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1、 中文翻译对高强耐磨钢NM360的模拟焊接热影响区的组织和冲击韧性的研究摘要：因为高的碳当量，被广泛应用在挖掘机械领域的高强耐磨钢NM360在制造过程中经常表现出焊接裂纹。在焊接接头中焊接热影响区（HAZ）是最脆弱的部分。在焊接生产中，大多数问题存在于热影响区，比如淬硬，冷裂，局部脆化和再热裂纹都和热影响区结构转变和产生有关。现阶段，在不同冷却速度下的NM360的热影响区的冲击韧性已经通过物理模拟方法得到研究，根据连续冷却转变曲线（CCT），冲击韧性的演变机制已被得到研究。NM360的热影响区的微观结构，硬度，淬透性，产生冷裂纹的可能性也可以通过CCT图预测。这个研究可以对NM360的可焊性和
2、焊接热影响区性能的探究提供数据并奠定实验基础。关键字：冲击韧性，物理模拟，CCT，耐磨钢引言高强耐磨钢NM360的冶金机制是增加碳和其他合金元素的组成，已经被广泛的应用在挖掘机械领域。其综合性能包括耐磨性，可焊性，塑性通过轧制后调质过程的沉淀和相转变得到提高1。在焊接生产中，大多数问题存在于热影响区，比如淬硬，冷裂，局部脆化和再热裂纹都和热影响区结构转变和产生有关。在实验中去测量热影响区的相转变是一个困难的工作，因为焊接接头中的相转变是非常快的，温度非常高转变时间很短。物理模拟是一种解决这问题的有效方法，根据热循环曲线，它可以放大热影响区的任意位置或者其他地方，然后可以观察到微观结构而且性能也
3、可以被方便的检测。采用最新的实验，可以代替以前经常用到的大量重复试验。因此，可以节省大量的人力物质资源。它提供了一个简单的方案去解决不能够被直观研究的复杂问题。材料和试验方法实验材料是高强耐磨钢NM360。将合金元素Mn，Cr，Ni，Mo，B,Si，Al和Ti加入NM360来提高淬透性，调和马氏体的抗力并细化晶粒。它的化学组成成分和机械性能分别显示在表1和表2中，在表2中可以看到NM360的硬度和强度非常高，但它的冲击韧性并不好。NM360已经通过轧制后的热精炼过程（950的淬火和500的回火）被处理，它的微观结构是带有马氏体特征的回火索氏体。NM360钢的微观结构显示在图1。表1 NM360
4、钢的化学成分 (wt.%)CSiMnPSCuAl0.1390.341.30.0260.00780.0390.031CrNiMoTiBN0.510.260.250.0180.00160.0035表2 NM360钢的机械性能bMPasMpa5%HBAKVJ(室温)120010001036042图1 高强耐磨钢NM360的微观结构在热模拟测试中，由Gleeble-1500D加热系统决定的试样尺寸是11mm11mm90mm。为了使编程曲线和实际热循环曲线重合，温度跨度在t8/5变化。样品的装配图显示在图22.A:夹块和夹头的接触表面B：夹块和样品的热点接触表面图2 样品的装配图用于这个模拟实验主要参数
5、显示在表3表3 用于这个模拟实验主要参数峰值温度1320在峰值温度tm的停留时间0.5s加热速度WH通过加热时间tH表现冷却速度Wc通过冷却时间t8/5表现用于热仿真参数说明:（1）峰值温度Tp鉴于实际因素，Tp选择为1320。热影响区粗晶粒的形成温度从1200到1400变化。对低碳低合金钢熔合线温度将在1300-1350。Gleeble-1500D将有10-20超调。（2）加热速度WH加热速度WH不仅对相转变温度AC1和AC3有影响，对相转变产物和它的特性也有影响。测量瞬时加热速度WH将会产生很大错误。在多数情况下，用加热时间tH代替WH。鉴于CO2气体保护焊的能量和预热温度超过100，tH
6、设置为从室温加热到1320的5秒钟。（3）峰值温度的停留时间tm峰值温度的停留时间tm对晶粒维度和奥氏体的稳定性有影响，鉴于实际焊接条件和热电偶的高温耐热性，tm在这个实验中选择为0.5秒。（4）冷去速度WC对于通常的低合金高强钢，热影响区的微观结构取决于540的冷却速度或者是冷却时间t8/5（从800到500的冷却时间）。因为800-500奥氏体的最不稳定阶段，t8/5最终决定热影响区的相转变产物，但是去测量每一个瞬时温度是困难的，所以常常用t8/5来代替冷却速度WC。t8/5是热影响区微观结构和性能的最重要影响因素。通常可以通过理论计算和实验得到。涉及到以下因素，t8/5被确定为5s、10
7、s、15s、20s、25s、30s、40s、50s、60s：中间组织，铁素体珠光体出现的关键冷却时间；马氏体转变温度Ms和Mf；CO2气体保护焊的t8/5的最大变化范围；NM360，15MnCrNiMo, 15MnMoVNRe, 14MnMoNbB, 14MnMoVN,BHW-35和HQ系列硬化调和钢的模拟热影响区连续冷却转变曲线（SH-CCT）。基于以上参数，用Quiksim软件输入模拟焊接热循环的程序。W-3R/W-25Re热电偶被焊接在试样的均匀温度区，试样安装在Gleeble-1500D的测试槽。热循环的模拟数据，膨胀时间膨胀温度可以在Quiksim软件中获得。3.结果和分析3.1冷却
8、时间对冲击韧性的影响根据热模拟GB2650-89，冲击试样被制作成带夏比v型缺口的尺寸为10mm10mm55mm的形状。冲击测试在25下JB-300夏比冲击测试机上进行。结果在表4中显示，AKV相关曲线在图3中显示。表4 t8/5和AKV数据序列测得t8/5实际t8/5AKVD0155.078D021010.978D031514.864D042019.776D052524.6134D063030.6139D074040.4135D085050.768待添加的隐藏文字内容2D096059.948图3 NM360热影响区粗晶粒区冲击韧性在图3中可以看到当t8/5在0s到20s变化时AKV很低且变化
9、很小，这是因为所有的合金结构是易脆的马氏体，这可以从图4（a）中看到。当t8/5在20s到40s变化时AKV达到最大值。这由于马氏体和贝氏体复合结构的出现，结构示图在图4（b）和图4（c）中。当t8/5是30s时AKV达到最大值139J。研究3-5表明低贝氏体马氏体复合结构和无碳贝氏体马氏体复合结构不仅提高钢的韧性还提高钢的强度。当贝氏体和马氏体的组成达到一定比例，钢就会具有高强度和高韧性的特点。当t8/5超过40s，由于粗晶区的大量马氏体AKV增加很快，这可以从图4（d）中看到。但是所有试样的AKV都比基本金属的（42J）高很多。图4 热影响区粗晶粒区金相照片3.2热影响区的冲击断口在扫描电
