In the paper, two grades of high-manganese steels with aluminum after a thermos - mechanical treatment were studied. Steel grades with an austenitic - ferritic structure with various contents of carbon, manganese and aluminum were selected for the studies. The main goal of the work was to define the most preferable parameters of heat treatment, rolling finish temperature and cooling rate in order to obtain the most favorable strength - ductility relation for the examined steels. The structural analysis was carried out using optical microscopy techniques. The evaluation of strength properties was carried out based on the results of static tensile test of steel sheets

A. Śmiglewicz

M. Jabłońska

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A study of mechanical properties of high manganese steels after different rolling conditions

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619METALURGIJA 54 (2015) 4, 619-622M. JABŁOŃSKA, A. ŚMIGLEWICZA STUDY OF MECHANICAL PROPERTIES OF HIGH MANGANESE STEELS AFTER DIFFERENT ROLLING CONDITIONSReceived – Primljeno: 2014-08-30Accepted – Prihvaćeno: 2015-02-12Original Scientific Paper – Izvorni znanstveni ISSN 0543-5846METABK 54(4) 619-622 (2015)UDC – UDK 669.74.15:621.771:620.17.18=111M. Jabłońska, A. Śmiglewicz, Silesian University of Technology, Fac-ulty of Materials Science and Metallurgy, Katowice, PolandIn the paper, two grades of high-manganese steels with aluminum after a thermos - mechanical treatment were studied. Steel grades with an austenitic - ferritic structure with various contents of carbon, manganese and alu-minum were selected for the studies. The main goal of the work was to define the most preferable parameters of heat treatment, rolling finish temperature and cooling rate in order to obtain the most favorable strength - ductility relation for the examined steels. The structural analysis was carried out using optical microscopy techniques. The evaluation of strength properties was carried out based on the results of static tensile test of steel sheets.Key words: high manganese steels, rolling, mechanical properties, microstructureINTRODUCTIONHigh-strength manganese-aluminum austenitic and austenitic-ferritic steels have a significant application potential as structural elements in automotive and rail-way industries because of their perfect combination of high mechanical properties and good plasticity. Their development and commercialization, as well as applica-tion as construction materials depend on improvement of their casting properties and deformability under con-ditions of plastic working. This may be obtained by a proper selection of chemical composition, modification of the initial microstructure, grain refining, and applica-tion of proper parameters of the thermo-mechanical treatment (TMT), ensuring an optimal combination of strength and plastic properties [1 - 9].In conventional steel grades, as well as in alloys for automotive industry, high strength properties may be obtained, however at the cost of significantly de-creased plastic properties. The new high - manganese-aluminum steels included into AHSS (advanced high strength) and UHSS (ultra high strength) groups are an exempt from this rule, allowing for a reduction in the vehicle weight, and thereby a reduction in fuel con-sumption. In consequence, many national and interna-tional research centers are working strenuously on ap-plication of these materials in automotive industry and railway engineering [4 - 10]. Integration of high strength properties and a good formability, ensuring high absorption of energy by structural components, enables application of these new high - manganese steels in elements critical for the safety, and replace-ment of dual phase (DP) steels. The newest high-man-ganese steels, such as transformation induced plastic-ity (TRIP), twinning induced plasticity (TWIP), or micro bands induced plasticity (MBIP), are different than conventional steels by their contents of alloying elements deciding about the microstructure stability, stacking fault energy (SFE) value and strength proper-ties [10 - 16]. Especially beneficial combination of properties in this group of AHSS steels have consist-ently two - phase, on which work has not been carried out. TEST MATERIALS AND METHODSHigh-manganese steels were the material for studies. Steel 1: Fe – 15 wt.