Interaction between M(C, N) and Ferrite in Electropulsing Microalloyed Steel

Abstract

Microstructure and M(C, N) significantly affect the quality of Nb microalloyed steel, and the control microstructure evolution and M(C, N) precipitation behavior is the key. In this study, the interaction between ferrite and M(C, N) with electropulsing is quantitatively analyzed. Results reveal that electropulsing promotes the precipitation of M(C, N) and ferrite phase from austenite phase. The precipitated M(C, N) affects the position of ferrite precipitation, and the precipitation of ferrite can then conversely affect the distribution of M(C, N). The influence of austenite to ferrite transformation on M(C, N) precipitation is much more significant than that of electropulsing. This observation can be applied to control of microstructure and M(C, N) in continuous casting.

1. Introduction

Nb microalloyed steel is a widely used low alloy high strength steel whose quality and performance are affected by γ/α and M(C, N).^1,2) Ma et al found that changing the different cooling rates can affect the γ/α and M(C, N) behaviors.³⁾ Kato et al found that γ/α and M(C, N) can be controlled by changing the cooling conditions and temperature.^4,5) But the method is challenging to implement in practical applications. Meanwhile, the electropulsing is a new material treatment method. It can refine the microstructure of pure aluminum,^6,7) 2024 Al alloy,⁸⁾ Mg–3Al–1Zn alloy,⁹⁾ ZK60 magnesium alloy.^10,11) With the deeping of the research, it is found that the electropulsing influences the solidification structure of steel,^12,13) the microstructure of hot-rolled sheet¹⁴⁾ and the performance of different steel.¹⁵⁾ It can break up grains into smaller ones,¹⁶⁾ and reduce the interlamellar spacing of low carbon pearlite steel.¹⁷⁾ Besides, the electropulsing can affect the solid phase precipitation including the behavior of precipitates in 2024 Al alloy,¹⁸⁾ the precipitate size of low carbon steel,¹⁹⁾ the precipitation of NbC in pre-deformed memory alloy,²⁰⁾ and the morphology of MnS in steel.²¹⁾ It can promote the decomposition of cementite in graphite iron and the formation of new graphite.²²⁾ Conrad believes that the electropulsing of different conditions can not only promote the precipitation behavior of the phase in the solid metal, but also have the inhibitory effect.²³⁾ Therefore, the electropulsing may affect the γ/α transformation and M(C, N) behavior in Nb microalloyed steel.

In this paper, the M(C, N) precipitation behavior and γ/α transformation of Nb microalloyed steel during the cooling process was studied quantitatively by experiments, and the interaction between the two was analyzed in depth.

2. Materials and Experiments

The test materials were low carbon steel and low carbon Nb microalloyed steel(Nb steel). The chemical composition of test materials is shown in Table 1. The schematic diagram of the experimental set-up is presented in Fig. 1. The sample was welded with steel wire, connected to pulse power supply through steel wire, and placed in the muffle furnace. The size of sample is 24 × 8 × 100 mm. The experimental scheme is shown in Table 2. The experiments included microstructure studies (Nos. 1–8) and precipitation studies (Nos. 9–13). The sample was incubated at 1200°C for 1 hour and cooled at the cooling rate of 6°C·min^{−1 24)} to the target temperature, and the sample is quenched in water. The microstructure and precipitate state of sample can be obtained at a high temperature. During the process, the sample was treated with different electropulsing according to Table 2, and electropulsing frequency is 30 kHz. The microstructure of sample’s cross section 24 × 8 mm was observed by metallographic microscope, and metal image analysis software was used to measure area rate of α phase within γ phase grain and average thickness of α phase omentum alone γ phase grain boundary from 15 fields of view. The thickness data is randomly taken 10 from each field of view.The mass fraction of M(C, N) phase was measured using physicochemical phase analysis.^25,26) Physicochemical phase analusis is employed to dissolve alloy matrix to obtain the electrolytic residue composed of the second phase (the second phase includes intermetallic compounds, carbides, nitrides, sulfides, and oxides, etc.) by using electrochemical method, then the phase separation is carried out by chemical method or the second phase is identified and analyzed by means of physical and chemical analysis instruments to obtain the qualitative and quantitative phase analysis results of the second phase. The structure of M(C, N) precipitates was identified by X-ray diffraction. The distribution of precipitates were determined by means of JEM-2100 TEM. In addition, the EDS was used to test the composition of the precipitates during the TEM analysis.