10、镜S-570分析下的热影响区的冲击断口显示在图5中。可以从图5（a）和图5（b）看到当t8/5小于20s时脊状撕裂和河流状花样存在于所有的裂纹中。原因是试样的冷却速度很低因此发生马氏体转变。众所周知，马氏体具有低韧性高硬度的特点所以发生准解理断裂。当t8/5从20s到40s变化时。图5（c）（d）表明断裂时纤维断裂。这是因为贝氏体转变的产生以及马氏体贝氏体复合结构可以提高钢的冲击韧性。在图5（e）（f）中可以看到随着t8/5它再次发生脆性破坏。图5 热影响区不同冷却速度冲击韧性的标准电子图像4讨论SH-CCT表格被广泛的用在焊接中并反映出过热区焊接工艺和结构转变过程的关系。在给定钢的焊接条件（
11、I，E，t8/5）下通过SH-CCT图就可以预见结构和相转变的过程。同时，在SH-CCT图中也可以选择与组织性能有关的冷却曲线来获得最佳的焊接参数6。从图3和图6可以看到对于NM360的焊接来说t8/5在20s到30s变化是合适的。在这个速度下冷却的热影响区粗晶区的结构是由一系列低碳马氏体和少量贝氏体（2-45%）组成的。因为高的冲击韧性（76J-139J）和接近于基体金属（380HV）的硬度（HV387-HV360），不论在结构和综合性能上热影响区粗晶区都有优秀的变现。同时，许多调查表明在低冷却速度下高强，低碳，低合金以及硬化调和钢的焊接的热影响区将会变得非常脆弱，因为低冷却速度下上贝氏体，
12、马氏体和贝氏体的结构。所以这是一个重要的方法通过改善高热输入来避免热影响区的破坏。相似的，冷裂纹可以通过预热来避免。但是要指出的是预热可能产生低的冷却速度从而导致结构脆性强度减小，和坏的韧性。通过低的热输入和适当的预热温度以及调整热影响区t8/5在Tb和Tm之间可以获得好的韧性和抵抗冷裂纹的能力。通过合理的焊接参数和高的冷却速度，没有焊后热处理热影响区也能获得优越的机械性能。图6NM360钢的模拟热影响区连续冷却转变曲线（SH-CCT）5结论（1）对NM360钢，随着冷却速度的增加热影响区粗晶区的冲击韧性将会先增加后减小。最好的冲击韧性在t8/5从25s到40s变化时取到，对应的AKV在134
13、J和139J之间。（2） 随着冷却速度的增加，冲击断裂的变化如下：解理断裂凹坑断裂解理断裂。这和热影响区粗晶粒区冲击韧性的变化是一致的。（3）NM360的热影响区粗晶粒区结构和冲击韧性的变化以及通过焊接工艺可以对焊接工艺参数的选择提供一个重要的基础依据并预测焊接接头性能。参考文献1 ZHONG Junjie, ZHU Hanhua, XIAO Changmo, et al. Experimental Research on the Anti-wear Properties of the Steel NM360 J. Journal of Wuhan University of Technolo
14、gy. 2006, 30(3): 395-397. 2 NIU Jitai. PHYSICAL SIMULATION IN MATERIALS AND HOT-WORKING M. Beijing: National Defence Industrial Press, 1999. 3 YANG Fubao, BAI Binzhe, LIU Dongyu, et al. MICROSTRUCTURE AND PROPERTIES OF A CARBIDE-FREE BAINITE/MARTENSITE ULTRA-HI GH STRENGTH STEEL J. ACTAMETALLURGICA
15、SINICA. 2004, 40(3): 296-300.4 Tomitay. Effect of martensite morphology on mechanical properties of low alloy steels having mixed structure of martensite and lower bainite J. Material Sci Technology. 1991, 7(4): 299-306. 5 Youngch, Bgadeshiahkdh. Strength of mixtures of bainite and martensite J. Mat
16、erial Sci Technology. 1994, 10(3): 209-214. 6 Li Deyuan ZZSD. Revision of a CCT Diagram of the Simulated ADI Weld Metal and Its Application in Actual Welding J. J. Mater. Sci. Technol. 1998(14): 147-150. 7 Yinshike W G. Influnce of Weld Thermal Cycle on Microstructures of 10Ni5CrMoV Steel J. Transac
17、tions of the China Welding Institution. 1996, 17(1): 25-30. 附录 英文原文Study on Microstructure and Impact Ductility of Simulated Weld HAZ of High-Strength Wear-Resistant Steel NM360Abstract: High-strength wear-resistant steel NM360 which is widely used in the field of excavating machinery always tends t
18、o welding crack during the manufacturing process due to the high carbon equivalent. The heat affected zone (HAZ) is the weakest part in a welding joint. In welding manufacture, most of the problems exist in HAZ such as harden quenching, cold crack, local brittleness as well as reheat crack are all r
19、elated to the structure transformation and its products in HAZ material. In the present work, the impact ductility of NM360s HAZ under different cooling rate has been studied by using physical simulation method. And the impact ductility evolution mechanism has been investigated according to the simu
