1、最后的专外通篇中黑体字表示该句话不敢确定其正确性，斜体字表示该句话需要自己去套用一下，很简单的（这句话不算在黑体字范围内）Welding Metallurgy（焊接冶金学）Welding Problems in Steels（钢中的焊接问题）Carbon and alloy steels are more frequently welded than any other materials owing to their widespread applications and good weldability.In general,carbon and alloy steels with hig
2、her strength levels are more difficult to weld,hydrogen cracking and reheat cracking being more likely to occur in these materials.Table 3.1 summarizes typical welding problems in carbon and alloy steels and their solutions.由于碳钢和合金钢被广泛的应用以及好的焊接性，所以，它们比其他材料更广泛的被用来焊接。通常情况下，具有高强度的碳钢和合金钢焊接起来更困难，氢致裂纹和再热裂
3、纹更容易在这些材料中发生。图表 3.1 总结了碳钢和合金钢的典型的焊接问题及其解决办法。3.2.1.2Characteristics of Phase Transformations during the Welding of Steels （钢材在焊接过程中其内部相特性的转变）The thermal processes during the welding and heat-treating of steels are different in a number of ways.First,the peak temperature of the HAZ during welding can
4、be rather high. In fact,near the fusion boundary,where difficulties such as grain coarsening and underbead cracking often arise,the peak temperature can reach 1400 or even higher.In the heat-treating of steels,on the other hand,the macimum temperrture involved is usually only around 950.Second,the h
5、eating rate is very high,and the retention time at high temperatures is very brief during most welding processes.In the heat-treating of steels,the geating rate si much slower and the high-temperature retention time is much longer.Figure 3.22 shows the thermal processes during the welding and heat-t
6、reating of two steels.在钢材焊接和热处理的过程中，热加工有很多不同的方式。首先，在焊接过程中，焊接热影响区的的最高温度能够达到相当高。事实上，在经常发生晶粒粗大以及焊道下裂纹的熔合线附近，最高温度能够达到 1400或是更高。另一方面，在钢的热处理过程中，所包含的最高温度通常在 950左右。其次，在大多数的焊接工序中，加热的速度是非常快的，在高温下的滞留时间是很短的。然而在钢材的热处理工序中，加热速度更慢，高温滞留时间更长。图表 3.22 显示了钢的焊接以及热处理两种热加工工序。As a result of the high heating rate during weld
7、ing,diffusional transformations,such as ferrite+pearliteaustenite,become more diffcult.Consequently,effective transformation temperatures,such as the lower critical temperature Ac1 and the upper critical temperature Ac3,tend to increase with increasing heating rate during welding(1,2).For steels con
8、taining greater amounts of carbide-forming elements(such as V,W,Cr,Ti,and Mo),the effect of the heating rate becomes more pronounced.This si because the diffusion rate of such elements more pronounced.This is because the diffusion rate of such elements is orders of magnitude lower than that of carbo
9、n and also because those elements hinder the diffusion of carbon.As a result,diffusional transformations are retarded to a greater extent.焊接过程中搞的加热速度会造成类似“铁素体和珠光体转变成奥氏体”的扩散转变更难进行。因此，在焊接过程中随着加热速度的升高实际转变温度（例如在临界温度 Ac1 和 Ac3 之间）也会升高。由于钢中包含大量的碳形成元素（例如钒，钨，铬，钛，钼） ，导致加热速度变得更加显著。这是因为这些元素的扩散速度比碳的扩散速度低几个数量级，还
10、因为这些元素妨碍了碳的扩散。结果，扩散转变被阻滞到了一个较低的程度。The high the heating rate,together with the brief high-temperature retention time,can also result in the formation of nongomogeneous austenite during welding.Such a nonhomogeneous austenite,upon subsequent rapid cooling,can cause the formation of localized high-carb
11、on-martensite colonies.Consequently,the microhardness of the HAZ tends to scatter over a wide range.在焊接过程中，加热速度越快，高温停留时间越短，越容易形成不均匀奥氏体。随后立即将该奥氏体冷却，会形成局部的高碳马氏体。因此，焊接热影响区的显微硬度有分散到较大范围内的倾向。As a result of high peak temperatures during welding,grain growth can take place near the fusion boundary.Steels c
12、ontaining grain growth inhibitors(carbide and nitride formers such as Al,Ti,V,Nb,etc)are more resistant to grain growth.The fine carbide or nitride particles tend to hinder the movement of grain boundaries,thus suppressing grain growth.In fact,the fine grain size in“microalloyed steels”is achieved b
13、y using such growth inbibitors.高的峰值温度会导致熔合线附近的晶粒长大。含有晶粒长大抑制剂的钢材（碳元素和氮元素形成元素，如铝，钛，钒，铌等等）会抑制晶粒的长大。细晶粒的碳氮微粒有抑制晶粒边界移动的倾向，因此，抑制了晶粒的长大。实际上，通过使用类似的成长抑制剂能够使细晶粒在微合金化钢中形成。Since the degree of grain growth increases with the high-temperature retention time,a higher heat-input welding process tends to produce mo
