分功率器壳体双面卧式攻丝专用组合机床设计（江苏）
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利用连续的等通道转角过程加工钢板Jong-Woo Park , Jin-Won Kim, Young-Hoon Chung韩国科学技术学院,131信箱, 重阳路, 韩国,汉城 摘要：等通道转角挤压试图使低碳钢的粒度改良从一个更低的区域开始。在剪切变形的同时很明显地使晶粒得到细化和pearlite带的消失。纳米大小的微粒渗碳体被观察到了在铁的晶粒内及晶界存在, 强度很明显的增加了。关键词： 钢; 微结构; 相变; ECAP过程1介绍我们知道金属晶粒的改良可是使材料的韧性和强度提高。在钢里面, 良好的晶粒可以由改进生核在受控辗压期间而得到, 并且在这个过程中要求重量的减轻 。为生产厚实的板材, 然而, 相当数量的减少是由板材的最后的测量仪器所限制, 并且良好的晶体结构在常规辗压过程是几乎不可能获得的。强烈的塑料剪变形可能被应用于金属的等通道转角挤压(ECAP)，但是它并没有减少厚度, 并且超良好的或纳米大小的晶粒可以由反复的挤压过程所实现。在常规的ECAP过程中,长的板材或板料由于间断性的挤压而不容易得到。最近, 一种独特的等通道转角挤压(ECAR)过程被当前作者的当中一个所提出, 这个方法被证明是非常有效的获得超良好的晶粒和高价值的铝板料。 ECAR过程也许可以被应用于钢板的热挤压过程或者冷挤压过程从而得到良好的晶粒和优良的机械性能。当前工作的目的是研究ECAR 方法的可行性在适当温度下通过剪切变形从而改良低碳钢晶粒的过程中。2. 实验方法一个加工厚实板材的ECAR 装置被设计和制造出来了如图1所示 。ECAR 系统包括了送料辊和ECAR 模具, 并且模具的角度是120度。5 毫米厚度, 10 毫米宽度和120 毫米长度的ECAR 热挤压钢板以由POSCO所提供的0.15C-1.1Mn-0.25Si-0.01Ti-0.03.Al 所构成。平行的栅格被事先雕刻在板材的边缘上以便与加工后对剪切角的测量。样品在900 度的电熔炉中被保持20分钟, 然后进行ECAR过程。在样品，卷，模子在被加热之前要在它们表面涂上石墨基的润滑剂。一个K 类型的热电偶被放置在距离样品头部20 毫米的地方,用来测量在ECAR过程中材料温度的变化。通过使用AIS 2000 用具和Vickers 硬度测试器来进行微凹进测试机械性能。在板材的纵向部分进行Metallographic测试。3%的材料被用来进行光学和扫描电子显微学(SEM) 测试。在Philips CM 30 电子显微镜解答了在双喷气机中的20% 高氯酸的酸和80% 甲醇后，显微学(TEM) 被广泛应用 图1. ECAR 系统概要图。 3. 结果和讨论 经过ECAR 扭屈的栅格样品显示在图2中。为调查变形的方式, ECAR在变形期间被中断, 把被扭屈了的样品和未被扭曲的样品放在一起进行观察。样品的挤出部分的网格图由剪变形而发生了弯曲, 当内部的样品仍然显示了最初的栅格。除了板材的低部显示弯曲的栅格,是由模子 9,10 或模腔 11 引起的几何作用, 最大的几何作用剪角度,倾斜的栅格角度是42度。实验用的剪切角度是接近ECAR 12 中的Al板材剪角度和使用了由Segal和Iwahashi 建议的通过计算等式得出的理论角度 49度。剪角度42度对应于工程学剪张力0.9 和有效的张力0.52 。这些结果都证明 ECAR 过程可适用于钢板, 并且剪变形可以有效地获得。剪切变形的量和强度可以通过调节模具的角度而改变，这些已由Segal 在ECAP 13 中提议 。图2. 样品由ECAR 扭屈的侧视图。 样品在ECAR 期间的温度变化被显示在图3中.在ECAR开始时温度迅速下降， 而在ECAR的结尾时温度迅速上升。温度迅速下降归结于在开始的 ECAR 阶段热传递从热的样品传向冷的设备, 温度的猛增是由样品的剪切变形产生的热量发生绝热热化导致的。变形温度的范围接近或略微高于有类似组成的1019钢的+cementite 区。由于在ECAP之前样品被加热到austenite区，才致使和相向碳体的转变。 图4 显示了传统的热挤压钢板和ECARed钢板的微观显微结构。原始的板材有粗糙的纯铁晶粒平均直径20 lm, 与一个粗糙的被结合的结构，被混合 pearlite 的容量分数大约为15% 。而经过ECAR 以后的样品中, 良好的纯铁晶粒被获得, 并且经常在传统挤压过程中被发现的通过-转变产生的粗糙的pearlite,结构，这种现象在ECAP中消失了。除了一小部份的几乎是大约2-5 lm 直径的纯铁晶体以外, 经过ECAR后大多纯铁晶粒呈现 2-5 lm 的宽度和5-10 lm的 长度。 图5 是一个SEM图片显示了被剪切的纯铁晶粒的一个大部分。多数纯铁晶粒是细长的, 而且倾斜的对着 ECAR 方向, 起因是由于在ECAR过程中产生的剪切变形。图3. 在ECAR 过程期间的冷却曲线。 图4. 光学微结构: (a) 被挤压的板材(b) ECARed 样品。图5. ECARed 样品陈列SEM 图6. ECARed 样品TEM显示渗碳体nano 微粒。 图6 显示了有高密度的细长的纯铁晶粒存在。 相似于铝合金在室温度 8 时的ECAR过程, 和钢在350 19时的ECAR过程, 意味着阶段变革从-发生在ECAR过程中, 并且纯铁期间服从了剪切变形。瘦长的subgrains物质宽度和长度在0.5-1 lm 和 1.5-3 lm的范围 。纳米大小的渗碳体颗粒存在与晶粒和晶界处, 或许对晶粒改良过程中的抑制晶粒长大有作用。一般认为ECAP过程的晶粒改良有以下3个因素：1 增加在ECAR过程中晶界处晶核的密度。 2 通过挤压变形提高晶核的产生率3 通过渗碳体来抑制晶粒的长大表1列出了样品的机械性能,，ECARed 钢的强度和改良后的晶粒有直接联系，如纳米渗碳体和位错密度。4. 总结钢板连续的剪切变形可以由ECAR 过程通过从更低的区冷却而成功地进行。从ECARed 板材测量出的剪切角接近理论上计算值。ECAR过程中发生了钢材晶粒的改良以及pearlite 带的失踪。大多钢材晶粒是细长的, 倾斜地对着ECAR 方向, 是由于在ECAR 过程期间的剪切变形。纳米大小的渗碳体被发现在晶粒中和晶界处存在，它们也许有助于晶粒的改良和抑制晶粒的长大。在产出的样品性能可以看出，材料的性能得到明显的改变，强度增强了超过100%，硬度和极限抗拉强度也有所提高。 出席作者感谢POSCO 为他们提供的财政支持。 参考文献：1 Pickering FB. Physical metallurgy and the design of steels.London: Applied Science Publishers Ltd; 1978. p. 62.2 Tanaka T. Int Metals Rev 1981;4:185.3 Segal VM. Mater Sci Eng A 1995;197:157.4 Valiev RZ, Ivanisenko YV, Rauch EF, Baudelet B. Acta Mater1996;44:4705.5 Low TC, Valiev RZ. JOM 2000;52:27.6 Shin DH, Pak JJ, Kim YK, Park KT, Kim YS. Mater Sci Eng A2002;323:409.7 Nam CY, Han JH, Chung YH, Shin MC. Mater Sci Eng A2003;347:253.8 Lee JC, Seok HK, Han JH, Chung YH. Mater Res Bull2001;36(6):997.9 Park JW, Seo JY. Metal Trans A 2001;32A:3007.10 Seo JY, Kim HS, Park JW, Chang JY. Scripta Mater 2001;44:677.11 Shan A, Moon