灰铸铁中常见的冶金缺陷

1、Common Metallurgical Defects in Grey Cast Irons灰铸铁中常见的冶金缺陷Causes and Cures原因及对策C.M.EcobCustomer Services Man ager, Elkem AS, Foundry Products Divisio n艾肯铸造产品部客户服务经理C.Hartu ngResearch Man ager,Elkem AS, Foundry Products Divisio n艾肯铸造产品部研发经理S-O.Olse nTech ni cal Service Man ager, Elkem Bjolvefosse n A

2、S艾肯技术服务经理Abstract摘要Whilst most foundries today recognise the types of defect found in grey cast irons, an appreciati on of the causes and therefore cures is not always appare nt.有时候很多铸造能够分辨出灰铸铁中的冶金缺陷，但相应的产生原因和对策却不是很清楚。This paper will exam ine some of the com mon metallurgical defects, which have bee

3、 n found duri ng exam in ati on of rejected cast ings in Elkems Research Cen tre in Norway.位于挪威的艾肯研究中心在检查报废的铸件时发现了一些铸造缺陷，本文将认真讨论和研究这些缺陷。Gas defects are particularly difficult to categorise and particular attention is paid to hydrogen, n itroge n and carb on mono xide gas holes.气孔类的铸造缺陷是最难分类的，主要的关注应该

4、集中在氢气孔、氮气孔、和一氧化碳气孔。Other defect types exam ined in clude shri nkage, flake compact ion, Widma nstatte n graphite and the com mon ly see n ferritic rim.其它要讨论的缺陷包括收缩、短片状石墨、和常见的铁素体边缘。In troductio n引言Metallurgical defects, whilst no rmally a small part of a foun drys defect cast ing perce ntage, can be

5、time consuming and expe nsive to classify and hence remedy .In this paper, some of the more com mon defects are described based on case studies from Elkems Research Centre. In the exam in ati on of any defect, good metallographic facilities are n ecessary to provide sufficie nt detail to avoid mista

6、kes in the correct identification of the defect, particularly when gas is suspected as the problem. Other defects, such as Widma nstatte n graphite, may require high magni ficati ons to be able to see the problem.虽然冶金缺陷只占多铸造厂产品缺陷的很小一部分，但要分析其原因和采取正确的措施却是及其费时和昂贵的。在本文中将根据艾肯研发中心的案例研究来描述一些最普通的冶金 缺陷。在任何缺陷

7、的检查过程中，必须拥有良好的设备以便为正确的分析缺陷形成原因提供足够的信息来避免错误，特别是当认为是主要原因的时候。其它的缺陷，像魏氏体石墨，就需要高放大倍数的显微镜。Hydrogen Pin holes氢引起的针孔These may be con sidered to be one of the most expe nsive defects as they are not no rmally revealed until after machining. They can be found both in grey and ductile irons and tend to appear

8、as small spherical holes just beneath the casting surface. The inner surface of the hole will have a con ti nu ous graphite lining and hence appear to be black and shiny on exam in ati on. This precipitati on of graphite onto the surface results in a graphite depleted area around the hydroge n gas h

9、ole as show n in Figure 1.氢气孔可能是代价最为高昂的一种缺陷，因为一般它们在机加工后才显露出来，在灰铁和球铁中都会出现，常以圆球状出现在铸件表皮之下。由于气孔的内壁被石墨所覆盖，因此检查的时候气孔内壁是黑色和发亮的。这种气孔内壁石墨的析出导致了气孔外壁产生了石墨的耗尽的区域，这些图片显示在图1当中。Hydroge n pin holes can be caused by several factors, either alone or in comb in ati on. Most commonly, high levels of aluminum or titani

10、um in the base iron causes a reaction with moisture from the gree nsand, damp tools or wet refractories. Other sources of moisture could be damp or oily charge materials (in clud ing rust), a build up of dead clay in the sand system which will tend to retain moisture or the use of old cores, which h