14、re severe grain growth.Of course,under high heat inputs,carbide and nitride particles have a greater tendency to dissolve and coarsen,and their effectiveness as grain growth inhibitors diminishes.During the heat-treating of steels,the maximum temperature employed is only about 100 to 200 above the u
15、pper critical temperature,and therefore no significant grain growth can occur.由于晶粒长大的等级同高温停留时间有关，焊接过程中较高的热输入会造成晶粒剧烈长大。当然，在高的热输入下，碳和氮的微粒的分解和粗化的倾向增加，其作用是减小晶粒长大抑制剂的效果。在钢的热处理过程中，最高的使用温度仅仅高于临界温度 100 到 200，因此，晶粒不会发生明显的长大。3.2.2.1 In autogenous welding ,the liquid metal of the weld pool is in intimate conta
16、ct with a substrate of identical composition(the unmelted part of the base metal).therefore ,grain growth initiates from the substrate at the fusion boundary and proceeds toward the weld centerline. Such a growth initiation process is called epitaxial growth (sometimes epitaxial nucleation).In this
17、process, grain growth is intiated by arranging atoms from the liquid phase on the existing crystalline substrate, thereby extending it without altering the crystallographic orientation.在气焊中，熔池中的液相金属与同它有相同成分的母材有着密切的联系（母材中未融化部分） 。于是，晶粒在熔合线处从母材开始长大，并向焊缝儿中心线生长。这样的开始长大方式被称为外延生长。 （有时也叫做外延形核） 。在这一过程中，液相中的原
18、子在已有晶体表面排列，晶粒开始长大，因此晶粒长大时不改变结晶方向。In the bulk of the weld,the grain structure is governed by a different mechanism known as competitive growth.在大量的焊接工序中，晶粒的组织由我们所熟知的竞争长大等不同的机制所控制。During solidification, grains tend to grow in the direction perpendicular to the solid/liquid interface ,since this is the
19、 direction of the maximum temperature gradient and thus the maximum driving force for solidification. However,grains also have their own preferred direction of growth called the easy growth direction-for example, in face-centered-cubic and body-centered-cubic metals. Therefore, during solidification
20、 ,grains with their easy growth direction parallel to the direction of the maximum temperature gradient will grow more easily and crowd out those other grains whose easy growth directinn deviates significantly from the direction of the maximum temperature gradient.在结晶过程中，晶粒有沿着固相和液相分界面垂直长大的倾向，这是由于这个方
21、向的最大温度梯度，因此也具有最大的结晶驱动力。然而，晶粒也有他们自己选择生长的方式被称为优先生长方式，例如，在面心立方结构以及体心立方结构的金属中的晶向。因此，在结晶过程中，优先生长方向和最大温度梯度方向平行的晶粒更容易生长，优先生长方向和最大温度梯度方向偏离较大的晶粒则容易被挤掉。At high welding speeds the weld pool tends to be elongated,where as at low welding portion of the tear-drop-shaped weld pool is essenually straight, the grain
22、s are also straight and growing essentially perpendicular to the pool boundary，as shown in Figure 3.23(a) .On the other hand ,since the boundary of the trailing portion of the elliptical weld pool is curved, the grains are also curved in order to grow perpendicular to the pool boundary，as shown in F
23、igure 3.23(b). Therefore, for weld metals free from heterogeneous nuclei, it can be expected that at high welding speeds columnar grains will grow straight toward the weld center line and that at low weld speeds they will curve and grow in the direction of the maximum temperature gradient.在较高的焊接速度下，
24、熔池有被延长的倾向，然而在较低的焊接速度下其有变成椭圆形的倾向。由于熔池中熔滴形成尾部的边界线是平的，因此晶粒也是平直的，而且在本质上垂直于熔池边界线生长，如图 3.2.（a）所示。另一方面，由于椭圆形熔池的尾部边界线是弯曲的，因此晶粒由于要垂直于熔池边界线生长也就保持弯曲，如图 3.23（b）所示。由于焊缝儿金属不受不同种类原子核的影响，因此，可以猜测到在高的焊接速度下，柱状晶沿着焊缝儿中心线直线生长，在较低的焊接速度下，它们呈弯曲状，并且沿着最大温度梯度方向生长。The growth of columnar grain can be interrupted by the formation
25、 of new grains,and if so,the development of grains structure in the fusion zone is no longer dominated by epitaxial and competitive growth of columnar grains.The formation of these new grain are often equiaxed rather than columnar.新晶粒的生成能够打断柱状晶的生长，如果这样的话，晶粒组织的长大就不再被柱状晶的外延长大和竞争长大所控制。这些新晶粒形成的更多的情况下是柱状
