【作者】 娄建新；

【导师】 李德元；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2014， 博士

【摘要】 随着珠光体钢与奥氏体钢异质材料焊接在工程中的广泛应用,大量的事故案例表明,珠光体和奥氏体熔合线两侧的碳迁移现象,是导致焊接接头失效的主要原因。本文针对电厂动力锅炉系统中典型的珠光体和奥氏体接头,通过模拟接头的实际工况制备试件,测定碳迁移情况。通过观察熔合线两侧的碳分布,发现了碳元素由珠光体钢一侧向奥氏体钢一侧的扩散现象,根据测定的碳和合金元素的成分,计算出熔合线的化学势梯度,再利用菲克定律推导出珠光体与奥氏体异质接头处的碳迁移公式。为了研制出可以抑制碳迁移的焊材,本文选取了A102、A402、R307、Ni317四种常用于珠光体钢与奥氏体钢焊接的焊材,并制备了各种焊材在焊态、时效处理、蠕变状态的试样。借助光学显微镜和扫描电镜分析并对比了各试样的组织和碳迁移情况,找到了影响碳迁移的主要因素,并以此为基础研制出了一种超低碳新型焊条。将新型焊条重复以上步骤进行试验,所得到的试样与之前四种焊材试样进行了组织、断口和碳迁移的比较。实验结果表明,碳迁移是影响蠕变断裂的主要因素,A102、A402、R307焊条所焊试件蠕变断裂的位置均发生在珠光体与奥氏体熔合线附近,通过断口形式分析和观察断裂部位的组织及碳分布,发现以上三种试样均发生了明显的碳迁移现象,蠕变断裂的断口均存在脆性断裂特征。在碳迁移层中发现了由渗碳体和碳铬化合物组成的有害的硬脆相。新型的超低碳焊条和Ni317试样则几乎没有碳迁移发生,蠕变断裂的断口呈现塑性断裂特征,熔合区部位只是由于两侧的碳元素浓度梯度的差异发生了少量的碳扩散。比较新型超低碳焊条和其它四种焊条的蠕变试样,发现新型的超低碳焊条的蠕变断裂时间超过了A102、A402、R307,只略逊于Ni317。由此可以得出结论,本文研制的超低碳焊条可以有效的抑制碳迁移,在高温力学性能上超过了工程上广泛应用的常规奥氏体和珠光体焊材,虽然略逊于镍基材料,但已经可以满足绝大部分工程需要。由于在价格上不仅远低于昂贵的镍基材料,就是和常规的奥氏体焊材相比,也有很大的价格优势,性价比高,具有很强的实用性。更多还原

【Abstract】 With widely applying of dissimilar material welding for pearlite and austenitic steel inproject engineer, more and more cases indicate that the main reason cause weld seam failure iscarbon migration on fusion line between pearlite steel and austenitic steel. This paper tookpower plant boiler system as background,weld classic joint by simulating actual workingstatus. Carbon migration was tested and recorded by using scanning electron microscopy(SEM). After analyzed the carbon distribution around fusion line, diffusion was from pearlitesteel to austenitic steel. Chemical potential gradient was calculated according to the measuredcomposition of carbon and other alloy elements. Carbon migration formula for pearlite andaustenitic dissimilar joint was derived by using Fick’s law and calculated chemical potentialgradients.Four commonly used welding consumables,A102,A402,R307,Ni317, were selected tocreate an effective welding consumable that could restrain carbon migration. Test specimenswere welded for all the above welding consumable in the stage of welding/agingtreatment/creep. Microstructure and carbon migration for different specimens were compared.The main effect factors were discovered for carbon migration,a new ultra-low carbon weldingconsumable was created base on the discovery. The same test specimens were welded andmachined. Comparison for specimens’ microstructure/facture/carbon migration between newultra-low carbon and four common welding consumables are performed.Examination results showed that carbon migration was main factor lead to creep rupture.Rupture location for A102/A402/R307test specimens occurred around fusion line of pearliteand austenitic. Obvious carbon migration was founded for above test specimens after analyzecreep rupture fracture and observe microstructure and carbon migration on rupture position.Brittle rupture features were discovered on facture. Harmful hard and brittlemicrostructure,compose of cementite and carbon chromium compounds,were founded incarbon migration layer.Carbon migration was almost not occurred for test specimens ofultra-low carbon and Ni317. Plastic rupture features were founded on facture. Only a smallamount of carbon diffusion occurred around fusion line because of difference carbonconcentration gradient on both sides. Creep rupture time for ultra-low carbon electrode was longer than A102/A402/R307,only slightly shorter than Ni317by comparing the five testspecimens.It could be concluded that the new type ultra-low carbon electrode wouldeffectively restrain carbon migration. High temperature mechanical properties of ultra-lowcarbon electrode were better than the commonly used austenitic and pearlite weldingconsumables. Although slightly worse than the nickel-based materials, but could meet most ofthe majority engineering request. This new type welding consumable had a great priceadvantage than the austenitic material,not to mention nickel-based material. So this kind ofwelding consumable wasa very practical,with a high cost-effective.更多还原