Thermodynamic Analysis on Precipitation of Nonmetallic Inclusions in Gear Steel


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In order to make nonmetallic inclusions with low melting point and improve the fatigue resistance of gear steel, thermodynamic analysis on precipitation of nonmetallic inclusions CaO(MgO)-Al2O3 system was investigated in this paper. The complex deoxidation equilibria of strong deoxidizing elements such as aluminum, calcium, magnesium and so on were calculated accurately with the second order and middle term of the activity coefficient expression. Thermodynamic conditions for the precipitation of spinel inclusion (MgO•Al2O3) is sufficient as the acid-soluble aluminum content is 0.04% and magnesium content is less than 0.0005% in the tested gear steel 20CrMoH. The relationship between precipitation of spinel and calcium aluminate inclusions in gear steel and the composition of molten steel at 1873K indicates that, the compositions of inclusions before and after calcium treatment are C12A7 and C3A respectively, while the reactions in ladle reach the equilibrium state.



Advanced Materials Research (Volumes 284-286)

Main Theme:

Edited by:

Xiaoming Sang, Pengcheng Wang, Liqun Ai, Yungang Li and Jinglong Bu




Y. Chen et al., "Thermodynamic Analysis on Precipitation of Nonmetallic Inclusions in Gear Steel", Advanced Materials Research, Vols. 284-286, pp. 1060-1066, 2011

Online since:

July 2011




[1] Itoh H, Hino M, Ban-Ya S. Thermodynamics on the formation of spinel nonmetallic inclusion in liquid steel [J]. Metallurgical and Materials Transaction, 1997 (28B): 953~956.


[2] Fuji K, Nagasaka T, Hino M. Activities of the constituents in spinel solid solution and free energies of formation of MgO, MgO·Al2O3 [J]. ISIJ International, 2000, 40 (11): 1059~1066.


[3] Taguchi K, Nakazato H. Complex deoxidation equilibria of molten iron by aluminium and calcium[J]. ISIJ international, 2005, 45(11): 1572~1576.


[4] Ohta H, Suito H. Activities in CaO-MgO-Al2O3 slags and deoxidation equilibria of Al, Mg and Ca[J]. ISIJ International, 1996, 36 (8): 983~990.


[5] Cho S W, Suito H. Assessment of Calcium-Oxygen equilibrium in liquid iron[J]. ISIJ International. 1994, 34 (3): 265~269.


[6] Park J H, Kim D S. Effect of CaO-Al2O3-MgO slags on the formation of MgO-Al2O3 inclusions in ferritic stainless steel[J]. Metallurgical and Materials Transaction, 2005(36B): 495~501.


[7] Cho S W, Suito H. Assessment of Aluminum-Oxygen equilibrium in liquid iron and activities in CaO- Al2O3-SiO2 slags[J]. ISIJ International, 1994, 34 (2): 177~185.


[8] Suito H, Inoue R. Thermodynamics on control of inclusions composition in ultra clean steels [J]. ISIJ International, 1996, 36 (5): 528~536.


[9] Ye G. Thermodynamics and kinetics of the modification of Al2O3 inclusions [J]. ISIJ International, 1996, 36(Supplement): 105~108.

[10] Huang X H. Fundamental of ferrous metallurgy (The third edition) (in Chinese)[M]. Beijing: Metallurgical Industry Press, (2005).

[11] Zhao P, Cheng G G, Shu S. Operative technology handbook of refining and hot metal pretreatment(in Chinese) [M]. Beijing: Metallurgical Industry Press, (2004).