灰鑄鐵的凝固結(jié)晶過程-外文文獻翻譯

1、山東建筑大學畢業(yè)論文外文文獻及譯文外文文獻：Solidification of gray cast ironAbstractThis article investigates the solidification of hypo, eutectic and hypereutectic gray cast irons, using novel techniques developed bythe authors. The nature of the revealed macro and microstructure suggests that the solidification mechani

2、sm is different from that usually accepted.Keywords: Solidification; Gray iron1. IntroductionSeveral authors have studied the solidification of eutectic gray cast iron of flake graphite morphology (GI)1 7. Commonly, the eutectic solidification unit is represented by a nearly spherical shape of auste

3、nite and graphite, as shown in Fig. 1. There is general agreement to consider that austenite and graphite grow cooperatively, being both in 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

4、 in Fig. 2, and by the fact that the inclusions, generally associated to the microsegregation at the last to freeze melt, are located between such units.Stead s reagent reveals the microsegregation of phosphorus in GI, and it can delineate the units schematically represented in Fig. 1 in high P iron

5、s, usually referred to as eutecticcells 8. Since austenite dendrites are not readily discernible, except ingray irons containing types Dand Egraphite, their formation and growth characteristics in GI have received limited attention. Some researchers haveconsidered the role of austenite dendrites in

6、the solidification of GI 2,6,7. There is no doubt that austenite of hypoeutectic GI grows dendritically. On the other hand, most of the 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

7、of the present article carried out investigations that challenged the validity of the more firmly established models of the solidification of ductile iron (DI) 9 11. The use of a specially developed technique, that allows to1山東建筑大學畢業(yè)論文外文文獻及譯文reveal the solidification macrostructure of DI, combined w

8、ith the use of color metallography techniques that reveal the microsegregation pattern, showed that the macrostructure of DI is formed by relatively large austenite grains, that contain a very large numbers of graphite nodules. This was the case for hypoeutectic, eutectic, and also hypereutectic DI.

9、The objective of this study is to investigate the solidification mechanism of GI by using the micro and macroscopic techniques, successfully applied for DI in earlier studies.Experimental methods2.1. MaterialsThe melts utilized in the present study were produced by using a 50 kg medium frequency ind

10、uction melting furnace. Low manganese pig iron, steel scrap and ferroalloys were used as raw materials. Melts were cast in resin bonded sand moulds 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

11、order to provide enough austemperability to carry out the DAAS macrography technique, which is described below.2.2. Micrographic techniqueThe color etching technique reveals the solidification microstructure through the use of a reagent that brings up the microsegregation patterns generated during s

12、olidification 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 with 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

13、 unit of eutectic GI.2山東建筑大學畢業(yè)論文外文文獻及譯文Fig. 2. Morphology of graphite ?akes of eutectic GI.2.3. Macrographic techniqueIn order to allow the observation of the macrostructure of DI it is necessary to carry out a thermal process called DAAS (Direct Austempering After Solidification)9. In this process,

14、 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 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 mi

15、n. A relatively high austempering temperature is used to obtain a high amount of retained austenite after treatment. After the DAAS treatment, the matrix microstructure shows a fine mixture of ferrite needles and retained austenite. A schematic of the thermal cycle is shown in Fig. 3a. The DAAS trea

16、tment is certainly laborious and cannot be used under usual molding circumstances. Nevertheless, it is the only method capable of revealing low alloy ductile cast iron macrostructures, to the best of the author s knowledge. After this procedure, the retained austenite keeps the crystalline orientati

17、on defined during solidification. Therefore, etching with Picral (5%) reveals the grain structure of the solidification austenite. It must be emphasized that such macrostructure will be not visible after a conventional austempering treatment, as that shown schematically in Fig. 3b, since the microst

18、ructure will be formed starting from a fine grain recrystallized austenite structure obtained after austenitizing. This technique has not been applied before to GI. As a first approach it will be used on GI following the same procedure developed for DI.3山東建筑大學畢業(yè)論文外文文獻及譯文Fig. 3. (a) DAAS thermal cycl

