Using the microstructure and mechanical behavior of steel materials to develop a new fire investigation technology

In the study, an A36 steel board, a frequently used building construction material, was heated to a high temperature, and then a metallographic replication experiment and tensile experiment were performed to obtain the composition and proportion of the microstructure and the mechanical behavior of fire‐damaged steel boards. When the steel board was heated to 800°C or higher and then rapidly water cooled, significant changes were found in its composition and proportion. More specifically, pearlite was completely lost, ferrite was reduced from 80% to 30%, bainite was increased to 30%, and martensite was also increased to 40%. The significant increase in the martensite phase altered the structure of the fire‐damaged steel board by making its structure more delicate and loose. Even though the yielding strength and tensile strength showed a tendency to increase, element ductility dropped from 32.5% to 15%. Reducing the extensibility substantially can make the steel board more likely to crack suddenly. The aim of the study is using changes in the structure and mechanical behavior of these steel components because of high‐temperature burning to reconstruct fire spread in fire investigation technology.