Sorry, probably necro-posting (necro-commenting?), but I really couldn't resist.
If you don't mind stealing a name from the Fallout series, you could call them the Brotherhood of Steel, otherwise you could call them the Iron Brotherhood or the Steel Brethren if you want a name along that same vein but that's also a bit more original. I got the idea from all the chains on his his armor, and I started thinking about what they might represent. With a name like the Brotherhood of Steel or the like, perhaps they use the chains as a symbol of their chapter's brotherhood, with each steel or iron link in the representing an individual marine. The chain as a whole represents their strong bonds with one another and their strong belief in cooperation and working towards a common goal or ideal, for if but a single link in a chain breaks or fails, the chain falls apart and tends to become useless for whatever purpose it was intended.
Also, I'd suggest having them be Iron Hands or White Scars successors, if you want to think that much into it, at least.
I like the design...but it is curious that u chose the old model of armour...because that was only pre-heresy (so basically it was the time when there were only 20 legions 2 of which were lost and had no known name, so technically 18, and half of which went corrupt). the old model of armour markers such as: no imperial seal on the chest (in the pre-heresy days only one legion wore that, the Emperor's Children...kind of ironic really when you think about it), those circles on the left shoulder plate stuff like that.