19、e, (b) regular austempering thermal cycle.3. Results and discussionFig. 4ac show the unetched microstructure of the 30 mm diameter samples of hypoeutectic, eutectic, and hypereutectic melts, respectively. Predominately type A lamellar graphite structure is observed in all cases. Fig. 5ac show the ma

20、crostructure 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 hypereutectic alloy. This is, to the best of our knowledge, the first time such structure is revealed on sand cast GI sa

21、mples 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 in Fig. 1.As it was mentioned before, the eutectic cells are usually revealed through the microsegregation of phospho

22、rus by the application of the Stead reagent. Nevertheless, it is important to point out that this method does not prove that areas separatedby microsegregation of phosphorus are in fact different grains, because it does not etch di?erentially grains, or volumes, of different crystal orientation.It i

23、s 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 a more pronounced columnar structure. Fig. 6 shows the macrostructure of4山東建筑大學畢業(yè)論文外文文獻及譯文the samples of 20, 30 and 46 mm

24、 diameter of the hypereutectic melt. Note that thegrain size slightly increases when thediameter increases.Fig. 4. Microstructure of unetched samples of 30 mm round bars. (a) Hypoeutectic melt, (b) eutectic melt, (c) hypereutectic melt.5山東建筑大學畢業(yè)論文外文文獻及譯文Fig. 5. Macrostructure of 30 mm diameter round

25、 bars. (a) Hypoeutectic melt, (b)eutectic melt, (c) hypereutectic melt.The presence of such large grains indicates that large portions of the sample have the6山東建筑大學畢業(yè)論文外文文獻及譯文same austenite crystalline orientation. It should then be possible to find indications of austenite growth inside a solidific

26、ation 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 investigated. As an example, Fig. 7 shows the solidification microstructure of

27、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 not been identified before, through the observation of the distribution

28、of flake graphite. It also suggests that flake graphite may grow to some extent, most probably during the last stages ofsolidification or during solid state graphitization, not in contact with the melt but by Cdiffusion through an austenite envelope.7山東建筑大學畢業(yè)論文外文文獻及譯文Fig. 6. Macrostructure of round

29、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 groups of them have a common origin in a very large austeni

30、te 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 that may be present in the melt at this stage are engulfed

31、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 supersaturatedintradendritic melt, make contact with austenite branches and begin cooperative growth, form

32、ing 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 relatively large austenite dendrites that provide a large densit

33、y 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.8山東建筑大學畢業(yè)論文外文文獻及譯文Fig. 7. Black and white print of hypereutectic melt after color etching.Fig. 8. Schem

34、atic 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, hyperand eutectic composition, and that the ucleation of eutectic austenit

35、e takes place onand near the primaryaustenite dendritesDioszegi. et al.7state that forhypoeutectic alloys the place for the eutectic nucleation is believed to be close to theinterface of primary austenite in thesegregated liquid . These studies do not state thatthere is no new nucleation of austenit

36、e, but they suggest that there is a link betweenaustenite 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 melt. The solidification model proposed in this work d

37、oes 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 larger number of smaller units of coupled eutectic ce

38、lls. 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.9山東建筑大學畢業(yè)論文外文文獻及譯文ConclusionsThe DAAS macrographic technique has been successfully applied to reveal the macrostructureof hypo, hyper and

39、 eutectic flake gray cast irons.The macrostructure of sand cast hypo, hyper and eutectic GI show relatively large grains in allcases.Color metallography techniques were used to reveal the austenite dendrites locations and itsinteraction with graphite flakes. Graphite flakes frequently cross austenit

40、e 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 butalso for hypereutectic gray irons.The units usually called eutecticcells are not solidification g