Table 1. Chemical composition of test materials (mass%).

Material	C	Si	Mn	P	S	Nb	Ti	N	Al
low carbon steel	0.102	0.38	1.40	0.019	0.007	0.003	<0.001	0.006	0.031
low carbon Nb microalloyed steel	0.099	0.18	1.34	0.011	0.003	0.024	0.002	0.005	0.025

Fig. 1.

The schematic diagram of the experimental set-up.

Table 2. Experimental scheme.

Material	No	Process	Temperature with electropulsing (°C)	Intensity (A)	End (°C)	Analysis object
low carbon steel	1	1200 (1 h), −6°C/min	950–750	10	750	micro-structure
	2	1200 (1 h), −6°C/min	950–750	20	750
	3	1200 (1 h), −6°C/min	950–750	40	750
	4	1200 ( 1 h), −6°C/min	950–750	60	750
low carbon Nb micro-alloyed steel	5	1200 (1 h), −6°C/min	950–750	10	750	micro-structure
	6	1200 (1 h), −6°C/min	950–750	20	750
	7	1200 (1 h), −6°C/min	950–750	40	750
	8	1200 (1 h), −6°C/min	950–750	60	750
	9	1200 (1 h)	–	–	1200	preci-pitation
	10	1200 (1 h), −6°C/min	–	–	950
	11	1200 (1 h), −6°C/min	–	–	750
	12	1200 (1 h), −6°C/min	1200–950	60	950
	13	1200 (1 h), −6°C/min	1200–750	60	750

3. Results

3.1. Microstructural Analysis Results

The influence of different electropulsing intensities on the microstructure of low carbon steel and Nb steel were shown in Figs. 2 and 3 respectively. It can be seen that the electropulsing has a significant influence on the microstructure of the both steel. Figures 4 and 5 are obtained from the statistical data, and the data is found to have regularity. It can be seen from Fig. 4 that when the electropulsing intensity is increased from 10 A to 60 A, the average thickness of the α phase omentum along the γ grain boundary is reduced from 51 μm to 10 μm at 750°C in the low carbon steel, and the average thickness of the α phase omentum along the γ grain boundary is reduced from 42 μm to 9 μm at 750°C in the Nb steel. The average thickness of the α phase omentum along the γ grain boundary in both of them is gradually thinner and the changing trend is the same, but the average thickness of the α phase omentum along the γ grain boundary in the Nb steel with the same electropulsing intensity is thinner than that in the low carbon steel. It can be seen from Fig. 5 that when the electropulsing intensity is increased from 10 A to 60 A, the average area rate of the α phase in the γ grains in the low carbon steel is increased from 25% to 41%, and the average area rate of the α phase in the γ grains in Nb steel is increased from 30% to 44%. The average area rate of the α phase in the γ grains in both of them is gradually growing and the trend is the same, but the average area rate of the α phase in the γ grains in the Nb steel with the same electropulsing intensity is larger than that in the low carbon steel, and the difference is more evident than the average thickness of the α phase omentum along the γ grain boundary.

Fig. 2.

Effect of different electropulsing intensities on microstructure of low carbon steel.

Fig. 3.

Effect of different electropulsing intensities on microstructure of Nb steel.

Fig. 4.

Effect of different electropulsing intensities on the average thickness of α phase omentum along the γ grain boundary.

Fig. 5.

Effect of different electropulsing intensities on the average area rate of α phase in the γ grains.

