Chrome moly if welded with 70 S2 filler will not form a carbon line.

Some folks weld with 4130 filler. This produces a carbon line a couple inches from joint.

It best to keep welding area warm with cage warm. This reduces flash temperature. And do not cool welds.

Every broken tube Ive ever seen was welded with hard filler rod. They all broke in carbon line. If welded correctly you can bend into a pretzel and not crack.