41、rains, as it is commonly accepted.A great number of them are present into each grain.References：Morrogh H, Olfield W. Iron Steel 1959;32:479.RuffGF, Wallace JF. AFS Trans 1976;84:705.Angus HT. Cast Iron: Physical and Engineering Properties. Butterworths; 1976. p.5.Stefanescu DM. Metals Handbook, Cas

42、ting. ASM International; 1988. p. 168.Roviglione AN. Doctoral Thesis. National University of La Plata, Argentina. 1998.Miyake H, Okada A. AFS Trans 1998;106:581.Diooszegi A. Millberg A, SvenssonIL. Proceedings of the International Conference on The Science of Casting and Solidification, 2001; p. 269

43、.Moore JC. Metals Handbook, Metallography, structures and phase diagrams. ASM10山東建筑大學畢業(yè)論文外文文獻及譯文International; 1973. p. 93.Boeri RE, Sikora JA. Int J Cast Metals Res 2001;13:307.Rivera GL, Boeri RE, Sikora JA. Mater Sci Technol 2002;18: 691.Rivera GL, Boeri RE, Sikora JA. AFS Trans 2003:111.Rivera G

44、L, Boeri RE, Sikora JA. Cast Metals 1995;8:1.中文譯文：灰鑄鐵的凝固結(jié)晶過程摘要：本文作者用由自己發(fā)展出的新穎的技術(shù)研究了亞共晶、 共晶和過共晶灰鑄鐵的結(jié)晶過程。這些被揭示的宏觀及微觀結(jié)構(gòu)表明灰鑄鐵的結(jié)晶機理與我們通常所接受的說法并不相符。關(guān)鍵詞：凝固結(jié)晶；灰鑄鐵導言：有幾位作者之前已經(jīng)研究了成片狀石墨形態(tài)共晶灰鑄鐵的凝固結(jié)晶過程。通常，共晶灰鑄鐵的結(jié)晶單元呈現(xiàn)出近似奧氏體與石墨的球狀形態(tài)，如圖1 所示。大家普遍認為奧氏體和石墨是同步生長的，原因是它們同時與液相接觸。 這種設(shè)想一方面被呈玫瑰狀的層狀石墨形態(tài)（如圖2）所支持；另一方面也被存在于晶間的夾

45、雜物所支持，這些夾雜物與最后結(jié)晶時的顯微偏析有關(guān)并存在于上述晶間。斯泰得的反應(yīng)物揭示了灰鑄鐵中磷的顯微偏析，它可以描畫出圖 1 中含磷量高的灰鑄鐵的金相所大體上呈現(xiàn)出的特征，通常被稱為共晶團。 由于奧氏體的樹枝狀結(jié)晶不易被辨別，除了在含有“D”型或“ E”型石墨的灰鑄鐵中，其他情況下它們的形成和生長特征沒有受到太多的關(guān)注。有一些研究人員也對奧氏體樹枝狀晶在灰鑄鐵結(jié)晶過程中的作用進行過研究。毫無疑問，亞共晶灰鑄鐵中的奧氏體是以樹枝狀生長的。 另一方面， 許多文獻表明。 奧氏體在碳含量達到或超過共晶點時會生長成其它不同的形態(tài)。去年，本文的作者們完成了一個研究，挑戰(zhàn)了被更加穩(wěn)固的建立的可鍛鑄鐵11山

46、東建筑大學畢業(yè)論文外文文獻及譯文的凝固結(jié)晶模型的權(quán)威性。 一項被特殊發(fā)展出的技術(shù)的應(yīng)用，使得揭示可鍛鑄鐵的結(jié)晶宏觀結(jié)構(gòu)成為可能，同時彩色金相技術(shù)的應(yīng)用展現(xiàn)出了顯微偏析的圖案。通過這些技術(shù)表明，可鍛鑄鐵的宏觀組織是由相互關(guān)聯(lián)的粗大奧氏體晶粒形成的，其中包含著數(shù)量眾多的石墨球。這就是亞共晶、共晶、過共晶可鍛鑄鐵的事實。這個研究的目的就是研究灰鑄鐵的凝固結(jié)晶機理， 通過使用顯微和目視的各種技術(shù)來完成。這些技術(shù)在之前的對可鍛鑄鐵的研究中被非常成功的應(yīng)用。實驗方法2.1 實驗材料現(xiàn)在研究中所用的鐵液是用50kg 中頻感應(yīng)爐生產(chǎn)的。低錳生鐵、廢鋼和鐵合金都被用作成產(chǎn)的原料。鐵液被澆注入樹脂砂模中來生產(chǎn)直徑

