国际低合金会议论文02钒作为一种合金元素在结构钢中的作用.docx

1、国际低合金会议论文02钒作为一种合金元素在结构钢中的作用Different Roles for Vanadium as a MicroalloyingElement in Structural Steels钒作为一种合金元素在结构钢中的作用HUTCHINSON Bevis(SwereaKIMAB, Swedish Corrosion and Metals Research Institute, Box 55970, SE-10216 Stockholm, Sweden)Abstract: Vanadium is the most versatile of the microalloying e

2、lements used in steels. The present paper describes three separate ways in which vanadium is used to optimize mechanical properties in different products. Firstly, precipitation of V(C,N) during the transformation or in ferrite during cooling provides strengthening that is especially useful in long

3、products and forgings. Additionally, VN particles which precipitate in austenite act as efficient intra-granular nucleants for ferrite, contributing improved strength and toughness in suitable process routes such as seamless pipe production. Thirdly, vanadium is supremely effective in preventing rec

4、overy in martensite and bainite. In this way it can be applied to maintain strength and reduces variability of properties in hot rolled strip steels.Key words: vanadium, precipitation, strength, toughness摘要：钒在钢中使用的合金元素中用途最广。本文描述钒被用于优化不同产品的机械性能的三种独立的方法。首先，转换过程中V(C，N)析出或冷却期间铁素体中V(C，N)析出提供强化作用，在长形产品或锻件

5、中这种作用尤其明显。第二，奥氏体中析出的VN粒子充当有效的铁素体晶间成核粒子，有助于在合适的工艺路线中，比如无缝管生产中，提高强度和韧性。第三，钒对防止马氏体和贝氏体中的回复特别有效。这样，钒可以被用于保持强度，减少热轧带钢性能的可变性。关键词：钒，析出，强度，韧性The important microalloying elements vanadium, niobium and titanium are often considered as being inter-changeable in steels but that is seldom the case in reality for

6、 reasons that depend on their respective affinities for the interstitial elements carbon and nitrogen 1 . This can be understood on the basis of Fig.1 which shows the solubility products of their carbides and nitrides in austenite as a function of temperature. Titanium forms an extremely stable nitr

7、ide that persists as particles in the steel even close to the melting point. These may be used to resist grain growth in austenite but they have virtually no effect on strength and may be disadvantageous with respect to toughness. Titanium carbide, on the other hand, has a high solubility and forms

8、principally inside the ferrite phase where it gives significant precipitationhardening although at the expense of some loss of toughness. Niobium carbides and nitrides are rather similar in stability and most frequently exist combined together as carbonitrides, Nb(C,N), at lower temperatures in aust

9、enite. Niobium is valuable because of its ability to interfere with recrystallisation in the later stages of hot rolling 2 and so encourage pancake grain structures in the austenite. This leads to grain refinement in the resulting ferrite after transformation, which increases strength and toughness

10、but is restricted in practice to flat rolled products with low finish rolling temperatures. Some further strengthening may also be obtained fromprecipitation in the ferrite phase. 重要的微合金化元素V、Nb、Ti经常被视为在钢中可以内部更换的，但是由于事实上却很少有这样的情况，原因是这取决于，它们各自对于间隙元素C和Ni的密切关系 1。这可以在图1的基础上理解，图1为作为温度的一个函数的奥氏体中碳化物和氮化物的溶度积

11、。Ti形成非常稳定的、一直作为钢中的粒子的氮化物，即使接近熔点。这些元素可被用于阻止奥氏体中晶粒长大，但它们对 强度几乎不产生影响，可能对韧性不利。另一方面，碳化钛具有较高的溶解度，主要在铁素体相内形成，在那里碳化钛产生强大的沉淀强化作用，尽管以损失一部分韧性为代价。铌碳化物和氮化物在稳定性方面非常相似，最常结合在一起，作为碳氮化物Nb(C,N)，在较低温度下存在于奥氏体中。由于在热轧后期Nb具有干扰再结晶的能力，Nb非常有价值，因此促使奥氏体中扁平状原奥氏体出现。这导致相变后的铁素体中的晶粒细化，提高强度和韧性，但对于低终轧温度的轧制扁材在实践中受到限制。在奥氏体相中也可能获得进一步的强化。

