外文文献翻译SolidificationOfGrayCastIron

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1、本科毕业论文外文文献及译文文献、资料题目：Solidification Of Gray Cast Iron文献、资料来源：Scripta Materialia文献、资料发表（出版）日期：2003.10.19 院 （部）： 材料科学与工程学院专 业： 材料成型及控制工程班 级： 姓 名： 学 号： 指导教师： 翻译日期： 山东建筑大学毕业论文外文文献及译文外文文献：Solidification of gray cast ironAbstract This article investigates the solidification of hypo, eutectic and hypereute

2、ctic gray cast irons, using novel techniques developed bythe authors. The nature of the revealed macro and microstructure suggests that the solidification mechanism is different from that usually accepted.Keywords: Solidification; Gray iron1. Introduction Several authors have studied the solidificat

3、ion of eutectic gray cast iron of flake graphite morphology (GI)17. Commonly, the eutectic solidification unit is represented by a nearly spherical shape of austenite and graphite, as shown in Fig. 1. There is general agreement to consider that austenite and graphite grow cooperatively, being both i

4、n contact with the liquid phase. This picture of the solidification of GI is supported by the morphology of the graphite flakes, that resemble a rosette, as shown in Fig. 2, and by the fact that the inclusions, generally associated to the microsegregation at the last to freeze melt, are located betw

5、een such units. Steads reagent reveals the microsegregation of phosphorus in GI, and it can delineate the units schematically represented in Fig. 1 in high P irons, usually referred to as eutectic cells 8. Since austenite dendrites are not readily discernible, except in gray irons containing types D

6、 and E graphite, their formation and growth characteristics in GI have received limited attention. Some researchers have considered the role of austenite dendrites in the solidification of GI 2,6,7. There is no doubt that austenite of hypoeutectic GI grows dendritically. On the other hand, most of t

7、he literature work state that austenite can grow with other morphologies when the carbon content reaches or exceeds the eutectic 3,7. During the last years the authors of the present article carried out investigations that challenged the validity of the more firmly established models of the solidifi

8、cation of ductile iron (DI) 911. The use of a specially developed technique, that allows to reveal the solidification macrostructure of DI, combined with the use of color metallography techniques that reveal the microsegregation pattern, showed that the macrostructure of DI is formed by relatively l

9、arge austenite grains, that contain a very large numbers of graphite nodules. This was the case for hypoeutectic, eutectic, and also hypereutectic DI. The objective of this study is to investigate the solidification mechanism of GI by using the micro and macroscopic techniques, successfully applied

10、for DI in earlier studies.Experimental methods2.1. Materials The melts utilized in the present study were produced by using a 50 kg medium frequency induction melting furnace. Low manganese pig iron, steel scrap and ferroalloys were used as raw materials. Melts were cast in resin bonded sand moulds

11、to produce round bars of 20, 30 and 46 mm diameter. Table 1 lists the chemical composition of the alloys used. The melts were alloyed with Cu and Ni in order to provide enough austemperability to carry out the DAAS macrography technique, which is described below.2.2. Micrographic technique The color

12、 etching technique reveals the solidification microstructure through the use of a reagent that brings up the microsegregation patterns generated during solidification 12. The etching reagent is made of 10 g NaOH, 40 g KOH, 10 g picric acid and 50 ml distilled water. It must be prepared and handled w

13、ith great care, since it is caustic and toxic. Etching is carried out at 120 (278 F) for about 2 min.Fig. 1. Schematic illustration of the solidification unit of eutectic GI.Fig. 2. Morphology of graphite ?akes of eutectic GI.2.3. Macrographic technique In order to allow the observation of the macro

14、structure of DI it is necessary to carry out a thermal process called DAAS (Direct Austempering After Solidification)9. In this process, the cast parts are shaken out from the mould short after casting, when their temperature is approximately 950 C, and transferred to a furnace held at 900 C, where