47、分別為20、30、和 60mm的棒條。表 1 列出了所用合金的化學成分。鐵液中加入銅和鎳是為了提供足夠的等溫淬火性能來獲得 DAAS宏觀檢測技術(shù)，這項技術(shù)將在下面進行介紹。2.2 微觀技術(shù)彩色腐蝕技術(shù)通過應(yīng)用一種試劑揭示了凝固結(jié)晶的微觀結(jié)構(gòu)。 這種試劑可以顯現(xiàn)出凝固過程中產(chǎn)生的顯微偏析的圖案。 這種腐蝕試劑是由 10gNaOH、40gKOH、10g 苦味酸和 50ml 蒸餾水組成的。這種腐蝕劑必須要被妥善制備和保管，因為它是有腐蝕性并且有毒的。腐蝕劑要在120（ 278F）下保溫 2 分鐘才能取出。圖 1 共晶灰鑄鐵凝固結(jié)晶單元示意圖12山東建筑大學畢業(yè)論文外文文獻及譯文圖 2 共晶灰鑄鐵石墨

48、形態(tài)2.3 宏觀技術(shù)為了能夠觀察可鍛鑄鐵的宏觀結(jié)構(gòu)， 我們需要提出一種熱處理過程， 被稱為DAAS（結(jié)晶后直接淬火） 。在這個過程中，當溫度大約達到 950時，鑄件被從鑄模中振出并被放到 900的加熱爐中保溫 30min，以便讓溫度穩(wěn)定下來。然后將鑄件放入 360的鹽浴中奧氏體等溫淬火 90 分鐘。相應(yīng)的高的奧氏體等溫淬火溫度是為了在熱處理后獲得大量的殘余奧氏體。經(jīng)過 DAAS處理后，鑄件的顯微組織表現(xiàn)出一種很好的針狀鐵素體和殘余奧氏體的混合體。 一個熱處理冷卻圖如圖 3a 所示。 DAAS處理當然是一種費力的方法，不應(yīng)用于通常的鑄造情形下。然而，據(jù)筆者所知，它是現(xiàn)在唯一一種能夠揭示低合金可鍛

49、鑄鐵宏觀組織的方法。經(jīng)過這一過程后， 殘余奧氏體保持了凝固時的結(jié)晶傾向。 因此，含有苦味酸的腐蝕劑揭示了結(jié)晶后奧氏體的晶粒結(jié)構(gòu)。 必須被強調(diào)的是這樣的宏觀組織是不能在傳統(tǒng)的奧氏體等溫淬火后觀察到的，如圖 3b 所示，因為其中的顯微組織會在奧氏體化后經(jīng)歷一次奧氏體晶粒重結(jié)晶過程。 這項技術(shù)還沒有被應(yīng)用于灰鑄鐵。 作為第一種途徑，它將像在可鍛鑄鐵中的發(fā)展一樣被應(yīng)用于灰鑄鐵。圖 3 (a)DAAS 熱處理冷卻圖 (b) 常規(guī)奧氏體等溫淬火冷卻圖13山東建筑大學畢業(yè)論文外文文獻及譯文結(jié)論與分析圖 4a-c 表現(xiàn)了未被腐蝕的直徑為30mm的分別為亞共晶、 共晶、過共晶的試樣的顯微組織結(jié)構(gòu)。在所有的情況下