11、ave picked up moisture from humid atmospheres.有几种因素能够引起单个的氢或成片的氢气针孔，最主要的原因就是铁液中的Al或钛与来自型砂、潮湿的工具，或潮湿的耐火材料中的水汽发生反应。水汽的其它来源可能是湿的空气或者被有污染的炉料、铁锈，型砂中积聚的死粘土也会使型砂的水分升高、也可能使用旧的芯子，因为这些芯子会从潮湿的大气中吸收水分。8 j& Example of hydroge n porosity revealedClose-up of hydroge n pin hole reveali ng inneron mach ininggraphite

12、 lining;机加工暴露出的氢气孔显示了具有内壁石墨膜的特写氢气孔Figure 1. Hydroge n pin hole.图1氢气针孔Pi nholes may be preve nted, or the occurre nee reduced, by restricti ng the alumi nium content of the base metal below 200ppm and minimising the titanium content. Careful control of steel scrap, avoidance of CG iron returns (if ma

13、de using Ti) and elimination of enamelled scrap will help in this respect. Some pig irons can also contain tita nium.通过将铁液中Al的含量限制在200ppm以下和最大程度的减小Ti含量和防止氢气孔的出现和减少其发生的几率。对废钢的仔细控制、避免使用蠕墨铸铁的回炉料(如果用Ti生产)和去除带釉的废钢有助于减少氢气孔的产生。一些生铁也含有较多的Ti。Care should be take n to fully dry refractory patches and coated to

14、ols before use and sufficie nt new sand added to the mouldi ng system to preve nt build up of dead clay. Moisture in the system should preferably be below 3%. Cores and water-based coatings should be fully cured and dry before the metal is poured into the mould.应该采取措施来使所用的耐火泥和涂工刷涂料具干燥，并向砂处理系统中加入足够的新

15、砂来阻止死粘土在型砂中的累积。型砂中的水分最好低于3%，在浇注之前，芯子和涂料必须完全干燥和熟化。In creas ing metal pouri ng temperatures and carb on equivale nts have also bee n no ted to reduce the in cide nce of this particular defect.现在已经注意到提高浇注温度和提高碳当量能够减少这种特殊缺陷的发生几率。Nitroge n Blowholes氮气孔Example of Nitroge n porosity defect inClose-up of de

16、fect show ing flake depleted rimgrey iron revealed on mach ining灰铸铁经过机加工后出现的氮气孔氮气孔周围石墨耗尽区域的特写Figure 2. Nitroge n Blowholes图2:氮气孔Nitroge n blowholes may be either a surface defect or a sub-surface occurre nee. The example shown in figure 2 was only revealed on machining, thus being detected at the mo

17、st expensive post-fo undry fini shi ng operati on. Blowholes appear more freque ntly in medium to heavy sect ion thick nesses and are ofte n adjace nt to resin bon ded core or mould materials. The holes, or fissures, are normally irregular in shape (as opposed to the more spherical hydrogen holes) a

18、nd are perpendicular to the casting surface, protruding some millimetres into the casting. The inner surface of the hole has a continuous or dis-continuous graphite lining coupled with the subsequent decarburisation in the immediate surrounding matrix. This is clearly seen in figure 2. Also seen in

19、this figure are dendrites, which have grown into the hole. On occasions,the graphite flakes aresee n to have become shorter and thicker, this being a typical sig n of high n itroge n.氮气孔缺陷可能在铸件表面或皮下出现，图2是经过昂贵的机加工后处理后在铸件皮下发现的氮气孔，氮气孔更容易在中等壁厚的铸件和靠近使用树脂粘结剂的芯子和造型材料。氮气孔和裂隙状氮气孔一般形状不规则(与圆的氢气孔相比较)，垂直于铸件表面，可深

