英语翻译

3.2.2.2
Solidification 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 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 to 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 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 susceptibility 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 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 continued 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 solidification 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 result 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 aluminum ,on the other hand , the eutectic liquid is so abundant that it backfills and “heals” incipient cracks ,resulting in low cracking sensitivity .Somewhere in between these two composition levels ,however ,the amount of eutectic liquid may be just large enough to form a continuous film at the grain boundary and render the materials rather susceptible to solidification cracking .
如图所示，裂纹敏感性最大出现在纯铝和有非常高的合金含量的铝合金之间。

当然，纯铝对凝固裂纹是不敏感的，但是由于在晶粒边界处存在低熔点共晶体导致产生凝固裂纹。

在高合金铝中，另一方面，液相共晶体充足到能够回填和愈合初期的裂纹，导致较低的裂纹敏感性。

然而，在这两种成分之间的某个区域，液相共晶体的数量大到可以在晶粒边界形成一个连续的薄膜，并且导致材料对于凝固裂纹具有相当的敏感性。

Sulfur and phosphorus tend to widen the freezing range of steels tremendously .Unlike the eutectic liquid in high-alloy aluminums ,the amount of low-melting-point segregates due to sulfur and/or phosphorus is too small to heal any incipient cracks .Since they have a rather strong tendency to segregate at grain boundary and form low-melting-point compounds (FeS in the case of S), they can cause severe solidification cracking even at relatively low concentrations .Sulfur and phosphorus can also cause severe solidification cracking in nickel-base alloy and ferritic stainless steels . In the case of austenitic stainless steels, their detrimental effect on solidification cracking can be significantly affected by the primary solidification phase.
硫和磷能够显著的增加钢的凝固区间。

不像高合金铝中的液相共晶体，由于硫和磷的含量太少而不能“愈合”初期的裂纹，所以造成低熔点共晶体分离。

（这句不会翻译，也许不对）由于它们在晶粒边界处有相当强的分离倾向并且形成低熔点合成物（假设FeS和S），即便是在相对低的含量下也能够形成剧烈的凝固裂纹。

在镍基合金和铁素体不锈钢中，硫和磷能够引起剧烈的凝固裂纹。

假设奥氏体不锈钢，其基本凝固相能够严重影响到它们对凝固裂纹的有害作用。

Figure 3.27 shows the effect ofδ-ferrite on the solidification cracking susceptibility of Cr (wCr=17.5%) stainless steels during casting .According to the Fe-Cr-Ni ternary phase diagram ,the primary solidification phase changes from austenite(γ) to 6-ferrite when the nickel content falls below 12%. It is evident from Figure 3.27 that, when austenite is the primary solidification phase , the ferrite content is practically zero ,and the cracking susceptibility is high .When the primary solidification phase switches to δ-ferrite ,the ferrite content increases ,and the cracking susceptibility decreases .
图3.27显示了在铸造过程中δ-ferrite对含铬百分之17.5的不锈钢中凝固裂纹敏感性的影响。

根据Fe-Cr-Ni 三重相图，当镍元素含量低于百分之十二时，基本凝固相由奥氏体转变为δ-ferrite。

如图3.27，当奥氏体作为基本凝固相时，铁素体含量基本为0，而且裂纹的敏感性很高。

当基本凝固相转变为δ-ferrite时，铁
素体含量增加，裂纹的敏感性下降。

The effect of the amount of the grain boundary liquid on the solidification cracking of weld metals has been mentioned. However , not only the amount but also the distribution of the grain boundary liquid can significantly affect the solidification cracking tendency of weld metals .Figure 3.28 shows the relationship between the surface tension ,the dihedral angle ,and the distribution of the grain boundary liquid .
大量的晶粒分界线对焊缝儿金属上的凝固裂纹的作用已经被提及到。