50、都可以看到大量的層狀石墨。圖5a-c 展示了在圖 4 中所示的相同試樣上采用 DAAS技術(shù)所獲得的宏觀組織結(jié)構(gòu)。在所有情況中，晶粒生長的相對比較大的組織都是在試樣的表面發(fā)現(xiàn)的， 包括過共晶合金。這就是說，據(jù)我們所知， 這是第一次正式在砂型鑄件中發(fā)現(xiàn)這種組織。 這些晶?；蛘呓Y(jié)晶單元的尺寸要比我們基于圖 1 中所示的球形晶粒建立的結(jié)晶模型的預想大得多。如前所述，共晶團通常是被由于加入穩(wěn)定劑產(chǎn)生的磷的顯微偏析所表現(xiàn)出來的。然而，需要指出的是， 這種方法不能證明被磷的顯微偏析分隔開的不同區(qū)域就是不同的晶粒，因為它沒有侵蝕到不同結(jié)晶傾向的不同晶粒或者體積。值得注意的是無論碳當量如何，相同直徑的試樣有著相

51、似的晶粒組織。唯一不同的是亞共晶灰鑄鐵表現(xiàn)出一種更加明顯的柱狀晶。圖 6 表現(xiàn)了直徑 20、30、60mm過共晶試樣的宏觀組織形貌。從中可以看出隨著試樣直徑的增加，晶粒尺寸略有增長。14山東建筑大學畢業(yè)論文外文文獻及譯文圖 4 未腐蝕的直徑 30mm試棒的顯微組織 (a) 亞共晶組織 (b) 共晶組織 (c) 過共晶組織15山東建筑大學畢業(yè)論文外文文獻及譯文圖 5 直徑 30mm試棒的宏觀形貌(a) 亞共晶組織 (b) 共晶組織 (c) 過共晶組織這種大晶粒的存在暗示了試樣中有很大一部分都具有相同的奧氏體結(jié)晶傾向。這之后使得找到在凝固結(jié)晶的晶粒中的奧氏體的生長的線索成為可能。 我們可以通過應(yīng)用

52、彩色金相技術(shù)追蹤每個晶粒內(nèi)的顯微偏析。 結(jié)果表明對于所有碳當量的灰鑄鐵來說， 樹枝狀奧氏體的存在值得研究。 舉個例子，圖 7 展現(xiàn)了過共晶鑄鐵的凝固結(jié)晶宏觀組織。 值得注意的是， 石墨群沒有表現(xiàn)出枝晶間的形態(tài)， 在許多地方反而被浸入樹枝狀晶中， 如圖中箭頭所指， 這就解釋了為什么這種樹枝晶之前僅僅通過對層片石墨的觀察沒有被鑒別出來。 這也表明層片狀石墨可以在生長到某種程度時， 大多數(shù)是在凝固結(jié)晶的最后一個過程或者是在凝固過程的石墨化過程中，在不與鐵液接觸的情況下，通過 C 的擴散穿過奧氏體的包裹。16山東建筑大學畢業(yè)論文外文文獻及譯文圖 6 過共晶組織試棒的宏觀形貌 (a)20mm(b)30mm(c)46mm這么大的晶粒以及顯微偏析的圖案形態(tài)表明， 所謂的共晶團實際上并不是獨立的凝固的凝固結(jié)晶單元。 但是它們之中的很大一部分是發(fā)源于一個非常巨大的奧氏體樹枝晶。 這些觀察引出了下面對于灰鑄鐵凝固結(jié)晶過程的解釋。 許多細小的奧氏體樹枝晶形核、 生長到圖 8 所示溫度或在此溫度以下。 任何有可能在鐵液中存在的石墨都被這些樹枝晶所吞沒。 這也很有可能在過共晶灰鑄鐵中實際的發(fā)17山東建筑大學畢業(yè)論文外文文獻及譯文生。已經(jīng)在樹枝狀晶中存在的石墨或者是在過飽和樹枝晶中新形核的石