedia Structural Integrity 43 (2023) 142–147 Author name / Structural Integrity Procedia 00 (2022) 000–000 5 Fig. 5. Frequency dependence of 304L/4307 specimens No. 9 and 10. 3.3. Microstructure evolution Applied cyclic loading results in formation of deformation structures. To accommodate plastic strain, dislocations are forming deformation structures, characteristic for FCC metals with low stacking fault energy. Typically, at the beginning of the fatigue life, the dislocation density is increased, resulting in the steep stress amplitude increase. With further cycling, the plastic deformation starts to localize, which is accompanied by a decrease in stress amplitude. At later stages of the fatigue life, a plateau in the stress amplitude is reached as the plastic deformation almost exclusively occurs within formed slip bands, where the formation of the strain-induced martensite can occur, Tamura (1982), Müller-Bollenhagen (2010). Extensive formation of the strain-induced martensite can result in a further increase of the stress amplitude, at the end of the fatigue life. Character and the magnitude of these changes strongly depends on the applied load amplitude. A more detailed study of the microstructure evolution in 304L steel during cyclic loading can be found in Jambor et al. 2021, and Šmíd et al. 2021. The changes in the resonance frequency observed during gigacycle fatigue tests are analogical to the changes of stress amplitude observed during low frequency loading. The initial increase in frequency is probably accompanied by an increase in temperature, as also shown in MüllerBollenhagen (2010). Note that in our case the temperature was not measured due to the water cooling. Figure 6 shows ECCI micrographs of the specimen from 1.4306 steel, after reaching 11010 cycles without failure. There is clearly visible high dislocation density within grains due to cyclic loading. Dislocations are arranged in the bands along {111} planes. Moreover, presence of the deformation induced α’ martensite was revealed in the structure. Fig. 6. Micrograph of specimen from 1.4306 steel after reaching of 1E10 cycles without failure. ECCI revealed strong dislocation activity, accompanied by formation of the strain induced α’ martensite. Loading direction is oriented vertically. 6 Author name / Structural Integrity Procedia 00 (2022) 000–000 4. Conclusions High frequency fatigue tests were performed on stainless steels DIN 1.4307 and DIN 1.4306. Fatigue lifetime was analyzed, where slightly higher number of cycles to fracture was observed for 1.4306 steel. The same steel exhibited higher fatigue limit. Frequency monitoring have shown the steep increase of the resonance frequency during 10 million of cycles (the first 8 minutes of the test) followed by the slow frequency decrease. This behavior is analogical to the changes of stress amplitudes during low frequency loading, and it is connected to dislocation density increase and the localization of plastic deformation. Knowledge of fatigue response of the studied stainless steels can contribute to more reliable design of steel structures. Acknowledgement Authors are grateful for the support of the research through the project Influence of material properties of stainless steels on reliability of bridge structures, project No. 20-00761S of the Czech Science Foundation. References Jambor M., Vojtek T., Pokorný P., Šmíd M. (2021) Effect of Solution Annealing on Fatigue Crack Propagation in the AISI 304L TRIP Steel. Materials 14, 1331 Kala Z., Omishore A., Seitl S., Krejsa M., Kala J. (2017) The effect of skewness and kurtosis on the probability evaluation of fatigue limit states (2017) International Journal of Mechanics, 11, 166–175 Klusák J., Horník V., Lesiuk G., Seitl S.: Comparison of highand low-frequency fatigue properties of structural steels S355J0 and S355J2. Fatigue Fract. Eng. Mater. Struct. 44 (2021) 3202-3213 Krejsa, M., Brozovsky, J., Lehner, P., Seitl, S. Kala, Z. (2018) Stochastic analysis for short edge cracks under selected loads”, AIP Conference Proceedings 1978, 150006. Lo, K.H., Shek, C.H. and Lai, J.K.L., 2009, Recent developments in stainless steels, Mater. Sci. Eng. R Rep., 65, pp. 39-104. Müller-Bollenhagen, C., Zimmermann, M., Christ, H.-J., 2010. Very High Cycle Fatigue Behaviour of Austenitic Stainless Steel and the Effect of Strain-Induced Martensite. Int. J Fatigue 32, 936–942. Seitl, S., Pokorný, P., Klusák, J., Duda, S., Lesiuk, G. (2022). Effect of Specimen Thickness on Fatigue Crack Growth Resistance in Paris Region in AISI 304 STEEL Fatigue and Fracture of Materials and Structures. Structural Integrity, Vol. 24. Springer Seitl S., Miarka P., Klusák J., Fintová S., Kunz L. (2018), Comparison of the fatigue crack propagation rates in S355 J0 and S355 J2 steel grades, Key Engineering Materials, 784, 91–96 Seitl S., Miarka P., Klusák J., Kala Z., Krejsa M., Blasón S., Canteli A.F. (2018a) Evaluation of fatigue properties of S355 J0 steel using ProFatigue and ProPagation software, Procedia Structural Integrity, 13, 1494–1501 Šmíd, M., Kuběna, I., Jambor, M., Fintová, S., 2021, Effect of solution annealing on low cycle fatigue of 304L stainless steel, Materials Science and Engineering: A, Volume 824, 141807. Trávníček L., Kuběna I., Mazánová V., Vojtek T., Polák J., Hutař P., Šmíd M. (2021) Advantageous Description of Short Fatigue Crack Growth Rates in Austenitic Stainless Steels with Distinct Properties. Metals 11, 475 Tamura, I., 1982. Deformation-Induced Martensitic Transformation and Transformation-Induced Plasticity in Steels. Metal Sci. 16, 245–253. Jan Klusák et al. / Procedia Structural Integrity 43 (2023) 142–147 147 Author name / Structural Integrity Procedia 00 (2022) 000–000 5 Fig. 5. Frequency dependence of 304L/4307 specimens No. 9 and 10. 