15、they remain for 30 min to allow temperature stabilization. The parts are then austempered in a molten salt bath held at 360 C, for 90 min. A relatively high austempering temperature is used to obtain a high amount of retained austenite after treatment. After the DAAS treatment, the matrix microstruc

16、ture shows a fine mixture of ferrite needles and retained austenite. A schematic of the thermal cycle is shown in Fig. 3a. The DAAS treatment is certainly laborious and cannot be used under usual molding circumstances. Nevertheless, it is the only method capable of revealing low alloy ductile cast i

17、ron macrostructures, to the best of the authors knowledge. After this procedure, the retained austenite keeps the crystalline orientation defined during solidification. Therefore, etching with Picral (5%) reveals the grain structure of the solidification austenite. It must be emphasized that such ma

18、crostructure will be not visible after a conventional austempering treatment, as that shown schematically in Fig. 3b, since the microstructure will be formed starting from a fine grain recrystallized austenite structure obtained after austenitizing. This technique has not been applied before to GI.

19、As a first approach it will be used on GI following the same procedure developed for DI.Fig. 3. (a) DAAS thermal cycle, (b) regular austempering thermal cycle.3. Results and discussion Fig. 4ac show the unetched microstructure of the 30 mm diameter samples of hypoeutectic, eutectic, and hypereutecti

20、c melts, respectively. Predominately type A lamellar graphite structure is observed in all cases. Fig. 5ac show the macrostructure revealed by the DAAS technique on the same samples of Fig. 4. In all cases, a relatively large grained macrostructure is observed on the sample surface, including the hy

21、pereutectic alloy. This is, to the best of our knowledge, the first time such structure is revealed on sand cast GI samples solidi?ed normally. The grains, or solidification units, are much larger than expected for the solidification model based on nearly spherical units (eutectic cells) represented

22、 in Fig. 1. As it was mentioned before, the eutectic cells are usually revealed through the microsegregation of phosphorus by the application of the Stead reagent. Nevertheless, it is important to point out that this method does not prove that areas separated by microsegregation of phosphorus are in

23、 fact different grains, because it does not etch di?erentially grains, or volumes, of different crystal orientation. It is remarkable that the grain structure has similar size among samples of the same diameter, regardless its carbon equivalent. The only difference is that the hypoeutectic GI shows

24、a more pronounced columnar structure. Fig. 6 shows the macrostructure of the samples of 20, 30 and 46 mm diameter of the hypereutectic melt. Note that the grain size slightly increases when thediameter increases.Fig. 4. Microstructure of unetched samples of 30 mm round bars. (a) Hypoeutectic melt, (

25、b) eutectic melt, (c) hypereutectic melt.Fig. 5. Macrostructure of 30 mm diameter round bars. (a) Hypoeutectic melt, (b) eutectic melt, (c) hypereutectic melt.The presence of such large grains indicates that large portions of the sample have the same austenite crystalline orientation. It should then

26、 be possible to find indications of austenite growth inside a solidification grain. This was investigated by tracing the microsegregation inside each grain by using the color metallography technique. The results show the presence of austenite dendrites for GI of all carbon equivalent values investig

27、ated. As an example, Fig. 7 shows the solidification microstructure of the hypereutectic melt. It is remarkable that the graphite colonies do not show an interdendritic morphology, but are immersed in the dendrite stem in many places, as pointed by the arrows. This explains why such dendrites have n

28、ot been identified before, through the observation of the distribution of flake graphite. It also suggests that flake graphite may grow to some extent, most probably during the last stages of solidification or during solid state graphitization, not in contact with the melt but by C diffusion through

29、 an austenite envelope. Fig. 6. Macrostructure of round bars of hypereutectic melt. (a) 20 mm, (b) 30 mm, (c) 46 mm. The presence of such large grains and the morphology of microsegregation patterns suggest that the so-called eutectic cells are not actual individual solidification units, but large g

