Development of High Strength Fire-Resistant Earthquake Steel

Fire is generally aftermath of an earthquake because of damaged gas pipelines, electrical short circuits, etc. This increases the vulnerability for greater damage to structures and human. In order to mitigate the damage, authors designed and developed an earthquake-resistant high strength steel with fire resistance using Thermo-Calc software. The designed micro-alloyed steel was produced in vacuum induction furnace and casted into ingots. Subsequently, the ingots were rolled to the preferred size in 2/4 high rolling mill. From the rolled plates, desired UTM samples were fabricated. The fabricated samples were quenched in different quench media like brine, water and forced air after preheating to 1050 °C in order to obtain TEMPCORE properties (martensite at the outer ring and ferrite plus pearlite at the core) in the final product. Though various quenching media were used, water quenched samples were giving desired results and hence these samples were used for further fire resistance studies. SEM and TEM studies were performed on these samples at various stages. It was observed that pearlite formed at the core and martensite at the outer ring transformed from the ferrite and the same was confirmed by EBSD. From the TEM studies, it was observed that there is formation of tempered martensite laths and nano-sized nodular carbides of V, Nb and Mo resulting in high yield strength of 715 and 477 MPa at room temperature as well as at elevated temperature of 650 °C, respectively.