3.2. Physicochemical Phase Analysis Results

The physicochemical phase analysis of M(C, N) in the Nb steel with or without electropulsing was carried out. The results are shown in Table 3. It can be seen that the mass fraction of the total precipitation of M(C, N) in the Nb steel is 0.0053% after solid solution at 1200°C for 1 h. When the temperature dropped to 950°C, the total precipitation of M(C, N) increased to 0.0102% without electropulsing, and the precipitation during the cooling process was 0.0049%. The total precipitation of M(C, N) increased to 0.0152% with electropulsing, and the precipitation during the cooling process was 0.0099%, which was twice that of the without electropulsing. When the temperature dropped to 750°C, the total precipitation of M(C, N) increased to 0.0186% without electropulsing, and 0.0084% precipitated during the cooling process. The total precipitation of M(C, N) increased to 0.0187% with electropulsing, which is almost equal to the amount of precipitation without electropulsing. But the precipitation during the cooling process was 0.0035%, which is less than half of the precipitation without electropulsing.

Table 3. The mass fraction of each element in the M(C, N) (mass%), 4 decimal places are effective, Error: ±0.0002%, grid size: 1 nm.

No	electro-pulsing	Nb	Ti	C	N	Σ	M(C, N) composition	End/°C
9	No	0.0035	0.0010	<0.0001	0.0008	0.0053	(Nb0.647Ti0.353)N	1200
10	No	0.0080	0.0008	<0.0001	0.0014	0.0102	(Nb0.835Ti0.165)N	950
11	No	0.0149	0.0012	0.0004	0.0021	0.0186	(Nb0.869Ti0.131) (C0.196N0.804)	750
12	Yes	0.0120	0.0012	0.0007	0.0013	0.0152	(Nb0.839Ti0.161) (C0.384N0.616)	950
13	Yes	0.0149	0.0012	0.0003	0.0023	0.0187	(Nb0.870Ti0.130) (C0.121N0.879)	750

The NbC, NbN, TiC, and TiN are solid-dissolved with each other because their structures are face-centered cubic system, and the precipitation amount of each substance is not the same, so the M(C, N) composition form by XRD analysis is not entirely the same. However, it can be noted that the precipitated M(C, N) is (Nb, Ti)(C, N) which is mainly composed of Nb(C, N), and titanium is residual in steel. The morphology and energy spectrum of M(C, N) can be observed by TEM, as shown in Fig. 6. It is consistent with Nb and Ti carbonitrides which is mainly composed of Nb(C, N) in the literauture.^27,28)

Fig. 6.

Morphology and energy spectrum of M(C, N). (a) Morphology. (b) energy. (Online version in color.)

4. Discussion

From the results of microstructure analysis and physicochemical phase analysis, it can be seen that the difference in microstructure between low carbon steel and Nb steel with electropulsing is mainly caused by the different behavior of M(C, N) precipitation, which is caused by electropulsing.

When the temperature is decreased from 1200°C to 950°C, the precipitation characteristics of M(C, N) in this process can be calculated according to the Eqs. (1), (2), (3), (4),²⁹⁾ and M can be Nb or Ti.   

$$log\frac{[M]\cdot [C]}{X}=B_1-A_1/T$$(1)

  

$$log\frac{[M]\cdot [N]}{1-X}=B_2-A_2/T$$(2)

  

$$\frac{M_o-[M]}{C_o-[C]}=\frac{W_M}{X{W}_C}$$(3)

  

$$\frac{M_o-[M]}{N_o-[N]}=\frac{W_M}{(1-X)W_N}$$(4)

Where X is the mole fraction of MC, (1-X) is the mole fraction of MN. A₁ and B₁ are the corresponding constants in the formula of MC solid solubility product. A₂ and B₂ are the corresponding constants in the formula of MN solid solubility product. W_M, W_C, and W_N are respectively the atomic weight of the M, C, and N elements. M₀, N₀, and C₀ are the initial mass percentages of the M, N, and C elements, respectively. [M], [N], and [C] are the equilibrium mass percentages of the M, N, and C elements, respectively. The amount of precipitation of Nb(C, N) in the γ phase was calculated by Eqs. (5) and (6). The amount of precipitation of Ti(C, N) in the γ phase was calculated by Eqs. (7) and (8). The results are shown in Fig. 7. It can be seen that during the process of decreasing from 1200°C to Ae3(826°C, Eq. (9)), Nb(C, N) and Ti(C, N) gradually precipitated in the γ phase with the decrease of temperature, and the precipitation amount is gradually increased. Among them, Nb(C, N) is mainly precipitated.   