20、lated HAZ continuous cooling transformation（CCT）diagram. The microstructure, hardness, tendency of hardenability, the possibility of generating cold crack of NM360s HAZ also can be predicted by the CCT. This work can provide the data and lays experimental foundation to the research of weldability an
21、d the HAZ performance for steel NM360.Key words：impact ductility; physical simulation; CCT; wear-resistant steelIntroductionHigh-strength wear-resistant steel NM360, whose metallurgy mechanism is to increase the content of carbon and the other alloying elements, has been widely used in the field of
22、excavating machinery. Th e combination property including the wear resistance, weldability and mouldability is improved by the precipitation and phase transition during the thermal refining after rolling1. In welding manufacture, most of the problems exist in heat affected zone (HAZ) such as harden
23、quenching, cold crack, local brittleness as well as reheat crack are all related to the structure transformation and its products in HAZ material. Its a difficult work to measure the HAZ phase transition in experiment because the phase transition in welding joint is very fast, as well as the tempera
24、ture is high and the transition time is short. Physical simulation is an effective way to solve this kind of problem. It can amplify any position in HAZ or some other place according to the thermal cycling curve. Then the microstructure can be observed and the property can be tested conveniently. By
25、 using the least experiment, plenty of repetitive experiments which usually used before can be replaced. Thus, a great quantity of manpower and material resources can be saved. It provides a simple solution to the complex problem which can not be investigated directly2.Materials and Experimental Met
26、hodThe experimental material is high-strength wear-resistant steel NM360. To improve the hardenability, temper resistance of martensite and refined grain, alloying elements Mn, Cr, Ni, Mo, B, Si, Al and Ti have been added into NM360. Its chemical compositions and mechanical properties are shown resp
27、ectively in Table 1 and Table 2. It can be seen from Table 2 that the hardness and strength of NM360 steel is excellent, however, its ductility propert y is not very good. NM360 steel has been processed by thermal refining process (950 quenching and 500 tempering) after rolling and its microstructur
28、e is tempered sorbite with martensite characteristics. Microstructure of NM360 steel is shown in Fig.1. Table 1 Chemical compositions of NM360 steel(wt.%)CSiMnPSCuAl0.1390.341.30.0260.00780.0390.031CrNiMoTiBN0.510.260.250.0180.00160.0035Table2 Mechanical properties of NM360 steelbMPasMpa5%HBAKVJ(Roo