然而，不仅是晶粒边界线的数量，晶粒边界线的分布也会对焊缝儿金属的凝固裂纹倾向造成重大的影响。

图3.28显示了表面张力，两面角以及晶粒边界线之间的关系。

If the surface tension between the solid grains and the grain boundary liquid is very low ,a liquid film will form between the grains ,and the solidification cracking susceptibility will be high. On the other hand ,if the surface tension is high ,the liquid phase will be globular and will not wet the grain boundary .Such discontinuous liquid globule do not significantly reduce the strength of the solid network and therefore are not as harmful. For example .FeS forms films at the grain boundary of steels whereas MnS forms globules .Because of its globular morphology and higher melting point ,MnS has been known to be far less harmful than FeS.
如果固相晶粒和液相晶粒边界之间的表面张力非常低，在晶粒之间就会形成液膜，凝固裂纹的敏感性就会很高。

另一方面，如果表面张力很高，液相就会呈球状并且不会润湿晶粒边界。

这样的液态小球体不会明显地减少液态网状物的强度，因此不是有害的。

例如，FeS 在钢的晶粒边界处形成液膜，然而MnS却形成球状。

由于其呈球状，并且有较高的熔点，因此，众所周知，MnS比FeS更有益。

Coarse columnar grains are often more susceptible to solidification cracking than fine equiaxed grains .This can be because fine equiaxed grains can deform to accommodate contraction strains more easily .Liquid feeding and the healing of incipient cracks can also be more effective in fine-grained material .Liquid feeding and the healing of incipient cracks can also be more effective in fine-granined material.In addition ,the grain boundary area is much greater in fine-grained material ,and harmful low-melting-point segregates are therefore less concentrated at the grain boundary.
粗大的柱状晶比细小的等轴晶更易于形成凝固裂纹。

这是由于细小的等轴晶能够通过变形来更加容易的适应晶粒的收缩。

液体的流动以及初期裂纹的愈合也会对细晶粒材料起到有效地作用。

此外，在细晶粒中，晶粒边界面积越大，低熔点共晶体越？？（有害），因此，越少在晶粒边界处集中。

It is interesting to note that ,owing to the steep angle of abutment between columnar grains growing from opposite sides of the weld pool, welds made with a tear-drop-shape weld pool have been reported to be more susceptible to weld centerline solidification cracking than welds made with an elliptical weld pool. A steep angle seems to favor the head-on impingement of columnar grains growing from opposite side of the weld pool and the formation of the continuous liquid film of low-melting-point segregates at the weld centerline .As a result ,center line solidification cracking occurs under the influence of transverse contraction stresses.
有趣的是，由于从熔池两侧生长的柱状晶之间的夹角很小，由泪滴状熔池形成的焊缝儿对焊缝儿中心线凝固裂纹的敏感性比椭圆形熔池形成的焊缝儿更大。

这个夹角似乎能够给予上述的柱状晶正面的冲击并且在焊缝儿中心线处形成低熔点共晶体的连续的液态薄膜。

结果，在横向收缩应力的作用下，中心线出产生凝固裂纹。

So far ,the metallurgical factors of weld solidification cracking have been described. But without the presence of stresses acting on adjacent grains during solidification no cracking can occur. Such stresses can be due to thermal contraction or solidification shrinkage or both. Austenitic stainless steels have relatively high thermal expansion coefficients (compared to mild steels) and are therefore often prone to solidification cracking. Aluminum alloys have both high thermal expansion coefficients and high
solidification shrinkage. As a result solidification cracking can be rather serious in some aluminum alloys, especially those with wide freezing ranges.
到目前为止，焊接凝固裂纹的冶金学因素已经被我们所描述。

但是，在结晶过程中相邻晶粒之间如果不存在应力，就不会有裂纹产生。

这样的应力是由于热收缩，凝固收缩，或是两者共同作用的结果。

奥氏体不锈钢有相对较高的热膨胀系数（相对于低碳钢），因此更加易于产生凝固裂纹。

铝合金不仅有较高的热膨胀系数还有较高的凝固收缩率。

因此，在一些铝合金中会产生相当严重的凝固裂纹，特别是那些凝固区间较大的铝合金。

The degree if restraint of the workpiece is another mechanical factor of the solidification cracking. For the same joint design and material, the greater the restraint of the workpiece, the more likely solidification cracking will occur.
工件的拘束度是另一个导致凝固裂纹的机械因素。

