How is N to C ratio measured in forming austenitic stainless steel?

Nitrogen is the future hope of stainless steel industry; since in the production of austenitic steel it can even completely replace nickel (which is relatively very expensive) in some cases and for another reason: it decreases the temperature at which carbides should form.


As a result, there is always an optimum carbon to nitrogen ratio. My problems are:


1. How is N decreasing the temperature of the formation of carbides? Is it a catalyst or something?
2. Resources, however, didn't mention how the N to C ratio is measured? How? Am I missing something very easy in here?


Update: I just found this [paper](http://gualstainless.com/htm/img/imatges_cms/pdf/document_tecnic_2.pdf) in which almost all of the info above can be found; but it's not my main reference.


