The frame is a steel alloy, and likely a high carbon variant, additions of substitutional elements could only be assessed by elemental analysis testing. I would speculate that the billet frame is machined from is forged, quenched and tempered. Ideally, a cycle of austenitization, water quench, and temper with the metal blank near net shape gives improved geometric stability after machining.
Being a carbon steel alloy, there are generalizations that can be made as to how hot and how long it may be heated, without affecting the desired design properties. One point of reference can be that if the metal has even the faintest red glow, red glow in a dark room is detected at about 725 F, it is likely heated beyond the point of maintaining confident control of metallurgical properties, For This Specific Context. Nothing is absolute here, because a range of possible primary processing for production results in a range of material response to heat and deformation.
For the sake if making fine deformations to re-align the barrel, my opinion is that no heat need be applied, as at the relative yield strength levels for this material in the range of reasonable temperatures (I suggest to 400 F max for any length of time) does not change much, and hot metal is harder to handle. Any cold tweaking should be executed in a very progressive and contolled fashion. Experience may give confidence, but does not change the methodology.
That said, I am looking to the future to at some time changing out barrels, either in a Mak or in a Feg (aluminum! frame), and i plan to heat the barrel hood (centered along a line at 12 o'clock) just before clamp force is applied. This is simply an attempt to get the two parts to release as easily as possible with the least amount of release stress on the barrel hood. The technique requires that the barrel be not similarly heated and I'm thinking of packing it with dry ice. The heat source will be a propane torch, with the inner bright blue flame never getting near the metal. Temperature control could be verified using a 350 F temp-stick as can be gotten from a welding supply.
