It is of great significance to reduce welding hot cracks and improve the corrosion resistance of nuclear power components by controlling the dilution ratio of the cladding weld bead formed by gas tungsten arc welding (GTAW). This paper presents a method to predict the dilution ratio by using the ratio of the thermal power of forming a unit length weld to the cross-section of the fuse, that is, the linear energy of forming a unit volume of deposited metal, which is characterized by the “Heat Equivalent for Melting Welding Wire” (HEMW). It is found that there is a linear positive correlation between the HEMW and the dilution ratio. With the increase in HEMW, the proportion of deposition heat energy in the whole effective heat input energy decreases, the proportion of base metal melting heat energy increases, and the proportion of non-melting heat energy diffused to the base metal remains basically unchanged. The HEMW is used to predict and control the dilution rate under the condition of pulse welding. By increasing the wire feeding speed under the condition of pulse peak current and reducing the welding speed, a high deposition efficiency, low dilution rate and low heat input is realized, which plays an important guiding role in improving the deposition quality.

During the welding of 690 nickel-based alloy, solidification cracking (SFC) and ductility-dip cracking (DDC) easily forms, which has a negative effect on the quality of welded joints and service life. The present study examined the effects of welding heat input and cladding layers on the SFC and DDC, as well as their formation mechanism. The microstructure observation, elemental distribution, and Varestraint test were carried out. The results show that SFC and DDC were formed for the Inconel filler metal 52M, and SFC is more prone to form than DDC. The alloy elements such as Fe, Si, C, and P from base metal can expand the solidification temperature range, such that the SFC sensitivity increases. With the increase of welding heat input, the grain size of cladding metal is increased with a great SFC sensitivity. The increasing welding heat input also makes DDC possible due to the formation of a large angle grain boundary.