Unmixing behaviour in dissimilar laser welds for duplex and austenitic stainless steels

Abstract

Metallurgical characteristics of single-mode laser dissimilar welds between super duplex (UNS S32750) and austenitic (type 316L) stainless steels is the existence of an unmixed zone that originates from each base metal. It was confirmed that the unmixed zone that flowed out from the 316L had the microstructural morphology of primary austenite with secondary δ-ferrite solidification mode, while the morphology of a δ-ferrite single phase solidification mode was observed within the unmixed zone that flowed out from the S32750. Furthermore, it could be speculated that each unmixed zone that flowed out from 316L and S32750 coexisted independently in terms of crystallographic aspect (orientation distribution function and predominant orientation relationship) analysed by electron backscatter diffraction.

Liquation cracking susceptibility of remelted and reheated weld metals in CM247LC superalloy using multi-bead Varestraint testing

“…The M 2 of lasers is a measure of the ability of a beam to be focused on a small spot for a given beam divergence angle. For single-mode fibre lasers, M 2 ranges from 1.05 to 1.30, whereas for multi-mode fibre lasers, this value ranges from 7 to 10 [22,23]. Therefore, single-mode fibre lasers deliver a high-quality beam and are easily focused and are thus useful for achieving ultrahigh-precision welding.…”

Autogenous Fiber Laser Welding of 316L Austenitic and 2304 Lean Duplex Stainless Steels

“…An important observation is that when laser welding is used for super duplex and austenitic steels, the ferrite/austenite phase balance is not significantly changed by different heat input values [39]. Existence of an unmixed zone that originated from each base material was stated by Chun et al [53]. The approximately 50:50 ferrite/austenite microstructural balance can be reached with solution annealing in the range of 1050-1100 • C, and it is especially important in autogenous welds [33].…”

“…However, among the various austenitic consumables, the most beneficial, both in terms of strength properties, as well as morphology and corrosion resistance, is the use of 309L [ 47 , 48 ] or super austenitic 904L filler metal [ 49 ]. The literature also describes attempts to weld such a material combination without filler material: using different variants of the TIG process [ 50 , 51 ] or concentrated welding sources [ 33 , 52 , 53 ]. Ridha Mohammed et al stated that the mechanical properties of the duplex-austenitic steel fiber laser joints were better compared with the base materials (BM) because of the small HAZ [ 52 ].…”

Liquation crack-free welding strategy for 247LC DS superalloy by control of pipeline diffusion via ultra-high-speed laser beam scanning

“…A single-mode fibre laser has a beam propagation factor (M 2 ), which represents the ability of a beam to be focused on a small spot for a given beam divergence angle. For single-mode fibre lasers, this ranges from 1.05 to 1.30, whereas for multi-mode fibre lasers, this value ranges from 7 to 10 [23,24]. Thus, at the same heat input condition, the energy density of a single-mode fibre laser at the focal point is much higher than that of a typical multi-mode fibre laser.…”