Unless you have a background specifically in the steel industry that utilized high-automation technology, the learning curve for you will be extremely high for a very long time. I have a background in automation (but not in the steel industry) and I still find this plant a bit overwhelming. The level of automation at this plant is so high that many seasoned employees still do not have a full understanding of how it works. This doesn't really bother me because I enjoy the challenge of learning about new technology, but some would consider this a con. You won't be able to "hop right in" to the work. It will take many months/years of shadowing other employees to get a grasp of what is going on.
If you are getting a job in the actual steel mill, be aware that most people in the mill use foul language occasionally, but it's all in good fun. There are no personal attacks or anything, just something to be aware of that it isn't a completely "professional" environment in that sense. This doesn't really bother me but some people might consider it a turnoff.
Another thing: Because ATI already has the automation system fully implemented, any jobs at this plant are basically jobs to just maintain the system even if they hire you as a software engineer (which is what they hired me for). ATI still finds small "bugs" in the system occasionally which is why they hire software engineers to fix the problem. However, the maintenance of their new facility is still in it's infancy and because of this, ATI still heavily relies on it's contractors who installed the automation system to help out when something goes wrong. It seems that ATI still hires full-time permanent employees (such as myself) with the hopes that years down the line, ATI will be able to (mostly) maintain/upgrade this system on their own. That being said, not much time is spent actually designing anything, typically you're just trying to keep the system up and running, and occasionally modifying the software for small tweaks to make it a bit better. Not sure if this is considered a "con" or not, but it's something you should be aware of before you get this job.