Q345－Zr－Q345焊接接头显微组织和纳米压痕研究

为了评价Zr与Fe之间的焊接性能，对焊缝中可能存在的金属间化合物的种类、分布以及性能进行了研究。采用钨极氩弧焊（TIG）方法对Q345低合金试板进行了以纯Zr作为填充金属的熔焊连接试验，并采用纳米压痕技术建立了焊缝典型组织和力学性能之间的依存关系。结果显示，Zr焊缝与Q345基体相连处主要由层片状共晶组织组成（α－Fe+Fe2Zr），该区域中Fe元素含量较高；焊缝中部区域主要由Fe2Zr胞状树枝晶组成，少量FeZr2组织分布在Fe2Zr胞状枝晶间；在Fe2Zr富集区域出现了裂纹。纳米压痕测试结果表明，Fe2Zr金属间化合物的硬度较高，平均硬度值达到20.1 GPa；层片状共晶组织（α－Fe+Fe2Zr）的硬度值相对较低，平均硬度值为6.8 GPa；FeZr2化合物的平均硬度值为8.9 GPa。Zr焊缝断口呈现出明显的枝晶形貌，EDS结果表明，这些枝晶主要由Fe2Zr金属间化合物组成。

Microstructure and Nanoindentation Investigation of Q345-Zr-Q345 Welded Joint

In order to evaluate the weldability between Zr and Fe， the type， distribution and properties of intermetallic compounds that may be present in the weld are investigated. In this paper, pure Zr filler was applied to join low alloy steel plate（Q345） by tungsten inert gas（TIG） welding method. The relationship between microstructures and mechanical properties of the welded metal were built by nanoindentation tests. The results indicated that Q345-Zr interface region was mainly consisted of lamellar eutectic production（α-Fe+Fe2Zr）. Fe element was rich in this region. Approaching the central of the welded metal， Fe2Zr cellular dendrites were dominant in this region with some FeZr2 intermetallics distributing among these dendrite structures. Cracks were observed in regions rich in Fe2Zr intermetallics. Nanoindentation results showed that Fe2Zr intermetallics had higher hardness value（average value reaches 20.1 GPa）； lamellar eutectic structure（α-Fe+Fe2Zr） presented with low hardness value（average value reaches 6.8 GPa）； FeZr2 intermetallics showed an averaged hardness value of 8.9 GPa. Dendrite structures were observed on the fracture surface of Zr welded metal. EDS results confirmed that these dendrites were consisted of Fe2Zr intermetallics.