Hello All,
Is this possible to increase Delta ferrite content of the weld by just varying the welding parameters or any thing else such as cooling rate heat input etc? I am given a job of increasing the delta ferrite content up to 14-16 % on a typical weld where base material is SS304L and filler is ER308L. I do not option to change either base material or filler wire composition.
My filler wire with GTAW welding process gives 5-6% ferrite content. I tried to increase the current to almost 200 AMPS. But there was no change in ferrite content (bead profile and colour was definitely very bad). I have just tested only one set of coupon. Please suggest me how should I proceed with my experimentation.
The main motive to increase the delta ferrite content on weld is to check its effect on corrosion resistance of weld metal.
Regards,
Ramakant
ER308L is a filler metal that actually solidifies first as Delta Ferrite. this is why ferrite exists at all in SS alloys at room temp. So, (although I have never done it myself I have heard of it being done), if you quench the weld while welding you can increase the delta ferrite content because you are not providing adequate time for the ferrite to austenite transformation.
But if I may ask, why so much ferrite?
Sorry, I slid past your last paragraph.
Be interesting to see what your elongation is with such high ferrite in 308.
Hi JS55,
Thanks for a very quick reply.
I agree ER308L filler wire first freezes as delta ferrite and then gets converted to Austenite leaving slight amount of Delta ferrite in the weld. It is required and essential too to avoid hot cracking of the weld.
I want to increase the delta ferrite content to 14-16% so that its effect on the corrosion property of the material may be tested. Can you help me on this? I am still not sure what should I do. I will definitely try to quench the weld immediately after welding. But I think the transformation of delta ferrite to Austenite is a high temperature phenomenon and by the time my welding is over, it may have already cooled down to a low temperatures and it may not be of any help. It is my pure guess but definitely i will give this a try on coming Monday.
Friends, any other idea to increase the ferrite content on SS304L weld?
Thanks and regards,
Ramakant
Copper chill bars can help I suppose. But given SS's low thermal conductivity I'm not sure how much. Maybe a little. As for quenching it definately would not be an easy thing to carry out. If your welding on pipe you could chill or quench the ID, or if plate, the bottom side. But of course, the thicker the material the less effective this will be.
And your right, once you've cooled below the transformation temp you've gotten all you're gonna get.
If you do end up quenching for this let us know the results.
If it is so hard (near impossible) to get this much ferrite in 308L, then why does it's corrosion resistance matter? I think you will be doing well to get it in the 10-12 FN range, which is hard to do. We have done a lot of 308L weld buildups on large diameter, heavy wall 304 pipe with water backing and struggled to get it in the 7-8 FN range with GTAW. A fast-freezing process with low heat input, such as GMAW, may help push it higher. Perhaps circulating brine inside the pipe at 32 F may help increase cooling rate.
With a change in filler, it's not only not impossible, it's likely to get an FN in the 12-15 range. Specifically Kobe filler is designed for a higher input. I've personally tested and witnessed this to be the case. In specific, at the low range it was 10, at the high range it was 16 depending on cooling rates and heat input. On the other hand, it's near
impossible to get that reading on fillers designed for the 5-6 range and still have something that could resemble a sound weld.
based on my vast storage of ignorance
what would be the possibility of pre cooling with nitrogen or wrapping the pipe in a cooling jacket leaving only the weld joint exposed
all sorts of coolants could be used
darren
Friends,
I have no choice to change my filler or base metal. The filler is designed to give ferrite reading in the range of 4 to 8 with the parent metal I have in my stock if welded in usual conditions. With the discussions we had, it seems that the cooling rate is really something to do with the percentage of ferrite in the weld metal. What I understood from the suggestions is that higher is the colling rate, it seems to be possible to attain higher ferrite. I will definitely give it a try in a day or two.
Regards,
Ramakant
I had a situation where I pumped water through a pipe while I welded it. Not for the reasons discussed in this thread.
Consider doing a root pass as would normally be done (purged with gas), but then pump water through the system while completing the fill and cover passes (if needed).
Best regards - Al
You may want to look into the effect of nitrogen pickup. As I recall, nitrogen pickup from the atmosphere, due to poor shielding or whatever, will tend to promote austenite formation, so you probably want to be very careful to avoid this.
i think ferrite number for combination(dilution during welding) of SS304L and ER308 is more or less fixed, may be slightly higher or lower based on chemical composite of the base and filler metal(namely Cr equivalent and Ni equivalent). if application requried ferrite content up to 14-16% u should select correct material in stead of trying something that outside the range of this combination. ---- personal view.
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