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Acta Metall Sin  2018, Vol. 54 Issue (3): 367-376    DOI: 10.11900/0412.1961.2017.00262
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Incomplete Bainite Transformation Accompanied with Cementite Precipitation in Fe-1.5(3.0)%Si-0.4%C Alloys
Huidong WU1,2, Goro MIYAMOTO3, Zhigang YANG1,2(), Chi ZHANG1,2, Hao CHEN1,2, Tadashi FURUHARA3
1 Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
2 Collaborative Innovation Center of Advanced Nuclear Energy Technology, Tsinghua University, Beijing 100084, China
3 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Cite this article: 

Huidong WU, Goro MIYAMOTO, Zhigang YANG, Chi ZHANG, Hao CHEN, Tadashi FURUHARA. Incomplete Bainite Transformation Accompanied with Cementite Precipitation in Fe-1.5(3.0)%Si-0.4%C Alloys. Acta Metall Sin, 2018, 54(3): 367-376.

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Abstract  

Steels containing bainite microstructure are widely applied in various industrial areas. Incomplete bainite transformation is frequently used to control volume fraction of retained austenite as well as its stability and is also closely related to bainite growth mechanism. It is generally accepted that incomplete bainite transformation could occur when carbide precipitation is absent. On the other hand, some new studies revealed that carbide with very fine size were observed in “carbide-free” bainite in Si added steels. Our previous study on bainite isothermal transformation kinetics together with its microstructural evolution with Fe-1.5(3.0)%Si-0.4%C alloys (mass fraction) at 400~500 ℃ found incomplete bainite transformation phenomenon for the 3.0Si alloy at 450 ℃ and for two alloys at 400 ℃. In contrast with the generally accepted view, cementite precipitation with Si depletion was observed at the beginning of incomplete transformation stage. Further analysis on three dimension atom probe results revealed that the carbide volume fraction as well as amount of C atoms in carbide hardly changes during incomplete transformation stage. Thermodynamic analysis revealed that small chemical driving force for cementite precipitation and/or the necessity of Si partition are two factors accounting for the extremely slow cementite precipitation kinetics. It is thus proposed that incomplete bainite transformation and carbide precipitation could co-exist. Conditions for incomplete bainite transformation are modified as follows. Firstly, bainitic ferrite growth is stopped before reaching equilibrium fraction. In addition, carbide precipitation should be absent or its kinetics should be slow enough.

Key words:  Si added medium carbon steel      incomplete bainite transformation      cementite      threedimensional atom probe (3DAP)     
Received:  03 July 2017     
Fund: Supported by National Natural Science Foundation of China (No.51471094)

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2017.00262     OR     https://www.ams.org.cn/EN/Y2018/V54/I3/367

Fig.1  Schematic of incomplete bainite transformation in which bainite transformation stops growing before volume fraction of bainite reaching equilibrium value (ICT—incomplete bainite transformation, BF—bainitic ferrite, fBF—fraction of bainitic ferrite, t—time)
Alloy Mass fraction of element / % Temperature / ℃
C Si Fe Para-Ae3 NPLE/PLE T0 Ms
1.5Si 0.375 1.48 Bal. 835 823 674 380
3.0Si 0.379 3.09 Bal. 902 879 688 379
Table 1  Nominal compositions and characteristic temperatures of Fe-1.5(3.0)%Si-0.4%C alloys
Fig.2  SEM images of 3.0Si alloy transformed at 450 ℃ for 30 s (a) and 120 s (b), bright field (c) and dark field (d) TEM images as well as SAED pattern with the key diagram taken from BF region in Fig.2a (e) (θ—cementite, M/A—martensite/austenite constituent) [17]
Fig.3  SEM images of 1.5Si alloy transformed at 400 ℃ for 30 s (a) and 120 s (b) [17], bright field (c) and dark field (d) TEM images as well as SAED pattern with the key diagram taken from BF region in Fig.3a (e)
Fig.4  3DAP measured distributions of C with iso-concentration surfaces at 10%C (a1, b1), 15%C (a2, b2), 20%C (a3, b3) in 3.0Si alloy transformed at 450 ℃ for 30 s (a1~a3) and 120 s (b1~b3)
Alloy Temperature Atomic fraction of C Ratio / %
30 s 120 s
3.0Si 450 >10% 1.23 1.06
>15% 0.57 0.51
>20% 0.37 0.32
3.0Si 400 >10% 1.65 1.64
>15% 0.60 0.63
>20% 0.17 0.17
1.5Si 400 >10% 2.45 1.82
>15% 1.51 1.21
>20% 0.69 0.44
Table 2  Ratios between number of substitutional atoms trapped in iso-concentration surfaces of 10%C, 15%C, 20%C and number of substitutional atoms in bainitic ferrite during incomplete bainite transformation stage (denoted as ratio in table) for 3.0Si alloy transformed at 450 ℃, 3.0Si alloy transformed at 400 ℃ and 1.5Si alloy at 400 ℃
  
