Brimstoner
you right, that is srange pair of alloys to compare, but the design department replace CA6NM with C12A in some hot sections and as you know castability and weldability of CA6NM is better. we dont have any experience about casting of C12A and how to control Nitrogen content of steel, I didnt find any document about casting C12A and its problems.
Dear Metengr
Thank you for your post. I had already valve magazine article about C12A but it is about properties of this steel.
How we can control Nitrogen content in steel making? How can measure Nitrogen content of steel?
There are several ways of controlling the amount of Nitrogen in the steel. First off your specification, you just need to specify how much you need. For your reference, BOF steels can typically have much lower Nitrogen content than EAF material. This has to do with how steel is made. That being said, 150 ppm Nitrogen is easily attainable using an EAF.
However, this is a very unique situation due to alloy content. Unless the supplying mill is primarily a "stainless" mill, you may encounter problems with a EBT type EAF, since all of the alloys will be added to the ladle, due to the hot heel practice.
What is driving the nitrogen up is the use of alloying elements. Since the amount of Chrome and Moly in a 9Cr-1Mo added is fairly extensive, there is alwaoys a little bit of nitrogen in the alloys so you will have to watch it.
Specifying a vacuum degas product will signficantly aid in the nitrogen reduction of the steel. So clean steel practices need to be employed. A VOD product will have even tighter nitrogen content, but at a significant cost premium.
In summary to a slightly rambling post, the only way you guarantee a particular nitrogen content is to specify it at time of order andh ave the mill agree to the limit. There are so many factors that determine the Nitrogen content as a function of production so there is no one answer to your question.
As far as analyzing the nitrogen content of a steel, there are two widely accepted industry methods. The first is combustion analysis, (Leco O/N2). Yes I know Leco is a brand name but everyone calls it that. And the second is through new OES. I am rather old school and prefer combustion, but there are many people that swear by OES. I hope this helps