20、入铸件表面以下几个mm。氮气孔内部都有连续的或者不连续的石墨析出膜，与这种析出膜相连的就是周围已经脱碳的基体组织，图2青楚的显示了这一情况，这这幅图片中还能看到伸进氮气孔壁内部的树枝状凸起。有时石墨会变得短而厚，这是氮含量高的典型信号。Nitroge n fissures are caused simply by excess n itroge n in the system .In cupola melted grey irons, this comes from high proportions of steel scrap in the charge which require high

21、 levels of coke, whereas in induction melting, poor quality, high nitrogen containing carburiser is normally the cause. The use of some resins in the product ion of cores or moulds can also lead to n itroge n pick up locally with in the casti ng, particularly at a pote ntial hot spot.系统中氮含量高是造成裂隙状氮气

22、孔的主要原因，在冲天炉熔炼铸铁中，高的氮含量来自于炉料中高比例的废钢， 熔化这些废钢需要较多的焦炭；在电炉熔炼当中，则是使用了质 量差的氮含量高的增碳剂；在制芯和造型中使用树脂粘结剂也可能导致但在铸件的局部累 积，特别是在潜在的热节处。Restrict ing the dissolved n itroge n content to 80 ppm in medium to heavy sect ions and 120ppm in thin, un cored sect ions will no rmally not give n itroge n blowhole problems. In a

23、dditi on, careful select ion of raw materials will also help reduce the pote ntial for blowhole problems. Titanium and zirconium are known to neutralise the effects of nitrogen by producing carbo-nitrides, however care should be taken when using titanium as this can then promote hydroge n pin holes

24、in the prese nee of alu minium and moisture as previously discussed. In creases in pouri ng temperature and carb on equivale nt are also known to reduce the in cide nce of n itroge n defects.一般情况下应把薄壁铸件中N的含量限制在120ppm以内，中厚壁的含量限制在80ppm以内，在没有芯子的铸件截面附近一般不会出现N气孔，此外，对认真的选择原材料也能减少N气孔的出现。Ti和Zr能够中和N的有害作用，但是使

25、用 Ti是要小心，因为如前面 讨论的那样，在较高的Al含量和水的含量下，Ti的存在易使铸件产生氢气孔。提高浇注温度和增加碳当量有助于减少氮气孔缺陷的发生几率。Often, it is very difficult to disti nguish betwee n hydroge n and n itroge n gas defects. An alysis of a defect sample may show that the con trol parameters for both eleme nts are with in limits, yet a gas hole, characte

26、ristic of hydrogen or nitrogen, will appear. In such cases, it is likely that there is a syn ergistic effect where the eleme nts have comb ined to form the hole. Here, a full exam in ati on of the causes for both gases n eeds to be un dertake n with tighter con trols put in place.一般情况下，很难区分出氢气孔和氮气孔，

27、分析缺陷试样有助于显示控制元素的是否在合理的范围之内，然而有时也会出现具有氢气孔和氮气孔特征的，在这种情况下，这些元素对形成氢气孔和氮气孔起共同作用，因此必须采取严密的控制措施来检查缺陷的发生原因。Carbon Mono xide Blowhole一氧化碳气孔The third of the com mon gas defects is the carb on mono xide blowhole. Figure 3 shows an example of this type of defect, which can no rmally be see n as a surface blow.C

28、O气孔是灰铸铁中第三种常见的气孔缺陷，图3显示了典型的CO气孔缺陷的例子，这种缺陷经常能够在铸件皮下看见。The carb on mono xide blow can appear as a hole a few millimetres across, as in the illustrati on here, or in large cast ings the hole can be large eno ugh to put a fist i nto. Normally see n in conj unction with slag and clouds of mangan ese sulp

29、hides, it is also possible to see den drites protrudi ng from the inner surfaces of the hole.像这儿描述的CO气孔直径有几个mm，在的铸件中，大的CO气孔可以塞进一只拳头,其内部常有渣或者硫化锰渣，在其内部也能发现伸进内壁的突出物。Example of surface slag blowhole in grey iron Close-up of defect show ing slag cluster灰铸铁中的表面渣孔聚集的渣的特写Figure 3. Carbon mono xide blowhole图

