|
|
EFFECTS OF DEFORMATION AND COOLING RATE ON NANO-SCALE PRECIPITATION IN HOT-ROLLED ULTRA-HIGH STRENGTH STEEL |
WANG Xiaonan1,2, DI Hongshuang1, DU Linxiu1 |
1. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819
2. Shagang School of Iron and Steel, Soochow University, Suzhou 215201 |
|
Cite this article:
WANG Xiaonan, DI Hongshuang, DU Linxiu. EFFECTS OF DEFORMATION AND COOLING RATE ON NANO-SCALE PRECIPITATION IN HOT-ROLLED ULTRA-HIGH STRENGTH STEEL. Acta Metall Sin, 2012, 48(5): 621-628.
|
Abstract In order to control nano-scale precipitation (Nb, Ti)C in hot-rolled 780 MPa grade C-Mn steel micro-alloyed with niobium and titanium for automobile frames, the effects of deformation and cooling rate on nano-scale precipitation were investigated by using the thermal simulation experiment technology, then through the transmission electron microscopy observation and statistical analysis. The result indicated, deformation could significantly improve density of dislocation, subgrain boundary and vacancy etc in microstructure, and promote heterogeneous nucleation of precipitation, and improve nucleation rate of precipitation and decrease the average diameter of precipitation. Deformation could improve vacancy concentration and promoted vacancy nucleation. The induction period of precipitation nucleation decrease with the increase of deformation amount and strain rate, and precipitation more easily to nucleate. Precipitation nucleation driving force was mainly supersaturation of microalloy in undeformed experimental steel, and the nucleation mechanism was mainly homogeneous nucleation. However, the nucleation mechanism was mainly heterogeneous nucleation in deformed experimental steel. In one fixed experimental deformation condition, when the cooling rate below 5℃/s, there was (Nb, Ti)C-PFZ (precipitate free zone) nearby original austenitic grain boundaries or subgrain boundaries, and the width of PFZ at cooling rate of 0.5, 1, 2 and 5℃/s were 46.9, 30.2, 28.1 and 0 nm, respectively, so the width of PFZ decreased with the cooling rate increasing. When the cooling rate reached 15℃/s, the nucleation of precipitation was totally inhibited during cooling process. The number of precipitation along with the cooling rate increases gradually decreases. With the increase of cooling rates, the nucleation zone of precipitation was transferred from austenite to ferrite or bainite, and the average diameter of precipitation was refined. Due to grain boundaries or the subgrain boundaries were main traps for supersaturated vacancy, but the diffusivity of vacancy was high, which made the vacancy concentration nearby grain boundaries or the subgrain boundaries lower than critical vacancy concentration for precipitation nucleation, so precipitate could not nucleate nearby grain boundaries or subgrain boundaries. Due to the diffusivity of vacancy was affected by temperature, when the cooling rate was slow, vacancy had enough time to diffuse and annihilate, which made wide PFZ formed. Whereas, when the cooling rate was high, the diffusivity of vacancy was reducing or disappearing, so the width of PFZ was small. In orde to ensure experimental steel had higher yield strength, austenite zone precipitation and (Nb, Ti)C-PFZ nearby boundaries should be inhabited, so the cooling rate should be more than 15 ℃/s in the practical rolling process.
