Investigation On Welding Procedures And Welded Joint For The J-groove CRDM Nozzle Mockups

In the welding process of nuclear reactor pressure vessel, J-groove weld will be formed by the intersection of the hemispherical head and CRDM, and conventional Welding method can hardly meet the the development of nuclear power industry requirements. Using the J-groove welding robot, through the method of welding experiment and comparative analysis of test results, the research obtains the most suitable automatic welding process parameters, to obtain a good J-groove weld microstructure, and provides the reference for the manufacture of nuclear reactor pressure vessel products. The conclusions obtained are as follows:(1) For J-groove automatic sealing welding, welding background level and peak current range should not be too wide, as the left part of the first test zone, part of the bead welding current is too large, so that found the undercut and crater defects in the visual inspection for the bead. And part of the bead welding current was too small, base metal of the test pieces has not been fully heating, the slag inclusions were observed in the microstructure of the area near the edge of the base metal, the base current proved to be controlled in 130-180A, the peak current proved to be controlled in the range of 220-280A, bead appearance and microstructure of the seal weld were optimum.(2) The inspection results of welding speed test zone shows that the fast welding speed leads to the temperature of the molten pool was not enough, resulting in poor weld formation and incomplete fusion. In addition, the solidification of molten pool so fast that the elements near the interface could not be fully spread and contribute to weld cracking. In the case of local welding speed was too slow, the molten pool keep high temperature too long time to cause the width of weld heat-affected zone increases, and the coarse grain appeared in the microstructure of welded joints, hardness and other mechanical properties decreased. When the welding speed of the welding seam on the right side was been adjusted to 80-120mm/min, bead formation and microstructure of the weld has improved significantly than the left.(3)Shielding gas flow is crucial in the process of J-groove automatic sealing welding, it is one of the main parameters of weld forming. The test results shows that the left part of the third test zone without ideal bead appearance and color when the shielding gas flow as smaller as 10-30L/min, and the carbide content in the microstructure significantly increased. On the right side of the weld, the shielding gas flow was adjusted to 3O-5OL/min, bead appearance and color has been significantly improved, austenite and carbide in the microstructure are more uniform.