Abstract
Differences in the nature of the thermal cycle run under welding conditions in comparison to that during conventional heat treatment are shown. The methods of investigations into microstructural changes of austenite under welding thermal cycles conditions developed and used at the Welding Institute in Gliwice are discussed. The investigation results, in the form of CTPC-S diagrams for construction steels of grades X12CrCoWVNbl 2-2-2 (VM12-SHC), 7CrMoVTiB10-10 (P24) and 10CrMo9-10 (P22), are presented and compared with those in the form of CTPC diagrams plotted for metallurgical conditions.