30、3 一氧化碳气孔The most com mon cause of this problem is the failure to totally empty ladles betwee n taps.This results in a lowering of the overall metal temperature and a build up of cold manganese sulphide/oxide rich slags. Eve ntually, the point is reached where a metal/slag react ion takes place as：造成

31、这种缺陷最普通的原因就是铁水包和出铁口内的铁液没有清理干净，这将导致较低的浇注温度和MnS渣或者氧化物渣在下一包中铁水的聚集。最终这些渣多到一定量就会发生下面的反应：MeO + C = Me = COThe defect may also be attributed to excess mangan ese an d/or sulphur in the system. These should be bala need accord ing to the equatio n:这种缺陷归因于铁液中过量的Mn和S，Mn和S的关系应根据下式来计算：%Mn = %S + 0.3Carbon mono

32、xide blowholes can no rmally be elim in ated by en suri ng a complete empty ing of ladles between taps, operating with clean ladles and preventing slag build up on the refractory. In creas ing metal temperature can also help.通过完全清理浇包和出铁口，使用干净的浇包和阻止渣在铁液中的累积，增加浇注温度也会对减少CO气孔会有所帮助。Shrin kage收缩缺陷IF“ 卄-；2

33、SSOverview of the positi on of the shri nkage. TheClose-up of the shri nkage show ingdefect was revealed after mach ining and wasden drites an dmetallic surfacelocated in the centre of the casting section with T-shape缺陷的简图显示了金属表面和内部枝晶的缩孔特写Figure 4. Example of a hot-spot shri nkage defect图4:热节收缩缺陷The

34、 example show n in Figure 4 is a typical shri nkage defect, typically the surface of the shrinkage hole will show dendrites, but without any graphitic lining as would be seen in a gas related defect .In the case illustrated, the shri nkage appears at the thermal centre of the cast ing and the cause

35、was attributed to the sharp radii and to poor metal flow design. Soft sand in the vicinity of the defect may have bee n a con tributory factor in this case.图4显示的例子是典型的收缩缺陷，缩孔的内壁表面有点型的树枝状枝晶，但是内壁没有石墨膜，石墨膜的出现一般与铸件的气孔缺陷有关。如图描述的收缩缺陷出现在铸件热节的中心，该处铸件较小的圆角和不良的浇注系统设计促使形成了此缺陷，此外热节周围松软的砂型对此缺陷的形成也起了一定的作用。In deed

36、, the majority of shri nkage defects found in the in dustry today may be attributed to a soft spot in the moulding sand. Otherwise there are many causes of shrinkage ；实际上，在铸件上发现的大部分的收缩缺陷的原因都归因于松软的砂型，除此之外， 还有几种收缩形成的原因：-Thicker sect ions of a casti ng that are not properly fed or have in adequate runn

37、 er/gate desig ns厚壁处的铸件补缩不良或内浇口不够-Low carb on or carb on equivale nt irons are more prone to shri nkage due to a lack of low den sity graphite being precipitated and not providing an expansion effect to counter the natural solidification shrinkageC低或者碳当量低，从而造成在凝固过程中没有足够的较低密度的石墨析出来抵消凝固 过程中的收缩。-I nsuf

38、ficie nt clamp ing or weighti ng of the mould can lead to lift ing锻铸型没有夹紧或者压铁重量不够造成抬箱-Under-ino culati on or over- ino culati on both in crease the pote ntial for shri nkage, the former due to the lack of precipitated graphite, the later produces too many eutectic cells which can result in porosity

39、betwee n the cells.孕育不足和过量孕育也能导致收缩缺陷。前一种情况导致了没有足够的石墨析出，而后一种情况导致了过多的共晶团，太多的共晶团也能导致共晶团之间的缩松。-High phosphorous conten ts, in excess of 0.1%te nd to promote shri nkage, as does excessive pouri ng temperatures含磷量超过0.1%也能促进缩松缩孔的形成，较高的浇注温度也一样。In ter-cellular Carbides晶间碳化物Figure 5. Example of grain boun dar