IG, Ko HS, Park JW. Scripta Mater 1999;41:353.12 Chung YH, Ahn JP, Kim HD, Hwang BB, Engler O, Huh MY.Mater Sci Forum, V 2002;408412:1495.13 Segal VM, Reznikov VI, Drobyshevskiy AE, Kopylov VI. RussMetall (Metally) 1981;1:99.14 Iwahashi Y, Wang J, Horita Z, Nemoto M, Langdon TG. ScriptaMater 1996;35:143.15 USS, isothermal transformation diagrams, 3rd ed. United StatesSteel; 1963. p. 17.16 Zrnik J, Kvackaj T, Sripinproach D, Sricharoenchai P. J MaterPro Tech 2003;133:236.17 Bakkaloglu A. Mater Lett 2002;56:200.18 Hong JW, Kim SY, Kim YG, Kang KB. Mater Sci Eng1983;61:275.19 Shin DH, Kim BC, Kim YS, Park KT. Acta Mater 2000;48:2247.Grain refinement of steel plate by continuous equal-channelangular processJong-Woo Park*, Jin-Won Kim, Young-Hoon ChungKorea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, South KoreaReceived 30 September 2003; received in revised form 9 February 2004; accepted 10 February 2004Available online 22 April 2004AbstractEqual-channel angular rolling was attempted to refine grain size of a low carbon steel cooling from a lower c region. Distinctrefinement of ferrite gains as well as disappearance of ferrite-pearlite bands occurred by shear deformation. Nano-size particles ofcementite were observed in ferrite grains as well as on grain boundaries, and strength increased appreciably.? 2004 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.Keywords: Steels; Microstructure; Phase transformations; ECA process1. IntroductionIt has been known that grain refinement of materialsleads to improvement in toughness as well as strength1. In steels, fine grains can be obtained by enhancing anucleation during controlled rolling, and heavy reduc-tion is required for this process 2. For the productionof thick plates, however, the amount of reduction islimited by the final gauge of the plates, and fine grainstructures are hardly obtainable in the conventionalrolling process.Severe plastic shear deformation can be applied tometalsbyequal-channelangularpressing(ECAP)without reducing thickness, and ultra-fine or nano-sizegrains can be produced simply by repeating the process36. In the conventional ECAP, however, long platesand sheets are not available owing to the discontinuityof the pressing process. Recently, a unique equal-chan-nel angular rolling (ECAR) process was proposed byone of the present authors, and this method has beenproved to be very effective for obtaining ultra-fine grainsand high r-values of aluminum sheets 7,8.The ECAR process may also be applicable to steelplates during hot rolling as well as steel sheets duringcold rolling to get fine grains and excellent mechanicalproperties. The purpose of the present work was toinvestigate feasibility of the ECAR method for grainrefining of low-carbon steel plates by shear deformationat elevated temperatures.2. Experimental procedureAn equipment of ECAR for thick plates was designedand fabricated as shown in Fig. 1. The ECAR systemconsisted of feeding rolls and ECAR dies, and the dieangle, /, was 120?. ECAR samples of 5 mm thickness,10 mm width and 120 mm length were prepared fromhot-rolled steel plates with a composition of 0.15C1.1Mn0.25Si0.01Ti0.03Al (wt.