SCollege of Materials Science and Engineering, Chongqing University, Chongqing 400044, China
Cite this article:
GUO Junli, WEN Guanghua, FU Jiaojiao, TANG Ping, HOU Zibing, GU Shaopeng. Influence of Cooling Rate on the Contraction of Peritectic Transformation During Solidification of Peritectic Steels. Acta Metall Sin, 2019, 55(10): 1311-1318.
Driven by the demand for the improving mechanical properties of steel products and the cost reduction in alloys, steels falling within the peritectic composition range are designed recently. However, notoriously cast surface defects such as cracks, deep oscillation mark formation and breakouts are found to occur frequently during continuous casting of steels, particularly at high casting speeds. This phenomenon is closely related to the shrinkage of phase transformation caused by the peritectic transformation. In order to understand the effects of cooling rate on the contraction of the peritectic transformation, the initial solidification processes of a peritectic steel (Fe-0.1C-0.21Si-1.2Mn, mass fraction, %) were observed using high-temperature confocal laser scanning microscopy under different cooling rates, and then variations in surface roughness were measured to reflect the degree of peritectic transformation contraction. The results show that the peritectic transformation occurs a massive transformation when the cooling rate exceeds the critical value. The massive transformation results in a sudden peritectic transformation contraction and surface roughness variations, which directly cause the occurrence of surface longitudinal cracks of slabs at high casting speeds. The contraction increases first and then decreases with the cooling rate increasing and the maximum surface roughness at the middle cooling rate (20 ℃/s) is about 2.8 times more extensive than that which occurs at the low cooling rate of 2.5 ℃/s. The phenomenon that the peritectic transformation contraction decreases under the high cooling rate may provide a new strategy to reduce cracks occurring in high speed casting.
Fig.2 The peritectic transformation of δ to γ under the cooling rate of 2.5 ℃/s
Fig.3 Image analyses of the δ/γ propagation of region A in Fig.2a
Fig.4 Two different modes of the peritectic transformation during solidification (G.B.—grain boundary)
Fig.5 Peritectic transformation temperatures under different cooling rates (T0-line is the thermodynamic equivalence of δ and γ)
Fig.6 Relationship between the cooling rate (dT/dt) and the undercooling (ΔT)
Fig.7 Surface morphologies under the cooling rates of 5 ℃/s (a) and 50 ℃/s (b)
Fig.8 Surface roughness (a) and the difference between maximum of roughness Ra(max) and minimum of roughness Ra(min) (φ) (b) under different cooling rates
Fig.9 Effect of the cooling rate and casting speed at the initial solidification in mold on the crack
[1]
Saleem S, Vynnycky M, Fredriksson H. The influence of peritectic reaction/transformation on crack susceptibility in the continuous casting of steels [J]. Metall. Mater. Trans., 2017, 48B: 1625
[2]
Ma N B, Lei Z S, Jin X L ,et al. Effect of temperature fluctuation on initial solidification process during peritectic steel continuous casting [J]. Acta Metall. Sin., 2008, 44: 1019
Cai Z Z, Zhu M Y. Microsegregation of solute elements in solidifying mushy zone of steel and its effect on longitudinal surface cracks of continuous casting strand [J]. Acta Metall. Sin., 2009, 45: 949
Ridolfi M R, De Vito A, Ferro L. Effect of alloying elements on thermal contraction and crack susceptibility during in-mold solidification [J]. Metall. Mater. Trans., 2008, 39B: 581
[6]
Emi T, Fredriksson H. High-speed continuous casting of peritectic carbon steels [J]. Mater. Sci. Eng., 2005, A413-414: 2
[7]