40、y carbides图5:晶界附近的碳化物Todays in dustry has to cope with decreases in the quality of affordable steel scrap. Often, the trace eleme nt content of the steel is higher tha n has bee n found previously and there is a result ing in crease in the in cide nce of in ter-cellular carbides. These are particula

41、rly no ted in thicker sect ion castings where the slow solidification time allows for segregation and a build up in the concentration of deleterious elements, such as molybdenum, vanadium, manganese, chromium and tita nium.现在的铸造产业必须面临所使用的废钢质量下降的问题。现在铸造厂所使用的废钢的微量元素含量比以前更高了，这就导致了出现晶间碳化物发生几率的增加。在厚壁铸件中应

42、特别注意这种情况，厚壁处较长的凝固时间使有害元素如Mo、V、Ti、Cr、Mn在晶界上析出和聚集。In some cases, in creased or more powerful ino culati on will help to disperse the carbide promoting elements and thus the effects of trace elements, avoid the formation of carbides. However, it must be no ted that the effects of trace eleme nts, such

43、as those no ted above, is cumulative and not in dividual to the particular eleme nts. Further, some carbide forms, for example Mo and Cr cannot be removed by subseque nt heat treatme nt.在某种情况下，增加孕育剂使用量和使用强效孕育剂可以冲淡碳化物成元素，从而避免碳化物的形成，但是应注意到碳化物元素形成碳化物的效果是累加的。另外对于有些碳化物形成的碳化物，如 Cr和Mo，是不能通过随后的热处理来消除这些碳化物的。

44、Avoidanee of grain boundary carbides is achieved by careful control of raw materials, particularly steel scrap and by optimis ing the ino cula nt additi on. In creases in carb on equivale nt may also help to disperse the un desirable eleme nts.通过控制原材料特别是废钢以及优化孕育剂的加入方法可以避免晶间碳化物的产生。增加碳当量也有助于稀释有害的微量元素。

45、Widma nstatte n Graphite魏氏体石墨Figure 6 shows a classical example of Widmanstatten graphite. This effect, sometimes referred to as spiky graphite is found when levels of the trace elements lead, bismuth or an tim ony become too high.图6显示了经典的魏氏体石墨组织。这种组织有时也被称作短棒状石墨，当微量元素如Pb、Bi、Sb的含量高时易在铸铁组织中发现。An tim o

46、ny will promote Widma nstatte n graphite in the prese nee of hydroge n, particularly in heavier secti on casti ngs, as will bismuth. The usual cause of this defect is the prese nee of lead, a 0.0005% additi on is likely to cause Widma nstatte n graphite forms.特别是铸件的壁厚比较大时，在有氢的存在条件下，Sb促进魏氏体石墨的形成。Bi和S

47、b的作用一样。产生这种石墨的普通原因就是Pb，当铅的含量为0.0005%时就有可能促进魏氏体石墨的形成。lD-Ju-02 0402WD：5.2n 15. DwWst 25Overview of the graphite structureClose-up of one of the graphite lamellas魏氏体石墨组织图魏氏体石墨的特写Figure 6. Example of Widma nstatte n graphite图6 :魏氏体石墨的组织照片The no rmal sources of lead are free cutt ing steels, old pain ted

48、 scrap, vitreous en amelled scrap, terne plate or contamination of the melt with white metals. Melting petrol engines from the days of leaded petrol can also be a source of lead con tam in ati on.一般情况下铅来自于废钢种的易切钢，被油污染的废料、带有搪瓷的废钢，镀锌铁板、或被轴承合金污染的废钢，使用废弃的含铅汽油发动机作为回炉料也是铅的一个来源。Widma nstatte n graphite has

