Evolution of the corrosion layer of Q235 steel in simulated fire-scene smoke

The ability to accurately identify fire patterns is the fundamental requirement for fire investigations. The corrosion layers of steel in fire scenes exhibit three distinct characteristics. First, due to steel's nonflammable nature, steel patterns can be preserved better at the fire site than patterns formed on other combustible materials; second, both the high temperature and the smoke during the fire affect the high-temperature oxidation process; and third, the corrosion layer of steels inevitably undergoes further evolution after the fire because of the subsequent room-temperature corrosion. This study focuses on investigating Q235 steel because of its extensive use in construction and vehicles. The pattern evolution processes of high-temperature oxidation at elevated temperatures in air, polyethylene (PE), and polyvinyl-chloride (PVC) combustion smoke and the corresponding subsequent corrosion at room temperature were systematically investigated from the perspective of macroscopic and microscopic morphology. The results showed that the smoke atmosphere played an important role in the formation of the corrosion layer of Q235 steel. Compared with samples oxidized in air, samples oxidized in PE combustion smoke exhibited a uniform and dense oxide layer on the surface, which inhibited the corrosion at room temperature further. The PVC combustion smoke accelerated the high-temperature oxidation of the sample, and its influence on the subsequent room-temperature oxidation process was closely correlated with the temperature of the high-temperature oxidation. The results of this study provide important references for understanding the formation of the corrosion layer of Q235 steel for fire investigations.