Formation and Removal Mechanism of Nonmetallic Inclusions in 42CrMo4 Steel during the Steelmaking Process

Abstract

Nonmetallic inclusions are harmful to the quality of 42CrMo4 steel. Therefore, the formation and removal mechanism of inclusions in 42CrMo4 steel during the steelmaking process is investigated by industrial trials. The characteristics of inclusions in specimens were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The main type of inclusions in molten steel in the early stage of ladle furnace (LF) refining is MgO-Al2O3 inclusions of irregular shape. CaO begins to appear in MgO-Al2O3 inclusions in the middle and late stages of LF. In the vacuum degassing (VD) refining stage, the inclusions in molten steel completely change into low-melting-point CaO-MgO-Al2O3 inclusions. The existence of [Mg] in molten steel is the fundamental reason for the formation of a large number of MgO-Al2O3 inclusions. Thermodynamic calculation shows that the refractory mainly transfers [Mg] to the liquid steel in the LF refining stage, whereas the slag mainly transfers [Mg] to the liquid steel in the VD refining stage. Kinetic calculation indicates that MgO-Al2O3 inclusions could be removed from molten steel faster than low-melting-point CaO-MgO-Al2O3 inclusions. The fundamental reason for the different removal behavior of the two types of inclusions is that the interfacial tension between the low-melting-point CaO-MgO-Al2O3 inclusions and the liquid steel is 50% lower than that of the MgO-Al2O3 inclusions.

Assessment of Inclusion Removal Ability in Refining Slags Containing Ce2O3

“…Therefore, Equations ( 3)-( 15) and ( 18)-( 22) are the governing equations of the developed thermodynamic model for calculating the mass action concentrations N i of the structural units or ion couples in the CaO-Ce 2 O 3 -SiO 2 -Al 2 O 3 slag. Specifically, the values of N 1 , N 2 , N 3 , and N 4 can be obtained by solving the Equation set ( 18)- (22), by taking Equations ( 3)- (15) and the specific values of T, b 1 , b 2 , and a 2 as the initial conditions. Then, N 5 -N 17 can be solved by substituting N 1 -N 4 into Equations ( 3)-( 15).…”

“…A new equation containing only N 1 S , N 2 S , N 3 S , and N 4 S is obtained by substituting the surface mass action concentration into the equilibrium constant expression in Equations ( 3)- (15), and then substituting the results into Equation (23).…”

“…Non-metallic inclusions are harmful to steel product quality [1][2][3], and they also influence the steelmaking process via clogging of the nozzles [4][5][6]. A great number of studies have focused on the analysis of inclusions during the whole steelmaking process [7][8][9][10][11][12][13][14][15]. Meanwhile, the inclusion formation and control in a steelmaking unit, for example, a ladle furnace [16][17][18], vacuum degassing [19][20][21][22], Ruhrstahl-Heraeus [23][24][25][26][27], and tundish [28][29][30][31] have also been widely studied.…”

“…This model could be categorized into a Lagrangian approach, which was based on Newton's second law. The model has been continuously developed by introducing the turbulent burst theory to calculate the possibility of the re-entrainment of inclusions [72], by applying it to solid inclusions of other compositions [15,33,73] and liquid inclusions [74,75], by extending the model to different shapes of inclusions, such as octahedral and plate-like, etc. [76][77][78], by introducing the slag dissolution kinetics [79], by improving the theory of a slag film capture [80], and by applying it to a study on the water model of particles [81,82].…”

Effects of Na2O, K2O and B2O3 on Deformability of SiO2-MnO-Al2O3 Inclusion in High-Carbon Steel

“…The control of inclusions is not only limited to the refining [12][13][14][15][16][17] and solidification processes [18][19][20], but also needs to pay attention to the evolution behavior of inclusions in the hot working process [21]. And in the study of steel samples, it was also found that there are hard, high-melting-point Al 2 O 3 inclusions.…”