X80管线钢的Fe基非晶焊接行为研究

发布时间：2018-06-23 05:37

  本文选题：Fe基非晶合金 + 药芯焊丝　； 参考：《中国石油大学(华东)》2015年硕士论文

【摘要】：Fe基非晶态合金具有独特的结构和优异的力学性能及耐腐蚀性能,其作为焊丝具有成分均匀、浸润性强等特点,是一种极具发展潜力的焊接新材料,具有广阔的应用前景。X80管线钢服役条件艰苦,对焊接接头的强度和耐腐蚀性能提出了更高的要求。利用TIG焊对X80钢进行非晶焊接,可充分利用非晶合金的优异性能,有效提高焊接接头强度和耐腐蚀性能。本文采用铁基非晶合金药芯焊丝,结合TIG焊技术对X80管线钢薄板进行了对接焊接,利用光学显微镜、X射线衍射仪、扫描电子显微镜、能谱仪、显微硬度计、电子万能试验机和电化学测试系统等设备分析了非晶焊接接头的组织结构、物相组成、力学性能和耐腐蚀性等性能。同时研究了熔合比、功率密度工艺参数和焊后热处理工艺对焊接接头组织结构和性能的影响规律,并探讨了焊接接头的断裂机制和腐蚀机理。研究结果表明,X80管线钢的非晶焊接接头是由(Fe,Cr)固溶体、Mn4B相及非晶等组成的复合组织。熔合区域为一条狭窄的平面晶,宽度约为10μm,焊缝由胞状树枝晶、灰色细条状组织、灰黑色长条状组织和白色细条状组织组成。当熔合比增大至0.68时,焊缝转变为灰色基体上分布着细小树枝晶的组织。随着功率密度的增加,焊缝区域的晶粒尺寸增大,硬度降低。焊接接头经热处理后,非晶结构发生了晶化,组织实现均匀化。TIG焊焊接接头焊缝区域的平均硬度为776.9Hv0.2。焊接接头具有拉伸正断的脆性行为和较低的冲击韧性。焊接接头抗拉强度为551MPa,延伸率为0.40%,冲击韧性为2.5J?cm-2,断口为准解理断裂和典型的非晶剪切带断裂混合类型。经热处理后,焊缝区域的显微硬度明显下降,焊接接头的拉伸强度变化不大,延伸率和冲击韧性增大。经过900℃热处理后,焊缝平均硬度约为417.5Hv0.2,比热处理前降低46.3%,焊接接头的抗拉强度为398.5MPa,延伸率为5.22%,冲击韧性为15J?cm-2,断口类型为低塑性的韧性断裂,相比于热处理前焊接接头的塑韧性得到明显的改善。非晶焊接接头焊缝区域自腐蚀电位为-344.8mV,自腐蚀电流密度为9.61μA/cm2,耐蚀性能较母材有较大的提高。拟合等效电路为R(Q(R(QR))),电极系统包括“总电极金属/溶液”界面和蚀孔内“溶液/金属”界面,钝化膜不够致密,有发生点蚀倾向。经过900℃热处理后,自腐蚀电位为-375.1mV,自腐蚀电流密度为10.30μA/cm2,拟合等效电路为R(QR),电极系统为“总电极金属/溶液”界面,表现为致密的钝化膜。
[Abstract]:Fe-based amorphous alloy has unique structure, excellent mechanical properties and corrosion resistance. As a welding wire, it has the characteristics of uniform composition and strong wettability, so it is a new welding material with great development potential. The service conditions of X80 pipeline steel have a broad application prospect. The strength and corrosion resistance of welded joints are required higher. The amorphous welding of X80 steel by TIG welding can make full use of the excellent properties of the amorphous alloy and effectively improve the strength and corrosion resistance of the welded joint. In this paper, the iron-based amorphous alloy flux-cored wire and TIG welding technology are used to weld the X80 pipeline steel sheet. The X ray diffractometer, scanning electron microscope, energy spectrometer, microhardness meter are used in the welding of X80 pipeline steel sheet. The microstructure, phase composition, mechanical properties and corrosion resistance of amorphous welded joints were analyzed by electronic universal testing machine and electrochemical testing system. At the same time, the influence of fusion ratio, power density process parameters and post-weld heat treatment process on the microstructure and properties of welded joints were studied. The fracture mechanism and corrosion mechanism of welded joints were also discussed. The results show that the amorphous welded joints of X80 pipeline steel are composed of (FetoCr) solid solution and amorphous phase. The fusion zone is a narrow planar crystal with a width of about 10 渭 m. The weld is composed of cellular dendrite, gray fine stripe, gray black long stripe and white fine stripe. When the fusion ratio is increased to 0.68, the weld is transformed into a structure with fine dendrites distributed on the gray matrix. With the increase of power density, the grain size of weld increases and the hardness decreases. After heat treatment, the amorphous structure was crystallized, and the average hardness of weld zone of TIG welded joint was 776.9 Hv0.2. The welded joint has tensile brittle behavior and low impact toughness. The tensile strength of the welded joint is 551 MPA, the elongation is 0.40, the impact toughness is 2.5 J / cm ~ (-2), the fracture surface is quasi-cleavage fracture and the typical mixed type of amorphous shear band fracture. After heat treatment, the microhardness of weld zone decreased obviously, the tensile strength of welded joint changed little, and the elongation and impact toughness increased. After heat treatment at 900 鈩，

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