30、roups of them have a common origin in a very large austenite dendrite. The observations lead to propose the following explanation of GI solidification. Very thin or skinny austenite dendrites nucleate and grow to large extent at, or below, the temperatures pointed on Fig. 8. Any graphite particles t

31、hat may be present in the melt at this stage are engulfed by this dendritic array. This is most probably effectively taking place in the case of hypereutectic GI. Existing particles at the intradendritic melt, or newly nucleated graphite nuclei at the supersaturated intradendritic melt, make contact

32、 with austenite branches and begin cooperative growth, forming the units called eutectic cells. It is possible to speculate that, for both hypereutectic and hypoeutectic GI, there is not a nucleation event for eutectic cells, but the solidification process is dominated by the initial growth of relat

33、ively large austenite dendrites that provide a large density of austenite seeds on which the formerly called eutectic cells can form. These units are not solidification grains, as it is commonly accepted. A great number of them are present into each grain.Fig. 7. Black and white print of hypereutect

34、ic melt after color etching.Fig. 8. Schematic section of the eutectic region of the FeC equilibrium diagram. The proposed mechanism is supported by observations of other authors. Ruff and Wallace 2 point out that austenite dendrites are present in gray iron of hypo, hyper and eutectic composition, a

35、nd that the nucleation of eutectic austenite takes place on and near the primary austenite dendrites. Dioszegi et al. 7 state that for hypoeutectic alloys the place for the eutectic nucleation is believed to be close to the interface of primary austenite in the segregated liquid. These studies do no

36、t state that there is no new nucleation of austenite, but they suggest that there is a link between austenite dendrites and the nucleation of eutectic austenite. Numerous experiments have demonstrated that the number of eutectic cells per unit area is increased by the addition of inoculants to the m

37、elt. The solidification model proposed in this work does not deny this mechanism. It is clear that the inoculation process increases the nucleation rate of graphite, then a larger number of graphite nuclei would cause a more frequent interaction between austenite branches and graphite, leading to a

38、larger number of smaller units of coupled eutectic cells. As it is well known the observations of the eutectic cells is very useful to relate solidification structure characteristics with properties of the cast part.Conclusions The DAAS macrographic technique has been successfully applied to reveal

39、the macrostructure of hypo, hyper and eutectic flake gray cast irons. The macrostructure of sand cast hypo, hyper and eutectic GI show relatively large grains in all cases. Color metallography techniques were used to reveal the austenite dendrites locations and its interaction with graphite flakes.

40、Graphite flakes frequently cross austenite dendrite stems, suggesting that such flakes can continue growing after they have been enveloped by austenite. This study proves that austenite dendrite growth is predominant not only for hypoeutectic but also for hypereutectic gray irons. The units usually

41、called eutectic cells are not solidification grains, as it is commonly accepted. A great number of them are present into each grain.References：1 Morrogh H, Olfield W. Iron Steel 1959;32:479.2 RuffGF, Wallace JF. AFS Trans 1976;84:705.3 Angus HT. Cast Iron: Physical and Engineering Properties. Butter

42、worths; 1976. p. 5.4 Stefanescu DM. Metals Handbook, Casting. ASM International; 1988. p. 168.5 Roviglione AN. Doctoral Thesis. National University of La Plata, Argentina. 1998.6 Miyake H, Okada A. AFS Trans 1998;106:581.7 Diooszegi A. Millberg A, Svensson IL. Proceedings of the International Confer

43、ence on The Science of Casting and Solidification, 2001; p. 269.8 Moore JC. Metals Handbook, Metallography, structures and phase diagrams. ASM International; 1973. p. 93.9 Boeri RE, Sikora JA. Int J Cast Metals Res 2001;13:307.10 Rivera GL, Boeri RE, Sikora JA. Mater Sci Technol 2002;18: 691.11 Rive

