Prior austenite orientation reconstruction of coherently transformed products and its application on austenite twinning
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摘要: 基于電子背散射衍射（EBSD）技術，利用極射赤面投影圖，提出了一種不依賴于殘余奧氏體，對協變相變產物的原奧取向進行重構的簡易方法.計算結果表明，利用鐵素體的{110}α極圖中三個貝恩組的交點可以成功重構出原始奧氏體取向，并且精度可達2°；同時，該方法還可以對局部微區或者變體選擇很嚴重的原奧取向進行重構，誤差仍可控制在2°之內，具有其他重構方法無可比擬的優點.位向關系具體種類并不影響對原奧取向的重構，采用該方法進行原奧取向重構時不需要預先知道具體的位向關系，并且適用于位向關系處在K-S與N-W關系之間的所有協變相變過程.通過運用該方法重構原奧取向，本文研究了高溫奧氏體化過程中的奧氏體行為.研究發現當采用較高的溫度奧氏體化時會出現奧氏體孿晶，奧氏體孿晶的出現與奧氏體化溫度有關.Abstract: High-angle grain boundaries and martensite/austenite (M/A) constituents are two critical factors that contribute to low impact toughness in metals. The generation mechanism of the high-angle grain boundaries is closely related to the crystallography of the transformed products, which are transformed by prior austenite. Austenite undergoes phase transformation when cooled to ambient temperature and cannot be retained. During coherent phase transformation, variant pairs, from which the high-angle grain boundaries originate, are transformed. Variant selection is a common phenomenon in coherent phase transformation. The properties of the prior austenite grain, such as its shape, size, orientation, texture, and particularity of formation, will affect the subsequent phase transformation dramatically, and the variant pairs are accordingly introduced. However, it is impossible to evaluate this effect when the prior austenite orientation is unclear. Hence, the orientation needs to be reconstructed. In this article, a simple method of reconstructing the prior austenite orientation during coherent phase transformation is proposed by employing the {110}α stereographic projection on the basis of electron backscatter diffraction (EBSD) measurements. Retained austenite is not necessary when applying this methodology. The results show that the prior austenite orientation is well reconstructed with superior precision of below 2°. This is especially applicable when strong variant selection occurs or when reconstructing a tiny part of the prior austenite grain. The specific unknown orientation relationship (OR) between prior austenite and ferrite has a little effect on the reconstruction process, averting complicated calculations of this specific unknown OR. It is still possible to reconstruct the austenite orientation when the actual OR is not accessible. Moreover, it can be employed to all the coherently transformed products that maintain an OR from K-S OR to N-W OR to the prior austenite grain. A specific example in which this method is adopted is given, and the austenizing behavior is studied. At higher austenization temperatures, a special type of austenite grain, i.e, an austenite twin, is transformed. This is difficult to occur at lower austenization temperatures, implying that the austenite twin formation is closely correlated to the austenization temperature. The formation mechanism of austenite twin and its effect on the following phase transformation remains unclear; thus, much emphasis should be placed on it.
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參考文獻
[1] Guo Z, Lee C S, Morris J W. On coherent transformations in steel. Acta Mater, 2004, 52(19):5511 [4] Bowles J S, Mackenzie J K. The crystallography of martensite transformations I. Acta Metall, 1954, 2(1):129 [5] Furuhara T, Maki T. Variant selection in heterogeneous nucleation on defects in diffusional phase transformation and precipitation. Mater Sci Eng A, 2001, 312(1-2):145 [6] Gey N, Humbert M, Gautier E, et al. Study of the β→α variant selection for a zircaloy-4 rod heated to the β transus in presence or not of an axial tensile stress. J Nucl Mater, 2004, 328(2-3):137 [7] Stanford N, Bate P S. Crystallographic variant selection in Ti-6Al-4V. Acta Mater, 2004, 52(17):5215 [8] Morito S, Huang X, Furahara T, et al. The morphology and crystallography of lath martensite in alloy steels. Acta Mater, 2006, 54(19):5323 [10] Kurdjumow G, Sachs G. Vber den mechanismus der Stahlhärtung. Z Phys, 1930, 64(5-6):325 [11] Cayron C, Barcelo F, de Carlan Y. The mechanisms of the fcc-bcc martensitic transformation revealed by pole figures. Acta Mater, 2010, 58(4):1395 [13] Bouyne E, Flower H M, Lindley T C, et al. Use of EBSD technique to examine microstructure and cracking in a bainitic steel. Scripta Mater, 1998, 39(3):295 [14] Gourgues A F. Microtexture induced by the bainitic transformation in steels during welding:effect on the resistance to cleavage cracking. Mater Sci Forum, 2003, 426-432:3629 [15] Gourgues A F, Flower H M, Lindley T C. Electron backscattering diffraction study of acicular ferrite, bainite, and martensite steel microstructures. Mater Sci Technol, 2000, 16(1):26 [16] Kitahara H, Ueji R, Tsuji N, et al. Crystallographic features of lath martensite in low-carbon steel. Acta Mater, 2006, 54(5):1279 [18] Miyamoto G, Takayama N, Furuhara T. Accurate measurement of the orientation relationship of lath martensite and bainite by electron backscatter diffraction analysis. Scripta Mater, 2009, 60(12):1113 [19] Humbert M, Blaineau P, Germain L, et al. Refinement of orientation relations occurring in phase transformation based on considering only the orientations of the variants. Scripta Mater, 2011, 64(2):114 [20] Germain L, Gey N, Mercier R, et al. An advanced approach to reconstructing parent orientation maps in the case of approximate orientation relations:application to steels. Acta Mater, 2012, 60(11):4551 [21] Abbasi M, Nelson T W, Sorensen C D, et al. An approach to prior austenite reconstruction. Mater Charact, 2012, 66:1 [22] Bernier N, Bracke L, Malet L, et al. An alternative to the crystallographic reconstruction of austenite in steels. Mater Charact, 2014, 89:23 [23] Takayama N, Miyamoto G, Furuhara T. Effects of transformation temperature on variant pairing of bainitic ferrite in low carbon steel. Acta Mater, 2012, 60(5):2387 [24] Miyamoto G, Iwata N, Takayama N, et al. Mapping the parent austenite orientation reconstructed from the orientation of martensite by EBSD and its application to ausformed martensite. Acta Mater, 2010, 58(19):6393 -
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