Microcracking in multipass weld metal of alloy 690 Part 1 – Microcracking susceptibility in reheated weld metal

Abstract

Microcracking behaviour in the gas tungsten arc multipass weld metal of alloy 690 was investigated. The majority of microcracks occurred within about 300 mm from the fusion line of the subsequent weld bead and propagated along the solidification boundaries in the multipass weld metal. The morphology of the crack surface indicated the characteristic texture of ductility dip cracking. The microcracking susceptibility of the reheated weld metal was evaluated via the spot Varestraint test using three different filler metals having varying contents of impurity elements such as P and S. Microcracking occurring in the spot Varestraint tests consisted predominantly of ductility dip cracking, with a small amount of liquation cracking. The ductility dip cracking temperature range was about 1350-1600 K in the weld metal FF1, and narrowed in the order of weld metals FF1.FF3.FF5. The ductility dip cracking susceptibility was reduced with decreasing contents of impurity elements in the filler metal. It was concluded that the amount of (PzS) in the filler metal should be reduced as much as possible (to about 30 ppm in total) to suppress microcracking in the multipass weldment.

Study on ductility dip cracking susceptibility in Filler Metal 82 during welding

“…Based on the above result, it can be concluded that the next-pass welding has most contribution to DDC in weld joint. The result turns out to be very similar to Nishimoto's study [6]. In his work, the multi-pass weld joint has Ductility Dip Cracks in every pass weld, except the last one.…”

Effects of Boron on the Microstructure, Ductility-dip-cracking, and Tensile Properties for NiCrFe-7 Weld Metal

“…It is also used in dissimilar welding between several Ni-base alloy, stainless steel and carbon steel in building nuclear power plants [9] . However, it has been pointed out that NiCrFe-7 weld metal is susceptible to ductility-dip-cracking (DDC) under heavy restraint conditions such as welding thick components [10][11][12][13] . DDC is a solid-state hot cracking, caused by GB embrittlement at homologous temperatures that ranges from about 0.5 to 0.8 of the alloy melting points, which is observed at grain boundaries (GBs) [14,15] .…”

“…Filler metal composition, such as S, P, H, C, Ti, Ta, Mo, La, Ce, and Nb, has a strong effect on DDC formation in austenitic weldments. Segregation of S, P, and H to GBs is a dominant factor for DDC aggravation in Ni-base alloys, whereas Ti, Ta, Mo, La, Ce, and Nb addition to a filler metal reduces the sensitivity of DDC [13,17,20,[27][28][29][30][31] .…”

Evaluation of thermal stressed state in welded joint of alloy Inconel 690

“…The welded joints of Inconel 690 with appropriate filler materials showed a high sensitivity to hot crack formation, particularly under the conditions of welding of thick-walled structural elements. The alloys manifest the highest tendency to the formation of ductility-dip cracks [2,3].As was shown previously [4], the ductility-dip cracks in welding of alloys of alloying system Ni-Cr-Fe occur at the temperature range of 1050-650 °C, the value of critical deformation of crack formation ε cr is about 1.2 %.The thermal processes in fusion welding have a decisive influence on the nature and kinetics of changes in the stress-strain state, structure and properties of weld and HAZ. In this regard, the analysis of temperature fields in welding of alloys of Ni-Cr-Fe alloying system with the aim of further investigations of kinetics of stress-strain state and evaluation of tendency to hot crack formation is an urgent problem.…”

“…The welded joints of Inconel 690 with appropriate filler materials showed a high sensitivity to hot crack formation, particularly under the conditions of welding of thick-walled structural elements. The alloys manifest the highest tendency to the formation of ductility-dip cracks [2,3].…”