44、ra GL, Boeri RE, Sikora JA. AFS Trans 2003:111.12 Rivera GL, Boeri RE, Sikora JA. Cast Metals 1995;8:1.中文译文：灰铸铁的凝固结晶过程摘要：本文作者用由自己发展出的新颖的技术研究了亚共晶、共晶和过共晶灰铸铁的结晶过程。这些被揭示的宏观及微观结构表明灰铸铁的结晶机理与我们通常所接受的说法并不相符。关键词：凝固结晶；灰铸铁1.导言：有几位作者之前已经研究了成片状石墨形态共晶灰铸铁的凝固结晶过程。通常，共晶灰铸铁的结晶单元呈现出近似奥氏体与石墨的球状形态，如图1所示。大家普遍认为奥氏体和石墨是同步生

45、长的，原因是它们同时与液相接触。这种设想一方面被呈玫瑰状的层状石墨形态（如图2）所支持；另一方面也被存在于晶间的夹杂物所支持，这些夹杂物与最后结晶时的显微偏析有关并存在于上述晶间。斯泰得的反应物揭示了灰铸铁中磷的显微偏析，它可以描画出图1中含磷量高的灰铸铁的金相所大体上呈现出的特征，通常被称为共晶团。由于奥氏体的树枝状结晶不易被辨别，除了在含有“D”型或“E”型石墨的灰铸铁中，其他情况下它们的形成和生长特征没有受到太多的关注。有一些研究人员也对奥氏体树枝状晶在灰铸铁结晶过程中的作用进行过研究。毫无疑问，亚共晶灰铸铁中的奥氏体是以树枝状生长的。另一方面，许多文献表明。奥氏体在碳含量达到或超过共晶

46、点时会生长成其它不同的形态。去年，本文的作者们完成了一个研究，挑战了被更加稳固的建立的可锻铸铁的凝固结晶模型的权威性。一项被特殊发展出的技术的应用，使得揭示可锻铸铁的结晶宏观结构成为可能，同时彩色金相技术的应用展现出了显微偏析的图案。通过这些技术表明，可锻铸铁的宏观组织是由相互关联的粗大奥氏体晶粒形成的，其中包含着数量众多的石墨球。这就是亚共晶、共晶、过共晶可锻铸铁的事实。这个研究的目的就是研究灰铸铁的凝固结晶机理，通过使用显微和目视的各种技术来完成。这些技术在之前的对可锻铸铁的研究中被非常成功的应用。2.实验方法2.1实验材料现在研究中所用的铁液是用50kg中频感应炉生产的。低锰生铁、废钢和

47、铁合金都被用作成产的原料。铁液被浇注入树脂砂模中来生产直径分别为20、30、和60mm的棒条。表1列出了所用合金的化学成分。铁液中加入铜和镍是为了提供足够的等温淬火性能来获得DAAS宏观检测技术，这项技术将在下面进行介绍。2.2微观技术彩色腐蚀技术通过应用一种试剂揭示了凝固结晶的微观结构。这种试剂可以显现出凝固过程中产生的显微偏析的图案。这种腐蚀试剂是由10gNaOH、40gKOH、10g苦味酸和50ml蒸馏水组成的。这种腐蚀剂必须要被妥善制备和保管，因为它是有腐蚀性并且有毒的。腐蚀剂要在120（278F）下保温2分钟才能取出。图1 共晶灰铸铁凝固结晶单元示意图图2 共晶灰铸铁石墨形态2.3宏

48、观技术为了能够观察可锻铸铁的宏观结构，我们需要提出一种热处理过程，被称为DAAS（结晶后直接淬火）。在这个过程中，当温度大约达到950时，铸件被从铸模中振出并被放到900的加热炉中保温30min，以便让温度稳定下来。然后将铸件放入360的盐浴中奥氏体等温淬火90分钟。相应的高的奥氏体等温淬火温度是为了在热处理后获得大量的残余奥氏体。经过DAAS处理后，铸件的显微组织表现出一种很好的针状铁素体和残余奥氏体的混合体。一个热处理冷却图如图3a所示。DAAS处理当然是一种费力的方法，不应用于通常的铸造情形下。然而，据笔者所知，它是现在唯一一种能够揭示低合金可锻铸铁宏观组织的方法。经过这一过程后，残余奥