12、 Vanadium differs in that its nitride is considerably more stable than its carbide but VN is still more soluble than Nb(C,N). Accordingly, vanadium has little effect in inhibiting recrystallisation in austenite 2 although particles of VN can form under suitable circumstances and these may subsequent

13、ly act as nucleants for ferrite as will be shown below. For this, and perhaps also for other reasons, vanadium and nitrogen additions have a marked beneficial effect of grain refinement in ferritepearlite steels. However, most of the vanadium is retained in solid solution until it precipitates as VN

14、 or nitrogen-rich V(C,N) at lower temperatures in ferrite where it provides a high degree of strengthening. A further benefit of vanadium is in steels with acicular bainitic or martensitic microstructures whereby recovery of the dislocation networks is strongly inhibited, so providing a significant

15、advantage in strength and processability as described below.V的氮化物比其碳化物更为稳定，但是VN可溶性仍比Nb(C,N)更强。因此，尽管VN粒子可以在合适的环境下在奥氏体中形成而且这些粒子可以充当铁素体成晶粒子，V对抑制奥氏体中再结晶影响还是很小。由于这个原因和其它原因，添加V和Ni对铁素体珠光体钢的晶粒细化产生显著的有利影响。但是，大多数V被保留在固溶体中，直到作为VN或富Ni V(C,N)在较低温度时在铁素体中析出，产生高级别的强化效果。V的另一个益处是通过针状贝氏体或马氏体显微组织对位错网络恢复产生强烈的抑制作用，因此对强度和

16、加工性能非常有利。图1 不同温度下重要的碳化物和氮化物的溶度积The stability of VN phase means that the efficacy of vanadium in steel is intimately connected with the nitrogen content so there is no point in pressing nitrogen levels to the lowest values that modern steelworks can achieve. Typical levels from electric arc furnaces

17、of 0.01%N represent a practical optimum and, where necessary, addition of nitrogen to around this level is recommended. In fact, in vanadium steels, nitrogen should be considered as a complementary microalloying element 3,4 .VN相的稳定性意味着钢中V的效力与Ni含量密切相关，因此将Ni水平压低到现代钢厂能达到的最低数值没有意义。0.01%N电弧炉典型水平代表一种实际优化，

18、如果必要，推荐添加接近此水平的Ni。实际上，在V钢中，Ni应被视为一种补充合金元素。1 Strengthening and grain refinement in ferrite-pearlite steels1 铁素体-贝氏体钢中强化和晶粒细化Since vanadium has a relatively high solubility in austenite there is little advantage in pursuing a strategy of low temperature controlled rolling in these steels. In fact, low

19、 rolling temperatures are not applicable for many products and it is here that vanadium offers a major advantage. Examples are profiles and other long products such as rebars as well as closed-die forgings where high working loads and die wear often necessitate deformation temperatures of 950C or hi

20、gher. Even for plate products there are often practical reasons for adopting a high finish rolling temperature since this allows faster rolling schedules and so higher productivity. In these situations, vanadium can be utilised with great effect for strengthening. The factors that are most influenti

21、al for precipitation hardening in ferrite-pearlite steels are V-content, N-content, cooling rate or isothermal hold temperature and, perhaps more surprisingly, the C-content 1.既然V在奥氏体中具有较高的溶度积，对这些钢采取低温控制轧制策略没有有利条件。实际上，低轧制温度对很多产品不适用。这正是V主要优势所在。型材和长材，比如钢筋和闭膜锻件是这样的例子，高工作载荷和模具使950C或更高的变形温度成为必需。即使对于板材，也常

22、常存在采用高终轧温度的实际理由，因为这允许较快的轧制制度和较高的生产率。对铁素体-贝氏体钢中析出硬化影响最大的因素是V含量、N含量、冷却速率或等温保温时间以及，可能更令人吃惊的是C含量。图2 带相间析出和随机析出近似区域的低碳钢CCT图Precipitates are typically formed during cooling after hot working and may adopt different morphologies depending on the steel chemistry and cooling schedule. This is shown somewhat