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{N}\mathrm{b}]\cdot [\mathrm{C}]\right\}}_{\gamma }=2.96-7\mathrm{\hspace{0.17em} }510/\mathrm{T}$$(5) ³⁰⁾

  

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{N}\mathrm{b}]\cdot [\mathrm{N}]\right\}}_{\gamma }=2.80-8\mathrm{\hspace{0.17em} }500/\mathrm{T}$$(6) ³¹⁾

  

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{T}\mathrm{i}]\cdot [\mathrm{C}]\right\}}_{\gamma }=2.75-7\mathrm{\hspace{0.17em} }000/\mathrm{T}$$(7) ³²⁾

  

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{T}\mathrm{i}]\cdot [\mathrm{N}]\right\}}_{\gamma }=0.32-8\mathrm{\hspace{0.17em} }000/\mathrm{T}$$(8) ³³⁾

  

$$\begin{array}{l}\mathrm{A}\mathrm{e}3=854.4-179.4[\mathrm{C}]-13.9[\mathrm{M}\mathrm{n}]\\ \hspace{1em}\hspace{1em}+44.4[\mathrm{S}\mathrm{i}]-1.7[\mathrm{C}\mathrm{r}]-17.8[\mathrm{N}\mathrm{i}]\end{array}$$(9) ³⁴⁾

Fig. 7.

Precipitation of M(C, N) in the γ phase. (Online version in color.)

According to the results of physicochemical phase analysis, the precipitation of M(C, N) with electropulsing can be doubled compared with the precipitation without electropulsing at 950°C. The solid solution [Nb], [Ti], and [N] in steel was greatly reduced. Therefore, the electropulsing can promote the precipitation of M(C, N). The reason is that the electropulsing can reduce the M(C, N) nucleation barrier. At the same time, it is also indicated that there are a large number of supersaturated elements [Nb], [Ti], and [N] in the steel without electropulsing.   

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{N}\mathrm{b}]\cdot [\mathrm{C}]\right\}}_{\alpha }=4.33-9\mathrm{\hspace{0.17em} }830/\mathrm{T}$$(10) ³⁵⁾

  

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{N}\mathrm{b}]\cdot [\mathrm{N}]\right\}}_{\alpha }=4.91-12\mathrm{\hspace{0.17em} }170/\mathrm{T}$$(11) ³⁵⁾

  

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{T}\mathrm{i}]\cdot [\mathrm{C}]\right\}}_{\alpha }=4.45-10\mathrm{\hspace{0.17em} }230/\mathrm{T}$$(12) ³⁵⁾

  

$$\mathrm{l}\mathrm{o}\mathrm{g}{\left\{[\mathrm{T}\mathrm{i}]\cdot [\mathrm{N}]\right\}}_{\alpha }=6.40-18\mathrm{\hspace{0.17em} }420/\mathrm{T}$$(13) ³⁵⁾

When the temperature drops to the equilibrium phase transition point Ae3 of γ→α (826°C) , after the α phase is precipitated, M(C, N) starts to precipitate in the α phase. The amount of precipitation of Nb(C, N) in the α phase was calculated by Eqs. (10) and (11). The amount of precipitation of Ti(C, N) in the α phase was calculated by Eqs. (12) and (13). The results are shown in Fig. 8. It can be seen that when the temperature drops below Ae3, the γ→α transformation just begins, and the precipitation of Nb(C, N) and Ti(C, N) increases rapidly, indicating Nb(C, N) and Ti(C, N) has a rapid precipitation characteristic in the α phase, which is significantly different from the slow precipitation characteristics in the γ phase. The reason is analyzed. It is found that the solubility product of Nb(C, N) and Ti(C, N) in the α phase is significantly smaller than the solubility product in the γ phase. When the γ phase containing a large number of supersaturated state elements [Nb], [Ti], and [N] enters the α phase, these supersaturated elements are rapidly precipitated in the α phase. According to the results of physicochemical phase analysis, at 950°C, the M(C, N) precipitation with electropulsing is 0.0152% higher than 0.0102% which is the M(C, N) precipitation without electropulsing. However, at 750°C, the total amount of M(C, N) precipitation with electropulsing is 0.0187%, which is close to 0.0186% when there is no electropulsing treatment. So the precipitation 0.0035% with electropulsing is obviously less than the precipitation 0.0084% without electropulsing in the cooling process from 950°C to 750°C. This indicates that the γ→α transformation promotes the precipitation of M(C, N) significantly so that the influence of electropulsing on the precipitation of M(C, N) in the α phase can be neglected.