对于具有相同设计和材料的工件儿，工件儿的拘束度越大，就会越容易产生凝固裂纹。

Essentially, the weld HAZ of low-carbon steels can be divided into three major regions. The partial grain-refining, grain-refining, and grain-coarsening regions. The partial grain-refining region was subjected to a peak temperature between the effective lower and upper critical temperatures, Ac1 and Ac3. The prior pearlite colonies in this region transformed to austenite (γ)and expanded slightly into the prior ferrite(α) colonies upon heating to above the Ac1 temperature and then decomposed into very fine grains of pearlite and ferrite during cooling, as illustrated schematically in figure 3.29. The prior ferrite colonies were essentially unaffected. The grain-refining region was subjected to a peak temperature just above the effective upper critical temperatures, Ac3 thus allowing austenite grains to nucleate. Such austenite grains decomposed into small pearlite and ferrite grains during subsequent cooling. The distribution of pearlite and ferrite is not exactly uniform. This is because insufficient time was allowed for the diffusion of carbon phase formed was therefore not uniform in composition. Finally, the grain-coarsening region was subjected to a peak temperature well above the Ac3 temperature, thus promoting the coarsening of austenite grains. Because of the relatively high cooling rate and the large grain size in this region, acicular，rather than blocky, ferrite formed at grain boundaries. Such a structure is often called the Widmanstatten structure.
本来，低碳钢的焊接热影响区能够被划分为三个部分：局部细晶区，细晶区，粗晶区。

局部细晶区会受到处于临界温度Ac1和Ac3之间的某一峰值温度的影响。

如图3.29所示，在该区域的珠光体群转变为奥氏体，并且在加热到Ac1温度之上时逐渐扩散到铁素体群中，之后在冷却的条件下细晶粒的珠光体和铁素体。

前面所述的铁素体群在本质上是不受影响的。

细晶区收到高于临界温度Ac3点的某一峰值温度的影响，因此，奥氏体能够形核。

这样的奥氏体晶粒在后续的过冷过程中会分解为细小的珠光体和铁素体晶粒。

珠光体和铁素体的分布不是完全统一的。

这是因为在焊接过程中快速的加热使得没有充足的时间让碳原子进行扩散，因而形成的奥氏体在组成上是不统一的。

最后，粗晶区同样受到高于Ac3的某一温度的影响，因而会导致奥氏体晶粒的粗化。

由于该区域相对较高的冷却速度和相对大的晶粒尺寸，在晶粒边界会生成针状的铁素体。

这样的组织被称为“魏氏组织”。

Although the HAZ contains both fine and coarse grains, its average grain size is much smaller than the coarse columnar grains of the fusion zone. Therefore, if the fusion zone of a weld pass is replaced by the HAZs of its subsequent passes, the fusion zone of this weld pass is “grain-refined”. Such grain refining is often desired in the multipass welding of carbon and alloy steels.
虽然焊接热影响区包含了细晶区和粗晶区，然而它的平均晶粒度比焊接熔合区的粗大柱状晶要小很多。

因此，如果焊道的熔合区被下一层焊道的焊接热影响区所取代，那么焊道的熔合区为“再结晶”。

如此细化晶粒的方式在碳钢和合金钢的多层焊中是十分渴望得到的。

The HAZ microstructure mentioned above is expected when normal welding conditions are involved.
However,when both the heating and the cooling rates are extremely high, as in the case of laser or electron bean welding, martensite can form in the HAZ of mild steels. The prior-pearlite colnies in the region subjected to peak temperature just above Ac1 did not have sufficient time to interact with their neighboring ferrite, and their carbon content consequently remained essentially unchanged. The austenite that formed in these prior-pearlite colonies during heating transformed into martensite during subsequent rapid cooling. The martensite formed is very hard and brittle because of high carbon content. Further up into the HAZ, both the peak temperature and the diffusion time increased. As a result, the prior-pearlite colonies expanded while being austenized and formed martensite colonies of lower carbon contents during subsequent cooling.
当正常焊接条件十分复杂时，上面所提到的焊接热影响区的微观组织使我们所期望的。

