Effect of Magnesium Treatment on Liquid Precipitation Behavior of TiN

doi:10.12068/j.issn.1005-3026.2024.07.008

Abstract

Abstract:

To investigate the effect of magnesium on TiN liquid precipitation in titanium microalloyed steel， the steel was melted in a vacuum induction furnace. The changes in inclusion composition and size in magnesium?treated steel at different billet positions were analyzed by SEM-EDS and imaging software and were compared with untreated steel. FactSage software was used to calculate inclusion formation. The results revealed that TiN inclusions form in the liquid phase at the solidification front. Higher nitrogen content increases TiN precipitation temperature and amount， and affects Ti₄C₂S₂ and MnS precipitation. Without magnesium treatment， the average sizes of TiN are 2.48 and 2.11 μm in the quarter and center of slab， respectively. After magnesium treatment， the sizes decrease to 1.50， 1.45， 1.48， and 1.38 μm， respectively， with increased number density. Traces of Mg enable the stable existence of MgO·Al₂O₃， serving as TiN solidification cores， aiding dispersion and reducing the formation of large-size TiN during steel cooling.

Key words: magnesium treatment, titanium microalloyed steel, TiN, precipitate, thermodynamics

CLC Number:

TF 704.7

Yong-yu ZHANG, Kun MA, Yi MIN, Cheng-jun LIU. Effect of Magnesium Treatment on Liquid Precipitation Behavior of TiN[J]. Journal of Northeastern University(Natural Science), 2024, 45(7): 967-973.

Figures/Tables 12

Table 1 Chemical compositions of raw materials(mass fraction)

原料	Fe	C	Si	Mn	S	Al	Mg	Ti	其他
工业纯铁	99.9	0.002	0.01	0.03	0.007	0.001	—	—	0.05
含镁包芯线	49.21	—	32.41	—	—	10.60	7.78	—	—
钛铁	27.10	0.08	0.20	0.10	0.005	1.60	—	70.90	0.01

Fig.1 Schematic diagram of smelting process

Table 2 Chemical compositions of steels(mass fraction)

炉次	C	Ti	Al（s）	Mg	O	N
1	0.049	0.037	0.025	-	0.003 4	0.003 4
2	0.051	0.026	0.028	0.000 5	0.001 1	0.006 6
3	0.047	0.028	0.058	0.000 5	0.000 8	0.009 1

Fig.2 Composition and morphology of inclusions in three furnace steels

Fig.3 Dominant area map of inclusions in different molten steel systems

Fig.4 Variation of inclusion density and average grain diameter with position

Fig.5 Percentage of inclusions less than 2 μm at different positions

Fig.6 Effect of Mg content on [Ti] and [N] activities

Fig.7 Equilibrium precipitation phase diagrams of three furnace steels during solidification

Fig.8 The content of TiN inclusions with different sizes at different positions in three groups of samples

Table 3 Statistical results of characteristics of all inclusions in steel

试样	位置	夹杂物数量	数密度/（个·mm^-2）	平均粒径/μm	平均面积/μm²
1	边部	1123	449.2	1.17	1.51
	1/4	417	166.8	2.46	3.14
	中心	404	161.6	2.03	2.83
2	边部	1122	448.8	1.00	1.04
	1/4	431	172.4	1.41	2.03
	中心	455	182.0	1.39	2.01
3	边部	954	381.6	1.08	1.24
	1/4	587	234.8	1.34	2.00
	中心	522	208.8	1.26	1.74

Fig.9 Percentage of different types of inclusions at different positions in three groups of samples

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