A Study On Laser Welding Joint Corrosion Resistant Performance Of Hastelloy C-22

Hastelloy C-22 is a Ni-alloy with good corrosion resistant performance. When it is used as the covering material for the conduct roll, the issues of its welding and the corrosion-resistant performance of its welding seam will be the key factors influencing the working life of the conduct roll.The failed welding joint of Hastelloy C-22 conduct roll is observed and analyzed in this thesis. The analysis result shows: The welding method of the conduct roll is filler TIG welding with no post-welding heat treatment and some incomplete penetration at the bottom of the welding seam. Through SEM, XRD and EDAX analysis on the fracture, stress corrosion cracking (SCC) is founded as the cause of the conduct roll’s cracking failure. On the basis of the analysis result above, the mechanics of the failure are studied. The failure analysis results provide a reference for the laser welding of Hastelloy C-22.Metallographic analysis and Chemical composition analysis are carried out on the base metal, the filler TIG welding seam, laser welding seam and the laser welding seam with post-welding heat treatment under different parameters to show the change of their metallurgical structures. Through the testing of the mechanical properties, electrode voltages, polarization curves and the chemical corrosion performances of the above samples, some regulations are found: the SCC-resistant abilities of the welding seams with the appropriate technique parameters, are ordered as the followings: laser welding seam with post-welding heat treatment > laser welding seam without post-welding heat treatment > filler TIG welding. After the corrosion mechanics of the welding joint are studied, the best post-welding heat treatment parameters are confirmed.The research results of this thesis are applied to produce some Hastolly C-22 conduct rolls. After the process of laser welding, circle rolling, post-welding heat treatment and heated installing etc., the finished products behaved well in the operation with excellent corrosion-resistant performance.