29、m temperature)120010001036042Fig.1 Microstructure of high-strength wear-resistant steel NM360In thermal simulation test, the specimen size which is decided by the heating system of Gleeble-1500D is 11mm11mm90 mm. In order to make the coincidence between the programming curve and the actu al thermal
30、cycling curve, the span between grips varies with t8/5. The assembly diagram of test sample is shown in Fig.22.A: Contact Surface between Fixture Block and ColletB: Contact Surface of Electric and Heat between Fixture Block and SpecimenFig.2 Assembly diagram of test sampleMain parameters used in thi
31、s simulation experiment is shown in Table 3.Table 3 Parameters used in thermal simulationPeak temperature T p1320Residence time during peak temperature tm0.5sHeating rateWHExpressed by heating timetHCooling rateWcExpressed by cooling timet8/5Instruction for parameters used in thermal simulation:Peak
32、 temperature TpIn consideration of the following factors, Tp was selected for 1320 . Temperature for the formation of coarse grain zone in HAZ range from 1200 to 1400 . Temperature of weld bond will be 1300 1350 for low carbon steel and low alloy steel. Gleeble-1500D will make 10 20 overshoot.Heatin
33、g rate WHHeating rate WH has an impact on not only the phase transition temperature of AC1 and AC3 but also the phase transition product and its feature. Measuring transient heating rate WH will yield great errors. In most cases, heating time tH was used to instead of WH. In view of CO2 gas shielded
34、 welding energy and preheating temperature more than 100, tH was set with 5 seconds for heating to 1320 from room temperature.(3) Residence time during peak temperature tm Residence time during peak temperature tm have an influence on crystallite dimension and stability of austenite. In view of actu
35、al welding condition and high temperature endurance of thermocouple, tm was selected for 0.5 second in this experiment. (4) Cooling rate Wc For common low-alloy and high strength steel, microstructure in overheated zone depend on cooling velocity at 540 or cooling time t8/5 (cooling time from 800 to
36、 500). Because 800 500 is the most unstability period for austenite, t8/5 will finally decide the phase transition products in HAZ. But it is difficult to measure every transient temperature, so cooling time t8/5 was used to instead of cooling rate Wc.t8/5 is the most important factor for HAZs micro
37、structure and property. Usually it can be obtained by theoretical computation and experience. t8/5 is determined as 5s、10s、15s、20s、25s、30s、40s、50s、60s by referring to the following factors:critical cooling time for appearance of intermediate structure, ferrite and pearlite; martensite transformation
38、 temperature Ms and Mf maximum range of t8/5 in CO2 gas shielded welding;Simulated HAZ continuous cooling transformation (SH-CCT) diagram of NM360, 15MnCrNiMo, 15MnMoVNRe, 14MnMoNbB, 14MnMoVN,BHW-35 and HQ series hardened and tempered steel.The Quiksim software has been select ed to input the progra