Fig. 8.

Precipitation of M(C, N) in the α phase. (Online version in color.)

Combined with the results of microstructure analysis, the average thickness of the α phase omentum in the Nb steel is thinner than that of the low carbon steel with the same electropulsing intensity, and the average area ratio of the α phase in the γ phase grains in the Nb steel is larger than that of the low carbon steel. The interaction between the microstructure and M(C, N) can be obtained with electropulsing from 1200°C to 750°C in the Nb steel, as shown in Fig. 9. First, the evolution of microstructure and M(C, N) in Nb steel without electropulsing is shown in Fig. 9 (no electropulsing).²⁾ Cooling down from 1200°C, a small amount of M(C, N) is continuously precipitated in the γ phase. There are a large number of precipitated phase elements in the supersaturated state in the steel. After the temperature is lower than Ae3, a large number of α phase begins to precipitate along the γ phase grain boundary, and α phase omentum along the γ phase grain boundary is formed, corresponding a small amount of α phase precipitates with M(C, N) particles in the γ phase as the core of the heterogeneous nucleus. Then a large number of precipitated phase elements in supersaturated state form M(C, N) which is rapidly precipitated in the α phase. Due to the relatively developed α phase omentum, a large number of M(C, N) particles have formed the distribution along the γ phase grain boundary, only a small amount of M(C, N) particles precipitated in the γ phase grains.

Fig. 9.

The evolution of microstructure and the precipitation behavior of M(C, N) in Nb steel without and with electropulsing. (Online version in color.)

Because of the interaction between the microstructure and M(C, N), the evolution of microstructure and the precipitation behavior of M(C, N) in Nb steel with electropulsing is significantly different from that without electropulsing, as shown in Fig. 9 (electropulsing). Cooling down from 1200°C, a large amount of M(C, N) is continuously precipitated in the γ phase because of electropulsing, which significantly reduces the precipitation phase element in the supersaturated state in steel. After the temperature is lower than Ae3, a large amount of α phase precipitates with M(C, N) particles in the γ phase as the core of the heterogeneous nucleus. At the same time, the electropulsing can reduce the nucleation barrier of α phase and promotes the precipitation of the α phase in the γ phase grains, only a small amount of α phase precipitates along the γ phase grain boundary and forms omentum along the γ phase grain boundary. Subsequent precipitation phase elements in the steel form M(C, N) which rapidly precipitates in the α phase. Due to the large number of α phase in the γ phase grains, a large number of M(C, N) particles are precipitated in the γ phase grains, corresponding a small amount of M(C, N) particles are precipitated in the α phase omentum, suppressing the distribution of M(C, N) along the γ phase grain boundaries. Therefore, the precipitation behavior of M(C, N) particles can affect the precipitation position of the α phase with electropulsing, and the change of the α phase precipitation position can conversely affect the precipitation distribution of M(C, N) particles.

This rule can be applied to avoid the heat transfer crack of Nb steel. Before the γ→α transformation of the surface of the slab during the continuous casting process, the surface of the slab is treated with electropulsing, so that the precipitated phase elements in the supersaturated state form M(C, N) precipitated in the γ phase, which can be avoided the distribution of M(C, N) particles along the γ phase grain boundaries, and to prevent the formation of heat transfer crack.

5. Conclusion

This study investigated the interaction between M(C, N) and α phase in Nb steel with electropulsing. Through the quantitative study of microstructure analysis and physicochemical phase analysis, it is known that the electropulsing can promote the precipitation of M(C, N), which is formed by the precipitated phase elements in the supersaturated state in the γ phase. Subsequent M(C, N) can act as the core of the α phase heterogeneous nucleation to allow the α phase to precipitate in the γ phase grains, and it changes the nucleation position of the α phase. The precipitated α phase conversely provides a new precipitation position for M(C, N), it changes the precipitation distribution of M(C, N) particles and inhibits the distribution of M(C, N) along the γ phase grain boundary. Besides, the electropulsing can promote the precipitation of the α phase in the γ phase grains. The effect of electropulsing on the precipitation of M(C, N) in the α phase is negligible concerning the promotion of M(C, N) precipitation by γ→α transformation. The interaction rule between M(C, N) and α phase can be applied not only to avoid the formation of heat transfer crack to improve the quality of slab.