23、schematically in connection with the CCT diagram in Fig.2. At higher temperatures during isothermal holding or slow cooling, inter-phase precipitation takes place 5,6 at the moving/ phase boundary resulting in sheets of particles that appear as rows in electron micrographs. The particle density beco

24、mes larger and the precipitate row spacing smaller as the nitrogen content of the steel increases, Fig.3(a) to (c). This is a result of the greater thermodynamic stability of VN than VC which causes more profuse nucleation of the precipitates and leads to significantly higher strength with higher ni

25、trogen contents 4,6 . At lower temperatures, homogeneous precipitation with random distributions of particles occurs within the ferrite phase after it forms and the precipitate dispersion becomes increasingly fine with reduction in temperature. 析出物在热加工后冷却期间形成，可能呈现出取决于化学和冷却进度表的不同形貌。高温时，等温或缓冷过程中，在/相界相

26、间出现析出，这导致粒子片成排出现在电子显微图片中。钢中Ni含量增加时，粒子密度增大，析出物行距变小，图3（a）(c)。这是VN热力学稳定性比VCQ强的结果，这导致更丰富的析出物成核和更高的强度和更高的Ni含量。低温时，在铁素体相内，出现粒子分布不规则的均匀沉淀。随着温度的下降，沉淀弥散变得越来越细小。图3 显示0.12%V钢的V(C,N)析出行列的TEM图像 （a）0.005%N, (b) 0.008%N, (c) 0.026%N ,(d) 0.01%N。C含量为：（a）（c）中0.1%C，(d)中0.04%CIt is worth noting also that V(C,N) precip

27、itation is not restricted to pro-eutectoid ferrite. The same particles may also form within the ferritic phase in pearlite 7 . This is utilised, for example, in fully pearlitic rail steels where the wear resistance can be enhanced and also in high carbon steel rods and wires.值得注意的是，V(C,N)析出不局限于先共析铁素

28、体。贝氏体中铁素体相内也可能形成同样的粒子。这被用于完全贝氏体轨钢，在这种钢中，耐磨性可被提高，在高碳钢棒和钢丝中也是这样。The size of precipitates and their volume fraction determine the extra strength level that vanadium microalloyed steels offer in comparison with plain carbon steels of similar composition. This can be evaluated from experimental measureme

29、nts of yield stress after correcting for the effects of solid solution hardening and grain size. The resulting parameter expressed as Rp is the strengthening due to precipitates in units of MPa. Various experimental results showing how precipitation hardening, Rp, depends on steel chemistry and proc

30、essing are presented in the following figures 1 .析出物的尺寸和体积比决定V微合金钢超出化学成分相似的普碳钢的强度水平。这可以根据固溶硬化效应和晶粒度纠错之后进行的屈服应力试验测量评判。下图显示出各种试验结果，这些试验结果显示析出硬化Rp如何取决于钢的化学成分和加工。The effect of different nitrogen contents in a typical plate steel composition (0.12%C, 0.35%Si,1.35%Mn and 0.095%V) is demonstrated in Fig.4.

31、 Raising the nitrogen from 0.006%N to 0.018%N produces about 80% greater precipitation hardening due to the progressive refinement of the precipitates as demonstrated in Fig.3. It can also be seen that low temperature controlled rolling actually somewhat reduces the precipitation hardening since som

32、e of the vanadium becomes combined as VN already in the austenite during deformation. These particles are larger than the ones that nucleate and grow in ferrite and so contribute much less strengthening to the steel. 图4显示出一个典型钢板成分中不同Ni含量的影响。由于图3所示的析出物的逐步细化，将Ni含量从0.006%N提高到0.018%N增加大约80%析出硬化。也可以看出，由于在变形过程中奥氏体中一些V合并为VN，低温控制轧制实际上某种程度上减少了析出硬化。这些粒子比在铁素体中成核和长大的粒子大，因此对钢的强化起着较小作用。图4 具有两种不同的模拟轧制表的钢板中V（C，N）引起的析出硬化，作为Ni含量的一个函数Some mechanical properties on industrially hot rolled plates 8 are summarised in Fig.5. These steels had base compositions of 0.09%C, 1.5%Mn, 0.08%V, 0.0