Alloy Temperature / ℃ Transformation time / s rγ / % rα / % rγ+rα / %
3.0Si 450 30 82.3 6.7 89.0
120 85.8 5.0 90.8
3.0Si 400 30 80.5 7.0 87.5
120 74.1 7.0 81.1
1.5Si 400 30 45.3 5.1 50.4
120 47.7 4.9 52.6
  
Fig.5  Isothermal phase diagram sections of Fe-Si-C system at 450℃ (a) and 400 ℃ (b) for discussion on cementite precipitation from austenite (Blue points represent 3DAP measured C contents at the beginning of incomplete bainite transformation stage[17] and red arrows represent supersaturation for cementite precipitation; Ortho-Acm and Para-Acm represent the austenite composition when cementite is formed from austenite following full equilibrium condition and para-equilibrium condition[18], respectively; Ortho-Ae3 and Para-Ae3 represent the austenite composition when ferrite is formed from austenite following full equilibrium condition and para-equilibrium condition[18], respectively; NPLE/PLE Ae3 represent NPLE/PLE transition line during austenite to ferrite transformation[19]; Tie-line connects compositions of two phases in full equilibrium)
Fig.6  Enlarged isothermal phase diagram sections of Fe-Si-C system at 450 ℃ (a) and 400 ℃ (b) at low carbon side for discussion on cementite precipitation from bainitic ferrite (Red arrows represent supersaturation for cementite precipitation. Blue lines denoted as CCE represent calculated C content of bainitic ferrite from experimentally measured C content in austenite and assuming same chemical potential of C between austenite and ferrite; Ortho-α/α+θ and Para-α/α+θ represent the ferrite composition when cementite is formed from ferrite following full equilibrium condition and para-equilibrium condition[18], respectively; Para-α/α+γ represent the ferrite composition when ferrite is formed from austenite following para-equilibrium condition[18])
[1] De Cooman B C. Structure-properties relationship in TRIP steels containing carbide-free bainite[J]. Curr. Opin. Solid State Mater. Sci., 2004, 8: 285
[2] Jacques P J.Transformation-induced plasticity for high strength formable steels[J]. Curr. Opin. Solid State Mater. Sci., 2004, 8: 259
[3] Zaefferer S, Ohlert J, Bleck W.A study of microstructure, transformation mechanisms and correlation between microstructure and mechanical properties of a low alloyed TRIP steel[J]. Acta Mater., 2004, 52: 2765
[4] Aaronson H I, Reynolds W T Jr, Purdy G R. The incomplete transformation phenomenon in steel[J]. Metall. Mater. Trans., 2006, 37A: 1731
[5] Bhadeshia H K D H, Christian J W. Bainite in steels[J]. Metall. Trans., 1990, 21A: 767
[6] Aaronson H I, Reynolds W T, Shiflet G J, et al.Bainite viewed three different ways[J]. Metall. Trans., 1990, 21A: 1343
[7] Fielding L C D. The bainite controversy[J]. Mater. Sci. Technol., 2013, 29: 383
[8] Reynolds W T, Liu S K, Li F Z, et al.An investigation of the generality of incomplete transformation to bainite in Fe-C-X alloys[J]. Metall. Trans., 1990, 21A: 1479
[9] Reynolds W T, Li F Z, Shui C K, et al.The incomplete transformation phenomenon in Fe-C-Mo alloys[J]. Metall. Trans., 1990, 21A: 1433