39、m of simulated weld thermal cycle based on above parameters . W-3R/W-25Re thermocouple was welded on the uniform temperature zone of test specimen and the test specimen was installed in the test groove of Gleeble-1500D. Simulated data of thermal cycle, expansion-time and expansion temperature can be
40、 obtained by the Quiksim.Results and AnalysisEffect of cooling time on impact ductilityImpact specimens were made into dimention of 10mm10mm55mm with charpy-V notch according to GB2650-89 after thermal simulation. Impact tests were proceeded on JB-300 charpy impact machine tester at 25.The results a
41、re shown in Table 4 and the relevant curve of Akv is shown in Fig.3.Table 4 Data of t 8/5 and AkvNumberDefault t8/5Actual t8/5AKVD0155.078D021010.978D031514.864D042019.776D052524.6134D063030.6139D074040.4135D085050.768D096059.948Fig.3 Impact ductility of coarse-grain zone in HAZ for NM360It can be s
42、een from Fig.3 that Akv is lower and it changes very little when t8/5 ranged from 0s to 20s. This is because all of the metallurgical structure is brittle martensite which can be seen from Fig.4(a). Akv reach the maximum when t8/5 ranged from 20s to 40s. The reason for that is the appearance of mart
43、ensite/bainite duplex structure which are shown in Fig.4(b) and Fig.4(c). When t8/5 is 30s, Akv achieve its maximum 139J. Researches3-5 indicate that lower bainite/martensite duplex structure as well as non-carbide bainite/martensite duplex structure can improve not only the steels ductility but als
44、o strength. When the content of bainite and martensite reaches a certain proportion, steel will be charactered with high strength and ductility. When t8/5 exceeds 40s, Akv decrease obviously due to the plenty of bainite in coarse-grain zone, which can be seen from Fig.4(d). But all of the Akv of the
45、 specimens are much higher than the base metals (42J).Fig.4 Metallograph of coarse-grain zone in HAZImpact fracture in HAZImpact fracture of HAZ shown in Fig.5 are analysed on the scanning electron microscope S-570. It can be seen from Fig.5 (a) and Fig.5 (b) that tearing ridges and river patterns e
46、xisted in all the fractures when t8/5 is less than 20s. The reason is that the cooling rates of specimens are low and thus the martensite transformation occurred. As is known to all, martensite is characterized with lower ductility and high hardness, so the quasi-cleavage fractures occurred. When t8
47、/5 range from 20s to 40s, Fig.5 (c) and Fig.5 (d) indicate that the fractures are ductile fractures. This is because of the occurrence of bainite transformation and the duplex structure of martensite/bainite can improve steelsimpact ductility. As shown in Fig.5 (e) and Fig.5 (f), with the increase of t8/5, it turns into brittle fracture again.Fig.5 SEM picture of impact fracture under differen
