Thermodynamics and Nucleation Kinetics Model of Nonalloyed Carbon Deoxidation of Bearing Steel

Abstract

Bearing steel is an important primary manufacturing material for mechanical equipment widely used in the military, aerospace, and transportation industries. Owing to the rapid development of the economy and society, better fatigue life and stable quality of bearing steel are required by engineers. The quality of bearing steel is improved by an important factor, cleanliness, that is, total oxygen content and inclusion control. [1] Currently, there are two main methods to control cleanliness: Al deoxidation and Si-Mn nonaluminum deoxidization. Using the former, [2][3][4][5][6][7][8][9] oxygen content in the molten steel can be rapidly reduced by controlling the deoxidation conditions and high-basicity slag, while total oxygen (TO) can be reduced to less than 5 ppm. However, this introduces spinel and calcium aluminate inclusions, which reduce the fatigue life of bearing steel, causing nozzle clogging. The Si-Mn nonaluminum deoxidization [5,[10][11][12] solves the problem of nozzle clogging and reduces calcium aluminate and spinel inclusions in bearing steel from the source. However, owing to the weak Si-Mn deoxidization ability, the TO in molten steel is higher than that of Al-deoxidized bearing steel. Excess oxygen precipitates at the grain boundary in the form of oxide inclusions, which greatly affects the ductility and corrosion resistance of steel.For decades, metallurgical scholars have conducted studies on inclusions in bearing steel. However, producing nonmetallic inclusions either by Al deoxidation or Si-Mn deoxidation is inevitable. To improve the structural integrity of steel, it is necessary to remove [13][14][15][16][17] or modify [9,[18][19][20][21][22] the inclusions. Using ferroalloy deoxidization to control cleanliness does not solve the contradiction of reducing the oxygen content and avoiding inclusions, which limits the improvement of high-quality bearing steel. Therefore, a new design of cleanliness control for bearing steel is required.To solve these issues, the author proposed two methods for producing high-quality bearing steel: 1) hydrogen deoxidation [23,24] and 2) vacuum carbon deoxidation. [23] Xiao Wei [25] found that the TO content of Si-deoxidized bearing steel after ladle furnace (LF) refining is about 20-30 ppm, and after Ruhrstal and Heraeus (RH) vacuum carbon deoxidization, it is reduced to 8-10 ppm, far higher than the theoretical carbon deoxidization under vacuum conditions. The deoxidation product of carbon deoxidation is CO, which can be spontaneously discharged from the molten steel to avoid residual inclusions. This solves the technical problem of fatigue failure caused by inclusions due to deoxidation. The nonalloyed carbon deoxidation process uses C-O reaction to generate CO gas. Many studies on the C-O reaction mechanism [26] and CO nucleation [27,28] were conducted. However, these researches involve smelting ultralowcarbon steel and blowing oxygen into molten steel to achieve rapid decarburization, and studies on the smelting of high-carbon ultralow-oxygen steel by carbon...

Thermodynamics of the Formation of Non-Metallic Inclusions during the Deoxidation of GCr15 Bearing Steel

“…As inclusions are distinctive from steel in terms of hardness, thermal expansion, deformability, and so on, they can easily cause stress concentrations and fatigue cracks in steel. Hence, scholars have carried out extensive research on reducing inclusions [6,7], inclusion modifications [8][9][10], inclusion formation thermodynamics [11][12][13], and clean deoxygenation technology [14,15]. However, there is a lack of systematic research on the deoxidation thermodynamics of alloys.…”