%, Mn – 4 wt.%, Al – 0.1 wt.% C; Steel 2: Fe – 30 wt.%, Mn – 9 wt.%, Al – 0.65 wt.% C. The steels were prepared in Institute for Ferrous Metal-lurgy, Gliwice, Poland, in a vacuum induction furnace from Balzers. The casting process was carried out under an argon atmosphere, via a hot tundish, to a water-cooled copper concast mould properly prepared earlier. The con-cast mould feedstock was rolled into square section with a dimension of 45 mm, then into flat bars with a thickness of 11 mm and flat bars with a thickness of 3 mm. The flat bars with a thickness of 11 mm were rolled in the Institute of Modelling and Control of Forming Processes in Os-trava’s VSB-TU, using a laboratory rolling line with a furnace and roller system simulating. The line includes two duo- type reversible rolling stands allowing for a change in the rolling direction in 0,1 sec. The flat bars were rolled at a varied rolling finish temperature, using water and air - cooling. The data including the tempera-tures between the finishing roll passes and cooling vari-ants may be found in Table 1.Mechanical properties of the studied steels were de-termined using a static tensile test on a Zwic/Roell Z100 testing machine. The structural analysis was carried out using optical microscopy techniques.620M. JABŁOŃSKA et al.: A STUDY OF MECHANICAL PROPERTIES OF HIGH MANGANESE STEELS AFTER DIFFERENT... METALURGIJA 54 (2015) 4, 619-622RESULTS AND DISCUSSIONThe studies was carried out on two grades of high-manganese steels with an austenitic-ferritic structure with various contents of carbon, manganese and alu-minum. The structural analysis was carried out on sam-ples cut out according to the rolling direction. Elongated ferrite grains were a characteristic feature of the ob-served austenitic-ferritic structures, resulting from low recrystallization propensity of the ferrite (Figures 1, 2).The results of the static tensile test were shown in the form of stress - strain curves for the samples having the same rolling finish temperature and cooled with the same rate. Based on Figures 3 - 6, the highest strength properties were obtained for the steel 2 - 1 100 MPa with the rolling finish temperature of 800 ºC while cooled in air, however ductility of the steel amounted to 35 %. The highest ductility, irrespective of the rolling finish temperature and cooling medium, was exhibited by the steel 1 - ca. 65 %, with the tensile strength in the range of 800 - 850 MPa.Based on the curves obtained while the static tensile test, proof stress R0,2, tensile strength Rm, as well as Table 1  Temperature and cooling rate variants for flat bars with a thickness of 3 mmTRated / °CTbefore the 5th roll pass / °CTbetween the 5th and 6th roll pass/ °CTafter the 6th roll pass / °C cool-ingSteel 1900 893 866 845 water800 798 790 768 water900 911 887 868 air800 816 788 773 airSteel 2900 911 885 872 water800 809 792 783 water900 913 886 872 air800 816 796 788 airFigure 1  Structure of the Fe – 15 wt.%, Mn – 4 wt.%, Al – 0,1 wt.% C steel rolled in the temperature range of 1 100 ºC - 800 ºC cooled in airFigure 2  Structure of the Fe – 30 wt.%, Mn – 9 wt.%, Al – 0,65 wt.