Influence of HAZ Microstructure on the Reheat Cracking Susceptibility of Fire Resistant Steels

摘要

Fire resistant (FR) steels for steel construction show 490-520MPa class strength steel. The characteristics of FR steel gurantees 2/3 values of the high temperature 9873K) yi8eld strength as compared to the room temperature yield strength obtaied by the TMCP treatment and minor addition of Mo+Nb type, Al+B type element. In this experiment, influence of HAZ microstructure on the reheat cracking susceptibility during Post-Weld Heat Treatment (PWHT) was discussed from viewpoint of precipitation behavior of inter- or transgranular alloying carbides and deformability of the matrix on each HAZ microstructures. As a result, the reheat cacking of FR steels were occured all HAZ structures at 900 - 1000K. These phenomena were very dangerous behavior for steel - rib construction. Especially, high temperature deformability of bainitic and lath-martensitic structures had a remarkable brittle tendency. These tendency was caused by the precipitation behavior of inter- or transgranular carbides on each HAZ microstructure during PWHT process.