National University of Science and Technology “MISIS” (Moscow, Russia):

A. N. Svyazhin, Dr. Eng., Prof., Chief Researcher, svyazhin@misis.ru
V. E. Bazhenov, Cand. Eng., Junior Researcher, V.E.Bazhenov@gmail.com
L. M. Kaputkina, Dr. Phys.-Math., Prof., Chief Researcher, kaputkina@mail.ru
I. V. Smarygina, Cand. Eng., Associate Prof., smarygina.inga@yandex.ru
V. E. Kindop, Cand. Eng., Deputy Head of Science Department, vk@misis.ru

Nitrogen and AlN solubility in Fe–Mn–Al–N, Fe–Mn–Al–C–N and Fe–Mn–Al–Ni–C–N alloys is calculated using the methods of interaction parameters and up-to-date thermodynamic data. The obtained values of balanced nitrogen solubility in these alloys are rather close to the convergence values obtained for liquid metal according to Thermo-Calc data base. Polythermic sections of the phase diagrams of these alloys are calculated and balanced residual values of dissolved nitrogen are determined for the liquidus and solidus temperatures; these temperatures are lower than nitrogen purity limited values, achieved by the modern technologies (0.0030%) for the most investigated alloys. It is possible to obtain up to 0.010% of dissolved nitrogen in the melts Fe–20%Mn–5%Al and Fe–25%Mn–5%Al at the temperatures of steel melting and alloying by nitrogen (1550–1600 °C), while in presence of carbon and with aluminium content more than 5% this value becomes lower than nitrogen purity limited value. Nitrogen content in a solid solution depends strongly on Al and C content. If Al content is 5 %, the maximal nitrogen content in a solid solution Fe–20%Mn–Al can be equal to 9.3·10–4% at the solidus temperature. This value does not correspond to possibilities of the up-todate industrial technologies. Thereby, AlN nitrides will form in liquid metal at micro-alloying of the steels of Fe–Mn–Al–Ni–C system by nitrogen, before and during crystallization. At the temperature lower 1100 °C, practically complete whole nitrogen is presented in the form of aluminium nitrides. It is displayed experimentally that complete nitrogen content in these alloys has effect on their strength (σ_max) at hot deformation towards its elevation. In the case of warm and cold deformation, the tendency of lowering of alloys strength with increase of nitrogen content in these alloys is observed.

The research was financially supported by the RF Ministry of education and science in the framework of the engineering part of the state task, target No. 11.1943.2014/K.

1. Kim H., Suh D. W., Kim N. J. Fe–Al–Mn–C lightweight structural alloys: a review on the microstructures and mechanical properties. Sci. Technol. Adv. Mater. 2013. Vol. 14. 014205.
2. Witkowska M., Zieliska-Lipiec A., Kowalska J., Ratuszek W. Microstructural changes in a high-manganese austenitic Fe–Mn–Al–C steel. Archives of Metallurgy and Materials. 2014. Vol. 59. Is. 3. P. 971–975.
3. Frommeyer G., Brux U. Microstructures and mechanical properties of high-strength Fe–Mn–Al–C light TRIPLEX steels. Steel Research International. 2006. Vol. 77. No 9–10. P. 627–633.
4. Bronz A. V., Kaputkin D. E., Kaputkina L. M., Kindop V. E., Svyazhin A. G. Effect of chemical composition on the crystal lattice and physical properties of iron-manganese alloys with high content of aluminum. Metal Science and Heat Treatment. 2014. Vol. 55. Is. 11. P. 647–651.
5. Svyazhin A. G., Kaputkina L. M. Steel alloyed with nitrogen. Steel in Translation. 2006. P. 64–76.
6. Kaputkina L. M., Prokoshkina V. G., Khadeev G. E., Elantsev S. N., Karpukhina I. V. Diagrams of the Hot and Warm Deformation and Strain Aging of Nitrogen-Bearing Austenitic Steels. Metal Science and Heat Treatment. 2013. Vol. 55. Is. 5. P. 322–327.
7. Svyazhin A. G. Termodinamika rastvorov azota v zhidkikh splavakh zheleza (Thermodynamics of nitrogen solutions in the liquid Fe alloys). Problemy chernoy metallurgii I materialovedeniya = Problems of ferrous metallurgy and material science. 2008. № 4. P. 46–51.
8. Kim W.-Y. Kang J.-G., Park Ch.-H., Lee J.-B., Pak J.-J. Thermodynamics of aluminum, nitrogen and AlN formation in liquid iron. ISIJ Iinternational. 2007. Vol. 47. Is. 7. P. 945–954.
9. Paek M.-K., Jang J.-M., Jiang M., Pak J.-J. Thermodynamics of AlN formation in high manganese-aluminum alloyed liquid steels. ISIJ Iinternational. 2013. Vol. 53. Is. 6. P. 973–978.
10. Sigworth G. K., Elliott J. F. The thermodynamics of liquid dilute iron alloys. Metal Science. 1974. Vol. 8. Is. 1. P. 298–310.
11. Bronz A. V., Kaputkin D. E., Kaputkina L. M., Kindop V. E., Svyazhin A. G. Mechanical and Physical Properties of Cast Fe–Mn–Al–C–N Alloys. Steel in Translation, 2014. Vol. 44. No. 11. P. 804–807.