49、氏体保持了凝固时的结晶倾向。因此，含有苦味酸的腐蚀剂揭示了结晶后奥氏体的晶粒结构。必须被强调的是这样的宏观组织是不能在传统的奥氏体等温淬火后观察到的，如图3b所示，因为其中的显微组织会在奥氏体化后经历一次奥氏体晶粒重结晶过程。这项技术还没有被应用于灰铸铁。作为第一种途径，它将像在可锻铸铁中的发展一样被应用于灰铸铁。图3 (a)DAAS热处理冷却图 (b)常规奥氏体等温淬火冷却图3.结论与分析图4a-c表现了未被腐蚀的直径为30mm的分别为亚共晶、共晶、过共晶的试样的显微组织结构。在所有的情况下都可以看到大量的层状石墨。图5a-c展示了在图4中所示的相同试样上采用DAAS技术所获得的宏观组织结构

50、。在所有情况中，晶粒生长的相对比较大的组织都是在试样的表面发现的，包括过共晶合金。这就是说，据我们所知，这是第一次正式在砂型铸件中发现这种组织。这些晶粒或者结晶单元的尺寸要比我们基于图1中所示的球形晶粒建立的结晶模型的预想大得多。如前所述，共晶团通常是被由于加入稳定剂产生的磷的显微偏析所表现出来的。然而，需要指出的是，这种方法不能证明被磷的显微偏析分隔开的不同区域就是不同的晶粒，因为它没有侵蚀到不同结晶倾向的不同晶粒或者体积。值得注意的是无论碳当量如何，相同直径的试样有着相似的晶粒组织。唯一不同的是亚共晶灰铸铁表现出一种更加明显的柱状晶。图6表现了直径20、30、60mm过共晶试样的宏观组织形

51、貌。从中可以看出随着试样直径的增加，晶粒尺寸略有增长。 图4未腐蚀的直径30mm试棒的显微组织 (a)亚共晶组织(b)共晶组织(c)过共晶组织图5 直径30mm试棒的宏观形貌 (a)亚共晶组织(b)共晶组织(c)过共晶组织这种大晶粒的存在暗示了试样中有很大一部分都具有相同的奥氏体结晶倾向。这之后使得找到在凝固结晶的晶粒中的奥氏体的生长的线索成为可能。我们可以通过应用彩色金相技术追踪每个晶粒内的显微偏析。结果表明对于所有碳当量的灰铸铁来说，树枝状奥氏体的存在值得研究。举个例子，图7展现了过共晶铸铁的凝固结晶宏观组织。值得注意的是，石墨群没有表现出枝晶间的形态，在许多地方反而被浸入树枝状晶中，如图

52、中箭头所指，这就解释了为什么这种树枝晶之前仅仅通过对层片石墨的观察没有被鉴别出来。这也表明层片状石墨可以在生长到某种程度时，大多数是在凝固结晶的最后一个过程或者是在凝固过程的石墨化过程中，在不与铁液接触的情况下，通过C的扩散穿过奥氏体的包裹。图6 过共晶组织试棒的宏观形貌 (a)20mm(b)30mm(c)46mm这么大的晶粒以及显微偏析的图案形态表明，所谓的共晶团实际上并不是独立的凝固的凝固结晶单元。但是它们之中的很大一部分是发源于一个非常巨大的奥氏体树枝晶。这些观察引出了下面对于灰铸铁凝固结晶过程的解释。许多细小的奥氏体树枝晶形核、生长到图8所示温度或在此温度以下。任何有可能在铁液中存在的