%) which were pro-vided by the POSCO. Parallel grid vertical to the rollingplane of the plate was carved in advance on the side ofthe samples to measure shear angles after deformation.The samples were held for 20 min at 900 ?C in an electricfurnace, and then deformed by ECAR. A graphite-baselubricant was coated on the surface of the samples, rollsand dies before heating them. A K-type thermocouplewas inserted into the sample at 20 mm distance from thesample head, and the change in temperature duringECAR was measured.Mechanical properties were tested by a micro-inden-tation method using AIS 2000 apparatus and Vickershardness tester. Metallographic examination was carriedout on the longitudinal section of the plate. 3% nitaletchant was used for optical and scanning electronmicroscopy (SEM). Thin foils for transmission electron*Corresponding author. Tel.: +82-2-958-5433; fax: +82-2-958-5449.E-mail address: jwparkkist.re.kr (J.-W. Park).1359-6462/$ - see front matter ? 2004 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.doi:10.1016/j.scriptamat.2004.02.022Scripta Materialia 51 (2004) 181184microscopy (TEM) were examined in a Philips CM 30electron microscope after twin-jet polishing in a solutionof 20% perchloric acid and 80% methanol.3. Results and discussionGrid on the sample deformed by ECAR is presentedin Fig. 2. For investigation of the deformation mode,ECAR was interrupted during deformation, and de-formed and undeformed parts of the sample were ob-served together. The outlet part of the sample exhibitsgrid pattern inclined by shear deformation duringECAR, while the inlet part shows initial grid vertical tothe rolling plane. Except the lower part of the plateshowing curved grid, which is frequently generated by ageometrical effect of dies 9,10 or billets 11, the max-imum shear angle, h, of the inclined grid was 42?. Theexperimental shear angle is close to the shear angle of Alsheets deformed by ECAR 12 and a theoretical valueof 49? calculated using the equation suggested by Segalet al. 13 and Iwahashi et al. 14. The shear angle, 42?corresponds to the engineering shear strain of 0.9 andeffective strain of 0.52. These results demonstrate thatthe ECAR process can be applied to steel plates, andshear deformation can be obtained effectively. Theamount of shear deformation per pass and the force forECAR can be controlled by adjusting the die angle, asproposed by Segal et al. for ECAP 13.Variation in temperature during ECAR is plotted inFig. 3. Temperature drops rapidly at the beginning ofECAR, followed by sharp increase at the end of ECAR.The rapid drop of temperature is due to heat transferfrom the hot sample to the cold equipment at the earlystage of ECAR, and the sharp increase in temperature iscaused by adiabatic heating of the sample during sheardeformation in the ECAR dies. The range of thedeformation temperature lies near or just above the noseof the c+a+cementite region in the TTT diagram 15of the 1019 steel (0.17C0.92Mn) which has a chemicalcomposition similar to the present one. As the samplewas heated initially to the austenite region beforeECAR, transformation from c to a and cementite mayoccur during ECAR.Fig. 4 shows optical microstructures of the originalhot-rolled steel plate and the ECARed sample. Theoriginal plate has coarse ferrite grains with an averagediameter of 20 lm, mixed with a coarse banded struc-ture of pearlite having a volume fraction of about 15%.After ECAR, however, fine ferrite grains are obtained,and the coarse banded structure of pearlite, which hasbeen often observed in steels rolled conventionallythrough the ca transformation temperature