然而，当加热和冷却的速度相当高的时候，才用激光或是电子束焊，在低碳钢的焊接热影响区会有马氏体生成。

在该区域的前面珠光体群收到高于Ac1的峰值温度的影响，没有充足的时间同与之相邻的的铁素体作用，因此剩余的含碳量在本质上是不变的。

加热时在该珠光体群中得到的奥氏体在随后立即冷却时都转变成了马氏体。

由于较高的含碳量，所得到的马氏体具有较高的硬度和脆性。

进一步深入到焊接热影响区，峰值温度同扩散时间都有所提高。

结果，当被奥氏体化时珠光体群扩张，并且在随后冷却的过程中形成低碳的马氏体群。

3.2.3.2 HAZ of Medium-and High-carbon Steels
The welding of medium-and High-carbon steels is more difficult than that of mild stells.This is because with higher carbon contents the tendency to form hard,brittle martensite in the weld HAZ is greater,and hence under-bead cracking is more likely to occur.Similar to the case of mild stells,the weld HAZ of a 1040 stell(the nominal carbon content of the stell is0.40%) weld can be divided into three main regions: the partial grain-refining,and the grain-coarsening regious. The miscrostructure in the grain-coarsening regio is essentially martensite,with a relatively.A relatively large amount of pearlite and a very small amount of ferrite and bainite are present at the grain boundary in the grain-refining region.The microstructure inside the grain is still essentially martensite.
中碳钢和高碳钢的焊接比低碳钢更难。

这是由于高的含碳量在焊接热影响区更容易形成硬的脆的马氏体，因此更容易形成焊道下裂纹。

同低碳钢的情况类似，40号钢（名义上含碳量为百分之0.4）在焊接时的焊接热影响区能够被分成是三个主要的区域：部分细晶区，细晶区和粗晶区。

本质上，粗晶区的微观组织是马氏体，在晶粒边界处还有少量的贝氏体和珠光体。

在细晶区的晶粒边界出存在着大量的珠光体和少量的铁素体和贝氏体。

晶粒内德微观组织在本质上仍然是马氏体。

In the grain-coarsening region, both the high cooling rate and the large grain size promote the formation of martensite.In the grain-refining region,both the lower cooling rate and the smaler grain size encourage the formation of pearlite and ferrite. The hardness profile of the HAZ is shown in Figure 3.30(a).when weledwith preheating,the size of HAZ increase,but the maximumhardness decreases,as shown in Figure 3.30(b).Examination of HAZ microstructure near the fusion boundary reveals more pearlite and ferrite but less martensite,apparently because of the lower cooling rate cause by preheating. 在粗晶区，高的冷却速度和较大的晶粒尺寸促使马氏体的生成。

在细晶区，在较低的冷却速度和较小的晶粒尺寸共同作用下会生成珠光体和铁素体如图3.30（a）的侧面显示了焊接热影响区的硬度。

如图3.30（b）所示，在预热的条件下焊接时，焊接热影响区的尺寸增加，然而最大硬度却下降。

在熔合线附近对焊接热影响区微观组织的试验显示有较多的珠光体和铁素体，只有少量的马氏体，这显然是由于在预热条件下较低的冷却速度造成的。

3.2.3.3 HAZ of alloy Steels
It is not intended here to give a complete discussion on the welding of various types of alloy steels.Instead, only two representative groups of alloy steel-quenchedand tempered alloy steels and heat-treatable alloy steels-are selectedfor discussion in this section.The welding of these three groups of
ally steels is uite different from that of mild steels and often requires special attention.Rolled and normalized low-alloy steels usually contant less than 0.25%carbon and have a yield strength level of 45 to 70kis.Miscroalloyed steels usually contain less than 0.15% carbon,with the additin of smallamounts of Cb,V,Mo,and N as alloying elements. Both of these groups of low-alloy steels usually have good weldability,and the welding of them is similar to that of mild steels,though a higher harded.
在这里不打算对合金钢的各种类型都给出一个完整的讨论。