26、晶而不是等轴晶。Figure 3.24(a) shows schematically the microstructure around the weld pool boundary of an alloy .Specifically,it shows dendrites in the mushy zone behind the trailing protion of the weld pool boundary and partially melted grains in the base metal adjacent to the leading portion of the weld p
27、ool boundary. Figure 3.24(a) illustrates there different mechanisms for the nucleation of new grains in the weld metal dendrite fragmentation ,grain detachment ,and heterogeneous nucleation.There is still another mechanism for the nucleation of new grains in the weld metal, surface nucleation ,as il
28、lustrated in Figure 3.24(b).图 3.24（a）显示了合金熔池边界线附近的微观组织。特别的，它显示了在熔池边界线尾部后面的固液共存区以及临近熔池边界线头部的母材中的部分融化的晶粒的树枝晶。图 3.24（a）显示了焊缝儿金属中新晶粒成核的三种不同的机制，树枝晶的破碎，晶粒的分离以及异质形核。在焊缝儿金属中的新晶粒形核还有另一种机制，表面形核，如图 3.24（b）所示。Weld pool convection occurs druing welding owing to various driving forces such as the electromagnetic
29、force .Weld pool convection can in principle cause fragmentation of dendrite tips in the mushy zone, as illustrated in Figure 3.24(a).These dendrite fragments are carried into the bulk weld pool, where if able to survive the weld pool temperature ,they can cat as nuclei for new grains to form.在焊接过程中
30、，由于各种各样的驱动力的作用， （例如电磁驱动力） ，而是熔池发生对流。如图 3.24（a）所示，熔池的对流主要引起固液共存区树枝晶尖端的破裂。这些树枝晶的碎片进入到熔池中，在熔池的温度范围内存活，并且充当新晶粒形成的原子核。Where partially melted grains are loosely held together by the liquid films between them weld pool convection can also cause partially melted grains to detach themselves from the base met
31、al immediately adjacent to the weld pool, asillustrated in Figure 3.24(a).Like dendrite fragments ,these partially melted grains ,if they survive in the weld pool, can act as nuclei for the formation of new grains in the weld metal.如图 3.24（a）所示，半融化的晶粒由处于这些晶粒之间的液态薄膜连在一起，熔池对流也能将这些半熔化的晶粒从紧邻熔池的母材上分离出来。就
32、像树枝晶的碎片，这些半熔化的晶粒，如果能够在熔池中存活，就会在焊缝儿金属中新晶粒形成的过程中充当原子核。According to the nucleation theory ,atoms in a liquid metal have to overcome a critical energy barrier so that they can form solid nuclei that are larger than a critical size in order to be stable and able to grow into solid grains .Unfortunately ,
33、this critical energy barrier is usually high and difficult to overcome if these nuclei are to be formed solely by the atoms in the liquid themselves-the so-called homogeneous nuclei. However, if the liquid metal already contains a significant number of foreign solid particles on which the atoms in t
34、he liquid metal can be arranged in a crystalline form,it is longer necessary for the atoms in the liquid metal to form nuclei solely by themselves. These foreign particles are called heterogeneous nuclei.根据形核理论，液相金属中的原子不得不克服临界能量的阻碍以便它们能够形成稳定而且能够长成液态晶粒并且比临界尺寸大的液态原子核。不幸的是，如果这些原子核被液相本身的原子形成，那么理解能力阻碍通常很
35、大而且很难克服这就是所谓的自发形核。然而，如果液相金属已经包含大量的外来的而且其中原子能够以结晶状排列的微粒，那么对于液相金属中的原子来说，自身的单独形核就不那么重要了。这些外来微粒被称为异质形核。The weld pool surface can be undercooled thermally to induce surface nucleation by expostire to a stream of cooling gas or by instantaneous reduction or removal of the heat input. When this occurs, sol
36、id nuclei can form at the weld surface, as illustrated in Figure 3.24(b).These solid nuclei then grow into new grains as they shower down from the weld pool surface, which they do because their density is higher than that of the surrounding liquid metal.熔池表面能够采用热的过冷通过暴漏在流动的冷气或是瞬时的较小或消除热输入来引起表面形核。如图
37、3.24（b）所示，当以上情况发生时，在焊缝儿表面形成固态的原子核。当固态原子核沿着熔池向下垂直生长时，它们能够长成新的晶粒，这是由于它们的密度高于周围液态金属的密度。3.2.2.2Solidification cracking , which is observed frequently in castings and ingots, can also occur in fusion welding .Such cracking is intergranular-that is ,along the grain boundaries of the weld metal .It occurs