as well asin nonrecrystallized c regions 1618, disappears. Ex-cept a small part of the nearly equiaxed ferrite grainswith about 25 lm diameter, most of the ferrite grains inthe ECARed sample exhibit elongated grains of around25 lm width and 510 lm length.Fig. 5 is an SEM micrograph of ECARed samplerevealing a large fraction of sheared ferrite grains. Mostof the ferrite grains are elongated, and inclined to theECAR direction, which resulted from shear deformationof ferrite grains transformed from austenite duringECAR process.A TEM micrograph of ECARed sample is shown inFig. 6 demonstrating elongated ferrite subgrains, someFig. 2. Side view of the sample deformed by ECAR. = 120oDieRollRollFig. 1. Schematic diagram of ECAR system.-50510152004006008001000ECARTemperature (oC)Time (sec)Fig. 3. Cooling curves during ECAR process.182J.-W. Park et al. / Scripta Materialia 51 (2004) 181184of which have a high density of dislocations. High dis-location density in the elongated subgrains, which issimilar to that in an aluminum alloy ECARed at roomtemperature 8, and a steel ECAPed at 350 ?C 19,means that phase transformation from c to a occurredduring ECAR, and the transformed ferrite was subjectedto shear deformation. The width and length of theelongated subgrains are in the range of 0.51 lm and1.53 lm. Together with fine film-like precipitates onsome ferrite grain boundaries, nano-size particles ofcementite are noted in some of the ferrite grains as wellas on grain boundaries, which may contribute to thegrain refinement by hindering the growth of the ferritegrains.It is considered that the grain refinement of the EC-ARed steel is caused by three factors as follows:(1) Increase in density of c grain boundary as a nucle-ation site of a grains during shear deformation ofECAR.(2) Increase in a nucleation rate enhanced by a strain-induced transformation.(3) Suppress of a grain growth by precipitation of nano-cementites.Mechanical properties are listed in Table 1, and anappreciable improvement in yield strength exceeding100% is noted with remarkable increase in micro-hard-ness and ultimate tensile strength. The strengthening ofthe ECARed steel is associated with grain refinement,nano-cementites and high dislocation density.4. SummaryContinuous shear deformation of steel plates wasperformed successfully by a unique ECAR processFig. 4. Optical microstructure of: (a) as-received plate and (b) ECARed sample.Fig. 5. SEM micrograph of ECARed sample showing sheared andelongated ferrite grains.Fig. 6. TEM micrograph of ECARed sample showing nano-particlesof cementite.Table 1Mechanical testing resultsSampleHvYS (MPa)UTS (MPa)As-received144275499As-ECARed250527760J.-W. Park et al. / Scripta Materialia 51 (2004) 181184183during cooling from a lower c region. The shear anglemeasured in the ECARed plate was close to the valuecalculated theoretically. Distinct refinement of ferritegains as well as disappearance of ferrite-pearlite bandsoccurred by ECAR. Most of the ferrite grains wereelongated, and inclined to the ECAR direction, whichresulted from shear deformation during ECAR process.Nano-size particles of cementite were noted in ferritegrains as well as on grain boundaries, which may con-tribute to the grain refinement by hindering the growthof ferrite grains. Appreciable improvement in yieldstrength exceeding 100% was
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