I was making tongs for putting metal pieces into a crucible from two 10mm round steel bars. I had to heat them for forging and bending and did it by holding two carbon rods connected to a welder which heats it quickly and locally, unlike a propane flame. That worked, but after forging and cooling I blunted a drill bit when drilling the hole to attach both tongs together. Using a file also felt like filing hardened steel. So I did it again with a (slow) propane flame and the issue did not appear anymore, it remained normal workable mild steel. Does steel absorb carbon that quickly ?