Appearances can be deceiving, that part that you consider sheet metal just may have some engineering and testing involved, it may be a specialty type of steel, they are not all the same, it could have a heat treat, or it may be just plain dangerous per it's application and super ceded by a better more intelligently designed part.
I have to be honest with you, you asked if you could use gas pipe for steering components, that worried me, it seems you are fabricating your own front end components, I just hope you are educating yourself properly as to what materials and design to use, a piece of tube is not just a piece of tube, you shouldn't build steering components from soft architectural steel that you can buy at the corner hardware store. Take a few pics of what you are doing and post them either here or the HAMB, ask questions, I don't want to see you make an innocent mistake that hurts you my friend.