[10] Liu Z Q, Miyamoto G, Yang Z G, et al.Carbon enrichment in austenite during bainite transformation in Fe-3Mn-C Alloy[J]. Metall. Mater. Trans., 2013, 46A: 1544
[11] Xia Y, Miyamoto G, Yang Z G, et al.Direct measurement of carbon enrichment in the incomplete bainite transformation in Mo added low carbon steels[J]. Acta Mater., 2015, 91: 10
[12] Hofer C, Leitner H, Winkelhofer F, et al.Structural characterization of "carbide-free" bainite in a Fe-0.2C-1.5Si-2.5 Mn steel[J]. Mater. Charact., 2015, 102: 85
[13] Quidort D, Brechet Y J M. Isothermal growth kinetics of bainite in 0.5%C steels[J]. Acta Mater., 2001, 49: 4161
[14] Tsuzaki K, Kodai A, Maki T.Formation mechanism of bainitic ferrite in an Fe-2pct Si-0.6pct C alloy[J]. Metall. Mater. Trans., 1994, 25A: 2009
[15] Papadimitrou G D, Génin J M R. Kinetic and thermodynamic aspects of the bainite reaction in a silicon steel [A]. Phase Transformation in Solids[C]. Greece: Materials Research Society, 1983: 746
[16] Toji Y, Matsuda H, Herbig M, et al.Atomic-scale analysis of carbon partitioning between martensite and austenite by atom probe tomography and correlative transmission electron microscopy[J]. Acta Mater., 2014, 65: 215
[17] Wu H D, Miyamoto G, Yang Z G, et al.Incomplete bainite transformation in Fe-Si-C alloys[J]. Acta Mater., 2017, 133: 1
[18] Hillert M.Paraequilibrium [R]. Stockholm: Swedish Inst. Met. Res., 1953
[19] Coates D E.Diffusion-controlled precipitate growth in ternary systems I[J]. Metall. Trans., 1972, 3: 1203
[20] Zener C.Kinetics of the decomposition of austenite[J]. Trans. Am. Inst. Min. Metall. Eng., 1946, 167: 550
[21] Andrews K W.Empirical formulae for calculation of some transformation temperatures[J]. J. Iron Steel Inst., 1965, 203: 721
[22] Cullity B D.Elements of X-Ray Diffraction [M]. Massachusetts: Addition-Wesley Publishing Company Inc., 1956: 199
[23] Miller M K, Russell K F, Thompson G B.Strategies for fabricating atom probe specimens with a dual beam FIB[J]. Ultramicroscopy, 2005, 102: 287
[24] Miyamoto G, Shinbo K, Furuhara T.Quantitative measurement of carbon content in Fe-C binary alloys by atom probe tomography[J]. Scr. Mater., 2012, 67: 999
[25] Caballero F G, Miller M K, Garcia-Mateo G.Opening previously impossible avenues for phase transformation in innovative steels by atom probe tomography[J]. Mater. Sci. Technol., 2014, 30: 1034
[26] Kobayashi A.Incomplete bainite transformation in Fe-11Ni-0.2C alloy [D]. Japan: Kyoto University, 1994
[27] Hehemann R F, Kinsman K R, Aaronson H I.Debate on the bainite reaction[J]. Metall. Trans., 1972, 3: 1077
[28] Huang D H, Thomas G.Metallography of bainitic transformation in silicon containing steels[J]. Metall. Trans., 1977, 8A: 1661
[29] Spanos G, Fang H S, Aaronson H I.A mechanism for the formation of lower bainite[J]. Metall. Trans., 1990, 21A: 1381
[30] Yada H.Discussion of “A mechanism for the formation of lower bainite[J]. Metall. Mater. Trans., 1991, 22A: 1674
[31] Franke P, Inden G.An assessment of the Si mobility and the application to phase transformations in silicon steels[J]. Z Metallkd., 1997, 88: 795
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