Mechanical properties of Q345 structural steel after artificial cooling from elevated temperatures

Water cannot be used to effectively extinguish fires that occur in chemical plants, oil and gas pipelines, and other flammable and combustible liquid storage structures. In such cases, firefighting foam is often used as a fireextinguishing agent. In this study, we experimentally investigate the mechanical properties of Q345 steel after subjecting it to temperatures of 200-900 degrees C, followed by artificial cooling using water or firefighting foam. The fire-affected specimens are subjected to tensile tests to observe their fracture characteristics and obtain their stress-strain curves. Below an exposure temperature of 600 degrees C, the mechanical properties of Q345 steel remain almost entirely unchanged, irrespective of the cooling method. Above 600 degrees C, the mechanical properties of Q345 steel experience significant changes based on the exposure temperature and the type of cooling method. When Q345 steel is exposed to temperatures of 800 degrees C and 900 degrees C and cooled using water, its yield strength and ultimate strength increase significantly. In contrast, the ductility of the Q345 steel that is water cooled from temperatures of 600-900 degrees C rapidly decreases with the increase in temperature. When Q345 steel is exposed to temperatures of 600-900 degrees C and cooled using firefighting foam, it experiences a significant reduction in both yield strength and ultimate strength. In contrast, the ductility of Q345 steel that is cooled using firefighting foam does not change significantly. Subsequently, the macroscopic and microscopic fracture morphologies are also analyzed to better understand the changes in the mechanical properties of Q345 steel. Finally, empirical equations are proposed to predict the mechanical properties of fire-affected Q345 steel that is cooled using water or firefighting foam. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The mechanical properties of Q345 steel undergo significant changes at different temperatures and with different cooling methods. Exposure to temperatures of 800-900 degrees C and cooling with water increases the yield strength and ultimate strength of the steel, while exposure to temperatures of 600-900 degrees C and cooling with firefighting foam results in a reduction in yield strength and ultimate strength. Additionally, the ductility of the steel also varies depending on the temperature and cooling method used.