Cromoly steel BMX frames, as well as other welded BMX parts, are often advertised as "fully post-weld heat-treated". Just what does this mean? Is it simply a normalisation process to relieve any stresses caused by deformation during welding? If not, what does it do?

How hot do they have to get the frame, and for how long? Is there some form of quenching involved?

I'm just curious here, it's not like I'm going to try it, but I figured this would be the best place to ask.

Thanks in advance