Transient Softening at the Fusion Boundary of Spot Welds in Advanced High-Strength Steels: Dark Horse of the Heat-Affected Zone

Sherepenko, Oleksii; Ramachandran, Dileep Chandran; Mohamadizadeh, Alireza; Biro, E.

doi:10.1007/978-3-031-17425-4_9

Cited by 2 publications

(5 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The formation of a weld halo during resistance spot welding of a TBF1000 steel was observed in welds produced with 16 or more weld cycles, after growth of the fusion zone stagnated, which is consistent with previous findings [6,8,20]. The weld halo forms as part of a heterogenous weld nugget: initial migration of the fusion boundary is associated with a cellular/planar front with carbon, manganese, and silicon segregation into the remaining liquid.…”

Section: Discussionsupporting

confidence: 89%

“…The increase in interface stability may also occur as the rate of heat extraction via the watercooled electrodes diminishes with movement of the interface away from the electrodes. It is not presently clear whether nucleation of 𝛿𝛿-Fe at the solid-liquid interface, as hypothesized by several authors [6,8,20], could explain the solidification morphologies shown here. It is presumed that the planar solidification front marks the end of the fusion boundary migration during welding.…”

Section: Discussionmentioning

confidence: 69%

“…2 support the hypothesis that the decrease in hardness of the halo and accompanying increase in hardness of the fusion zone are primarily influenced by the carbon content of the martensite that forms upon cooling of the weld. Further characterization of the phase transformation products in the halo is ongoing in consideration of the nonmartensitic transformation products identified by others [8,18,20,24].…”

Section: Discussionmentioning

confidence: 99%

“…2(b) along with the trend in martensite hardness vs. carbon content observed by Bain [23], are consistent with the hypothesis that the decrease in the halo microhardness and the increase in inner fusion zone microhardness in this steel are primarily controlled by the local carbon content. Additional analysis of the halo microstructure is ongoing since non-martensitic transformation products have been reported by others [8,18,20,24], but initial observations suggest a martensitic microstructure in the halo.…”

mentioning

confidence: 91%

“…Halo formation has been observed in press hardened-steels [4,9], dual phase steels [10], and high strength low-alloy steels [11], and while halo formation has not been previously identified in Gen3 RSWs, weld failure [12][13][14][15][16][17][18] and localized softening [18,19] along the fusion boundary have been reported. Halo formation has been hypothesized to occur by one of two mechanisms, either carbon depletion due to segregation at the fusion boundary [3,10], or the formation of 𝛿𝛿-Fe at the solid-liquid interface [6,8,20] once nugget growth stagnates. The intent of this paper is to further the understanding of the halo formation mechanism and provide insight on fusion zone characteristics that may influence RSW mechanical performance.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Solute Enrichment in the Fusion Zone during Resistance Spot Welding of a Third Generation Advanced High Strength Steel

Marshall,

Schenck,

Hines

et al. 2023

KEM

View full text Add to dashboard Cite

Resistance spot welding is a critical joining technique in automobile assembly. The load carrying properties of spot welds are generally accepted to correlate with weld diameter, which increases with increasing weld current or duration. The formation of a softened layer, or weld halo, surrounding the fusion zone in a spot-welded third generation (Gen3) advanced high strength steel (AHSS) was recently reported in the literature. To optimize weld performance by schedule design, it is necessary to understand the halo formation characteristics and potential impacts. Accordingly, welding of a Gen3 AHSS was performed using weld times between 130 – 1300 ms. Microhardness mapping characterized weld microhardness and the evolution of the halo during welding. Electron probe microanalysis and timeof-flight secondary ion mass spectrometry enabled measurement of solute distributions through the weld halo, while scanning electron microscopy was used for microstructural characterization. The solidified structure was examined using light-optical microscopy, and with the microhardness and compositional data, used to infer the mechanism by which the halo forms during welding. It was found that the halo develops due to solute rejection from a cellular solidification front that advances towards the center of the fusion zone while weld current is applied. Extended weld times increase the size of the weld halo and the solute content of the inner fusion zone. The decrease in weld halo microhardness and the increase in inner fusion zone microhardness is largely explained by the changes in local carbon content associated with halo formation.

show abstract

Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 69%