|
Received: 20 February 2012
|
Fund: ;National Natural Science Foundation of China |
[1] Jiao Z B, Liu J C. Mater China, 2011; 30: 6 (焦增宝, 刘锦川. 中国材料进展, 2011; 30: 6)[2] Kashima T, Muka Y. “R$\&$D” Kobe Steel Eng Rep, 2002; 52: 19[3] Tetsuo S, Yoshimasa F, Shinjiro K. JFE Technol Rep, 2004; 4: 25[4] Kazuhiro S, Yoshimasa F, Shinjiro K. JFE Technol Rep, 2007; 10: 19[5] Misra R D K, Nathani H, Hartmann J E, Siciliano F. Mater Sci Eng, 2005; A394: 339[6] Lu J X, Wang G D. Iron Steel, 2005; 40: 69 (陆匠心, 王国栋. 钢铁, 2005; 40: 69)[7] Sha Q Y, Li G Y, Yan P Y, Ao L G, Hao S. Mater China, 2011; 30: 23 (沙庆云, 李桂艳, 严平沅, 熬列格, 郝森. 中国材料进展, 2011; 30: 23)[8] Zhou J, Kang Y L, Mao X P, Li L J, Lin Z Y. Iron Steel, 2006; 41(Suppl.): 343 (周建, 康永林, 毛新平, 李烈军, 林振源. 钢铁, 2006; 41(增刊): 343)[9] Huang Q Y, Yan H W, Pan Y L, Yang J R. Min Metall, 2008; 53: 45(黄庆渊, 颜鸿威, 潘永林, 杨哲人. 矿冶, 2008; 53: 45)[10] Chen C Y, Yen H W, Kao F H , Li W C, Huang C Y, Yang J R, Wang S H. Mater Sci Eng, 2009; A499: 162[11] Wang T P, Kao F H, Wang S H, Yang Z R, Huang C Y, Chen H R. Mater Lett, 2011; 65: 396[12] Wang X N, Du L X, Zhang H L, Di H S. J Iron Steel Res, 2011; 23: 45 (王晓南, 杜林秀, 张海仑, 邸洪双. 钢铁研究学报, 2011; 23: 45)[13] Wang X N, Du L X, Xie H, Di H S, Gu D H. Steel Res Int, 2011; 82: 1417[14] Okamoto R, Borgenstam A, Agren J. Acta Mater, 2010; 58: 4783[15] Jia Z, Misra R D K, O'Malley R, Jansto S J. Mater Sci Eng, 2011; A528: 7077[16] Xu G, Gan X L, Ma G J, Luo F, Zou H. Mater Des, 2010; 31: 2891[17] Niakan H, Najiafizadeh A. Mater Sci Eng, 2010; A527: 5410[18] Olasolo M, Uranga P, Rodriguez-Ibabe J M, Lopez B. Mater Sci Eng, 2011; A528: 2559[19] Okamoto R, Borgenstam A, Agren J. Acta Mater, 2010; 58: 4783[20] Yong Q L. Secondary Phases in Steels. Beijing: Metallurgical Industry Press, 2006: 145 (雍岐龙. 钢铁材料中的第二相. 北京: 冶金工业出版社, 2006: 145)[21] He X L, Shang C J, Yang S W, Wang X M, Guo H. High Performance Low Carbon Bainite Steel. Beijing: Metallurgical Industry Press, 2008: 202 (贺信莱, 尚成嘉, 杨善武, 王学敏, 郭晖. 高性能低碳贝氏体钢. 北京: 冶金工业出版社, 2008: 202)[22] Manohar P A, Dunne D P, Chandar T, Killmore C R. ISIJ Int, 1996; 36: 194[23] Kang Y L, Fu J, Liu D L, Yu H.Control of Microstructure and Properties in Thin Slab Casting and Rolling Steel.Beijing: Metallurgical Industry Press, 2006: 144 (康永林, 傅杰, 柳得橹, 于浩. 薄板坯连铸连轧钢的组织性能控制. 北京: 冶金工业出版社, 2006: 144)[24] Dutta B, Sellars C M. Mater Sci Technol, 1987; 3: 197[25] Porter D A, Easterlin K E. Phase Transformations in Metals and Alloys.New York: Van Nostrand Reinhold Company Ltd., 1981: 303[26] Takashi S, Shuji K, Sadao H, Akio S, Takao O, Kuniaki O. JFE Technol Rep, 2004; 2: 1 |
No Suggested Reading articles found! |
|
|
Viewed |
|
|
|
Full text
|
|
|
|
|
Abstract
|
|
|
|
|
Cited |
|
|
|
|
|
Shared |
|
|
|
|
|
Discussed |
|
|
|
|