Cai K K. Quality Control of Continuous Casting Strand [M]. Beijing: Metallurgical Industry Press, 2010: 163
[7]
(蔡开科. 连铸坯质量控制 [M]. 北京: 冶金工业出版社, 2010: 163)
[8]
Mondragón J J R, Trejo M H, de Jesús Castro Román M, et al. Description of the hypo-peritectic steel solidification under continuous cooling and crack susceptibility [J]. ISIJ Int., 2008, 48: 454
[9]
Trejo M H, Lopez E A, Mondragon J J R ,et al. Effect of solidification path and contraction on the cracking susceptibility of carbon peritectic steels [J]. Met. Mater. Int., 2010, 16: 731
[10]
Konishi J, Militzer M, Samarasekera I V, et al. Modeling the formation of longitudinal facial cracks during continuous casting of hypoperitectic steel [J]. Metall. Mater. Trans., 2002, 33B: 413
[11]
Hu Z G, Ma C L, Liu L, et al. Region of peritectic reaction in thin slab casting process of CSP [J]. J. Iron Steel Res., 2006, 18(7): 10
Yasuda H, Nagira T, Yoshiya M ,et al. Massive transformation from δ phase to γ phase in Fe-C alloys and strain induced in solidifying shell [J]. IOP Conf. Ser.: Mater. Sci. Eng., 2012, 33: 012036
[13]
Shibata H, Arai Y, Suzuki M, et al. Kinetics of peritectic reaction and transformation in Fe-C alloys [J]. Metall. Mater. Trans., 2000, 31B: 981
[14]
Griesser S, Bernhard C, Dippenaar R. Effect of nucleation undercooling on the kinetics and mechanism of the peritectic phase transition in steel [J]. Acta Mater., 2014, 81: 111
[15]
Guo J L, Wen G H, Pu D Z, et al. A novel approach for evaluating the contraction of hypo-peritectic steels during initial solidification by surface roughness [J]. Materials, 2018, 11: 571
[16]
Pu D Z, Wen G H, Fu D C, et al. Study of the effect of carbon on the contraction of hypo-peritectic steels during initial solidification by surface roughness [J]. Metals, 2018, 8: 982
[17]
Becker R. Effects of strain localization on surface roughening during sheet forming [J]. Acta Mater., 1998, 46: 1385
[18]
Fu J X, Li X D, Hwang W S. Study of the coefficient of thermal expansion for steel Q235 [J]. Adv. Mater. Res., 2011, 194-196: 326
[19]
Ueshima Y, Mizoguchi S, Matsumiya T ,et al. Analysis of solute distribution in dendrites of carbon steel with δ/γ transformation during solidification [J]. Metall. Trans., 1986, 17B: 845
[20]
Nishimura T, Morishita K, Nagira T ,et al. Kinetics of the δ/γ interface in the massive-like transformation in Fe-0.3C-0.6Mn-0.3Si alloys [J]. IOP Conf. Ser.: Mater. Sci. Eng., 2015, 84: 012062
[21]
Bhattacharyya S K, Perepezko J H, Massalski T B. Nucleation during continuous cooling—Application to massive transformations [J]. Acta Metall., 1974, 22: 879
[22]
Wolf M M. Mold heat transfer and lubrication control—Two major functions of caster productivity and quality assurance [A]. Process Technology Conference Proceedings [C]. Nashville: Iron and Steel Society, 1995: 99
[23]
Hanao M, Kawamoto M, Yamanaka A. Growth of solidified shell just below the meniscus in continuous casting mold [J]. ISIJ Int., 2009, 49: 365
[24]
Kanazawa T, Hiraki S, Kawamoto M, et al. Behavior of lubrication and heat transfer in mold at high speed continuous casting [J]. Tetsu Hagáne, 1997, 83: 701
Cicutti C, Boeri R. Analysis of solute distribution during the solidification of low alloyed steels [J]. Steel Res. Int., 2006, 77: 194
[26]
Edvardsson T, Fredriksson H, Svensson I. A study of the solidification process in low-carbon manganese steels [J]. Met. Sci., 1976, 10: 298
[27]
Mizukami H, Suzuki T, Umeda T, et al. Initial stage of rapid solidification of 18-8 stainless steel [J]. Mater. Sci. Eng., 1993, A173: 361
[28]
Dhindaw B K, Antonsson T, Fredriksson H, et al. Characterization of the peritectic reaction in medium-alloy steel through microsegregation and heat-of-transformation studies [J]. Metall. Mater. Trans., 2004, 35A: 2869