38、during the terminal stages of solidification ,when the stresses developed across the adjacent grains exceed the strength of the almost completely solidified weld metal .Such stresses can be induced either by the tendency of the workpiece to contract during colling,by the tendency of the weld metal t
39、o contract during solidification,or both.The severity of such contraction stresses increases with both the degree of constraint and the thickness of the workpiece.结晶裂纹，经常在铸件或是铸锭中发生，在熔化焊中也时有发生。这类裂纹是晶间裂纹，也就是说，它们沿着焊缝儿金属的晶粒边界。它在结晶的后期，当临近晶粒间的应力超过即将完全凝固的焊缝儿的强度时出现。这类应力可以通过冷却时工件的收缩，结晶时焊缝儿金属的收缩，以及两者共同作用产生。收缩
40、应力的大小同工件的约束程度以及厚度有关。The various theories of solidification cracking are effectively identical and embody the concept of the formation of a coherent interlocking solid network separated by essentially continuous thin liquid films which are ruptured by the contraction stresses .If a sufficient amount
41、of liquid metal is present near the cracks ,it can “backfill” and “heal” the incipient cracks. Otherwise, the cracks appear as open tears .The tear fracture surface often reveals the dendritic morphology of the terminal stage of solidification .各种关于凝固的理论实际上都是一致的，都包含了这样的概念，即形成相互联结的固相物网络，而这些固相物被基本连续的液
42、态薄膜隔开，在收缩应力的作用下，液态薄膜被破坏。如果在裂纹附近有足够多的液态金属，它就能“回填”和“愈合”初期裂纹。然而，裂纹以开放状裂纹出现。在凝固的最后阶段，裂纹破碎表面经常呈现树枝状。Many different methods have been recommended for testing the solidification cracking susceptibility of weld metals .One is the “Houldcroft”, which is often used for evaluating the solidification cracking s
43、usceptibility of sheet gage materials .The Design of the test specimen is shown in Figure 3.25. The specimen is free from constraints and a progression of slots of varying depth allows the dissipation of stresses within it .In such a test , solidification cracking initiates from the starting edge of
44、 the test specimen and propagates along its centerline .As the heat source moves Inward from the starting edge of the test specimen ,solidification begins there immediately .The solidifying structure is torn apart ,for the starting edge of the test specimen continues to expand as a result of continu
45、ed heat input to the specimen .Because of the presence of the slots ,the weld bead is subjected to a decreasing amount of stress along its length .The crack length from the starting edge of the test specimen is an index of solidification cracking sensitivity .许多不同的方式被推荐用来检验焊缝儿金属凝固裂纹的敏感性。其中一种经常被用来评估薄
46、板规格材料敏感性的试验被称为鱼骨状裂纹试验。试验的图样如图 3.25 所示。试样不受到约束条件的影响，而且如图上的连续狭缝的不同深度也允许了其内部应力的损耗。在该试验中，凝固裂纹开始于试样的起始边界并且沿着中心线增殖。由于热源从试验边缘向其内部移动，凝固裂纹就立即在那儿形成。由于试样开始的边界继续扩张，致使热量继续输入到试样中，导致固态组织的撕裂。由于狭缝的存在，焊缝儿沿着其长度收到不断减少的应力的制约。从试样初始边界开始的裂纹的长度是凝固裂纹敏感性的一个索引。Several metallurgical factors have been known to affect the solidif
47、ication cracking susceptibility of weld metals.众所周知，一些冶金学的因素影响着焊缝儿金属凝固裂纹的敏感性。Generally speaking ,the wider the freezing range ,the larger the mushy zone ,and thus the larger the area that is weak and susceptible to weld solidification cracking .The freezing range of an alloy can be increased as a re
48、sult either the intentional addition of alloying elements or the presence of undesirable impurities .The addition of Cu, Mg, or Zn in aluminum alloy is an example of the former case,and the presence of S and P in steels or nickel-bace alloys is an example of the latter .一般来说，凝固范围越大，脆性温度区间越大，不稳定和对焊接凝
49、固裂纹敏感的区域面积也就越大。合金的凝固范围的增加能够通过有意的添加合金元素或是本身存在不良的杂质来实现。前者的例子可以在铝合金中加入铜，镁或者是锌，后者则是在镍基合金中加入硫和磷。The effect of composition on the solidification cracking sensitivity of several aluminum alloys is shown in Figure 3.26.合成物对一些铝合金凝固裂纹的敏感性的作用如图 3.26 所示。As shown ,the maximum cracking sensitivity occurs somewhere between pure aluminum and aluminum alloys with substantially high alloying contents .Pure aluminum is, of course ,not susceptible to solidification cracking , since there is no low-melting-point eutectic present at the grain boundary to cause solidification cracking .In high alloy alumi
