I answered your question, because I was curious myself. I hope you (or anybody) aren't planning on making a FIA-spec cage from T45 or the 15xx series grades I posted. The heat treatment is more trouble than it is worth in possible weight savings. Why not just use an easy to weld, no heat treat needed low carbon 10xx grade that meets the FIA requirements? The FIA calls for a cold-drawn seamless unalloyed carbon steel with a minimum strenght of 350N/mm^2. Their definition of unalloyed steel is a maximum additive content of 1% manganese and 0.5% other elements with a max carbon of 0.3%.
Here's a list that wiil meet spec from the Metals Handbook: 1018, 1019, 1020, 1021, 1022, 1023, 1025, 1026, 1030. The top 3 in tensile strength are 1030, 1026, & 1022 and any steel warehouse can get those for you.
Good advice from Tom...anything that requires normalization when welding is way too much trouble for the general privateer and not necessary. Any approved mild steel DOM will be much easier to work with than alloys. The weight difference is negligible and can be made up elsewhere in the build-up of the car.
No, I wasn't planning on it... I just heard a bunch of people at CT say "T45 cage" and I was curious. I would ONLY use 1010, 1020, or 4130 for roll cages (obviously some sanctioning organizations have different requirements as to which alloys are allowed). I won't give my opinion on 4130 normalizing because people think I'm some sort of monster when I do....
--Roy "never normalized a chromoly weld in my life" Dean
I have contacted the supplier of most of the T45 rollcage material and they are in touch with the FIA rgearding this issue. According to them almost all top level Rally cars use T45 cage material and very few, if any, do any post welding treatment. This is the primary reason that T45 is so popular, 4130 like strength with no "stress releiving" required.