相反的，在这一章里挑选两种代笔性的合金钢进行讨论，分别是淬火和回火合金钢以及热处理合金钢。

焊接这三种合金钢同焊接低碳钢有着很大的不同并且经常却要特别的关注。

轧制和正火低合金钢的含碳量通常小于0.25%并且屈服强度在45到70ksi之间。

微合金钢的含碳量通常小于0.15%并且加入了少量的钶，钒，钼和氮等作为合金元素。

这些低合金钢通常具有好的焊接性，并且焊接过程同低碳钢类似，然而一个较高的淬透性是被期望的。

Quenched and Tempered Alloy Steels（淬火和回火合金钢）
The quenched and tempered alloy steels considerde here as a group are those characterized by their high strength, remarkable thoughness,remrkable toughness,and good wldability.Such alloys usually have low carbon contents(typically from 0.10% to 0.25%)and , therefore , are also relatively easy to weld ; relatively low or no preheating is needde,and post-weld heat-treating is usually not required.
这里我们所提到的合金钢是具有高强度，不寻常的韧性，以及好的焊接性。

这样的合金钢通常都有较低的含碳量（通常从0.1%到0.25%），因此，也比较容易进行焊接；采用较低的预热，或是不预热，并且，通常不采用焊后热处理。

Low carbon content is desired in such alloy for two reasons-tominimize the hardness of the martensite , and to raise the Ms tempreature so that any martensite formed can be tempered automatically during cooling.Because of the formatio of low-carbon autotempered martensite,both high strength and good thoughness can be obtained. The hardenability of such alloys is ensured by alloying with Mn, Cr, Ni, and Mo.The use of Ni also significanticantly increases the thoughness and lower the ductile-brittle transition temperature in these alloys.
由于两方面的原因希望这些低合金钢中的含炭量低：第一，减小马氏体的硬度；第二，提高Ms点温度，使得形成的马氏体在冷却过程中能发生自回火。

由于生成了低碳的自回火马氏体，所以，能够得到较高的强度以及较好的韧性。

这样钢的淬透性由钢中的锰，铬，镍和钼元素来决定。

这些合金中的镍元素能够很大程度上提高韧性并且降低脆性转变温度。

The welding of quenched and tempered alloy steels is described below using T-1 steel as an example . The continuous cooling transformation curves of T-1 steel are shown in Figure 3.31
如下图所示通过使用T-1钢作为一个例子可以来描述淬火和回火合金钢焊接的过程T-1钢的连续冷却转变曲线如图3.31所示。

If the cooling rate during welding is too low , for example, between curve “p”and the hatched area indicated in the Figure, a substantial amount of ferrite forms .This can in fact be harmful since the ferrite phase tends to reject carbon atoms and turn its surrounding areas into high –carbon austenite.Such high-carbon austenite can in turn transform to high-carbon martensite and bainite during cooling , thus resulting in brittle weld HAZs.Therefore, the heat input and the preheating of the workpiece should be limited when welding quenched and tempered alloy steels.
如果在焊接过程中冷却速度非常低，例如，就像图中曲线P与阴影面积之间的区域显示的那样，有大量的铁素体形成。