% C steel rolled in the temperature range of 1 100 ºC - 800 ºC cooled in airFigure 3  Stress-strain curve for the samples rolled in the temperature range of 1 100 ºC - 900 ºC, cooled in waterFigure 4  Stress-strain curve for the samples rolled in the temperature range of 1 100 ºC - 800 ºC cooled in waterFigure 5  Stress-strain curve for the samples rolled in the temperature range of 1 100 ºC - 900 ºC cooled in airStress / MPaElongation / %Stress / MPaElongation / %Stress / MPaElongation / %Steel 2Steel 1Steel 2Steel 1Steel 2Steel 1621M. JABŁOŃSKA et al.: A STUDY OF MECHANICAL PROPERTIES OF HIGH MANGANESE STEELS AFTER DIFFERENT...METALURGIJA 54 (2015) 4, 619-622tents in the steel increases the strength properties, while it has no unequivocal influence on the ductility and im-pact resistance.Comparing the Rm×A indices for the examined steels and with the literature data [2, 17], it may be ascertained that the steel 1 achieves the highest Rm×A relation (Fig-ure 7) thanks to its high ductility at the tensile strength of ca. 800 MPa. The steel 2 exhibited a Rm×A relation on the level of 40 000 MPa × %.CONCLUSIONSIn the paper, samples of high-manganese steels with aluminum after a thermo-mechanical treatment were studied. Steel grades with an austenitic-ferritic structure with various contents of carbon, manganese and alu-minum were selected for the studies. The main goal of the work was to evaluate quality of the studied steels and to determine the most preferable parameters of heat treatment, rolling finish temperature and cooling rate in order to obtain the most favorable strength-ductility re-lation for the examined steels. Structural elements made of MnAl steel may achieve a higher quality then the ele-ments made of conventional steels of DP, TRIP, IF types, thanks an enhanced strengthening effect during TMT. In order to achieve this goal, post - TMT treatment with varied cooling conditions were used (Table 1).Based on the investigations carried out, an influence of chemical composition on strength-plasticity relations for the studied high-manganese steels was ascertained.It was shown that the final properties of an MnAl steel may be fashioned using TMT. A decrease in the rolling finish temperature improves mechanical proper-ties, however it decreases plasticity of the steel.No significant influence of changes in cooling rate on the strength properties and plasticity of steel sheets made of the studied steels was ascertained. Thus, a good quality of the products may be achieved by cooling the sheets in air. Simplification of the technology leads to a reduction in costs of the manufactured component parts.AcknowledgmentsWork conducted within the Research and Develop-ment Project of National Centre for Research and Devel-opment No. 15 0012 06 as well as BK-220/RM3/2015. elongation A5 were determined. The results are gathered in Table 2.Table 2  Mechanical properties obtained after different conditions of rolling for flat bars with a thickness of 3 mmT rolling fi nish / ˚CR0,2 / MPaRm/ MPaR0,2\Rm A5 / %Rm × A5/ MPa × %Steel 1 900water551 817 0,67 66 53 922800water604 860 0,70 65 55 900900air529 799 0,66 67 53 533800air599 845 0,71 63 53 235Steel 2 900water964 1 087 0,89 36 39 132800water990 1 075 0,92 33 35 475900air929 1 063 0,87 37 39 331800air999 1 106 0,90 36 39 816The Fe – 15 wt.%, Mn – 4 wt.%, Al – 0,1 wt.% C steel obtains higher mechanical properties after cooling in water; reduction of the rolling finish temperature has a similar effect. The R0,2/Rm ratio is significantly lower for samples cooled in air. Ductility of this steel is higher in case of samples cooled in water, while the influence of the band temperature after the last rolling pass on ductility cannot be ascertained unequivocally. The re-duction in the rolling finish temperature is accompanied by an increase in the strength properties.A high R0,2/Rm ratio after TMT allows for using the element for car body parts requiring a high rigidity. Ele-ments with a lower R0,2/Rm may be used in the zones enhancing the safety and absorbing energy during a col-lision. The lowest ratio of the stress proof and the ten-sile strength R0,2/Rm is exhibited by the Fe – 15 wt.%, Mn – 4 wt.%, Al – 0,1 wt.% C steel, while the highest, amounting to 0,92 – by the Fe – 30 wt.%, Mn – 9 wt.%, Al – 0,65 wt.