Acknowledgements

This work was supported financially by the National Natural Science Foundation of China (Nos. 51974003, Nos. 51304003), the National Key Research and Development Program of China(Nos. 2017YFB0305100) and Open Research Fund from the State Key Laboratory of Rolling and Automation, Northeastern University(Nos. 2018RALKFKT006).

References

• 1)   B.  Mintz: ISIJ Int., 39 (1999), 833. https://doi.org/10.2355/isijinternational.39.833
• 2)   Z. H.  Zhu and  S. T.  Qiu: Adv. Mater. Res., 557–559 (2012), 120. https://doi.org/10.4028/www.scientific.net/AMR.557-559.120
• 3)   F. J.  Ma,  G. H.  Wen,  P.  Tang,  X.  Yu,  J. Y.  Li,  G. D.  Xu and  F.  Mei: Ironmaking Steelmaking, 37 (2010), 211. https://doi.org/10.1179/030192309X12595763237085
• 4)   T.  Kato, Y.  Ito,  M.  Kawamoto,  A.  Yamanaka and  T.  Watanabe: ISIJ Int., 43 (2003), 1742. https://doi.org/10.2355/isijinternational.43.1742
• 5)   Y.  Ito,  T.  Kato,  A.  Yamanaka and  T.  Watanabe: Tetsu-to-Hagané, 89 (2003), 1023 (in Japanese). https://doi.org/10.2355/tetsutohagane1955.89.10_1023
• 6)   J. H.  Ma,  J.  Li,  Y. L.  Gao,  L. X.  Jia,  Z.  Li and  Q. J.  Zhai: Ironmaking Steelmaking, 36 (2009), 286. https://doi.org/10.1179/174328108X380654
• 7)   R. S.  Qin,  A.  Rahnama,  W. J.  Lu,  X. F.  Zhang and  B.  Elliott-Bowman: Mater. Sci. Technol., 30 (2014), 1040. https://doi.org/10.1179/1743284714Y.0000000533
• 8)   R. A.  Fard and  M.  Kazeminezhad: J. Mater. Res. Technol., 8 (2019), 3114. https://doi.org/10.1016/j.jmrt.2019.02.023
• 9)   W.  Wu,  Y.  Wang,  J.  Wang and  S.  Wei: Mater. Sci. Eng. A, 608 (2014), 190. https://doi.org/10.1016/j.msea.2014.04.071
• 10)   R. S.  Qin: Sci. Rep., 7 (2017), Article No. 41451. https://doi.org/10.1038/srep41451
• 11)   A.  Rahnama and  R. S.  Qin: Mater. Sci. Eng. A, 627 (2015), 145. https://doi.org/10.1016/j.msea.2014.12.084
• 12)   J.  Li,  J. H.  Ma,  C. J.  Song,  Z. J.  Li,  Y. L.  Gao and  Q. J.  Zhai: J. Iron Steel Res. Int., 16 (2009), 7. https://doi.org/10.1016/S1006-706X(10)60019-2
• 13)   A.  Rahnama and  R. S.  Qin: J. Mater. Res., 30 (2015), 3049. https://doi.org/10.1557/jmr.2015.268
• 14)   Y.  Liu,  J.  Fan,  H.  Zhang,  W.  Jin,  H.  Dong and  B.  Xu: J. Alloys Compd., 622 (2015), 229. https://doi.org/10.1016/j.jallcom.2014.10.062
• 15)   J.  Ma,  J.  Li,  Y.  Gao and  Q.  Zhai: Mater. Lett., 63 (2009), 142. https://doi.org/10.1016/j.matlet.2008.09.036
• 16)   J.  Li,  J.  Ma,  Y.  Gao and  Q. J.  Zhai: Mater. Sci. Eng. A, 490 (2008), 452. https://doi.org/10.1016/j.msea.2008.01.052
