Are you talking about very short-term overheating, a so-called 'excursion'?
X-grade pipe materials are intended for low temperature service. They experience temperatures far in excess of 600°F during welding, but that is very short-term. It comes down to Time AND Temperature.
However, you do not want to take it to a PWHT temperature range, since prolonged exposure causes embrittlement due to the spices added to these steels.