Ductile iron with special properties

Ductile Iron with special properties is a form of malleable cast iron (DITG type - ductile iron developed by S&P Group TRIBOFATIGUE Ltd and JSC Gomselmash) which possess a complex of high mechanical properties: strength and plasticity, crack and contact fatigue resistance, self-lubrication at friction and ability to dampen the dynamic loading. The following specific feature can be seen in the "strength vs plasticity" diagram: plasticity increases with the increase in strength. Such properties can be explained by the balanced chemical composition with an optimal ratio of three modifying elements: Mo-Ni-Cu (that's why the DITG material is called MONICA) and are assured by the corresponding microstructure which is obtained by the respective heat treatment.

Chemical composition[edit]

The chemical composition corresponds to high-strength cast iron with spherical graphite (DI, ADI), but with the total carbon equivalent of about СE = 5.0 … 5.5. For three elements (Mo-Ni-Cu) this equivalent is equal to СE⁽³⁾ = 0.35…0.45.

Microstructure[edit]

Depending on the heat treatment modes, the microstructure characteristic of ADI^[1] is obtained; it possesses the following specific feature: under certain conditions molybdenum evolutions are formed.

Mechanical properties[edit]

At strength limit σ_u~1300…1400 MPa the plasticity reaches the values of 3…5 %. Critical coefficient of intensity of stresses is equal to K_c=60…75 MPa ${\sqrt[{2}]{m}}$ at σ_u=1100…1200 MPa. The contact fatigue limit (under the conditions of initial point contact) is p_f=3750 MPa based on the tests of 10⁸ cycles. High resistance to fatigue is explained by the fact that modification with molybdenum is more effective than the one with nickel and copper: in order to obtain the steel bending fatigue limit with rotation of σ₋₁=150 MPa, the amount of nickel shall be approximately 10 times higher than the amount of molybdenum.

Wear resistance[edit]

MONICA displays high self-lubrication properties since its microstructure contains graphite, molybdenum and copper. Availability of these elements helps to reduce the coefficient of friction for MONICA to ~50…70 % (as compared to steel) and to decrease the wear to ~30…50 %.

Application[edit]

The material is used to manufacture the parts of critical heavily loaded tribo-fatigue systems (see, for example, Figure 1).^[2]^[3]^[4]^[5]

References[edit]

↑ Rundman, K. B., Moore, D. J., Hayrynen, K. L., Dubensky, W. J., & Rouns, T. N. (1988). The Microstructure and Mechanical Properties of Austempered Ductile Iron. J. Heat Treat., 5(2), 79-85. Retrieved May 23, 2019.
↑ Sosnovskiy, L. A. Iron and steel in tribo-fatigue systems of modern machinery and equipment / L. A. Sosnovskiy, P. A. Vityaz, V. A. Gapanovich, N. V. Psyrkov, N. A. Makhutov // Mechanics of machines, mechanisms and materials. – 2014. – № 4 (29). – P. 5–20. (In Russian).
↑ Sosnovskiy, L. A. Experimental construct a complete pair «VCHTG ductile iron / steel 18HGT» rolling fatigue curve and its analysis / L. A. Sosnovskiy, V. V. Komissarov, E. S. Taranova, S. A Tyurin // Mechanics of machines, mechanisms and materials. – 2014. – № 1 (26). – P. 32–39. (In Russian).
↑ Sosnovskiy, L. A. New structural material for railway rails: mechanical and service properties / L. A. Sosnovskiy, V. V. Komissarov, V. I. Matvetsov, N. E. Miroshnikov // Bulletin of BelSUT. – 2014. – № 2 (29). – P. 77–82. (In Russian).
↑ Komissarov, V. V. On the experience of manufacturing and operation of gears from the new structural material «MONICA» / V. V. Komissarov, E. S. Taranova, P. S. Drobyshevskiy, V. O. Zamyatnin, S. A. Tyurin, L. A. Sosnovskiy // Bulletin of IzhGTU name M. T. Kalashnikov. – 2017. – V. 20. – № 2. – P. 107–112. (In Russian).

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[1] Rundman, K. B., Moore, D. J., Hayrynen, K. L., Dubensky, W. J., & Rouns, T. N. (1988). The Microstructure and Mechanical Properties of Austempered Ductile Iron. J. Heat Treat., 5(2), 79-85. Retrieved May 23, 2019.

[2] Sosnovskiy, L. A. Iron and steel in tribo-fatigue systems of modern machinery and equipment / L. A. Sosnovskiy, P. A. Vityaz, V. A. Gapanovich, N. V. Psyrkov, N. A. Makhutov // Mechanics of machines, mechanisms and materials. – 2014. – № 4 (29). – P. 5–20. (In Russian).

[3] Sosnovskiy, L. A. Experimental construct a complete pair «VCHTG ductile iron / steel 18HGT» rolling fatigue curve and its analysis / L. A. Sosnovskiy, V. V. Komissarov, E. S. Taranova, S. A Tyurin // Mechanics of machines, mechanisms and materials. – 2014. – № 1 (26). – P. 32–39. (In Russian).

[4] Sosnovskiy, L. A. New structural material for railway rails: mechanical and service properties / L. A. Sosnovskiy, V. V. Komissarov, V. I. Matvetsov, N. E. Miroshnikov // Bulletin of BelSUT. – 2014. – № 2 (29). – P. 77–82. (In Russian).

[5] Komissarov, V. V. On the experience of manufacturing and operation of gears from the new structural material «MONICA» / V. V. Komissarov, E. S. Taranova, P. S. Drobyshevskiy, V. O. Zamyatnin, S. A. Tyurin, L. A. Sosnovskiy // Bulletin of IzhGTU name M. T. Kalashnikov. – 2017. – V. 20. – № 2. – P. 107–112. (In Russian).

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