1) Don't use pulse... "The formation of interpass position swirls was promoted when using pulsed parameters and intra-pass position swirls were exacerbated by using constant current conditions... Overall, the formation of swirls was facilitated by the lower heat input parameters...
The use of constant current parameters minimised the perturbations caused during welding and led to the formation of fewer intrapass swirls Constant current parameters resulted in fewer intra-pass swirls, although their presence was not eliminated entirely, and lower heat input tended to promote the formation of inter-pass swirls exhibiting martensite laths (Zone M)...
2) Read this: "Increasing the heat input seems to be the best way to minimize the formation of swirls and mitigate the formation of martensite region... The complete elimination of swirls seems unlikely...
However, moving to a lower carbon forging would seem to offer the most practical means of reducing the consequence of martensite in swirl positions, both by reducing hardness and ensuring a chemistry that is tempered during PWHT..."3) "To summarize, lower heat input would improved the susceptibility to hydrogen embrittlement by producing a less susceptible microstructure at the dissimilar interface....
On the other hand, it would promote the formation of swirls of partially diluted steel penetrating into the weld metal, favourable to martensite formation...
This would impair the performance of the dissimilar interface... The dissimilar combination 8630M/625 has a high susceptibility to hydrogen embrittlement and the problem cannot be eliminated by controlling the welding parameters...
Employing a lower carbon content forging has important benefits as no martensite would form at intra and inter-pass position and the formation of Zone Φ could be controlled by the welding parameters...Some work carried out at TWI demonstrated that MIG welding could produce a Ni-rich Zone Φ and its environmental performance is being established..."
The following conclusions are drawn:
1. The hydrogen embrittlement resistance of subsea dissimilar joints depends on three primary factors:
(i) material selection, (ii) butter welding procedure, (iii) postweld heat treatment. Each of these governs the microstructure and chemistry across the dissimilar interface and unless specifically modified to take hydrogen embrittlement into account, can lead to a joint susceptible to environmental failure.
2. Two microstructural zones dominate fracture path in environmental tests: Zone Φ; a hard, carbon-supersaturated, austenitic, solid solution immediately adjacent to the fusion boundary, which fails by cleavage; and zone M, which contains martensite in highly-diluted weld material particularly at swirls of diluted steel penetrating into the butter deposit.
3.
The present work demonstrated the difficulty of eliminating both Zone Φ and Zone M, simultaneously in arc welded butter deposits. Zone Φ could be eliminated by employing a low arc energy. However, Zone M, could only be limited by employing high arc energy. Thus, the elimination of a susceptible microstructure at the dissimilar interface, at least between 8630M and alloy 625 butter deposits, could not be prevented by modifying welding parameters alone.4.
Hydrogen embrittlement resistance was improved by using low temperature PWHT, limiting the carbon-supersaturation of Zone Φ.5. The best environmental performance was obtained for a friction welded dissimilar joint given a PWHT of 10 hours at 1100F, achieved by a combination of the elimination of Zones Φ and M, and the mitigation of carbon diffusion during PWHT."
Btw, Great article Scott! It pretty much spells it out for you Marktski.
Respectfully,
Henry
