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Acta Metall Sin  2013, Vol. 49 Issue (1): 26-34    DOI: 10.3724/SP.J.1037.2012.00372
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CALCULATION OF TRANSFORMATION DRIVING FORCE FOR THE PRECIPITATION OF NANO-SCALED CEMENTITES IN THE HYPOEUTECTOID STEELS THROUGH ULTRA FAST COOLING
WANG Bin, LIU Zhenyu, ZHOU Xiaoguang, WANG Guodong
State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819
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Abstract  

In order to meet both the development requirements for reduction in cost and strengthening, recently,the research of precipitation of cementites, as the most economical and common precipitates in steels, has drawn wide attention in the field of precipitation strengthening again, because if cementites could be effectively refined to the scale of a few nanometers, it could also generate very strong precipitation strengthening effects to replace the strengthening role of the precipitates of micro-alloying elements. However, the cementites in hypoeutectoid steels usually form lamellar pearlite structure in near-equilibrium conditions, unable to form the precipitation of nanoscale particles, and they tend to be coarsened significantly at high temperatures after hot rolling. Therefore,the non-equilibrium precipitation of cementites only could be realized by increasing cooling rate after hot rolling, and the thermodynamic feasibility for the formation of nanoscale cementite precipitates during cooling has to be determined. In this work, according to the austenitic transformation mechanism of KRC and LFG models in Fe—C alloys, the transformation driving force of undercooled austenite was calculated systematically in a thermodynamic view, and the effect of ultra fast cooling (UFC) after hot rolling on the precipitation behavior ofnano-scale cementite particles was investigated. Based on the calculation results, the driving force of degenerated pearlitic transformation is the most negative in the three transformation mechanisms, at the same undercooled temperature, which theoretically indicates that the degenerated pearlitic transformation of undercooled austenite can easily occur to form cementite and ferrite with the equilibrium concentrations. In practical manufacturing, the diffusion of carbon atoms could be restrained by decreasing temperature in short time in the application of UFC, as a result that cementites would most likely dispersed in the form of nano-scaled particles directly, rather than being fully grown up into lamellar pealites. Due to the UFC, a large number of dispersed nano-scaled cementite areas were found in the microstructure of hot-rolled hypoeutectoid experiment steels, where the size of the cementites was within the range of ten to tens nanometers. The precipitation of nano-scaled cementites was realized without the micro-alloying elements. Moreover, there were a lot of carbon-rich areas in the microstructure of undercooled austenite, based on the equilibrium concentration calculation, in which the local mole fraction of carbon could be from 0.04 to 0.08, and this part of austenite with the high carbon concentration was apt to decompose and form likely the precipitation of nano-scaled cementites.

Key words:  nano-scaled cementite      ultra fast cooling (UFC)      undercooled austenite      thermodynamics model      transformation driving force     
Received:  18 August 2012     

Cite this article: 

WANG Bin, LIU Zhenyu, ZHOU Xiaoguang, WANG Guodong. CALCULATION OF TRANSFORMATION DRIVING FORCE FOR THE PRECIPITATION OF NANO-SCALED CEMENTITES IN THE HYPOEUTECTOID STEELS THROUGH ULTRA FAST COOLING. Acta Metall Sin, 2013, 49(1): 26-34.

URL: 

https://www.ams.org.cn/EN/10.3724/SP.J.1037.2012.00372     OR     https://www.ams.org.cn/EN/Y2013/V49/I1/26

 


[1] Freeman S, Honeycombe R W K. Met Sci, 1977; 11: 59

[2] Ricks R, Howell P R. Acta Metall, 1983; 31: 853

[3] Kestenbach H. J Mater Sci Technol, 1997; 13: 731

[4] Charleux M, Poole W J, Militzer M, Deschamps A. Metall Mater Trans, 2001; 32A: 163

[5] Kagechika H. ISIJ Int, 2006; 46: 939

[6] Shin D H, Kim Y S, Lavernia E J. Acta Mater, 2001; 49: 2387

[7] Fu J, Li G Q, Mao X P, Fang K M. Metall Mater Trans, 2011; 42A: 3797

[8] Ivanisenko Y, Lojkowski W, Valiev R Z, Fecht H J. Acta Mater, 2003; 51: 5555

[9] Leeuwe Y V, Onink M, Sietsm J, Zwaag S. ISIJ Int, 2001; 41: 1037

[10] Funakawa Y, Shiozaki T, Tomita K, Yamamoto T, Maeda E. ISIJ Int, 2004; 44: 1945

[11] Yen H W, Huang C Y, Yang J R. Adv Mater Res, 2010; 89-91(suppl): 663

[12] Yong Q L. Secondary Phases in Steels. Beijing: Metallur

gical Industry Press, 2006: 159

(雍启龙. 钢铁材料中的第二相. 北京: 冶金工业出版社, 2006: 159)

[13] Yen H W, Huang C Y, Yang J R. Scr Mater, 2009; 61: 616

[14] Kaufman L, Radcliffe S V, Cohen M. Decomposition of Austenite by Diffusional Processe.New York: Interscience, 1962: 313

[15] Lacher J R. Proc Cambridge Phil Soc, 1937; 33: 518

[16] Fowler R H, Guggenheim E A. Statistical Thermodynamics. New York: Cambridge University Press, 1939: 442

[17] Wang G D. Shanghai Met, 2008; 30(2): 1

(王国栋. 上海金属, 2008; 30(2): 1)

[18] Lucas A, Simon P, Bourdon G, Herman J C, Riche P, Neutjens J, Harlet P. Steel Res Int, 2004; 75: 139

[19] Liu Z C, Yuan Z X, Liu Y C. Solid Phase Transformation. Beijing: China Machine Press, 2010: 73

(刘宗昌, 袁泽喜, 刘永长. 固态相变. 北京: 机械工业出版社, 2010: 73)

[20] Mou Y W, Hsu T Y. Acta Metall, 1984; 32: 1469

[21] Machlin E S. Trans TMS-AIME, 1968; 242: 1845

[22] Aaronson H I, Domain H A, Pound G M. Trans TMS-AIME, 1966; 236: 753

[23] Shiflet G J, Bradley J R, Aaronson H I. Metall Trans, 1978; 9A: 999

[24] Hsu T Y. Transformation Principle. Beijing: Science Press, 1988: 61

(徐祖耀. 相变原理. 北京: 科学出版社, 1988: 61)

[25] Kaufman L, Clougherty E V, Weiss R J. Acta Metall, 1963; 11: 323

[26] Mogutnov B M, Tomilin I A, Shartsman L A. Thermodynamics of Fe-C

Moscow: Metallurgy Press, 1972: 109

[27] Orr R L, Chipman J. Trans TMS-AIME, 1967; 239: 630

[28] Darken L S, Gurry R W. Physical Chemistry of Metals. New York: McGraw-Hill, 1953: 401
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