% C steel. Based on the determined strength properties and ductility, one may ascertain that an increase in carbon, manganese and aluminum con-Figure 6  Stress-strain curve for the samples rolled in the temperature range of 1 100 ºC - 800 ºC cooled in airStress / MPaElongation / %Figure 7  Classification of steels in respect of Rm × A, MPa × % index, with the studied steels marked in black [prepared based on 17].Steel 2Steel 1622M. JABŁOŃSKA et al.: A STUDY OF MECHANICAL PROPERTIES OF HIGH MANGANESE STEELS AFTER DIFFERENT... METALURGIJA 54 (2015) 4, 619-622REFERENCES[1] A. S Hamada, Manufacturing, mechanical properties and corrosion behaviour of High-Mn TWIP steels, Universita-tis Ouluensis (2007), 1 - 56.[2] D. Kuc, E. Hadasik, G. Niewielski, I. Schindler, E. Mazan-cová, S. Rusz, P. Kawulok, Structural and mechanical pro-perties of laboratory rolled steels high-alloyed with man-ganese and aluminum, Archives of Civil and Mechanical Engineering 12 (2012), 312 - 317.[3] S. Lasek, E. Mazancova, Influence of thermal treatment on structure and corrosion properties of high manganese tri-plex steels, Metalurgija 52 (2013) 4, 441 - 444.[4] E. Mazancova, I. Ruziak, I. Schindler, Influence of rolling conditions and aging process on mechanical properties of high manganese steels, Archives of Civil and Mechanical Engineering 12 (2012), 142 - 147.[5] S. Wiewiórowska, Analysis of the Influence of Drawing Process Parameters on the Mechanical Properties of TRIP-Structure Steel Wires Arch. of Metal. And Mater. 58 (2013) 2, 573 - 578.[6] M. Jabłońska, A. Śmiglewicz, Analysis of substructure of high - Mn steels in the context of dominant stress mecha-nism, Defect and Diffusion Forum 334-335 (2013), 177 - 181[7] W. Bleck, K. Phiuon: Effects of Microalloying in Multi Phase Steels for Car Body Manufacture, 14. Sӓsiche Fachtagung Umformtechnik, Werkstoffe und Komponen-ten für Fahrzeugen, Freiberg (2007), 38 - 55.[8] M. Jabłońska, A. Śmiglewicz, G. Niewielski, M. Hetmańczyk, Heat treatment of high manganese type X57MnAl27-5 austenitic steel, Technologies and Proper-ties of Modern Utilised Materials, Book Series: IOP Con-ference Series - Materials Science and Engineering 22 (2011), 1 - 5.[9] A. I. Z. Farahata, O. Hamedb, A. El-Sisi, M. Hawash, Ef-fect of hot forging and Mn content on austenitic stainless steel containing high carbon, Materials Science and Engi-neering A 530 (2011) 98 - 106.[10] M.B. Jabłońska, Mechanical properties and fractographic analysis of high manganese steels after dynamic deforma-tion tests, Arch. of Metal. And Mater. 59 (2014) 3, 1193 - 1197.[11] A. Kokosza, J. Pacyna, Formation of medium carbon trip steel microstructure during annealing in the intercritical temperature range, Arch. of Metal. And Mater. 59 (2014) 3, 1017 - 1022.[12] A. Grajcar, M. Różanski, M. Kaminska, B. Grzegorczyk, Study on non - metallic inclusions in laser - welded TRIP - aided Nb-microalloyed steel, Arch. of Metal. And Mater. 59 (2014) 3, 1164 - 1169.[13] W. S. Yang, C. M. Wan, The influence of aluminum con-tent to the stacking fault energy in Fe –Mn - AI -C alloy system, Journal of Materials Science 25, (1990), 1 - 3.[14] S. Wiewiórowska, Z. Muskalski, The influence of the partial single reduction on mechanical properties wires made from trip steel with 0,43 % C, Metalurgija 54 (2014), 184 - 186.[15] R. Kuziak, R. Kawalla, S. Waengler, Advanced high strength steels for automotive industry, Archives of Civil and Mechanical Engineering 2 (2008), 103 - 118.[16] L. Chen, Y. Zhao, X. Qin, Some aspects of high manganese twinning - induced plasticity (TWIP) steel, Acta Metall. Sin. 26 (2013), 1 - 15.[17] G. Frommeyer, U. Brüx. Microstructure and mechanical properties of High-Strength Fe - Mn - Al -C Light - Weight TRIPLEX Steels, Steel Research 77, (2006) 9-10, 627 - 633.Note: The responsible translator for English language is Dr. Janusz Mrzigod, Katowice, Poland

A study of mechanical properties of high manganese steels after different rolling conditions

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