• 17)   X.  Xu,  Y.  Zhao,  B.  Ma,  J.  Zhang and  M.  Zhang: Mater. Sci. Eng. A, 612 (2014), 223. https://doi.org/10.1016/j.msea.2014.06.057
• 18)   W. B.  Liu,  Y. H.  Wen,  N.  Li and  S. Z. Yang: J. Alloys Compd., 472 (2009), 591. https://doi.org/10.1016/j.jallcom.2008.05.024
• 19)   X. F.  Zhang,  W. J.  Lu and  R. S.  Qin: Scr. Mater., 69 (2013), 453. https://doi.org/10.1016/j.scriptamat.2013.05.033
• 20)   H.  Conrad: Mater. Sci. Eng. A, 287 (2000), 227. https://doi.org/10.1016/S0921-5093(00)00780-2
• 21)   W.  Jin,  J.  Fan,  H.  Zhang,  Y.  Liu,  H.  Dong and  B.  Xu: J. Alloys Compd., 646 (2015), 1. https://doi.org/10.1016/j.jallcom.2015.04.196
• 22)   Q. C.  Li,  R. X.  Li,  D. S.  Lin,  G. W.  Chang and  Q. J.  Zhai: J. Iron Steel Res. Int., 19 (2012), 66. https://doi.org/10.1016/S1006-706X(13)60034-5
• 23)   H.  Guo,  X.  Zeng,  J.  Fan,  H.  Zhang,  Q.  Zhang,  W.  Li,  H.  Dong and  B.  Xu: J. Mater. Sci. Technol., 35 (2019), 1113. https://doi.org/10.1016/j.jmst.2018.11.008
• 24)   Z. H.  Zhu,  S. T.  Qiu,  Y.  Gan and  E.  Yue: Iron Steel, 44 (2009), 31 (in Chinese). https://doi.org/10.13228/j.boyuan.issn0449-749x.2009.10.014
• 25)   D. L.  Li,  J. F.  Fang,  Q. B.  Liu,  C. F.  Lu and  J. Y.  Zhang: Metall. Anal., 28 (2008), 1 (in Chinese). https://doi.org/10.1016/B978-012374173-8.50015-6
• 26)   K.  Zhang,  H.  Wang,  X. J.  Sun,  F. L.  Sui,  Z. D.  Li,  E. X.  Pu,  Z. H.  Zhu,  Z. Y.  Huang,  H. B.  Pan and  Q. L.  Yong: Acta Metall. Sin. (Engl. Lett.), 31 (2018), 997. https://doi.org/10.1007/s40195-018-0726-4
• 27)   Z. H.  Zhu and  S. T.  Qiu: Adv. Mater. Res., 472–475 (2012), 1889. https://doi.org/10.4028/www.scientific.net/AMR.472-475.1889
• 28)   K. M.  Banks,  A.  Tuling and  B.  Mintz: Mater. Sci. Technol., 27 (2011), 1309. https://doi.org/10.1179/026708309X12584564052139
• 29)   Q. L.  Yong: Secondary Phases in Steels, The Metallurgical Industry Press, Beijing, (2006), 174 (in Chinese).
• 30)   H.  Nordberg and  B.  Aronsson: J. Iron Steel Inst., 12 (1968), 1263.
• 31)   K.  Narita: Trans. Iron Steel Inst. Jpn., 15 (1975), 145. https://doi.org/10.2355/isijinternational1966.15.145
• 32)   K. J.  Irvine,  F. B.  Pickering and  T.  Gladman: J. Iron Steel Inst., 205 (1967), 161.
• 33)   A.  McLean and  D. A. R.  Kay: Microalloying ’75, eds. by M. Korchynsky et al., Union Carbides Corporation, New York, (1976), 215.
• 34)   J. X.  Chen: Book of Chart and Data for Steel-Making, The Metallurgical Industry Press, Beijing, (1984), 389 (in Chinese).
• 35)   E. T.  Turkdogan: Iron Steelmaker, 16 (1989), 61.