事实上这是有害的，由于铁素体相不吸收碳原子并且将其周围均转变为高碳奥氏体。

这样的高碳奥氏体能够在冷却过程中转变为高碳马氏体和贝氏体，因此，形成脆性的焊接热影响区。

因此在焊接淬火和回火合金钢时，工件儿的热输入和预热必须得到控制。

On the other hand ,if the colling rate during welding too fast(to the left of curve “z” in Figure 3.31),insufficient time is acailable for the autotempering of martensite. This can result in hydrogen
cracking,if hydrogrn is present .Therefore low-hydrogen electrodes or welding processes are preferred,and a small amout of preheating is often recommended.The hatched area in Figure 3.31 repressents the region of best colling rates of weld T-1steel. The amount of preheating needed for a given material increases with increasing plate thickness . This is because for a givenheat input the cooling rate is higher in a thicker plate, In addition to the higher cooling rate , athicker plate often has a slightly higher carbon content to ensure proper hardening during the heat-treating step of the steeel making process.
另一方面，如果在焊接过程中的冷却速度很快（达到3.31图中曲线z的左侧），那么马氏体就没有足够的时间进行自回火。

如果有氢的存在，这就会发生氢致裂纹。

因此，要选用低氢型焊条或焊接工艺，并且通常采用较小程度的预热。

图3.31中阴影部分描述了焊接T-1钢的最佳冷却速度区域。

对给定材料的预热程度随着板材厚度的增加而增加。

这是由于在较厚的钢板中，冷却速度要高于给定的热输入。

除了较高的冷却速度之外，在钢材制作的热处理工序中，为了确保有合适的硬度较厚的钢板要有一个稍微高的碳含量。

To meet the requirements of both limited heat inputs and proper preheating, multipass weleing is often used in welding thick setions of high-strength quenched and tempered at the same level as the preheat temperature . In fact ,multipass welding offers another important advantage-bead tempering.In other words, the martensite in the HAZ of a weld pass is temperedby the heat resulting from deposition in subsequent pass .As a result , the overall toughness of the weld metal is enhanced .Figure 3.32 clearly demonstrates the effect of bead tempering. The HAZ of bead D,unlike that of bead E, was not quite tempered edough by bead F.As aresult,the hardness of the HAZ of bead D was significantly higher than that of bead E.
为了同时限制热输入以及合适的预热两个必要的条件，多层焊一般被用来焊接高强度的淬火和回火合金钢较厚的部位。

这样做的目的是为了使焊层间温度同预热温度保持在同一个等级。

事实上，多层焊的另一个好处就是焊道回火。

换句话说，下一层焊道沉积物的热量造成了该层焊道焊接热影响区马氏体的回火。

结果，焊缝儿金属的整体韧性得到了提高。

图3.32清晰地显示了焊道回火的影响。

焊道D的焊接热影响区不像焊道E那样没有被下一层焊道F充分回火。

结果，焊道D的焊接热影响区的硬度明显高于焊道E。

Heat-treatable Alloy Steels（热处理合金钢）
The heat-treatable alloy steels to be discussed here as a group refer to those that must be heat-treated after welding . Such alloys, usually have higher carbon contents (typically from 0.30% to 0.50% ) and hence high strength and lower toughness than the quenched and tempered alloy steels.
这里所讨论的热处理合金钢总的来说是指焊接之一定要被热处理的合金钢。

这样的合金钢，通常具有较高的碳含量（通常上是从0.3%到0.5%），因此也就比淬火和回火合金钢具有更高的强度和更低的韧性。

Heat-treable alloy steels are usually welded in annerled ( or normalized ) conditions. After welding , the entire weldment is then heat-treated in order to obtain the best combination of properties offered by the steel.For the weld metal to respond to the same postweld heat treatment, the filler metal should be similar to the base metal in composition.
热处理合金钢通常在常规或是退火的条件下进行焊接。

焊接之后，为了使刚能够获得最好的结合性能要对整个钢件进行热处理。

由于焊缝儿金属同样进行了焊后热处理，所以，填充材料一定要与母材的成分保持一致。

Since high-carbon martensite is hard and brittle, proper preheating and low-hydrogen electrodes should be used to avoid underbead cracking.A convenient way of estimating the amount of preheating required is to use the so-called equivalent carbon content. The equivalent carbon content,or carbon equivalent, is intended among other purposes to be used as a measure for the hydrogen-carcking sensiticity of a weld. For ordinary C-Mn steels, for example, the following equation for the equivalent carbon content has been used:
Equivalent carbon con tent =Wc+1/4Wmn+1/4Wsi
由于高碳马氏体的硬度和脆性，为了避免焊道下裂纹，要采用合适的预热以及低氢型焊条。