53、石墨都被这些树枝晶所吞没。这也很有可能在过共晶灰铸铁中实际的发生。已经在树枝状晶中存在的石墨或者是在过饱和树枝晶中新形核的石墨，与奥氏体的枝干相接处继而协同生长，形成了所谓的共晶团。我们有理由这样猜测：无论是过共晶灰铸铁还是亚共晶灰铸铁，都没有一个对于共晶团的形核过程。但是凝固结晶过程是被相对大一些的奥氏体树枝晶的主要的生长所主宰的，这些树枝晶在之前所提到的共晶团的形成区域提供了大量的高密度的奥氏体晶核。但是正如我们所广泛认可的，这些单元并不是结晶产生的晶粒。它们中的许多存在于每个晶粒中。图7 彩色腐蚀后的过共晶组织的黑白图片图8 铁碳相图中的共晶区域示意图这里所提出的机理也被其他作者的观察研

54、究所证实。Ruff和Wallace指出：奥氏体树枝晶存在于亚共晶、过共晶以及共晶成分的灰铸铁中，共晶奥氏体的形核发生在初生奥氏体树枝晶上或者在其附近。Dioszegietal这样陈述亚共晶合金：我相信共晶团的形核是发生在离分隔开的铁液中的初生奥氏体树枝晶的表面很近的区域。这些研究没有表明不存在奥氏体的新形核过程。但是他们指出在奥氏体树枝晶和共晶奥氏体的形核之间存在着某种联系。无数的实验证明单位区域内共晶团的数量是随着铁液中孕育剂的加入而增加的。在这次研究中所提出的凝固结晶模型没有否认这一原理。很明显，孕育过程增加了石墨的形核几率，然后大量的石墨晶核将会导致奥氏体树枝晶和石墨之间更加频繁的相互反

55、应，进而导致大量的更小的共晶体的结晶单元的形成。正如大家所知道的，对于共晶团的观察研究对于了解凝固结晶的组织特征与铸铁的性能之间的关系是非常有用的。4.总结DAAS宏观技术已经被成功的应用于揭示亚共晶、过共晶以及共晶层片状灰铸铁的宏观组织。砂型铸造的亚共晶、过共晶和共晶灰铸铁的宏观组织均表现出了相对粗大的晶粒。彩色金相技术被用来研究奥氏体树枝晶的位置和它与层片状石墨之间的反应。石墨层频繁穿越奥氏体树枝晶的枝干，这也表明这些石墨可在被奥氏体树枝晶包围后继续生长。本次研究证实：奥氏体树枝晶并不只在亚共晶灰铸铁中占统治地位，在过共晶灰铸铁中也同样如此。正如我们所广泛认可的，被称为“共晶团”的结晶单元

56、并不是结晶产生的晶粒。它们中有许多存在于每个晶粒中。参考文献：1 Morrogh H, Olfield W. Iron Steel 1959;32:479.2 RuffGF, Wallace JF. AFS Trans 1976;84:705.3 Angus HT. Cast Iron: Physical and Engineering Properties. Butterworths; 1976. p. 5.4 Stefanescu DM. Metals Handbook, Casting. ASM International; 1988. p. 168.5 Roviglione AN. D

57、octoral Thesis. National University of La Plata, Argentina. 1998.6 Miyake H, Okada A. AFS Trans 1998;106:581.7 Diooszegi A. Millberg A, Svensson IL. Proceedings of the International Conference on The Science of Casting and Solidification, 2001; p. 269.8 Moore JC. Metals Handbook, Metallography, structures and phase diagrams. ASM International; 1973. p. 93.9 Boeri RE, Sikora JA. Int J Cast Metals Res 2001;13:307.10 Rivera GL, Boeri RE, Sikora JA. Mater Sci Technol 2002;18: 691.11 Rivera GL, Boeri RE, Sikora JA. AFS Trans 2003:111.12 Rivera GL, Boeri RE, Sikora JA. Cast Metals 1995;8:1.20