I have to disagree with Kou to a certain extent. Introducing nitrogen in duplex is used for the very purpose of reducing ferrite to get the ferrite/austenite balance as close to the 50% as possible, which is desirable. Thats why its called duplex. If your getting below 50% ferrite you don't need nitrogen in your shielding.
The idea that introducing nitrogen can lead to hot cracking in duplex is almost unimaginable, in my opinion, considering that with 300 series SS's you have to get almost to 0% ferrite (some studies have microfissuring manifest at = or < 2% for most 300 alloys if memory serves) before its considered a serious problem. Many specifications require ~4% mins. and thats with a considerable margin of error to accomodate things such as section thicknesses and restraint, and other contributing factors like high residuals. If your getting down that low in ferrite with duplex you have far more serious problems than nitrogen. Like maybe the wrong alloy all together. And once you get below 30% you're probably going to fail at least 90% of the specs out there. If you're remaining in the duplex ferrite region you are not anywhere near close to 'hot cracking' range.
If you're out of that region your corrosion and strength will most likely not hold up in service, and therefore microfissuring is the least of your problems, considering microfissuring has existed in countless weldments for years/decades without failure (quite common in NiCrMo-3 weldments in AL6XN where CbN contribute to microfissuring).
In fact, if your ferrite is that low, you don't have duplex AT ALL. You have an austenitic.
And another thing, its not really hot cracking in the sense that most people understand that is the problem with low ferrite. Its microfissuring. Which is hot cracking to be sure, but a form that is not visible. Often not even by PT. Hot cracking, usually manifest as centerline cracking or crater cracking (very visisble by PT) is caused more by too high of welding parameters, to high of depth to width ratio, restraint, or insufficent fill on the craters.
The real problem with too much nitrogen is the formation of chromium nitrides which can be selectively attacked in some services.
Bottom line, if you're achieving your phase balance you don't need it. If you need for phase balance don't worry about hot cracking since you have to stay over 30% ferrite by many specs anyway (I think some go as low as 25% but most I believe are actually at ~35% if memory serves).