49、 a catastrophic effect on the mecha nical properties of the iron, the spikes on the graphite flakes acting as points of weakness to reduce tensile strength values dramatically. The problems with lead tend to arise in induction melted irons as the lead stays with in the bath, but is rarely see n in c

50、upola melted metal as the lead disappears up the stack.魏氏体石墨对灰铸铁的力学性能有着灾难性的影响，石墨上的尖钉起着裂纹的作用，极大的降低了灰铸铁的抗拉强度。用电炉熔炼时铅的含量会上升，而用冲天炉熔炼时则很少出 现这种状况，因为铅在加入的批料中铸件消失了。Once lead has appeared in grey iron, there is no real cure except to use a rare earth containing ino cula nt/prec on diti oner to try to scave n

51、ge the lead from the iron.一般铅在灰铸铁中的含量超标以后，很少有有效的措施来减少铅的含量，除非使用含有稀土的孕育剂或者是预处理剂来将铅从灰铸铁中清除出来。Steadite斯氏体Steadite in thick secti onSteadite in th in secti on厚壁件中的斯氏体薄壁件中的斯氏体Figure 7. Steadite in grey iron图7:灰铸铁中的磷共晶Steadite, more commonly known as the phosphide eutectic, is really a precipitation of iro

52、n phosphides. Normally this is not regarded as a defect uni ess excess phosphorus en ters the system and clusters are detected at the grain boun daries.斯氏体，一般叫做磷共晶，实际上是一种磷化铁的析出物。除非铸铁中含有过量的磷共晶或者在晶界上有磷共晶被发现，一般情况下，这不被认为是一种铸造缺陷。Phosphorus has the ben efits in iron of in creas ing fluidity and wear resis

53、ta nce whe n prese nt in the right amounts. Less than 0.04% may lead to metal penetration and finning, whilst levels of 0.1%and above can lead to the formation of a network of steadite at grain boundaries with subseque nt problems of shri nkage and embrittleme nt. Some irons are deliberately produce

54、d with higher phosphorous levels where fluidity is a big issue, radiator castings, stove plates and some electrical cas ings for example.当铸铁中的磷在合适的范围之内，磷能够提高铁液的流动性和铸件的耐磨性，少于的0.04%的可能导致铸件渗漏，大于0.04的磷会使在晶界上析出连续的斯氏体，这会使铸铁产生收缩缺陷和使铸铁变脆。The cure for excess steadite, apart from reduci ng the levels of phosp

55、horous, is to disperse the phosphorous within the cast ing by improvi ng in oculati on or to in crease the solidificati on rate. Care should be taken in the selection of scrap to avoid domestic heating castings and analysis should be made of the pig iron as some brands contain higher levels of phosp

56、horous.除了降低原材料中磷的含量之外，还可以通过加大孕育量和冷却速率来减少铸铁中斯氏 体的含量。应该仔细检查废钢和原材料避免家庭供暖用铸件作为炉料，还应该对生铁的磷含量作分析，因为有些品牌的生铁磷含量比较高。Slag渣Example of grey iron slag in clusi on cluster Close-up of slag cluster show ing various phases灰铸铁中的夹渣显示了多相的夹渣特写Figure 8. Example of slag in clusi ons图8夹渣缺陷Slag in clusi ons may be found bo

57、th at the surface of the cast ing, as illustrated here, or withi n the body of the casti ng. They are recog ni sable as havi ng no decarburisati on associated with them and the slag usually seems to have several differe nt phases withi n the particle.夹渣也有可能像在这儿描述的一样在铸件表面被发现，也有可能在铸件内部发现夹渣。砂粒周围没有脱碳层并且

58、夹渣是多相共存的，可以通过这种特征来识别夹渣。Slag defects are caused by in adequate slag removal duri ng the melt ing and pouri ng phase or by a build up of slag in the pouri ng ladle or receiver-see also the sect ion on the carb on mono xide blowhole. Slag traps or filters built into the running system ofte n help with the removal of slag, but do not help with the root cause of