Processing and cooling effects on post-fire mechanical properties of high strength structural steels

Abstract

High strength structural steel (HSSS) can be divided into TMCP (Thermo-Mechanical Controlled Process) and QT (Quenched and Tempered) types according to the manufacturing process. Most previous studies on the post-fire mechanical properties of HSSS were conducted on QT HSSS, while few studies were conducted on TMCP HSSS. In order to identify the effect of manufacturing process on the post-fire mechanical properties of HSSS, experimental studies were carried out on TMCP Q550 and TMCP Q690 HSSS and the results were compared with the previous studies on corresponding QT Q550 and QT Q690 HSSS. The static tensile tests were conducted at ambient temperature on TMCP Q550 and TMCP Q690 HSSS specimens heated up to nine pre-selected temperatures ranging from 200 to 900 °C and then cooling in air and water respectively to simulate various post-fire situations. It can be found that the heating and cooling process had little influence on elastic modulus but significant effect on strength and ultimate elongation once the heated temperature exceeded 600 °C, and the cooling way and manufacturing process became critical once the heated temperature exceeded 700 °C. In general, the post-fire strength and ultimate elongation was always less for TMCP HSSS than QT HSSS.