Characteristics of dissimilar welding of alloy 690 to 304L stainless steel

Abstract

The object of the present work is to research the dissimilar welding of nickel based 690 alloy and SUS 304L stainless steel using two alternative Inconel filler metals, namely, 82 (I–82) and 52 (I–52). Gas tungsten arc welding with identical parameters and procedures was used to carry out single V groove butt welding with six passes in four layers on nickel based alloy 690 and 304L stainless steel. Mechanical and corrosion resistance tests were performed. Metallographical, fractographical, and compositional analysis were used to study filler metal dissimilarities. Mechanical tests show that the I–82 weldment, owing to its denser dendrites and formation of abundant niobium enriched precipitates, has a higher strength and hardness than the I–52 weldment. Rupture occurred in the alloy 690 base metal. In comparison, the I–52 weldment, with coarse dendrites and no niobium enriched precipitates, exhibits superior corrosion resistance to the I–82 weldment but has a lower tensile strength and ruptured in the fusion zone. Microstructural investigation reveals that I–52 is a mixture of cellular dendrites and columnar dendrites whereas I–82 is mainly columnar dendrites with niobium enriched precipitates.

The microstructure and fracture behavior of the dissimilar alloy 690-SUS 304L joint with various Nb addition

“…Therefore, the constitutional cooling of the fusion zone near the SUS 304L is greater than that which takes place near the alloy 690 and so the dendrites in the first region are denser than those in the second. The study carried out by Lee and Jeng [17] observed the same phenomenon.…”

Dissimilar welding of nickel-based Alloy 690 to SUS 304L with Ti addition

“…This is particularly the case for dissimilar weldments. These weldments permit a reduction in the constructional cost of components [7], and consequently they continue to be the subject of considerable research. However, one problem associated with dissimilar weldments is that the obvious compositional variation and alloy transfer associated with the dilution of the two different base metals may result in failure of the weld [8].…”

Effects of beam offset on mechanical properties and corrosion resistance of Alloy 690–SUS 304L EBW joints for nuclear power plant

“…The corrosion resistance of nickel-based Alloy 690 is known to be significantly better than that of SUS 304L SS [8,[11][12][13]. Furthermore, shifting the centerline of the electron beam toward the Alloy 690 BM during the EBW fabrication of Alloy 690-SUS 304L SS dissimilar joints yields a considerable improvement in the corrosion resistance of the weldment since it increases the amount of Ni and Cr in the FZ.…”

“…However, the increased heat input into the weldment as a result of the higher number of welding passes prompts carbide precipitation at the grain boundaries and leads to the formation of chromium depletion zones in the FZ. As a result, the corrosion resistance of the weldment is significantly impaired [6][7][8][9][10][11][12][13][14].…”