Boron addition to T-316L ... why?

[rd400guy]

For an ultra-low sulfur version of T-316L, our melter asked if we should add boron. We typically add 20lb. of ferroboron to our standard version of T-316L, and we make the addition in the ladle when tapping the AOD (40 ton heat). I know the boron won't have any affect on the sulfur, but it got me to do some investigating.

Per Shieldalloy's Ferroalloys and Alloying Additives Handbook (

http://www.shieldalloy.com/contents.html),

boron reacts readily with oxygen and nitrogen in liquid steel. Although the steel is fully killed when our ladle ferroboron addition is made, we have a nitrogen spec of 0.070-0.095, which I would think is more than enough to react completely with the amount of boron that we add. Our ferroboron is 17.5% B.

So my question is this, why add the boron at all? I've asked a few folks around here, but haven't gotten a straight answer yet, so I figured I'd throw it out to all of you. Any insight would be appreciated.

 

[gieter]

Boron can be used to increase high-temperature properties (strength and creep) with additions of about 0.1%. It's detremental to tensile properties at room temperature (gross grain-boundary precipitates). Elongation can drop as low as 5%!
I've heart of boron additions to stainless for nuclear applications (ion-absorption), but that was for 304.