3.3. Microstructure evolution Applied cyclic loading results in formation of deformation structures. To accommodate plastic strain, dislocations are forming deformation structures, characteristic for FCC metals with low stacking fault energy. Typically, at the beginning of the fatigue life, the dislocation density is increased, resulting in the steep stress amplitude increase. With further cycling, the plastic deformation starts to localize, which is accompanied by a decrease in stress amplitude. At later stages of the fatigue life, a plateau in the stress amplitude is reached as the plastic deformation almost exclusively occurs within formed slip bands, where the formation of the strain-induced martensite can occur, Tamura (1982), Müller-Bollenhagen (2010). Extensive formation of the strain-induced martensite can result in a further increase of the stress amplitude, at the end of the fatigue life. Character and the magnitude of these changes strongly depends on the applied load amplitude. A more detailed study of the microstructure evolution in 304L steel during cyclic loading can be found in Jambor et al. 2021, and Šmíd et al. 2021. The changes in the resonance frequency observed during gigacycle fatigue tests are analogical to the changes of stress amplitude observed during low frequency loading. The initial increase in frequency is probably accompanied by an increase in temperature, as also shown in MüllerBollenhagen (2010). Note that in our case the temperature was not measured due to the water cooling. Figure 6 shows ECCI micrographs of the specimen from 1.4306 steel, after reaching 11010 cycles without failure. There is clearly visible high dislocation density within grains due to cyclic loading. Dislocations are arranged in the bands along {111} planes. Moreover, presence of the deformation induced α’ martensite was revealed in the structure. Fig. 6. Micrograph of specimen from 1.4306 steel after reaching of 1E10 cycles without failure. ECCI revealed strong dislocation activity, accompanied by formation of the strain induced α’ martensite. Loading direction is oriented vertically. 6 Author name / Structural Integrity Procedia 00 (2022) 000–000 4. Conclusions High frequency fatigue tests were performed on stainless steels DIN 1.4307 and DIN 1.4306. Fatigue lifetime was analyzed, where slightly higher number of cycles to fracture was observed for 1.4306 steel. The same steel exhibited higher fatigue limit. Frequency monitoring have shown the steep increase of the resonance frequency during 10 million of cycles (the first 8 minutes of the test) followed by the slow frequency decrease. This behavior is analogical to the changes of stress amplitudes during low frequency loading, and it is connected to dislocation density increase and the localization of plastic deformation. Knowledge of fatigue response of the studied stainless steels can contribute to more reliable design of steel structures. Acknowledgement Authors are grateful for the support of the research through the project Influence of material properties of stainless steels on reliability of bridge structures, project No. 20-00761S of the Czech Science Foundation. References Jambor M., Vojtek T., Pokorný P., Šmíd M. (2021) Effect of Solution Annealing on Fatigue Crack Propagation in the AISI 304L TRIP Steel. Materials 14, 1331 Kala Z., Omishore A., Seitl S., Krejsa M., Kala J. (2017) The effect of skewness and kurtosis on the probability evaluation of fatigue limit states (2017) International Journal of Mechanics, 11, 166–175 Klusák J., Horník V., Lesiuk G., Seitl S.: Comparison of highand low-frequency fatigue properties of structural steels S355J0 and S355J2. Fatigue Fract. Eng. Mater. Struct. 44 (2021) 3202-3213 Krejsa, M., Brozovsky, J., Lehner, P., Seitl, S. Kala, Z. (2018) Stochastic analysis for short edge cracks under selected loads”, AIP Conference Proceedings 1978, 150006. Lo, K.H., Shek, C.H. and Lai, J.K.L., 2009, Recent developments in stainless steels, Mater. Sci. Eng. R Rep., 65, pp. 39-104. Müller-Bollenhagen, C., Zimmermann, M., Christ, H.-J., 2010. Very High Cycle Fatigue Behaviour of Austenitic Stainless Steel and the Effect of Strain-Induced Martensite. Int. J Fatigue 32, 936–942. Seitl, S., Pokorný, P., Klusák, J., Duda, S., Lesiuk, G. (2022). Effect of Specimen Thickness on Fatigue Crack Growth Resistance in Paris Region in AISI 304 STEEL Fatigue and Fracture of Materials and Structures. Structural Integrity, Vol. 24. Springer Seitl S., Miarka P., Klusák J., Fintová S., Kunz L. (2018), Comparison of the fatigue crack propagation rates in S355 J0 and S355 J2 steel grades, Key Engineering Materials, 784, 91–96 Seitl S., Miarka P., Klusák J., Kala Z., Krejsa M., Blasón S., Canteli A.F. 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