Effects of Boron on the Microstructure,Ductility-dip-cracking,and Tensile Properties for NiCrFe-7 Weld Metal

Wenlin Mo^1,2，Xiaobing Hu¹，Shanping Lu^1,2，Dianzhong Li¹，Yiyi Li¹

1. Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences2. Key Laboratory of Nuclear Materials and Safety Assessment,Institute of Metal Research,Chinese Academy of Sciences

摘 要：The distribution of boron and the microstructure of grain boundary（GB） precipitates(M₂₃（C,B）₆ and M₂B)have been analyzed with their effects on the susceptibility of ductility-dip-cracking（DDC） and tensile properties for NiCrFe-7 weld metal,using optical microscopy（OM）,secondary ion mass spectroscopy（SIMS）,scanning electron microscopy（SEM）,and transmission electron microscopy（TEM）.The results show that boron segregates at GBs in NiCrFe-7 weld metal during the welding process.The segregation of boron at GBs promotes the formation of continuous M₂₃（C,B）₆ carbide chains and M₂B borides along GBs.The addition of boron aggravates GB embrittlement and causes more DDC in the weld metal,by its segregation at GBs presenting as an impurity,and promoting the formation of larger and continuous M₂₃（C,B）₆ carbides,and M₂B borides along GBs.DDC in the weld metal deteriorates the ductility and tensile strength of the weld metal simultaneously.

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