Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni-based filler metal is one of the most important filler metals in building the key components of nuclear power plants, however, ductility- dip- cracking (DDC) and inclusion defects form easily in the weldment and need to be repaired afterward. The precipitation of M23C6 (M=Cr, Fe) at grain boundaries will promote the nucleation and propagation of DDC. Adding Ti can form Ti(C, N) and reduce M23C6 precipitate at grain boundaries, which reduces DDC in the weld metal. However, the increase of Ti content in filler metal will cause the inclusion defects. Nb replacing part of Ti in Ni-based filler metal is proposed in this work. The reduction of Ti in filler metal is to reduce the sensitivity of inclusion defects in the weld metal. Nb can form MX (M=Nb, Ti, X=C, N) precipitates to reduce the M23C6 and DDC in weld metal. The effect of Nb on the size, number, and location of MX and M23C6 in Ni-based weldment has been investigated systematically in this work. Phase diagram calculations show that Nb is an element forming high temperature MX precipitate, and its affinity with oxygen is poor and not easy to form oxide. According to the phase diagram calculations, five different filler metals are designed and made with 0, 0.4%, 0.7%, 0.85%, 1.1%Nb content. The results show that the intragranular precipitates are distributed along sub grain boundaries. The intragranular precipitate for the Nb-free weld metal is Ti(C, N), whereas the intragranular precipitate in the Nb-bearing weld metals is MX. For the increased Nb in weld metals, more MX is produced, and more C is fixed within the grain. As the Nb content increased in weld metals, the initial precipitation temperature of M23C6 decreases, the intergranular M23C6 precipitate decreases and M23C6 turns discreted at grain boundaries. As Nb content increases in weld metals, the total crack length of DDC decreases. When the Nb content is over 0.85%, little DDC is found in the weld metals. The addition of Nb can improve the tensile strength, plasticity and bending property of the weld metals.
Hits
Hits
Downloads
Comment