当量碳含量是一种用来评估所需的预热程度的较为便捷的方式。

当量碳含量，即是，碳当量，其另一个用途是被用来判断焊缝儿氢致裂纹的敏感性。

例如，对于普通的C-Mn钢，应用如下的碳当量的方程式：
碳当量=碳的百分含量+1/4锰的百分含量+1/4硅的百分含量
The relationship between this equivalent carbon content and the average underbead cracking
( one form of hydrogen cracking ) sensitivity of C-Mn steels is shown in Figure 3.33.
C-Mn钢中碳当量与平均焊道下裂纹（氢致裂纹的一种形式）敏感性的关系如图3.33所示。

A typical formula for determining the equivalent carbon content of a steel containing not more than Wc=0.5%,Wmn,=1.5% , Wni=3.5% , Wcr=1% , Wmo=0.5% is given below:
Equivalent carbon content=Wc+Wn/6+Wni/15+Wcr/5+Wcu/13+Wmo/4
对于各种含量之多想如上各种元素这么多的钢，对于确定该钢中碳当量的公式如下：
碳当量= Wc+Wn/6+Wni/15+Wcr/5+Wcu/13+Wmo/4
（这个地方有张表，不过估计不能考，详见page 161）
The above suggested preheat temperatures are for arc welding processes. They may be affected by the thickenss of the workpiece. For gas welding processes, however, preheating is usually not required owing to the slow cooling rates associated with such welding processes.
如上的预热温度是适用于电弧焊的。

它们收到工件厚度的影响。

然而，对于气焊来说，由于该焊接工序对应的较低的焊接速度，所以，预热通常不是必须的。

In addition to the use of preheating , the weldment of heat-treatable alloy steels is often immediately heated for stress-relief heat treatment, martensite is tempered, and the weldment can therefore be cooled to room temperarute without danger of cracking . Afrer this , the weldment can be postweld heat-treated to develop the strength and toughness the steel is capable of attaining. A sketch of the thermal history during welding and postweld stress relieving is shown in Figure 3.34.
除了预热的使用之外，热处理合金钢的焊件经常被立即加热作为消应处理，马氏体回火，因此，焊件被冷却到室温时没有产生裂纹的危险。

之后焊件能够通过焊后热处理来提升它的强度和热性到其本身能够达到的程度。

在焊接以及焊后热处理过程中的热经历如图3.34所示。

It should be noted that the weld heat-affected zone should be cooled down to a temperature slightly below the martensite-finish temperature Mf before being heated up for stress relieving. This is to prevent any untransforned austenite from decomposing into ferrite and pearlite during stress relieving to transforming to untempered martensite uponm cooling to room temperature after stress relieving.
需要注意的是，在加热到应力消除之前，焊接热影响区一定要冷却到稍微低于马氏体完成温度Mf点得某一温度。

这是为了阻止应力消除后在应力消除过程中为转变的奥氏体分解的铁素体和珠光体在冷却到室温的过程中转变为未回火的马氏体。

In cases where heat-treatable alloy steels cannot be postweld heat-treated and must be welded in heat-treated conditions,the softening , as well as the hydrogen cracking, of the HAZ can be a serious problem, as shown in Figure 3.35 . To minimize the softening problem, lower heat input per unit length of weld should be employed, and the preheat, interpass, and stress-relief temperatures should be at least 50℃lower than the tempering temperature of the bace metal before welding.Since postweld heat-treatment of the weldment is not involved, the composition of the filler metal can be substantially different from that of that of the base metal, depending on the strength level of the weld metal required. 假如热处理合金钢不能进行焊后热处理，并且一定要在热处理的条件下进行焊接，那么不仅是软化和氢致。